电力电子技术第5版 教学课件 作者 王兆安 chapter08.pptVIP

Pursuing of higher switching frequency 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 Outline 8.1 Basic concepts on soft-switching 8.2 Classification of soft-switching techniques 8.3 Typical soft-switching circuits and techniques 8.1 Basic concepts on soft-switching The concept of soft-switching 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 8.2 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) The concept of basic switch cell Quasi-Resonant Converter—QRC ZVS QRC ZCS QRC ZVS MRC (multi-resonant converter) Resonant DC link converter ZVS PWM converter and ZCS PWM converter Feature: use of auxiliary switch ZVT PWM converter and ZCT PWM converter Feature: auxiliary switch is in parallel with main switch 8.3 Typical soft-switching circuits  and techniques ZVS QRC Resonant DC link converter Phase-shift full bridge ZVS PWM converter ZVT PWM converter ZVS QRC to ~ t1 t1 ~ t2 Resonant DC link converter 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 Phase-shift full-bridge ZVS PWM converter Circuit Phase-shift full-bridge ZVS PWM converter Eq