Fault-Tolerant Control for Neutral-Point-Clamped Converter Based on a Fourth Asymmetric Leg

A new fault-tolerant four-legged three-level topology for the neutral-point-clamped (NPC) converter by adding an additional two-level leg is proposed in this paper. And the corresponding fault-tolerant control strategy on the basis of SVPWM control is also presented. Under normal operation mode, the fourth leg can help in removing the lowfrequency NP voltage fluctuation of converters. While an opencircuit or short-circuit failure of power switches for the converter occurring, three different fault-tolerant solutions and a novel asymmetric modulation strategy based on SVPWM are applied to guarantee the safe operation of converters. These proposed solutions are focused on not only endowing the system with fault-tolerant ability, but also improving the transient performance of the system during fault reconfiguration. Simulation results validate the proposed fault-tolerant control strategy and scheme.