CANmotion Evaluation Platform with BLDC Motor featuring XC886CM Flash Microcontroller

Application Note, V1.0, April 2007
AP08060
CANmotion
Evaluation Platform with BLDC Motor
featuring XC886CM Flash Microcontroller
Vers i on 2007/ 10
Microcontrollers
Edition 2007-04
Published by
Infineon Technologies AG
81726 München, Germany
© Infineon Technologies AG 2007.
All Rights Reserved.
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AP08060
CANmotion BLDC Evaluation Platform
CANmotion
Revision History: V1.0, 2007-04
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Application Note
V1.0, 2007-04
AP08060
CANmotion BLDC Evaluation Platform
Table of Contents
Table of Contents
1
1.1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Key Features of XC886 which enable Field Oriented Control . . . . . . . . . . . 4
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
CANmotion Board Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Microcontroller Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
On-Chip Debug Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Voltage Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Current Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
CAN Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Two-Layer PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3
3.1
3.2
3.3
Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motor Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Application Note
1
13
13
13
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CANmotion BLDC Evaluation Platform
Overview
1
Overview
The CANmotion board was designed to provide an easy to use BLDC motor control
platform. The board is equipped with a reverse polarity safe power supply with a DC/DC
converter for 5 V supply line, a high performance 8 bit microcontroller with 32 kB flash
memory, an operational amplifier for the DC-link current measurement, a resistor
network for back EMF and DC-link voltage measurement, a CAN interface and of course
an inverter with discrete gate driver.
24V
DC/DC
5V
XC886CM
CANH
CANL
CAN
gate
driver
circuitry
U
I DClink
V
W
BEMF
interface
BlockDiagram.emf
Figure 1
Block Diagram CANmotion Board
Thus, this platform can be used for various motor control schemes supporting DC-link
voltage and current measurement as well as back EMF voltage measurement. As a
result, sensorless block commutation can be executed as well as sinusoidal
commutation schemes like sensorless FOC. The focus of this evaluation platform are
sensorless control techniques. In order to provide a comprehensive platform, hall sensor
based control techniques can also be taken into account. The bottom side of the PCB is
equipped with test points which are directly connected to the dedicated hall sensor inputs
of the microcontroller.
This application note is intended to describe the CANmotion board in detail in order to
serve as a design guideline for low voltage three phase BLDC drivers with XC886C(L)M.
Although the design can be used for various control schemes, it is best for sensorless
field oriented control. The gate driver is tuned in terms of minimum switching time and
the current measurement is provided by a shunt in the DC-link. Please refer to the
application note AP08059 for details on how to implement a sensorless FOC algorithm
with the XC886/8C(L)M. There are additional application notes available describing
sensorless block commutation using the Back-EMF method.
Figure 2 shows the CANmotion board mounted with the 24 V BLDC motor.
Application Note
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CANmotion BLDC Evaluation Platform
Overview
Figure 2
FOC Drive Application Kit
Application Note
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CANmotion BLDC Evaluation Platform
Overview
1.1
•
•
•
Key Features of XC886 which enable Field Oriented Control
High performance 16-bit vector computer (CORDIC + MDU)
– Vector rotation and transformations like Park and Clarke transformation
– Normalizing and scaling
– Interrupt based operation with minimum CPU load
PWM unit for advanced motor control (CapCom6E)
– 16-bit resolution for high precision space vector PWM generation
– Dead time control for minimum hardware effort (direct control of MOSFET/IGBT)
– CTRAP provides hardware overload protection
A fast 10-bit A/D Converter (sample time of 0.25 µs)
– Hardware synchronization to PWM unit reduces CPU load
– Two out of four result registers to maximize sampling performance
– Enables single shunt current measurement
– Fast ADC reduces torque ripple due to minimized blind angle in sensorless FOC
Figure 3
Block Diagram of XC886/8CM
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CANmotion BLDC Evaluation Platform
CANmotion Board Design
2
CANmotion Board Design
This chapter is intended to describe the electrical design of the CANmotion evaluation
platform including the circuit diagram and PCB layout. The version described here, which
is also printed at the bottom layer of the PCB, is version 2007/10.
2.1
Figure 4
Microcontroller Unit
Microcontroller Unit
The MCU chosen for the CANmotion evaluation platform is an 8051 compatible
XC886CM with 32 kilobyte flash memory. Following signals and peripherals are used for
motor control:
•
10 bit fast ADC
– Two ADC channels (ch3 & ch4) for current measurement
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CANmotion BLDC Evaluation Platform
CANmotion Board Design
•
•
– Three ADC channels (ch5, ch6, ch7) for measurement of the inverter’s output
voltage for Back-EMF measurement
– One ADC channel (ch2) for DC-link voltage measurement
PWM Unit CapCom6E
– Delivering the input signals for the inverter (CC6x, COUT6x)
– handling dead time control
– providing emergency shut-down in overload condition (CTRAP)
– triggering the ADC measurement by hardware events
– Supporting hall sensor inputs (HALLx)
CAN Interface (one of two CAN nodes)
– used for flash download and debug communication
– used for parameter setup like reference speed
2.2
On-Chip Debug Support
For flash download and debug purposes, a JTAG connector providing on-chip debug
support is available in the design. This connector is not mounted to the board, because
debugging a motor control application can easily destroy the inverter or the motor.
