ETC DRM030

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Freescale Semiconductor, Inc.
3-Phase Switched
Reluctance Motor
Drive Control with
Encoder Using
56F805
Designer Reference
Manual
56800
Hybrid Controller
DRM031/D
Rev. 0, 03/2003
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3-Phase Switched
Reluctance motor Control
with Encoder Using 56F805
Designer Reference Manual — Rev. 0
by:
Peter Balazovic
Motorola Czech System Laboratories
Roznov pod Radhostem, Czech Republic
DRM031 — Rev. 0
Designer Reference Manual
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Revision history
To provide the most up-to-date information, the revision of our
documents on the World Wide Web will be the most current. Your printed
copy may be an earlier revision. To verify you have the latest information
available, refer to:
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The following revision history table summarizes changes contained in
this document. For your convenience, the page number designators
have been linked to the appropriate location.
Revision history
Date
Revision
Level
January
2003
1
Description
Initial revision
Designer Reference Manual
Page
Number(s)
N/A
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
List of Sections
Section 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
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Section 2. Target Motor Theory . . . . . . . . . . . . . . . . . . . . 21
Section 3. Switched Reluctance Motor Control Techniques with Encoder Position Sensor. . . . . . . . . . . . . . . 35
Section 4. System Description. . . . . . . . . . . . . . . . . . . . . 43
Section 5. Hardware Design. . . . . . . . . . . . . . . . . . . . . . . 65
Section 6. Software Design . . . . . . . . . . . . . . . . . . . . . . . 77
Section 7. System Setup . . . . . . . . . . . . . . . . . . . . . . . . . 99
Appendix A. References. . . . . . . . . . . . . . . . . . . . . . . . . 115
Appendix B. Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . 117
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List of Sections
Designer Reference Manual
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
Table of Contents
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Section 1. Introduction
1.1
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
1.2
Application Benefit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.3
Motorola DSP Advantages and Features . . . . . . . . . . . . . . . . . 16
Section 2. Target Motor Theory
2.1
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
2.2
Switched Reluctance Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3
Mathematical Description of SR Motor . . . . . . . . . . . . . . . . . . . 24
2.4
Digital Control of SR Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
2.5
Voltage and Current Control of SR Motors . . . . . . . . . . . . . . . . 30
Section 3. Switched Reluctance Motor Control Techniques with Encoder Position Sensor
3.1
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
3.2
Encoder Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.3
Commutation Angle Calculation . . . . . . . . . . . . . . . . . . . . . . . . 37
3.4
Commutation Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
3.5
Current Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Section 4. System Description
4.1
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
4.2
System Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
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Table of Contents
4.3
Application Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
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Section 5. Hardware Design
5.1
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
5.2
System Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.3
DSP56F805EVM Controller Board . . . . . . . . . . . . . . . . . . . . . . 67
5.4
3-Phase SR High-Voltage Power Stage . . . . . . . . . . . . . . . . . . 68
5.5
Optoisolation Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.6
Motor-Brake Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . .72
5.7
Hardware Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Section 6. Software Design
6.1
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77
6.2
Data Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
6.3
State Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.4
Software Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.5
Scaling of Quantities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
6.6
Velocity Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Section 7. System Setup
7.1
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
7.2
Application Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
7.3
Application Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
7.4
Application Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
7.5
Project Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
7.6
Application Build and Execute . . . . . . . . . . . . . . . . . . . . . . . . 111
7.7
Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Designer Reference Manual
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Appendix A. References
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Appendix B. Glossary
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Table of Contents
Designer Reference Manual
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
List of Figures
Figure
Title
Page
3-Phase 6/4 SR Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Phase Energizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Magnetization Characteristics of SR Motor . . . . . . . . . . . . . . . 25
Electrical Diagram of One SR Motor Phase . . . . . . . . . . . . . . . 26
3-Phase SR Power Stage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Soft Switching and Hard Switching. . . . . . . . . . . . . . . . . . . . . . 30
Voltage Control Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Voltage Control Technique - Voltage and Current Profiles. . . . 32
Current Control Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Current Control Technique - Voltage and Current Profiles . . . . 34
Quadrature Encoder Signals . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Commutation Angle Calculation . . . . . . . . . . . . . . . . . . . . . . . . 38
Commutation Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Phase Voltage Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
System Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Start-Up Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Quadrature Encoded Signals . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Decoder and Timer Arrangement . . . . . . . . . . . . . . . . . . . . . . . 51
Commutation Algorithm Flowchart . . . . . . . . . . . . . . . . . . . . . . 53
Current Controller Utilization. . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Shunt Resistors Current Sensors . . . . . . . . . . . . . . . . . . . . . . . 56
Soft Switching Current Sensed on ADC . . . . . . . . . . . . . . . . . . 58
Phase Current Measured at Current Shunt Resistors . . . . . . . 59
Measured 3-Phase Currents without and with
Implemented Noise Correction . . . . . . . . . . . . . . . . . . . . . . . . . 62
4-11 Temperature Sensing Topology . . . . . . . . . . . . . . . . . . . . . . . . 63
5-1
3-Phase SR High Voltage Platform Configuration . . . . . . . . . . 66
5-2
Block Diagram of the DSP56F805EVM . . . . . . . . . . . . . . . . . . 68
5-3
3-ph. SR HV Power Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
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2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9
2-10
3-1
3-2
3-3
3-4
4-1
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
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List of Figures
5-4
6-1
6-2
6-3
6-4
6-5
7-1
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7-2
7-3
7-4
7-5
7-6
7-7
Inductance Characteristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
System Data Flow I - SR Motor Control . . . . . . . . . . . . . . . . . . 78
System Data Flow II - AD Converter. . . . . . . . . . . . . . . . . . . . .79
Application State Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Software Design - General Overview . . . . . . . . . . . . . . . . . . . . 87
Electrical Angle Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
RUN/STOP Switch and UP/DOWN Buttons
on DSP56F805EVM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
USER and PWM LEDs on DSP56F805EVM . . . . . . . . . . . . . 103
PC Master Software Control Window . . . . . . . . . . . . . . . . . . . 105
Setup of 3-Phase SR Motor Control Application
Using DSP56F805EVM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
DSP56F805EVM Jumper Reference . . . . . . . . . . . . . . . . . . . 108
Target Build Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Execute Make Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
List of Tables
Table
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1-1
4-1
5-1
5-2
5-3
7-1
7-2
Title
Page
Memory Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Commutation Sequence of the Reference Phase . . . . . . . . . . 60
Electrical Characteristics of Power Stage. . . . . . . . . . . . . . . . . 71
Electrical Characteristics of Optoisolation Board . . . . . . . . . . . 72
Motor - Brake Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Motor Application States. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
DSP56F805EVM Jumper Settings . . . . . . . . . . . . . . . . . . . . . 108
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List of Tables
Designer Reference Manual
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
Section 1. Introduction
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1.1 Contents
1.2
Application Benefit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.3
Motorola DSP Advantages and Features . . . . . . . . . . . . . . . . . 16
1.2 Application Benefit
This Designer Reference Manual describes the design of an advanced
3-phase Switched Reluctance (SR) motor drive. It is based on
Motorola’s DSP56F80x family dedicated for motor control devices.
SR motors are gaining wider popularity among variable speed drives.
This is due to their simple low-cost construction characterized by an
absence of magnets and rotor winding, high level of performance over a
wide range of speeds, and fault-tolerant power stage design. For
numerous applications, availability and a moderate cost of the
necessary electronic components, the SR drives make a viable
alternative to other commonly used motors like AC, BLDC, PM
synchronous or universal motors.
The concept of this application is an advanced speed closed loop SR
drive with encoder position sensor. An inner current loop with PI
controller is included. The encoder position sensor provides an accurate
measurement of the actual rotor position necessary for proper
commutation. This application serves as an example of an advanced SR
motor control. The application helps to start the development of the
advanced SR drive dedicated to the targeted application.
This Designer Reference Manual includes a description of Motorola DSP
features, basic SR motor theory, system design concept, hardware
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Introduction
implementation, and software design including a use of the software
visualization tool.
1.3 Motorola DSP Advantages and Features
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The Motorola DSP56F80x family is well suited for digital motor control,
combining a DSP’s computational ability with an MCU’s controller
features on a single chip. These DSPs offer many dedicated peripherals
like a Pulse-Width-Modulation (PWM) unit, Analog-to-Digital Converter
(ADC), timers, communications peripherals (SCI, SPI, CAN), on-board
Flash and RAM. Generally, all family members are well-suited for
Switched Reluctance motor control.
One typical member of the family, the DSP56F805, provides the
following peripheral blocks:
•
Two Pulse Width Modulator modules (PWMA and PWMB), each
with six PWM outputs, three Current Sense inputs, and four Fault
inputs; fault tolerant design with deadtime insertion; supports both
Center- and Edge- aligned modes
•
Twelve bit, Analog to Digital Converters (ADCs), supporting two
simultaneous conversions with dual 4-pin multiplexed inputs; the
ADC can be synchronized by PWM
•
Two Quadrature Decoders (Quad Dec0 and Quad Dec1), each
with four inputs, or two additional Quad Timers A and B
•
Two dedicated General Purpose Quad Timers totalling 6 pins:
Timer C with 2 pins and Timer D with 4 pins
•
CAN 2.0 A/B Module with 2-pin ports used to transmit and receive
•
Two Serial Communications Interfaces (SCI0 and SCI1), each
with two pins, or four additional GPIO lines
•
Serial Peripheral Interface (SPI), with configurable 4-pin port, or
four additional GPIO lines
•
Computer Operating Properly (COP) Watchdog Timer
•
Two dedicated external interrupt pins
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Motorola DSP Advantages and Features
•
Fourteen dedicated General Purpose I/O (GPIO) pins, 18
multiplexed GPIO pins
•
External reset pin for hardware reset
•
JTAG/On-Chip Emulation (OnCE)
•
Software-programmable, Phase-Locked-Loop-based frequency
synthesizer for the DSP core clock
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Table 1-1. Memory Configuration
DSP56F801
DSP56F803
DSP56F805
DSP56F807
Program Flash
8188 x 16-bit
32252 x 16-bit
32252 x 16-bit
61436 x 16-bit
Data Flash
2K x 16-bit
4K x 16-bit
4K x 16-bit
8K x 16-bit
Program RAM
1K x 16-bit
512 x 16-bit
512 x 16-bit
2K x 16-bit
Data RAM
1K x 16-bit
2K x 16-bit
2K x 16-bit
4K x 16-bit
Boot Flash
2K x 16-bit
2K x 16-bit
2K x 16-bit
2K x 16-bit
The most interesting peripherals, from the switched reluctance motor
control point of view, are the fast Analog-to-Digital Converter (ADC) and
the Pulse-Width-Modulation (PWM) on-chip modules. They offer
extensive freedom of configuration, enabling efficient control of SR
motors.
The PWM module incorporates a PWM generator, enabling the
generation of control signals for the motor power stage. The module has
the following features:
•
Three complementary PWM signal pairs, or six independent PWM
signals
•
Complementary channel operation
•
Deadtime insertion
•
Separate top and bottom pulse width correction via current status
inputs or software
•
Separate top and bottom polarity control
•
Edge-aligned or center-aligned PWM signals
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Introduction
•
15 bits of resolution
•
Half-cycle reload capability
•
Integral reload rates from 1 to 16
•
Individual software-controlled PWM output
•
Programmable fault protection
•
Polarity control
•
20mA current sink capability on PWM pins
•
Write-protectable registers
The SR motor control application utilizes the PWM module set in
independent PWM mode, permitting fully independent generation of
control signals for all switches of the power stage. In addition to the PWM
generators, the PWM outputs can be controlled separately by software,
allowing the setting of the control signal to logical 0 or 1. Thus, the state
of the control signals can be changed instantly at a given rotor position
(phase commutation) without changing the contents of the PWM value
registers. This change can be made asynchronously with the PWM duty
cycle update.
The Analog-to-Digital Converter (ADC) consists of a digital control
module and two analog sample and hold (S/H) circuits. It has the
following features:
•
12-bit resolution
•
Maximum ADC clock frequency is 5MHz with 200ns period
•
Single conversion time of 8.5 ADC clock cycles (8.5 x 200 ns =
1.7µs)
•
Additional conversion time of 6 ADC clock cycles (6 x 200 ns =
1.2µs)
•
Eight conversions in 26.5 ADC clock cycles (26.5 x 200 ns =
5.3µs) using simultaneous mode
•
ADC can be synchronized to the PWM via the sync signal
•
Simultaneous or sequential sampling
•
Internal multiplexer to select two of eight inputs
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Introduction
Motorola DSP Advantages and Features
•
Ability to sequentially scan and store up to eight measurements
•
Ability to simultaneously sample and hold two inputs
•
Optional interrupts at end of scan at zero crossing or if an
out-of-range limit is exceeded
•
Optional sample correction by subtracting a pre-programmed
offset value
•
Signed or unsigned result
•
Single ended or differential inputs
The application utilizes the ADC on-chip module in simultaneous mode
and sequential scan. The sampling is synchronized with the PWM
pulses for precise sampling and reconstruction of phase currents. Such
a configuration allows instant conversion of the desired analog values of
all phase currents, voltages and temperatures.
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Introduction
Designer Reference Manual
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
Section 2. Target Motor Theory
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2.1 Contents
2.2
Switched Reluctance Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3
Mathematical Description of SR Motor . . . . . . . . . . . . . . . . . . . 24
2.4
Digital Control of SR Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
2.5
Voltage and Current Control of SR Motors . . . . . . . . . . . . . . . . 30
2.2 Switched Reluctance Motor
A Switched Reluctance (SR) motor is a rotating electric machine where
both stator and rotor have salient poles. The stator winding is comprised
of a set of coils, each of which is wound on one pole. The rotor is created
from lamination in order to minimize the eddy-current losses.
SR motors differ in the number of phases wound on the stator. Each of
them has a certain number of suitable combinations of stator and rotor
poles. Figure 2-1 illustrates a typical 3-phase SR motor with a 6/4
(stator/rotor) pole configuration.
