Abstract
The irreversible demagnetization of permanent magnets causes the deterioration of the performance in permanent magnet synchronous motors (PMSMs), which are used for electric vehicles. NdFeB, which is the permanent magnet most commonly used in PMSMs for electric vehicles, is easily demagnetized at high temperatures. Because traction motors for electric vehicles reach high temperatures, and a high current can be instantaneously applied, permanent magnets of PMSM can be easily demagnetized. Therefore, it is important to study the demagnetization phenomenon of PMSMs for electric vehicles. However, since the demagnetization analysis procedure is complicated, previous studies have not been able to perform optimization considering demagnetization characteristics. In this study, we optimized the shape of a PMSM for electric vehicles by considering the demagnetization characteristics of permanent magnets using an automated design of experiments procedure. Using this procedure, a finite element analysis for each experimental point determined by a sampling method can be performed quickly and easily. The multi-objective function minimizes the demagnetization rate and maximizes the average torque, and the constraints are the efficiency and torque ripple. Various metamodels were generated for each of the multi-objective functions and constraints, and the metamodels with the best prediction performance were selected. By applying a multi-objective genetic algorithm, 1902 various optimal solutions were obtained. When the weight rate of the demagnetization rate to the torque was set to 0.1:0.9, the demagnetization rate and average torque were improved by 4.45% and 2.7%, respectively, compared to those of the initial model. The proposed multi-objective optimization method can guide the design of PMSMs for electric vehicles with high reliability and strong demagnetization characteristics.
Highlights
As traction motors for electric vehicles, permanent magnet synchronous motors (PMSMs) have been widely used owing to their high power density and efficiency
We optimized the shape of a PMSM for electric vehicles to minimize the demagnetization rate of permanent magnets and maximize the torque of the motor
Fifty experimental points were determined by optimal Latin hypercube design (OLHD), and an automated design of experiments (DOE) procedure combined with finite element analysis (FEA) and optimization was applied
Summary
As traction motors for electric vehicles, permanent magnet synchronous motors (PMSMs) have been widely used owing to their high power density and efficiency. In most PMSMs, NdFeB series magnets are used. These magnets have high residual magnetic flux density and coercivity, they have the disadvantage of being demagnetized at high temperatures. When a permanent magnet is demagnetized irreversibly, the motor performances, such as the torque and efficiency, are deteriorated. This is problematic because traction motors for electric vehicles work at high temperatures and high currents, so the permanent magnet is demagnetized. It is important to study the demagnetization phenomenon of PMSMs for electric vehicles
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