Design Of Outer Rotor Permanent Magnet High-Speed Motor And Dynamic Characteristics Analysis For Rotor

The permanent magnet brushless motor has the following characteristics: small size,high efficiency,high precision,simple structure,etc.It is used in many occasions.The permanent magnet brushless motor is divided into two kinds: inner rotor permanent magnet brushless motor and outer rotor permanent magnet brushless motor.Compared with the internal rotor high speed motor,it is more difficult to design the outer rotor permanent magnet brushless motor for high speed motor.When the outer rotor motor works,its unique thin-walled rotor yoke structure is prone to vibration at high speed,and the film mode is formed,Which will cause the air gap is not uniform so that rotor output torque and speed are instable.On the other hand,the unbalanced electromagnetic force caused by the unevenness of the air gap make deformation of the out rotor structure vibration become more powerful,and the two are coupled to each other to reduce the overall performance of the motor.Therefore,the reasonable design of the out rotor structure,the accurate calculation of the electromagnetic field and the vibration characteristic analysis of the outer rotor structure are the key technologies for the design of out rotor permanent magnet high speed motor.The main contents of the study are as follows:(1)This paper summarizes the design analysis of out rotor permanent magnet motor and the research results of rotor dynamic characteristics for the domestic and foreign scholars.Some problems of motor design are put forward at this stage.(2)The main dimensions of out rotor permanent magnet high-speed motor are determined from the rotor strength,stiffness,rotor dynamics and electromagneticproperties.And outer rotor radial structure and stator structure are designed.(3)The static field and transient field of motor electromagnetic performance are analyzed by Ansoft Maxwell.The back electromotive force constant and the torque coefficient of motor output performance are calculated.And the cogging torque is optimized.Different rotor eccentric state models are established.The characteristics of the air gap magnetic field are analyzed,and the electromagnetic forces of the rotor are calculated.(4)The dynamic characteristics of the outer rotor structure of the motor are studied.Firstly,the natural frequency and mode of the rotor structure are analyzed.On the basis of which,the influence of the electromagnetic force,the bearing stiffness and the bearing span on the modal mode of the rotor is analyzed and the critical speed of the rotor is solved to obtain the Campbell diagram.(5)Electromagnetic force wave in frequency domain at the working speed is extracted by ANSYS Workbench.When the electromagnetic force is applied to the rotor magnet,the harmonic response of the outer rotor system is analyzed and the frequency of forced vibration is obtained.Aiming at the frequency of forced vibration,the sensitivity of the rotor structure size is analyzed and optimize it with the method of response surface.(6)Finally,a prototype is developed which based on the simulation parameters.The correctness of the dynamic characteristics analysis of the rotor is verified by the modal experiment.The motor performance test shows that the prototype meets the design requirement.