Ground leakage current reduction in single-phase grid-connected power converter

Abstract

One of the major concerns during the design of grid-connected converters is meeting the electromagnetic interference (EMI) standards. Ground leakage current is another aspect which has a stringent limit due to safety concerns. Presence of high frequency pulses, with high dv/dt due to switching actions, in common-mode (CM) voltage excite parasitic capacitances of the power converters. This results in injection of peaky current to ground and causes high EMI noise level. In this paper a new method is proposed to make the CM voltage, of a single-phase grid-connected converter, sinusoidal and free of high frequency pulses. The proposed method consists of two parallel connected H-bridge power converters, which uses unipolar PWM with carrier interleaving angle of 180°. The proposed method reduces the ground leakage current by more than an order of magnitude. A modification to the LCL filter is adopted which further reduces the leakage current by 48%. It is shown that these modifications make the overall system insensitive to circuit nonidealities. Experimental results based on ground leakage current and EMI measurements on a 7.5kW parallel single-phase PWM-rectifier are presented. These results validate the effectiveness of the proposed method.