A Nonisolated Symmetric Bipolar Output Four-Port Converter Interfacing PV-Battery System

A bipolar dc microgrid is desirable as it enhances the system reliability and efficiency. However, the conventional bipolar dc microgrid requires multiple dc-dc converters to feed the power to the load, which leads to large volume and weight and high cost. In this article, a novel four-port converter is proposed to integrate photovoltaic (PV) module and battery to the bipolar dc microgrid system, realizing the single-stage energy conversion. The main advantages of this converter are that three switches are used to realize PV generation, battery charging and discharging, as well as symmetrical bipolar output voltage, and all input ports and output ports share the common reference ground. Depending on relationships between the energies of the source and the load, three different operation modes are defined. Then, the detailed parameter design is provided by analyzing different operation modes of the converter. Energy management and control strategies of the bipolar dc microgrid using this converter are explained in detail. Finally, experimental verifications are given to illustrate the feasibility and effectiveness of the proposed converter.