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 T-type inverter a very challenging task along with fault tolerant control. To deal with the problem of reduced degrees of freedom in pulsewidth 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 zero-sequence voltage for regulating the NP voltage. The solutions and detailed implementation procedures for various types of open-circuit faults are provided, and have been verified by experimental results.