An Improved Fault-Tolerant Method Based on Floating Capacitor Voltage Balance for Hybrid T²C-HB Converter

Hybrid multilevel converters have gained more popularity due to their unique superiority. Thus, the T 2 C-HB converter is adopted in this article which consists a T-type converter (T 2 C) and three H-bridge (HB) cells. This hybrid converter combines the advantages of these two topologies and can output the same voltage level by adopting fewer switching devices compared with other multilevel converters. However, due to the high switching frequency of the HB switches, they may fail in practice which will cause serious deterioration in the output waveform and compromise the reliability of the entire system. Thus, a fault-tolerant control method based on floating capacitor voltage balance is proposed in this article. First, based on the level-shifted pulse width modulation (LS-PWM) method, the fault-tolerant control is accomplished by modifying the three-phase reference voltage. Second, a strategy which bypasses the HB equivalently when the absolute value of output voltage exceeds the peak value of the dc-link voltage is proposed to balance the floating capacitor voltage. Besides, the three-phase reference voltage is modified again utilizing the similar idea in order to balance the line voltage. Consequently, the line voltage remains unchanged during postfault operation and the floating capacitor voltage can restore balance without excessive fluctuation. Finally, the feasibility and correctness of the proposed method are verified by simulation and experimental results.