Low-leakage current two-stage transformerless grid-connected converter for residential PV application

Abstract

Conventional PV-fed three-level DC-DC converter has greater leakage current due to varying common mode (CM) voltage, and thus requires galvanic isolation if interfaced with on-grid inverters. To reduce the leakage current and eliminate the requirement of galvanic isolation, a low-leakage three-level DC-DC converter is proposed for residential application. Efficacy of the converter is demonstrated by proposing a two-stage single-phase on-grid PV system by interfacing with a three-level transformerless single-phase inverter topology. The DC-DC converter has reduced leakage current, which decreases the overall leakage current in the PV inverter system. In addition, smaller filter magnetics are required for both the three-level converter and three-level inverter. The CM analysis of the proposed system is presented. The proposed system is simulated using PSCAD and a laboratory prototype is developed for experimental evaluation. The experimental results show a part-load efficiency of >96% for the overall system. Furthermore, the measured leakage current in the proposed system is <;10 mA, which is below the prescribed RMS limit, as specified in German DIN VDE 0126-1-1 standard.