A Comprehensive Study of Common Mode Voltage Reduction and Neutral Point Potential Balance for a Back-to-Back Three-Level NPC Converter

A comprehensive study of common-mode voltage (CMV) reduction and neutral point (NP) potential balance for a back-to-back three-level NPC converter is proposed in this article. Based on phase-disposition PWM, a zero-sequence voltage (ZSV) injection method is adopted. The ZSV is divided into two parts: ZSV for CMV reduction, and ZSV for NP potential balance. The specific selection method is discussed in detail in this article. After using the proposed ZSV injection method, the CMV can be reduced to 1/6 of the dc bus voltage, and the NP potential fluctuations can also be suppressed. Simulation and experimental results verify the effectiveness of the proposed method.