DC Decoupling-Based Three-Phase Three-Level Transformerless PV Inverter Topology for Minimization of Leakage Current

Abstract

This letter presents a three-phase three-level cascaded photovoltaic (PV) inverter configuration based on the dc decoupling strategy. The given configuration requires two additional decoupling switches for the minimization of the leakage current. The leakage current is minimized by avoiding or restricting the change in terminal voltages, during the common zero state. Further, a common zero state in all the three phases is obtained using a phase opposition disposition pulsewidth modulation technique. Once the common zero state is realized, the dc decoupling switches are used to isolate the PV source and output load. Apart from the terminal voltage, the proposed configuration also reduces the transitions in the common-mode voltage. Further, this letter also presents an analysis of the terminal voltage using the switching function concept. From the given switching function analysis, an analytical expression of the terminal voltage is derived and is used to obtain the analytical waveform, which matches with the simulation results. In addition to the terminal voltage, the leakage current waveform is also given. Fast Fourier transform spectrums of both are shown. These results are further supported by the experimental waveforms which match both simulation and analytical waveforms. Further, the proposed cascaded multilevel inverter (CMLI) is also compared with the conventional CMLI.