Analysis and implementation of a three‐level hybrid dc–dc converter with the balanced capacitor voltages

In this study, a three-level hybrid dc/dc converter by integrating the full-bridge circuit, resonant circuit and three-level flying capacitor circuit is presented to achieve the main advantages of low-voltage stress of power devices, low circulating loss, low-voltage ringing on the rectifier diodes and low-output filter inductor for medium-voltage dc-based systems. Two full-bridge circuits are connected in series to effectively reduce the voltage stress of switches. Half-bridge resonant circuit shared the lagging-leg switches of full-bridge circuit is used and operated at fixed switching frequency to extend the zero-voltage switching (ZVS) range from low load to full load. Thus, the drawback of narrow ZVS range in the conventional full-bridge converter is improved. A flying capacitor is adopted to automatically balance input split capacitor voltages in each switching cycle without any additional active components or complexity control scheme. The circulating loss in the full-bridge circuit is reduced to zero by parallel connection of outputs of full-bridge circuit and half-bridge resonant circuits. Finally, the theoretical analysis and performance of the proposed converter are verified by the experiments with a 1.92 kW prototype circuit.