Optimal Design Of Permanent Magnet Brushless DC Motors Based On Bonded Magnetic Rings

The rapid development and performance improvement of rare earth permanent magnet materials contribute to enhancing the performance of permanent magnet brushless DC motors and expanding their application areas.However,this progress also introduces complexities into the design process,as the high magnetic energy of these materials increases the motor’s output torque and power density.Nevertheless,it inevitably leads to an increase in torque pulsation,which adversely affects the motor’s NVH(Noise,Vibration,and Harshness)performance and limits its application in certain high-precision fields.To address these challenges,this thesis investigates the optimal design of the body structure of a permanent magnet brushless DC motor based on bonded magnetic rings.The primary objective is to improve its overall performance and facilitate its effective utilization in high-precision applications.Firstly,the crucial design indicators of the motor system are determined based on the specific requirements of permanent magnet brushless DC motors.Subsequently,by combining empirical equations from permanent magnet motor design and electromagnetic design theories,the stator and rotor key parameters of the motor are compared and analyzed under various scenarios,thereby achieving the initial design of the motor’s body structure.Secondly,a multi-parameter and multi-objective optimization method for permanent magnet motors is proposed to further enhance the motor’s performance,taking into consideration the characteristics of bonded magnetic rings.Using the equivalent magnetic circuit method,the theoretical equation for air gap magnetic density is derived.The optimization variables are selected based on their significant impact on the air gap magnetic density,while the optimization objectives are determined in accordance with the motor’s performance requirements,with the constraints being the motor’s vibration noise and permanent magnet demagnetization resistance.To establish the sample dataset for the optimization variables and targets,an orthogonal experimental table is employed.Subsequently,a quadratic response surface regression model is fitted,and the optimal parameter solution is determined using an ant colony algorithm.The optimization scheme is then applied to fabricate a prototype,which undergoes experimental testing.The results demonstrate that the motor’s performance aligns with the design specifications.However,the challenge of significant vibration and noise remains,necessitating further investigation.Finally,in order to mitigate the torque pulsation of the motor,the optimal design of the bonded ring structure is analyzed to examine the influence mechanism of segmented diagonal pole and pole-arc cutting pole structures on the motor’s torque pulsation.Leveraging the advantages of the high degree of freedom provided by bonded ring forming,the theoretical equation for slot torque is derived using the energy method for the slant pole structure.The optimum slant pole angle for the motor is analyzed,designed,simulated,and experimentally verified specifically for the segmented slant pole structure.Concurrently,to further improve the utilization rate of the permanent magnet material,a study is conducted on the performance of the cut-pole structure.Firstly,the outer contour function of the magnet is theoretically analyzed for different pole-cutting structures.Subsequently,through simulation and experimental verification,it is demonstrated that the pole-cutting structure can significantly reduce the harmonic content of the air-gap magnetic density,thereby substantially mitigating torque pulsation during motor operation.In summary,this thesis utilizes a novel optimization algorithm to design a highspeed permanent magnet brushless DC motor for 200W power tools,while also optimizing the design of the bonded magnet ring structure.The feasibility of the design is verified through theoretical derivation,simulation analysis,and experimental studies.