Multimaterial Topology Optimization Method of Surface-Mounted PMSM Rotor Poles Based on Variable Density Representation

Conventionally, the designers of electrical machines assume the employment of regular shaped magnets, such as rectangular, sector, or tiled-shapes. The geometry of magnet poles is fixed, and the design purpose is mainly to optimize the dimensional values. However, these regular shapes employed may not be the best choice, unavoidably limiting the final design result, and compromising the output performance of the electrical machines. An alternative scheme is to conduct topology optimization for rotor poles. By this method, the geometrical shape of magnets along with the iron core is no longer fixed, but automatically obtained through the optimal distribution of materials, such as iron, magnet, and air. It helps to achieve better optimization results with less shape constrains. Therefore, this article proposes a multimaterial topology optimization method based on variable density representation for surface-mounted permanent-magnet synchronous motor to obtain an optimal rotor pole pattern, and thus improve the output performance of electrical machines, especially the torque density, which is crucial in aerospace industry. The computational speed is increased by improving the objective function and the arbitrary volume constraints become clear by combining size and topology optimization. To validate the design method, theoretical, numerical and experimental studies are conducted. First, the operating principle, design variables, constrains, optimization objective, and procedure of the method are introduced in detail. Then, the optimization method is implemented into the rotor design of one surface-mounted electric machine, and the result is presented and discussed. Subsequently, the magnetic flux density and torque output of electric machine with the optimized rotor poles is compared with conventional design, and it shows that the former can achieve better output performance relatively. Finally, one research prototype of the electrical machine is developed, and experiments are carried out on torque output and back-electromotive force. The experimental results validate the optimization method.