In this study, a three-level hybrid dc/dc converter by integrating the full-bridge circuit, resonant circuit and threelevel 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.
A 1.44 kW DC/DC converter with zero voltage switching (ZVS) for medium voltage applications is proposed in this study. Two half-bridge circuits with split capacitors are connected in series at high voltage side to limit voltage stresses of power switches at V in /2. Three DC/DC circuits are adopted to share load current and reduce the current stress of rectifier diodes, transformers and output filter inductors. Two balance capacitors are used in the proposed circuit to automatically balance input split capacitor voltages in every switching cycle. The current doubler rectifier is adopted at low voltage side to partially cancel ripple current so that the root-mean-square current at output capacitor is reduced. Asymmetric pulse-width modulation is used to adjust the duty cycle of power switches and regulate output voltage. The output capacitance of power switches and the external resonant inductance are resonant at the transition interval and power metal-oxide-semiconductor field-effect transistors can be turned on under ZVS. The proposed converter can be applied for high input voltage applications such as a three-phase 380 V/480 V utility system. Experimental results from a 750-800 V input and 24 V/60 A output are provided to demonstrate the performance of proposed converter.
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