New mathematical model from system standpoint to analyse and mitigate PV leakage current of large PV strings/arrays

Abstract

One of the recently arisen issues for transformerless grid-connected photovoltaic (PV) systems is high-frequency leakage current, which flows through the parasitic capacitance of PV system and the neutral grounding resistor (NGR) of the grid. This paper deals with a systemic analysis on the capacitance of large PV systems considering the interconnecting conductors. A new Y-bus model is proposed to analyse the leakage current of PV strings/arrays of any size in high-frequency domain. In the model, different capacitances of PV panels and the inductance and capacitance of interconnecting cables are considered. Subsequently, a two-port circuit is derived by its admittance parameters, which is useful in leakage current studies. In the second step, a novel model for the common mode (CM) analysis of voltage-source inverters is derived based on which, a new leakage current mitigation technique is proposed which provides capacitive CM paths for both the negative and positive legs of the inverter. The model is assessed using different simulations in various conditions. The results confirm the usefulness of the proposed model.