Design of multiphase induction motor for electric ship propulsion

When high power levels are required, the use of six-phase machines is one of the alternatives in industry. For variable speed applications, power electronic converters are used to drive the machine and the power level of the converter has to match the machine and the load. Limitations on the power level of semiconductor devices establish a barrier to the increase of converter ratings. To get rid of this limitation, multilevel converters have been developed where switches of reduced rating are used to construct high power level converters. Instead of multilevel converters, multi-phase machines are used: By dividing the handled power between multiple phases, generally more than three, high power levels can be achieved even using limited rated power electronic converters. Also the efficiency and torque is improved as an added advantage compared to multilevel converter and three phase counterpart. This paper discusses in detail about the novel design of six phase induction motor applicable to six phase machine with any arbitrary angle of displacement between the two three phase winding sets whereas all control schemes have been developed for 30 degrees displacement.