Six-Switch and Seven-Switch Grid-Connected Current Source Inverters for Transformerless Photovoltaic Applications

Transformerless single-stage Current Source Inverter (CSI) is a very promising power electronic converter due to its inherent boost capability and ease of control. This paper investigates the performance of two traditional CSI topologies with different switch count (conventional six-switch CSI and seven-switch CSI7), for grid-connected Photovoltaic (PV) applications. Both topologies are controlled using the Space Vector with Pulse Width Modulation (SVPWM) technique. The performance of the proposed topologies are assessed by means of numerical simulations and the results are compared in terms of Common Mode Voltage (CMV), ground leakage current, and injected grid-current harmonic distortion THD. Furthermore, conduction and switching semiconductor power losses are computed and simulated over a grid period. Simulations are carried-out at different operating points of the converter to evaluate the performance of both topologies for grid-connected PV applications. The obtained results prove that the CSI7 topology strongly reduces the fluctuations of the CMV and, therefore, results in lower ground leakage current. It also allows the injection of high quality currents with lower THD into the power grid and, commonly, reduces power losses in power semiconductors. With respect to conventional CSI, the CSI7 topology offers high performance criterion and increased efficiency at the cost of one additional power switch.