I. Introduction Permanent magnet (PM) motors have been widely used in electric vehicles due to its high torque/power density and high efficiency. Yet, a relatively constant airgap magnetic field of PM motors may limit the speed range to large extent, which is still the shortfall for the further applications in EVs. In recent years, a type of variable-flux-leakage PM motor is emerged, which draws intense interest from academics of motor field because of the achievement of flux-controllable capability [1]. In this type of motors, the leakage flux can be varied by designing flux bridge and magnetic barrier, and it can be controllable through the change of q-axis current of winding. Compared with conventional PM motor, the variable flux is essentially derived from active design of flux leakage. So, the magnetic field distribution of leakage flux is sensitively linked to the flux controllability. Then, in [2], a variable-flux-leakage PM Motor is proposed, where a unique flux leakage path is purposely considered by arranging the PM position and magnetic barrier reasonably. The results indicate that the relatively obvious capability of flux regulation is achieved by effectively controlling the leakage flux. Yet, in flux-regulated process, the magnetoresistance characteristic of the motor is changed appreciably caused by the variation of leakage flux. It means that different flux-leakage operation modes of the motor will bring the characteristic differences of output torque. For instance, the varied main flux caused by leakage flux greatly leads to the change of PM torque, while the variation of inductance characteristics induced by magnetic saturation bring about the change of reluctance torque. Therefore, to the variable-flux-leakage PM motor, it is necessary and meaningful to comprehensively consider the torque characteristics at various flux-leakage operation modes. And, in this case, how to realize the optimal distribution of different torque components is full of challenge. In this paper, a flux-controllable permanent magnet (FC-PM) motor is proposed. The key of the study is to conduct torque characteristics analysis and optimization by combining with typical operation conditions. Then, based on different flux-leakage operation modes, a reasonable optimization strategy considering torque components is developed. The results reveal that, based on optimization, the comprehensive torque is effectively improved while maintaining a desirable flux regulation region. II. Motor Topology and Simulation Result Fig.1(a) shows the structure of the FC-PM motor with independent separated flux leakage branches. It can be seen that the q-axis is equipped with multi-layer arc and ellipse magnetic barriers to obtains good magnetic flux leakage controllable performance, which further broadens the motor speed regulation range. Fig.1(b) shows the magnetic density distributions of the FC-IPM motor under different flux-leakage operation modes, and the corresponding requirements of torque components distribution are listed. In Fig. 2(a) and (b), the sensitivity of each design variable to different design objectives is evaluated, and three variables with high sensitivity are selected for further optimization. Fig. 2(c) and (d) show the result of torque distribution under different flux-leakage Operation Modes, which can be seen that through the multi-objective optimization proposed in this paper, the torque quality is improved as expect. The torque performances and corresponding torque component distribution under different modes are shown in Fig.2 (d) and (f). The prototype of proposed FC-IPM motor and corresponding experiment result of back-EMF are shown in Fig. 2(g) and Fig. 2(h), respectively. In additional, III. Conclusion In this paper, a FC-PM motor is purposely designed, and a multi-objective optimization method is also newly proposed, where the optimal distribution of torque components under different flux-leakage operation modes is considered. Through optimization, the PM torque becomes the main component under less flux leakage, and the reluctance torque as the main component under more flux leakage. It means that the optimal proportion of different torque components of the FC-PM motor is realized. Both the simulation and experiment results not only verify the reasonability of the proposed motor but also confirm the effectiveness of the proposed optimization method. The more electromagnetic performance analysis and experimental results will be provided in the full paper.

**References:**

[1] X. Zhu, W. Wu, S. Yang, Z. Xiang and L. Quan, in IEEE Transactions on Energy Conversion, vol. 33, no. 4, pp. 2260-2269, Dec. 2018. [2] T. Kato, M. Minowa, H. Hijikata, K. Akatsu and R. D. Lorenz, in IEEE Transactions on Industry Applications, vol. 51, no. 5, pp. 3811-3821, Sept.-Oct. 2015.

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 Torque Characteristics Investigation of A Flux-controllable Permanent Magnet Motor Considering Different Flux-leakage Operation Modes

*Session Chair: Rong-Jie Wang, Stellenbosch University*

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Torque Characteristics Investigation of A Flux-controllable Permanent Magnet Motor Considering Different Flux-leakage Operation Modes

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