A Fault-Tolerant Control Strategy for T-Type Three-Level Rectifier With Neutral Point Voltage Balance and Loss Reduction

This article presents a fault-tolerant control strategy when an open-circuit fault (OCF) occurs in T-type three-level rectifiers, in which the neutral-point (NP) voltage balance and loss reduction are considered simultaneously. When an OCF occurs, one fundamental period is classified into two time intervals: the normal time interval (NTI), and abnormal time interval (ATI). In the NTI, a time-offset is utilized to achieve the NP voltage balance and loss reduction within a switching period. Aside from this, the extra switching event between the switching periods is also reduced by employing an appropriate carrier. In the ATI, the proposed method is explained by dividing fault into two conditions: the faulty condition of half-bridge switches, and NP switches. When OCF occurs at HB switches, a restriction of the time-offset is introduced during the ATI. While, if an OCF occurs at NP switches, the two-level modulation strategy is applied in the faulty phase during the ATI. Besides, the principle of carrier selection of the faulty phase is changed correspondingly to avoid the extra switching event. The performance of the fault-tolerant control with respect to the NP voltage balance and loss reduction is illustrated and verified by the simulation and experimental results.