Zero-Voltage Switching Control of an Interleaved Bi-Directional Buck–Boost Converter With Variable Coupled Inductor

This paper investigates an approach for achieving zero-voltage switching of an interleaved bi-directional buck-boost converter over a wide input-output voltage operating range by utilizing a coupled inductor with a variable coupling coefficient. The approach is based on regulating the value of the coupling coefficient by means of a direct current depending on the converter conversion ratio, thereby controlling the amplitude and duration of the resonant voltage transition. The impact of the controllable value of the coupling coefficient on the equivalent inductance, the zero-voltage transition period, and the resonant amplitude is analyzed in detail by applying analytical modeling. In comparison to the converter with a fixed coupled inductor operating over a wide input-output voltage span, the variable coupled inductor significantly improves the soft-switching range and reduces the circulating energy. Outside of the controllable resonant amplitude region, the converter with a variable coupled inductor still achieves reduction in the duration of the resonant transition period. To validate theoretical analysis, experimental results are recorded on the gallium nitride interleaved bi-directional buck-boost converter prototype. Improvements in efficiency at both full and half loads in comparison to the prototype with a fixed coupled inductor are achieved.