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ELECTRICAL DRIVES An Application of Power

Electronics

Dr. Nik Rumzi Nik Idris, (Senior Member

IEEE) Department of Energy Conversion, Universiti

Teknologi Malaysia Skudai, JOHOR

CONTENTS

Power Electronic Systems

Modern Electrical Drive Systems

Power Electronic Converters in Electrical Drives

DC and AC Drives

Modeling and Control of Electrical Drives

Current controlled Converters

Modeling of Power Converters

Scalar control of IM

Power Electronic Systems

What is Power Electronics ?

A field of Electrical Engineering that deals with

the application of power semiconductor devices

for the control and conversion of electric power

Power Electronics Converters

- Input
- Source
- AC
- DC
- unregulated

Output - AC - DC

POWER ELECTRONIC CONVERTERS the heart of power

a power electronics system

Power Electronic Systems

Why Power Electronics ?

ON or OFF

Ploss vsw isw 0

Losses ideally ZERO !

Power Electronic Systems

Why Power Electronics ?

Power Electronic Systems

Why Power Electronics ?

D

C

iD

ic

VDS -

VCE -

G

G

S

E

Power Electronic Systems

Why Power Electronics ?

High frequency transformer

Passive elements

Power Electronic Systems

Why Power Electronics ?

Power Electronics Converters

IDEALLY LOSSLESS !

Power Electronic Systems

Why Power Electronics ?

Other factors

- Improvements in power semiconductors fabrication

- Power Integrated Module (PIM), Intelligent Power

Modules (IPM)

- Decline cost in power semiconductor

- Advancement in semiconductor fabrication

- ASICs

- FPGA

- DSPs

- Faster and cheaper to implement complex algorithm

Power Electronic Systems

Some Applications of Power Electronics

Typically used in systems requiring efficient

control and conversion of electric energy

Domestic and Commercial Applications Industrial

Applications Telecommunications Transportation Gen

eration, Transmission and Distribution of

electrical energy

Power rating of

Tens or hundreds Watts (Power supplies for

computers /office equipment)

kW to MW drives

Hundreds of MW in DC transmission system (HVDC)

Modern Electrical Drive Systems

- About 50 of electrical energy used for drives

- Can be either used for fixed speed or variable

speed

- 75 - constant speed, 25 variable speed

(expanding)

- Variable speed drives typically used PEC to

supply the motors

DC motors (brushed)

- AC motors
- - IM
- PMSM

SRM

BLDC

Modern Electrical Drive Systems

Classic Electrical Drive for Variable Speed

Application

- Bulky
- Inefficient
- inflexible

Modern Electrical Drive Systems

Typical Modern Electric Drive Systems

PowerElectronic Converters

Modern Electrical Drive Systems

Example on VSD application

Variable Speed Drives

Constant speed

Modern Electrical Drive Systems

Example on VSD application

Variable Speed Drives

Constant speed

Modern Electrical Drive Systems

Example on VSD application

Variable Speed Drives

Constant speed

Modern Electrical Drive Systems

Example on VSD application

Electric motor consumes more than half of

electrical energy in the US

Variable speed

Fixed speed

Improvements in energy utilization in electric

motors give large impact to the overall energy

consumption

HOW ?

Replacing fixed speed drives with variable speed

drives

Using the high efficiency motors

Improves the existing power converterbased drive

systems

Modern Electrical Drive Systems

Overview of AC and DC drives

DC drives Electrical drives that use DC motors

as the prime mover

Regular maintenance, heavy, expensive, speed limit

Easy control, decouple control of torque and flux

AC drives Electrical drives that use AC motors

as the prime mover

Less maintenance, light, less expensive, high

speed

Coupling between torque and flux variable

spatial angle between rotor and stator flux

Modern Electrical Drive Systems

Overview of AC and DC drives

Before semiconductor devices were introduced

(

- AC motors for fixed speed applications
- DC motors for variable speed applications

After semiconductor devices were introduced

(1960s)

- Variable frequency sources available AC motors

in variable speed applications

- Coupling between flux and torque control
- Application limited to medium performance

applications fans, blowers, compressors

scalar control

- High performance applications dominated by DC

motors tractions, elevators, servos, etc

Modern Electrical Drive Systems

Overview of AC and DC drives

After vector control drives were introduced

(1980s)

