Chapter 6 Thyristor Converters Thyristor circuits and their

Chapter 6 Thyristor Converters • Thyristor circuits and their control • Line-frequency phase-controlled rectifiers and inverters • line-frequency ac <-> controlled dc 6 -1

Thyristor Converters • Two-quadrant conversion • positive Vd implies rectification • negative Vd implies inverter mode 6 -2

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 6 -3

Primitive circuits with thyristors (2) R L load • The current is zero until t= • The current lags voltage vd • At Instant 2 current becomes zero 6 -4

Primitive circuits with thyristors (3) L Load with dc voltage 6 -5

Thyristor Gate Triggering Delay angle is 6 -6

Full-Bridge Thyristor Converters (1) 6 -7

Full-Bridge Thyristor Converters (2) • constant dc current load 6 -8

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 -9

Thyristor Converter Waveforms (2) 6 -10

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 -11

Inverter mode • 90º < < 180º • average vd is a negative value 6 -12

Average DC Output Voltage • Assuming zero ac-side inductance 6 -13

Input Line-Current Waveform • input line current is harmonics 6 -14

THD, Power Factor, Power • THD • Power Factor PF 6 -15

Effect of Ls • Finite ac-side inductance; constant dc output current 6 -16

Finite ac-side inductance (1) • finite comutation interval u • during u all thyristors conduct (vd=0) 6 -17

Finite ac-side inductance (2) 6 -18

Input line current is • Is has a trapezoidal waveform • DPF is • The RMS value of fundamental frequency is 6 -19

Practical Thyristor Converter • waveform for =45º • average value of vd 6 -20

Thyristor Converter Waveforms: Discontinuous Conduction Mode • PSpice-based simulation 6 -21

DC Voltage versus Load Current • at constant , if Id falls below a certain value, Vd increases sharply 6 -22

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 Is 1 RMS cos 1 is negative 6 -23