High efficiency transformerless PV power converters

Transformer-less photovoltaic (PV) inverters offer better efficiency compared to inverters connected to the grid through a transformer providing galvanic isolation. However, in case the transformer is omitted, the generated common-mode voltage greatly influences the leakage current flowing to ground through the parasitic capacitance of the PV array. Hence, both the power stage and the modulation strategy of the converter, shall be properly designed to avoid leakage current while guaranteeing high efficiency and reactive power handling capability that are requested by national grid codes. In this paper, three single phase transformer-less inverter topologies are analyzed: the Highly Efficient and Reliable Inverter Concept converter (HERIC), a recently published topology based on a combination of step-down converters and a recently patented modification of the Neutral Point Clamped converter (NPC) optimized for MOSFET use. Simulation results are used to show: current waveform, reactive power handling capability, efficiency and produced common-mode voltage.