An improved transformerless grid connected photovoltaic inverter with reduced leakage current

• An improved transformerless inverter topology is proposed with low leakage current.
• The relationship among the switches junction capacitance is proposed.
• Efficiency is increased by replacing high-frequency IGBTs with ultra-fast MOSFETs.
• The design considerations are investigated for optimal design.
• The simulation and experimental results verify the theoretical analysis.

Transformerless inverters are most preferred for grid connected photovoltaic (PV) generation system due to higher efficiency and lower cost. However, to meet the safety regulations, the leakage current which deteriorates the power quality and generates electro-magnetic interference in transformerless PV inverter, has to be addressed carefully. In order to eliminate the leakage current, an improved H5 topology is proposed in this paper. The operating principle, common mode (CM) characteristics, and the impact of junction capacitance of the switches on the CM voltage are investigated in details. The desired relationship among the junction capacitances is proposed to eliminate the CM leakage current. Three-level output voltage is achieved in the improved inverter employing unipolar sinusoidal pulse width modulation (SPWM). Furthermore, the European efficiency is improved by replacing the high frequency IGBT switches with MOSFETs. The proposed topology is compared with other transformerless topologies in terms of leakage current, different mode (DM) characteristics, and efficiency. The improved inverter topology is simulated in MATLAB/Simulink software to validate the accuracy of the theoretical explanations. Finally, a 1 kW laboratory prototype has been built and tested. The experimental results show that the proposed inverter has a maximum efficiency of 98.0% and 97.45% European efficiency with 16 kHz switching frequency.