A GaN based doubly grounded, reduced capacitance transformer-less split phase photovoltaic inverter with active power decoupling

Transformer-less PV inverters are gaining widespread applications with lower cost, reduced footprint, and improved efficiency. This paper proposes a topology that can eliminate the common mode leakage current which is a major challenge in transformer-less PV inverters. In addition, an active power decoupling strategy is implemented in this topology instead of using large energy storage element for double line frequency power decoupling which is a common problem in single phase inverters / rectifiers, thus achieving a smaller volume and replacing electrolytic capacitors with film capacitors to increase reliability. A constant input voltage with negligible double line frequency ripple component less than 2% ensuring high MPPT efficiency is achieved in this topology through control strategy. Compared with previous topology, the 120 Hz inductor current ripple in the boost stage is reduced significantly resulting in the decrease of the RMS current value by 14% and the peak current value by 41%. Also the RMS current in the input capacitor is decreased by 91%. The dc link capacitor volume is also decreased with the increase of the voltage level. Finally, a 1 kW, 100 kHz single-phase prototype with 200 V DC nominal input and 120 V/60 Hz AC output in split phase configuration using GaN FETs has been built to validate the theoretical analysis. The control strategy and modulation scheme are implemented in DSP TMS320F28335.