Research on Optimal Fault-Tolerant Technique for Three-Level Active-Neutral-Point-Clamped Inverter Based on Switching Modulation Wave

The traditional fault-tolerant technique based on space vector PWM can realize the fault-tolerant operation of three-level active-neutral-point-clamped (ANPC) inverter without adding hardware equipment, but it has the defects of two-level jump, unbalanced neutral-point voltage, and output current distortion. To solve the above problems, this paper first analyzes the effective switching state of three-level ANPC inverter in the case of open-switch fault, and then deduces the modulation wave that can control three-phase only output negative, zero levels and positive, zero levels. On this basis, the modulation wave is selected according to the direction of the fault phase current, and the effective switching state is used to output the three-phase level, thus the optimal fault-tolerant technique based on switching modulation wave (OFTBSM) and its neutral-point voltage balance control strategy are proposed. Finally, the fault-tolerant performance, neutral-point voltage fluctuation, and harmonic performance of OFTBSM are analyzed. Simulation and experimental results prove that OFTBSM can make the ANPC inverter operate smoothly when the single-phase up to four switching devices have open-switch fault at the same time, and can prevent two-level jump, reduce current harmonics, and control the neutral-point voltage balance. In addition, OFTBSM also has the advantages of strong robustness, simple calculation, and convenient implementation. © 2022 Chinese Machine Press. All rights reserved.