Study on Optimization of High-Speed Permanent Magnet Motor Rotors Structure with Tangentially Embedded Trapezoidal Magnets

In the context of small power high-speed permanent magnet motors, to meet the stress requirements of the rotor structure and simplify the production process, a tangentially embedded rotor structure based on trapezoidal magnets is proposed. Under the premise of meeting the basic design requirements of the motor, the rotor structure parameters are optimized. Finite element simulation is employed to analyze the effects of pole arc coefficient and rotor surface structure on cogging torque, average torque, and torque ripple. Structural stress checks are also conducted.

To further simplify the manufacturing and assembly process of the motor rotor, making it more suitable for high-speed applications, this study proposes a new tangentially embedded rotor structure based on trapezoidal magnets for small power permanent magnet motors using fractional-slot concentrated windings. With the stator using a segmented core structure, the rotor surface structure is optimized. Detailed analysis of how these rotor structure parameters influence torque ripple and average torque provides valuable reference for the design of such motors.

The motor adopts fractional-slot concentrated windings, and the stator uses a segmented assembly structure, facilitating automated winding processes and reducing production and processing costs. The rotor employs a tangentially embedded structure, with trapezoidal magnets directly inserted into the rotor slots. Compared to traditional tangential rotor structures, this new design reduces rotor core processing costs and simplifies assembly processes.

The optimization of the motor rotor structure is divided into two parts: optimization of the magnet structure parameters and the rotor surface structure parameters. The magnet structure parameters include the width of the lower base L1, the width of the upper base L2, and the height. The width of the lower base L1 and the height can be preliminarily determined based on the motor structure. The rotor's inner diameter is limited by the motor shaft, and considering the rotor processing and assembly requirements, the thickness of the rotor's inner ring is essentially fixed. Thus, the height of the magnets is predetermined and not considered an optimization parameter.

Without considering saturation, the volume of the magnets in the rotor is proportional to the permanent magnetic flux linkage of the motor rotor. To ensure the motor's torque output capability, the width of the lower base of the trapezoidal magnets must be maximized before optimizing the rotor structure. However, a larger lower base width results in a smaller connecting bridge width in the rotor core, affecting the rotor's stress. The principle for determining the lower base width of the magnets is to minimize the bridge width while ensuring the rotor stress meets the requirements. Once the lower base width is determined, finite element methods are used to define the dimensions of the upper base.

To ensure the mechanical strength of the motor rotor structure meets operational requirements, a three-dimensional model of the rotor structure is established using finite element methods. Applying the rotational inertia load of the motor's rated speed, the structural stress of the rotor is verified. Figure 2 shows the stress distribution cloud map of the motor rotor, indicating a maximum rotor core stress of 0.98 MPa. Given that the motor rotor material is silicon steel with a yield strength of 405 MPa, the maximum stress under these conditions is below the yield strength, confirming that the rotor structure meets mechanical requirements.

For high-speed small power permanent magnet motors, a tangentially embedded rotor structure based on trapezoidal magnets is proposed to simplify the production process. Finite element simulation results indicate that determining the magnet parameters requires comprehensive consideration of output torque, torque ripple, manufacturing processes, and errors. Optimizing the rotor's outer surface can further reduce torque ripple. The study shows that the new motor rotor structure significantly simplifies rotor processing and costs with minimal impact on torque performance, providing valuable engineering design experience and reference for optimizing this type of motor.