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

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.