Fault-tolerant control strategies for quad inverter induction motor drives with one failed inverter

In this paper post-fault-tolerant control strategies for quad-inverter multiphase-multilevel induction motor drives are investigated. More specifically, four standard 2-level three-phase voltage source inverters (VSIs) supplying the open-end windings of a dual three-phase induction motor (asymmetric six-phase machine) is considered, quadrupling the power capability of a single VSI with given voltage and current ratings. In healthy conditions, the control algorithm is able to generate multilevel voltage waveforms, equivalent to the ones of a 3-level inverter and to share the total motor power among the four dc sources in each switching period. This sharing capability is investigated under post-fault operating conditions, when one VSI must be completely insulated due to a severe failure on it. In this case, the conversion power units can operate with a reduced power rating by a proper modulation of the remaining three VSIs. The whole ac motor drive has been numerically implemented to verify the effectiveness of the proposed control strategies under healthy and post-fault operating conditions.