Download Introduction to BLDC Motor Control - Renesas e

ID 610C: Introduction to BLDC Motor Control
Avnet
Jim Carver
Technical Director, Advanced Architectures
12 October 2010
Version 1.0
Renesas Technology and Solution Portfolio
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& Microprocessors
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Advanced and
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* MCU: 31% revenue
basis from Gartner
"Semiconductor
Applications Worldwide
Annual Market Share:
Database" 25
March 2010
** Power MOSFET: 17.1%
on unit basis from
Marketing Eye 2009
(17.1% on unit basis).
2
Renesas Technology and Solution Portfolio
Microcontrollers
& Microprocessors
#1 Market share
worldwide *
Solutions
for
Innovation
ASIC, ASSP
& Memory
Advanced and
proven technologies
Analog and
Power Devices
#1 Market share
in low-voltage
MOSFET**
* MCU: 31% revenue
basis from Gartner
"Semiconductor
Applications Worldwide
Annual Market Share:
Database" 25
March 2010
** Power MOSFET: 17.1%
on unit basis from
Marketing Eye 2009
(17.1% on unit basis).
3
Microcontroller and Microprocessor Line-up
Superscalar, MMU, Multimedia
High Performance CPU, Low Power
High Performance CPU, FPU, DSC
 Up to 1200 DMIPS, 45, 65 & 90nm process
 Video and audio processing on Linux
 Server, Industrial & Automotive
 Up to 500 DMIPS, 150 & 90nm process
 600uA/MHz, 1.5 uA standby
 Medical, Automotive & Industrial
 Up to 165 DMIPS, 90nm process
 500uA/MHz, 2.5 uA standby
 Ethernet, CAN, USB, Motor Control, TFT Display
 Legacy Cores
 Next-generation migration to RX
General Purpose
 Up to 10 DMIPS, 130nm process
 350 uA/MHz, 1uA standby
 Capacitive touch
4
Ultra Low Power
Embedded Security
 Up to 25 DMIPS, 150nm process  Up to 25 DMIPS, 180, 90nm process
 190 uA/MHz, 0.3uA standby
 1mA/MHz, 100uA standby
 Application-specific integration  Crypto engine, Hardware security
Microcontroller and Microprocessor Line-up
Superscalar, MMU, Multimedia
High Performance CPU, Low Power
High Performance CPU, FPU, DSC
 Up to 1200 DMIPS, 45, 65 & 90nm process
 Video and audio processing on Linux
 Server, Industrial & Automotive
 Up to 500 DMIPS, 150 & 90nm process
 600uA/MHz, 1.5 uA standby
 Medical, Automotive & Industrial
 Up to 165 DMIPS, 90nm process
 500uA/MHz, 2.5 uA standby
 Ethernet, CAN, USB, Motor Control, TFT Display
 Legacy Cores
 Next-generation migration to RX
General Purpose
 Up to 10 DMIPS, 130nm process
 350 uA/MHz, 1uA standby
 Capacitive touch
5
Ultra Low Power
Embedded Security
 Up to 25 DMIPS, 150nm process  Up to 25 DMIPS, 180, 90nm process
 190 uA/MHz, 0.3uA standby
 1mA/MHz, 100uA standby
 Application-specific integration  Crypto engine, Hardware security
Agenda
 Motor Types Overview
 BLDC Motor Applications
 Comparison of DC to Brushless DC Motors
 Hall Sensors
 Six-Step Commutation
 Sensorless Commutation with Back-EMF
 Vector Motor Control basics
 Closed-Loop Speed Control
 Introduction to BLDC Motor Control Evaluation Kit
 Summary
6
Motor Types
7
Expanding BLDC Motor Control Applications
Transition to
AC, DC
and
Universal
Motors
8
As consumers demand
more energy efficient
products, more BLDC
motors are being used.
BLDC
Brushed DC Motors Review
 A winding assembly (armature) within a
stationary magnetic field
 Brushes and Commutators switch current
to different windings in correct relation to
the outer permanent magnet field.
