Research On Co-excitation Control Method Of A Magnetic Bearing Switched Reluctance Motor

The Switched Reluctance Motor(SRM)has simple structure,high temperature resistance,high speed adaptability,and has unique application characteristics in aerospace,military and civil fields.Electromagnetic bearings have adjustable magnetic flux,large inherent stiffness,large bearing capacity,and flexible control,and are widely used in high-speed motors.The Magnetic Bearing Switched Reluctance Motor(MBSRM)composed of electromagnetic bearing and SRM can not only effectively solve the bearing support problem of high-speed motor,but also further exert the high-speed advantage of SRM.However,in the traditional MBSRM system,the magnetic bearing and the motor are usually designed and independently controlled,the system is huge and the integration is low.In addition,the electromagnetic bearing requires a large bias current,resulting in large suspension power consumption.Therefore,it is of great theoretical and practical significance to study the comprehensive integration technology of magnetic bearings,SRM,power converters and control systems.In this paper,a new type of co-excitation system of magnetic bearing motor composed of E-type stator tooth electromagnetic bearing and 12/8-pole SRM and its control method are proposed.In order to improve the problems of low integration and huge control system of the traditional MBSRM system,the joint excitation of electromagnetic bearing and SRM is adopted,and the idea of co-excitation system is proposed.The realization of co-excitation control with different coexcitation power converters and SRMs is studied,and the basic theory of two degrees of freedom MBSRM co-excitation is given.In order to further improve the integration of the co-excitation system and reduce the hardware cost of the control system,a two-phase three-arm switching power amplifier is used for the electromagnetic bearing suspension control,and a suspension control method based on the prediction model of the suspension winding to select the switch state is studied.Different from the independent control of the suspension and rotation of the traditional MBSRM system,the suspension and rotation in the co-excitation system are coordinated and connected to each other.In order to make the motor float and rotate normally,according to the open-loop starting method of the SRM,a constant current is passed through the armature winding of one phase,so that the axes of the rotor and the stator are coincident,and the bias current is constant to control the rotor suspension.When the co-excitation system is under light load or no-load operation,the bias current amplitude is small,which is not conducive to rotor suspension.In order to solve this problem,it is proposed to use the characteristic of zero average torque in the flat-top section of the inductor,increase the limit of the chopping current to increase the bias current amplitude,and increase the conduction interval to increase the average output torque.In order to break the limitation of bus voltage and change the output torque of SRM to realize the active control of bias current,a two-stage boost co-excitation power converter is proposed by combining Boost circuit and asymmetric half-bridge circuit,in which the bias winding is multiplexed as the energy storage inductor of the Boost circuit.Simulation studies on the output torque and bias current of MBSRM under low-speed and high-speed conditions prove that the bias current is controllable.Under other working conditions,the control method based on the co-excitation system of the diode rectifier co-excitation power converter is used to simulate and verify the feasibility of the co-excitation control.