Dual three-phase operation of single neutral symmetrical six-phase machine for improved performance

Among multiphase machines of different phase numbers, six-phase machine is one of the most popular and widely studied multiphase machine. By displacing the two three-phase windings with an angle of 30 degrees, 60 degrees or 0 degree, the machine can be configured as an asymmetrical six-phase, symmetrical six-phase or dual three-phase machine respectively. At the same time, the stator windings can be configured with either two or single neutral point. Till date, most discussions on six-phase machines focus mainly on two neutrals configuration, due to the simpler control requirements and better dc-bus utilization. Nevertheless, single neutral connection should be given due attention, considering the fact that this structure offers better fault tolerance. In this paper, the performance of symmetrical six-phase with single neutral point is investigated. It is shown that by altering the winding terminals' connections, a symmetrical six-phase machine can operate as a dual three-phase machine. By doing so, zero-sequence voltage injection becomes possible, hence giving improved performance.