Driving of a Brushless DC Motor without Sensors-description

App lication Note, V 1.0, Oc t. 2005
AP16090
XC164CM
Driving of a Brushless DC Motor
without Sensors
Microcontrollers
N e v e r
s t o p
t h i n k i n g .
XC164CM
Revision History:
2005-10
Previous Version:
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Subjects (major changes since last revision)
V 1.0
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Edition 2005-10
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AP16090
Sensorless Control of BLDC
Table of Contents
Table of Contents
Page
1
1.1
1.2
1.3
1.4
Introduction ................................................................................................... 5
Why use brushless DC motors (advantages/disadvantages)? ...................... 5
Functional principle of a brushless DC motor................................................ 5
Brushless DC motor with Hall sensors .......................................................... 6
Brushless DC motor without Hall sensors ..................................................... 6
2
2.1
2.1.1
2.1.2
2.1.3
2.1.4
2.1.5
2.1.6
2.2
2.2.1
2.2.2
Operation of a brushless DC motor............................................................... 8
Visualization of the rotation including appropriate switches of a 3-phase
brushless DC motor (0° mechanical to 180° mechanical) ........................... 8
Position ‘ 0° ’ ............................................................................................. 9
Position ‘ 30° ’ ......................................................................................... 10
Position ‘ 60° ’ ......................................................................................... 11
Position ‘ 90° ’ ......................................................................................... 12
Position ‘ 120° ’ ....................................................................................... 13
Position ‘ 150° ’ ....................................................................................... 14
System description ...................................................................................... 16
Block commutation using Hall sensors.................................................... 16
Block commutation without sensors ........................................................ 17
3
3.1
3.1.1
3.2
3.2.1
3.2.2
Block commutation mode with BACK-EMF detection.................................. 18
General ....................................................................................................... 18
Back–EMF sensing ................................................................................. 19
Required peripherals ................................................................................... 21
CAPCOM6 .............................................................................................. 21
ADC......................................................................................................... 23
4
4.1
4.1.1
4.1.2
4.2
4.2.1
4.2.2
4.2.2.1
4.2.2.2
4.2.3
4.2.3.1
4.3
Implementation............................................................................................ 24
Functional description ................................................................................. 24
General description ................................................................................. 24
Management of commutation, demagnetization and zero cross detection
................................................................................................................ 25
Implementation of the software ................................................................... 25
Initialization ............................................................................................. 26
Function Main() ....................................................................................... 27
Function Start() .................................................................................. 28
Function Stop()................................................................................... 29
Interrupt routines ..................................................................................... 30
Function commutation() ..................................................................... 33
CPU load..................................................................................................... 34
5
Get it started................................................................................................ 36
Application Note
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Sensorless Control of BLDC
Table of Contents
5.1
5.2
General ....................................................................................................... 36
Monitor ........................................................................................................ 37
6
Conclusion .................................................................................................. 39
7
Glossary ...................................................................................................... 40
8
8.1
8.1.1
8.1.2
8.1.3
8.1.4
8.1.5
8.1.6
8.1.7
8.1.8
8.1.9
8.1.10
8.1.11
8.1.12
8.1.13
8.1.14
8.1.15
8.1.16
8.1.17
8.1.18
8.1.19
8.1.20
8.1.21
8.1.22
8.1.23
8.1.24
8.1.25
8.1.26
Addendum................................................................................................... 41
Flow Charts ................................................................................................. 41
Call graph of Main Function .................................................................... 41
Flow chart of Main_vinit Function ............................................................ 42
Flow chart of Main Function .................................................................... 43
Flow chart of Start Function .................................................................... 45
Flow chart of Stop Function..................................................................... 46
Flow chart of Commutation_init Function ................................................ 48
Flow chart of Init_control Function .......................................................... 49
Flow chart of voltage_ref_ramp Function ................................................ 50
Call graph of Error Interrupt-Program (CCU6_viNodeI1)......................... 51
Flow chart of Interrupt CCU6_viNodeI1................................................... 51
Call graph CC62 Interrupt (CCU6_viNodeI2) .......................................... 52
Flow chart of Interrupt CCU6_viNodeI2................................................... 52
Flow chart of Speed_calculation Function............................................... 54
Call graph T13 period match Interrupt Program (CCU6_viNodeI3) ......... 55
Flow chart CCU6_viNodeI3 Program ...................................................... 56
Flow chart of Start_up Function .............................................................. 58
Flow chart of Ramp Function .................................................................. 59
Flow chart of Commutation Function....................................................... 61
Flow chart State 0 of Commutation Function (Positioning)...................... 62
Flow chart State 1 of Commutation Function (frequency ramp) .............. 64
Flow chart State 2 of Commutation Function .......................................... 66
Flow chart state 3 of Commutation Function (normal operation mode) ... 68
Flow chart State 4 of Commutation Function .......................................... 70
Call graph CC2-Interrupt ......................................................................... 71
Call graph AD-Converter Interrupt (ADC_viError) ................................... 71
Flow chart ADC_viError Interrupt ............................................................ 72
Application Note
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Sensorless Control of BLDC
Introduction
1
Introduction
1.1
Why use brushless DC motors (advantages/disadvantages)?
Brushless DC motors are synchronous motors suitable for use as a simple means of
controlling permanent drives (e.g. ABS pumps, EHPS pumps, fuel pumps or cooling
fans). This type of 3-, 4- or 5-phase brushless DC motor will increasingly replace
brushed DC motors. Brushed DC motors require maintenance, e.g. to service carbon
brushes and commutator. Another major problem with a brushed DC machine is the
possibility of brush burnout in the event of an overload or stall condition.
One of the main advantages of brushless DC motors is their robustness against
obsolescence (due to the absence of brushes), another major benefit is the high
efficiency and high torque of a brushless DC motor.
