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

• Published in: Solar energy 2017-01, Vol.142, p.243-252
• Main Authors: Kim, Kwang-Seop, Lee, Sung-Ho, Cha, Woo-Jun, Kwon, Bong-Hwan
• Format: Article
• Language: English
• Subjects: Common mode voltage; Three-level step-up converter; Three-phase two-leg inverter; Two-stage PV system
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2016.11.044

•The three-phase three-level transformerless inverter has low leakage current.•The circuit structure fixes the common mode voltage to a constant value.•The dc-link capacitor voltages are easily balanced.•The modified T-type inverter has only two legs and reduced number of components. 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 10kW prototype to evaluate its performance.