A high performance T-type single phase double grounded transformer-less 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, thus achieving a smaller volume. A constant input voltage with negligible double line frequency ripple component ensuring high MPPT efficiency is achieved in this topology. Compared to the previously proposed topology, a T-type branch is added as an improvement to fully take advantage of the inherent three level structure resulting in much reduced switching loss and inductor current ripple. A 1 kW, 100 kHz single-phase prototype with 200 V DC input and 120 V/60 Hz AC output using SiC MOSFETs has been built to validate the theoretical analysis. The control strategy and modulation scheme are implemented in DSP TMS320F28335 resulting in 24% reduction in the total loss and 50% reduction in the inductor current ripple.