ESC 2008: Design Techniques for Power-Efficient Motor · PDF file · 2008-04-29Pulse Width Modulation (PWM) - Basics ... Design Techniques for Power-Efficient Motor Control Pulse

Ravi Pragasam Senior Manager, Fusion Product Marketing April 2008

Design Techniques for Power-Efficient Motor Control

Feb 29 08

Need for power-efficient motor controlImproving motor efficiencies using Programmable System Chips

Integrated Pulse Width Modulation Power efficiency schemes

Quadrature encoder interfaceLoad matching and variable speed controlSlip control

Summary


Agenda

Electronic motors have become increasingly ubiquitousWith this growth comes increasing requirements for improved performance, efficiency and flexibilityElectric motors use half of all US electricity consumed

In 2005, US consumed 4,055 billion KWh of electrical power More than 50% of this was consumed by electric motors

Design Techniques for Power-Efficient Motor Control Feb 29 08

Motor Control Power Consumption Profile

High cost of control and power electronics has been a major barrier to deployment of intelligent power management solutions Implemented broadly, efficient electronic motor control could result in savings of as much as 15% of the power consumed in the U.S.

An annual reduction of as much as 300 billion kWh and $15 billion saved

Feb 29 08Design Techniques for Power-Efficient Motor Control

The Need for Power-efficient Motor Control

Feb 29 08

Consumer Appliance (White Goods)

Industrial/HVAC Industrial Servo

Applications ToysModel AircraftsDVD/CD Players

RefrigeratorsWashers/DryersDish Washers

PumpsConveyersCompressorsInvertersMeters

Material Handler RobotInstrumentationOffice Equipment

Type of Motor and Applied Control Algorithm

BLDCTrapezoidal

StepperHalf/Full StepMicro Step

ConventionalShuntWound

PMSMFOCTrapezoidal

ACIMV/FSlip Optimization

ConventionalShuntWound

PMSMFOCTrapezoidal

ACIMFOCV/FSlip Optimization

StepperHalf/Full/Micro Step

PMSMFOCTrapezoidal

ACIMFOCSlip Optimization

StepperHalf/Full/Micro Step

Control Scheme Open-Loop Open-LoopClose-Loop

Sensorless

Open-LoopClose-Loop

SensorSensorless

Close-LoopSensorSensorless


Motors, Motors Everywhere

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Integrated Pulse Width Modulation Power-efficiency schemes


Summary


Agenda


Traditional Motor Control Implementation

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Component selection processSelection depends on application needs and type of motor being controlled

ADC – how many bits of resolution, accuracy, sampling rate, conversion time…Interface – number of input channels, signal conditioning, amplifiers, filters…Sensors – hall effect, back EMF,…CPU – processor cores (ARM, 8051, State Machines,…)Network Interfaces – connectivity needs, what is the interface, how fast is the data rate transfer, any protocols,…

Traditional solutions offer one or more function, but not allDetermine if some of the above functions can be achieved with a microcontroller Designer will need to make a decision based on the following

Power needsPerformance needsOverall system costDesign environment knowledge Design cycle

Once selection made, use the design environment to generate the applicationWhen design complete, debug and validate to ensure that the specification is met


Traditional Motor Control Design

94/29/2008

Component selection process Ideal solution will integrate several functions into oneSeveral benefits can be obtained with an integrated solution

Lower overall powerLower system costLess design complexityBetter signal integritySingle platform that can be scaled

Optional functions can be included based on needsPlatform needs to be flexible to accommodate different needs

Use design environment to generate the applicationWhen design complete, debug and validate to ensure that the specification is met


Changing Motor Control Design

Incorporate analog functions, embedded flash memory and FPGA fabric in a single chipFlexible platform for scalabilityOffers benefits of monolithic design environment


Programmable System Chips - PSCs

114/29/2008Feb 29 08

GPIO

FLASH Memory

JTAG Port

FPGA Fabric(incl. SRAM, CCC/PLL, IO)

Xtal OSC,RC OSC,

RTC, Vreg

PSC Offers Analog IntegrationSuccessive Approximation Register (SAR) ADC

Up to 12 bit or 600 KspsBetter than 1% total channel accuracy with calibrationInternal reference voltage

Built in sample and holdIncreases accuracy of dynamic signals

Analog I/O± 12 V TolerantUp to 30 channels inputCurrent monitor block

2 mV resolutionTemperature monitor block

+ 3o C accuracy+ 5O C Offset

MOSFET Gate driver outputProgrammable drive strengthP and N channel devices

AnalogInputs

MOSFETOutputs

A/DAna

Mux

Ana

Mux

Essence of Motor Control Offers the analog interface, sensing with signal conditioning functions required

