Researches on active magnetic bearings (AMBs) are mainly based on equivalent magnetic circuit (EMC) method with the assumption that there is no magnetic saturation in magnetic circuit. However, this assumption about magnetic saturation is no longer valid for special solutions, such as aero‐engines. In this case, limitations exist for the application of EMC method. This research focuses on an analytical bearing capacity model for AMBs based on a non‐linear magnetic circuit method (NMCM) with magnetic saturation taken into account. First, the error factors of EMC method are analysed by using finite element analysis software when the air gap increased. Then, aiming at the main factors, including fringing flux, flux leakage and magnetic saturation, the air‐gap magnetic flux model and the flux leakage model are developed based on the magnetic field division method. On this basis, a NMCM based on magnetic saturation is proposed to create the analytical bearing capacity model of AMBs. Additionally, the analytical model is verified by comparing with the results of finite element analysis and experiments. Eventually, the analytical model of hybrid magnetic bearing with single degree of freedom based on NMCM is verified by experiments.

The harmonic response caused by unbalanced excitation vibration for the high-speed rotating machinery will reduce the control accuracy and stability of the maglev high-speed motor, and limit the increase of its speed. When the active magnetic bearing is used to solve the unbalanced vibration, it will increase additional electromagnetic force and energy consumption, sometimes leading to the saturation of the power amplifier, and will transfer to the bearing foundation, causing the foundation to vibrate. In this paper, we analyzed periodic unbalance excitation force and the principle of rotor unbalanced vibration suppression, and the unbalance vibration model of the maglev rotor is derived. The Least-Mean-Square (LMS) algorithm is introduced into the PID control, an unbalance vibration control strategy based on real-time filtering compensation of rotor displacement signal is proposed, the vibration is eliminated by filtering the synchronous frequency and harmonic signal of the input of the PID control. The experimental results show that the proposed method can improve the maglev rotor’s rotation accuracy, reduce the magnetic bearing’s maximum control current, and decrease the vibration of the supporting foundation.

The magnetic suspended dual‐rotor system (MSDS) can effectively increase the thrust weight ratio of aeroengines. However, the MSDS dynamic characteristics have rarely been investigated. In this research, a MSDS with the outer rotor supported by two active magnetic bearings (AMBs) is designed, and the PID control is employed. The Riccati transfer matrix method using complex variables is adopted to establish the MSDS dynamic model. Subsequently, the influences of AMBs’ control parameters on the MSDS dynamic characteristics are explored. According to the analysis, two rigid mode shapes remain unchanged with the variation of the relationship between their corresponding damped critical speeds (DCSs). Moreover, the rigid DCSs disappear with large derivative coefficient. Eventually, the validity of the dynamic model and the appearance of rigid DCSs are verified.

The Maglev motor has the characteristics of high-speed and high-power density, and is widely used in compressors, molecular pumps and other high-speed rotating machinery. With the requirements of miniaturization and high speed of rotating machinery, the rotor of the maglev motor will operate above the bending critical speed, and the critical vibration control of the flexible rotor is facing challenges. In order to solve the problem of the critical vibration suppression of the maglev high-speed motor, the system model of the maglev motor is established, the rotordynamics of the flexible rotor are analyzed and the rotor model is modal truncated to reduce the order. Then, the μ–controller is designed, and the weighting functions are designed to deal with the modal uncertainty. Finally, an experimental platform of the maglev motor with the flexible rotor is built to verify the effect of the μ–control on the suppression of the critical vibration of the maglev rotor.

The magnetic suspended dual-rotor system (MSDS) has the advantage of a high power density. The system can be used in high-speed rotating machinery. The major purpose of this study is to predict the unbalance response of the MSDS considering the nonlinear bearing characteristics of active magnetic bearings (AMBs). Firstly, the nonlinear bearing model was established by a non-linear magnetic circuit method (NMCM). The model considers magnetic flux leakage, magnetic saturation, and working position flotation accurately. Then, the dynamic model of the system was established by using the finite element method and solved by the Newmark-β method. Finally, the effects of external load, rotational speeds, and control parameters were studied. Axial trajectory diagrams, stability zone diagrams, and waterfall diagrams were employed to analyze the dynamic behaviors of the MSDS. The results indicate that the external load, rotational speeds, and control parameters have a significant impact on the unbalance response of the system. Super harmonics of rotational frequencies and their combined frequencies may be excited by heavy load conditions. Appropriate control parameters can suppress the nonlinear phenomena. The obtained results of this research will contribute to the design and fault diagnosis of MSDSs.