Discontinuous Modes on a DC–DC Converter Using a Three-Phase Transformer With Zero-Phase Current

In this study, discontinuous operation modes of a high-frequency isolation circuit using zero-phase current of a three-phase transformer are investigated. In the circuit system, the amount of power transmitted between primary and secondary bus bars is controlled by the phase difference between the output voltages of the primary and secondary circuits. The circuit system also controls the voltage ratio between the primary power supply and the primary bus bar based on the duty ratio output by the primary side. By adjusting the primary bus bar voltage, the circuit can regulate the amount of current flowing through the three-phase transformer and simultaneously superimpose the current to achieve soft switching and suppress the conduction loss. Moreover, the discontinuous modes of the circuit system are analyzed to clarify the conditions necessary to achieve soft switching, the limitation of the amount of power transmission due to peak current will be analyzed, and the operation is verified by simulations. The soft-switching operation is also verified using actual equipment, and the operating efficiency measured. The circuit has a broad soft-switching area, especially in the low-power range. Thus, it can be effectively used in demand and supply adjustment applications wherein small charge and discharge operations are frequently required. As a result, the proposed circuit scheme improved the power-grid efficiency for renewable energy utilization. We expect this to significantly contribute toward the realization of a sustainable society.