This paper describes H^∞ robust control design for a magnetic suspension system of double flexible beam which simplifies both an elastic rotor and body in a magnetic bearing system. A magnetic bearing requires feedback control since it is inevitably unstable. Moreover, it is desirable that the controller guarantees robust stability at presence of a variety of uncertainties; errors of parameters, neglected nonlinearities, or unmodeled dynamics.
At first, the magnetic suspension system is introduced. Next, its linearized model with disturbance terms as unmodeled uncertainties is formulated in a state space form. In order to deal with the uncertainties, the generalized plant is constructed from LQ differential game theoretic point of view, which involves weighting matrices for state variables and control input and frequency weighting functions for uncertainty models. Then the control systems are designed with both H^∞ control and PID control, which are implemented by a digital controller using a digital signal processor. Finally, several experiments are made for the evaluation of the control performance, where the proposed control is compared with PID control.