Natural Fault-Tolerant VV-DTC for Healthy and Postfault Operation of an Asymmetrical Six-Phase Induction Machine Drive System With Single Neutral

This article discusses a virtual vector-direct torque control (VV-DTC) strategy for an asymmetrical six-phase induction machine drive system that makes use of an isolated single neutral. The objectives of the proposed method are eliminating low-frequency 3{\text{rd}} and 5{\text{th}} current harmonic components during healthy operation and providing fault-tolerant operation when the system is submitted to open-phase faults. By means of simulations and experiments, it is shown that the proposed method provides proper healthy and postfault operation when the system is submitted to open-phase faults in one, two or three phases, and the natural fault-tolerance feature is observed, since the control algorithm does not need to be reconfigured when the system migrates from healthy to postfault operation. At last, for both healthy and postfault modes, satisfactory low rotor speed operation is also attested, as well as suitable dynamic response when the drive system undergoes speed and torque step changes.