BLDC Motor Control with ST72141 Microcontroller

1
BLDC Motor Controlwith ST72141 Microcontroller

• Motor Control Competence Center Application Team

2
ST72141 MicrocontrollerPresentation contents

• Introduction
• A. Permanent Magnet DC Motor Basics
• B. ST72141 description
• - General features
• - Core
• - Motor Control Peripheral
• - Current mode / Voltage mode
• C. Summary of Benefits of ST72141
• D. Appendix - Starting sequence - Speed-up of
  demagnetisation
• Conclusion

3
PMDC Basics (Generalities)

• Main advantages
• High efficiency (up to 98)
• Variable speed
• Silent operation
• Reliable/long life time (no brushes)
• High Size/Power ratio
• High torque at start-up
• Major applications (where above advantages are
  required)
• Compressor (air conditioner, refrigerator)
• Appliances (washing machine, vacuum cleaner,
  food processor)
• Industrial fan
• Electric vehicles
• Automotive (fuel and waterpumps, cooling fan,
  climate control)
• Office Automation (laser printer, copy machine)

4
PMDC Basics (1)

• Operating principle
• Synchronous Stator flux and rotor mechanical
  rotation speed are same.
• Stator description 3 phase winding (1 or 2 or
  more pairs of poles)
• Rotor description Permanent magnet
• For 1 pair of pole 1 electrical cycle (6 steps)
  1 mechanical cycle

2
3
South Pole
1
4
5
6
5
PMDC Basics (2)

• Drive mode 6 steps Principle

Current in winding A,B,C
300V DC
T1
T5
T3
A
U
V
B
W
C
2
T4
T6
T2
-
T1 T1 T3 T3 T5 T5 T4 T6 T6 T2 T2 T4
6
One pair pole motor
7
Two pairs pole motor
A
A
A
T3-T6
1
1
N
N
1
1
S
N
S
S
S
S
2
S
N
N
N
1
B
C
B
C
B
C
3
T1-T6
T1-T4
A
A
5
A
4
T5-T4
N
S
S
S
1
N
N
N
S
N
N
1
1
S
S
B
C
B
C
B
C
6
T3-T2
T5-T2
8
PMDC Basics (3)

• Control Method
• It requires to know the position of the rotor at
  all timesin order to reach the status of auto
  commutation (best efficiency). At least 2 common
  ways are available to know the rotor position.
• Hall effect sensors (sensor mode)
• Back emf (1) detection (sensorless mode)
• The autocommutation happens when the current in a
  winding is in phase with the b-emf in this same
  winding.
• The control process will be about keeping these
  2 signals in phase
• Current generated by inverter in the motor
  windings
• Back-emf Voltage induced (by Permanent Magnet) in
  the motor windings

• (1) B-emf is the voltage induced in a winding by
  the movement of the magnet in from of this
  winding edj/dt. It is independant of
  the energy supply to the motor (just by spinning
  by hand the rotor for example it is
  possible to generate back-emf).

9
PMDC Basics (4)

• Signals in one of the 3 phases

Back-EMF
current
t
10
Implementation of control B-emf detection
Conventional Method (1)
300V
BUS
BUS
divider filter
N
N
5V
N
N'
N'
POWER GND
POWER GND
POWER GND
virtual ground
weaknesses - Voltage dividers give reduced
sensitivity difficulty for low speed operation
- Filtering is optimised for narrow speed
range
11
Implementation of control B-emf zero crossing
Conventional Method (2)
Phase current
Filtered Phase voltage
Filtered voltage of rebuilt reference node N'
filt1.hgl
Zero crossing event
12
Implementation of control ST72141 patented
Sensorless method
300V
T1 PWM "ON"
A
V/2
B
C
bemf
T4 always ON
GND

• back-EMF whole signal sensing
• high sensitivity large speed range very
  low speed operation starting with full torque
• no filtering delay
• high signal to noise ratio

13
Implementation of control ST72141 Patented
Sensorless Method
----- phase current ------
------ phase voltage---- --
End of demagnetisation