1.2
Functional principle of a brushless DC motor
Figure 1 shows a three-phase brushless DC motor with two pole pairs. The rotation of
the electrical field (vector) has to be applied twice as fast as the desired mechanical
speed of the brushless DC motor. The three coils of the stator are split into two groups
of coils (A, B, C and A’, B’, C’). When a brushless DC motor is energized in block
commutation mode, only two of the three phases are active at a given time. Illustrated
in Figure 1, coils A and C are energized and coil B is not energized. A 0° to 180°
rotation will be shown in detail in section 2.1 to explain the setting of the appropriate
switches of the B6 bridge pattern, the appropriate voltages relating to the coils, and the
energized coils of the motor with the suitable rotor position between 0° and 180°
mechanical.
Figure 1
Functional principle of a brushless DC motor
Application Note
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Sensorless Control of BLDC
Introduction
1.3
Brushless DC motor with Hall sensors
A synchronous motor mainly depends on synchronous processes, e.g. ADC
measurement has to be absolutely synchronous with the energizing pattern of the coils
realized by the switches of the B6 bridge. In this context, the change of state of the
three Hall sensors gives an indication of the specific time at which the next pattern of
the B6 full-bridge has to be applied. Each of these Hall sensors costs about $0.15 $0.30, so they have a big impact on the total cost of the whole application. Typically,
external hardware is needed, such as three comparators for sensor signal
conditioning.
Figure 2
1.4
Block diagram for brushless DC motor drive with Hall Sensors
Brushless DC motor without Hall sensors
The aim of this application note is to eliminate position sensors altogether. The
XC164CM 16-bit µC in its small P-TQFP 64 package (12*12 mm incl. pins) fits this
type of application very well because of its flexible capture compare unit (CAPCOM6),
with two 16-bit timers and 6 + 1 output channels. Many other features are listed at the
end of the application. Three channels of the 10-bit ADC of the XC164CM and only a
two-resistor voltage divider with a capacitor at each of the three phases are the
hardware necessary to realize a viable sensorless brushless DC motor. The most
important point – and at the same time a big advantage of this hardware configuration
– is the aspect of minimized costs, because even the comparators that would normally
be necessary are superfluous. A 16-bit microcontroller delivering high CPU
performance, with a fast and accurate 10-bit ADC, has a big advantage at higher
speeds because of the very acceptable CPU load even in these conditions. A very
important point in relation to the cost-effective back-EMF sensing is the very low
Application Note
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AP16090
Sensorless Control of BLDC
Introduction
leakage current of the XC164CM ADC (+/- 300 nA), because the back-EMF is low at
low speeds and the use of a high-impedance voltage divider is necessary.
Figure 3
General block diagramm for sensorless BLDC motor drive
The brushless DC motor rotor position has to be evaluated by the zero crossing of the
back-EMF which can be evaluated by measuring the non-energized phase. The
voltage value of the back–EMF has to be half of the maximum value to detect the
precise point for changing the coil-energizing pattern for the following 30° mechanical
rotation. It is very important to find the precise point for the next change in the
energizing pattern to ensure smooth operation of this type of motor. A big advantage in
this context is the fact that the back–EMF is proportional to the mechanical rotation
speed. This means that the XC164CM can process directly the 10-bit ADC values
without any type of linearization algorithm. This allows the use of very fast regulation
software. The amount of back-EMF is a function of the number of coil windings,
mechanical speed, and flux (E = N x φ x n). Taking account of a low rotation speed, it
is very important to have a high resolution with regard to the ADC microcontroller (10bit +/- 2 LSB minimum) to evaluate the Back-EMF with the application necessary
demand. The 16-bit wide code and data core and the MAC unit as part of the
XC164CM instruction set e.g. allows fast processing of the 16-bit integer or even PI
speed regulator.
Application Note
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Sensorless Control of BLDC
Operation of a brushless DC motor
2
Operation of a brushless DC motor
2.1
Visualization of the rotation including appropriate switches of
a 3-phase brushless DC motor (0° mechanical to 180°
mechanical)
Only two of the three phases are energized in each state of the B6 full-bridge. The
non-energized phase can therefore be used to detect the zero crossing of the backEMF as explained later (cf. the black arrow in the voltage diagram shown in Figures 5,
7, 9, 11, 13, 15, 17). The following explanation will show you the turning of a two polepair brushless DC motor as a function of the state of the appropriate switches shown in
Figures 4, 6, 8, 10, 12, 14, 16. In fact, driving a two pole-pair motor means that the
rotation speed of the electrical field has to be double the speed of the desired
mechanical rotation speed (Ω = ω / p, where Ω is the mechanical rotation speed, ω the
rotation frequency of the electrical field and p is the number of pole pairs).
Application Note
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AP16090
Sensorless Control of BLDC
Operation of a brushless DC motor
2.1.1
Position ‘ 0° ’
Figure 5 shows the voltage-energizing coils C and A (stator) and the permanent
magnet realized with two pole pairs (rotor), as well as indicating the zero-crossing
detection coil B. Figure 4 shows the active switches of the B6 bridge, and Figure 5
again the appropriate rotor position (0°):
Figure 4
Appropriate switches T1, T6 of the B6 full-bridge (coil c:pos.,coil
A:neg.)
