An Improved Dual-Stator Cup Rotor Interior Permanent Magnet Synchronous Machine

Abstract

Interior permanent magnet synchronous machine (IPMSM) is considered the best candidate for various applications such as traction and electric vehicle applications [1] [2]. In some cases, the IPMSM must have a high amount of torque density, power density, and wide speed range [3]. Recently, researchers have tried to increase the torque density of the vernier motor [4]. However, the vernier motor suffers a low power factor because of a high reluctance due to a large amount of leakage flux in the airgap [5] [6].In this draft, a new dual stator interior permanent magnet synchronous motor (DS-IPMSM) is developed, comprised of 72 slots and 8 pole-pairs. In the proposed design, a new inner stator is inserted using the unused space of the rotor. The slots of inner stator are shifted by half pole pitch to attain the maximum amount of torque and to aid the flux lines of an inner and outer stator with each other. Although the torque of the proposed design increases; however, due to a new stator, the amount of losses increases. Hence, instead of silicon steel (50A1000), a soft magnetic amorphous material (2605SA1) is used in the outer and inner stator to reduce the proposed design losses. Fig. 1 (a) shows the configuration of the proposed designs. To reduce the inner winding temperature, a cup rotor is presented, as shown in Fig. 1 (b). It shows that the inner stator is attached to the inner stator shaft to support it mechanically. The rotor is attached to the shaft in the form of a cup. Moreover, the bearing is used between the inner stator support shaft and output rotor shaft to align the rotor. Because of cup shape rotor configuration, the inner windings' heat is removed from one side of the motor. The slot area of the inner and outer stators is not the same because of its geometry. To reduce the inner winding temperature, the inner stator's current density is less than the outer stator. Therefore, the proposed design uses two inverters, as shown in Fig. 1 (c).The proposed DS-IPMSM using conventional steel sheets are presented by PD-1; however, the design using the amorphous material is presented by PD-2. Fig. 2 shows the analysis and comparison of the proposed and conventional designs. Fig. 2 (a) shows the back EMF of the conventional and proposed designs. Additionally, the back EMF of outer stator PD-1 and PD-2 is identical with the back EMF of a conventional single stator model. Fig. 2 (b) shows the dramatic improvement in the torque compared to the conventional model. In the end, the losses of PD-1, PD-2, and conventional design (CD) are compared. It shows that although the torque performance of the PD-1 and PD-2 increased by a huge amount as compared to conventional modal. Contrary, the losses are also increased by 25 % due to a second stator in the conventional design. The total losses in the conventional design are 556.3 W, and the losses in the PD-1 are 753.2 W. The efficiency of the conventional design is 98.45 %, whereas it is decreased to 98.39% due to an increase in motor losses. To cope with the problem of increased losses, the amorphous material is introduced to the stator; thus, decreasing the overall losses of the motor up to 493.5 W, resulting in increased efficiency of 98.90 %. **