Leakage Current Elimination in Single Phase Transformer less Grid Connected Power Systems

Eliminating the leakage current is one of most important issues for transformer less inverters in grid connected photovoltaic applications. The technical challenge is how to keep the common mode voltage constant to reduce the leakage current. For this purpose an improved single phase transformer less inverter is proposed. It has two additional switches connected in the dc side. The PWM pulses for those switches are given in such a way that the condition for making the common mode voltage constant is completely met. The common mode voltage can remain a constant during all the modes in the improved inverter. Both uni polar and double frequency control strategies are applied. By adopting uni polar PWM strategy, the leakage current reduced and a higher quality and lower THD of grid connected current are obtained using double frequency PWM.