Series resonant type soft-switching grid-connected single-phase inverter employing discontinuous-resonant control applied to photovoltaic AC module

This paper presents a high-frequency transformer link single-phase inverter system using a series resonant softswitching scheme applied to photovoltaic AC modules. The proposed high-frequency transformer link inverter circuit consists of a full-bridge inverter, a series resonant circuit, an isolation transformer with center tap winding in secondary side and low-frequency distribution switches synchronized with a grid voltage. An AC output current is controlled by the discontinuous-resonant action that has constant on-time pulse pattern synchronized with the resonant frequency. Thus, the inverter switches are operated under zero current switching (ZCS). The basic operating principle and fundamental analysis to design the circuit parameters for the proposed inverter are described in the paper. The effectiveness of the proposed inverter is evaluated by using a prototype of 200W output capacity employing 190kHz resonant frequency based on Power MOSFET devices and a frequency modulation controller by MCU. The proposed series resonant inverter employing discontinuous-resonant control achieves maximum efficiency of 94.8% at 200W output power.