Optimised full‐bridge transformerless photovoltaic grid‐connected inverter with low conduction loss and low leakage current

Abstract

The unipolar sinusoidal pulse width modulation (SPWM) full‐bridge inverter brings high‐frequency common‐mode voltage, which restricts its application in transformerless photovoltaic grid‐connected inverter. The freewheeling path added in ac side is adopted to restrict leakage current, but the common‐mode voltage is variable at switching frequency scale. To solve this problem, an improved full‐bridge structure with two switches and a capacitor divider has been proposed, which guarantees that freewheel path is clamped to half of input voltage in freewheel period. Sequentially, the high‐frequency common‐mode voltage has been avoided in unipolar SPWM full‐bridge inverter. The operation mode and the clamping mode are analysed, and several related topologies are discussed. Finally, the differential‐mode and common‐mode performance of the proposed topology are verified by a universal prototype inverter rated at 1 kW.