A New Fully Soft-Switched, Single-Stage Llc Resonant Based Grid Connected Inverter

A new single-stage fully soft-switched resonant grid-connected inverter is proposed in this paper. The proposed inverter is able to provide ZVS turn-on for all the switches without requiring complex switching modulation or using additional passive auxiliary circuits. A front-end half-bridge LLC resonant inverter is connected to a high frequency AC link, where galvanic isolation is provided. On the secondary side of the high frequency AC link, two switch pairs are controlled with sinusoidal PWM and they are connected to an output LC-type filter to provide the required sinusoidal grid side current. The operating stages of the proposed circuit and the circuit's characteristics are discussed. A closed loop control algorithm based on a proportional resonant and a harmonic compensator controller is implemented so that the output grid current is synchronized with the grid voltage and can achieve very low THD. Results are provided on 1.5kW system, an input voltage range of 200 - 300V and an AC output voltage of 120Vac, rms with a switching frequency of 103 kHz to validate the performance of the proposed inverter.