An Improved Three-Phase Transformerless Neutral Point Clamped Inverter Topology for Common Mode Voltage Reduction

Abstract

Transformerless photovoltaic (PV) inverters are more effective, lighter in weight, and less expensive than transformer-based topologies. However, a leakage current $(i_{Leakage})$ is produced when transformers are removed due to the direct connection between the PV panel and the grid. This current reduces the life of the insulation, causes safety problems, and increases the harmonic distortion in the grid current. To overcome these issues, an improved three-phase transformerless neutral point clamped (NPC) topology is proposed by employing two additional switches on the primary side of a traditional NPC inverter. This arrangement reduces the iLeakage significantly and improves the harmonic behavior of the grid current by operating the additional switches in zero switching states. Furthermore, when compared to a conventional H8 inverter, its multilevel capability reduces voltage stress on semiconductor devices. Finally, the proposed topology is validated with the help of the Simulink model in MATLAB by comparing it to a traditional three-phase H8 inverter, considering $i_{Leakage},$ common-mode voltage (CMV), and the grid current total harmonic distortions (THD).