Imagine the inverter switching and suddenly stopping operation. Stopping means
maintaining the latest state as a direct current.
Figure 5
OCDS - JTAG Interface
The CANmotion evaluation platform provides a CAN interface, described in
Chapter 2.6, for debug, parameter setup and download purposes.
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CANmotion BLDC Evaluation Platform
CANmotion Board Design
2.3
Inverter
The inverter is designed by a discrete driver and MOSFETs. Each of the three channels
for motor phase U, V and W are identically designed. In this subsection, channel U
represents the design of all output channels.
Figure 6
Inverter Design - Output Channel U
Note: This discrete MOSFET driver is realized providing no protection at all. Please note
that any cross current (activation of high-side and low-side switch simultaneously)
will destroy the MOSFETs.
Each output of an inverter can be divided in two main parts, the high-side and the lowside part. The high-side part is connected to the positive supply voltage. The low-side
part to the negative supply voltage. The high-side and low-side switches can be realized
by various concepts. Here, MOSFETs are used as power semiconductors. The gate
driver and level shifter is realized by bipolar transistors.
A MOSFET is operating in it’s RDS(ON) range and showing switching behavior, when the
gate-source voltage is high enough compared to the threshold voltage. On the other
hand, there is a destructive upper voltage limit for the MOSFET as well. The used
MOSFETs (BSO 615 C G) are rated by a maximum gate-source voltage of 20 V, the
threshold voltage is less than 2 V.
The bipolar transistor pair T2 and T3 are used as collector follower, meaning they
provide a current gain in both directions, but almost no voltage gain. As a result, the
voltage at the input (base) is almost equal to the voltage at the output (collector).
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CANmotion BLDC Evaluation Platform
CANmotion Board Design
The resistor network to the left of this current amplifier adjusts the voltages in the safe
operating range of the gate-source voltage. It is adjusted to a gate-source voltage of
about 16 V. The transistor T1 which is a dual NPN transistor is used as level shifter from
the 5 V domain of the MCU to the 24 V domain of the inverter. It is part of the gate driver
adjustment.
The switching time depends on the gate charge of the MOSFETs, the charge and
discharge current of the driver and the delay time of the level shifter. Resistor R4 and R5
reduce the base voltage to make sure the level shifter is reacting as fast as possible. The
switching time of the MOSFETs are defined in a constant approximation by following
equation:
Q = C⋅U = I⋅t
(1)
The gate charge is equal to the multiplication of capacitance and voltage and as well
equal to the current flowing to (or from) the gate multiplied by the time.
The resistor network defines the charge and discharge current, whereas the collector
follower amplifies this charge current.
2.4
Figure 7
Voltage Measurement
Back EMF and DC-link Voltage Measurement
A resistor divider is available in order to implement a Back EMF based sensorless control
scheme. The divided outputs of the inverter are available at ADC channel 5, 6 and 7.
Channel 2 supports monitoring of the DC-link voltage.
Application Note
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CANmotion BLDC Evaluation Platform
CANmotion Board Design
2.5
Current Measurement
There are two current measurement circuits available. First a current comparator in order
to switch off the inverter in case of overload condition via CTRAP input pin. Second a
shunt based current measurement with a difference amplifier.
Figure 8
Current Measurement
The over load current threshold Vcth is setup by the reference voltage defined by R16 and
R17.
R17
V cth = R shunt ⋅ I max = V AREF ⋅ ------------------------R16+R17
(2)
The capacitor C1 and the resistor R20 are not mounted. By mounting C1 a delay and
spike filter can be implemented, R20 can be used to implement a hysteresis.
The current amplification of the differential amplifier is defined as follows:
R14
G = ----------R13
Application Note
,
R15 = R13
9
(3)
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CANmotion BLDC Evaluation Platform
CANmotion Board Design
2.6
CAN Interface
The XC886CM provides a CAN interface with two CAN nodes. One CAN node is
connected to the CAN transceiver TLE 6250 including the terminating resistor R21.
Figure 9
CAN Interface
The CAN interface can be used for bootstrap download, parameter adjustment and
debugging by sending dedicated CAN messages with debug information.
2.7
Power Supply
The 5 V power supply for the MCU and the CAN transceiver is built by a DC/DC
converter. The current consumption of the components does not necessarily require a
DC/DC converter, but by this implementation there is enough current capability available
for additional circuitry like LEDs or supply for hall sensors.
Figure 10
Power Supply
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CANmotion BLDC Evaluation Platform
CANmotion Board Design
2.8
Two-Layer PCB Layout
Figure 11
PCB Layout TOP Layer
Figure 12
PCB Layout BOTTOM Layer
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CANmotion BLDC Evaluation Platform
CANmotion Board Design
Figure 13
PCB Layout Component Names
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CANmotion BLDC Evaluation Platform
Motor
3
Motor
The CANmotion evaluation platform comes with a BLDC motor mounted ready to use.
In this chapter, the motor data (revision April 2006) can be found. Please refer directly to
Maxon Motor internet page http://www.maxonmotor.com for the latest information.
3.1
Figure 14
3.2
Figure 15
Motor Data
Motor Data
Operating Range
Operating Range
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CANmotion BLDC Evaluation Platform
Motor
3.3
Figure 16
Geometry
Geometry
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