Three-level three-phase transformerless inverter with low leakage current for photovoltaic power conditioning system

This paper presents a three-level three-phase transformerless inverter with low leakage current for photovoltaic (PV) power conditioning systems (PCS). The proposed PCS consists of a three-level step-up converter and a modified three-phase T-type inverter and is developed for a corner grounded delta system. By connecting the grounded S-phase directly to the midpoint of the input and the dc-link capacitors, the common mode voltage is fixed to a constant value and leakage current is suppressed. The three-level step-up converter not only lowers switching and conduction losses with reduced voltage stress but also guarantees balancing of the dc-link capacitor voltages using a simple control algorithm. As the modified three-phase T-type inverter has only two legs, the number of components is reduced and power loss is minimized. The direct nominal voltage compensation control algorithm enables the PCS to obtain high grid power quality. The proposed PCS is theoretically analyzed in detail, and experimental and simulation results are applied to a 10 kW prototype to evaluate its performance.