Leakage current and energy efficiency analyses of single phase grid connected multi-kva transformerless photovoltaic inverters

Özkan, Ziya
In order to inject solar power to the utility grid, among various types of inverters, Grid Connected Transformerless Solar Inverters (GCTSI) are mostly preferred for residential or commercial applications. This preference is because of the high energy efficiency and low cost due to the absence of a line frequency or a high frequency transformer. Peak value of the efficiency characteristics of GCTSIs can reach 98%, which are selected topology, component optimization, switching strategy and operating condition dependent. In spite of the attractive energy efficiency characteristics of GCTSIs, due to the lack of galvanic isolation, these inverters are vulnerable to leakage currents, which are prohibitive for the safety and the maintenance reasons. The purpose of this research is to analyze GCTSIs in terms of their leakage current and energy efficiency characteristics. In the research, the leakage current mechanisms of GCTSIs are identified and grid connected solar inverters are classified in terms of their leakage current characteristics including the GCTSIs. In addition to the existing ones, several novel topologies are proposed enriching the family of GCTSIs. The leakage current and the inductor current ripple performances of GCTSI topologies are analyzed and evaluated by detailed simulations for 3 kVA and 10 kVA single-phase systems. In addition, the energy efficiency characteristics of GCTSIs are investigated in these power levels by making use of Calculated Average Power Per Switching Cycle (CAPPSC) method. The efficiency studies with CAPPSC method provide design guidelines and comparison of the GCTSI topologies in terms of their energy efficiency characteristics.