A novel single-phase five-level transformer-less photovoltaic (PV) inverter

Multilevel inverters are preferred solutions for photovoltaic (PV) applications because of lower total harmonic distortion (THD), lower switching stress and lower electromagnetic interference (EMI). In order to reduce the leakage current in the single-phase low-power PV inverters, a five-level transformer-less inverter is proposed in this paper. A total of eleven switches are required, while six of them only withstand a quarter of the dc-bus voltage, so the costs for them are low. Another four switches are turned on or off at the power line cycle, the switching losses for them are ignored. In addition, the flying-capacitors (FCs) voltages are only a quarter of the dc-bus voltage, and they are balanced at the switching frequency, which further reduces the system investment. The experimental results based on a 1 kW prototype show that the proposed modulation strategy can balance the FCs voltages at Vdc/4 very well. And the leakage current can be reduced to about 27 mA under both active and reactive operations, which satisfies the VDE 0126-1-1 standard.