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Power Electronics

Power Electronics. Chapter 8 Soft-Switching Techniques. Pursuing of higher switching frequency. Better waveform PWM waveform will be closer to expected waveform Harmonics is easier to be filtered. Benefits. Smaller volume and weight 4.44 fN f =4.44 fNAB.

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Power Electronics

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  1. PowerElectronics Chapter 8 Soft-Switching Techniques

  2. Pursuing of higher switching frequency • Better waveform • PWM waveform will be closer to expected waveform • Harmonics is easier to be filtered Benefits • Smaller volume and weight • 4.44fNf =4.44fNAB Faster response

  3. Disadvantages of higher switching frequency Disadvantages • Higher power losses on power semiconductor devices • Power loss=f x Energy loss at each switching • More severe electromagnetic interference (EMI) • Steeper edges introduce more noises • Easier to be radiated Solution • Soft-switching techniques

  4. Outline 8.1 Basic concepts on soft-switching 8.2 Classification of soft-switching techniques 8.3 Typical soft-switching circuits and techniques

  5. 8.1 Basic concepts on soft-switching Hard-switching b) Turning-off a) Turning-on The process of power semiconductor device hard-switching

  6. The concept of soft-switching Soft-switching b) Turning-off a) Turning-on The process of power semiconductor device soft-switching

  7. Two types of soft-switching ZVS—Zero-voltage switching • Specifically means zero-voltage turn-on, i.e., the voltage across the device is reduced to zero before the current increases ZCS—Zero-current switching • Specifically means zero-current turn-off, i.e., the current flowing through the device is reduced to zero before the voltage increases

  8. 8.2 Classification of soft-switching techniques • Quasi-resonant soft-switching • ZVS PWM (zero-voltage-switching PWM) and ZCS PWM (zero-current-switching PWM) • ZVT PWM (zero-voltage-transition PWM) and ZCT PWM (zero-current-transition PWM)

  9. The concept of basic switch cell

  10. Quasi-Resonant Converter—QRC • ZVS QRC • ZCS QRC • ZVS MRC (multi-resonant converter) • Resonant DC link converter Basic switching cells for QRC

  11. ZVS PWM converter and ZCS PWM converter Feature: use of auxiliary switch Basic switching cells for a) ZVS PWM and b) ZCS PWM

  12. ZVT PWM converter and ZCT PWM converter Feature: auxiliary switch is in parallel with main switch Basic switching cells for a) ZVT PWM and b) ZCT PWM

  13. 8.3 Typical soft-switching circuits and techniques • ZVS QRC • Resonant DC link converter • Phase-shift full bridge ZVS PWM converter • ZVT PWM converter

  14. to ~ t1 t1 ~ t2 S t O u ( u ) S C r t O i S t O i L r t O u VD t O t t t t t t t t 0 1 2 3 4 6 5 0 ZVS QRC

  15. Resonant DC link converter Circuit Equivalent circuit to RDCL

  16. Summary of QRC • Disadvantages • Voltage stress increased due to the resonant peak • Current RMS value increased due to large circulating energy • Variable switching frequency due to pulse-frequency modulation (PFM) control

  17. Circuit Phase-shift full-bridge ZVS PWM converter

  18. Equivalent circuit during t1 ~ t2 Equivalent circuit during t3 ~ t4 Phase-shift full-bridge ZVS PWM converter

  19. Summary of ZVS or ZCS PWM converter • Improvement over QRC • Voltage and current are basically square-wave, therefore stresses are greatly reduced • Constant switching frequency due to pulse-width modulation (PWM) control

  20. Circuit ZVT PWM converter Equivalent circuit during t1 ~ t2

  21. Summary of ZVT or ZCT PWM converter • Improvement over ZVS or ZCS PWM converter • Soft-switching can be achieved in a wider range of input voltage and load current • Circulating energy is reduced to minimum so that efficiency is increased

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