- AC motors used in high performance applications

elevators, tractions, servos - AC motors favorable than DC motors however

control is complex hence expensive

- Cost of microprocessor/semiconductors decreasing

predicted 30 years ago AC motors would take over

DC motors

Modern Electrical Drive Systems

Overview of AC and DC drives

Extracted from Boldea Nasar

Power Electronic Converters in ED Systems

Converters for Motor Drives (some possible

configurations)

DC Drives

AC Drives

DC Source

AC Source

DC Source

AC Source

Power Electronic Converters in ED Systems

Converters for Motor Drives

Configurations of Power Electronic Converters

depend on

Sources available

Type of Motors

Drive Performance - applications

- Braking

- Response

- Ratings

Power Electronic Converters in ED Systems

DC DRIVES

Available AC source to control DC motor (brushed)

AC-DC-DC

AC-DC

Uncontrolled Rectifier Single-phase

Three-phase

DC-DC Switched mode 1-quadrant, 2-quadrant

4-quadrant

Controlled Rectifier Single-phase

Three-phase

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC

Vo ?

50Hz 1-phase

Average voltage over 10ms

50Hz 3-phase

Vo ?

Average voltage over 3.33 ms

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC

Vo ?

90o

180o

50Hz 1-phase

Average voltage over 10ms

50Hz 3-phase

Vo ?

90o

180o

Average voltage over 3.33 ms

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC

- Operation in quadrant 1 and 4 only

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC

Cascade control structure with armature reversal

(4-quadrant)

iD

w

Firing Circuit

iD,ref

Current Controller

wref

Speed controller

_

_

iD,ref

Armature reversal

iD,

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

control

Uncontrolled rectifier

Switch Mode DC-DC 1-Quadrant 2-Quadrant 4-Quadrant

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

control

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

DC-DC Two-quadrant Converter

Va

T1

D1

Vdc ?

ia

Q1

Q2

Ia

Va -

D2

T2

T1 conducts ?? va Vdc

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

DC-DC Two-quadrant Converter

Va

T1

D1

Vdc ?

ia

Q1

Q2

Ia

Va -

D2

T2

T1 conducts ?? va Vdc

D2 conducts ?? va 0

Quadrant 1 The average voltage is made larger

than the back emf

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

DC-DC Two-quadrant Converter

Va

T1

D1

Vdc ?

ia

Q1

Q2

Ia

Va -

D2

T2

D1 conducts ?? va Vdc

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

DC-DC Two-quadrant Converter

Va

T1

D1

Vdc ?

ia

Q1

Q2

Ia

Va -

D2

T2

T2 conducts ?? va 0

Quadrant 2 The average voltage is made smallerr

than the back emf, thus forcing the current to

flow in the reverse direction

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

DC-DC Two-quadrant Converter

vA -

vc

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

DC-DC Four-quadrant Converter

leg A

leg B

D3

D1

Vdc ?

Q1

Q3

Va ?

D4

D2

Q4

Q2

Positive current

va Vdc when Q1 and Q2 are ON

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

DC-DC Four-quadrant Converter

leg A

leg B

D3

D1

Vdc ?

Q1

Q3

Va ?

D4

D2

Q4

Q2

Positive current

va Vdc when Q1 and Q2 are ON

va -Vdc when D3 and D4 are ON

va 0 when current freewheels

through Q and D

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

DC-DC Four-quadrant Converter

leg A

leg B

D3

D1

Vdc ?

Q1

Q3

Va ?

D4

D2

Q4

Q2

Positive current

Negative current

va Vdc when Q1 and Q2 are ON

va Vdc when D1 and D2 are ON

va -Vdc when D3 and D4 are ON

va 0 when current freewheels

through Q and D

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

DC-DC Four-quadrant Converter

leg A

leg B

D3

D1

Vdc ?

Q1

Q3

Va ?

D4

D2

Q4

Q2

Positive current

Negative current

va Vdc when Q1 and Q2 are ON

va Vdc when D1 and D2 are ON

va -Vdc when D3 and D4 are ON

va -Vdc when Q3 and Q4 are ON

va 0 when current freewheels

through Q and D

va 0 when current freewheels

through Q and D

Power Electronic Converters in ED Systems

DC DRIVES

Bipolar switching scheme output swings between

VDC and -VDC

AC-DC-DC

Power Electronic Converters in ED Systems

DC DRIVES

Unipolar switching scheme output swings between

Vdc and -Vdc

AC-DC-DC

Vdc

vA -

vB -

vc

_

-vc

Power Electronic Converters in ED Systems

DC DRIVES

AC-DC-DC

DC-DC Four-quadrant Converter

Unipolar switching scheme

Bipolar switching scheme

- Current ripple in unipolar is smaller

- Output frequency in unipolar is effectively

doubled

Power Electronic Converters in ED Systems

AC DRIVES

AC-DC-AC

control

The common PWM technique

CB-SPWM with ZSS

SVPWM

Modeling and Control of Electrical Drives

- Control the torque, speed or position

- Cascade control structure

Modeling and Control of Electrical Drives

Current controlled converters in DC Drives -

Hysteresis-based

Vdc -

ia

Va ?