A
B'
N
N
C'
N
Coil A
B
C
S
S SS
S
NN
N
S
S
S
NN
S
N
A'
A'
Coil B
SSS
C
B
N
N
N
C'
B'
Coil C
A
Figure 5
Energized coils C and A of a 2 pole-pair BLDC motor (mechanical
position : 0 °)
Application Note
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Sensorless Control of BLDC
Operation of a brushless DC motor
2.1.2
Position ‘ 30° ’
Figure 7 shows the voltage-energizing coils C and B (stator) and the permanent
magnet realized with two pole pairs (rotor), as well as indicating the zero-crossing
detection coil A. Figure 6 shows the active switches of the B6 bridge, and Figure 7
again the appropriate rotor position (30°):
T1 - T4 : +C, -B
T1
T3
T5
BLDC
Coil A
Coil B
Coil C
Motor
T2
Figure 6
T4
T6
Appropriate switches T1, T4 of the B6 full-bridge (coil C:pos.; coil
B:neg.)
A
B'
N
N
C'
N
Coil A
B
C
S
S SS
S
NN
N
S
S
S
NN
S
N
A'
A'
Coil B
SSS
C
B
N
N
N
C'
B'
Coil C
A
Figure 7
Energized coils C and B of a 2 pole-pair BLDC motor (mechanical
position 30°)
Application Note
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Sensorless Control of BLDC
Operation of a brushless DC motor
2.1.3
Position ‘ 60° ’
Figure 9 shows the voltage-energizing coils C and B (stator) and the permanent
magnet realized with two pole pairs (rotor), as well as indicating the zero-crossing
detection coil C. Figure 8 shows the active switches of the B6 bridge, and Figure 9
again the appropriate rotor position (60°):
T5 - T4 : +A, -B
T1
T3
T5
BLDC
Coil A
Coil B
Coil C
Motor
T2
Figure 8
T4
T6
Appropriate switches T1, T4 of the B6 full-bridge (coil C:pos., coil
B:neg.)
A
C'
S
S
B'
S
Coil A
B
C
NNN
N
N
SS
N
S
N
SS
S
N
A'
A'
Coil B
N
NNN
C
B
S
C'
S
S
B'
Coil C
A
Figure 9
Energized coils A and B of a 2 pole-pair BLDC motor (mechanical
position 60°)
Application Note
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AP16090
Sensorless Control of BLDC
Operation of a brushless DC motor
2.1.4
Position ‘ 90° ’
Figure 11 shows the voltage-energizing coils A and C (stator) and the permanent
magnet realized with two pole pairs (rotor), as well as indicating the zero-crossing
detection coil B. Figure 10 shows the active switches of the B6 bridge, and Figure 11
again the appropriate rotor position (90°):
T5 - T2 : +A, -C
T1
T3
T5
BLDC -
Coil A
Coil B
Coil C
Motor
T2
Figure 10
T4
T6
Appropriate switches T2,T5 of the B6 full-bridge (coil A: pos.,coil
C:neg.)
A
C'
S
B'
S
S
Coil A
B
C
N
N
N
SSS
N
NN
A'
A'
Coil B
N
SSS
N
N
NN
N
C
B
S
C'
S
S
B'
Coil C
A
Figure 11
Energized coils A and C of a 2 pole-pair BLDC motor (mechanical
position: 90°)
Application Note
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AP16090
Sensorless Control of BLDC
Operation of a brushless DC motor
2.1.5
Position ‘ 120° ’
Figure 13 shows the voltage-energizing coils B and C (stator) and the permanent
magnet realized with two pole pairs (rotor), as well as indicating the zero-crossing
detection coil A. Figure 12 shows the active switches of the B6 bridge, and Figure 13
again the appropriate rotor position (120°):
T3 - T2 : +B, -C
T1
T3
T5
BLDC
Coil A
Coil B
Coil C
Motor
T2
Figure 12
T4
T6
Appropriate switches T2, T3 of the B6 bridge (coil B: pos.; coil
C:neg.)
A
C'
B'
S
N
N
S
Coil A
S
N
N
NN
SS
A'
A'
Coil B
B
C
S
S
N
SS
N
N
N
B
C
S
N
S
Coil C
S
N
C'
B'
A
Figure 13
Energized coils B and C of a 2 pole-pair BLDC motor (mechanical
position : 120°)
Application Note
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AP16090
Sensorless Control of BLDC
Operation of a brushless DC motor
2.1.6
Position ‘ 150° ’
Figure 15 shows the voltage-energizing coils B and A (stator) and the permanent
magnet realized with two pole pairs (rotor), as well as indicating the zero-crossing
detection coil C. Figure 14 shows the active switches of the B6 bridge, and Figure 15
again the appropriate rotor position (150°):
T3 - T6 : +B, -A
T1
T3
T5
BLDC
Coil A
Coil B
Coil C
Motor
T2
Figure 14
T4
T6
Appropriate switches T3, T6 of the B6 full-bridge (coil B: pos., coil
A: neg.)
A
B'
N
Coil A
C'
N
N
B
C
S
S
A'
NNN
S
A'
Coil B
S
NNN
S
SS
S
SS
S
S
C
B
N
N
N
C'
B'
Coil C
A
Figure 15
Energized coils A an C of a 2 pole-pair BLDC motor (mechanical
position :150°)
Application Note
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AP16090
Sensorless Control of BLDC
Operation of a brushless DC motor
Figure 17 shows the voltage-energizing coils C and A (stator) and the permanent
magnet realized with two pole pairs (rotor), as well as indicating the zero-crossing
detection coil B. Figure 16 shows the active switches of the B6 bridge, and Figure 17
again the appropriate rotor position (180°):
T1 - T6 : +C, -A
T1
T3
T5
BLDC
Coil A
Coil B
Coil C
Motor
T2
Figure 16
T4
T6
Appropriate switches T1, T6 of the B6 full.bridge (coil C: pos.; coild
A: neg.)