 Pros:
 Electronic control is simple, no need to
commutate in controller
 Requires only four power transistors
 Cons:
 A sensor is required for speed control
 The brushes and commutator create sparks
and wear out
 Sparks limit peak power
 Heat in armature is difficult to remove
 Low power density
9
Brushless DC Motors
 Permanent magnet rotor within
stationary windings
Pros:
 No brushes or commutator to wear out
 No sparks and no extra friction
 More efficient than DC motor
 Higher speed than DC motor
 Higher power density than DC motor
Cons:
 Rotor sensor OR sensorless methods
needed to commutate
 Requires six power transistors
10
Stator
windings
Permanent
Magnet
Rotor
Brushed DC Commutation
 The windings in the
armature are switched to
the DC power by the
brushes and armature
+
 Each winding sees a
positive voltage, then a
disconnect, then a negative
voltage
 The field produced in the
armature interacts with the
stationary magnet,
producing torque and
rotation
+
U
11
-
N
S
DC Motor Bridge
 The DC motor needs four
transistors to operate the DC
motor
 The combination of transistor
is called an H-Bridge, due to
the obvious shape
 Transistors are switched
diagonally to allow DC current
to flow in the motor in either
direction
 The transistors can be Pulse
Width Modulated to reduce the
average voltage at the motor,
useful for controlling current
and speed
12
1
0
0
1
0
1
0
Three-Phase Bridge to Drive BLDC Motor
 The Brushless DC motor is really a DC motor constructed
inside-out, but without the Brushes and Commutators
 The mechanical switches are replaced with transistors
 The windings are moved from the armature, to the stator
 The magnet is moved from the outside to become the rotor
N
13
S
U
V
W
N
S
Six-step Commutation
STEP1
STEP2
STEP3
STEP4
U
V
W
U
V
W
14
STEP5
STEP6
STEP1
STEP2
STEP3
Six-Step Current Waveform
 Here we see the individual steps in a real trapezoidal
current waveform
 The PWM ripple is visible when the phase is active
 The rising and falling edges are sloped, giving the
trapezoidal shape
 The amount of slope is a function of the winding inductance
15
Hall Sensors
Hall Sensors detect magnetic fields, and
can be used to sense rotor angle
The output is a digital 1 or 0 for each
sensor, depending on the magnetic field
nearby
Each is mounted 120-degrees apart on
the back of the motor
As the rotor turns, the Hall sensors
output logic bits which indicate the angle
H1
H1
N
S
H2
H3
16
H3
H2
Hall Sensor Commutation
STEP1
H1
The combination of all
three sensors produce
six unique logic
combinations or steps
These three bits are
decoded into the motor
phase combinations
H2
H3
U
V
W
17
STEP2
STEP3
STEP4
STEP5
STEP6
STEP1
STEP2
STEP3
3-Phase PWM
U
We can divide up the
phase data into
individual transistor
gate signals
Now we can see how
we can modulate one
transistor at a time to
regulate the motor
voltage, and also the
speed
V
W
UP
UN
VP
VN
WP
WN
18
Sensorless Commutation
 Instead of using sensors like Halls, we can let the motor tell
us which phase should be energized
 The Brushless DC motor acts as a generator when it rotates,
creating voltages
 The three phases produce three voltages 120-degrees apart
 The voltage generated by the motor is called Back ElectroMotive Force, a.k.a. Back-EMF or just BEMF
19
Brushless DC Motor BEMF
 The Back-EMF is the voltage generated in stator windings as the
rotor moves
 BEMF voltages are more or less sinusoidal (depending on the
motor) and are symmetrical from phase to phase
 We detect the zero crossings of each phase to commutate
 The motor MUST be moving to generate BEMF voltages
20
Brushless DC Motor BEMF
 The Back-EMF is the voltage generated in stator windings as the
rotor moves
 BEMF voltages are more or less sinusoidal (depending on the
motor) and are symmetrical from phase to phase
 We detect the zero crossings of each phase to commutate
 The motor MUST be moving to generate BEMF voltages
21
Startup of BEMF System
 Since only a spinning motor generates BEMF signals
 Start the motor in open loop
 First align rotor to a known angle
 Then energize the windings to step rotor to next
step
 Accelerate steps until speed is sufficient to “see”
BEMF zero crossings reliably
 Switch to BEMF commutation
 Once operating, this is almost identical to six-step
operation with Hall sensors
22
Sinusoidal Methods
 Stepped commutation methods work well, but…
 The Back-EMF waveform is more sinusoidal than trapezoidal
 If we can match the sinusoidal waveform, we can improve
performance
 We will show two sinusoidal methods:
