Dynamic behavior of active magnetic bearings-rotor system with coupling misalignment

Active magnetic bearings offer contactless support for rotor systems, making them increasingly popular in high-speed rotating machinery. However, when the rotor is connected to the motor through mechanical couplings, misalignment caused by manufacturing defects, assembly errors, or prolonged wear can introduce asymmetric excitation forces that degrade the system's dynamic performance. Existing studies often rely on idealized coupling models, fail to adequately explain experimentally observed odd-order harmonics, and lack methods for predicting the safety threshold of coupling misalignment, thereby limiting their practical value in accurately modeling rotor system dynamics and supporting engineering applications. This study investigates the dynamic behavior of an active magnetic bearings-rotor system subject to coupling misalignment. A nonlinear, time-varying stiffness model is developed by identifying harmonic components and stiffness characteristics from both simulations and experimental data. Unlike existing approaches that rely on idealized coupling assumptions, the proposed model incorporates realistic structural parameters and explains the occurrence of both even- and odd-order harmonic responses observed in practice. Based on the model, time- and frequency-domain analyses are performed under different misalignment conditions to evaluate vibration behavior and stability. Moreover, the study quantifies threshold ranges for parallel and angular misalignment under both critical and rated speeds, offering engineering guidance for safe operation. These findings offer valuable insights into the vibration mechanisms of active magnetic bearings-rotor systems with coupling misalignment and establish a foundation for condition monitoring and fault diagnosis.