Fixed frequency control of LCL-T resonant power converter with capacitive output filter

In this paper, a fixed-frequency phase shift control is proposed for a 1-phase series-parallel LCL-T resonant converter. Zero-voltage switching (ZVS) of the inverter switches for wide variations in input voltage and load is achieved by designing the converter to operate in above resonance mode. Steady state approximate AC circuit analysis method is used to analyze the converter with fixed-frequency phase shift control. LCL-T converter offers a built-in protection against short-circuiting of the load. LCL-T converter with fixed-frequency control requires a very small change in phase shift to regulate the output voltage for wide variations in input voltage and load. Due to ZVS for the entire input voltage and load variations, the operating efficiency of the converter is high. A 300 W, DC-DC, LCL-T resonant converter is designed for solar energy generation applications. The performance of the converter with the proposed fixed-frequency phase shift control is studied with PSIM simulations. The theoretical and simulation results are compared and presented.