This work focuses on the analysis of rotor geometry parameters and added flux barriers design to improve the anti-demagnetization capability of fractional slot concentrated windings interior permanent magnet motor (IPM) for electric vehicle (EV) traction applications. A 2.5kW V-shape IPM motor (12 slots and 8 poles) is designed to achieve high torque density and wide constant power speed range (CPSR), which is selected to study in this paper. The influence of rotor geometry parameters variation (such as the magnet position and angle, the width and thickness of magnet) on the relation of characteristic current (Ich) and demagnetization in wide-speed range operation is firstly investigated under high-temperature and high current density operation. Then, the impact of added flux barriers design on the anti-demagnetization capability of the IPM motor is evaluated. The analysis results show that the increase of magnet angle of V-shape IPM would improve the anti-demagnetization capability but would reduce Ich; meanwhile, the increase of magnet thickness would increase Ich and simultaneously improve the anti-demagnetization capability. In addition, the added flux barriers design significantly affects the anti-demagnetization capability of the V-shape IPM motor. Finally, a unique multi-objective genetic algorithm is applied for the rotor geometry optimization of the V-shape IPM motor to achieve good anti-demagnetization capability, excellent CPSR, and high efficiency. Finite element analysis (FEA) is used for evaluation, and experiments are conducted to validate the analysis. I.Introduction In order to achieve the power and torque requirements of an EV motor, magnetic loading and electrical loading need to be improved. However, due to the saturation of the electrical steel sheet, a high current density design is unavoidable. In a high current operating environment, due to the high temperatures and strong armature magnetic field presented in the motor, the magnetic field provided by the magnet is usually reduced. Under these conditions, the magnet can suffer from irreversible demagnetization. For this reason, a higher current will be required to achieve the originally expected performance. To avoid this type of problem is very important to design a motor with high resistance to demagnetization for the safety and reliability of the product. II.Target Models and Analysis Method A 2.5 kW fractional slot concentrated windings V-shape IPM motor with 12 slots and 8 poles is applied to study here. The rotor configuration of V-shape IPM with the design parameters is shown in Fig. 1(a) and the design of different flux barriers is presented in Fig. 1(b). Finite element analysis (FEA) is utilized to comprehensively evaluate the impact of rotor geometry parameters variation and design characteristic of added flux barriers on the relation of characteristic current (Ich) and the anti-demagnetization capability of the V-shape IPM motor. The details will be reported in the full paper. III.Analysis Results and Experiments Fig. 2 shows the comparison of magnetic flux density distribution on PM without and with added flux barriers design during no-load and load conditions. It can be seen that the added flux barriers design significantly affects the demagnetization risk on PM. Fig. 3 presents the comparison of back EMF of V-shape IPM motor without and with the added flux barriers design before and after demagnetization. The result shows that the added flux barriers design significantly reduces the demagnetization risk on PM of V-shape IPM motor. Fig. 4(a) shows the rotor configuration after optimized of the V-shape IPM motor which is made as a prototype for validating the analyses. Fig. 4(b) shows the comparison of back EMF of V-shape IPM motor between the simulation and experiment at 1500 rpm speed. The phase voltage of back EMF is 13.45 V in the simulation, thus the peak-to-peak of back EMF is 23.3 V; meanwhile, the measured back EMF is 24.8 V. The error between the simulation and experiment is only 6%, thus the analysis results are reliable. Fig. 5(a) shows the torque and power versus speed curves of the V-shape IPM motor. The output torque of the motor is 9.17 Nm for simulation and 8.9 Nm for the experiment, respectively. Fig. 5(b) presents the comparison of back EMF of IPM motor before and after demagnetization in the experiment. The back EMF of the motor after fully demagnetized magnets only has an error of 2%. The accuracy of the simulation is thus verified by the experiment results. Detail analysis and experiment will be reported in the full paper. IV.Conclusion This digest has analyzed the impact of rotor geometry parameters variation and design characteristic of added flux barriers on the performance and the anti-demagnetization capability of fractional slot concentrated windings V-shape IPM motor. The added flux barriers design significantly affects the performance and anti-demagnetization capability of the V-shape IPM motor. The detail analysis and experimental results will be reported in the full paper.

**References:**

[1] H. Chen, R. Qu, J. Li and D. Li, "Demagnetization Performance of a 7 MW Interior Permanent Magnet Wind Generator With Fractional-Slot Concentrated Windings," IEEE Transactions on Magnetics, vol. 51, no. 11, pp. 1-4, Nov. 2015. [2] K. Imamura, M. Sanada, S. Morimoto, and Y. Inoue, "Improvement of Demagnetization by Rotor Structure of IPMSM with Dy-Free Rare-Earth Magnet," in Proceeding of IEEE International Electrical Machines and Systems Conference, Sapporo, 2012.

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 Design and Optimization of Fractional Slot Concentrated Windings Interior Permanent Magnet Traction Motor Considering Anti-Demagnetization Capability

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Design and Optimization of Fractional Slot Concentrated Windings Interior Permanent Magnet Traction Motor Considering Anti-Demagnetization Capability

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