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 low-frequency NP voltage fluctuation of converters. While an open-circuit 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.