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Target Motor Theory
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Target Motor Theory
Phase C
Phase A
Phase B
Stator (6 poles)
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Stator
Winding
Rotor (4 poles)
Aligned position
on Phase A
Figure 2-1. 3-Phase 6/4 SR Motor
The motor is excited by a sequence of current pulses applied at each
phase. The individual phases are consequently excited, forcing the
motor to rotate. The current pulses need to be applied to the respective
phase at the exact rotor position relative to the excited phase. When any
pair of rotor poles is exactly in line with the stator poles of the selected
phase, the phase is said to be in an aligned position, i.e., the rotor is in
the position of maximal stator inductance (see Figure 2-1). If the
interpolar axis of the rotor is in-line with the stator poles of the selected
phase, the phase is said to be in an unaligned position - the rotor is in a
position of minimal stator inductance. The inductance profile of SR
motors is triangular shaped, with maximum inductance when it is in an
aligned position and minimum inductance when unaligned. Figure 2-2
illustrates the idealized triangular-like inductance profile of all three
phases of an SR motor with phase A highlighted. The individual Phases
A, B, and C are shifted electrically by 120o relative to each other. The
interval, when the respective phase is powered, is called the dwell angle
- θdwell. It is defined by the turn-on θon and the turn-off θoff angle.
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Switched Reluctance Motor
Freescale Semiconductor, Inc...
When the voltage is applied to the stator phase, the motor creates torque
in the direction of increasing inductance. When the phase is energized
in its minimum inductance position, the rotor moves to the forthcoming
position of maximal inductance. The movement is defined by the
magnetization characteristics of the motor. A typical current profile for a
constant phase voltage is shown in Figure 2-2. For a constant phase
voltage the phase current has its maximum in the position when the
inductance starts to increase. This corresponds to the position when the
rotor and the stator poles start to overlap. When the phase is turned off,
the phase current falls to zero. The phase current present in the region
of decreasing inductance generates negative torque. The torque
generated by the motor is controlled by the applied phase voltage and
by the appropriate definition of switching turn-on and turn-off angles. For
more details, see Miller, T.J.E., Switched Reluctance Motors and Their
Control.
As is apparent from the description, the SR motor requires the position
feedback for motor phase commutation. In many cases, this requirement
is addressed by using position sensors, like encoders, Hall sensors, etc.
The result is that the implementation of mechanical sensors increases
costs and decreases system reliability. Traditionally, developers of
motion control products have attempted to lower system costs by
reducing the number of sensors. A variety of algorithms for sensorless
control have been developed, most of which involve evaluation of the
variation of magnetic circuit parameters that are dependent on the rotor
position, see AN1912/D of Motorola Inc.
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Aligned
Unaligned
Aligned
Stator Phase A
Rotor
Freescale Semiconductor, Inc...
LC
iphA
LB
LA
position / time
θdwell
phase A
energizing
θon_phA
θoff_phA
position / time
Figure 2-2. Phase Energizing
The motor itself is a low cost machine of simple construction.
High-speed operation is possible, thus the motor is suitable for high
speed applications, like vacuum cleaners, fans, white goods, etc. As
discussed above, the disadvantage of the SR motor is the need for
shaft-position information for the proper switching of individual phases.
Also, the motor structure causes noise and torque ripple. The greater the
number of poles, the smoother the torque ripple, but motor construction
and control electronics become more expensive. Torque ripple can also
be reduced by advanced control techniques, such as phase current
profiling.
2.3 Mathematical Description of SR Motor
An SR motor is a highly non-linear system, so a non-linear theory
describing the behavior of the motor was developed. Based on this
theory, a mathematical model can be created. On one hand, it enables
the simulation of SR motor systems, and on the other hand, it makes the
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Target Motor Theory
Mathematical Description of SR Motor
development and implementation of sophisticated algorithms for
controlling the SR motors easier.
The electromagnetic circuit of the SR motor is characterized by
non-linear magnetization. Figure 2-3 illustrates a magnetization
characteristic for a specific SR motor. It is a function between the
magnetic flux ψ, the phase current i and the motor position θ. The
influence of the phase current is mostly apparent in the aligned position,
where saturation effects can be observed.
Freescale Semiconductor, Inc...
The magnetization characteristics curve defines the non-linearity of the
motor. The torque generated by the motor phase is a function of the
magnetic flux, therefore the phase torque is not constant for a constant
phase current for different motor positions. This creates torque ripple
and noise in the SR motor.
Figure 2-3. Magnetization Characteristics of SR Motor
A mathematical model of an SR motor can be developed. The model is
based on the electrical diagram of the motor, incorporating the phase
resistance and phase inductance. The diagram for one phase is
illustrated in Figure 2-4.
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iph
rph
Lph=f(θ)
Freescale Semiconductor, Inc...
uph
Figure 2-4. Electrical Diagram of One SR Motor Phase
According to Figure 2-4, any voltage applied to a phase of the SR motor
can be described as a sum of voltage drops in the phase resistance and
induced voltages on the phase inductance:
u ph ( t ) = r ph ⋅ i ph ( t ) + u Lph ( t )
(EQ 2-1.)
where:
uph
is the voltage applied to a phase
rph
is the phase resistance
iph
is the phase current
uLph
is the induced voltage over the phase inductance.
The equation (EQ 2-1.) supposes that all phases are independent and
have no mutual influence.
The induced voltage uLph is defined by the magnetic flux linkage Ψph ,
that is a function of the phase current iph and the rotor position θph. So
the induced voltage can be expressed as:
∂Ψ ph ( i ph, θ ph ) di ph ∂Ψ ph ( i ph, θ ph ) dθ ph
dΨ ph ( i ph, θ ph )
u Lph ( t ) = ---------------------------------- = ----------------------------------- ⋅ --------- + ----------------------------------- ⋅ ---------∂i ph
∂θ ph
dt
dt
dt
(EQ 2-2.)
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Target Motor Theory
Mathematical Description of SR Motor
Then the phase voltage can be expressed as:
dΨ ph ( i ph, θ ph )
u ph ( t ) = r ph ⋅ i ph ( t ) + ---------------------------------dt
(EQ 2-3.)
or:
∂Ψ ph ( i ph, θ ph ) di ph ∂Ψ ph ( i ph, θ ph )
- ⋅ --------- + ----------------------------------- ⋅ ω
u ph ( t ) = r ph ⋅ i ph ( t ) + ---------------------------------∂i ph
∂θ ph
dt
Freescale Semiconductor, Inc...
(EQ 2-4.)
where:
ω
is the angular speed of the motor.
The torque Mph generated by one phase can be expressed as:
I ph
M ph =
∫
∂Ψ ph ( i ph, θ ph )
----------------------------------- di ph
∂θ ph
(EQ 2-5.)
0
The mathematical model of an SR motor is then represented by a
system of equations, describing the conversion of electromechanical
energy.
For 3-phase SR motors the equation (EQ 2-4.) can be expanded as
follows:
∂Ψ a ( i a, θ a ) di a ∂Ψ a ( i a, θ a )
u a ( t ) = r a ⋅ i a ( t ) + --------------------------- ⋅ ------ + --------------------------- ⋅ ω
∂i a
∂θ a
dt
(EQ 2-6.)
∂Ψ b ( i b, θ b ) di b ∂Ψ b ( i b, θ b )
- ⋅ ------- + --------------------------- ⋅ ω
u b ( t ) = r b ⋅ i b ( t ) + -------------------------∂i b
∂θ b
dt
(EQ 2-7.)
∂Ψ c ( i c, θ c ) di c ∂Ψ c ( i c, θ c )
u c ( t ) = r c ⋅ i c ( t ) + -------------------------- ⋅ ------ + --------------------------- ⋅ ω
∂i c
∂θ c
dt
(EQ 2-8.)
where a, b, c index the individual phases.
As stated in the above equations, the mutual effect between individual
phases is not considered.
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2.4 Digital Control of SR Motor
Freescale Semiconductor, Inc...
The SR motor is driven by voltage strokes coupled with the given rotor
position. The profile of the phase current together with the magnetization
characteristics define the generated torque and thus the speed of the
motor. Due to this fact, the motor requires electronic control for
operation. Several power stage topologies are being implemented,
according to the number of motor phases and the desired control
algorithm. The particular structure of the SR power stage structure
defines the freedom of control for an individual phase.
A power stage with two independent power switches per motor phase is
the most used topology. Such a power stage for 3-phase SR motors is
illustrated in Figure 2-5. It permits control of the individual phases fully
independent of each other and thus allows the widest freedom of control.
Other power stage topologies share some of the power devices for
several phases, thus saving on power stage cost, but with these, the
phases cannot be controlled fully independently. Note, that this
particular topology of SR power stage is fault tolerant, in contrast to
power stages of AC induction motors, because it eliminates the
possibility of a rail-to-rail short circuit.
During normal operation, the electromagnetic flux in SR motor is not
constant and must be built for every stroke. In the motoring period, these
strokes correspond to the rotor position when the rotor poles are
approaching the corresponding stator pole of the excited phase. In case
of Phase A, shown in Figure 2-1, the stroke can be established by
activating the switches Q1 and Q2. At low-speed operation the Pulse
Width Modulation (PWM), applied to the corresponding switches,
modulates the voltage level.
Two basic switching techniques can be applied:
•
Soft switching - where one transistor is turned on during the whole
commutation period and PWM is applied to the other one
•
Hard switching - where PWM is applied to both transistors
simultaneously
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Target Motor Theory
Digital Control of SR Motor
DC Voltage
Q1
PWM_Q1
+
D1
Phase A
Q3
PWM_Q3
Phase B
Q5
PWM_Q5
D1
Phase C
Cap
D2
D2
Q2
Freescale Semiconductor, Inc...
D1
PWM_Q2
D2
Q4
PWM_Q4
Q6
PWM_Q6
GND
Figure 2-5. 3-Phase SR Power Stage
Figure 2-6 illustrates both soft and hard switching PWM techniques. The
control signals for upper and lower switches of the above-described
power stage define the phase voltage and thus the phase current. The
soft switching technique generates lower current ripple compared to the
hard switching technique. Also, it produces lower acoustic noise and
less EMI. Therefore, soft switching techniques are often preferred for
motoring operation.
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Unaligned
Aligned
Unaligned
Aligned
Stator Poles
Rotor Poles
Inductance
PWM
Upper Switch
PWM
Freescale Semiconductor, Inc...
PWM
Lower Switch
+VDC
+VDC
Phase Voltage
-VDC
-VDC
Phase Current
Turn On
Turn Off
Position
Turn On
Soft Switching
Turn Off
Position
Hard Switching
Figure 2-6. Soft Switching and Hard Switching
2.5 Voltage and Current Control of SR Motors
A number of control techniques for SR motors exist. They differ in the
structure of the control algorithm and in position evaluation. Two basic
techniques for controlling SR motors can be distinguished, according to
the motor variables that are being controlled:
•
Voltage control - where phase voltage is a controlled variable
•
Current control - where phase current is a controlled variable
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Target Motor Theory
Voltage and Current Control of SR Motors
2.5.1 Voltage Control of an SR Motor
In voltage control techniques, the voltage applied to the motor phases is
constant during the complete sampling period of the speed control loop.
The commutation of the phases is linked to the position of the rotor.
Freescale Semiconductor, Inc...
The voltage applied to the phase is directly controlled by a speed
controller. The speed controller processes the speed error, the
difference between the desired speed and the actual speed, and
generates the desired phase voltage. The phase voltage is defined by a
PWM duty cycle implemented at the DC-Bus voltage of the SR inverter.
The phase voltage is constant during a complete dwell angle. The
technique is illustrated in Figure 2-7. The current and the voltage
profiles can be seen in Figure 2-8. The phase current is at its peak at the
position when the inductance starts to increase (stator and rotor poles
start to overlap) due to change in the inductance profile.
.
Power Stage
Controller
ωdesired
Σ
-
ωerror
ωactual
Speed
Controller
PWM Output
Duty Cycle
PWM
Generator
θon
θoff
Figure 2-7. Voltage Control Technique
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L
iph
UDC-Bus*PWM
θoff
position / time
uph
position / time
PWM = Speed
Controller Output
Freescale Semiconductor, Inc...
θon
phase current
decays through
the fly back diodes
-UDC-Bus
Figure 2-8. Voltage Control Technique - Voltage and Current Profiles
2.5.2 Current Control of an SR Motor
In current control techniques, the voltage applied to the motor phases is
modulated to reach the desired current at the powered phase. For most
applications, the desired current is constant during the complete
sampling period of the speed control loop. The commutation of the
phases is linked to the position of the rotor.
The voltage applied to the phase is controlled by a current controller with
an external speed control loop. The speed controller processes the
speed error, the difference between the desired speed and the actual
speed, and generates the desired phase current. The current controller
evaluates the difference between actual and desired phase current and
calculates the appropriate PWM duty cycle. The phase voltage is
defined by a PWM duty cycle implemented at the DC-Bus voltage of the
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Voltage and Current Control of SR Motors
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SR inverter. Thus, the phase voltage is modulated at the rate of the
current control loop. This technique is illustrated in Figure 2-9.
The processing of the current controller needs to be linked to the
commutation of the phases. When the phase is turned on (commutated),
a duty cycle of 100% is applied to the phase. The increasing actual
phase current is regularly compared to the desired current. As soon as
the actual current slightly exceeds the desired current, the current
controller is turned on. Current controller controls the output of the duty
cycle until the phase is turned off (following commutation). The
procedure is repeated for each commutation cycle of the motor. The
current and the voltage profiles can be seen in Figure 2-10. In ideal
cases, the phase current is controlled to follow the desired current.
Power Stage
Controller
ωerror
ωdesired
Σ
-
idesired
Speed
Controller
ωactual
Current
Controller
Σ
-
PWM Output
Duty Cycle
ierror
iactual
θon
PWM
Generator
θoff
Figure 2-9. Current Control Technique
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L
idesired
iph
θon
θoff
Freescale Semiconductor, Inc...
UDC-Bus
phase current
decays through
the fly back diodes
position / time
uph
PWM = Current
Controller Output
PWM = 100%
position / time
-UDC-Bus
Figure 2-10. Current Control Technique - Voltage and Current Profiles
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
Section 3. Switched Reluctance Motor Control Techniques
with Encoder Position Sensor
Freescale Semiconductor, Inc...
3.1 Contents
3.2
Encoder Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.3
Commutation Angle Calculation . . . . . . . . . . . . . . . . . . . . . . . . 37
3.4
Commutation Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
3.5
Current Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
3.2 Encoder Sensor
Whenever mechanical rotary motions have to be monitored, the encoder
is the most important interface between the mechanics and the control
unit. Encoders transform rotary or linear movement into a sequence of
electrical pulses. A rotary encoder can differentiate a number of discrete
positions per revolution. The number of segments determines the
resolution of the movement and hence the accuracy of the position and
this number is called points-per-revolution. The speed of an encoder is
in counts-per-second.
