AC Motor Control and EV Applications

Pulse-Width Modulation andInverter

Chapter 10

Switching Turn-on / off Losses

On loss Conduction loss Off loss

VCE

IL

VCE

IL On

Off

t

t

(a) (b)

Pole and Line-to-line Voltages

Line to linevoltages

Polevoltages

Q3

Q2

Q4

Q6

Q5

Q6

Q2

Q1Q1

Q3

Phase Voltages

Motorphase

voltages

vas

t

vbs

t

vcs

t

vsn

t

2Vdc /3Vdc /3

2Vdc /3Vdc /3

2Vdc /3 Vdc /3

Vdc / 6

-Vdc / 6

Six Step Operation

Sinusoidal PWM

Vdc /2

-Vdc/2

Van

Sa 1

0

Vdc/2

-Vdc/2

Van

+ -comparator

Addition of 3rd Order Harmonics

3rd order harmonics lowers the peak of the fundamental component.

Addition of 3rd order harmonicsprovide a room to increase the fundamental component.

Overmodulation

Over modulation area

360

180

Overmodulatedwave form

Space Vector PWM

V1 (1,0,0) V2 (1,1,0) V3 (0,1,0) V4 (0,1,1) V5 (0,0,1) V6 (1,0,1)

q

asds

bs

cs

V1(1,0,0)

V2(1,1,0)V3(0,1,0)

V4(0,1,1)

V5(0,0,1) V6(1,0,1)

Sector 1

Sector 2

Sector 3

Sector 4

Sector 5

Sector 6

V0(0,0,0)

V7(1,1,1) 2/3Vdc

s

SVPWM

Overmodulationregion

Small voltage

Max.voltage

Space Vector PWM (sector 1)

Sector 1

V2(1,1,0)

V1(1,0,0)

Va

V0(0,0,0) Va1

Va2

Space Vector PWM

1 1 1 1 1 1 00

1 1 1 10 0 0 0

1 10 0 0 0 0 0

Ts

Sector 1

0 1 1 1 1 0 00

1 1 1 10 1 1 0

1 10 0 0 0 0 0

T2

Sa

Sector 2

V0 V3 V2 V7

T1

Sb

Sc

Sa

Sb

Sc

V0 V1 V2 V7

T1 T2

Ts

0 0 1 1 0 0 00

1 1 1 10 1 1 0

1 10 0 1 1 0 0

Ts

Sector 3

Sa

Sb

Sc

V0 V3 V4 V7

T1 T2

Space Vector PWM

0 0 1 1 0 0 00

1 1 1 10 0 0 0

1 10 1 1 1 1 0

T2

Sa

Sector 4

V0 V5 V4 V7

T1

Sb

Sc

Ts

0 1 1 1 1 0 00

0 1 1 00 0 0 0

1 10 1 1 1 1 0

Ts

Sector 5

1 1 1 1 1 1 00

0 1 1 00 0 0 0

1 10 0 1 1 0 0

T2

Sa

Sector 6

V0 V1 V6 V7

T1

Sb

Sc

Sa

Sb

Sc

V0 V5 V6 V7

T1 T2

Ts

SVPWM

Sector Finding Method

START

Y

N

YSector 2

N

YSector 1

N

Sector 3

YSector 5

N

Y

Sector 6

N

Sector 4

Sector 1

Sector 2

Sector 3

Sector 5

Sector 4 Sector 6

Overmodulation

Overmodulationregion

SPWM versus SVPWM

SPWM

SVPWM– Voltage Usage : 15.5% increase– No of switching decreases.

Current Sampling

1 1 1 1 1 1 00 11 1 1 1 100

(a) Symmetric (b) Asymmetric

currentaveragecurrent

currentsampling

averagecurrent

current

currentsampling

Vdc /2

-Vdc /2

0

Sa

Sa ’

0-Vdc

(b) Ias <0

Vdc /2

0

Sa

Sa ’

0

(a) Ias >0

Vdc

Gate signalwith

dead time

Terminalvoltage

Dead timevoltageerror

Gate signalwith

dead time

Terminalvoltage

Dead timevoltageerror

i

i

Original PWM

Original PWM

Dead Time Effects Depending on Current Direction

Dead Time Effects on Current

Zero Current Clamping

(a)

Distortedvoltageby dead time

current

(b)

Distortedvoltageby dead time

current

(b) Ias <0(a) Ias >0

Sa

Sa ’

With dead timecompensation

Original PWM

Original PWM

Gate signalafter providingdead time

Sa

Sa ’

With dead timecompensation

Gate signalafter providingdead time

Dead Time Compensation

LED

Encoder

Photo TR

ABZ

Slit

Disk

1 2 3 4 1 2 3 4

Encodersignal

Referencepulses

(a) (b)

Speed

Mea

sure

men

t erro

r

M-method T-method

Frequency

M/T Method

1-Input, 2-Output Resolver

Rotating coilStationary coil

+

+

Flux linkageRotary transformer

Output 1

Output 2Input

Resolver Signal Processing

LPF PI V/Fconverter

demodulator

Pulsecounter

to processor

+

-

PI+

-

Current Sensors

+-

+

-

(a) Voltage type (b) Current type

PI

Rotating coil

Stationary coil

AC sourcefor rotor excitation

+

+

Flux linkage

Rotary transformer

Input 1

Input 2

Output