Unbalanced three-phase control using offset-voltage for H-bridge multilevel inverter with faulty power cells

In this paper, unbalanced three-phase control method is proposed to increase the fault tolerance for H-bridge multilevel inverter under the conditions of faulty power cells. It is possible to generate a balanced three-phase line-to-line voltage by phase-shifting and bypassing faulty power cells with a minimum voltage drop. In this method, the concept of voltage modulation by using offset voltage is applied to an unbalanced three-phase control method. Especially, it is possible to use the maximum output voltage of inverter by adopting the real time unbalanced control method of phase voltage irrespective of the fault location and the number of disabled power cells. Also, the feasibility of the proposed method is proved by the H-bridge multilevel inverter test composed of 7-level.