Although there are various kinds of digital encoders, the most common
one is the optical encoder. Rotary and linear optical encoders are used
frequently for motion and position sensing. A disc or a plate containing
opaque and transparent segments passes between a light source (such
as LED) and detector to interrupt a light beam. The electronic signals
that are generated are then fed into the DSP controller where position
and velocity information is calculated based upon the signals received.
Many incremental encoders also have a feature called the index pulse.
In rotary encoders, an index pulse occurs once per encoder revolution.
It is used to establish an absolute mechanical reference position within
one encoder count of the 360° encoder rotation. The index signal can be
used to do several tasks in the system. It can be used to reset or preset
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Switched Reluctance Motor Control Techniques
the position counter and/or generate an interrupt signal to the system
controller.
90° el
Freescale Semiconductor, Inc...
Phase A
Phase B
time
Figure 3-1. Quadrature Encoder Signals
Quadrature encoders are a particular kind of incremental encoder with
at least two output signals, generally called Phase A and Phase B. As
seen in Figure 3-1, channel B is offset 90 degrees from channel A. The
addition of a second channel provides direction information in the
feedback signal. This signal, leading or lagging by 90 electrical degrees,
guarantees the exact determination of the direction of rotation at all
times. The ability to detect direction is critical if encoder rotation stops on
a pulse edge. Without the ability to decode direction, the counter may
count each transition through the rising edge of the signal and lose
position. Another benefit of the quadrature signal scheme is the ability to
electronically multiply the counts during one encoder cycle. In the
times-1 mode, all counts are generated on the rising edges of channel
A. In the times-2 mode, both the rising and falling edges of channel A are
used to generate counts. In the times-4 mode, the rising and falling
edges of channel A and channel B are used to generate counts. This
increases the resolution by a factor of four. For encoders with sine wave
output, the channels may be interpolated for very high resolution.
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Switched Reluctance Motor Control Techniques with Encoder Position Sensor
Commutation Angle Calculation
3.3 Commutation Angle Calculation
In an SR motor, the switched-on and switched-off angles are complex
functions of many parameters and are variable for optimum operation.
Their fine tuning is necessary to maintain optimum performance at
different motor speed and load conditions. The control of firing angle can
be accomplished in a number of ways and strongly depends on position
sensor. If the position information is precisely acquired, it is possible to
suitably utilize a sophisticated algorithm.
Freescale Semiconductor, Inc...
This control technique varies the firing angle continuously with the fixed
dwell angle. The switched-on angle is calculated in such a way that the
excitation current should reach the maximum defined value at the
beginning of the stator and rotor tooth overlap. The phase current is built
up in corresponding windings of the stator since the inductance is at a
minimum level in an unaligned position and there is adequate time to
increase it to the desired value before the motoring torque is being
produced. The conduction angle remains fixed through the entire run of
the application to ensure the phase current is decreased before reaching
the braking region (following the aligned position). The calculation
neglects the stator winding resistance, which simplifies the equation.
The resistance neglect can be recognized only at large values of
resistance R, which is the case of very small switched reluctance
machines.
Figure 3-2 explains the proposed algorithm for advance angle
calculation. The computation method is derived from (EQ 2-6.) (EQ 2-8.) and is rearranged into the following expression as:
di ph
dL ph
u ph = r ph i ph + L ph ⋅ -------- + i ph ⋅ ----------- ⋅ ω
dt
dθ
(EQ 3-1.)
where:
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uph
is the voltage applied to a phase
rph
is the phase resistance
iph
is the phase current
Lph
is the phase inductance
θ
is the rotor position
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idesired
iphase
Lunaligned
Freescale Semiconductor, Inc...
0°
uapplied
θon
position / time
100% PWM
Figure 3-2. Commutation Angle Calculation
The unaligned phase inductance is considered as constant near the
turn-on instant. If voltage drop across phase resistance is neglected,
then the following expression is given as (EQ 3-2.) using a first order
approximation:
i desired
θ on = L unaligned ⋅ --------------⋅ ω actual
u ph
(EQ 3-2.)
where:
θon
is the advance angle
idesired is the desired current to be achieved
Lunaligned is the unaligned inductance
uphase is the applied phase voltage
ωactual is the actual rotor speed
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Switched Reluctance Motor Control Techniques with Encoder Position Sensor
Commutation Strategy
3.4 Commutation Strategy
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In general, the commutation strategy determines the performance of the
SR motor. The commutation method uses rotor position feedback to
derive the commutating signals for the inverter switches. The controlled
parameters are the applied phase voltage and the turn-on angle θon. The
dwell angle is fixed prior to the motor starts. The number of
commutations per mechanical revolution is proportional to the number of
rotor poles and number of stator phases (EQ 3-3.). It arises from the
mechanical construction of the SR motor. The number of motor
commutations is calculated as follows:
NumOfCommut = N r ⋅ m
(EQ 3-3.)
where:
NumOfCommut is the number of commutations per one mechanical
revolution
Nr
is the number of rotor poles
m
is the number of stator phases
An SR motor is usually described in terms of low-speed and high-speed
regions. The low-speed operating region is graphically depicted in
Figure 3-3. In this low-speed operating area, the phase current can be
arbitrarily controlled to any desired value. Increasing the rotor speed
makes it difficult to control the phase current. There is an influence of
back-EMF effect combined with a diminishing amount of time to perform
the commutation.
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Switched Reluctance Motor Control Techniques
Current
Actual Inductance
Estimated Inductance
iph
Freescale Semiconductor, Inc...
idesired
0°
θadvance
θon
UDC-Bus
θedge
uapplied
θoff
360°
Position / Time
idesired reached
PWM = 100%
PWM = Current
Controller Output
-UDC-Bus
Figure 3-3. Commutation Strategy
The commutation itself can be performed in a number of ways. The
presented control technique utilizes the encoder sensor information to
initiate the commutation routine, which ensures turn-off of the previous
stator phase, and consecutively the next stator phase is turned on
depending on the direction of the rotor rotation. The appropriate firing
angle, θon, is calculated through advance angle calculation (see
Section 3.3). The commutation software algorithm determines the
necessary advance angle, θadvance, for turning on the correct stator
phase. In the θadvance instant, full DC-Bus voltage is applied after
switching on the correct phase. If actual value of the phase current
exceeds desired current value then the current controller with sufficient
controller initialization is started to maintain actual value of the phase
current within the requested magnitude. This is achieved by chopping
the DC-Bus voltage.
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Switched Reluctance Motor Control Techniques with Encoder Position Sensor
Current Controller
The simplest scheme is to leave the lower transistor on during current
regulation and to switch the upper one on and off at a high fixed PWM
frequency with a varying duty cycle. This strategy is often called soft
switching (see Figure 2-6). The current waveform during soft switching
is similar to that shown in Figure 3-3.
3.5 Current Controller
Freescale Semiconductor, Inc...
Basically, there are three different modes of operation, namely, voltage
control, current control, and single-pulse control. The current control
method is normally used to control the torque efficiently, while
single-pulse mode is entered for high-speed operation. Major difficulty,
when designing switched reluctance motor current controllers, is that the
winding back electromotive force (back-EMF) and the electrical time
constant vary significantly within one electrical cycle and with the motor
speed and the phase current level. The voltage equation of the SRM is
given by (EQ 2-4.). This equation indicates a non-linear model, which is
dependent on position, current and speed. The electrical time constant
of a phase winding and the back-EMF vary greatly with current and rotor
position.
As Figure 3-3 implies, the current controller is switched on when the
desired stator phase current is reached. At this point, the slope of
increasing inductance (inductance derivation over position) is
considered as a constant value, and the phase current is preserved at a
defined target value; then (EQ 2-4.) can be rearranged as follows:
dL ph ( θ ph )
u phase_applied ( t ) = r ph ⋅ i ph ( t ) + i ph ( t ) ⋅ -----------------------⋅ω
dθ ph
(EQ 3-4.)
The applied phase voltage is roughly maintained near the value of
(EQ 3-4.), where iph is the desired phase current, and ω is the actual
angular speed of the rotor. Derivation over the position of the
corresponding phase inductance is determined from motor parameter
measurements. Knowing these parameters, the initial current controller
is set up using (EQ 3-4.) in the time instance (see the red point in
Figure 3-4) when the controller is switched on.
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Switched Reluctance Motor Control Techniques
idesired reached
uapplied
UDC-Bus
uapplied
Position / Time
Freescale Semiconductor, Inc...
PWM = 100%
PWM = Current
Controller Output
-UDC-Bus
Figure 3-4. Phase Voltage Generation
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
Section 4. System Description
Freescale Semiconductor, Inc...
4.1 Contents
4.2
System Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.3
Application Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.2 System Outline
This system is designed to drive a 3-phase SR motor. The application
meets the following performance specifications:
•
Speed control of an SR motor with Encoder position sensor with
an inner current closed loop
•
Targeted for DSP56F803EVM, DSP56F805EVM,
DSP56F807EVM
•
Running on a 3-phase SR HV motor control development platform
at a variable line voltage of between 115V AC and 230V AC
(voltage range -15% ... +10%)
•
The control technique incorporates
– current SRM control with speed closed loop
– motor starts from any motor position with rotor alignment
– one direction of rotation
– motoring mode
– minimal speed 600 rpm
– maximal speed 2600 rpm at input power line 230V AC
– maximal speed 1600 rpm at input power line 115V AC
•
Encoder position reference for commutation
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Freescale Semiconductor, Inc...
System Description
•
Manual interface (Start/Stop switch, Up/Down push button control,
LED indicator)
•
PC master software control interface (motor Start/Stop, speed
setup)
•
Power stage identification
•
DC-Bus over-voltage, DC-Bus under-voltage, DC-Bus
over-current and over-heating fault protection
•
PC master software monitor
– graphical control page (required speed, actual motor speed,
operational mode PC/manual, start/stop status, drive fault
status, DC-Bus voltage level, identified power stage boards,
system status)
– speed scope (observes actual and desired speeds)
– current controller (observes actual and desired phase current,
applied phase voltage)
4.3 Application Description
For the drive, a standard system concept was chosen (see Figure 4-1).
The system incorporates the following hardware parts:
•
A 3-phase SR high-voltage development platform (power stage
with optoisolation board, motor brake)
•
Feedback sensors: DC-Bus voltage, phase A current, phase B
current, phase C current, temperature
•
A DSP56F80x controller board
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System Description
Application Description
3-Phase SR Power Stage
Line AC
AC
6
SRM
DC
Voltage
Current
Temperature
DSP56F80x
Freescale Semiconductor, Inc...
Speed
Cmd.
Speed
Error
DOWN
Speed
Controller
-
LOAD
E
ADC
Fault Protection
START
STOP
PWM
Current
Cmd.
Current
Error
Current
Controller
Desired
Duty
Volatge DC-Bus Cycle
Ripple
Elimination
PWM
Generation
-
UP
MUX
DC Bus
Voltage
PC Remote
Control
Commutation
Phase Current
SCI
Commutation
Angle
Calculation
Speed Feedback
Speed Feedback
Speed
Calculation
Position
Feedback
Quad
Dec
Figure 4-1. System Concept
The DSP runs the main control algorithm. It generates 3-phase PWM
output signals for the SR motor power stage according to the user
interface input and feedback signals.
The drive can be controlled in two different ways (or operational modes):
•
In Manual operational mode, the required speed is set by a
Start/Stop switch and Up and Down push buttons.
•
In PC master software operational mode, the required speed is set
by the PC master software
After RESET, the drive is initialized and it automatically enters MANUAL
operational mode. Note, that PC master software can only take over the
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System Description
control when the motor is stopped. When the Start command is detected
(using the Start/Stop switch or the PC master software “Start” button)
and while no fault is pending, the start-up sequence with the rotor
alignment is performed and the motor is started.
Freescale Semiconductor, Inc...
Rotor position is evaluated using an encoder position sensor. The
commutation angle is calculated according to the desired speed, the
desired current and the actual DC-Bus voltage. When the actual position
of the rotor is equal to the reference position, the commutation of the
phases in the desired direction of rotation is done; the actual phase is
turned off and the following phase is turned on.
The actual motor speed is derived from the position information, so an
additional velocity sensor is unneeded. The reference speed is
calculated according to the control signals (Start/Stop switch, Up/Down
push buttons) and PC master software commands (when controlled by
the PC master software). The acceleration/deceleration ramp is
implemented. The comparison between the reference speed and the
measured speed gives a speed error. Based on the speed error, the
speed controller generates the desired phase current. When the phase
is commutated, it is turned on with a duty cycle of 100%. Then, during
each PWM cycle, the actual phase current is compared with the desired
current. As soon as the actual current exceeds the desired current, the
current controller is turned on. The current controller controls the output
duty cycle until the phase is turned off (following commutation). Finally,
the 3-phase PWM control signals are generated. The procedure is
repeated for each commutation cycle of the motor.
DC-Bus voltage, DC-Bus current, and power stage temperature are
measured during the control process. The measurements are used for
DC-Bus over-voltage, DC-Bus under-voltage, DC-Bus over-current and
over-temperature protection of the drive. The DC-Bus under-voltage and
the over-temperature protection are performed by software, while the
DC-Bus over-current and the DC-Bus over-voltage fault signals utilize
fault inputs of the DSP on-chip PWM module. The line voltage is
measured during initialization of the application. According to the
detected level, the 115VAC or 230VAC mains are recognized. If the line
voltage is detected outside the -15% ... +10% range of the nominal
voltage, the fault "Out of the Mains Limit" disables the drive operation. If
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System Description
Application Description
Freescale Semiconductor, Inc...
any of the above mentioned faults occur, the motor control PWM outputs
are disabled in order to protect the drive. The fault status can only be
exited when the fault conditions have disappeared and the Start/Stop
switch is toggld through the STOP position. The fault state is indicated
by the on-board LED.
The SR power stage uses a unique configuration of power devices,
different than AC or BLDC configuration. The SR software would cause
the destruction of AC or BLDC power stages due to simultaneous
switching of the power devices. Since the application software could be
accidentally loaded into an AC or BLDC drive, the software incorporates
a protection feature to prevent this could happen. Each power stage
contains a simple module which generates a logic signal sequence that
is unique for that type of power stage. During the initialization of the chip,
this sequence is read and evaluated according to the decoding table. If
the correct SR power stage is not identified, the fault, "Wrong Power
Stage", disables the drive operation.
4.3.1 Initialization and Start-Up
Before the motor can be started, the rotor alignment and initialization of
the control algorithms must be performed (see Figure 4-2) since the
absolute position is not known.