A
B'
N
Coil A
N
C'
N
B
C
S SS
S
S
NN
N
S
S
S
NN
S
N
A'
A'
Coil B
S SS
C
B
N
N
N
C'
B'
Coil C
A
Figure 17
Energized coils A and C of a 2 pole-pair BLDC motor (mechanical
position : 180°)
Application Note
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AP16090
Sensorless Control of BLDC
Operation of a brushless DC motor
2.2
System description
2.2.1
Block commutation using Hall sensors
Figure 18 shows a typical structure of a three-phase BLDC motor drive suitable for use
in automotive applications, e.g. fan cooling or water pump. The XC164CM
microcontroller monitors the hall pattern and generates the rotation patterns for the
stator field and can be used for speed or torque control.
The communication with other sub systems of the application may be realized with
high speed CAN transceiver or with LIN transceiver.
The voltage regulator specially designed for microcontroller with dual supply voltage
(2.6 V / 5 V) features an integrated reset circuitry, low quiescent current consumption
and overtemperature/ overload protection. Further it handles the power sequencing for
dual voltage microcontroller.
The BTS 7960 is a fully integrated high current half bridge for motor drive applications.
It consists of one p-channel highside MOSFET, one n-channel lowside MOSFET and
an integrated driver IC in one package. With three of them a 3 phase drive
configuration can be combined. Dead time generation, adjustable slewrate, current
limitation and current sense are only some of the mentioned features.
Figure 18
Block diagram of block commutation using Hall sensors
Application Note
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Sensorless Control of BLDC
Operation of a brushless DC motor
2.2.2
Block commutation without sensors
Figure 19 shows a typical structure of a three-phase BLDC motor drive with B-EMF
detection. It looks similar to the BLDC drive application with Hall sensors. The only
difference is shown in the detection of the rotor position. The back–EMF voltage is
recorded directly at each phase. A signal conditioning unit is required to trim the
voltage (filtering, etc.). The zero cross voltage is detected for calculation of the next
commutation pattern via the AD channels.
Figure 19
Block diagram of block commutation with B-EMF detection
TLE4274
Application Note
TLE 6280GP
17
XC164CM
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AP16090
Sensorless Control of BLDC
Block commutation mode with BACK-EMF detection
3
Block commutation mode with BACK-EMF detection
3.1
General
As described in a previous section, the commutation of a brushless DC motor is
performed electronically. The rectangular-shaped three-phase voltage system (see
Figure 20) is used to generate a rotational field. Applied voltage with this easy-tocreate shape helps ensure control and drive simplicity. The rotor position must be
known at certain angles in order to align the applied voltage with the back-EMF, which
is induced in the stator windings due to the movement of the permanent magnets on
the rotor. Achieving alignment between the back-EMF and the commutation events is
one of the main tasks. Under these conditions the motor behaves like a DC motor and
runs at the best operating points. Simplicity of control and good performance makes
this kind of motor a good choice in low-cost and high–efficiency applications.
Voltage
Phase A
Phase B
Phase C
60
120
VAN
180
240
VBN
+BEMF
300
360 [degrees]
VCN
Z
-BEMF
C
C
C
C
C
C
C
C = Commutation
Z = Zero Crossing
Figure 20
Simplified 3 phase voltage system/ back-EMF
Application Note
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Sensorless Control of BLDC
Block commutation mode with BACK-EMF detection
3.1.1
Back–EMF sensing
The back-EMF sensing technique is based on the fact that only two phases of a DCbrushless motor are connected at the same time, so the third phase can be used to
sense the back-EMF voltage. Figure 21 uses a simple model to illustrate the situation
when phases A and B are energized and phase C is used to measure the back-EMF.
Figure 21
Simplified model of 3-phase BLDC (coils A and B are energized, coil
C is analyzed)
General methods to detect the zero crossing of the back-EMF often described in the
literature utilize additional hardware such as amplifiers or other circuitry. Also, a speeddependent phase delay time has been implemented to ensure proper commutation,
and the external circuitry has been configured for a fixed motor speed. Overall, the
costs for these additional components have an impact on total system costs.
To reduce system costs further, provide more flexibility and even chop one or both of
the phases, another system approach might be considered. Each phase is connected
via voltage divider circuitry and a low-pass filter to an AD channel of the XC164CM.
Each revolution of the rotor of a motor is divided into 6 commutation windows, each 60
degrees wide. For each window, an appropriate AD channel has been selected to
detect the zero cross point in order to switch to the right commutation pattern after a
dedicated phase delay time.
Application Note
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Sensorless Control of BLDC
Block commutation mode with BACK-EMF detection
Figure 22
Passive network for zero cross detection
Basically, the external circuitry consists of a passive network such as that shown in
Figure 22. The network includes a voltage divider circuit and a low-pass filter. The cutoff frequency is dependent of the application. One network is required for each phase.
Because the back-EMF voltage is a function of the rotor speed, an AD converter with a
higher resolution, at least 10-bit, is required.
Figure 23 shows the monitored Back-EMF (Channels 1 to 3) of a 3-phase BLDC motor
with one pole-pair. The rotation speed of the motor is around 6000 rpm.
Figure 23
Back-EMF voltage after low-pass filter
Application Note
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Sensorless Control of BLDC
Block commutation mode with BACK-EMF detection
3.2
Required peripherals
3.2.1
CAPCOM6
The CAPCOM6E unit of the XC164CM has been designed for applications with a
requirement for digital signal generation and event capturing (e.g. pulse width
modulation, pulse width measurement). It supports generation and control of timing
sequences on up to three 16-bit capture / compare channels plus one additional 10-bit
compare timer. This peripheral fulfills all requirements for controlling 3-phase or
multiphase motor drives.
Figure 24
Block diagram of CAPCOM6E unit for Block Commutation
For BLDC Motors, usually the Multi-Channel Mode is used, see figure 24. The
generated patterns need to be output in relation to the angular position of the motor.
