Identification Of Stiffness And Damping Coefficients Of Magnetic Bearings

The stiffness and damping coefficients of active magnetic bearings(AMBs) have great influence on the dynamic response of a rotor-bearing system, design of the controller and stable operation of the high-speed rotor system.This paper focus on identification of stiffness and damping coefficients of AMBs.Finite element model of the rotor supported by AMBs has direat influence on the dynamic character of rotor-bearing system. The rotor stiffness parameters may be incorrect since it is difficult to simulate the connections among silicon steel coil, Sensor reference ring and the sleeve. It is required to identify the main physical parameters of connected part of the rotor to obtain the better finite element model. The response surface about modal frequencies and modal assurance criterion(MAC) were established to update finite element model of the rotor supported by AMBs. The response surface has high precision. The modal frequencies and MAC are determined through simulation and compared with the experimental measurements. The close agreements between the simulation results and measurements validate the proposed identification method.The previous identification methods of AMBs’ parameters are based on rigid rotor model. When the rotor speed is close to the critical speed, due to the bending deformation, the identified results based on rigid rotor model become inaccurate. To solve this problem, this paper proposes a new method to identify AMBs’ parameters supporting high-speed flexible rotor accurately. The internal rotor displacements were derived by kinetic equation of the flexible rotor. Another method is proposed to identify the stiffness and damping coefficients of an experimental rotor AMB system based on hybrid genetic algorithm. The accurate supporting parameters can be obtained using hybrid genetic algorithm by comparing the experimental unbalance response calculated through the transfer matrix method. Then, an experiment with imbalance excitation is conducted to verify the method using experimental measurements. Afterwards, the identified stiffness and damping coefficients are combined with the finite element model to form a full model of the rotor-AMB test rig, from which the model unbalance responses at various rotating speeds are determined through simulation and compared with the experimental measurements. The close agreements between the simulation results and the measurements validate the proposed identification method.Finally, we investigated the influence factors of stiffness and damping coefficients of AMBs we have studied the effects of different unbalance mass excitation and different identification methods; this paper also shows the difference between hybrid genetic algorithm and finite element method. It is concluded that the two methods can effectively identify the stiffness and damping coefficients of AMBs.