On Optimal Design Of Permanent Magnet Motor For Field Weakening Control

Permanent magnet synchronous motor(PMSM)has many advantages,such as high efficiency,high output torque,high power density and good dynamic performance,and more and more are applied to transport vehicles,industrial and commercial electrical appliances and aviation.For ordinary electric motor,permanent magnet motor excitation is not adjustable,for low speed constant torque,high speed constant power operation under the field of field weakening magnetic expansion is particularly important.In this thesis,Taguchi method and time-step finite element method is used to optimize the magnetic circuit structure of the built-in "V" PMSM.Firstly,the important parameters which influence the speed regulation of synchronous motor are obtained by the motor speed control theory,and the two methods of inductance are compared.At the same time,the performance of permanent magnet motors with different rotor structures is compared,and the rotor structure is optimized.The 2D finite element model of 11 KW internal PMSM motor is established by Ansoft Maxwell software.Secondly,in order to meet the requirement of constant torque output and high speed constant power area of permanent magnet motor,four variables of PMSM are selected as optimization variables,including: Angle,magnetic distance from the shaft,eccentricity and air gap length.Based on the combination of the Taguchi method and the time-step finite element method,the parameters of the magnetic circuit structure of the motor are optimized to improve the saliency and reduce the cogging torque.By comparing the results,the superiority of the method is verified..Thirdly,cogging torque is a permanent magnet motor,a phenomenon that can cause the motor output torque is not smooth,resulting in vibration and noise.In order to reduce the cogging torque,this thesis chooses the method of matching slot number and pole number and slotting on the stator teeth with rotor oblique pole.By optimizing the comparison of front and rear cogging torque,the results show that both methods can reduce the tooth Slot torque.Finally,in order to verify whether the rotor can withstand the centrifugal force caused by high-speed rotation of the permanent magnet after the field-weakening,the electromagnetic-mechanical stress coupling field of the permanent magnet motor rotor is studied in ANSYS Workbench software platform.The results show that,with the design of the structure sizes of the rotor,when the motor is running at high speed,the maximum point of the rotor stress is still in the yield limit of silicon steel sheet DW465.The rotor stress will not damage the rotor.