• back-EMF zero crossing

back-EMF zero crossing
End of demagnetisation
14
ST7141 Back-emf detection Patent
ST Method
GE Method
Patent Registration
US 5,859,520 "control of a brushless motor"
US 4,654,566
Principle
full digital - B-emf is clamped to 5V by
on-chip diode. - After end of demagnetisation
of winding to read, and when high side
transistor is off, the N point is at potential
0. - The comparator can then read b-emf zero
crossing.
analog method - need to build an artificial N
(neutral), divide voltage, and filter it. -
need to divide voltage and filter output
voltage of winding to read. - The comparator can
read the b-emf zero crossing.
Drawback
Requires to limit the duty cycle of the PWM below
100.
- Requires a filter and a voltage divider - Low
flexibility voltage and frequency dependent.
Limited speed range - Components need to be
dimensionned for a nominal operation of the
motor
Benefit
Large speed range detection Sensorless, no
external components Cost saving
Sensorless
NO PATENT INFRINGMENT REDUCED COST
15
Application Environment (3)Sensorless PMDC, in
current Mode
16
PMDC 6 STEPS DRIVE WITH ST72141Saving components
CPU ressources
CPU discharged ofStator commutation Power
drive



M
T3
MCU
T5
DAC



E n a b l e
Hall sensors Bemf detector
Current regulation
Position feedback
17
Fuel-Pump Brushless DC-Motor Drive
V Batt
U431
ST72141
5V
VReg.. Reset
Supply
Current Limit
Osc.
Timer 2
Temp.
3-Phase Motor
Diagn.
IO ADC Interface
Timer 1
Gate Drive
Enable
8 bit Core
8 k ROM
TX
Data Transc.
RX
256 B RAM
PWM Gate Drive
Phase Commu- tation
Logic Inter- face
BEMF Cero Crossing
To ECU
18
ST72141 MicrocontrollerPresentation contents

• Introduction
• A. Permanent Magnet DC Motor Basics
• B. ST72141 description
• - General features
• - Core
• - Motor Control Peripheral
• - Current mode / Voltage mode
• C. Summary of Benefits of ST72141
• D. Appendix - Starting sequence - Speed-up of
  demagnetisation
• Conclusion

19
ST72141 Synchronous Motor controller

• General Features
• 8K ROM/OTP/EPROM
• 14 multifunctional bidirectional I/Os with -
  External interrupt - 13 alternate function
  lines - 3 high sink outputs (20mA in open drain)
• Two 16bit timers with - 2 input captures -
  2 output compares - external clock input - PWM
  and pulse generator mode
• SPI synchronous serial interface
• 8 bit ADC with 8 channels
• SDIP32 or SO34S packages
• Supply and Safety features
• enhanced reset (onchip) system
• Low voltage supervisor
• 3 power saving modes
• Configurable watchdog reset

20
ST72141 CORE for a whole motor system
21
ST72141 DEDICATED PMDC DRIVERAutomate
Coprocessor
DELAY MANAGER
BEMF ZERO-CROSSING DETECTOR
MCIA
BEMF0
MCIB
Z
MTIM
DELAY
CAPTURE Zn
MCIC
TIMER
WEIGHT
Internal V
REF
DELAY WEIGHT x Zn
?
COMMUTE C
MCO5
MCO4
(I)
MEASUREMENT
CURRENT
MCO3
WINDOW
GENERATOR
MCO2
VOLTAGE
(V)
MCO1
MCO0
(I)
(V)
MODE
NMCES
MCCFI
(V)
PWM (1)
OCP1A
(I)
PWM MANAGER
CHANNEL MANAGER
Note 1 The PWM signal is generated by the ST7
16-bit Timer Z Back EMF Zero-crossing event Z
n Time elapsed between two consecutive Z
events C Commutation event C n Time delayed
after Z event to generate C event (I) Current
mode (V) Voltage mode
22
ST72141 Synchronous Motor controller
Peripheral description (1)

• Back-emf Zero Crossing Detector
• 3 analog inputs for sensorless rotor position
  detection.(same inputs -logical-are used in case
  of sensor operation)
• On chip clamping diodes
• End-of-demagnetisation detection by comparator
  output sampling at 800KHz. There are 4
  selectable reference voltage for Hardware
  Demagnetisationdetection 0.2V, 0.6V, 1.2V,
  2.5V
• Possibility of implementing simulated
  demagnetisation based on last low side
  demagnetisation result.
• Back-emf zero-crossing detection On-chip phase
  voltage comparator is directly refered to the
  full b-emfwithout attenuation for zero crossing
  detection - 200mV sensitivity and 100mV
  hysteresis. - 4 selectable voltages for the
  hysteresis comparator (same voltages as
  demagnetisation)

