Identification of bearing dynamic parameters and unbalance states in a flexible rotor system fully levitated on active magnetic bearings

Abstract

An identification algorithm for the estimation of dynamic parameters of Active Magnetic Bearings (AMBs) and rotor residual unbalances has been presented for a flexible rotor system. The proposed algorithm is suitable for the state of the art rotors that are fully levitated on AMBs. Due to a partial attenuation of unbalance responses by AMBs, difficulty arises in getting the correct estimations from unbalance responses alone, which is not the case with the conventional bearings. For latter bearings responses do reflect real effects of unbalances. Thus, the present algorithm is based both on the measured AMB controlling currents and rotor unbalance responses, and uses these to identify AMB dynamic parameters of each AMB and residual unbalances in flexible rotors at predefined balancing planes. The algorithm is based on the least-squares fit technique in frequency domain. AMB dynamic parameters consist of the force–displacement and the force–current coefficients in two orthogonal transverse directions for each AMB. The finite element method has been used to obtain a unified model of the flexible rotor fully levitated with AMBs for the numerical study, in which the PID controller is used. Numerical simulations have been performed to illustrate the reliability of proposed algorithm. The algorithm is also tested against the measurement noise and modelling errors to investigate its robustness. The proposed algorithm has been finally applied to an experimental data (from Technical University of Darmstadt, Germany) from a fully levitated five-disc flexible rotor test rig with the help of two AMBs. Estimates of AMB dynamic parameters are found to be in close range with that of theoretical values.