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System Description
B
Start Command Accepted
{
C
A
Any Rotor Position
Turn on Phases B & C
Freescale Semiconductor, Inc...
Wait to Ensure the Initial Pulse
Turn Off Phase C
Wait 550msec
Rotor Stabilized
{
Measure Phase Resistance
as an Average of
32 Measurements
B
C
A
Phase B Aligned
Commutate Phases
(Turn off Phase B, Turn on Phase A)
Motor Starts
Figure 4-2. Start-Up Sequence
First, the rotor needs to be aligned to a known position to be able to start
the motor in the desired direction of rotation. This is done in the following
steps:
1. Two phases are turned on simultaneously (phases B & C)
2. After 50msec, one phase is turned off (phase C), the other phase
stays powered (phase B)
3. After an additional 550 msec, the rotor is stabilized enough in the
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System Description
Application Description
aligned position with respect to the powered phase (phase B).
Freescale Semiconductor, Inc...
Step 1 provides the initial impulse to the rotor. If phase B is exactly in an
unaligned position and thus does not generate any torque, phase C
provides the initial movement. Then, phase C is disconnected and phase
B stays powered (Step 2). The stabilization pulse to phase B must be
long enough to stabilize the rotor in the aligned position with respect to
that phase.
In total, the stabilization takes 1 sec. After this time, the rotor is stable
enough to reliably start the motor in the desired direction of rotation.
4.3.2 Position and Speed Sensing
The position information is used to generate accurate switching instants
of the power converter, ensuring drive stability and fast dynamic
response. Velocity feedback is derived from the position information, so
that an additional velocity sensor is unneeded. All members of the
Motorola DSP56F80x family, except for the 56F801, have an on-chip
quadrature decoder module connected to a quadrature timer. This
peripheral is commonly used for position and speed sensing.
The quadrature decoder position counter counts up/down each edge of
phase A and phase B signals according to their order (see Figure 4-3).
The phase A and the phase B inputs of the DSP controller are routed
through a switch matrix to a general purpose timer module and
quadrature decoder module as well (see Figure 4-4). The timer module
can use all four available inputs as normal timer input capture channels.
This does not preclude a use of the quadrature decoder module. Both
timer and decoder take an advantage of the digital filter incorporated in
the quadrature decoder module.
Figure 4-3. Quadrature Encoded Signals
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System Description
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The presented application uses the quad decoder module approach for
speed measurement using a 16-bit position difference counter. The
counter acts as a differentiator, whose count value is proportional to the
change in position, since the last time the position counter was read. The
speed can be computed by calculating the change in the position
counter per unit time, or by reading the position difference counter
register (POSD) and calculating the speed. The second method is
employed in this application for the rotor speed measurement and also
as a feedback signal to the speed controller. The position difference
register (POSD) is regularly scanned at the pre-defined time period and
consecutively this value is used to compute the actual rotor speed.
In addition, quadrature decoder module 0 shares pins with quadrature
timer module A. If the shared pins are not configured as timer outputs,
then the pins are available for use as inputs to the quad decoder
modules. The quad timer module contains four identical counter/timer
groups. Due to wide variability of quad timer modules, it is possible to
use this module to decode quadrature encoder signals and to sense the
position and the speed as well. The presented application uses the
configuration arranged for position sensing and commutation instance
determination. The quad timer A0 and the quad timer A1 decode primary
and secondary external inputs as quad-encoded signals generated by
the rotary sensor to monitor movement of the motor shaft. Quad signal
decoding provides both count and direction information. The A0 timer is
programmed to count up to a programmed value that corresponds to one
electric revolution and then immediately to re-initialize after the terminal
count value is reached. This A0 timer is assigned as a master and
broadcast compares signals to quad timer, A1. The A1 timer is
configured to be re-initialized to a predetermined value when a master
timer’s compare event occurs. This counter continues repeatedly
counting past the compare value. When the count matches the compare
value, an interrupt is enabled and the compare register 2 value is used
for commutation instances generation.
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System Description
Application Description
Not used
WATCHDOG
TIMER
Decoder 0 module
Freescale Semiconductor, Inc...
Phase A
Phase B
Index
Home
EDGE
DETECT
STATE
MACHINE
POSITION
DIFFERENCE
COUNTER
POSITION
COUNTER
REV
COUNTER
GLITCH
FILTER
Timer Input
Capture
Channels
DELAY
SWITCH
MATRIX
Timer
A0
Timer
A2
Timer
A1
Timer
A3
Timer A module
Figure 4-4. Decoder and Timer Arrangement
4.3.3 Commutation Algorithm
The SR motor commutation strategy uses rotor position feedback to
drive the commutating signals for the inverter switches. The core of the
control algorithm includes the calculation of the commutation angle, and
phases commutation. The calculation of the commutation angle is
performed according to (EQ 3-2.). It is calculated regularly during motor
operation.
The commutation algorithm is described in Figure 4-5. After the finish of
the start-up routine, which includes the alignment procedure and
initialization of the necessary commutation variables, the rotor is
sufficiently stabilized and is ready for run mode. This is the point from
which the commutation routine has to start. The first procedure of the
commutation routine is to turn on the corresponding phase. Choosing
the correct phase to switch it on depends on the defined rotation of the
rotor. The turn on angle is at the unaligned position, and the current rises
linearly until the poles begin to overlap.
In a regular switched reluctance motor, the angle of rising inductance is
half of the pole-pitch. The pole-pitch is the angle of rotation between two
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successive aligned positions. Ideally, the flux should be zero throughout
the period of falling inductance, because a current flowing in that period
produces a negative (or braking) torque. To avoid this, the dwell angle
θdwell can be restricted. In practice, a dwell angle of 120 electrical
degrees is usually used, because the gain in torque-impulse during the
increasing inductance exceeds the small braking torque impulse. This
condition occurs when the current has a tail extending beyond the
aligned position. The torque is negative during this tail period, but it is
small. The turn-off angle θoff instant is determined.
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System Description
Application Description
START
Turn ON
PHASE
Freescale Semiconductor, Inc...
θoff = θdwell + θon
θon=f(ω, i, u, L)
θon > θoff
NO
YES
NO
θoff = θon
θactual > θoff
YES
Turn OFF
PHASE
NO
θactual > θon
YES
Figure 4-5. Commutation Algorithm Flowchart
The next step of the proposed commutation algorithm is to calculate the
advance turn-on angle. The entire calculation explanation is presented
in 3.3 Commutation Angle Calculation. The firing angle θon is set up
for the next commutation instant. The presented commutation algorithm
does not allow parallel current conduction of two phases at the same
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System Description
time. The angle comparison of turn-on θon and turn-off θoff assures that
the current phase is turned off before the following phase is turned on.
In the case of 120-electrical-degree dwell angle, the switching on and
switching off are performed simultaneously. If the conduction (dwell)
angle is restricted, the turning off overtakes turning on, as is clear in
Figure 4-5. The comparison θactual > θoff block waits for an appropriate
position to commutate off the corresponding stator phase, and in the
next comparison θactual > θon block the algorithm remains the same until
the proper position occurs to switch on the following stator phase. The
algorithm loop is closed and ready for other commutation occurrences.
4.3.4 Current Controller Implementation
The current controller utilization flowchart reveals the algorithm process
of the controller switching. If the appropriate stator phase is turned on,
the DC-Bus voltage is applied to the corresponding rotor phase. The
phase current rises almost linearly until a predefined target value is
attained. At this point, by processing of the proposed algorithm, the
current controller is switched on and maintains the actual current flowing
within the desired value.
Before the current controller is switched on, the necessary initialization
is required. It is mainly concerned with the integral portion in the k-1 step
of the current PI controller. This part of the controller structure is preset
according to equation (EQ 3-4.). The following commutation instance
turns the controller flag off so the corresponding rotor phase is fully
voltage loaded until reaching the desired value of phase current.
Figure 4-6 clarifies the entire controller usage algorithm.
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System Description
Application Description
START
Commutate
?
NO
YES
Freescale Semiconductor, Inc...
Controller OFF
NO
Controller
OFF ?
YES
iphase>idesired
NO
YES
Controller ON
Controller INIT
uapplied =U_dc_bus
uapplied = controller
Figure 4-6. Current Controller Utilization
4.3.5 Current and Voltage Measurement
Precise measurement of phase current and DC-Bus voltage is a key
factor for current control implementation.
4.3.5.1 Current Sensing
Current measurement needs to be investigated according to the used
current sensors and the influence of the noise on the measurement.
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The quality of current measurement depends heavily on the type of
current sensors used. The most useful are Hall effect sensors.
Unfortunately, these sensors are expensive and thus not suitable for
most cost-sensitive applications. Therefore, current shunt resistors
inserted into the current path of the phase are often implemented (see
Figure 4-7). The phase current is sensed as a voltage drop across the
sense resistor.
Freescale Semiconductor, Inc...
+ DC Bus Voltage
T1
D1
PWM_T1
Phase A
D2
T2
PWM_T2
R3
sense
R2
R4
GND
V_ref
ADC
+
R_sense
R1
-
sense
OP
1.65V ref
Figure 4-7. Shunt Resistors Current Sensors
When the power switches’ soft switching is used (the lower switch is left
on during a complete commutation period, while the upper switch is
modulated by the PWM), the current is not visible on the shunt resistor
all the time. The soft switching phase current, measured at the shunt
resistor, is shown in Figure 4-8. The phase current is visible only when
both switches are turned on (the phase current flows through switches
and the sensing resistor) or when both switches are turned off (the phase
current flows through the freewheeling diodes and the sensing resistor).
When both switches of the phase are turned on, the measured current is
negative, so it needs to be inverted. The diagram shows that for a
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System Description
Application Description
reliable current shape reconstruction, the sensing needs to be
synchronized with the PWM frequency at the center of the PWM pulse
and both positive and the negative voltage drop polarities should be
measured. The zero current may be set to half of the ADC range, so both
the positive and the negative voltage drops on the phase current shunt
resistors can be measured. The voltage drop is then amplified according
to the ADC range. Proceeding like this, the current can be read with
accuracy and credibility.
Freescale Semiconductor, Inc...
Figure 4-9 illustrates the actual phase currents of a 3-phase motor,
measured on the shunt resistors as described above.
The previously specified current sensing method is described from the
DSP processor point of view. It seems the measured phase current is
negative, which is caused by inverting differential amplifier. Actually, the
measured phase current flowing through shunt resistor is sensed and
consecutively inverted by a differential amplifier.
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Top
Switch
(T1)
Time
Bottom
Switch
(T2)
Time
Sensed Voltage Drop
Actual Phase Current
Freescale Semiconductor, Inc...
T 1 T 2 D1 T 2
T1 T 2
D1 D2
0
Time
0
Time
ADC Synchronization
Figure 4-8. Soft Switching Current Sensed on ADC
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System Description
Application Description
Phase A
Current Sensing
Phase B
Phase C
0.4
Freescale Semiconductor, Inc...
Phase Current [A]
0.2
0
0
0.01
0.02
0.03
0.04
0.05
-0.2
-0.4
-0.6
-0.8
Time [sec]
Figure 4-9. Phase Current Measured at Current Shunt Resistors
The low-cost shunt resistor sensors create one serious issue. Due to the
low-voltage drop sensed across the shunt current resistors, the
measured signals are susceptible to noise.
A technique for noise elimination has been developed and successfully
implemented. The technique is based on the assumption that the same
noise is induced simultaneously on all measured signals. The method
supposes the measurement of two signals simultaneously, one known
signal (a reference) and one signal to be measured. Then the reference
signal consists of a known signal and noise, while the measured signal
consists of an actual signal and the same noise.
MeasuredSignal = ActualSignal + Noise
(EQ 4-1.)
ReferenceSignal = KnownSignal + Noise
(EQ 4-2.)
If the noise is the same, it can be eliminated by subtraction of the
reference signal from the measured signal. As described above, the
necessary condition is the simultaneous sampling of both signals,
ensuring that the noise on both signals is identical.
ActualSignal=MeasuredSignalReferenceSignal
+KnownSignal(EQ 4-3.)
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This technique has been implemented for phase current sensing. The
SR motor is controlled in a way in which the phases are commutated
sequentially, which means that when the working phase is turned off, the
following phase, in the direction of rotation, is turned on. Thus one phase
of the motor is never powered during a complete commutation interval.
This phase is considered as a reference. Because the reference phase
is not powered, the reference phase current should be equal to zero. The
measured value of the reference current can be then considered as
noise for a given commutation interval. The actual phase current is equal
to the difference between the measured current and the reference
current:
Iph = Isensed - Ireference
(EQ 4-4.)
The reference signal needs to be commutated together with the
commutation of the phases. Table 4-1 defines the active, discharge and
reference phases for the commutation sequence C - B - A - C. It is
derived from Figure 4-9.
Table 4-1. Commutation Sequence of the Reference Phase
Step
Active Phase
Discharge Phase
Reference Phase
1
C
A
B
2
B
C
A
3
A
B
C
1
C
A
B
The efficiency of the current sensing noise reduction technique is
illustrated in Figure 4-10. The figures illustrate the phase current as it is
measured (active phase current is inverted - compared to Figure 4-9),
and the same current with the implemented noise reduction technique.
As can be seen, the implemented technique improves current sensing
significantly. It eliminates not only the noise on the current sensors, but
also the noise induced on the sensing cables and the noise of the ADC
reference power supply.
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4.3.5.2 Voltage Sensing
The DC-Bus voltage sensor is represented by a simple voltage divider.
DC-Bus voltage does not change rapidly. It is nearly constant with the
ripple given by the power supply structure. If a bridge rectifier for
rectification of AC line voltage is used, the ripple frequency is two times
the AC line frequency. The ripple amplitude should not exceed 10% of
the nominal DC-Bus value, if the power stage is designed correctly.
Freescale Semiconductor, Inc...
The measured DC-Bus voltage needs to be filtered in order to eliminate
noise. One of the most useful techniques is at moving average filter, that
calculates an average value from the last N samples:
–N
u DCBus =
∑
u DCBus ( n )
(EQ 4-5.)
n=1
In order to increase the precision of the voltage sensing, the voltage drop
on the power switches and on the diodes of the power stage can be
incorporated into the determination of the actual voltage present in the
motor phase.
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I active not corrected
0.7
I discharge not corrected
0.6
Freescale Semiconductor, Inc...
current [A]
0.5
0.4
0.3
0.2
0.1
0
0
0.01
0.02
0.03
0.04
0.05
0.03
0.04
0.05
-0.1
time [sec]
I active
0.7
I discharge
0.6
current [A]
0.5
0.4
0.3
0.2
0.1
0
0
0.01
0.02
-0.1
time [sec]
Figure 4-10. Measured 3-Phase Currents without and with
Implemented Noise Correction
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4.3.6 Power Module Temperature Sensing
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The measured power module temperature is used for thermal protection.
