A Hybrid Modulation and Control Strategy for Neutral-Point Voltage Control of Three-Phase Three-Level Rectifier

Except the inherent neutral-point (NP) voltage oscillation problem, the NP voltage imbalance of three-level rectifier are often caused due to the inconsistent characteristics of the switching device and DC capacitor and external disturbances, which increases the current harmonic and the voltage stress of switching device, and even damages the switching device and breaks down DC capacitor, seriously threatening the safe and stable operation of the system. Therefore, this paper proposed a hybrid modulation and control strategy for NP voltage control of T-type three-level rectifier. Firstly, the effect of different types of vectors on NP voltage is analyzed, and a finite time controller is designed, which can realize fast NP voltage balance control by changing the action time of P/N-type redundant small vectors. Further, the NP voltage mathematic model of rectifier system is established, and then the dwell time of three-phase state [O] is precisely adjusted to complete the NP oscillation suppression. As a result, the proposed method simultaneously achieves fast NP balancing and oscillation suppression of T-type rectifier system. Compared with the traditional NP voltage control methods, the proposed method has a faster NP balance speed, but also has a good NP oscillation suppression effect. Finally, the effectiveness of proposed method is verified by experimental results.