Three-phase Soft-switching Bi-directional DC-DC Converter for Low Voltage High Power Applications

This paper presents a novel modulation technique for a three-phase dc-dc converter with bi-directional power transfer capability. The topology is geared towards dc microgrid and fuel cell vehicle applications, where a high step-up ratio converter is required to enable efficient energy exchanges between two dc buses of different voltage magnitudes. The proposed converter achieves zero-current switching (ZCS) of all primary switches and zero-voltage switching (ZVS) of secondary switches. Without any need for active clamping or passive snubbers, ZCS is achieved by secondary modulation which clamps the reflected output voltage across primary devices naturally, thereby eliminating the switch turn-off voltage spike issue associated with current-fed converters. Equal current sharing between the three phases over high-frequency (HF) cycles, reduces the peak current stresses and conduction losses within devices. Three-phase switching increases the effective operating frequency of the converter by a factor of 3, thereby reducing input current ripples, output voltage ripples and filtering requirements, eventually. Higher operating frequency also reduces sizes of magnetics, leads to better transformer core utilization and increased power density of the converter. Steady-state analysis and operation of the converter are described. Simulation for a 1 kW prototype is performed in PSIM 9.3. Results validate the accuracy of the analysis and the predicted performance of the proposed converter.