Research on the Mechanism of Neutral-point Voltage Fluctuation and Capacitor Voltage Balancing Control Strategy of Three-phase Three-level T-type Inverter Gangui Yan*, Shuangming Duan†, Shujian Zhao*, Gen Li**, Wei Wu* and Hongbo Li*

Corresponding Author: School of Electrical Engineering, Northeast Electric Power University, China. ([email protected]) * School of Electrical Engineering, Northeast Electric Power University, China. ([email protected], [email protected], [email protected], [email protected])

 Abstract – In order to solve the neutral-point voltage fluctuation problem of three-phase threelevel T-type inverters (TPTLTIs), the unbalance characteristics of capacitor voltages under different switching states and the mechanism of neutral-point voltage fluctuation are revealed. Based on the mathematical model of a TPTLTI, a feed-forward voltage balancing control strategy of DC-link capacitor voltages error is proposed. The strategy generates a DC bias voltage using a capacitor voltage loop with a proportional integral (PI) controller. The proposed strategy can suppress the neutral-point voltage fluctuation effectively and improve the quality of output currents. The correctness of the theoretical analysis is verified through simulations. An experimental prototype of a TPTLTI based on Digital Signal Processor (DSP) is built. The feasibility and effectiveness of the proposed strategy is verified through experiment. The results from simulations and experiment match very well.
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