Typically Hall sensors or Back-EMF sensing are used to determine the rotor position.
Application Note
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Sensorless Control of BLDC
Block commutation mode with BACK-EMF detection
The CAPCOM6 provides a mode for the Timer T12 block especially targeted for
convenient control of a Brushless DC-Motors, see figure 27. In order to suppress
spikes on the Hall inputs a noise filter (6 Bit timer) can be used. Channel 0 can be
used to measure the speed of the motor. With channel 1 a phase delay may be
implemented and channel 2 monitors a time out criteria. Timer 13 is used to modulate
the outputs to influence the speed/torque of the motor. The CTRAP functionality
provides a feature to switch off immediately the output pins if the trap input becomes
active. Figure 25 shows are possible configuration for a Hall Senor Mode. For more
detailed information about the CAPCOM6E unit please refer to the XC164CM manual.
Figure 25
BLDC Motor Control with Timer T12 Block
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Sensorless Control of BLDC
Block commutation mode with BACK-EMF detection
3.2.2
ADC
The Analog Digital Converter of the XC164CM has been designed to measure analog
sources with 8-bit or 10-bit resolution. It consists of a sample and hold circuit. A
multiplexer allows up to 14 analog input channels to be selected. To fulfill the different
requirements of embedded applications, the peripheral supports several conversion
modes, such as fixed channel conversion, autoscan conversions or channel injection
modes. By hardware the channel injection can be triggered with a period match of
timer T13 and with a capture/compare event of CC31.
The minimum conversion time is dependent on the CPU frequency and can be
configured individually. The minimum conversion time for a 10bit resolution is 2.55 µs
(fcpu @ 40 MHz). For more detailed information please refer to the datasheet or the
user manual.
Figure 26
Block diagram of ADC unit
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Sensorless Control of BLDC
Implementation
4
Implementation
4.1
Functional description
The application node includes an example code and a monitor program to configure
and control the BLDC motor drive application.
4.1.1
General description
The application is divided into several sub-functions. First, all relevant peripherals are
configured in the function MAIN_vinit(). In the function START() , the ramp-up phase
of the motor is handled. During this phase, the commutation speed and the phase
voltage are increased continuously until the back-EMF voltage is interpretable. Now
the application switches to the closed loop mode and the motor is accelerated until it
reaches the nominal voltage level. Further an optional PI controller for speed or torque
control may be activated. The function STOP() is used to stop the motor in a regular
way.
∆V
∆t
Figure 27
∆f
∆t
Acceleration phase
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Sensorless Control of BLDC
Implementation
4.1.2
Management of commutation, demagnetization and zero cross
detection
The commutation patterns are generated and modulated with timer T13 and parts of
the capture-compare unit 6. Timer T12 and the corresponding register CC61SR are
used to generate the phase delay and to control the defined time-out criteria. Register
CC62 is used to trigger on each slope of the B-EM. Further the acceptance window for
the zero cross detection is defined. CC60 can be used to measure the rotor speed.
The measurement of the phase voltage is done by three ADC channels via PEC.
These channels can be triggered and periodically analyzed either by the timer t13
period match or by CC31 of the CAPCOM2 unit. Additionally a fourth channel is used
for current measurement. All tasks are interrupt driven and consume less CPU-time.
4.2
Implementation of the software
The software is divided into several routines:
Main loop:
•
Initialization (CPU, I/O ports, CAPCOM6, CAPCOM2, ADC, ASC
(monitor) )
•
Start, Stop, communication (monitor program)
Interrupt routines:
•
CAPCOM 6
•
Timer T13
•
Error handling
•
Speed measurement
•
CAPCOM2
•
ADC
•
ASC (monitor program)
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Implementation
4.2.1
Initialization
A number of small routines perform all the necessary initializations before the motor is
started:
Port initialization:
P1L.x is used as alternate output for the CAPCOM6 output
(CC6x,COUT6x).
Interrupt initialization:
CAPCOM6 emergency trap, timeout (CC62), timer 13
period match, speed measurement (CC60), ADC interrupt
with PEC, ADC error, ASC receive interrupt.
CAPCOM6 initialization:
Enable multi-channel mode, enable hall sensor mode,
passive output level is low, Timer T13 edge aligned mode.
Enable trap function for emergency cases.
CAPCOM2 initialization:
Add additional time base timer T7, CC19, CC31 (optional if
phase current /voltage is measured at the same time).
ADC initialization:
Select P5.1-P5.4 as AD channels, 10bit, fixed-channel
single conversion, sample time 400ns, conversion time
2,55µs.
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Implementation
4.2.2
Function Main()
Figure 30 shows the call graph of the function Main(). All sub-programs can be called
over the main function.
Figure 28
Call graph of function Main()
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Implementation
4.2.2.1
Function Start()
The variable Status_word includes the state on/off and all possible error flags. The
variable v_start_ref which present the start voltage, is initialized every time when the
function is activated. The function Commutation_init() activates the modulation of the
CAPCOM6 output pins. The function Init_control() initializes all variables for the motor
control.
Figure 29
Function Start()
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Implementation
4.2.2.2
Function Stop()
The function Stop() is called either by the user or when an error occurres. Basically the
function Stop() disable all relevant drivers, like CAPCOM6 or status variables.
Figure 30
Function Stop()
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Implementation
4.2.3
Interrupt routines
The interrupt routine CCU6_viINodeI2 is executed when a CC62 compare match
occurs. If the motor is working in normal operation mode (state3) then a speed
calculation can be done. The state of the Back EMF measurement is given in the
variable slope.
