Choice of Phase Number for a Multiphase Traction Motor to Meet Requirements on Fault Tolerance

The electrification of vehicles and their autonomous operation is a current topic. The resulting high requirements on reliability for safety-critical applications leads to the need of fault tolerance in order to provide fail-operational modes. One possibility to increase fault tolerance of electric traction drives is increasing the number of phases of the machine, since a performance degradation is possible while using multiple phases. This paper targets a method to find the optimal number of phases considering fault tolerance based on the requirements on system performance. It is shown that a higher phase number is not always the best choice regarding fault tolerance and reliability. This fact is depending on the performance demand after failure required in order to assure a fail-operational mode.