Misalignment safety threshold and stability driven controller tuning for AMBs–rotor systems

Active magnetic bearings (AMBs)–rotor systems are widely used in high precision machinery and energy equipment due to their contactless support capability. In these systems, coupling misalignment caused by manufacturing, assembly, or wear can induce asymmetric forces, leading to excessive rotor vibrations and decreased stability. Although controller parameter tuning methods are commonly based on empirical rules, classical control design, or numerical optimization, most existing approaches focus on conventional performance indices. They rarely consider coupling misalignment tolerance as an explicit design objective, making it difficult to guarantee system robustness and safety under varying misalignment conditions. Herein, a controller parameter tuning method based on both the misalignment safety threshold and system stability constraints is proposed. Specifically, the misalignment safety threshold is defined by the allowable misalignment area from the nonlinear electromechanical model of the AMBs–rotor system with coupling misalignment, while system stability is evaluated through root locus analysis. Simulation and experimental verifications under coupling misalignments are conducted. This method maximizes the system’s tolerance to coupling misalignment while maintaining stability margins and introduces a novel criterion for tuning controller parameters in AMBs–rotor systems.