System management and motor control benefit from

Integrated current, temperature and voltage monitoring Supports up to 30 channelsFET gate driver output to drive H-BridgeUnique positive and negative polarity support Pre-scaler ranges: 1, 2, 4, 8, 12, 16 VoltsSelectable ADC reference (internal vs external) 8/10/12-bit selectable resolution


PSC Analog Quad – I/O Structures

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Methodology For Flexible Functionality

Graphical productivity toolsADC sampling

Digital low-pass filtering

Threshold comparisons

State filtering

Analog input

High current output

Flash memory access

Automatically connects FPGA, flash and analog block with required functions


Using PSCs for Motor Control

Programmable System Chip

PSC

PSC can integrate multiple functions into a single platform

Take analog inputs from motor with the analog interface and ADCLeverage CPU for processing and control (Cortex-M1, 8051)Utilize flash memory to store the program and embedded SRAM blocks to store dataUse clock circuitry for generating signals needed for control (RC Oscillator)Interface to external components with network and peripheral interface Utilize soft PWM cores to generate current or voltage for gate drivers

Features Programmable System Chip (PSC)

Discrete Solutions(Microcontroller/DSP)

PWM Frequency Control

On-board PLL and clock generators can target a wide range of motors

Software-generated PWM; Use of internal timers to generate PWM frequencies; Algorithm/computing resources stressed

Sensing & Protection

Internal threshold flags control and protect; Drive over-current, over-temperature …

External implementation results in increased BOM cost

Real Time Monitoring System

Internal real-time counter (RTC) to log/record drive parameters and characteristics

Would require RTC and NVM

Configuration Storage

On-board NVM to store configuration data for fast and efficient drive operationReprogrammable in H/W and S/W

Need external NVM and hardware to store configuration data

Damping Dedicated on-board PWM IP coasting/braking possible

Timer based; Software overhead

BEMF – Zero Crossing

Sensorless operation using internal ADCs possible with minimal external components

External comparator circuit required for sensorless operation

Multiple Drive support

Rich I/O features and flexibility to drive multiple motors on single platform

Would require additional devices


PSCs versus Discrete Solutions

PWM control works by switching the power supplied to the motor on and off very rapidlyDC voltage is converted to a square-wave signal, alternating between fully on and zero, giving the motor a series of power "kicks"If switching frequency is high enough, the motor runs at steady speed due to fly-wheel momentumBy adjusting the signal’s duty cycle, the average power and motor speed can varyUsed to implement closed loop control of motorsCan be implemented by discrete components


Pulse Width Modulation (PWM) - Basics

Standard PWM solutions offer very little flexibilityNot a “one size fits all” for all motor control apps

Number of windings, voltage/current ratings, torque profiles and other parameters widely vary

PSC implementation allows the designer to customize PWM instead of “making do” with MCU or DSP capabilities

Programmable System Chip

Integrated Pulse Width Modulation in PSC


Feb 29 08

8 PWM digital outputsEdge control based on configurable 8-bit PWM period

8-bit pre-scaler valueDuty cycle – 0% to 100%

Can perform closed-loop control

Combined with processor or simple state machine


Pulse Width Modulation IP with PSC

Feb 29 08

Allows designer to define parameters based on need

Number of outputsNegative or positive edge of each output Interrupt maskEnable PWMDuty cycle

Effectively provides power-sensitive motor control based on environmental need


PWM Implementation Methodology

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Integrated Pulse Width ModulationPower-efficiency schemes


Summary


Agenda

214/29/2008

Quadrature Encoder - Background

Light Source

00011110

Code Track on DiskChannel AChannel B

Channel A

Channel B

Quadrature Encoder Output

90o

Counter Clockwise Clockwise

00101101

A

B

Quadrature encoder is composed of a light source, wheel and receptorTechnique uses sinusoidal signal generated from light source to represent position in BLDC motorsInformation is communicated to other machine interfacesReceptor output can be in the form of pulses based on wheel positionBenefits

Simpler to implement Improved reliabilityImmune to noise

Most high-precision motors, like the servo-type stepper motors, support quadrature-encoder interfaces Control system must provide quadrature-encoder interface logic to determine accurate speed, position and acceleration of the motion rotorsWith a PSC, accuracy and dynamic speed can be adjusted, depending on the characteristics of the motor

FPGA

Index

Filter

Filter

QuadratureDecoder

Up/DownCounter

DIR(U/D)

Reset

CNT

ChA

ChB

CCC/PLL

FPGA LogicFusion Block

Filter

QEB

QEA


Implementing Quadrature Encoder Interface

Uses discrete componentsDSP chips (filters) Timers (clocks)Quadrature encoder block (Schmitt Triggers or pulse generators) Logic (counters)