 180-Degree Sinusoidal
 “Field Oriented” or “Vector” control
23
180° Sinusoidal Commutation
 Modulates sine waves in all three windings
 Pros:
 No square edges
 Lower Torque Ripple then six-step drive
 Lower audible noise
 Higher efficiency and torque
 Stator angle is rotated smoothly rather
than in 60 degree jumps
 Each phase is utilized all of the time
 Cons:
 Needs higher resolution feedback to
calculate sine waves with low distortion
 Needs more sophisticated processing to
calculate sine PWM values on the fly
 Bandwidth of currents are limited due to
motor impedance, this hurts high speed
performance
24
Vector (Field Oriented Control) Drive
 This method mathematically converts the 3-phase voltage
and current into a simple DC motor representation
 Uses this data to calculate the best angle for commutation
 Creates new 3-phase sinusoidal PWM based on calculation
 Repeats the calculations at PWM frequency
 Pros:




Highest Torque efficiency
Highest Bandwidth
Widest Speed Range 

Lowest Audible Noise
*
r
r
 Cons:
 Complicated Algorithm
 Needs powerful processor
DC Bus
r
iq
*
Speed Regulator
id  0
*
id
iq
iq PI
Regulator
Uq
*
d,q
*
U
*
to
id PI
Regulator
Ud
*
, 
T 1 ( )

iq
PWM1~6
, 
to
a, b, c
to
d,q
ia
i
T ( )
r
Voltage
Source
3-phase
Inverter
SIN
PWM
Motor Model
Based Flux and
Position Observer
, 
id
25
U
a,b,c
to
i
, 

Speed Estimation
ib
3-phase
PMSM
BLDC Motor Speed Control
 The goal of most Electronic Motor Control Systems is Speed
Control
 Speed Control systems are more or less complicated,
depending on accuracy required
 The simplest speed control is Open-Loop, that is, without
speed feedback
 In this configuration, a speed command is converted to a
fixed voltage (PWM duty) which is sent to the motor
 The motor may go the right speed, or it may not, it depends
on the load
 Without feedback, there is no way to tell internally what the
real speed is and so may require outside adjustment
Speed
Command
26
Pulse Width
Modulator
Transistors
Motor
Load
Closed-Loop Control
 To get automatic speed control, feedback is needed
 Feedback systems could be Hall Sensors, Encoders,
Resolvers, tachometers or other devices
 The resolution and bandwidth of the feedback sensor limit
the resolution and bandwidth of the speed loop
 Below is a block diagram of a simple control loop
 Our Reference Command is the speed we desire, and the
Control Mechanism is our motor and motor control
Feedback
Reference
Command
27
+
Control
Mechanism
Sensor
Closed Loop Speed Control
 The generic terms can be replaced with terms common to
motor control
 The speed is often referred to as the Greek Letter Omega 
and motor angle is Theta θ
 The Reference input is shown as Omega star  *
 The Control Mechanism is a mathematical function, usually
a Proportional-Integral (PI) algorithm
 The speed sensors can be the same Hall sensors used for
commutation, where the speed is calculated from the time
between steps
Motor
PI
Controller
ω*
θ
ω
Speed
Calculation
28
PWM
Generation
Hall
Sensors
Closed Loop Speed Control
 The way the loop works is to first measure the difference
between the commanded speed and the actual speed
 If the speed is to low, the PI controller increases the PWM
duty which sends more voltage to the motor, correcting
speed
 If the speed to too high, the PI controller reduces the PWM,
reducing the average voltage, so the motor slows down to
the correct speed
 The Proportional and Integral parameters have to be tuned
to optimized the speed loop response-prevent speed Motor
oscillations
PI
Controller
ω*
θ
ω
Speed
Calculation
29
PWM
Generation
Hall
Sensors
Motor Kit for Trapezoidal Control
 BLDC Motor, Board, Software, Schematics, Tool and GUI
R8C/25
30
Motor Control Evaluation Kit
 In order to help users decide on what kind of motor control
they need, Renesas has introduced the YMCRPR8C25 Motor
Control Evaluation Kit
 The kit includes all that is needed to try Hall and BEMF
commutated Brushless DC motor control with closed speed
loops including, the control board, motor, debugger, power
supply and software
31
YMCRPR8C25 Block Diagram
R8C25 MCRP Kit
V
B
U
S
CN-4
24v DC
Supply
Power Supply
&
Conditioning
TP-1
TP-5
BLDC
Motor
Speed
Control
R8C/25
MCU
6-PWM
International
Rectifier
(IPM)
CN-1
M
Shutdown
RS232
I/F
Comparators
( Back-EMF)
E8
Debug
I/F
TP-2
OP-AMP
(Signal Conditioning)
Jumper-1
Hall Sensor
Inputs
Shunt
Current
LCD Segment
Display
CN-3
32
CN-2
TP-3
TP-4
4-LED
PWM / PWR
Status
Push-Button
Switch
Motor Control Board
 IGBT module capable of 10
amps.
