Model Reduction via Subsystem Decomposition for Flexible Rotor-Magnetic Bearing with Gyroscopic Effect

In this study, we propose a model reduction method using subsystem decomposition for magnetic bearing flexible rotor with gyroscopic effect. The magnetic bearing can rotate fast because of a non-contact bearing. It is necessary to use a flexible rotor in order to increase the angular velocity of the rotor. Model reduction is required to design controller because the order of the model increase in the case of using the flexible rotor. There are difficulties of skewness and speed dependence when the order of the magnetic bearing system is reduced. We consider decomposing dynamics of the magnetic bearing into horizontal dynamics and vertical dynamics for the difficulties. The magnetic bearing system can be represented as a closed loop system of the horizontal model without gyro term, the vertical model without gyro term and two gyro terms connecting each system. We can use general reduction methods because the horizontal and vertical dynamics without gyro terms are each linear time-invariant system. Hence, it is not necessary to calculate every time the angular velocity of the rotor is varied because the proposed reduction procedure doesn't depend on the angular velocity of the rotor. The order of the matrix in the proposed method is half of that in the conventional method based on singular value decomposition. Thus, the proposed method can reduce the numeric error in the reduction. The effectiveness of the proposed model reduction method is illustrated by Bode diagrams.