Research On High Integration Multi-DOF Active Bearingless Axial Flux Motor

Bearing is an important part connecting the stator and rotor of the motor,which undertakes the task of supporting the rotor and reducing the rotation resistance.At the same time,bearing failure is one of the most common failures in motor,depending on the capacity of the motor,the percentage of bearing failure among motor failures is between40% and 70%.Moreover,in flywheel energy storage,aerospace,medical and other emerging fields,high vacuum,high radiation,high purity,ultra-high/low temperature and other special working environment characteristics put forward more demanding requirements for motor bearings.Due to the characteristics of no mechanical contact and no grease lubrication,the bearingless motor,which combines the functions of magnetic bearing and rotary motor,has become a research hotspot in the academia and industry.Among them,the multi-degree-of-freedom active bearingless axial flux motor(Multi-DOF ABLAM)is expected to be a new type of bearingless motor with strong anti-disturbance capability,high integration,low control complexity due to the advantages of high active control degree of freedom and simple structure,and has broad prospects for engineering applications.In this paper,the Multi-DOF ABLAM is taken as the research object,the analytical model,suspension mechanism and topology innovation are studied to improve the integration.The main research of this paper includes the following aspectsFirstly,the existing research of bearingless motors is reviewed.The advantages and disadvantages are summaried and the potential advantages of Multi-DOF ABLAM are clarified.An analytical model of the active suspension forces/torques is proposed for the general Multi-DOF ABLAM.The inherent coupling between the active suspension force along the radial axis and the active suspension torque around the radial axis,which is the unique characteristic of the Multi-DOF ABLAM,is emphasized.At the same time,the components of the active suspension force/torque of each DOF are analyzed,and it is pointed out that the radial active suspension force has different effect on the active suspension torque depending on the number of the suspension winding pole pairs.The design criterion for the pole number of suspension windings in the Multi-DOF ABLAM,which is one-pole-pair less than the rotor permanent magnet,is proposed.The correctness of the analytical model and the design criterion is verified by 3D finite element analysis and experiments.Then,a high integration Multi-DOF ABLAM topology based on single-side windings structure is proposed in this paper.The current control DOFs in the three-phase winding and its inverter is improves by concentrating the windings distributed on two stators to one stator.As a result,the number of required three-phase windings and inverters is reduced,leading to an increase in integration.Based on the analytical analysis,finite element analysis and experiments,the proposed topology is deeply investigated.The pole-slot combination criterion is derived,the analytical model of the proposed topology is established and several performance targets are constructed.The influence of design parameters on the performance target is analyzed and the correctness of the proposed analytical model and suspension principle are verified.At the same time,a novel class of high integration Multi-DOF ABLAM using harmonic magnetic fields is proposed in this paper.First,the harmonic magnetic field design criteria are derived.Then,two new topologies,one with consequent-pole rotor Multi-DOF ABLAM topology and the other with consequent-pole flux reversal Multi-DOF ABLAM topology,are proposed for the rotor permanent magnet and the stator permanent magnet excitation structure,respectively.The methods to satisfy the design criteria by generating harmonic magnetic field through the rotor tooth modulation effect or using the stator tooth harmonic magnetic fields are studied.Further,the suspension mechanisms are investigated by analytical analysis and finite element analysis,the effects of their design parameters on performances are studied.For the passive suspension DOF of the rotor in this class of high integration Multi-DOF ABLAM,the stable suspension conditions are analyzed,and the stable suspension conditions are presented.