ID 610C: Introduction to BLDC Motor Control

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ID 610C Introduction to BLDC Motor Control
Avnet Jim Carver Technical Director, Advanced
Architectures 12 October 2010
Version 1.0
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Renesas Technology and Solution Portfolio
Microcontrollers Microprocessors1 Market
shareworldwide
SolutionsforInnovation
Analog andPower Devices1 Market sharein
low-voltageMOSFET
ASIC, ASSP MemoryAdvanced and proven
technologies
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
Renesas Technology and Solution Portfolio
Microcontrollers Microprocessors1 Market
shareworldwide
SolutionsforInnovation
Analog andPower Devices1 Market sharein
low-voltageMOSFET
ASIC, ASSP MemoryAdvanced and proven
technologies
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
4
Microcontroller and Microprocessor Line-up

• Up to 1200 DMIPS, 45, 65 90nm process
• Video and audio processing on Linux
• Server, Industrial Automotive

Superscalar, MMU, Multimedia

• Up to 500 DMIPS, 150 90nm process
• 600uA/MHz, 1.5 uA standby
• Medical, Automotive Industrial

High Performance CPU, Low Power

• Up to 165 DMIPS, 90nm process
• 500uA/MHz, 2.5 uA standby
• Ethernet, CAN, USB, Motor Control, TFT Display

High Performance CPU, FPU, DSC

• Legacy Cores
• Next-generation migration to RX

R32C
M16C
H8S
H8SX
General Purpose
Embedded Security
Ultra Low Power

• Up to 10 DMIPS, 130nm process
• 350 uA/MHz, 1uA standby
• Capacitive touch

• Up to 25 DMIPS, 150nm process
• 190 uA/MHz, 0.3uA standby
• Application-specific integration

• Up to 25 DMIPS, 180, 90nm process
• 1mA/MHz, 100uA standby
• Crypto engine, Hardware security

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Microcontroller and Microprocessor Line-up

• Up to 1200 DMIPS, 45, 65 90nm process
• Video and audio processing on Linux
• Server, Industrial Automotive

Superscalar, MMU, Multimedia
All Of Them!

• Up to 500 DMIPS, 150 90nm process
• 600uA/MHz, 1.5 uA standby
• Medical, Automotive Industrial

High Performance CPU, Low Power

• Up to 165 DMIPS, 90nm process
• 500uA/MHz, 2.5 uA standby
• Ethernet, CAN, USB, Motor Control, TFT Display

High Performance CPU, FPU, DSC

• Legacy Cores
• Next-generation migration to RX

R32C
M16C
H8S
H8SX
General Purpose
Embedded Security
Ultra Low Power

• Up to 10 DMIPS, 130nm process
• 350 uA/MHz, 1uA standby
• Capacitive touch

• Up to 25 DMIPS, 150nm process
• 190 uA/MHz, 0.3uA standby
• Application-specific integration

• Up to 25 DMIPS, 180, 90nm process
• 1mA/MHz, 100uA standby
• Crypto engine, Hardware security

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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

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Motor Types
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Expanding BLDC Motor Control Applications
Transition to
As consumers demand more energy efficient
products, more BLDC motors are being used.
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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

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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

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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

-
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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

0
1
1
0
1
0
0
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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

U
V
W
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Six-step Commutation
U
V
W
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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

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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
H2
H3
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Hall Sensor Commutation

• The combination of all three sensors produce six
  unique logic combinations or steps
• These three bits are decoded into the motor phase
  combinations

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3-Phase PWM

• 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

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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
  Electro-Motive Force, a.k.a. Back-EMF or just
  BEMF

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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

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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

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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

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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

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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

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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
• Cons
• Complicated Algorithm
• Needs powerful processor

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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
Pulse Width Modulator
Transistors
Motor
Load
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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
-
Control Mechanism
Sensor
Reference Command

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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 w and motor angle is Theta ?
• The Reference input is shown as Omega star w
• 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

?
?
?
Speed Calculation
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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 oscillations

Motor

?
?
?
Speed Calculation
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Motor Kit for Trapezoidal Control

• BLDC Motor, Board, Software, Schematics, Tool and
  GUI

R8C/25
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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

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YMCRPR8C25 Block Diagram
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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.

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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

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Commutation Options

• Back-EMF detection comparators
• Jumper selection (no soldering) between Hall and
  BEMF modes
• Input connector for Hall signals from motor

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Debugging Capabilities

• Optically Isolated RS-232 communication
• Optically Isolated E8(a) connector
• Prototyping areas (under LCD)
• LEDs for monitoring PWM lines, and GPIO
• Abundant test points

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Motor Control Graphical User Interface
Speed Slider
Target Speed
Actual Speed
Stop
Motor Current
System Status
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HEW Development Environment
Source Code Editor
Project Navigator
Output Window
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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

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Questions?
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Appendix
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Renesas MCU and MPU Solutions
SH-4 240MHz
Application Processor
SH-3 200MHz
SH-4A 600MHz
32-bit
32-bit
32-bit
V850ES 50MHz
RX600 100MHz
High-end Connectivity
SH-2A 200MHz
32-bit
32-bit
32-bit
SH-2A 200MHz
RX600 100MHz
TFT LCD Control
H8S/SX 50MHz
32-bit
32-bit
32-bit
Ultra Low Power
78K0 10MHz
78K0R 20MHz
V850ES 20MHz
32-bit
8-bit
16-bit
General Purpose
R8C 20MHz
M16C 32MHz
R32C 50MHz
8-bit
16-bit
32-bit
Application Focused Solutions
WiFi SH, RX, R8C
Motor Control SH, V850, RX, 78K0R, R8C
Capacitive Touch R8C
Industrial CAN R8C, R32C, SH
Lighting 78K0
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Motor Control Applications Renesas Solutions
SuperH
RX
V850
78K0R
R8C
High-End
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Renesas Motor Control Solutions

• Renesas covers every motor control application
  from low-end 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

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Motor Control Solution Summary
Motor Type Algorithm R8C 78K0R V850 RX SH2/ SH2A
1-Ø ACIM (PSC) V/f, Open Loop Y  
1-Ø BLDC Fixed Duty (Hall) Y  
1-Ø BLDC Closed Loop (Hall) Y  
Universal (Brushed) DC TRIAC Control ( speed loop w/Tachometer) Y  
Universal (Brushed) DC PWM Chopper (speed loop w/Tachometer) Y  
3-Ø ACIM V/f, Open Loop Y Y
3-Ø ACIM Speed Loop w/Tachometer   Y
3-Ø ACIM Sensorless Vector Control   Y Y Y
3-Ø BLDC 120-deg Trapezoidal (Hall) Y Y
3-Ø BLDC 120-deg Trapezoidal (BEMF) Y  
3-Ø BLDC 180-deg Sine (HALL) Y  
3-Ø BLDC Sensor based Vector Control Y Y
3-Ø BLDC Position Control (Encoder Hall) Y
3-Ø BLDC Sensorless Vector Control, 2 DCCT, 3-shunt, 1-shunt Y Y Y Y



Under development
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