Neutral-Point Potential Balancing Control for Three-Level NPC Rectifiers by Injecting Zero-Sequence Voltage

摘要

A significant problem with neutral-point-clamped (NPC) three-level rectifiers is the fluctuation in the neutral-point (NP) potential. In this paper, the mathematical model of NP potential in αβo coordinates is founded firstly, as a degree of freedom, the function of the o-axis component (zero-sequence component) of the control input is revealed for the balancing of the capacitors voltages. And a new control method which can eliminate completely the fluctuation of NP potential is presented, the analytical method to accurately calculate the zero sequence voltage and the inherent relationship for NP potential balancing control are given by theoretical calculation. In order to obtain the signs of reference voltages, the paper also analyses the real-time property of the control method and accordingly the real-time algorithm. Simulations of the system validate the proposed model, theoretical analysis and good performance of the proposed control strategy.