6-1 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Chapter 6 Thyristor Converters Thyristor circuits and their control Line-frequency phase-controlled rectifiers and inverters line-frequency ac controlled dc

6-2 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Thyristor Converters Two-quadrant conversion positive V d implies rectification negative V d implies inverter mode

6-3 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Primitive circuits with thyristors (1) R load The current is zero until  t=  The current and voltage v d are in phase Average voltage of load R controlled by adjusting 

6-4 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Primitive circuits with thyristors (2) The current is zero until  t=  The current lags voltage v d At Instant  2 current becomes zero R L load

6-5 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Primitive circuits with thyristors (3) L Load with dc voltage

6-6 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Thyristor Gate Triggering Delay angle  is

6-7 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Full-Bridge Thyristor Converters (1)

6-8 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters constant dc current load Full-Bridge Thyristor Converters (2)

6-9 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Thyristor Converter Waveforms (1) Assuming zero ac-side inductance at  t=0 thyristors 1,2 are triggered At  t=  thyristors 3,4 are triggered

6-10 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Thyristor Converter Waveforms (2)

6-11 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Thyristor Converter Waveforms (3) The drop in the average value due to  is The average power in the converter is Average power becomes negative when  > 90º ; this is inverter mode of operation

6-12 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Inverter mode 90º <  < 180º average v d is a negative value

6-13 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Average DC Output Voltage Assuming zero ac-side inductance

6-14 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Input Line-Current Waveform input line current i s harmonics

6-15 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters THD, Power Factor, Power THD Power Power Factor PF

6-16 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Effect of L s Finite ac-side inductance; constant dc output current

6-17 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Finite ac-side inductance (1) finite comutation interval u during u all thyristors conduct (v d =0)

6-18 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Finite ac-side inductance (2)

6-19 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Input line current i s I s has a trapezoidal waveform DPF is The RMS value of fundamental frequency is

6-20 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters waveform for  =45º average value of v d Practical Thyristor Converter

6-21 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Thyristor Converter Waveforms: Discontinuous Conduction Mode PSpice-based simulation

6-22 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters DC Voltage versus Load Current at constant , if I d falls below a certain value, V d increases sharply

6-23 Copyright © 2008 by Jose Bastos Chapter 6 Thyristor Converters Inverter mode 90º <  < 180º average v d is a negative value on dc side average power I d is negative on ac side average power V S RMS I s1 RMS cos  1 is negative