Decoupled control of an active magnetic bearing system for a high gyroscopic rotor

Control design for coupled MIMO-Systems (Multiple Input and Multiple Output) like a 5-DOF (degree of freedom) AMB (active magnetic bearing) system needs a high knowledge in control theory. This paper describes a model based approach for decoupled control design. To decouple the system an input and an output transformation is used and all control parts are developed in the so called center of gravity (COG) coordinate system. One of the main problems is the stabilization of the rotor for a high speed range. This problem is solved by a parameter variant feedback path, which transforms the linear parameter variant system in a linear parameter invariant system. This feedback path requires the angular velocity and the velocities of the degrees of freedom for calculation. The angular velocity can be used from the motor controller. For the other velocities a Kalman observer is used. This Kalman observer is developed only in the center of gravity coordinates, because in this coordinate system the observer needs less computing power. The stability and robustness of the closed loop system is verified by simulations and experimental results.