 3-Phase output capable of
running DC and BLDC
motors
 15V and 5V regulators on
board.
 Voltage input from a single
24V (18-36VDC) supply,
no shock hazard.
33
Board User Interface
 Large potentiometer
for speed control
setting
 2x8 LCD display with
contrast pot for
monitoring speed,
current, etc.
 Four push-buttons
 Bus voltage monitoring
to MCU
 Current monitoring to
the module for
automatic protection
34
Commutation Options
 Back-EMF detection
comparators
 Jumper selection (no
soldering) between
Hall and BEMF
modes
 Input connector for
Hall signals from
motor
35
Debugging Capabilities
 Optically Isolated RS232 communication
 Optically Isolated
E8(a) connector
 Prototyping areas
(under LCD)
 LED’s for monitoring
PWM lines, and GPIO
 Abundant test points
36
Motor Control Graphical User Interface
Speed Slider
Target Speed
Actual Speed
Stop
Motor
Current
System
Status
37
Project Navigator
HEW Development Environment
Source Code Editor
Output Window
38
Summary
 DC and BLDC motors were compared
 BLDC motors were shown to offer better performance
 A large number of applications are moving from other motor
types to BLDC motors
 Electronic BLDC motor control can be as simple as six-step
or as complicated as Vector Control
 Closed Loop Speed Control was explained
 The Renesas BLDC Motor Control Evaluation Kit was
introduced as a way to help get started in BLDC motor
control development
39
Questions?
40
Appendix
41
50MHz
M16C
20MHz
32MHz
32-bit
32-bit
R32C
78K0R
100MHz
V850ES
32-bit
General
Purpose
20MHz
RX600
100MHz
200MHz
H8S/SX
8-bit
32-bit
V850ES
RX600
SH-3
78K0
8-bit
Ultra Low
Power
200MHz
32-bit
32-bit
SH-2A
200MHz
240MHz
32-bit
TFT LCD
Control
High-end
Connectivity
600MHz
SH-4
16-bit
32-bit
SH-2A
Application
Processor
16-bit
32-bit
SH-4A
32-bit
32-bit
Renesas MCU and MPU Solutions
R8C
50MHz
50MHz
10MHz
20MHz
Application Focused Solutions
WiFi
SH, RX, R8C
42
Motor Control
SH, V850, RX,
78K0R, R8C
Capacitive
Touch
R8C
Industrial CAN
Lighting
R8C, R32C, SH
78K0
Motor Control Applications & Renesas Solutions
SuperH
RX
V850
78K0R
R8C
Fans, Kitchen Appliances,
Pumps, Power-Tools
SPEED CONTROL
Torque Control (Limited)
Low-Range
43
Medical
Industrial, Washers,
Compressors
Motion Control
Pool Pumps, Washers
Health-Equipment
Compressors
SPEED + TORQUE
CONTROL
Mid-Range
SPEED + DYNAMIC TORQUE
+ MOTION CONTROL
High-End
Renesas Motor Control Solutions
 Renesas covers every motor control application from lowend to high-end
 Renesas can provide all motor algorithms from Trapezoidal
control to Sensor-less Vector control
 Wide product portfolio
 16bit MCU (20MHz): R8C, 78K0R
 32bit MCU (48MHz to 200MHz): RX, V850, SH
 These products have peripherals dedicated for Motor
Control such as Timers and ADC
44
Motor Control Solution Summary
Motor Type
1-Ø ACIM (PSC)
1-Ø BLDC
Universal
(Brushed) DC
3-Ø ACIM
Algorithm
R8C
V/f, Open Loop
Y
Fixed Duty (Hall)
Y
Closed Loop (Hall)
Y
TRIAC Control ( speed loop
w/Tachometer)
Y
PWM Chopper (speed loop
w/Tachometer)
Y
V/f, Open Loop
Y
78K0R
RX
Y
Y
Speed Loop w/Tachometer
Y
Sensorless Vector Control
3-Ø BLDC
V850
SH2/
SH2A
120-deg Trapezoidal (Hall)
Y
120-deg Trapezoidal (BEMF)
Y
180-deg Sine (HALL)
Y
Y
*
Y
Y
*
Y
Y
Sensor based Vector Control
Y
Position Control (Encoder + Hall)
Sensorless Vector Control,
2 DCCT, 3-shunt, 1-shunt
45
Y
Y
*
Y
Y
*: Under development