A sliding mode observer and controller for stabilization of rotational motion of a vertical shaft magnetic bearing

In this paper we present the development of (1) a sliding mode controller for stabilization of the rotational dynamics of a vertical shaft magnetic bearing in addition to providing tracking capabilities, and (2) a sliding mode observer for state and disturbance estimation. Rotor imbalance causes sinusoidal disturbances which necessitates robustness inherent in sliding mode observers and controllers. The sliding mode control design includes (1) the definition of an equilibrium manifold upon which the magnetic bearing has the desired stability and tracking properties, and (2) the control selection from one of several potential control strategies for driving the system to this manifold and maintaining it there. A sliding mode observer strategy is proposed to estimate derivatives of measured signals in the presence of unmatched disturbances by filtering discontinuous approximations of the derivatives. Simulation results demonstrate the utility and robustness of a sliding mode controller and observer for stabilizing the rotational dynamics of a magnetic bearing.