Review of Three Phase Transformer-less PV Converters

Research in solar photovoltaics over the past decade has resulted in significant improvement of the PV array efficiency. To further improve efficiency, transformerless PV inverter topologies are developed and are successfully employed in single phase PV systems. However, as the output power of solar PV becomes more than 15 kW it is recommended to use three phase converters instead of single phase owing to the size of the DC link capacitor and its lifetime. Due to the lack of galvanic isolation in case of transformerless inverter, the parasitic capacitance between the PV surface and grid ground faces varying common mode voltage across it. This results in the flow of common mode leakage current and compromises overall safety of the inverter. This paper discusses some of the prominent three phase grid connected transformer-less Voltage source inverters (VSI) for solar photovoltaic (PV) application. Various topological modifications and control strategies proposed in literature to minimize the ground current or the common mode current are presented.