Active magnetic bearings dynamic parameters identification from experimental rotor unbalance response Yuanping Xu a , Jin Zhou a,n , Long Di b , Chen Zhao a a College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China b Rotating Machinery and Control Laboratory (ROMAC), University of Virginia, Charlottesville, VA 22904-4743, USA article info Article history: Received 14 July 2015 Received in revised form 9 May 2016 Accepted 10 June 2016 Available online 29 June 2016 Keywords: Active magnetic bearings Dynamic parameters identification Finite element method Stiffness and damping abstract Active magnetic bearings (AMBs) support rotors using electromagnetic force rather than mechanical forces. It is necessary to accurately identify the AMBs force coefficients since they play a critical role in the rotordynamic analysis including system stability, bending critical speeds and modes of vibrations. This paper proposes a rotor unbalance response based approach to identifying the AMBs stiffness and damping coefficients during rotation. First, a Timoshenko beam finite element (FE) rotor model is created. Second, an identification procedure based on the FE model is proposed. Then based on the experimental rotor unbalance response data from 1200 rpm to 30,000 rpm, the AMBs dynamic force parameters (stiffness and damping) are obtained. Finally, the identified results are verified by comparing the estimated and ex- perimental rotor unbalance responses, which shows high accuracy. & 2016 Elsevier Ltd. All rights reserved. 1. Introduction Active magnetic bearings generate forces through magnetic fields rather than mechanical forces as in lubricated fluid films or contact of rolling element bearings; therefore, the special advantage of AMBs is that there is no contact between bearing and rotor, and this permits operation with no lubrication, no mechanical wear, long life, lower costs and high attainable rotating speed [1,2]. Another attractive advantage of AMBs is that the dynamic force parameters, stiffness and damping, are closely related to the feedback controller parameters, which can be changed easily [3], such that the ro- tordynamics can be controlled and changed actively through the bearings. For either AMBs or traditional mechanical bearings, it is vital to accurately obtain the dynamic force bearing parameters since these coefficients for a rotor system are the foundation for the rotor dynamics analysis including system stability, bending critical speeds, modes of vibrations, and response of rotating dynamic systems. The force coefficients of the tra- ditional mechanical bearing are commonly modeled as stiffness and damping, which are also used for the AMBs. Compared with traditional bearing system, the AMBs system is open loop unstable and feedback control is needed for levitation. Apart from the rotor dynamics analysis, from the control design point of view, it is also vital to accurately predict the AMBs dynamics parameters to optimize the control strategies design since the AMBs stiffness and damping are closely related to the feedback controller parameters. Humphris et al. [4] investigated the stiffness and damping properties of a magnetic bearing with two control algorithms Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ymssp Mechanical Systems and Signal Processing http://dx.doi.org/10.1016/j.ymssp.2016.06.009 0888-3270/& 2016 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail addresses: ypxu@nuaa.edu.cn (Y. Xu), zhj@nuaa.edu.cn (J. Zhou). Mechanical Systems and Signal Processing 83 (2017) 228–240