Abstract
Current stiffness and displacement stiffness are two important parameters of radial active magnetic bearing (RAMB) that are generally considered as constants in a control system. However, such presumption may lead to the probable degradation of the control performance of the RAMB system when the perspective that the current and displacement stiffness should be variable due to variations in the speed. On this regard, a structure analysis and stiffness measurement method based on non-variable stiffness would not be feasible for RAMB under high-speed conditions. This paper presented an analysis of the dynamic stiffness characteristics of RAMB by means of a dynamic equivalent magnetic circuit method and laid out a comparison between the results of the theoretical analysis and the simulation results of finite element method. In particular, a novel dynamic stiffness measurement method of RAMB under high-rotation frequency was introduced. Results of experiments on the dynamic stiffness of RAMB demonstrated an excellent agreement with the theoretical research and the finite element analysis results, thereby verifying the rationality of the discussed dynamic stiffness characteristics. Practically, the proposed measurement method of RAMB dynamic stiffness provides an accurate analysis for the dynamic stiffness and contributes inspiring research significance for the dynamic properties of RAMB.
Highlights
The two most commonly used magnetic bearing types are the passive and active magnetic bearings
Some researchers have found that the stiffness of radial active magnetic bearing (RAMB) would decline in a discernible manner with an increase in rotor frequency and would influence the stability of the radial magnetic bearing system in the process[23,24]
This aside, the frequency response of the displacement stiffness is not analysed nor measured. It is necessary implement the meterage of dynamic stiffness of RAMB for the magnetically suspended molecular pump (MSMP)
Summary
The two most commonly used magnetic bearing types are the passive and active magnetic bearings. Passive magnetic bearings with low power consumption realise the passive suspension of rotor through the interaction between the stator and rotor permanent magnets or the reluctance suction between the stator and rotor[10,11,12] These bearings lack active controllability and exhibit low damping and stiffness. The literature presented depict that the frequency response of the current stiffness could be obtained by addition of a balancing mass; the method is complicated and no explicit description of measuring current stiffness is provided in this research This aside, the frequency response of the displacement stiffness is not analysed nor measured. The proposed dynamic stiffness measurement method of RAMB is verified by prototyped experiments via comparison of results of the theoretical and FEM analyses
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