EMI and ground leakage current reduction in single-phase grid-connected power converter

Ground leakage current in a power converter is a major concern, which has stringent limitations due to safety concerns. Presence of high-frequency pulses, with high dv/dt due to switching actions in common-mode (CM) voltage, result in injection of current waveforms with large di/dt spikes into the ground and causes high electromagnetic interference (EMI) noise level. In this study, a new method is proposed to make the CM voltage, of a single-phase grid-connected inverter, sinusoidal and free of high-frequency pulses. The proposed method consists of two parallel connected H-bridge power converters, which uses unipolar pulse width modulation (PWM) with carrier interleaving angle of 180 degrees. The proposed method reduces the ground leakage current by more than an order of magnitude. A novel modification to the LCL filter is proposed which further reduces the leakage current by 48%. It is shown that these modifications make the overall system insensitive to circuit non-idealities. Experimental results based on ground leakage current measurements on a 7.5 kW parallel single-phase PWM rectifier are presented. These results validate the effectiveness of the proposed method.