6-1

Thyristor Converters

EE 442-642

6-2

Thyristor Converters

• Two-quadrant conversion

6-3

Simple half-wave circuits with thyristors

6-4

Thyristor Triggering

• ICs available

st

controloo

V

v

ˆ180

6-5

Case of Pure Resistive Load

6-6

Full-Bridge Thyristor Converters – Constant DC Current

6-7

DC-Side Voltage

sdo

dod

VV

VV

9.0

cos

Average DC voltage:

where

6-8

AC-Side Current

cos9.0 dsdd IVIVP

cos9.0

cos

%43.481)8/(100

,...7,5,3,/

9.0)/22(

2

1

1

PF

DPF

THD

hhII

III

II

ssh

dds

dsRSM value of source current

RMS value of fundamental current

RMS value of harmonic current

Current THD

Displacement Power Factor

Power Factor

6-9

Effect of Source Inductance

)5.0cos(

)/2(cos9.0

)5.0cos(

2cos9.0

2

2cos)cos(

2

1

s

dsds

s

dds

dssd

s

ds

V

ILIV

DPFV

IVI

DPF

ILVV

V

ILCommutation angle:

Average of DC-side voltage:

Displacement Power Factor

RMS fundamental current

6-10

Thyristor Converter with DC Source

Continuous current conduction mode

Discontinuous current conduction mode

6-11

AC-Side Current Waveform (continuous conduction mode)

PSpice-based simulation example: Vs = 240 V, f = 60 Hz,

Ls = 1.4 mH, α = 45 deg., Ld = 9 mH, Ed = 145 V.

Solution: Is = 60.1 A, Is1 = 59.7 A, DPF = 0.576, PF =

0.572, THD = 12.3%

6-12

DC Voltage versus Load Current

6-13

Inverter Mode (α > 90o)

6-14

Inverter Mode with DC Voltage Source

• For a large value of Ld, id can be assumed constant (= Id), then

dSsdd ILVVE

2

cos9.0

6-15

Inverter Mode: Extinction Angle

Importance of extinction angle in inverter mode: The extinction time

interval should be greater than the thyristor turn-off time:

)(180 o

qtt

6-16

3-Phase Thyristor Converters: Simplified Case

6-17

DC-side voltage waveforms

assuming zero ac-side inductance

cos35.1

cos23

cos

LL

LL

dod

V

V

VV

6-18

Input Line-Current Waveform

6-19

Input line-current waveforms assuming zero ac-side inductance

cos955.0cos3

cos

%31]1)9/([100

,...7,5,3,/

78.0)/6(

816.03/2

2

1

1

PF

DPF

THD

hhII

III

III

ssh

dds

dds

6-20

3-Phase Thyristor Converter with AC-side Inductance

)5.0cos(

3cos35.1

2

2cos)cos(

DPF

ILVV

V

IL

dsLLd

LL

ds

6-21

Input Line-Current Harmonics

6-22

Input Line-Current Harmonics

Typical Passive Filter Block (for each phase)

6-23

12-Pluse Phase Controlled Rectifier

Harmonic Order: 1, 11, 13, 23, 25, …

6-24

3-Phase Thyristor Converter with Realistic Load

Continuous conduction

Mode

Discontinuous conduction

mode

6-25

3-Phase Thyristor Inverter – Constant Current

6-26

Thyristor Inverter – Constant Voltage & Current

6-27

Thyristor Inverter Operation: Extinction Angle

6-28

Thyristor Converters: Voltage Notching

sin2

2

LL

ds

V

IL

02

1

s

ss

L

LL

dsn ILA 2

sin2 LLn VV Depth:

Area:

Width:

6-29

Limits on Notching and Distortion

In practice, the notch depth at PCC depends on Ls1 relative to Ls2. Let depth

factor be defined by

Given Ls1 , a higher value of Ls2 results in a smaller notch.

21

1

ss

s

LL

L