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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. Thyristor Converters. Two-quadrant conversion positive V d implies rectification negative V d implies inverter mode.

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Chapter 6 Thyristor Converters

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

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

  3. 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  Chapter 6 Thyristor Converters

  4. 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 Chapter 6 Thyristor Converters

  5. Primitive circuits with thyristors (3) L Load with dc voltage Chapter 6 Thyristor Converters

  6. Thyristor Gate Triggering Delay angle  is Chapter 6 Thyristor Converters

  7. Full-Bridge Thyristor Converters (1) Chapter 6 Thyristor Converters

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

  9. Thyristor Converter Waveforms (1) • Assuming zero ac-side inductance • at t=0 thyristors 1,2 are triggered • At t=  thyristors 3,4 are triggered Chapter 6 Thyristor Converters

  10. Thyristor Converter Waveforms (2) Chapter 6 Thyristor Converters

  11. 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 Chapter 6 Thyristor Converters

  12. Inverter mode • 90º <  < 180º • average vd is a negative value Chapter 6 Thyristor Converters

  13. Average DC Output Voltage • Assuming zero ac-side inductance Chapter 6 Thyristor Converters

  14. Input Line-Current Waveform • input line current is harmonics Chapter 6 Thyristor Converters

  15. THD, Power Factor, Power • THD • Power • Power Factor PF Chapter 6 Thyristor Converters

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

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

  18. Finite ac-side inductance (2) Chapter 6 Thyristor Converters

  19. Input line current is • Is has a trapezoidal waveform • DPF is • The RMS value of fundamental frequency is Chapter 6 Thyristor Converters

  20. Practical Thyristor Converter • waveform for =45º • average value of vd Chapter 6 Thyristor Converters

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

  22. DC Voltage versus Load Current • at constant , if Id falls below a certain value, Vd increases sharply Chapter 6 Thyristor Converters

  23. 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 Chapter 6 Thyristor Converters

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