The hardware realization is shown in Figure 4-11. The circuit consists of
four diodes connected in series, a bias resistor, and a noise suppression
capacitor. The four diodes have a combined temperature coefficient of
8.8 mV/οC. The resulting signal, Temp_sense, is fed back to an A/D input
where a software can be used to set safe operating limits. In the
presented application, the temperature in degrees Celsius is calculated
according to the conversion equation:
Temp_sense - b
temp = -------------------------------------a
(EQ 4-6.)
where:
temp
is the power module temperature in degrees Celsius
Temp_sense is voltage drop on diodes which is measured by ADC
a
is diode-dependent conversion constant (a = -0.0073738)
b
is diode-dependent conversion constant (b = 2.4596)
+3.3V_A
R1
2.2k - 1%
D1
D2
ADC
BAV99LT1
BAV99LT1
C1
100nF
Figure 4-11. Temperature Sensing Topology
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System Description
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
Section 5. Hardware Design
Freescale Semiconductor, Inc...
5.1 Contents
5.2
System Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.3
DSP56F805EVM Controller Board . . . . . . . . . . . . . . . . . . . . . . 67
5.4
3-Phase SR High-Voltage Power Stage . . . . . . . . . . . . . . . . . . 68
5.5
Optoisolation Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.6
Motor-Brake Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . .72
5.7
Hardware Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.2 System Configuration
The application is designed to drive the 3-phase SR motor. The
application is controlled by the Motorola DSP56F805 motor control DSP.
It consists of the following modules (see Figure 5-1):
•
DSP56F805EVM Control Board
•
3-Ph. SR High Voltage Power Stage
•
Optoisolation Board
•
3-phase Switched Reluctance Motor
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Hardware Design
Figure 5-1. 3-Phase SR High Voltage Platform Configuration
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DSP56F805EVM Controller Board
5.3 DSP56F805EVM Controller Board
The DSP56F805EVM is used to demonstrate the abilities of the
DSP56F805 and to provide a hardware tool allowing the development of
applications that use the DSP56F805.
Freescale Semiconductor, Inc...
The DSP56F805EVM is an evaluation module board that includes a
DSP56F805 part, peripheral expansion connectors, external memory
and a CAN interface. The expansion connectors are for signal
monitoring and user feature expandability.
The DSP56F805EVM is designed for the following purposes:
•
Allowing new users to become familiar with the features of the
56800 architecture. The tools and examples provided with the
DSP56F805EVM facilitate evaluation of the feature set and the
benefits of the family.
•
Serving as a platform for real-time software development. The tool
suite enables the user to develop and simulate routines, download
the software to on-chip or on-board RAM, run it, and debug it using
a debugger via the JTAG/OnCETM port. The breakpoint features of
the OnCE port enable the user to easily specify complex break
conditions and to execute user-developed software at full-speed,
until the break conditions are satisfied. The ability to examine and
modify all user accessible registers, memory and peripherals
through the OnCE port greatly facilitates the task of the developer.
•
Serving as a platform for hardware development. The hardware
platform enables the user to connect external hardware
peripherals. The on-board peripherals can be disabled, providing
the user with the ability to reassign any and all of the DSP's
peripherals. The OnCE port's unobtrusive design means that all
of the memory on the board and on the DSP chip are available to
the user.
The DSP56F805EVM provides the features necessary for a user to write
and debug software, demonstrate the functionality of that software and
interface with the customer's application-specific device(s). The
DSP56F805EVM is flexible enough to allow a user to fully exploit the
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DSP56F805's features to optimize the performance of their product, as
shown in Figure 5-2.
DSP56F805
Freescale Semiconductor, Inc...
RESET
LOGIC
RESET
MODE/IRQ
LOGIC
MODE/IRQ
Program Memory
64Kx16-bit
Address,
Data &
Control
SPI
SCI #0
RS-232
Interface
SCI #1
Peripheral
Expansion
Connector(s)
TIMER
Debug LEDs
PWM LEDs
Over V Sense
GPIO
Over I Sense
Memory
Expansion
Connector(s)
Zero Crossing
Detect
JTAG
Connector
DSub
25-Pin
DSub
9-Pin
CAN Interface
CAN
Data Memory
64Kx16-bit
4-Channel
10-bit D/A
JTAG/OnCE
PWM #1
A/D
Parallel
JTAG
Interface
PWM #2
Low Freq
Crystal
XTAL/EXTAL
3.3 V & GND
Primary
UNI-3
Secondary
UNI-3
Power Supply
3.3V, 5.0V & 3.3VA
Figure 5-2. Block Diagram of the DSP56F805EVM
5.4 3-Phase SR High-Voltage Power Stage
Motorola’s embedded motion control series high-voltage (HV) switched
reluctance (SR) power stage is a 180 watt (1/4 horsepower), 3-phase
power stage that will operate off of DC input voltages from 140 volts to
230 volts and AC line voltages from 100 volts to 240 volts. In
combination with one of Motorola’s Embedded Motion Control Series
control boards and an optoisolation board, it provides a software
development platform that allows algorithms to be written and tested,
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3-Phase SR High-Voltage Power Stage
without the need to design and build a power stage. It supports a wide
variety of algorithms for controlling switched reluctance motors.
Freescale Semiconductor, Inc...
Input connections are made via 40-pin ribbon cable connector J14.
Power connections to the motor are made on output connector J13.
Phase A, phase B, and phase C are labeled Ph. A, Ph. B, Ph. C on the
board. Power requirements are met with a single external 140-volt to
230-vo lt DC power supply or an AC line voltage. Either input is supplied
through connector J11. Current measuring circuitry is set up for 2.93
amps full scale. Both bus and phase leg currents are measured. A
cycle-by-cycle overcurrent trip point is set at 2.69 amps.
The HV SR power stage has both a printed circuit board and a power
substrate.
The printed circuit board contains IGBT gate drive circuits, analog signal
conditioning, low-voltage power supplies, power factor control circuitry,
and some of large passive power components. This board also has a
MC68HC705JJ7 microcontroller used for board configuration and
identification. All of the power electronics that need to dissipate heat are
mounted on the power substrate. This substrate includes the power
IGBTs, brake resistors, current-sensing resistors, a power factor
correction MOSFET, and temperature sensing diodes. Table 5-3 shows
a block diagram.
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HV POWER
INPUT
SWITCH MODE
POWER SUPPLY
SIGNALS
TO/FROM
CONTROL
BOARD
PFC CONTROL
dc BUS BRAKE
3-PHASE IGBT
POWER MODULE
3-PHASE SR
TO
MOTOR
GATE
DRIVERS
Freescale Semiconductor, Inc...
PHASE CURRENT
PHASE VOLTAGE
BUS CURRENT
BUS VOLTAGE
MONITOR
BOARD
ID BLOCK
Figure 5-3. 3-ph. SR HV Power Stage
The electrical characteristics in Table 5-1 apply to operation at 25°C with
a 160-Vdc supply voltage.
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Optoisolation Board
Table 5-1. Electrical Characteristics of Power Stage
Freescale Semiconductor, Inc...
Characteristic
Symbol
Min
Typ
Max
Units
DC input voltage
Vdc
140
160
230
V
AC input voltage
Vac
100
208
240
V
Quiescent current
ICC
—
70
—
mA
Min logic 1 input voltage
VIH
2.0
—
—
V
Max logic 0 input voltage
VIL
—
—
0.8
V
Input resistance
RIn
—
10 kΩ
—
Analog output range
VOut
0
—
3.3
V
Bus current sense voltage
ISense
—
563
—
mV/A
Bus voltage sense voltage
VBus
—
8.09
—
mV/V
Peak output current
IPK
—
—
2.8
A
Brake resistor dissipation
(continuous)
PBK
—
—
50
W
Brake resistor dissipation
(15 sec pk)
PBK(Pk)
—
—
100
W
Pdiss
—
—
85
W
Total power dissipation
5.5 Optoisolation Board
Motorola’s embedded motion control series optoisolation board links
signals from a controller to a high-voltage power stage. The board
isolates the controller, and peripherals that may be attached to the
controller, from dangerous voltages that are present on the power stage.
The optoisolation board’s galvanic isolation barrier also isolates control
signals from high noise in the power stage and provides a noise-robust
systems architecture.
Signal translation is virtually one-for-one. Gate drive signals are passed
from controller to power stage via high-speed, high dv/dt, digital
optocouplers. Analog feedback signals are passed back through
HCNR201 high-linearity analog optocouplers. Delay times are typically
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250 ns for digital signals, and 2 µs for analog signals. Grounds are
separated by the optocouplers’ galvanic isolation barrier.
Freescale Semiconductor, Inc...
Both input and output connections are made via 40-pin ribbon cable
connectors. The pin assignments for both connectors are the same. For
example, signal PWM_AT appears on pin 1 of the input connector and
also on pin 1 of the output connector. In addition to the usual motor
control signals, an MC68HC705JJ7CDW serves as a serial link, which
allows controller software to identify the power board.
Power requirements for controller side circuitry are met with a single
external 12-Vdc power supply. Power for power stage side circuitry is
supplied from the power stage through the 40-pin output connector.
The electrical characteristics in Table 5-2 apply to operation at 25°C,
and a 12-Vdc power supply voltage.
Table 5-2. Electrical Characteristics of Optoisolation Board
Characteristic
Symbol
Min
Typ
Max
Units
Notes
Power Supply Voltage
Vdc
10
12
30
V
Quiescent Current
ICC
70(1)
200(2)
500(3)
mA
DC/DC converter
Min Logic 1 Input Voltage
VIH
2.0
—
—
V
HCT logic
Max Logic 0 Input Voltage
VIL
—
—
0.8
V
HCT logic
Analog Input Range
VIn
0
—
3.3
V
Input Resistance
RIn
—
10
—
kΩ
Analog Output Range
VOut
0
—
3.3
V
Digital Delay Time
tDDLY
—
0.25
—
µs
Analog Delay Time
tADLY
—
2
—
µs
1. Power supply powers optoisolation board only.
2. Current consumption of optoisolation board plus DSP EVM board (powered from this power supply)
3. Maximum current handled by DC/DC converters
5.6 Motor-Brake Specifications
The SR motor-brake set incorporates a 3-Ph. SRM and attached BLDC
motor brake. The detailed specifications are listed in Table
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Motor-Brake Specifications
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The SR motor has six stator poles and four rotor poles. This combination
yields 12 strokes (or pulses) per single mechanical revolution. The SR
motor is characterized by a dedicated inductance profile. The motor
inductance profile as a function of mechanical position is shown in
Figure 5-4. The mechanical angle 90omech corresponds to one electrical
period of the stroke. The presented profile was used for the
determination of the advanced commutation angle.
On the motor brake shaft, a position encoder and position Hall sensor
are attached. They allow position sensing if it is required by the control
algorithm. The introduced drive uses the Encoder for the position
determination
Table 5-3. Motor - Brake Specifications
Set Manufacturer
Motor Specification:
Brake Specification:
EM Brno, Czech Republic
eMotor Type:
SR40V
(3-phase SR Motor)
Stator / Rotor Poles:
6/4
Speed Range:
< 5000 rpm
Nominal Voltage:
3 x 300V
Nominal Current:
1.2A
Brake Type
SG40N
3-phase BLDC Motor
Nominal Voltage:
3 x 27V
Nominal Current:
2.6 A
Type
Baumer Electric
BHK 16.05A 1024-12-5
Pulses per Revolution
1024
Position Encoder
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0.8
0.7
Inductance [H]
0.5
Phase A
Phase B
0.4
Phase C
0.3
0.2
0.1
60
50
40
30
20
10
0
-10
-20
-30
0
-40
Freescale Semiconductor, Inc...
0.6
mechanical angle [deg]
Figure 5-4. Inductance Characteristic
5.7 Hardware Documentation
All the system parts are supplied and documented according to the
following references:
•
U1 - Controller Board for DSP56F805:
– supplied as: DSP56805EVM
– described in: DSP56F805EVMUM/D DSP Evaluation Module
Hardware User’s Manual
•
U2 - 3-phase SR High-Voltage Power Stage
– supplied as a kit with an Optoisolation Board as:
ECOPTHIVSR
– described in: MEMC3PSRHVPSUM/D Motorola Embedded
Motion Control 3-phase SR High-Voltage Power Stage User’s
Manual
•
U3 - Optoisolation Board
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Hardware Documentation
– supplied with 3-ph. SR High Voltage Power Stage as:
ECOPTHIVSR
– or supplied alone as: ECOPT - optoisolation board
– described in: Motorola Embedded Motion Optoisolation Board
User’s Manual MEMCOBUM/D
•
MB1 Motor-Brake AM40V + SG40N
– supplied as: ECMTRHIVAC
Freescale Semiconductor, Inc...
Detailed descriptions of individual boards can be found in
comprehensive User’s Manuals belonging to each board. The manuals
are available on the Motorola Web. The User’s Manual incorporates the
schematic of the board, description of individual function blocks and a bill
of materials. An individual board can be ordered from Motorola as a
standard product.
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
Section 6. Software Design
Freescale Semiconductor, Inc...
6.1 Contents
6.2
Data Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
6.3
State Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.4
Software Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.5
Scaling of Quantities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
6.6
Velocity Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
6.2 Data Flow
The control algorithm of a closed loop SR drive is described in
Figure 6-1 and Figure 6-2. It is based on the system description.
The individual processes are described in detail in the following sections.
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PC
MASTER
SPEED
SETTING
omega_required_mech
POSITION
SENSOR
omega_reqPCM_mech
Acceleration
position_difference
position_actual
Speed Calculation
see next page
Freescale Semiconductor, Inc...
Ramp
see next page
omega_actual
omega_desired
u_dc_bus
I_active
Speed Controller
I_active
Commutation Angle
Calculation
I_desired
Current Controller
theta Off
theta On
u_desired
DC-Bus Ripple
Elimination
Commutation
outputDutyCycle
&srmCmtData
PWM Generation
PWM Outputs
Pwm_AT
Pwm_AB
Pwm_BT
Pwm_BB
Pwm_CT
Pwm_CB
Figure 6-1. System Data Flow I - SR Motor Control
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Data Flow
DC-Bus Volatge
A-D Converter
3-Phase CURRENTS
A-D Converter
Freescale Semiconductor, Inc...
