A Novel Single-Phase Transformerless Grid-connected Inverter

Nowadays, the transformerless inverters have become a widespread trend in the single-phase grid-connected photovoltaic (PV) systems because of the low cost and high efficiency concerns. Unfortunately, due to the non-galvanic isolation configuration, the ground leakage current would appear through the PV parasitic capacitance into the ground, which induces the physical danger and serious EMI problems. A novel transformerless single-phase inverter with two unipolar SPWM control strategies is proposed in this paper. The inverter can guarantee no ground leakage current and high reliability by applying either of the SPWM strategies. Meanwhile, the low total harmonic distortion (THD) of the grid-connected current is achieved thanks to the alleviation of the dead time effect. Besides, the required input DC voltage is the same low as that of the full-bridge inverter. Furthermore, the output filter inductance is reduced greatly due to the three-level output voltage, which leads to the high power density and high efficiency. At last, a 1kW prototype has been built and tested to verify the theoretical analysis of the paper.