Abstract
Modern control techniques can improve the performance and robustness of a rotor active magnetic bearing (AMB) system. Since those control methods usually rely on system models, it is important to obtain a precise rotor AMB analytical model. However, the interference fits and shrink effects of rotor AMB cause inaccuracy to the final system model. In this paper, an experiment based model updating method is proposed to improve the accuracy of the finite element (FE) model used in a rotor AMB system. Modelling error is minimized by applying a numerical optimization Nelder-Mead simplex algorithm to properly adjust FE model parameters. Both the error resonance frequencies and modal assurance criterion (MAC) values are minimized simultaneously to account for the rotor natural frequencies as well as for the mode shapes. Verification of the updated rotor model is performed by comparing the experimental and analytical frequency response. The close agreements demonstrate the effectiveness of the proposed model updating methodology.
Highlights
As potential alternatives to conventional mechanical bearings, active magnetic bearings have been increasingly used in compressors, pumps, and many other high-speed rotating machineries [1]
In order to enhance the robustness, modern control techniques such as H∞ and μ synthesis have been applied to rotor active magnetic bearing (AMB) system
Since these multiple input and multiple output (MIMO) control methods usually rely on system models, it is important to obtain a precise rotor AMB analytical model and obtaining an analytical model close to the actual system is an inevitable step before the controller design [4, 5]
Summary
As potential alternatives to conventional mechanical bearings, active magnetic bearings have been increasingly used in compressors, pumps, and many other high-speed rotating machineries [1]. Iterative methods need an objective or error function to represent the discrepancy in frequency response such as resonance frequency, antiresonance frequency, MAC, or mode shapes between experimental and theoretical results. After building a rotor finite element model, we update the rotor model using NelderMead nonlinear unconstrained optimization method and provide an objective function, combining first four MAC values and bending frequency errors together. The advantages of this combination are that the mode shapes calculated by the updated model are highly accurate as well as the normal modal frequencies.
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