A Modified Common-Mode Filter with Enhanced Attenuation Performance in Single-Phase Grid-Tied Solar PV Inverters

This paper analyzes the common-mode currents (CM) flowing in a single-phase full-bridge PV grid-tied inverter (GTI) system, and compares the performance of different common-mode filter configurations. The comparison is carried out in the context where local loads with metallic enclosures are connected at the point of common coupling (PCC). The effect of such loads is shown to cause additional common-mode ground leakage currents to flow in the system, which not only exceeds the safety limits set by compliance standards, but also causes spurious behavior of loads in the form of false tripping. It is shown through analysis that the standard electro-magentic interference (EMI) filter topology and the modified LCL (MLCL) filter although address the spurious load behavior, also possess downsides in terms of leakage current magnitude and inductor losses. A modified-CM (MCM) filter configuration is employed that addresses the issue of spurious load trips as well as minimizes the ground leakage current adequately in the system. Experimental results on a 5 kVA PV fed GTI validate the analysis and comparative study carried out in this paper.