23
PHASE INPUT Block Diagram (1)
24
ST72141 Synchronous Motor controller
Peripheral description (2)

• Delay Manager
• Delay manager automatic and programmable delay
  between b-emf zero crossing and next
  commutation.
• HW coprocessor 88 multiplication and /32
  division for automatic computing of delay or
• SW calculation/look-up of the delay (no
  computation) at motor start-up or for other motor
  than PMDC (when no b-emf is available).
• Automatic compensation for disymetrical motors
  (by use of n-1 time between zero-crossings for
  delay computing)

Kf (motor characteristics, application,
speed) 0255
C
Z
Z
T
(TxK)/32
T/32
25
Control Principles of PMDC Maximum efficiency
with delay manager
back-EMF
switching time of step n1
current
t
C commutation Z Zero Crossing
Z
D
image of ST72141 Motor control timer (MTIM)
D end of demagnetisation
c
c
Z
t
zero crossing detection times
26
ST72141 DEDICATED PMDC DRIVERDELAY MANAGER
27
ST72141 Synchronous Motor controller
Peripheral description (3)

• PWM Manager
• On chip comparator for current loop control (see
  previous slide) - Current regulation in current
  mode - Voltage regulation/Current limitation in
  voltage mode
• Measurement window generator for b-emf zero
  crossing detection.

28
ST72141 DEDICATED PMDC DRIVERPWM MANAGER
(I) Current mode
(V) Voltage mode
29
PWM manager Current Mode, Voltage Mode

• Current Mode
• Current in windings is imposed
• True DC current in the motor
• Fine control of the current for each of the 6
  steps
• Allows fine control of torque
• Voltage Mode
• Voltage control by PWM cycle
• no fine control of current (only max current
  limitation)
• Can be used in applications with high torque
  variations

30
Current limitation in voltage mode control
31
Current loop regulation in current mode control
32
ST Solution for compressor control
Current mode control
true DC current in the motor
Acceleration / Torque control
by current reference setting
Speed control
via Torque regulation
Speed range
ratio of a 100
Maximum speed
reach limits of optimum conditions thanks to
real time de-flux control
Starting torque
limited only by motor characteristics
Starting speed
few steps required
Starting time
few tenths of second typical
motor configuration characteristic
accept Star or Delta with no hardware
modification as well as salient or smooth poles
33
Control Principles of PMDC B-emf detection and
phase commutation delay
current reference
I
t
t
clock
Motor Voltage
back-EMF
t
step time
step time
switching time of step n1
T1-T4
T1-T6
current
t
C commutation Z Zero Crossing
Z
D
image of ST72141 Motor control timer (MTIM)
D end of demagnetisation
c
c
Z
t
zero crossing detection times
34
ST72141 Synchronous Motor controller
Peripheral description (4)

• Channel Manager
• Commutation step control
• 6 PWM output channels - 1 or 2 groups
  (oddeven) - multiplexing of PWM output
  according to group and phase selected. -
  programmable output polarity channel by channel
  - 195Hz to 25KHz output - off-time between 5µS
  and 30µS (fixed 1.25µS in sensor mode)
• acceleration of demagnetisation feature (by
  selecting correct transistor to switch).
• 1 emergency stop input pin to force all outputs
  in Hiz (active at low level)
• SW enable bit to force all outputs in Hiz

35
ST72141 MicrocontrollerPresentation contents

• Introduction
• A. Permanent Magnet DC Motor Basics
• B. ST72141 description
• - General features
• - Core
• - Motor Control Peripheral
• - Current mode / Voltage mode
• C. Summary of Benefits of ST72141
• D. Appendix - Starting sequence - Speed-up of
  demagnetisation
• Conclusion

36
ST72141 Summary of Benefits(1)

• Reduced cost
• Currently, only available dedicated MCU for PMDC
  motor with low pin count (SO34S or SDIP32)
• Typically lower cost than available DSP offer
• OTP at 1.5 to 2 times the price of ROM
• Reduced system cost
• ST patented Sensorless rotor positioning (no
  sensor/ reduced external components)
• On chip current monitoring loop (no external
  components)
• On chip clamping diodes and high current outputs
• On chip reset circuit
• Reduced power consumption (15-20mA) for small
  dimensioning pf P.S

