A high efficiency transformerless PV grid-connected inverter with leakage current suppression

This paper presents a new diode free freewheeling and common-mode voltage (CMV) clamping branches for single phase transformerless grid connected photovoltaic (PV) inverter for complete leakage current elimination and low conduction losses. In the past, various isolation techniques have been proposed for leakage current elimination in transformerless PV inverters. However, galvanic isolation only cannot completely eliminate leakage current due to that a resonant path is created by the switch junction capacitors, which also generate leakage current. The proposed freewheeling branch consists of four MOSFETs along with a clamping branch, which consists of two MOSFETs and a capacitor divider. The divider is connected to the DC side of the converter to keep constant CMV in the freewheeling path. As a result, the improved CMV clamping has been achieved for complete leakage current elimination. The unipolar sinusoidal pulse width modulation (SPWM) technique and modified HERIC topology with AC-decoupling for galvanic isolation is adopted for lower conduction losses. The proposed topology consists of only MOSFET in the freewheeling and clamping path which provides lower conduction losses compared with diode based topologies. The performances of the proposed topology in terms of common mode characteristics, leakage current, total harmonic distortion and conversion efficiency are analyzed and compared with H5, H6, HERIC and HBZBR topologies. The detail analyses are performed using MATLAB/Simulink and PSIM.