Parameter patterns of an AMB-flexible rotor in linear operating conditions

Nonlinear characteristics analysis of active magnetic bearing-rotor systems is crucial for control system optimization. Current studies often overlook the strong nonlinearity of magnetic forces under magnetic saturation, typically considering only simplified single-bearing-rotor models and assuming that the target electromagnetic forces can be precisely obtained, leading to significant discrepancies from actual operating conditions. To address these limitations, this paper takes the high-pressure rotor of a certain gas turbine in power plants as the research object, establishes a dynamic bearing force model that considers the coupling effect between the dynamic variation of core magnetic reluctance and the Hertzian forces in backup bearings, and develops an integrated mechanical-electromagnetic dynamic model for the active magnetic bearing-flexible rotor system with current constraints incorporated. The transient dynamics are solved by combining the general self-starting single-solution explicit integration algorithm with a subdomain solution strategy, and the steady-state dynamics near the first- and second-order critical speeds of the flexible rotor are analyzed through shaft center trajectories, bifurcation theory, and Poincaré mapping. The results reveal that bearing forces introduce bistable regions in the rotor system, exhibiting soft spring characteristics. Improper selection of control parameters expands the frequency range where the rotor vibrations transition into quasi-periodic or even chaotic states, and during contact between the rotor and the protective bearing, phenomena such as jumps, whirling, and even precession are observed. This study, for the first time, delineates the linear vibration parameter regions at active magnetic bearing nodes under various rotor unbalance conditions, offering a new direction for controller optimization in active magnetic bearing-flexible rotor systems.