New line currents and neutral point balancing technique of three-level three-phase NPC converter

In this paper, the authors propose a new technique applied to three level NPC rectifier which permits line currents and neutral point balancing while maintaining unity power factor operation. The idea of line current balancing is based on the symmetrical components theory. Indeed, In order to balance three phase line currents, the negative sequence component of fine current references is eliminated. First, we compute for the active power component in synchronous reference frame, and then dq/abc transformation is applied to generate the equivalent fine current references. These references are thereafter used to estimate both positive and negative sequences using the complex plan. An inverse transformation imposing zero negative sequence leads finally to balanced current references which are used to control the rectifier switches using SPWM. The obtained simulation results confirm the validity of the proposed algorithm in both steady state and dynamic regimes.