Thyristor Converters

EE 442-642

6-1 Thyristor Converters

• Two-quadrant conversion

6-2 Simple half-wave circuits with thyristors

6-3 Thyristor Triggering

v  o 180o control ˆ Vst

• ICs available 6-4 Case of Pure Resistive Load

6-5 Full-Bridge Thyristor Converters – Constant DC Current

6-6 DC-Side Voltage

Average DC voltage: Vd  Vdo cos where Vdo  0.9Vs

6-7 AC-Side Current

P Vd Id  0.9Vs Id cos

RSM value of source current I s  Id

RMS value of fundamental current I s1  (2 2 / )Id  0.9Id

RMS value of harmonic current I sh  I s1 / h, h  3,5,7,... Current THD THD 100 ( 2 /8) 1  48.43% Displacement Power Factor DPF  cos Power Factor PF  0.9cos

6-8 Effect of Source Inductance

2L I Commutation angle: cos(  )  cos  s d 2Vs

2Ls Id Average of DC-side voltage: Vd  0.9Vs cos   Displacement Power Factor DPF  cos(  0.5) 2 Vd Id 0.9Vs Id cos  (2 / )Ls Id RMS fundamental current I s1   Vs DPF Vs cos(  0.5) 6-9 Thyristor Converter with DC Source

Continuous current conduction mode

Discontinuous current conduction mode 6-10 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%

6-11 DC Voltage versus Load Current

6-12 Inverter Mode (α > 90o)

6-13 Inverter Mode with DC Voltage Source

• For a large value of Ld, id can be assumed constant (= Id), then 2 Ed Vd  0.9Vs cos  LS Id  6-14 Inverter Mode: Extinction Angle

 180o (  ) Importance of extinction angle in inverter mode: The extinction time interval should be greater than the thyristor turn-off time:  t   t   q 6-15 3-Phase Thyristor Converters: Simplified Case

6-16 DC-side voltage waveforms assuming zero ac-side inductance

Vd  Vdo cos 3  2V cos  LL

1.35VLL cos

6-17 Input Line-Current Waveform

6-18 Input line-current waveforms assuming zero ac-side inductance

I s  2 / 3Id  0.816Id

I s1  ( 6 / )Id  0.78Id

I sh  I s1 / h, h  3,5,7,... THD 100[ ( 2 / 9) 1]  31% DPF  cos 3 PF  cos  0.955cos 

6-19 3-Phase Thyristor Converter with AC-side Inductance

2L I cos(  )  cos  s d 2VLL 3L I V 1.35V cos  s d d LL  DPF  cos(  0.5)

6-20 Input Line-Current Harmonics

6-21 Input Line-Current Harmonics

Typical Passive Filter Block (for each phase)

6-22 12-Pluse Phase Controlled Rectifier

Harmonic Order: 1, 11, 13, 23, 25, …

6-23 3-Phase Thyristor Converter with Realistic Load

Continuous conduction Mode

Discontinuous conduction mode

6-24 3-Phase Thyristor Inverter – Constant Current

6-25 Thyristor Inverter – Constant Voltage & Current

6-26 Thyristor Inverter Operation: Extinction Angle

6-27 Thyristor Converters: Voltage Notching

Depth: Vn  2VLL sin

Ls1  Ls

Ls2  0 Area: An  2Ls Id

2Ls Id Width:   2VLL sin

6-28 Limits on Notching and Distortion

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

L   s1

Ls1  Ls2

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

6-29