ADC Correction
Current MUX
u_dc_bus
i_active
see next page
Figure 6-2. System Data Flow II - AD Converter
6.2.1 Acceleration Ramp
This process calculates the desired speed based on the required speed
according to the acceleration / deceleration ramp. The required speed is
set either manually, using the push buttons (when in manual operating
mode), or by PC master software (when in PC master software operating
mode).
6.2.2 Speed Calculation
The process calculates the actual speed of the motor. The calculation is
based on the evaluation of the position information. The on-chip
quadrature decoder provides information on position difference through
a 16-bit counter. When the position register is read, the position
difference of the counter’s contents are copied into the position
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difference hold register (POSDH) and position difference counter is
cleared.
Freescale Semiconductor, Inc...
The register is regularly read and the captured value is used for speed
calculation. The speed is computed by reading the position difference
counter register per pre-defined time sample.
A software for moving average filter is applied to the speed
measurement is incorporated into the process for greater noise
immunity. The actual motor speed is calculated as the average value of
the last four measurements.
6.2.3 Speed Controller
This process calculates the desired phase current according to the
speed error. Speed error is the difference between the actual speed and
desired speed. A Proportional-Integrational (PI) type of controller is
implemented. The constants of the speed controller are tuned
experimentally according to the load profile and the speed limits.
6.2.4 Current Controller
This process calculates the duty cycle of the PWM based on phase
current error. Phase current error is the difference between the actual
phase current and desired phase current. A PI type of controller is
implemented. The current controller constants are tuned experimentally
according to the type of used motor used.
6.2.5 DC-Bus Ripple Elimination
This process provides the elimination of the voltage ripple on the
DC-Bus. It compensates an amplitude of the desired phase voltage
generated by the PI current controller. The output of the calculation is the
duty cycle of the PWM that is applied to corresponding stator phase.
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Data Flow
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6.2.6 PWM Generation
This process sets the on-chip PWM module for generation of the control
pulses for the 3-Ph. SRM power stage. Generation of these pulses is
based on the software control register that is formulated by the process
of the Commutation Calculation and is based on the required duty cycle
generated by the Speed Controller process. The calculated software
control word is loaded into the proper PWM register and the PWM duty
cycle is updated according to the required duty cycle. The PWM
Generation process is accessed regularly at a rate given by the PWM
frequency. It is frequent enough to ensure the precise generation of
commutation pulses.
6.2.7 ADC Correction and Current MUX
This process takes care of the Analog-to-Digital Converter. The
sampling of the ADC is synchronized to the PWM pulses. The process
selects the proper ADC channels to be converted and reads and
processes the results of the ADC conversion.
The active and discharge phase currents are selected and corrected
using the measured reference noise signal. The DC-Bus voltage and
temperature are filtered using a moving average filter. See 4.3.5 Current
and Voltage Measurement for a detailed description.
6.2.8 Commutation Angle Calculation
This process calls the commutation angle calculation routine which
calculates the advanced angle according to the actual speed, the
DC-Bus voltage and the desired current (see 3.3 Commutation Angle
Calculation).
The algorithm 3-Phase SR Motor Commutation Angle Calculation
srmcacAngleCalc generates the required advance angle of
commutation according to the principle described in 3.3 Commutation
Angle Calculation. Before the calculation routine call, the scaling
constant must be properly determined (see 6.5 Scaling of Quantities).
/* scaling constant */
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scale_const = FRAC16((L_UN*I_MAX*OMEGA_MAX*4)/(U_MAX*60));
The following functions of the algorithm need to be called in order to
calculate the commutation angle:
Freescale Semiconductor, Inc...
adv_angle
/*
/*
/*
/* routine call */
= srmcacAngleCalc(i_ph,u_ph,w_actual,scale_const);
u_ph
=> voltage across phase winding */
i_ph
=> phase current
*/
w_actual
=> actual speed */
These functions are called in the Process Commutation. A detailed
description of the algorithm can be found in the SDK algorithm
documentation.
6.2.9 Commutation
This process provides the comutation of the motor phases.
The DSP on-chip PWM module is used in a mode for generation of
independent output signals that can be controlled either by software or
by the PWM module.
The commutation technique distinguishes the three following cases:
•
When the PWM output needs to be modulated, the PWM
generator controls the channel directly
•
When the PWM output needs to be switched to an inactive state
(0), the software output control of the corresponding PWM
channel is handed over and the channel is turned off manually
•
When the PWM output needs to be switched to the active state (1),
the software output control of the corresponding PWM channel is
handed over and the channel is turned on manually
The on-chip PWM module enables control of the outputs from the PWM
module either by the PWM generator, or by using the software. Setting
the output control enable bit, OUTCTLx, enables software to drive the
PWM outputs instead of the PWM generator. In independent mode, with
OUTCTLx = 1, the output bit OUTx controls the PWMx channel. Setting
or clearing the OUTx bit activates or deactivates the PWMx output. The
OUTCTLx and OUTx bits are in the PWM output control register.
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State Diagram
This control technique requires the preparation of the output control
register. For the calculation of the OUTCTLx and OUTx bits in the PWM
output control register, a dedicated commutation algorithm, 3-Phase SR
Motor Commutation Handler for H/W Configuration
2-Switches-per-Phase, srmcmt3ph2spp, was developed. The
algorithm generates an output control word according to the desired
action and the desired direction of rotation. For example, when phase A
needs to be turned off, the algorithm sets the corresponding OUTCTLx
bits to enable the output control of the required PWMs and clears the
OUTx bits to turn off the PWMs. The other output control register bits are
not affected.
6.3 State Diagram
The processes described above are implemented in a single state
machine, as illustrated in Figure 6-3. The state machine provides a
transition amongst the application states INIT, STOP, RUN, FAULT. The
following variables are used to invoke the transition between the
individual states:
•
switchState (Stop, Run): state of the Start/Stop switch
•
appFault (NO_FAULT, any fault): fault occurrence
•
appOpMode (change from Manual to PC and vice versa): change
operational mode
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RESET
INIT State
appFault = NO_FAULT
&
switchState = Stop
switchState = Stop
appFault <> NO_FAULT
Freescale Semiconductor, Inc...
appOpMode change
STOP State
switchState = Run
&
appFault = NO_FAULT
FAULT State
appFault <> NO_FAULT
switchState = Stop
&
appFault = NO_FAULT
appFault <> NO_FAULT
RUN State
Figure 6-3. Application State Diagram
6.3.1 Application State - INIT
After RESET the application enters the INIT state. In this state, the drive
is disabled and the motor cannot be started.
If any fault is detected, the application transits to the FAULT state
(protection against faults). If no fault is present, and the Start/Stop switch
is detected in the STOP position, the application transits to the STOP
state (protection against starting after reset if the Start/Stop switch is
accidentally in the START position).
6.3.2 Application State - STOP
The STOP state can be entered either from the INIT state or from the
RUN state. In the STOP state, the drive is enabled and the application
waits for the START command.
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When the application is in the STOP state, the operating mode can be
changed, either from MANUAL mode to PC master software mode or
vice versa. When the operating mode is changed, the application always
transits to the INIT state.
Freescale Semiconductor, Inc...
If any fault in the STOP state is detected, the application enters the
FAULT state (fault protection). If no fault is present and the start
command is accepted, the application transits to the RUN state and the
motor is started.
6.3.3 Application State - RUN
The RUN state can be entered from the STOP state. In the RUN state
the drive is enabled and the motor is running.
If any fault in the RUN state is detected, the application enters the
FAULT state (fault protection). If no fault is present and the STOP
command is accepted the application transits to the STOP state and the
motor is stopped.
6.3.4 Application State - FAULT
The STOP state can be entered from any state. In the FAULT state, the
drive is disabled and the application waits for the faults to be cleared.
When it is detected that the fault has been eliminated, and the fault clear
command is accepted (the Start/Stop switch is moved to the STOP
position), then the application transits to the INIT state.
6.4 Software Design
The general software diagram incorporates: (1) the Main routine entered
from Reset, and (2) the Interrupt Service Routines (ISR). The diagram is
illustrated in Figure 6-4.
After Reset, the Main routine provides board identification, initialization
of the DSP, initialization of the application, and then it enters an infinite
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background loop. The background loop contains Fault Detection,
Application State Machine, and a scheduler routine.
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The scheduler routine provides the timing sequence for two tasks called
Timeout 1 and Timeout 2. The Timeout 1 and Timeout 2 flags are
periodically set to predetermined intervals by the ADC Conversion
Completed ISR. The scheduler utilizes these flags and calls the required
routines:
•
The routine in Timeout 1 provides a user interface, calculates the
required speed, the start-up routines and the speed ramp
(acceleration/deceleration).
•
The routine in Timeout 2 calculates the Speed Controller.
The Timeout 1 and Timeout 2 tasks are performed in the run state,
instead of interrupt routines, in order to reduce time and avoid software
bottlenecks. The following interrupt service routines are utilized:
•
ADC Conversion Completed ISR - services ADC and provides all
the control tasks linked to the event; the ADC is synchronized with
the PWM pulses.
•
Fault ISR - services faults invoked by external hardware faults.
•
SCI ISR - services PC master software communication.
•
Push Button Up ISR - services the Up Push Button.
•
Push Button Down ISR - services the Down Push Button.
•
Timer A1 Compare ISR - services Commutation Callback
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Interrupt Service Routines
ADC Conversion
Completed Interrupt
RESET
ADC
Interrupt
Handlers
Initialize
DSP &
Application
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done
done
Background Tasks
PWM Fault Interrupt
Fault Detection
Fault
Interrupt
Handler
done
done
Application
State Machine
SCI Interrupt
done
SCI & PC master
software
Interrupt
Handler
Timeout 1
done
NO timeout
IRQ0, IRQ1 Interrupt
Timeout 1
S/W Timeout
?
done
Timeout 2
done
Push Buttons
Interrupt
Handlers
done
Timeout 2
TMRA1 Compare Interrupt
Commutation
Interrupt
Handler
done
Figure 6-4. Software Design - General Overview
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6.4.1 Initialization
After Reset, the initialization of the DSP is performed. At the beginning
of the initialization, interrupts are disabled; at the end of initialization they
are enabled.
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DSP Initialization:
•
Disable Interrupts
•
Identify power stage board
– identify SR High-Voltage H/W set
•
Initialize ADC on-chip module
– ADC triggered simultaneously
– associate interrupt with ADC conversion completed event
– 1st sample of ADC_A: Current Phase A
– 2nd sample of ADC_A: DC-Bus Voltage
– 3rd sample of ADC_A: Temperature
– 1st sample of ADC_B: Current Phase B
– 2nd sample of ADC_B: Current Phase C
– 3rd sample of ADC_B: void
•
Initialize Quadrature Timer A0 on-chip module (position
measurement)
– set Quad count mode
– count repeatedly up to 1024
•
Initialize Quadrature Timer A1 on-chip module (commutation
callback)
– set Quad count mode
– count repeatedly, the binary roll over
•
Initialize Quadrature Decoder on-chip module
– sets digital filter for input signals
– connects Quadrature Decoder signals to the Quadrature Timer
A1
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•
Initialize PWM on-chip module:
– center aligned independent PWM mode, positive polarity
– set PWM modulus for PWM frequency at 16kHz
– set PWM interrupt reload of each PWM pulse
– set FAULT2 (DC-Bus over-current fault) in manual mode,
interrupt enabled
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– set FAULT1 (DC-Bus over-voltage fault) in manual mode,
interrupt enabled
– associate interrupt with PWM Fault events
•
Initialize brake driver
•
Initialize LED driver
•
Initialize push buttons
– push buttons on interrupts IRQ0, IRQ1
•
Initialize switch driver
– switch driver used for DSP56F805EVM and DSP56F807EVM
Application initialization:
•
Set individual parameters of the application to their initial values
•
Start ADC conversion
•
Measure offset of individual current sensors
•
Measure DC-Bus voltage and temperature
•
Calculate application parameters according to DC-Bus voltage
•
Initialize Quadrature Timer C2 Driver (ADC-PWM
Synchronization)
– set ADC synchronization delay to 0
– enable Quadrature Timer C2 to be started on first SYNC
•
Initialize ADC Driver
– set ADC synchronization ON
– enable 8-sample conversion
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•
Initialize all variables for motor start-up
•
Set ADC according to start-up phase
•
Enable interrupts
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6.4.2 Fault Detection
The Fault Detection routine checks application faults. If a fault occurs, it
disables the PWM outputs and sets the application FAULT status. Note
that in the case of DC-Bus over-current and DC-Bus over-voltage faults,
PWM outputs are disabled directly via internal PWM module fault
protection see 6.4.7 Fault ISR.
6.4.3 Application State Machine
The Application State Machine provides transition between the
individual states of the application: INIT, STOP, RUN, and FAULT. For
reference, see 6.3 State Diagram.
6.4.4 Scheduler Timeout 1
This routine is accessed from the main scheduler in a period of Timeout
1 (10 msec). The following tasks are then performed:
•
Push button filter - debounces push button switching noise
•
Start/Stop switch filter - debounces Start/Stop switch noise
•
According to the operating mode, desired speed is calculated
– in manual mode according to the push buttons
– in PC master software control mode, according to the PC
master software command
•
Start-up routine is performed if required and start-up switching
pattern is generated. For a detailed description refer to 4.3.1
Initialization and Start-Up.
•
Speed command is calculated using the acceleration /
deceleration ramp using the desired speed setup
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•
LED is controlled according to the state of the drive. It can indicate
a STOP state, RUN state or FAULT state.
6.4.5 Scheduler Timeout 2
This state is accessible from the main scheduler in a period of Timeout
2 (2.5 msec). The following tasks are then performed:
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•
Speed controller calculates the desired phase current according to
the actual and the desired speed. The speed controller constants
are determined experimentally and set during the initialization of
the chip.
6.4.6 ADC Conversion Completed ISR
The ADC Conversion Completed ISR is the most critical routine and the
most demanding the processor time. Most of the application control
processes need to be linked with this ISR.
The Analog-to-Digital converter is initiated synchronously with a PWM
reload pulse (center of the PWM pulse). It scans all three phase currents,
the DC-Bus voltage and the temperature at once. When the conversion
is finalized, the ADC Completed ISR is called.
