Development of a two-stage transformerless grid-tied photovoltaic inverter system using SiC devices

The problem of ever-increasing energy demand and depletion of conventional resources is well known. In order to meet this growing demand, residential rooftop Photovoltaic (PV) systems, which can cater to the household demand and also supply excess power to the grid, are being encouraged. In this paper, a two-stage transformerless single-phase grid-tied PV system for residential rooftop application is proposed. A analysis for Common mode (CM) voltages present in the proposed system is provided. The proposed system is simulated in PSCAD and a 2.5 kVA laboratory prototype is developed. The proposed system has a very low leakage current, due to which, galvanic isolation is not required at any stage. Use of Wide band Gap material like Silicon Carbide (SiC) based devices can benefit PV power systems with high system efficiency, ability to operate with high switching frequency and reduction in the size of required magnetics and heat sinks. Accordingly, SiC MOSFETs and diodes are used in the laboratory prototype of the proposed system. The developed system has an overall part-load system efficiency of greater than 92%. The measured leakage current in the proposed system is less than 30 mA (rms), which is compliant with the German standard DIN VDE0126-1-1.