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 %.

**References:**

[1] Toba and T. A. J. I. t. o. i. a. Lipo, "Generic torque-maximizing design methodology of surface permanent-magnet vernier machine," vol. 36, no. 6, pp. 1539-1546, 2000. [2] F. Zhao, T. A. Lipo, and B. Kwon, "Magnet flux focusing design of double stator permanent magnet vernier machine," in Proc. COMPUMAG, 2013. [3] C. Liu, K. Chau, J. Zhong, W. Li, and F. J. I. T. o. a. s. Li, "Quantitative comparison of double-stator permanent magnet vernier machines with and without HTS bulks," vol. 22, no. 3, pp. 5202405-5202405, 2011. [4] Y. Wang, M. Cheng, M. Chen, Y. Du, and K. J. I. E. p. a. Chau, "Design of high-torque-density double-stator permanent magnet brushless motors," vol. 5, no. 3, pp. 317-323, 2011. [5] Y. Gao, R. Qu, D. Li, H. Fang, J. Li, and W. J. I. T. o. M. Kong, "A novel dual-stator Vernier permanent magnet machine," vol. 53, no. 11, pp. 1-5, 2017. [6] Y. Shi and T. J. I. T. o. M. Ching, "Power Factor Analysis of Dual-Stator Permanent Magnet Vernier Motor with Consideration on Turn-Number Assignment of Inner and Outer Stator Windings," 2020.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/c7c840fe8ec575c6432af4af42c1dc3c.jpg)
Fig. 1. (a) Geometry of the proposed and conventional designs; (b) Proposed dual stator cup type rotor; (c) Configuration of the inner and outer stator with the inverter.

![](https://assets.underline.io/uploads/markdown_image/1/image/98f1f27479c5fc2af1c76c2798071cee.jpg)
Fig. 2 (a) Back EMF of the conventional and proposed designs; (b) torque comparison; and (c) losses comparison.

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

Interior permanent magnet synchronous motor (IPMSM) are widely used for industrial and traction applications. IPMSM's are known for high efficiency, reliability, and power density. For certain applications, like traction in hybrid electric vehicles, a high torque and power density with wide range of speed is of high importance. The efficiency of the motors can be increased in two ways: (1) increasing the output torque of the motor or (2) reducing the losses of the motor. The torque of various motors has been improved by introducing dual rotor structure and dual excitation using the unused space in electrical machine [1, 2]. The authors in [3] compares number of electrical motors. A quantitative analysis of three types of dual stator flux modulation permanent magnet (PM) motors including magnetic geared motor, and vernier machine. High torque density has been achieved in [4] for double stator brushless PM motors. The design has also been optimized based on split ratio to achieve maximum torque density. Recently, a lot of research has been carried out on vernier permanent magnet motors (VPMMs). The authors proposed a dual stator VPMMs and performs a comparative analysis of proposed design with regular VPM [5]. The proposed design achieved high efficiency and torque density and lower cogging torque. Similarly, power factor based analytical and FEM analysis have been provided in [6] on dual stator VPMM. A high torque density VPMM with dual stator topology has been proposed in [7]. This draft proposes a drum type configuration of dual stator IPMSM with improvement in the torque density, rotor alignment and inner winding temperature compared to single stator IPMSM by utilizing the unused space in the motor. The new design of dual stator IPMSM with 16-poles and 72-slots in each stator are presented with the aim of improving the average torque and torque ripple for industrial and traction applications. The presented design is then compared with the commercial design of single stator IPMSM to show the direct and fair comparison. Fig. 1 (a) shows the proposed design (PD) and conventional design (CD). The CD uses tangential type rotor with rare-earth PMs mounted inside the surface of rotor. The conventional IPMSM offers a good torque capability, but this torque capability can be improved by utilizing the unused space of the rotor. For this purpose, another stator with the same number of stator slots has been added to replace the unused space of rotor resulting in a proposed dual stator IPMSM. To increase the torque of the proposed models, the inner stator is shifted by a half slot pitch to aid the flux lines of outer stator with the inner stator. As the slots of inner stator are aligned with the outer stator-teeth, hence the slot area of an inner stator is somewhat smaller compared to the outer stator-slots. The number of turns of the inner stator-slots are double compared to the outer stator-slots to reduce the current density and inner winding temperature. Due to the addition of an inner stator, the cup rotor is the suitable. However, the cup type rotor configuration decreases the rotor alignment because of only one bearing towards the rotor shaft. Hence, in this draft, the drum type rotor is introduced comprising of two bearing on both sides of stator to support the inner stator shaft and to improve the alignment of the rotor. Furthermore, to reduce the inner winding temperature, the curve-windows are introduced in the drum configuration for the air inlet to reduce the inner winding temperature as presented in Fig. 1 (b). The analysis is performed on the conventional and proposed designs to show the competency of the proposed model. The Fig. 2 (a), and (b) shows the back EMF of the inner and outer stator. Moreover, the back EMF of the conventional design is identical to the outer stator back EMF of the proposed model due to same geometry of outer stator. Moreover, the Fig. 2 (b) shows the substantial improvement in the average torque and torque ripple of the proposed model compared to the conventional design.

**References:**

[1] A. Toba and T. A. Lipo, "Generic torque-maximizing design methodology of surface permanent-magnet vernier machine," vol. 36, no. 6, pp. 1539-1546, 2000. [2] F. Zhao, T. A. Lipo, and B. Kwon, "Magnet flux focusing design of double stator permanent magnet vernier machine," in Proc. COMPUMAG, 2013. [3] C. Liu, K. Chau, J. Zhong, W. Li, and F. J. I. T. o. a. s. Li, "Quantitative comparison of double-stator permanent magnet vernier machines with and without HTS bulks," vol. 22, no. 3, pp. 5202405-5202405, 2011. [4] Y. Wang, M. Cheng, M. Chen, Y. Du, and K. J. I. E. p. a. Chau, "Design of high-torque-density double-stator permanent magnet brushless motors," vol. 5, no. 3, pp. 317-323, 2011. [5] Y. Gao, R. Qu, D. Li, H. Fang, J. Li, and W. J. I. T. o. M. Kong, "A novel dual-stator Vernier permanent magnet machine," vol. 53, no. 11, pp. 1-5, 2017. [6] Y. Shi and T. J. I. T. o. M. Ching, "Power Factor Analysis of Dual-Stator Permanent Magnet Vernier Motor with Consideration on Turn-Number Assignment of Inner and Outer Stator Windings," 2020. [7] N. Baloch, B.-i. Kwon, and Y. J. I. T. o. M. Gao, "Low-cost high-torque-density dual-stator consequent-pole permanent magnet Vernier machine," vol. 54, no. 11, pp. 1-5, 2018.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/e08dd9b8ef2a303357bf995cb72dbe36.png)
Fig. 1. (a) Geometry of the proposed and conventional designs; (b) Proposed dual stator drum type rotor; (c) Configuration of the inner and outer stator with the inverter.

![](https://assets.underline.io/uploads/markdown_image/1/image/5d21bfb823abd43232cbdc236793432a.jpg)
Fig. 2. Back EMF of the (a) Inner Stator; (b) Outer Stator; and (c) torque comparison.

 Dual Stator Drum Rotor Interior Permanent Magnet Synchronous Motor with Improvement in Torque Density, and Rotor Alignment

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