The routine provides the following services and calculations:
•
Reads the ADC conversion results (phase currents, noise,
DC-Bus voltage, temperature)
•
Calculates the ADC offsets for phase currents
•
Current controller calculates the desired phase voltage according
to the desired and the actual phase current
•
Provides commutation if required
•
Records selected recorder variables (PC master software)
•
Loads PWM registers
•
Calculates the references for software timers Timer1 and Timer2
•
Enables the next ADC synchronization trigger
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6.4.7 Fault ISR
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The PWM Fault ISR is the highest priority interrupt implemented in the
software. In the case of a DC-Bus over-current or a DC-Bus over-voltage
fault detection, the external hardware circuit generates a fault signal, that
is detected on the Fault input pin of the DSP. The signal disables the
motor control PWM outputs in order to protect the power stage and
generates a Fault interrupt, where the fault condition is handled. The
routine records the corresponding fault source to the fault status register.
6.4.8 SCI ISR
This interrupt handler provides SCI communication and PC master
software service routines. These routines are fully independent of the
motor control tasks.
6.4.9 Push Button Up/Down ISR
The Push Button Interrupt Handlers take care of the push buttons
service. The Up Button Interrupt Handler sets the Up Button flag, the
Down Button Interrupt Handler sets the Down Button flag. The desired
speed is incremented/decremented according to the debounced
Up/Down Button flag.
6.4.10 TMRA1 Compare ISR
The compare interrupt handler takes care of commutation call. This
callback routine sets-on the commutate flag to indicate that the
commutation is required. The commutation flag is regularly checked in
the ADC conversion-completed routine and upon a successful compare,
the commutation routine is called to perform commutation itself.
6.5 Scaling of Quantities
The SR motor control application uses a fractional representation for all
real quantities except time. The N-bit signed fractional format is
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Scaling of Quantities
represented using 1.[N-1] format (1 sign bit, N-1 fractional bits). Signed
fractional numbers (SF) lie in the following range:
– 1.0 ≤ SF ≤ +1.0 -2
–[ N – 1 ]
(EQ 6-1.)
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For words and long-word signed fractions, the most negative number
that can be represented is -1.0, whose internal representation is $8000
and $80000000, respectively. The most positive word is $7FFF or 1.0 2-15, and the most positive long-word is $7FFFFFFF or 1.0 - 2-31.
The following equation shows the relationship between the real and the
fractional representations:
Real Value
Fractional Value = ----------------------------------------------Real quantity range
(EQ 6-2.)
where:
Fractional Value
is the fractional number of the real value [Frac16]
Real Value
is the real value of the quantity [V, A, rpm, etc.]
Real quantity range
is the maximal range of the quantity, defined in the
application [V, A, rpm, etc.]
6.5.1 Voltage Scaling
The application voltages are scaled to the maximal measured voltage.
For DC-Bus voltage the scaling equation is the following:
V DC_BUS
u_dc_bus = ----------------------------V MAX
(EQ 6-3.)
Where:
u_dc_bus
is the scaled variable of the DC-Bus voltage [Frac16]
VDC_BUS
is the measured DC-Bus voltage [V]
VMAX
is the maximal measurable DC-Bus voltage [V]
In the application, VMAX = 407V for the high voltage platform.
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The other application voltage variables are scaled in the same way
(active phase voltage u_active, discharge phase voltage
u_discharge, DC-Bus under-voltage limit, start-up voltage).
6.5.2 Phase Current Scaling
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The application phase currents are scaled to the maximal measured
phase current. For the active phase current the scaling equation is the
following:
i active
i_active = ------------------------------i phase_max
(EQ 6-4.)
Where:
i_active
is the scaled variable of the active phase current [Frac16]
iactive
is the measured active phase current [A]
iphase_max
is the maximal measurable phase current [A]
In the application, iphase_max = 5.86A for the high-voltage platform.
The other application phase current variables are scaled in the same
way (desired current i_desired, discharge current i_discharge,
current offsets i_phase_A_offset, i_phase_B_offset,
i_phase_C_offset).
6.5.3 Electrical Angle Scaling
The application electrical angle is scaled to the electrical angle in the
aligned position (see Figure 6-5). For the electrical commutation angle
the scaling equation is the following:
ϑ on_el
theta_on_el = -------------------------------ϑ aligned_el
(EQ 6-5.)
Where:
theta_on_el
[Frac16]
is the scaled variable of the electrical commutation angle
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Scaling of Quantities
ϑon_el
is the desired commutation angle [oel]
ϑaligned_el
is the electrical angle in aligned position [oel].
In the application, ϑaligned_el = 360oel
The other application electrical angle variables are scaled in the same
way (angle where stator and rotor poles start to overlap theta_edge).
Freescale Semiconductor, Inc...
A
U
A
L
θstart_to_overlap
−180
ο
θaligned
0
180
position
ο
Figure 6-5. Electrical Angle Definition
6.5.4 Speed Scaling
Speed is scaled to the maximal speed of the drive. For the desired
start-up speed, the scaling equation is the following:
ω start_up
omega_desired_startup = -------------------------ω MAX
(EQ 6-6.)
Where:
omega_desired_startup is the scaled variable of the desired start-up speed
[Frac16]
ωstart-up
is the desired start-up speed [rpm]
ωMAX
is the maximal speed of the drive [rpm]
In the application, ωMAX = 3000 rpm.
The other application speed variables are scaled in the same way
(actual speed, omega_actual_mech, speed limits,
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omega_reqMAX_mech & omega_reqMIN_mech, push button speed
increment, omega_increment_pb).
6.5.5 Duty Cycle Scaling
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The duty cycle is scaled to the maximal duty cycle of the drive. For the
output duty cycle the scaling equation is the following:
duty_cycle output
output_duty_cycle = ---------------------------------------------duty_cycle MAX
(EQ 6-7.)
Where:
output_duty_cycle
is the scaled variable of output duty cycle [Frac16]
duty_cucleoutput
is the desired output duty cycle [%]
duty_cycleMAX
is the max. applicable duty cycle [%]
In the application, duty_cycleMAX = 100 %
The other application duty cycles are scaled in the same way (high and
low duty cycle limits for speed controller, start up output duty cycle
outputDutyCycleStartup).
6.6 Velocity Calculation
The actual speed of the motor is calculated from the time,
TimeCaptured, captured by the on-chip Quadrature Timer between the
two following edges of the position Hall sensors. The actual speed,
OmegaActual is calculated according to the following equation:
SpeedCalcConst
OmegaActual = -------------------------------------------TimeCaptured
(EQ 6-8.)
where:
OmegaActual
is the actual speed [rpm]
TimeCaptured is the time, in terms of number of timer pulses, captured
between two edges of the position sensor [-]
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Velocity Calculation
SpeedCalcConst
is a constant defining the relationship between the
actual speed and number of captured pulses between the two edges of the
position sensor
The constant SpeedCalcConst is calculated as:
SpeedCalcConst = 2
15
SpeedMin
× ---------------------------SpeedMax
(EQ 6-9.)
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where:
SpeedMin
is the minimal measured speed [rpm]
SpeedMax
is the maximal measured speed [rpm]
Minimal measured speed, SpeedMin, is given by the configuration of the
sensors and parameters of the DSP on-chip timer used for speed
measurement. It is calculated as:
1
-------------------------------------------- × 60
NoPulsesPerRev
SpeedMin = ----------------------------------------------------------15
2
-------------------------------------- × Presc
BusClockFreq
(EQ 6-10.)
where:
NoPulsesPerRev
is the number of sensed pulses of the position
sensor per single revolution [-]
Presc
is the prescaler of the Quadrature Timer used for
speed measurements
BusClockFreq
is the DSP Bus Clock Frequency [Hz]
Maximal measured speed, SpeedMax, is selected as:
SpeedMax = k × SpeedMin
(EQ 6-11.)
where:
k
is an integer constant greater than 1
Then the speed calculation constant is determined as:
60
SpeedCalcConst = BusClockFreq × ---------------------------------------------------------------------------------------------------NoPulsesPerRev × Presc × SpeedMax
(EQ 6-12.)
In the application:
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NoPulsesPerRev = 12 Hall sensor pulses per 1 revolution of the motor
Presc = 128
BusClockFreq = 36*106 Hz
SpeedMax = 3000 rpm
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Then, SpeedCalcConst = 468 [rev-1]
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
Section 7. System Setup
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7.1 Contents
7.2
Application Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
7.3
Application Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
7.4
Application Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
7.5
Project Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
7.6
Application Build and Execute . . . . . . . . . . . . . . . . . . . . . . . . 111
7.7
Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
7.2 Application Outline
The system is designed to drive a 3-Ph. SR motor. The application has
the following specifications:
•
SR motor control using Encoder for position determination
•
Targeted for DSP56F805EVM and for DSP56F805 Controller
Board
•
Running on 3-Ph. SR HV Power Stage 180 W
•
Uses optoisolasion board for HV/LV isolation
•
Speed control loop
•
Motor mode in single direction of rotation
•
Minimum speed of 600 rpm
•
Maximum speed of 2500 rpm
•
Manual interface (RUN/STOP switch, UP/DOWN push buttons
control, LED indication)
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•
Overvoltage, undervoltage and overcurrent fault protection
•
PC remote control interface (speed set-up)
•
PC master software remote monitor
– PC master software monitor interface (applied voltage,
required voltage, required and actual speed, START/STOP
switch state, fault status, hardware ID)
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– PC master software speed scope (observes actual and desired
speed, currents: active, desired, discharge, output duty cycle)
7.3 Application Description
The 3-Ph. SR Motor Control with Encoder Application demonstrates the
switched reluctance motor control application using position sensor on
the DSP56F805 processor.
7.3.1 Control Process
After RESET the application enters the INIT state in MANUAL mode.
When the Start/Stop switch is detected (using Start/Stop Switch or PC
master command) in STOP position and there are no faults pending the
STOP application state is entered. When the start command is detected
(using Start/Stop switch or PC master Start button), the drive enters
RUN application state - motor is started. The following start-up sequence
with the rotor alignment is provided:
•
MOTOR_STOPPED, motor stopped
•
ALIGNMENT_COMMAND, alignment command accepted
•
ALIGNMENT_STAGE_ONE, alignment in progress - phases B&C
switched on
•
ALIGNMENT_STAGE_TWO, alignment in progress - phase B
switched on
•
START_UP_FINISHED, alignment finalized, motor running,
start-up finalized
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System Setup
Application Description
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The rotor position is evaluated with encoder position sensor through
timer module A of channel 0, which is set into quadrature mode. Channel
1 of the same module performs commutation call under successful
comparing of CMP2. Every commutation occurrence, the CMP2 is anew
loaded with recently calculated value, which is adjusted by advance
angle routine considering actual speed, desired current and applied
voltage across corresponding phase. The individual phase is supposed
to be switched on before overlapping rotor and stator teeth.
According to the control signals (Start/Stop switch, Up/Down push
buttons) and PC master commands (in case of PC master control), the
reference speed command is calculated using an
acceleration/deceleration ramp. The comparison between the actual
speed command and the measured speed generates a speed error.
Based on the error, the speed controller generates desired phase
current. When the phase is commuted, it is turned-on with duty cycle
100% (or Output_duty_cycle_startup during motor start-up). Then
during each PWM cycle, the actual phase current is compared with the
desired current. As soon as the actual current exceeds the command
one, the current controller is turned-on. The procedure is repeated for
each commutation cycle of the motor. The current controller generates
the desired duty cycle. Finally, the 3-phase PWM SR Motor Control
signals are generated.
7.3.2 Drive Protection
The DC-Bus voltage, DC-Bus current and power stage temperature are
measured during the control process. They are used for overvoltage,
undervoltage, overcurrent and overtemperature protection of the drive.
The undervoltage and overtemperature protection is performed by
software while the overcurrent and overvoltage fault signal utilizes a fault
inputs of the DSP. The power stage is identified using board
identification. If the correct power stage is not identified, the "Wrong
Power Stage" fault disables the drive operation. The line voltage is
measured during application initialization. According to the detected
level, the 115 VAC or 230 VAC mains is set. If the line voltage is detected
out of the -15% .. +10% of nominal voltage, the "Out of the Mains Limit"
fault disables the drive operation.
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If any of the above mentioned faults occur, the motor control PWM
outputs are disabled in order to protect the drive, and the application
enters the FAULT state. The FAULT state can be left only when the fault
conditions disappear and the Start/Stop switch is toggled through the
STOP position.
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The application can run on:
•
External RAM or Flash memory
•
3-phase SR High-Voltage Power Stage powered by 115V AC or
230V AC
•
Manual or PC Master Operating Mode
The correct power stage and voltage level is identified automatically and
the appropriate constants are set.
The 3-phase SR motor control application can operate in two modes:
1. Manual Operating Mode
The drive is controlled by the RUN/STOP switch. The motor speed
is set by the UP and DOWN push buttons (see Figure 7-1). The
actual state of the application is indicated by the user LEDs (see
Figure 7-2). If the application runs and motor spinning is disabled
(i.e., the system is ready), the GREEN user LED will flash at a
frequency of 2Hz. When motor spinning is enabled, the GREEN
user LED will be On. If a fault occurs on the power stage, the
GREEN user LED will flash at a frequency of 8Hz. The actual state
of the PWM outputs are indicated by PWM output LEDs.
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System Setup
Application Description
Figure 7-1. RUN/STOP Switch and UP/DOWN Buttons
on DSP56F805EVM
Figure 7-2. USER and PWM LEDs on DSP56F805EVM
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Table 7-1. Motor Application States
Application State
Motor State
Green LED State
Stopped
Stopped
Blinking at a frequency of 2Hz
Running
Spinning
On
Fault
Stopped
Blinking at a frequency of 8Hz
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2. PC master software (Remote) Operating Mode
The drive is controlled remotely from a PC through the SCI
communication channel of the DSP device via an RS-232 physical
interface. The drive is enabled by the RUN/STOP switch, which
can be used to safely stop the application at any time. PC master
software enables to set the required speed of the motor.
The following PC master control actions are supported:
•
Set PC master mode of the motor control system
•
Set manual mode of the motor control system
•
Start the motor
•
Stop the motor
•
Set the required speed of the motor
PC master displays the following information:
•
Required speed of the motor
•
Actual speed of the motor
•
Application status - Init/Stop/Run/Fault
•
DC Bus voltage level
•
Identified line voltage
•
Fault Status No_Fault/Overvoltage/Overcurrent/Undervoltage/Overheating
•
Identified power stage
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System Setup
Application Description
Start the PC master software window application by the executing the
3ph_srm_Encoder.pmp. Figure 7-3 illustrates the PC master software
control window after this project has been launched.
