The improved voltage balancing control for high power three-level NPC rectifiers under standby and light load conditions

The voltage balancing control (VBC) ability of the three-level neutral point clamped (NPC) rectifier under standby and light load conditions is weakened because the phase current direction changes very quickly and the self-balancing ability of conventional space vector modulation (SVM) is not ensured. In order to improve the VBC ability, current prediction method together with the multi-sampling technique is proposed to obtain the current polarity information of next PWM carrier period so as to regulate the time assignment of small vectors correctly. Meanwhile, in order to improve the self-balancing ability of SVM for relieving the burden of VBC, the synchronized NP-SVM is adopted and one synchronization method is proposed in this paper. All these analyses and the effectiveness of the proposed method are firstly verified by simulation results, and are validated further in a 75kVA laboratory prototype.