iref

ierr

q

_

q

- High bandwidth, simple implementation,

insensitive to parameter variations - Variable switching frequency depending on

operating conditions

ierr

Modeling and Control of Electrical Drives

Current controlled converters in AC Drives -

Hysteresis-based

ia

Converter

ib

ic

- For isolated neutral load, ia ib ic 0

?control is not totally independent

3-phase AC Motor

- Instantaneous error for isolated neutral load can

reach double the band

Modeling and Control of Electrical Drives

Current controlled converters in AC Drives -

Hysteresis-based

- For isolated neutral load, ia ib ic 0

?control is not totally independent

- Instantaneous error for isolated neutral load can

reach double the band

Modeling and Control of Electrical Drives

Current controlled converters in AC Drives -

Hysteresis-based

- Vdc 600V

- Dh 0.3 A

- Sinusoidal reference current, 30Hz

- 10W, 50mH load

Modeling and Control of Electrical Drives

Current controlled converters in AC Drives -

Hysteresis-based

Current error

Actual and reference currents

Modeling and Control of Electrical Drives

Current controlled converters in AC Drives -

Hysteresis-based

Current error

Actual current locus

0.6A

0.6A

0.6A

Modeling and Control of Electrical Drives

Current controlled converters in DC Drives -

PI-based

Modeling and Control of Electrical Drives

Current controlled converters in DC Drives -

PI-based

ia

Converter

ib

ic

- Sinusoidal PWM

Motor

- Interactions between phases ? only require 2

controllers - Tracking error

Modeling and Control of Electrical Drives

Current controlled converters in DC Drives -

PI-based

- Perform the 3-phase to 2-phase transformation
- - only two controllers (instead of 3) are

used

- Perform the control in synchronous frame
- - the current will appear as DC

- Interactions between phases ? only require 2

controllers - Tracking error

Modeling and Control of Electrical Drives

Current controlled converters in AC Drives -

PI-based

ia

Converter

ib

ic

Motor

Modeling and Control of Electrical Drives

Current controlled converters in AC Drives -

PI-based

ia

3-2

Converter

ib

ic

Motor

Modeling and Control of Electrical Drives

Current controlled converters in AC Drives -

PI-based

id

iq

Modeling and Control of Electrical Drives

Current controlled converters in AC Drives -

PI-based

Stationary - id

Stationary - ia

Rotating - ia

Rotating - id

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

Controlled rectifier

?

va(s)

vc(s)

DC motor

The relation between vc and va is determined by

the firing circuit

It is desirable to have a linear relation between

vc and va

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

Controlled rectifier

Cosine-wave crossing control

Vm

Input voltage

Cosine wave compared with vc

Results of comparison trigger SCRs

Output voltage

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

Controlled rectifier

Cosine-wave crossing control

Vscos(?t)

Vscos(?) vc

Vm

A linear relation between vc and Va

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

Controlled rectifier

Va is the average voltage over one period of the

waveform - sampled data system Delays

depending on when the control signal changes

normally taken as half of sampling period

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

Controlled rectifier

Va is the average voltage over one period of the

waveform - sampled data system Delays

depending on when the control signal changes

normally taken as half of sampling period

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

Controlled rectifier

Single phase, 50Hz

vc(s)

Va(s)

T10ms

Three phase, 50Hz

T3.33ms

Simplified if control bandwidth is reduced to

much lower than the sampling frequency

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

Controlled rectifier

Va

firing circuit

current controller

?

vc

iref

controlled rectifier

- To control the current current-controlled

converter - Torque can be controlled
- Only operates in Q1 and Q4 (single converter

topology)

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

Controlled rectifier

- Closed loop current control with PI controller

- Input 3-phase, 240V, 50Hz

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

Controlled rectifier

- Closed loop current control with PI controller

- Input 3-phase, 240V, 50Hz

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Vdc

Switching signals obtained by comparing control

signal with triangular wave

Va -

vtri

q

vc

We want to establish a relation between vc and Va

?

