Common-mode voltage reduction method for three-level NPC converter

It is well known that commonly used neutral-point clamped (NPC) three-level inverter modulation schemes generate common-mode voltages. Common-mode voltages may cause motor shaft voltages and bearing currents and electromagnetic interference (EMI). Therefore, it is important to reduce the common-mode voltage in power converter, especially at high voltage with large capacity. This paper introduces a new algorithm for approaching the reference vector, which is easy to be realized. Based on the analysis of the characteristic and rule for the Three-level NPC converter, each voltage space vector and redundancy states were discussed in detail, and the relationship between redundancy switching states and common-mode voltage was found. At the same time a common-mode voltage reduction method for Three-level NPC converter was proposed. The simulation results are provided to verify the proposed method.