Basic Research On Axial Actively Regulated Bearingless Motor

Bearingless / Self-bearing Motor,which can realize the no mechanical contact between the stator and the rotor,has been brought into cooling fan motors due to the friction caused by the traditional mechanical bearing lead to heat of the motor rotor,the shortened service life of the bearing,the decrease of the working efficiency and other problems.The bearingless fan motors would be subjected to the mutative axial load with wind speed when the fan motors are running,thus it is necessary to actively control the axial freedom.However,the increase in the number of actively positioned DOFs(Degree of freedoms)causes increases in the number of required inverters,so the increase in the number of power devices and displacement sensors,size,power consumption,and cost.So some scholars have proposed a single-drive/one-axis bearingless motor concept.The existing single-drive/one-axis actively regulated bearingless motor mainly uses the d-axis current,id,to actively regulate the axial suspension force,which may cause permanent magnet irreversible demagnetization,motor starting failure,reduced torque output and a series of problems.Considering the common situation of single-drive/one-axis actively regulated bearingless motor,a novel axial actively regulated slotless skew winding bearingless motor(SSWBM)is proposed,which uses the special stator skew winding structure to produce the required axial suspension force.The SSWBM realizes the torque and axial suspension force decoupling control only by the q-axis.Then,the mathematical model of BEF(Back Electromotive Force),axial suspension force and electromagnetic torque of the SSWBM is derived,and the principle and performance of the motor are studied by using finite element method to provide the feasibility for mechanical processing.Afterwards,according to the principle of the motor,the process of the motor design was expounded in detail from three aspects: material selection,optimization design of main electromagnetic parameters and mechanical structure design.Firstly,the materials of electromagnetic components,including stator parts and rotor parts,have been selected in this chapter.Then abide by the design target and process,the parameters such as the windings skew angle,the thickness of permanent magnet,the turns of winding,the gap between the two layers of windings and so on,were calculated.Finally based on the results obtained,a principle prototype was achieved.Lastly,due to the decoupling control block diagram of axial suspension force and torque,the digital control system of the motor was designed by using three closed-loop control methods of current,speed and axial displacement.The veracity of rotor position angle detection is verified by experiment.The no-load loss and no-load torque of the motor were obtained under open-loop of current.When the speed and the load are suddenly changed in the closed-loop experiments of speed,it is found that the hysteresis loss in the solid stator core and the friction between the motor shaft and the bearing when using the mechanical bearing instead of the passive magnetic bearing have a certain influence on the performance of the motor.The static and dynamic suspension experiment are conducted to verify the principle and the design feasibility,and control methods effectiveness of the SSWBM.