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

0.5

-Vtri

For vc -Vtri ? d 0

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

0.5

-Vtri

For vc -Vtri ? d 0

For vc 0 ? d 0.5

For vc Vtri ? d 1

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

0.5

-Vtri

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Thus relation between vc and Va is obtained as

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Taking Laplace Transform on the AC, the transfer

function is obtained as

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Bipolar switching scheme

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Bipolar switching scheme

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Unipolar switching scheme

The same average value weve seen for bipolar !

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Unipolar switching scheme

va(s)

vc(s)

DC motor

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

DC motor separately excited or permanent magnet

Extract the dc and ac components by introducing

small perturbations in Vt, ia, ea, Te, TL and ?m

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

DC motor separately excited or permanent magnet

Perform Laplace Transformation on ac components

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

DC motor separately excited or permanent magnet

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Closed-loop speed control an example

Design procedure in cascade control structure

- Inner loop (current or torque loop) the fastest

largest bandwidth

- The outer most loop (position loop) the slowest

smallest bandwidth

- Design starts from torque loop proceed towards

outer loops

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Closed-loop speed control an example

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Closed-loop speed control an example

- PI controllers

- Switching signals from comparison of vc and

triangular waveform

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Torque controller design Open-loop gain

compensated

compensated

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Speed controller design

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Speed controller design

Open-loop gain

compensated

compensated

Modeling and Control of Electrical Drives

Modeling of the Power Converters DC drives with

SM Converters

Large Signal Simulation results

Speed

Torque

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

INDUCTION MOTOR DRIVES

Scalar Control

Vector Control

Const. V/Hz

isf(wr)

FOC

DTC

Rotor Flux

Stator Flux

Circular Flux

Hexagon Flux

DTC SVM

Control of induction machine based on

steady-state model (per phase SS equivalent

circuit)

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Te

Pull out Torque (Tmax)

Trated

?r

?s

s

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Given a load T? characteristic, the steady-state

speed can be changed by altering the T? of the

motor

Variable voltage (amplitude), variable frequency

(Constant V/Hz) Using power electronics converter

Operated at low slip frequency

Pole changing Synchronous speed change with no.

of poles Discrete step change in speed

Variable voltage (amplitude), frequency

fixed E.g. using transformer or triac Slip

becomes high as voltage reduced low efficiency

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Variable voltage, fixed frequency

e.g. 3phase squirrel cage IM V 460 V Rs

0.25 ? Rr0.2 ? Lr Ls 0.5/(2pi50)

Lm30/(2pi50) f 50Hz p 4

Lower speed ? slip higher

Low efficiency at low speed

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Constant V/Hz

To maintain V/Hz constant

Approximates constant air-gap flux when Eag is

large

Eag k f ?ag

Speed is adjusted by varying f - maintaining

V/f constant to avoid flux saturation

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Constant V/Hz

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Constant V/Hz

f

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Constant V/Hz

Rectifier

VSI

3-phase supply

IM

C

f

Pulse Width Modulator

Ramp

V

?s

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Constant V/Hz

Simulink blocks for Constant V/Hz Control

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Constant V/Hz

Speed

Torque

Stator phase current

1

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Problems with open-loop constant V/f

At low speed, voltage drop across stator

impedance is significant compared to airgap

voltage - poor torque capability at low speed

Solution 1. Boost voltage at low speed 2.

Maintain Im constant constant ?ag

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

A low speed, flux falls below the rated value

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

With compensation (Is,ratedRs)

- Torque deteriorate at low frequency hence

compensation commonly performed at low frequency - In order to truly compensate need to measure

stator current seldom performed

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

With voltage boost at low frequency

2

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Problems with open-loop constant V/f

Solution 1. Compesate slip 2. Closed-loop

control

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Constant V/f open-loop with slip compensation

and voltage boost

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

A better solution maintain ?ag constant. How?

?ag, constant ? Eag/f , constant ? Im,

constant (rated)

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Constant air-gap flux

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Constant air-gap flux

- Current is controlled using current-controlled

VSI - Dependent on rotor parameters sensitive to

parameter variation

Modeling and Control of Electrical Drives

Modeling of the Power Converters IM drives

Constant air-gap flux

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