Transformerless Three Phase NPC Inverter with Reduced Switches

In a photovoltaic grid connected system, the attenuation of the common mode voltage is one of the main issues. Many single phase inverters have been proposed to improve the common mode characteristic. However, few studies have been focused on the topological improvement for common mode behavior of the three phase inverter. This paper proposed two types of novel three phase NPC inverters with low leakage current. The common mode characteristic of the inverter can be improved by the proposed NPC circuit. Firstly, the common mode model of the three phase inverter is analyzed. Then, the improved three phase NPC circuit and the variation topology are introduced with the operating principles. Thirdly, a comparison between the improved NPC inverters and the traditional three phase NPC inverters illustrated that the proposed topologies have the advantages in the aspect of device cost and conduction losses. Finally, the simulation results verified the theoretical findings.