Design of a 7-phase Surface-mounted PM machine with tooth-concentrated winding

The paper addresses the design of a seven phase Surface-mounted Permanent Magnet (SPM) machine with tooth-concentrated winding. As the fundamental winding factor is lower than the third, the rated control strategy aims at generating a third harmonic current component greater than the fundamental. For this control, the magnet layer is designed with the constraint of maximizing the average torque and minimizing the ripple torques. Solutions where the pole consists of several identical radially-magnetized magnets (regularly space shifted along the pole arc) are explored: designing the rotor with two identical radially magnetized magnets that cover about three-quarters the pole arc appears as the best solution. In addition, fifth harmonic current injection can be performed to slightly enhance the torque without increasing the ripples. 2D FEA confirms these results. Furthermore, according to analytical approach, positive impacts on some parasitic effects (as the radial stress and the magnet losses) are expected.