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Comparative study between different SVPWM algorithms for NPC inverters in terms of common mode voltage reduction

Transformerless photovoltaic (PV) inverters offer several advantages in terms of weight and cost reduction as well as a higher efficiency compared to the topologies with transformers. However, the removal of transformers results in the establishment of a direct connection between the PV panels and the electrical grid which, consequently, leads to the generation of a leakage current. This current is flowing from the ground to the PV array through the stray capacitors causing undesirable distortions in the grid's output current in addition to several losses in the power conversion system. The high frequency variation of the common mode voltage (CMV) represents the main cause of this current. To overcome this issue, three innovative Space Vector Modulation (SVPWM) techniques were recently developed for NPC inverters with the aim to stabilize the CMV. These techniques are namely Long Medium Zero Vectors Modulation LMZV, Three Medium Vectors Modulation 3MV, and, Two Medium One Zero Vectors Modulation 2MV1Z. This paper evaluates the performance of the aforementioned techniques through a comparative analysis based on numerical simulations carried out on a three-phase three-level NPC inverter.