Research On Flux-weakening Of Dual-stator Conical-rotor Permanent Magnet Synchronous Motor

Permanent magnet synchronous motor(PMSM) due to its high efficiency, highpower density, etc. to obtain favor, but its flux-weakening problem has not beenable to get a better solution, become scholars research hot spot. Dual-stator conicalrotor structure of PMSM is given in this paper, the outer motor is conical rotorPMSM structure，the stator and rotor has the same length, used to output rotatetorque, the inner motor is linear motor structure, used to control the hollow-cuprotor axial movement. Increasing the axial displacement of the conical rotor, on theone hand can reduce the coupling area of the outer conical motor, on the other handcan increase the outer motor air gap length, to achieve the outer motor flux-weakening operation. The motors have dual advantages of high torque at low speedand wide constant power region, applied to the wheel motor, can removemechanical gears, using direct drive mode, both realize at low speed when climbinghas enough power, and to possess a wide speed range to help overtaking. Thisarticle have studied the dual-stator conical rotor PMSM flux-weakening from thefollowing several aspects.First an overview of the dual-stator motor, conical rotor motor and PMSMflux-weakening structure research and development present situation, give severalkinds of common structure of the dual-stator motor, analysis the characteristics ofthe different structure, then based on the research object structure and its workingprinciple of this paper for detailed analysis. Through the theoretical derivationshows the motor working principle of flux-weakening, analysis the magneticresistance torque and permanent magnet torque generation principle of PMSM, andbriefly introduced maximum torque per ampere control, flux-weakening control andd axis current equal to zero control principle, provide the basis for the motor controlmethod, and put forward the dual stator conical rotor PMSM control method. Fromthe equivalent magnetic network analysis of the conical rotor PMSM, explain thenecessity of the motor uses the three dimensional finite element analysis method.Then study the air gap flux density different between conical rotor PMSM andcylindrical rotor PMSM, establish conical rotor PMSM three dimensional finiteelement simulation model, with finite element analysis software Flux, simulationresearch the magnetic field distribution and air gap flux density along with thechange of cone angle and the rotor axial displacement of the motor. Defining coneangle and rotor axial displacement contribution to the flux-weakening of motorrespectively, presented its computation method, simulation and experimental validation. Investigate the influence factors of affect the cone angle contribution,provide theoretical basis for the cone angle and rotor axial displacement design ofthe conical rotor PMSM.The axial magnetic pulling force is one of the most important parameters ofconical rotor motor, in this paper, the axial magnetic pull force is decomposed intonormotopia force component and cone angle force component, theoreticalderivation the axial magnetic pull force component of the calculation method andsimulation validation respectively, and experiment validation cone angle forcecomponent. Research on d axis and q axis current’s influence on the axial magneticpull force, provide a reference for rotor’s axial displace control. According to thesize of the axial magnetic pull force of the outer motor and the rotor axialdisplacement demands, structure scheme of the inner motor and its design principlewas given, and simulation to study the feasibility.In the final analysis of the motor’s flux-weakening performance, calculate thehighest speed output through the motor no load back EMF, analysis the expandingspeed ratio of different cone angle and the rotor axial displacement. Analysis coneangle and the rotor axial displacement influence on motor inductance, from twoaspects of theory analysis and simulation verification to research electromagnetictorque and power output along with the change of cone angle and the rotor axialdisplacement, show the principle that the motor has wide constant power region.