Reluctance Torque and Output Improvement of Concentrated Winding IPMSM With Asymmetric Slit

In recent years, the interior permanent magnet synchronous motors of distributed winding are widely used as full-size traction motors in both hybrid electric and electric vehicles. Since the reluctance torque of concentrated winding motors is smaller than that of distributed winding motors, concentrated winding suffers a disadvantage in terms of torque and power densities compared to distributed winding. In this article, we discuss the small reluctance torque of concentrated winding from flux-line diagrams using 2D-FEA and conclude that such torque is caused by the balance of the magnetic attraction force at a specific rotation angle. We propose an asymmetric rotor structure to avoid the balance of the magnetic attraction force, and 2D-FEA results show a 1.9% total torque increase compared to a conventional symmetric rotor structure. Furthermore, the asymmetric rotor structure can improve the maximum output by 9.0% if the maximum torque was identical as conventional structure. Finally, a prototype of the asymmetric rotor structure was made and tested.