A Nine-Level Grid-Connected Converter Topology for Single-Phase Transformerless PV Systems

This paper presents a single-phase transformerless grid-connected photovoltaic converter based on two cascaded full-bridges with different DC-link voltages. The converter can synthesize up to nine voltage levels and needs only a single DC supply bus, since one of the full bridges is supplied by a flying capacitor. The multilevel output reduces harmonic distortion and electromagnetic interference. A suitable switching strategy is employed to regulate the flying capacitor voltage, improve the efficiency (most devices switch at grid frequency) and minimize the common-mode leakage current with the help of a novel dedicated circuit (transient circuit). Simulations and experiments confirm the feasibility and good performance of the proposed converter.