Study of a particular magnet shape for a five-phase surface-mounted PM machine

This paper investigates the adaptation of the magnet shape for a low speed surface-mounted PM synchronous machine. For the considered marine propulsion application, the reduction of the ripple torques is of critical importance which explains the choice of a five-phase winding. From a multi-machine modelling of the five-phase machine, a reference back-emf spectrum is determined as design objective. To fulfill this requirement, it is decided to adapt the magnet shape. To perform this task, an analytical air gap field computation is developed and validated by using a finite element analysis software (FEMM). A particular trapezoid magnet shape is then determined for the case study. In comparison with the initial rotor made with fully pole-pitch magnets, the new magnet shape almost eliminates the pulsating torque. Furthermore, the average torque to magnet volume is improved which can be considered as a better use of the magnet material.