Analysis of Stiffness and Damping Properties of Active Magnetic Bearing Using Cross Feedback Control

Stiffness and damping properties of the magnetic bearings are mainly determined by the parameters of system controller, both of which are the function of rotor frequency. In the system of magnetic suspensionfly wheel (MSFW), the rotor applied has a large moment of inertia ratio, resulting in a strong gyroscopic effect at high speed. Decentralized PID controller cannot assure the stability of suspension at high speed. Therefore, cross feedback control must be added to the control loop of the system. The cross stiffness and damping terms will be introduced to the matrix of stiffness and damping of the system. In this paper, the magnetic bearing rotor system with displacement and velocity cross feedback is discussed from the perspective of the stiffness and damping. The results show that, equivalent stiffness of the rotor approximates a negative constant in low frequency, and with rotation increasing, it increases continually after approaching to zero, Equivalent rotor damping approximates a constant, and decreases continually in high frequency with rotation speed increasing. The filters have influence on stiffness and damping characteristics of magnetic bearing in different frequency range.