Nonlinear Curve Fitting Approach for Position and Current Stiffness Parameter Identification in AMB Rotor Systems

Abstract

Accurate linearized stiffness parameters of active magnetic bearings (AMBs) are essential for rotor-dynamics modelling, controller design and performance assessment. This paper presents a reproducible, physics-informed time-domain identification method to estimate the position and current stiffness of two radial AMBs supporting a rigid rotor. Open-loop tests without outer position feedback controller are performed using the inner current control, where step current excitations are applied separately to each AMB while the collocated position sensor records the radial displacement. A hyperbolic-cosine model is fitted to the transient displacement via non-linear least squares, and the fitted pole like parameter is converted to stiffness using the effective mass. The method is validated on both linear and nonlinear actuator models using a detailed simulation model as well as on experimental data collected from a modular test rig. The findings indicate that the proposed method can accurately estimate stiffness parameters, demonstrating its suitability for system commissioning with limited knowledge.