37
ST72141 Summary of Benefits(2)

• Fast time to market / High flexibility
• Industry standard 8bit MCU architecture for short
  learning time and accessibility (compared to DSP)
• MCU Flexibility (compared to ASIC)
• Pin to pin compatible OTP (2weeks L/T) or FastROM
  (4weeks L/T) for fast production ramp-up
• Most adequate performance and safety
• Powerful 8bit core
• Optimized for scalar control Most adequate
  performance for control of PMDC motors in Home
  appliances and automotive.
• Dedicated Motor Control cell to free CPU
  ressources
• Emergency input pin (to put driver outputs in
  HiZ)
• Watchdog, LVD, safe reset
• ESD sensitivity (human body model) Product
  passes 3500V

38
ST72141 Summary of Benefits(3)

• Technical support
• Dedicated Application Support WW
• High performance C Compiler (Hiware/Cosmic)
• Emulator/programmers
• Application Notes
• Reference SW (generic, compressor control...)
• Reference and quality
• ST7 Core products 400Million units shipped to
  leading customers WW.
• ST72141 now in design with leading home
  appliance and automotive
  manufacturers WW.

39
ST72141 for Sensorless PMDC controlmain features
(2)

• Applications
• Refrigerator
• Air con
• Washing Machine
• Blower or Fan
• Medical Equipment
• Vending machine
• Automotive (fan, fuel pump, starter...)
• Pump drives

40
ST72141 for Sensorless PMDC controlmain features
(3)

• Support
• Emulator/Programmer...............Now
• Demokit with PMDC motor, inverter, PC
  interface...............Now- Evaluation of
  ST72141 with motor provided- Customisation of SW
  for user's own motor- Generation of optimised
  SW- On board programming
• Standard ASM routine library....Now
• Standard C routine Library.......Q3/00
• Application Notes.....................Q3/00
• Application Support...................Now

41
ST72141 MicrocontrollerPresentation contents

• Introduction
• A. Permanent Magnet DC Motor Basics
• B. ST72141 description
• - General features
• - Core
• - Motor Control Peripheral
• - Current mode / Voltage mode
• C. Summary of Benefits of ST72141
• D. Appendix - Starting sequence - Speed-up of
  demagnetisation
• Conclusion

42
CURRENT versus Back EMF PHASE SHIFT
Poor efficiency
High efficiency operation
zero crossing detection available
Starting few tenth of seconds typical.
t
43
STARTING SEQUENCE
rotation speed (rpm)
2000
closing the regulation loop
1000
synchronous sequence
waiting for BEMF
1
3
2
enabling auto-commutated mode
time (sec)
44
Pre-positioning step
T1-T4-T6
300V DC
A
T1
T5
T3
U
V
N
W
C
S
B
T4
T6
T2
3
6
-

• Put in an intermediary position
• Not an ordinary polarization
• Using the 3 windings generate a more important
  flux
• Less oscillations around the start position

45
Pre-positioning ramp

• The pre-positioning phase lenght can be set by
  software

46
Acceleration ramp
47
back-EMF MONITORING INTERVAL depends on current
amplitude
I2
I1
t
back-EMF monitoring interval
demagnetisation time is increasing when current
is high
48
back-EMF MONITORING WINDOWdepends on line voltage
current slope proportional to the line voltage
I1
t
demagnetisation time is increasing when line is
low
back-EMF monitoring window
49
Case We want 2 consecutive Z events to valid
auto-switched mode
50
SPEED REGULATION STRATEGY
51
Demagnetisation Speed Up Principle on High Side
V
V
V
T1
PWM
T1
T1
A
A
A
D3
V/2
B
B
C
C
D2
C
B
GND
bemf
bemf
T6
V/2 --gt GND
T4
T6
Step 2
Commutation 1-2 B Demagnetisation
Step 1
52
Demagnetisation Speed Up Principle on Low Side
V
V
V
T5
bemf
T3
T3
D1
A
A
A
B
D6
B
C
C
C
V/2
B
bemf
T2
T2
T2
V/2 --gt V
PWM
Step 2
Commutation 2-3 A Demagnetisation

• Step 3

53
BLDC Inverter Air-Conditioner

• Main advantages
• Quick cooling heating
• Temperature regulation
• Energy saving
• Reliable/long life time (no brushes)
• Super quite operation
• High torque at start-up

