Hybrid transformer ZVS/ZCS DC-DC converter for photovoltaic microinverters

This paper presents a high boost ratio dc-dc converter with hybrid transformer for non-isolated photovoltaic (PV) microinverters. The proposed converter incorporates the resonant operation mode into the traditional high boost ratio active-clamp coupled-inductor PWM converter, achieving ZVS turn-on of the switches and ZCS turn-off of the diodes. As a result of the inductive and capacitive energy being transferred simultaneously within both turn-on and turn-off intervals of the main switch, the dc bias of the magnetizing current is reduced and hence the size of magnetics can be reduced. The magnetizing inductance is designed with a small value to utilize ripple magnetizing current to assist ZVS of main switch, while maintaining low RMS conduction losses. The voltage stresses on the active switches and diodes are maintained at a low level and are independent of the wide changing input PV voltages as a result of the resonant capacitor in series in the energy transfer loop. The experimental results based on 250 W prototype circuit show system CEC efficiencies greater than 96.7% over 20 V to 45 V PV voltage range.