A Modular Three-Phase Photovoltaic Inverter with Elimination of Phase Unbalance and Reduction of Second Harmonic Voltage Ripple

Cascaded module topology is widely used in large scale photovoltaic system because of its easy expansion and small output harmonic. For traditional photovoltaic three-phase inverter topology, the power generation of each phase bridge can be unequal because of nonuniform solar illumination, partial shading, or unequal module temperatures, resulting in the interphase power imbalance. The DC-link capacitance is usually very large to decouple the fluctuating power, resulting in a large volume of the converter. In this paper, a novel modular three-phase converter topology applied to large scale photovoltaic systems is proposed, which can realize the automatic interphase power balance, and make the fluctuating power offset in a four-winding transformer, greatly reduce the size and cost of the converter and improve the power density of the PV system. The feasibility of the proposed topology is verified by simulation.