Boost-type common-ground PV inverter based on quasi-Z-source and switched-capacitor

Abstract

Common-ground type of transformerless photovoltaic (PV) inverters is an effective means to eliminate common-mode leakage current. Recent years, switched-capacitor (SC) technique with the advantage of voltage boosting has been successfully used in this field. In order to inherit the merits of SC-based common-ground PV inverters, and to further improve the performance in the aspects of inrush charging current, input current quality and boost capability of SCs, a new boost-type common-ground (BCG) inverter is developed by inserting a quasi-Z-source (qZS) unit in an SC-based common-ground inverter. Specifically, an SC unit employed in the BCG inverter is fed by the qZS circuit rather than a voltage source, so that the inrush charging current is effectively limited by inductors of the qZS unit. Meanwhile, the boost capacity is further improved and the input current has been continuous. Both circuit configurations of single-phase and three-phase as well as their operation principle and modulation are analyzed in detail. Especially in the three-phase configuration, only one qZS unit is used to feed three SC units and the input current is almost constant. The feasibility of the proposed BCG inverter is experimentally verified by a downscale three-phase prototype.