Research On Soft Switching Modulation Method For Three-Phase Four-Wire Inverter

The traditional hard switching Three-Phase Four,Wire inverter uses sinusoidal pulse width modulation(SPWM)method,the switching frequency is mainly limited by the dynamic loss of power devices,resulting in a larger volume of the output filter element,ultimately limits the miniaturization of the inverter.Soft switching technology is an effective way to solve this problem.Compared to other soft switching inverters,The Zero-Voltage-Switching pulse width modulation(ZVS-PWM)inverter has the advantages of simple structure,small switching voltage stress,etc.In this paper,ZVS-PWM is introduced into Three-Phase Four-Wire inverter,with an added auxiliary switch and two small passive components,the ZVS of all the switches under unbalanced load can be achieved.This paper introduces the ZVS-PWM method for Three-Phase Four-Wire inverter,On the basis of analyzing the working process of the circuit,the ZVS condition is deduced,according to the ZVS condition,the theoretical values of auxiliary switch off duty ratio and resonant inductance current.etc.are calculated,and the method of designing resonent circuit parameters is given.The ZVS condition of ZVS-PWM Three-Phase Four-Wire inverter is related to the resonant capacitor,which contains of the output capacitor of the switching device.The output capacitor of the wide band gap device SiC MOSFET is nonlinear,and its capacitor will change with the Drain-to-Source voltage.Because the Drain-to-Source voltage of SiC MOSFET changes in the resonant process between zero and the maximum value,so that the resonant capacitor also change with the the Drain-to-Source voltage,causing error of theoretical analysis.In this paper the influence of output capacitor of power device on ZVS realization is analyzed,and a method of extracting the equivalent output capacitor is discussed,so the calculated value of ZVS condition can be corrected.Finally,the proposed ZVS-PWM method and the equivalent output capacitor extracting method is verified on a 10 kW SiC MOSFET ZVS-PWM Three-Phase Four-Wire inverter.