The leakage current suppression of transformerless three-level photovoltaic grid-connected inverter

Abstract

Transformerless PV grid-connected inverters, although simple in construction and highly efficient, suffer from serious current leakage problems. There is no electrical isolation between the PV panels and the grid, and the parasitic capacitance causes the inverter to form a common mode loop with the earth, creating strong resonances in the high-frequency range and generating huge leakage currents. Today, the two main methods of leakage current suppression are topology and modulation. This paper observes leakage current suppression by comparing two modulation methods, SVPWM and 3D-SVPWM. In the case of the LCCL filter, the conventional SVPWM modulation causes the common mode voltage to oscillate at high frequencies of the order of magnitude of the carrier frequency, causing large leakage currents in the common mode loop. With 3D-SVPWM modulation, however, the common mode voltage pulses are equal in the positive and negative areas, attenuating the CM resonance and balancing the NP voltage, thus producing a smooth common mode voltage and effectively suppressing high-frequency leakage currents.