Figure 31
Interrupt speed measurement CCU6_viNodeI2
•
Slope = 0 Æ B-EMF Measurement pos. edge with zero crossing detection
•
Slope = 1 Æ B-EMF Measurement neg. edge with zero crossing detection
•
Slope = 2 Æ B-EMF Measurement neg. edge without zero crossing detection
•
Slope = 3 Æ B-EMF Measurement pos. edge without zero crossing detection
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Implementation
Function 32 shows the function Speed_calculation().
Figure 32
Function Speed_calculation
The values of the time measurement are saved in a circular buffer. Six values are used
to minimize errors from B-EMF measurement. The variable counter counts the
commutation events and builds the average value for the speed calculation.
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Implementation
The interrupt CCU6_viNode3 is executed every 50 µs when the Timer T13 period
match happens. At first the function commutation() is called. It is a state-machine and
handles the different operation modes. Then, depending of the actual pulse pattern the
accordant AD-channel is chosen for Back-EMF measurement.
Figure 33
Interrupt Timer T13PM (CCU6_viNodeI3)
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Implementation
4.2.3.1
Function commutation()
This function can handle 5 different operation modes (state 0 to 4) of a motor
application, which are illustrated in figure 34.
commutation()
State = 4
YES
5
NO
State =3
YES
4
NO
State = 2
YES
3
NO
YES
State = 1
2
NO
State = 0
YES
1
NO
Return
Figure 34
Function commutation()
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Implementation
4.3
CPU load
The following hardware requirements are needed:
CPU:
XC164Cx , fcpu @ 40 MHz
ROM:
5 kByte
RAM:
360 bytes plus system stack
Peripherals:
CAPCOM6 unit:
ADC: 4-channel, 10-bit resolution, 2,55µs conversion time
CCU2: Timer: 16 timer, 25ns resolution
CPU Load:
12 % (independent of the motor speed)
The CPU load is measured in a simple way. A flag of a dedicated port pin is set each
time an interrupt routine is entered. The flag is reset after the interrupt routine is exited.
Figure 35
CPU load
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Implementation
Figure 36
CPU load in detail
In this implementation the CPU load is independent of the motor speed, because each
50µs a B-EMF phase analysis is done. The CPU load can be reduced by the following
actions:
•
Reduce the number of phase samples (currently each 50µs)
•
Focus the sampling on the outer field of the zero crossing
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Get it started
5
Get it started
5.1
General
Additional parts of a complete evaluation platform are available:
•
Source code for the XC164x family for the Toolchain Keil, Tasking
•
Monitor program based on the RS232 interface
The target board and the BLDC motor should be customer specific and is not part of
this evaluation platform.
The source code can be programmed in the internal Flash with MEMTOOL via RS232
interface. Of course using one of the mentioned tool chains the code can be
downloaded and debugged.
Figure 37
Overview
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Get it started
5.2
Monitor
The monitor brdc_monitor controls the application. Three windows can be selected.
Display (Display of variables)
Input (Control and initialization of the application / variables)
Graphic (Up to three curves can be stored)
Within the major window the com port is selected and the communication with the
application board is established.
Figure 38
Major window
Before the application is started the initialization of the application is mandatory.
Therefore the Input window is selected, all parameters are checked and the data are
sent to the microcontroller. After that the application can be turned on.
Application Note
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Get it started
Figure 39
Input Window
If additional special function registers or variables should be monitored an easy to
handle drag and drop functionality is available.
Figure 40
All windows
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Sensorless Control of BLDC
Conclusion
6
Conclusion
There is an increasing demand in the automotive industry for applications using BLDC
motors. In the past, many applications were addressed with DC motors. Automotive
suppliers would like to use BLDC motors in order to achieve greater robustness and
efficiency. Currently, the only limitation is the price gap between BLDC motors and DC
motors. On the other hand, automotive suppliers are intensely price-driven and need
smart solutions to meet the requirements of the market.
This application note aims to provide an understanding of the functionality of a BLDC
motor explains how such a motor is driven, describes all the necessary components
and the necessity of knowing the positioning of a synchronous motor. Furthermore, the
back-EMF technique is discussed and a method to implement the back-EMF algorithm
in the XC164CM is presented. To achieve a good price/performance ratio, all the
components used for back-EMF detection have been replaced by software. Thanks to
the high performance of the microcontroller and its powerful peripherals, this software
solution consumes only limited CPU resources.
The system approach discussed might be considered as a starting point for designing
a complete system-specific closed-loop BLDC application
Application Note
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Glossary
7
Glossary
ADC:
Analog Digital Converter
B-EMF :
Back electromagnetic force
B6 :
Bridge with 6 switches (e.g. MOSFET) for 3 phases
BLDC:
Brushless DC
CAN:
Controller Area Network
CAPCOM:
Capture Compare Unit, peripheral that measure events or
provide PWM signal
CPU:
Central Processor Unit
EHPS:
Electro Hydraulic Power Steering
LIN:
Local Interconnect Network
PI:
Proportional Integral
PWM:
Pulse width modulation
ROM:
Read only memory
RAM:
Read Access Memory
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Addendum
8
Addendum
8.1
Flow Charts
8.1.1
Call graph of Main Function
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Addendum
8.1.2
Flow chart of Main_vinit Function
MAIN_vInit
MAIN_vUnlockProtecReg()
Set CPU frequency
IO_vInit()
ASC0_vInit()
CC2_vInit()
ADC_vInit()
CCU6_vInit()
Adc_offset()
sio_init()
initializes variables
Set global interrupt enable
PSW_IEN = 1
Return
Name
Type
Init value
Change
direction
Int
0x0000
Intern
Once
Int
0x0000
Intern
Status_word
Int
0x0002
Intern
direction gives the rolling direction of the motor.
Once is a flag, which will be set in the start program.
Status_word is a variable, which shows the status- and error bits of the control.
