Abstract: Aiming at the internal tube fault of T-type three-level inverters,this paper presented a fault-tolerant control strategy based on discontinuous pulse width modulation (DPWM).This strategy can not only operate safely and reliably after single-phase,two-phase and three-phase internal tube faults,but also minimize the fluctuation of neutral point voltage.Firstly,the control method of neutral point voltage is analyzed,and two modulation methods are put forward according to the influence of fault on current direction.Secondly,the necessary condition of system balance in fundamental wave period is explored,and the optimal clamping method in non-fault state is found.Thirdly,according to fault type and modulation method,the selection of clamping methods under various fault states is detailed analyzed,and the DPWM fault-tolerant control with minimum neutral point voltage fluctuation is realized.Finally,the feasibility and superiority of DPWM fault-tolerant control are verified by experiments.

Key words: T-type three-level inverter, discontinuous pulse width modulation (DPWM), fault-tolerant control, three level converter