Comparison of two 5-phase Permanent Magnet machine winding configurations. Application on naval propulsion specifications.

This paper describes a design approach dedicated to multiphase surface mounted permanent magnet SMPM machines. Based on a vectorial multimachine modelling that splits the multiphase machine in a set of magnetically independent fictitious machines, this approach allows to determine a pertinent control topology in case of pulse width modulation (PWM) voltage source inverter (VSI) supply. Design rules to reduce the parasitic currents and the torque ripples can also be deduced. This method is applied to improve the adaptation of a naval propulsion PM 5-phase machine to its converter. From a classical initial design with fully-pitched concentrated winding, the machine is improved by performing a new fractional-slot winding which drastically decreases the cogging torque. To make this winding possible, only the pole number has been modified (from 16 to 14). Iron, magnet and copper volumes are unchanged. For the two machines, a vector control to have sinusoidal currents is considered. For a same average torque, a decrease of the copper losses (less 35%) is observed mainly due to the reduction of parasitic currents. Furthermore a significant diminution (less 36%) of the torque ripples is obtained as a consequence of weakened interactions between the harmonics of the electromotive force and current. In comparison with the full-pitched concentrated winding, the fractional-slot winding improves significantly the torque quality (better density and lower ripples) and makes the current control easier without over-sizing the electronic components.