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Addendum
8.1.3
Flow chart of Main Function
Application Note
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Addendum
Name
Type
Init value
Change
monitor_ein_aus
bit
0
User
Ctrap
Bit
0
Intern
increment_free
Int
0x0000
Intern
Time_step
long
0x0000
Intern
Trap_reset
Int
0x0000
User
counter1
long
0x0000
Inter
Ramp_up_time
long
0x0000
User
V_start_ref0
Int
Intern
V_end_ref
Int
User
Duty_cycle
Unsigned Int
Intern
monitor_ein_aus is the On/Off signal from the monitor program resp. the user.
CTrap is an error flag from the driver board.
increment_free is a flag for the reference ramp.
Time_step gives the time basis for the increment of reference ramp.
Trap_reset is used from user to delete the Trap.
Counter1 is a timer for the determination of time basis of the reference ramp.
Ramp_up_time determine the time for the reference ramp.
V_start_ref0 is the memory for the start value of the voltage reference ramp in
operation mode.
V_end_ref is the final value of the voltage reference ramp.
Duty_cycle is the value of the duty cycle.
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Addendum
8.1.4
Flow chart of Start Function
.
Name
Type
Init value
Change
Once
Int
0x0000
Intern
Status_word
Int
0x0002
Intern
V_start_ref
Int
User
V_start_ref0
Int
Intern
V_ref
Int
Intern
V_end_ref
Int
User
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Addendum
Once is a flag, which will be set in the start program.
Status_word is a variable, which shows the status- and error bits of the control.
V_ref is the value of voltage reference for the control.
V_start_ref is the start value of the voltage reference ramp by startup.
V_start_ref0 is the memory for the start value of the voltage reference ramp in
operation mode.
V_end_ref is the final value of the voltage reference ramp.
8.1.5
Flow chart of Stop Function
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Addendum
Name
Type
Init value
Change
Intern
On
bit
0x0000
Off
bit
0x0000
Direction
Int
0x0000
Intern
direction_user
Int
0x0000
User
/
User
Intern
/
User
On is a bit, which shows that the motor is running (Status_word).
Off is a bit, which shows that the motor is stopped (Status_word).
direction gives the rolling direction of the motor.
direction_user is a variable to choose the rolling direction of the motor by the user.
Application Note
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Addendum
8.1.6
Flow chart of Commutation_init Function
Application Note
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Addendum
8.1.7
Flow chart of Init_control Function
.
Application Note
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Addendum
8.1.8
Flow chart of voltage_ref_ramp Function
Name
Type
Init value
Change
V_ref
Unsigned Int
0x0000
Intern
V_end_ref
Unsigned Int
0x0000
User
Duty_cycle
Unsigned Int
Intern
V_ref is the value of voltage reference for the control.
V_end_ref is the final value of the voltage reference ramp.
Duty_cycle is the value of the duty cycle.
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Addendum
8.1.9
Call graph of Error Interrupt-Program (CCU6_viNodeI1)
8.1.10
Flow chart of Interrupt CCU6_viNodeI1
Name
Type
Init value
Change
Time_out
Bit
0
Intern
Ctrap
Bit
0
Intern
Time_out is the error flag from Timer 12 overflow.
CTrap is the error flag from driver board.
Application Note
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Addendum
8.1.11
Call graph CC62 Interrupt (CCU6_viNodeI2)
Figure 4.2.2.13 CC62_INT (CC62 compare-match)
.
8.1.12
Flow chart of Interrupt CCU6_viNodeI2
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Addendum
+ U BEMF
zerocrossin g
− U BEMF
-
Slope = 0 Æ B-EMF Measurement pos. edge with zero crossing detection
-
Slope = 1 Æ B-EMF Measurement neg. edge with zero crossing detection
-
Slope = 2 Æ B-EMF Measurement neg. edge without zero crossing detection
-
Slope = 3 Æ B-EMF Measurement pos. edge without zero crossing detection
Name
Type
Init value
Change
Time_measur
Unsigned Int
0x0000
Intern
speed_counter
Int
0x0000
Intern
Slope
Int
0x0000
Intern
Speed_CC61
Unsigned Int
0x0000
Intern
Time_measur is the time between two zero crossings and serves as parameter for
speed calculation.
speed_counter counts the number of commutations and serves as parameter for
speed calculation.
Speed_CC61 is the actual speed.
Application Note
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Addendum
8.1.13
Flow chart of Speed_calculation Function
Name
Type
Init value
Change
Speed_buffer[6*Pp]
Int
0x0000
Intern
circ_index
Int
0x0000
Intern
Speed_accumm
Long
0x0000 0000
Intern
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Addendum
Speed_buffer[6*Pp] is the circular memory for average calculation of time
measurement.
circ_index is a counter, which contains the offset for the circular memory.
Speed_acumm is the integral of the measured values for time determination.
8.1.14
Call graph T13 period match Interrupt Program
(CCU6_viNodeI3)
Application Note
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Addendum
8.1.15
Flow chart CCU6_viNodeI3 Program
Application Note
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Addendum
Name
Type
Init value
Change
Bemf_aux
Int
0x0000
Intern
Adc_ctr_Bemf
Int
0x9691
Intern
Bemf_aux is the memory for the old pulse pattern, which is compared with the new
one.
Adc_ctr_Bemf contains the configuration of the ADC_CTR register to start a fixed
channel single conversion. This happens with PECC2-Transfer.
Application Note
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Addendum
8.1.16
Flow chart of Start_up Function
Name
Type
Init value
Change
direction
Int
0x0000
Intern
Vector
Int
0x0000
Intern
direction gives the rolling direction of the motor and it is the offset for the pulse pattern
table.
Vector is a pointer, which rotates and indicates to the corresponding pulse pattern.
