Three Legged High-gain Phase-modulated DC-AC Converter for Mitigation of Device Capacitance Induced Ringing Voltage

In this paper, a method is proposed to eliminate the voltage ringing problem in a phase-modulated dc–ac converter, also known as a micro-inverter. The basic idea is to apply a time-critical two-stepped voltage waveform to the input of the converter bridge connected to the filter inductor. This method is implemented by a new topology that has one more switching leg added to the full bridge voltage fed converter. It produces a second voltage level and adds it to the first by using a transformer. The advantages of the proposed method are as follows. It almost eliminates the requirement of a voltage clamp, there is no circulating current in the freewheeling state, and the secondary side devices have less voltage and current stress compared to a conventional phase-modulated converter. The overall benefit is an improvement in converter efficiency even for a high-voltage conversion ratio application. The proposed topology operates with a secondary side modulation scheme that achieves zero-voltage switching of four devices on the primary side and either zero-voltage switching or zero-current switching of all the devices on the secondary side, over the entire line cycle of the ac output. Finally, the experimental results verify the proposed method.