A single phase transformerless string inverter with large voltage swing of half-bridge capacitors for active power decoupling

The transformerless single phase inverters are becoming common due to its advantages of reduced volume, lower cost, and higher efficiency but it has two implementation challenges-high frequency capacitive ground current and decoupling of double line frequency power. This paper proposes an optimized power decoupling topology for a single phase string inverter which addresses both the challenges as well as minimizes capacitance required to decouple the ripple power. Unlike conventional power decoupling techniques in full bridge converters, the proposed technique does not significantly increase the voltage stress on the devices. The combination of a half-bridge inverter and a buck boost converter ensure the complete elimination of high frequency capacitive coupled ground currents. The proposed technique requires only 40 μF/kW at 600 V for power decoupling. A closed loop controller design for the converter is detailed and the experimental results at 1 kW, 120 V, 60 Hz output for closed loop operation are provided.