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Addendum
8.1.17
Flow chart of Ramp Function
Application Note
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Addendum
Name
Type
Init value
Change
Freq_increment
Int
User
Volt_increment
Int
User
Start_freq
Int
User
Freq_step
Int
0x0000
Intern
v_counter
Int
0x0000
Intern
f_counter
Int
0x0000
Intern
State
Int
0x0000
Intern
Angle_inc
Int
0x0000
Intern
Start_angle
Long
0x00490000
Intern
Duty_cycle
Unsigned Int
Intern
Volt_increment is a variable to change the increase of voltage at the phase.
Freq_increment gives the value for the increase of frequency.
Angle_Inc represents a linear increase.
freq_step is an upstream integrator and represents a quadratic increase.
Start_angle specifies the frequency and the moment of commutation.
State is the state of the state machine.
Duty_cycle is the value of the duty cycle.
v_counter is a counter for time basis of voltage ramp.
f_counter is a counter for time basis of frequency ramp.
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Addendum
8.1.18
Flow chart of Commutation Function
commutation()
State = 4
YES
NO
5
State =3
YES
NO
4
State = 2
YES
3
NO
YES
State = 1
NO
2
State = 0
YES
NO
1
Return
Name
State
Type
Init value
Int
0x0000
Change
Intern
State is the state of the state machine.
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Addendum
8.1.19
Flow chart State 0 of Commutation Function (Positioning)
Application Note
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Addendum
Name
Type
Init value
Change
s_counter0
Unsigned Int
4000
User
s_counter1
Unsigned Int
0x0000
User
s_counter2
Unsigned Int
0x0000
Intern
State
Int
0x0000
Intern
Duty_cycle
Unsigned Int
direction
Int
0x0000
Intern
Vector
Int
0x0000
Intern
Intern
State is the state of a state machine.
Duty_cycle is the duty cycle.
direction gives the rolling direction of the motor and it is the offset for the pulse pattern
table.
Vector is a pointer, which rotates and indicates to the corresponding pulse pattern.
s_counter0 gives the duration of each voltage vector.
s_counter1 is a counter for the switching of the voltage vector.
s_counter2 gives the time basis for the switching of the voltage vector.
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Addendum
8.1.20
Flow chart State 1 of Commutation Function (frequency ramp)
Application Note
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Addendum
Name
Type
Init value
Change
s_counter0
Unsigned Int
0x0000
User
s_counter1
Unsigned Int
0x0000
User
State
Int
0x0000
Intern
Angle_inc
Unsigned Int
0x0000
Intern
Back_emf_measur
Int
0x0000
Intern
Slope
Int
0x0000
Intern
Slope is a state variable, which indicates the state of BACK-EMF measurement.
Angle_Inc is a value, which is proportional to the frequency.
Back_emf_measur is the measurement of BACK-EMF.
s_counter0 counts the events, when the BACK-EMF is higher or lower of the limit.
s_counter1 serves as filter for the comparison of the BACK-EMF measurement.
Application Note
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Addendum
8.1.21
Flow chart State 2 of Commutation Function
The time measurement between two zero crossings of the B-EMF.
Application Note
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Addendum
Name
Type
Init value
Change
s_counter2
Unsigned Int
0x0000
Intern
s_counter1
Unsigned Int
0x0000
Intern
State
Int
0x0000
Intern
Back_emf_measur
Int
0x0000
Intern
Slope
Int
0x0000
Intern
Vector
Int
0x0000
Intern
Time_measur
Unsigned Int
0x0000
Intern
Time_measur is the time between two zero crossings.
State is a state of the state machine.
Slope is a state variable, which indicates the state of BACK-EMF measurement.
Vector is a pointer, which rotates and indicates to the corresponding pulse pattern.
Back_emf_measur is the measurement of the BACK-EMF.
s_counter2 is the counter for time out function.
s_counter1 serves as filter for the comparison of the BACK-EMF measurement.
Application Note
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Addendum
8.1.22
Flow chart state 3 of Commutation Function (normal operation
mode)
Application Note
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Addendum
Name
Type
Init value
0x0000
Change
s_counter1
Unsigned Int
Intern
Back_emf_measur
Int
Slope
Int
0x0000
Intern
Vector
Int
0x0000
Intern
Time_measur
Unsigned Int
0x0000
Intern
Intern
Time_measur is the time between two zero crossings.
Slope is a state variable, which indicates the state of BACK-EMF measurement.
Vector is a pointer, which rotates and indicates to the corresponding pulse pattern.
Back_emf_measur is the measurement of the BACK-EMF.
s_counter1 serves as filter for the comparison of the BACK-EMF measurement.
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Addendum
8.1.23
Flow chart State 4 of Commutation Function
Name
Type
Init value
Change
Monitor_ein_aus
Bit
0
User
Time_out
Bit
0
Intern
Time_out is the error flag of Timer 12 overflow.
monitor_ein_aus is the On and Off signal for the monitor program resp. the user.
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Addendum
8.1.24
Call graph CC2-Interrupt
8.1.25
Call graph AD-Converter Interrupt (ADC_viError)
START
Stop()
End
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Sensorless Control of BLDC
Addendum
8.1.26
Flow chart ADC_viError Interrupt
Name
Type
Init value
Change
Current
Unsigned Int
i_counter
Unsigned Int
0x0000
Intern
Overcurrent
Bit
0
Intern
i_mpattern
Int
0x0000
Intern
Application Note
Intern
72
V 1.0, 2005-10
AP16090
Sensorless Control of BLDC
Addendum
Current is the actual measurement of current
i_counter is a time counter for current monitoring.
i_mpattern is the memory for the actual pulse pattern.
Overcurrent is the flag for over current (Status_word).
Application Note
73
V 1.0, 2005-10
http://www.infineon.com
Published by Infineon Technologies AG
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