Fault-tolerant operation of a nine-phase induction machine with open phases

Multiphase machines have several advantages, specially the reliability, when compared to three-phase machines and are attractive for some applications. When one or more phases are opened, the motor is still capable of starting up and running. Despite it, post-fault currents can be reconfigured to improve the operation, by producing a balanced magnetomotive force. Consequently, the torque pulsation can be eliminated. For this purpose, this paper develops two methods. The first method is very intuitive and provides the lowest stator copper losses. The second one produces the same current magnitudes for all the remaining phases. For one open phase, to produce the same rated torque, the first method causes a slight increase in stator copper losses of 16.6 %. The second method allows all the healthy currents to increase just 16.19 % in magnitude. This value is lower than the increase verified for machines of an original number of phases between 3 and 7, with an open phase. Postfault currents reconfiguration in the case of two open phases is also addressed. Simulation results show the elimination of torque pulsation by applying the proposed methods. Finite element analysis also evaluates the effectiveness of the Methods.