Research on the Reliability of NPC Three‐Level Inverter Based on Low Common‐Mode Voltage Modulation

As a core component for connecting renewable energy to the power grid, the Neutral Point Clamped (NPC) three‐level inverter suffers from issues such as common‐mode voltage and neutral‐point potential imbalance during operation, which can easily lead to insulation damage of grid equipment, degradation of output power quality, and other risks, seriously threatening the safety and reliability of the power system. To address these problems, this paper proposes an improved virtual vector modulation method. First, virtual vectors featuring low common‐mode voltage and neutral‐point voltage balancing characteristics are reconstructed, and the sector division and switching sequence design are optimized. Second, a time adjustment factor based on capacitor voltage deviation is introduced into the switching sequence to achieve active regulation of initial neutral‐point voltage imbalance. Finally, a simulation model is built in Simulink software for verification. The results show that the proposed modulation method yields smooth phase voltage waveforms, a total harmonic distortion of only 2.83% for the current, and a steady‐state neutral‐point voltage fluctuation of less than 0.13 V. Moreover, the method limits the peak common‐mode voltage to U dc /6, representing a 50% reduction compared to conventional modulation methods, thereby effectively enhancing the electromagnetic compatibility performance and operational reliability of the system.