Not optimized for efficiency and powerHigher design complexity with little flexibility

FPGA

Index

Filter

Filter

QuadratureDecoder

Up/DownCounter

DIR(U/D)

Reset

CNT

ChA

ChB

CCC/PLL


Filter

QEB

QEA


Traditional Quadrature Encoder Interface Implementation

PSC used to implement all the above functions in a single integrated solutionCan be optimized for application to deliver a power-efficient solution

Each function customized to address the application needHighly flexible and less design complexity


PSC Quadrature Encoder Interface Implementation

FPGA

Index

Filter

Filter

QuadratureDecoder

Up/DownCounter

DIR(U/D)

Reset

CNT

ChA

ChB

CCC/PLL


Filter

QEB

QEA

For applications that need to be operated at a constant speed, intelligent load matching is a great way to deliver an efficient solution

Load sensed and matched with the proper input power, maximizing efficiency and minimizing power consumption and operating costs

Variable-Frequency Drives (VFD)For low-cost drives suitable for applications with known loading, VFDsused to vary the motor's rotational speed to match current load condition

Vector Control Schemes (Field oriented)Use real world feedback (speed or torque) to adjust to load variationsDeals with varying operating conditions and allows responsive and accurate speed control with a changing load Offers optimum efficiency even during motor transitionTraditional solutions use microcontrollers and DSPs to implement the closed loop control for speed and torqueUsing PSCs allow a single device to be used to control a range of motor types, including permanent-magnet AC and brushless DC motors


Load Matching and Variable Speed Control

A slip is a percentage of synchronous speedWhen none of the motors run with a fixed level of loading, the load can set a “slip” in the motor and determine the actual speed of the motor shaftThe slip affects the torque and operation of the motor In the control algorithm, slip frequency is often the key variable

Voltage to

HightimePWM

SpeedCalculator

PI Controller

Motor Frequency (fr)

Frequency

Current & Slip Tables

Volts

Slip Frequency (fs)

++

Current Sensor

ADCib

Actual CurrentDesired

Torqueia

SpeedSensor

V/F to 3φ

va

vb

vc

CurrentMagnitude Calculation

Commanded Current

Power Stage

Bottleneck Area

Voltage to

HightimePWM

SpeedCalculator

PI Controller


Frequency

Current & Slip Tables

Volts

Slip Frequency (fs)

++

Current Sensor

ADCib

Actual CurrentDesired

Torqueia

SpeedSensor

V/F to 3φ

va

vb

vc

CurrentMagnitude Calculation

Commanded Current

Power Stage

Bottleneck Area


Slip Control

An optimized slip control mechanism is the key factor in getting the required torque and efficiencyAn optimized slip control compensation system can benefit power saving in typical AC motors, according to U.S. Environmental Protection Agency

0

20

40

60

80

100

120

140

160

40:16 50:25 60:36 70:49 80:64 90:81 95:90

Speed:Torque

Red

uctio

n in

Inpu

t Pow

er

Power Reduction due to Slip Control Compensation (Input Power = 8477W)


Efficiencies from Slip Control

Feb 29 08

PWM Gate Drive

Power Stage

PMSMACIM

Encoder

Encoder Interface

PID Controller


Frequency

CPU

Slip Frequency (fs)

++

Ib

+

Desired torque

NVM

Ia

S/H

IqSRAM

+

_

Id

_Vd

Slip Freq Calculator

Vq

PID Controller

IQ

ID

ParkTransformation

ClarkTransformation

S/H

ADC

Modulator

Soft IP Function Option in

PSC

PSC Hard Function

SW on CPU (option in

PSC)


The slip frequency calculator implemented as software running on CPU The other functions needed can be optional soft IP on PSCThis scheme will provide an efficient slip control method and deliver a power-optimized motor

Slip Control Using Mixed-signal PSCs

294/29/2008Feb 29 08Feb 29 08

Need for power-efficient motor controlImproving motor efficiencies usingProgrammable System Chips

Integrated Pulse Width ModulationPower-efficiency schemes


Summary


Agenda

Feb 29 08

Increasing demand for energy savings and lower power puts pressure on designers to use more efficient motorsTraditional solutions may not offer the best solution for efficient motorsHighly integrated, flexible PSCs allow designers to implement the most efficient design for their application and also use the same device across motor applications Implemented broadly, electronic motor control could result in savings of as much as 15% of the power used in the U.S.


Summary

Documents

ESC 2008: Design Techniques for Power-Efficient Motor · PDF file · 2008-04-29Pulse Width Modulation (PWM) - Basics ... Design Techniques for Power-Efficient Motor Control Pulse