54
Traditional Split Air-Conditioner System
1. Liquid coolant
4. Liquid coolant
(Low temp pressure)
Expansion
(low temp high pressure)
Valve
Outdoor Unit
Indoor Unit
Condenser Air-cooled
Air Cooling Coil
Refrigerant
Evaporator
Outside air
Return air
M
M
Outdoor fan
Indoor fan
Temperature
Absorb heat from room
3. Coolant in gaseous state
Sensing
and deliver cool air
(high temp pressure)
Air is forced through
2. Coolant in gaseous state
- condensation
M
Compressor
(high temp low pressure)
Temperature
Sensing
55
ON/OFF Control of Traditional Air-con(Fixed
Motor Speed)
56
Continuous Control of Inverter Air-Con(Variable
Motor Speed Control)
T
Setting temperature
Very small temperature fluctuation
Room temperature
Time
t
57
ST72141 Regulation loops(simplified diagram)
Target Motor Speed
Step Time
Motor
P.I.D or Fuzzy regulation
b. emf
I
Feedback Speed
Motor efficiency regulation loop
Speed regulation loop
58
Close Loop regulation Parameter

• Irefn I0 P en I(?ni0 ?i)
• 
  STP int
• With
• Starting Value I0
• Proportional Element P ?n
• Integer Element I(?ni0 ?i)
• P 1/K1 Proportionnal Coefficient
• I 1/K2 Integer Coefficient
• STPint(0) 0

59
PI Principle

• IrefnI0 PEnI(?i0n Ei)
• I0start value
• PEnproportional element
• I(?i0n Ei)integer element
• P4/K1proportional coefficient
• I4/K2Integral coefficient
• STPint(0)0
• Error Stp_moy - Targ_speed
• If motor speed gt target speed then Error lt0
• If motor speed lt target speed then Error
  gt0Stp_moy average of step time on one
  mechanical cycle

60
PI flowchart (1)
61
PI flowchart (2)
62
PI flowchart (3)
63
PI flowchart (4)
64
PI flowchart (5)
Is_duty_max
yes
Max_duty-Iclosegt0?
no
IcloseMax_duty
Iclose-Min_dutygt0?
yes
no
Iclose(n)Min_duty
IrefIclose
Prog_Iref
RAZ
IRET
65
TIPS
66
Timer Data for one targeted speed

• For a 2P poles motor at N(rpm) targeted speed
• Step Time St60/(N6P)
• Ratio is extracted from table depending on
  the step time
• Timer value (Tv) is extracted from
• Tv(Stf)/eRLn2
• Speed TargetTv6Pk
• With k mechanical rotation number used for
  regulation
• Example 4 poles motor at 2000rpm regulate on 3
  mechanical cycles
• Step time St 60/ (200062)2.5ms
• Tv(2.510-32106)/e5Ln2 156
• Speed Target 156623422500

With Step time (St) Ratio (R) MC Clock (f)
67
Current regulation

• 60 duty cycle on the timer A. At 100 duty
  cycle, we have 5V. So, with 60 we have 50.6 3V
  (A)
• The divider has a value of 0.7 (70K/(30K70K)).
  So after the divider we have 30.7 2.1V (B)
• At OCP1A pin we have 2.1V. So, 2.1 V applied on
  MCCFI for the current regulation
• 2.1V on MCCFI pin means 2.1/10 (amplifier) 0.21
  V at C and so with the 0.05 Ohms resistor, this
  means 0.21/0.05 4.2A
• So, with a 60 duty cycle, 4.2A are applied to
  the motor.

68
Motor Control Training

• STRATEGY
• BLDC MOTOR CONTROL ST72141
• Microcontroller
• Peripheral
• SW and driving modes
• Kanda kit hand-on

69
BLDC Control Strategy
70
ST72141 Flow Chart
71
Basic Initialization of MC Peripheral
72
MC Peripheral Initialization
73
Synchronous Starting Ramp up
74
Main Program in Speed Closed Loop Mode
75
O (Multiplier overflow) E (Emergency Stop)
Interrupt Routine
76
C (commutation) D (end of demagnetization)
Interrupt Routine
77
C (1) Commutation
78
C(2) Synchronous Mode
79
C(3) Val_autosw
80
C(4) Set_ki_autosw
81
C(5) SDM_autosw (a)
82
C(6) SDM_autosw (b)
83
C(7) Carry_Set
84
C(8) End_C_action
End-C_action
prepare data for next C event
Change Delay (chang_ki 0) ?
no
yes
yes
chang_ki 10 ?
no
restore selected register to compute delay
chang_ki 10
yes
new_ki 0 ?
select synchronous mode clear MCOMP select
auto-swicthed mode
no
write MDREG
select MZREG
C_action_end
85
C(9) C_action_End
86
C(10) Crossing
87
R (ratio) Z (bemf) Interrupt Routine
88
RMI event
89
RPI event
90
Z event