H _∞ control of the magnetic bearing considering initial state uncertainties

This paper deals with an application of H _∞ control attenuating initial-state uncertainties to the magnetic bearing and examines the H _∞ control problem, which treats a mixed Disturbance and an Initial-state uncertainty Attenuation(DIA) control. The mixed H _∞ DIA problem supplies H _∞ controls with good transients and assures H _∞ controls of robustness against initial-state uncertainty. On the other hand, active magnetic bearings allow contract-free suspension of rotors and they are used for various industrial purposes. We derive a mathematical model of the magnetic bearing which has complicated rotor dynamics and nonlinear magnetic property. Then we apply this proposed H _∞DIA control for the magnetic bearing, and design a robust H _∞ controller both for exogenous disturbances and for initial state uncertainties of the plant. Experimental results show that the proposed robust control approach is effective for improving transient response and robust performance.