Improved single-phase transformerless inverter with high power density and high efficiency for grid-connected photovoltaic systems

This study proposes an improved single-phase transformerless inverter with high power density and high efficiency for grid-connected photovoltaic systems. The proposed inverter is comprised of the dual-paralleled-buck inverter and two auxiliary circuits for the zero-current switching turn-off of the diodes. The dual-paralleled-buck inverter and auxiliary circuits are joined by two coupled inductors. To achieve high power density, the proposed inverter operates at high switching frequency of 40 kHz. This leads to lower filter inductors and lower conduction losses of the filter inductors than conventional full-bridge inverters. Moreover, two auxiliary circuits reduce the switching losses caused by high switching frequency operation. Furthermore, the proposed inverter provides the low common-mode leakage current, which satisfies the criteria given by VDE-0126-1-1. Thus, the proposed inverter achieves the maximum efficiency of 99%. The operation principle of the proposed inverter is analysed and verified. Experimental results for a 1 kW prototype are obtained to show the performance of the proposed inverter.