Novel shunt-less filters for grid-connected transformerless photovoltaic applications

Abstract

The existing ground leakage current suppression methodologies are effective when Photovoltaic (PV) arrays' stray capacitors are small (in several nano-Farads). In such case, the High Frequency (HF) content of the inverter's Common-Mode (CM) noise is dominating the ground leakage current Root-Mean-Square (RMS) value. However, when the PV parasitic capacitors are large (in several micro-Farads), which is realistically the case with higher power ratings (i.e. Po > 5 kW); the grid CM noise is the major contributor to the ground leakage current. In fact, this makes the existing approaches for leakage current suppression ineffective. Therefore, this paper proposes novel filter topologies for transformerless grid-connected PV applications with a novel CM control scheme that suppress the ground leakage current when the PV parasitic capacitors are large. These filters are termed as Shunt-less filters. Additionally, the proposed topologies are equivalent to well-established filters, such as LCL, LLCL and LCL-LrCr. This fact makes the selection of their parameters as conventional filters. The theoretical analyses are validated with a 10 kW / 240 Vrms grid-tied PV system. The results have demonstrated that the proposed control scheme can reduce the ground leakage current RMS value from 1.8 A to 60 mA.