Fault-Tolerant Control Strategy for T-Type Three-Level Inverter with Neutral-Point Voltage Balancing

In this paper, an improved fault-tolerant control strategy with neutral-point (NP) voltage balancing for T-type three-level inverter when an open-circuit fault occurs is proposed. Different from the existed fault-tolerant control strategies, this method can not only restore the output current but also balance the neutral-point voltage. The proposed strategy is illustrated by dividing fault into two conditions: the faulty condition of half-bridge switches and NP switches. When a half-bridge switch fails, the NP voltage is controlled by adjusting the amplitude of the three-phase reference voltages. In cases of the open-circuit fault in a NP switch, the balance and oscillations of the neutral-point voltage are considerably controlled by adding a proper offset value to switch turn-on times of three-phase reference voltages. The presented method does not require any additional hardware and complex calculations. Experimental results show the performance of the proposed control strategy.