Operation of the Step-Up/Down Bidirectional Partial Power Converter Near Zero Series Voltage

The advantages of step-up/down series partial power converters (S-PPCs) are comprehensively addressed in the literature. However, their functionality at the critical point of equal port voltages is neglected. This paper analyzes a bi-directional step-up/down S-PPC to confirm its correct operation at this critical point. This S-PPC contains a four-quadrant DC-DC stage. Two modulation strategies are applied to the converter depending on the power flow direction. The phase shift modulation (PSM) regulates the current and voltage in the buck mode of the DC-DC stage. The reverse power flow control can extend the boost function of the DC-DC stage in the S-PPC when it works in the second and fourth quadrants. The series port voltage is decreased to almost zero to investigate the functionality of the S-PPC in all modes. The experimental prototype is tested under 5A current and 350V port voltage and the results confirm the correctness of the theoretical analysis.