Double Ring Magnetic Steel Brushless DC Motor For Magnetic Bearing Gyrowheel

The brushless DC motor(BLDCM)of the magnetic suspension gyro flywheel(MSFW)uses a cup-type stator instead of a conventional iron-core stator,eliminating the eddy current loss and cogging torque ripple generated by the conventional ron-core stator when the motor rotates at a high speed.The non-stator core brushless DC motor of the existing magnetic suspension gyro flywheel adopts a single-ring magnetic steel scheme.Through quantitative analysis,the flat top width of the equivalent air gap flux density waveform is narrow,and the equivalent air gap magnetic density is small,thus resulting in a smaller motor output torque and lower torque accuracy.In order to overcome the above shortcomings,this paper presents a non-stator core dual-ring magnetic steel structure and a detailed example design.The specific work of this article is as follows:(1)Introduce the magnetic design principle of the non-stator core brushless DC motor.Introduce the equivalent polar arc coefficient concept and the equivalent flux leakage coefficient concept for the air gap magnetic density distribution characteristics analysis of a statorless brushless DC motor.(2)Analysis the the air gap magnetic density distribution characteristics of this two kinds of motor schemes,using the concept of equivalent polar arc coefficient and equivalent flux leakage coefficient.Then reveal that the equivalent air gap magnetic density waveform width is wider and the air gap magnetic density amplitude is larger compared with the same thickness single-turn magnetic steel structure.(3)Based on the the constant magnetic field basic theory,the equivalent surface current principle for the calculation of the motor air gap magnetic field is derived.Based on the principle of equivalent plane current,a mathematical model of air gap flux density was established for single and double ring magnets,and the key structural parameters affecting air gap flux density were obtained.(4)The finite element method software is used to compare and analyze the equivalent air gap flux density waveform distribution law of the single and double-ring magnetic steel scheme.It is further verified that the double-turn magnetic steel scheme has better air-gap magnetic flux characteristics than the single-turn magnetic steel scheme.(5)In order to further improve the air gap magnetic density distribution characteristics,this paper proposes a dual ring non-equal-thickness magnetic steel scheme on the basis of the dual-turn magnetic steel scheme,and carries out a detailed example design.The design results show that the equivalent pole-arc coefficient and the equivalent air-gap magnetic-amplitude amplitude increase from 0.76 and 0.45 T in a single ring to 0.847 and 0.463 T respectively,which are 11.5% and 2.9% respectively.The improved double-ring magnet scheme BLDCM can effectively realize the high-speed drive and precise shift of the MSCSG rotor.