6-1 copyright © 2008 by jose bastos chapter 6 thyristor converters chapter 6 thyristor converters...

Copyright © 2008 by Jose Bastos

Chapter 6 Thyristor Converters 6-1

Chapter 6

Thyristor Converters

• Thyristor circuits and their control• Line-frequency phase-controlled rectifiers and inverters• line-frequency ac <-> controlled dc



Thyristor Converters

• Two-quadrant conversion

• positive Vd implies rectification

• negative Vd implies inverter mode



Primitive circuits with thyristors (1)

R load

• The current is zero until t=• The current and voltage vd are in phase• Average voltage of load R controlled by adjusting

)cos1(2

sin2

1

V

dxxVvd




• The current is zero until t=• The current lags voltage vd

• At Instant 2 current becomes zero

R L load

0)()(1

)()(1

)(

)()(1

)(

2

1

1

2

dvvL

dvvL

i

dvvL

ti

vvdt

diLv

RdRd

t

Rd

RdL

Rv




L Load with dc voltage

dEvti

Evdt

diLv

t

dd

ddL

2

)()(



Thyristor Gate Triggering

st

controlo

V

vˆ

180

Delay angle is



Full-Bridge Thyristor Converters (1)



• constant dc current load

Full-Bridge Thyristor Converters (2)



Thyristor Converter Waveforms (1)

• Assuming zero ac-side inductance

• at t=0 thyristors 1,2 are triggered

•At t= thyristors 3,4 are triggered

RMSRMSd VVV

tdtVv 9.0222

)()sin(1

0

0




cos9.0cos

22cos

2)()sin(

1RMSRMSd VV

VtdtVv

0




• The average power in the converter is

• Average power becomes negative when > 90º ; this is inverter mode of operation

cos9.01

1

0

0

RMSddd

T

dd

T

dd

VIvIdtvT

I

dtivT

P



Inverter mode

• 90º < < 180º• average vd is a negative value• on dc side average power <vd>Id is negative• on ac side average power VS RMS Is1 RMS cos 1 is negative

º90



Average DC Output Voltage

• Assuming zero ac-side inductance



Input Line-Current Waveform

• input line current is harmonics

h

IIIII

tItItIti

sshdds

ssss

11

531

9.022

with

)5(sin)3(sin)(sin)(



Power, Power Factor

• Power

• Power Factor PF

cos9.0cos1

_

_1

__

s

s

RMSs

RMSs

RMSsRMSs I

IDPF

I

I

IV

PPF

cos9.0cos __1_ dRMSsRMSsRMSs IVIVP



Effect of Ls

• Finite ac-side inductance; constant dc output current



Finite ac-side inductance (1)

• finite comutation interval u• during u all thyristors conduct (vd=0)



Finite ac-side inductance (2)

dRMSdRMS

d

u

d

d

d

du

d

u

u

d

I

I

s

u

sLsd

ILVILV

ILV

tdtVtdtVv

vV

ILu

ILuVA

ILtdtVA

ILdiLtdtV

dt

diLvvv

d

d

2cos9.0

2cos22

2cos

2

)()sin()()(sin1

by obtained becan

2)cos()cos(

2)cos()cos(

2)()sin(

2)()sin(

:interval comutation over the integrate u, find to

0



Input line current is

• Is has a trapezoidal waveform• DPF is

• The RMS value of fundamental frequency is

)2/cos(cos 1 uDPF

)2/cos(

/2cos9.0 2

1

1

uV

ILIVI

IvDPFIV

RMSs

ddRMSsRMSs

ddRMSsRMSs



• waveform for =45º

• average value of vd

Practical Thyristor Converter

min,

2cos9.0 dRMSsd ILVv



Inverter mode with finite AC inductance

• 90º < < 180º

6-1 copyright © 2008 by jose bastos chapter 6 thyristor converters chapter 6 thyristor converters...

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