Optimal Design of the Resonant Tank of the Soft-Switching Solid-State Transformer

The Soft-Switching Solid-State Transformer (S4T) is a minimal single-stage current source topology with high frequency isolation and soft switching across the entire load range. The resonant tanks, consisting of a resonant LC circuit and an auxiliary switch, are crucial to the proper operation of the S4T by setting the zero voltage switching conditions across all the power devices. The selection of the resonant inductor and capacitor greatly affects the overall converter design in terms of voltage and current stress, achievable switching frequency and DC link utilization. This paper presents a detailed analysis of the resonant tanks operation and interaction with the transformer magnetizing and leakage inductances. The main relations are derived analytically and explained physically. Based on this mathematical framework, a Pareto optimization of the resonant circuits is proposed for a given set of transformer parameters. Finally, simulation and experimental results verifying the analysis are presented.