If the PC master software project (.pmp file) is unable to control the
application, it is possible that the wrong load map (.elf file) has been
selected. PC master software uses the load map to determine
addresses for global variables being monitored. Once the PC master
software project has been launched, this option may be selected in the
PC master software window under Project/Select Other Map FileReload.
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NOTE:
Figure 7-3. PC Master Software Control Window
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7.4 Application Setup
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Figure 7-4 illustrates the hardware set-ups for the 3-phase SR motor
control applications. The motor’s Encoder connector attached to
connector J23 on the EVM Board is not required for the motor operation.
It serves only for PC master position reference.
Figure 7-4. Setup of 3-Phase SR Motor Control Application
Using DSP56F805EVM
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System Setup
Application Setup
The system consists of the following components:
•
Switched reluctance motor Type 40 V, EM Brno s.r.o., Czech
Republic
•
Load Type SG 40N, EM Brno s.r.o., Czech Republic
•
Encoder BHK 16.05A1024-12-5, Baumer Electric, Switzerland
•
3-ph. SR HV Power Stage 180 W:
Freescale Semiconductor, Inc...
– supplied as ECINLHIVSR
•
Optoisolation Board
– ECOPT
•
DSP56F805 Board:
– DSP56F805 Evaluation Module, supplied as DSP56F805EVM
– or DSP56F805 Controller Board
•
The serial cable - needed for the PC master software debugging
tool only.
•
The parallel cable - needed for the Metrowerks Code Warrior
debugging and s/w loading.
•
Command Converter Cable - needed for the DSP56F805
Controller Board only.
For detailed information, refer to the dedicated application note (see
References).
7.4.1 Application Setup Using DSP56F805EVM
To execute the SR Motor Control with Encoder, the DSP56F805EVM
board requires the strap settings shown in Figure 7-5 and Table 7-2.
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System Setup
JG6
3
1
9
6
3
3
JG10
3
7
2
4
1
1
JG14 JG12
3
2
1
JG13
8
7
2
1
JG4
1
USER
9
6
3
7
4
1
JG14
JG10
PWM
JG15
Y1
J23
JG17
JG6
1
3
2
1
JG13
JG12
JTAG
DSP56F805EVM
1
JG16
1
JG4
Freescale Semiconductor, Inc...
JG1
JG15 JG1 JG2
1
1
1
JG18
J29
JG16
U1
JG3
JG8
JG8
1
S/N
3
U15
S4
S5
S6
GP1
S1
GP2
S2
RUN/STOP
S3
P3 IRQA
IRQB
RESET
JG7
1
JG9
JG2
1
3
J24
3
2
1
1
LED3
JG11
P1
U9
JG5
JG5
U10
P1
3
JG9
1
JG3
3
2
JG18
7
JG17
1
JG7
JG11
8
Figure 7-5. DSP56F805EVM Jumper Reference
Table 7-2. DSP56F805EVM Jumper Settings
Jumper Group
Comment
JG1
PD0 input selected as a high
1-2
JG2
PD1 input selected as a high
1-2
JG3
Primary UNI-3 serial selected
1-2, 3-4, 5-6, 7-8
JG4
Secondary UNI-3 serial selected
1-2, 3-4, 5-6, 7-8
JG5
Enable on-board parallel JTAG Command Converter
Interface
NC
JG6
Use on-board crystal for DSP oscillator input
2-3
JG7
Select DSP’s Mode 0 operation upon exit from reset
1-2
JG8
Enable on-board SRAM
1-2
JG9
Enable RS-232 output
1-2
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Connections
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Project Files
Table 7-2. DSP56F805EVM Jumper Settings
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Jumper Group
Comment
Connections
JG10
Secondary UNI-3 Analog temperature input unused
NC
JG11
Use Host power for Host target interface
1-2
JG12
Primary Encoder input selected for quadrature encoder
signals
2-3, 5-6, 8-9
JG13
Secondary Encoder input selected
2-3, 5-6, 8-9
JG14
Primary UNI-3 3-phase Current Sense selected as Analog
Inputs
2-3, 5-6, 8-9
JG15
Secondary UNI-3 Phase A Overcurrent selected for FAULTA1
1-2
JG16
Secondary UNI-3 Phase B Overcurrent selected for FAULTB1
1-2
JG17
CAN termination unselected
NC
JG18
Use on-board crystal for DSP oscillator input
1-2
NOTE:
When running the EVM target system in a stand-alone mode from Flash,
the JG5 jumper must be set in the 1-2 configuration to disable the
command converter parallel port interface.
7.5 Project Files
•
The SR motor control application is composed of the following
files:
•
...\3ph_srm_Encoder\srm_Encoder.c, main program
•
...\3ph_srm_Encoder\3ph_srm_Encoder.mcp, application
project file
•
....\3ph_srm_Encoder\ApplicationConfig\appconfig.h,
application configuration file
•
...\3ph_srm_Encoder\SystemConfig\ExtRam\linker_ram.cmd,
linker command file for external RAM
•
...\3ph_srm_Encoder\SystemConfig\Flash\linker_flash.cmd,
linker command file for Flash
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•
...\3ph_srm_Encoder\SystemConfig\Flash\flash.cfg,
configuration file for Flash
•
...\3ph_srm_Encoder\PCMaster\3ph_srm_Encoder.pmp, PC
master software file
These files are located in the application folder.
Freescale Semiconductor, Inc...
Motor control algorithms used in the application:
•
...\controller.c, .h: source and header files for PI controller
•
...\ramp.c, .h: source and header files for ramp generation
•
...\SrmCmt3Ph2spp.c, .h: source and header files for SR Motor
commutation algorithm
•
...\srmcac.c, .h: source and header files for the mechanical and
the electrical quantities calculation algorithms
Other functions used in the application:
•
...\boardId.c, .h: source and header files for the board
identification function
All the necessary resources (algorithms and peripheral drivers) are part
of the application project file. All the resources are copied into the
following folder under the application folder:
•
...\3ph_srm_Encoder_sa\src\include, folder for general
C-header files
•
...\3ph_srm_Encoder_sa\src\dsp56805, folder for the device
specific source files, e.g. drivers
•
...\3ph_srm_Encoder_sa\src\pc_master_support, folder for PC
master software source files
•
...\3ph_srm_Encoder_sa\src\algorithms\, folder for algorithms
•
...\3ph_srm_Encoder_sa\src\bsp\, folder for the board
identification function source file
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System Setup
Application Build and Execute
7.6 Application Build and Execute
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When building the 3-Ph. SR motor control application with encoder, the
user can create an application that runs from internal Flash or External
RAM. To select the type of application to build, open the
3ph_srm_Encoder.mcp project and select the target build type, as
shown in Figure 7-6. A definition of the projects associated with these
target build types may be viewed under the Targets tab of the project
window.
Figure 7-6. Target Build Selection
To make this application, open the 3ph_srm_Encoder.mcp project file
and execute the Make command, as shown in Figure 7-7. This will build
and link the 3-phase SR Encoder Motor Control application.
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System Setup
Figure 7-7. Execute Make Command
To execute the 3-phase SR Motor Control application, select
Project\Debug in the CodeWarrior IDE, followed by the Run command.
For more help with these commands, refer to the CodeWarrior tutorial
documentation in the following file located in the CodeWarrior
installation folder:
<...>\CodeWarrior Documentation\PDF\Targeting_DSP56800.pdf
If the Flash target is selected, CodeWarrior will automatically program
the internal Flash of the DSP with the executable code generated during
Build. If the External RAM target is selected, the executable code will be
loaded to off-chip RAM.
Once, the Flash has been programmed with the executable, the EVM
target system may be run in a stand-alone mode from Flash. To do this,
set the JG5 jumper in the 1-2 configuration to disable the parallel port,
and press the RESET button.
Once the application is running, move the RUN/STOP switch to the RUN
position; the SR motor will be spinning. The speed can be changed by
means of the UP/DOWN push buttons from its minimal value up to its
maximal value.
NOTE:
If the RUN/STOP switch is set to the RUN position when the application
starts, toggle the RUN/STOP switch between the STOP and RUN
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System Setup
Warning
positions to enable motor spinning. This is a protection feature that
prevents the motor from starting when the application is executed from
CodeWarrior.
Freescale Semiconductor, Inc...
You should also see a lighted green LED, which indicates that the
application is running. If the application is stopped, the green LED will
blink at a 2Hz frequency. If an undervoltage fault occurs, the green LED
will blink at a frequency of 8Hz.
7.7 Warning
This application operates in an environment that includes dangerous
voltages and rotating machinery.
Be aware, that the application power stage and optoisolation board are
not electrically isolated from the mains voltage - they are live with risk of
electric shock when touched.
An isolation transformer should be used when operating off an AC power
line. If an isolation transformer is not used, power stage grounds and
oscilloscope grounds are at different potentials, unless the oscilloscope
is floating. Note, that probe grounds and, therefore, the case of a floated
oscilloscope are subjected to dangerous voltages.
The user should be aware, that:
•
Before moving scope probes, making connections, etc., it is
generally advisable to power down the high-voltage supply.
•
To avoid inadvertently touching live parts, use plastic covers.
•
When high voltage is applied, using only one hand for operating
the test setup minimizes the possibility of electrical shock.
•
Operation in lab setups that have grounded tables and/or chairs
should be avoided.
•
Wearing safety glasses, avoiding ties and jewelry, using shields,
and operation by a personnel trained in high-voltage lab
techniques is also advisable.
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Power transistors, the PFC coil, and the motor can reach
temperatures hot enough to cause burns.
•
When powering down; due to storage in the bus capacitors,
dangerous voltages are present until the power-on LED is off.
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•
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
Appendix A. References
Freescale Semiconductor, Inc...
1. Miller, T.J.E., Switched Reluctance Motors and Their Control,
Magna Physics Publishing and Clarendon Press, ISBN
0-19-859387-2, 1993
2. AN1937 3-Phase Switched Reluctance Motor Control with
Encoder Using DSP56F80x, Motorola Inc., 2002
3. DSP56F80x 16-bit Digital Signal Processor, User’s Manual,
DSP56F801-7UM/D, Motorola Inc., 2001
4. DSP56F800 16-bit Digital Signal Processor, Family Manual,
DSP56F800FM/D, Motorola Inc., 2001
5. Motorola Embedded Motion Control 3-Phase Switched
Reluctance High-Voltage Power Stage User’s Manual,
MEMC3PSRHVPSUM/D, Motorola Inc., 2000
6. Motorola Embedded Motion Control 3-Phase Switched
Reluctance Low-Voltage Power Stage User’s Manual,
MEMC3PSRLVPSUM/D, Motorola Inc., 2000
7. DSP56F805 Evaluation Module Hardware User’s Manual,
DSP56F805EVMUM/D, MotorolaInc., 2001
8. Motorola Embedded Motion Optoisolation Board User’s Manual,
MEMCOBUM/D, Motorola Inc., 2000
9. DSP Parallel Command Converter Hardware User’s Manual,
MCSL, MC108UM2R1
10. User Manual for PC master software, Motorola Inc., 2001
11. CodeWarrior for Motorola DSP56800 Embedded Systems,
CWDSP56800, Metrowerks, 2001
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References
Designer Reference Manual
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References
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Designer Reference Manual — 3-Ph. SR Motor Control with Encoder
Appendix B. Glossary
AC — Alternating Current.
Freescale Semiconductor, Inc...
ADC — Analogue-to-Digital Converter
brush — A component transfering electrical power from non-rotational
terminals, mounted on the stator, to the rotor.
BLDC — Brushless DC motor
commutation — A process providing creation of a rotation field by
switching of power transistor (electronic replacement of brush and
commutator).
commutator — A mechanical device alternating DC current in DC
commutator motor and providing rotation of DC commutator motor.
COP — Computer Operating Properly timer
DC — Direct Current
DSP — Digital Signal Prosessor
DSP56F80x — A Motorola family of 16-bit hybrid controller dedicated for
motor control.
DT — see “Dead Time (DT)”
Dead Time (DT) — short time that must be inserted between the turning
off of one transistor in the inverter half bridge and turning on of the
complementary transistor due to the limited switching speed of the
transistors.
duty cycle — A ratio of the amount of time the signal is on versus the
time it is off. Duty cycle is usually represented by a percentage.
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Glossary
Electromagnetic Interference (EMI) — Electrical interference with
radio communications
GPIO — General Purpose Input/Output
Hall Sensors - A position sensor giving six defined events (each 60
electrical degrees) per electrical revolution (for 3-phase motor).
Freescale Semiconductor, Inc...
input/output (I/O) — Input/output interfaces between a computer
system and the external world. A CPU reads an input to sense the level
of an external signal and writes to an output to change the level on an
external signal.
ISR — interrupt service routines
interrupt — A temporary break in the sequential execution of a program
to respond to signals from peripheral devices by executing a subroutine.
JTAG — Interface allowing On-Chip Emulation and Programming.
LED — Light Emitting Diode
logic 1 — A voltage level approximately equal to the input power voltage
(VDD).
logic 0 — A voltage level approximately equal to the ground voltage
(VSS).
PI controller — Proportional-Integral controller
phase-locked loop (PLL) — A clock generator circuit in which a voltage
controlled oscillator produces an oscillation which is synchronized to a
reference signal.
PM — Permanent Magnet
PMSM - Permanent Magnet Synchronous Motor
PWM — Pulse Width Modulation
Quadrature Decoder — A module providing decoding of position from
a quadrature encoder mounted on a motor shaft.
Quad Timer — A module with four 16-bit timers.
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Glossary
reset — To force a device to a known condition.
RPM — Revolutions per minute
SCI — See "serial communications interface module (SCI)"
serial communications interface module (SCI) — A module that
supports asynchronous communication.
Freescale Semiconductor, Inc...
serial peripheral interface module (SPI) — A module that supports
synchronous communication.
software (SW) — Instructions and data that control the operation of a
microcontroller.
software interrupt (SWI) — An instruction that causes an interrupt and
its associated vector fetch.
SPI — See "serial peripheral interface module (SPI)."
SRM — Switched Reluctance Motor
SR Motor — see "SRM"
timer — A module used to relate events in a system to a point in time.
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Glossary
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USA/EUROPE/LOCATIONS NOT LISTED:
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JAPAN:
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81-3-3440-3569
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ASIA/PACIFIC:
Motorola Semiconductors H.K. Ltd.;
Silicon Harbour Centre, 2 Dai King Street,
Tai Po Industrial Estate, Tai Po, N.T., Hong Kong
852-26668334
Information in this document is provided solely to enable system and software
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integrated circuits based on the information in this document.
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