Characteristic analysis of PWM pattern for three-phase ZVS inverter

Recently, more attention is paid to ZVS PWM inverter. Its basic idea is to use ZVS circuit which makes the main circuit of inverter resonate at every beginning of carrier period, so each power devices can be commutate when the voltage of main circuit´s DC bus line is zero. To ensure the resonant circuit operates properly, sawtooth with alternate slope (positive or negative) is proposed as carrier. But the action time of zero voltage vectors with such PWM pattern has great difference to that of traditional hard-switching PWM pattern. This paper discusses the locus of flux linkage under soft-switching PWM pattern by using space voltage vector in detail. It points out that under the hard-switching PWM pattern, the movement speed of flux linkage is adjusted by zero space voltage vector, but when soft-switching PWM pattern is used, effect time of space voltage vector vary greatly, sometimes even no zero space voltage vector exist. So non-zero space voltage vector has been used to make the speed of flux linkage locus equals to that of hard-switching PWM pattern. The reason of soft-switching PWM inverter´s current distortion has also been discussed, according to flux linkage locus circle, corresponding compensation methods are put forward. Experiment results prove such method can effectively improve output current waveform of inverter.