E第7章软开关技术

1、Disadvantages of higher switching frequencyDisadvantagesHigher 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 radiatedSolutionSoft-switching techniquesOutline7.1

2、Basic concepts on soft-switching7.2 Classification of soft-switching techniques7.3 Typical soft-switching circuits and techniques7.1 Basic concepts on soft-switchingHard-switchingThe process of power semiconductor devicehard-switchingThe concept of soft-switchingSoft-switchingThe process of power se

3、miconductor devicesoft-switchingTwo types of soft-switchingZVSZero-voltage switchingSpecifically means zero-voltage turn-on, i.e., the voltage across the device is reduced to zero before the current increasesZCSZero-current switchingSpecifically means zero-current turn-off, i.e., the current flowing

4、 through the device is reduced to zero before the voltage increases7.2 Classification of soft-switchingtechniquesQuasi-resonant soft-switchingZVS 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)Th

5、e concept of basic switch cellQuasi-Resonant ConverterQRCZVS QRCZCS QRCZVS MRC (multi-resonant converter)Resonant DC link converterBasic switching cells for QRCZVS PWM converter and ZCS PWM converterFeature: use of auxiliary switchBasic switching cells for a) ZVS PWM and b) ZCS PWMZVT PWM converter

6、and ZCT PWM converterFeature: auxiliary switch is in parallel with main switchBasic switching cells for a) ZVT PWM and b) ZCT PWM7.3 Typical soft-switching circuitsand techniquesZVS QRCResonant DC link converterPhase-shift full bridge ZVS PWM converterZVT PWM converterZVS QRCResonant DC link convert

7、erSummary of QRCDisadvantages Voltage stress increased due to the resonant peak Current RMS value increased due to largecirculating energy Variable switching frequency due to pulse-frequency modulation (PFM) controlPhase-shift full-bridge ZVS PWM converterPhase-shift full-bridge ZVS PWM converterSum

8、mary of ZVS or ZCS PWM converterImprovement over QRC Voltage and current are basically square-wave, therefore stresses are greatly reduced Constant switching frequency due to pulse-width modulation (PWM) controlZVT PWM converterSummary of ZVT or ZCT PWM converterImprovement over ZVS or ZCS PWM converter Soft-switching can be achie