| Active Magnetio Bearing (AM1B) is a kind of novel high performance bearing, which can suspend the rotor by magnetic force. Because of its contact-free manner between the rotor and stator, the rotor can rotate at a very high speed and it has longer lifetime, lower power loss, lower noise, almost no wear and needs no lubrication. In addition, it can improve the rotor dynamic behavior via feedback control. Compared with the conventional bearings, magnetic bearing has great advantages in many application domains.In this paper, a new approach, called adaptive autocentering(AAC) control, is presented to compensate for transmitted force due to imbalance in an AIvliB system. Under the proposed control law, a rigid rotor achieves rotation about the mass center and principal axis of inertia. The basic principle of this approach is to perform on-line identification of the physical characteristics of rotor imbalance and to use the identification results to tune a stabilizing controller. Unlike the adaptive feedforward compensation, adaptive autocentering control is frequency independent and works under varying rotor speed. A simple and effective way is adopted to find a contour plot of the maximum of the real parts of the closed-loop system. A thorough analysis has been done to the stability of the closed-loop system. Some important relationship between the control parameters and the performance of the closed-loop system is found. This relationship can be used to guide the design of the control system. A mathematical model and a simulated program of the system with an AMB supporting a rigid rotor is established. The process, that the rotor is drived and is passed through the critical speed, is studied. The different situations of the imbalance parameter are discussed. The AAC method is effective when gyroscopic effect is small. Performance and robustness of the control algorithm are demonstrated by simulation examples for the case of rigid rotors with static or dynamic imbalance.
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