A Simple Method for Common-Mode Voltage Reduction and Neutral-Point Potential Balance of Back-to-Back Three-Level NPC Converters

Common-mode voltage (CMV) is harmful to the motor bearing in converter systems. In order to reduce the high amplitude CMV and balance the neutral-point potential (NPP) of back-to-back three-level neutral-point clamped (NPC) converters, a simple dual-side zero-sequence voltage (ZSV) injection method based on carrier-based pulse-width modulation (CBPWM) is proposed in this paper. Two optimal ZSVs are injected into the rectifier side and inverter side respectively, which can reduce the amplitude of CMV to 1/6 of the DC-bus voltage and balance the NPP effectively at the same time. This proposed method based on CBPWM is much easier to be implemented compared with the SVPWM-based method. Experimental results demonstrate the effectiveness of the proposed method.