Common-Mode Voltage Suppression Strategy for T-Type Three-Level Inverters Based on Model Predictive Control and Virtual Vectors

This paper addresses the problem of high common-mode voltage (CMV) in the output phase voltages of three-level inverter systems controlled by conventional model predictive control (MPC) algorithms. To mitigate this issue, an improved MPC method based on virtual vectors is proposed. The approach synthesizes a set of virtual vectors by combining medium vectors that inherently produce zero CMV, which are used to replace the small vectors responsible for generating high CMV during voltage modulation. This substitution effectively reduces the overall CMV generated by the inverter. Additionally, a five-segment modulation strategy is introduced, incorporating zero vectors alongside the medium vectors to further enhance modulation performance. This scheme contributes to reducing the total harmonic distortion (THD) of the grid-side current and stabilizes the output current waveform. Simulation results demonstrate that the proposed virtual-vector-based MPC method can significantly lower both the CMV and THD, while maintaining the quality of the output current, thus improving the safety and reliability of the inverter system.