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1、,Power Electronics,Chapter 8 Soft-Switching Techniques,Pursuing of higher switching frequency,Benefits,Better waveform PWM waveform will be closer to expected waveform Harmonics is easier to be filtered,Faster response,Smaller volume and weight 4.44fNf =4.44fNAB,Disadvantages of higher switching fre
2、quency,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-switchin
3、g 8.2 Classification of soft-switching techniques 8.3 Typical soft-switching circuits and techniques,8.1 Basic concepts on soft-switching,Hard-switching,a) Turning-on,b) Turning-off,The process of power semiconductor device hard-switching,The concept of soft-switching,Soft-switching,a) Turning-on,b)
4、 Turning-off,The process of power semiconductor device soft-switching,Two types of soft-switching,ZVSZero-voltage switching Specifically means zero-voltage turn-on, i.e., the voltage across the device is reduced to zero before the current increases ZCSZero-current switching Specifically means zero-c
5、urrent 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 P
6、WM) and ZCT PWM (zero-current-transition PWM),The concept of basic switch cell,Quasi-Resonant ConverterQRC,ZVS QRC ZCS QRC ZVS MRC (multi-resonant converter) Resonant DC link converter,Basic switching cells for QRC,ZVS PWM converter and ZCS PWM converter,Feature: use of auxiliary switch,Basic switch
7、ing cells for a) ZVS PWM and b) ZCS PWM,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,8.3 Typical soft-switching circuits and techniques,ZVS QRC Resonant DC link converter Phase-shift full bridge
8、ZVS PWM converter ZVT PWM converter,ZVS QRC,to t1 t1 t2,Resonant DC link converter,Circuit,Equivalent circuit to RDCL,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-f
9、requency modulation (PFM) control,Phase-shift full-bridge ZVS PWM converter,Circuit,Phase-shift full-bridge ZVS PWM converter,Equivalent circuit during t1 t2,Equivalent circuit during t3 t4,Summary of ZVS or ZCS PWM converter,Improvement over QRC Voltage and current are basically square-wave, theref
10、ore stresses are greatly reduced Constant switching frequency due to pulse-width modulation (PWM) control,ZVT PWM converter,Circuit,Equivalent circuit during t1 t2,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,
