A Unified Fault Tolerant Control and Neutral-Point Voltage Balance Strategy for Three-Level T-Type Inverters under Double Signal PWM

Ensuring a high reliability of three-level T-type inverters in case of open-circuit faults is of great significance for their industrial applications, which can be achieved by adopting a high performance open-circuit fault tolerant control. However, the faulty switches would reduce the available switching states, making the neutral-point (NP) voltage balance in three-level Ttype inverter a very challenging task along with fault tolerant control. To deal with the problem of reduced degrees of freedom in pulse-width modulation (PWM) operations when open-circuit fault occurs, a unified approach by using zero-sequence voltage injection along with double-signal PWM is proposed in this article, which has the ability to flexibly adjust the dwell time of zero voltage level for NP voltage balance under open-circuit faults, creating a new degree of freedom in addition to zerosequence voltage for regulating the NP voltage. The solutions and detailed implementation procedures for various types of opencircuit faults are provided, and have been verified by experimental results