Wide area stabilization of a magnetic bearing using exact linearization

An active magnetic bearing (AMB) is a bearing used to suspend a rotor by magnetic forces without any contact. Feedback control is indispensable for a magnetic bearing, because it is essentially an unstable system. To design a feedback control system, a linear mathematical model of the plant is convenient; however, the force of the electromagnet is highly nonlinear. Thus, usually a linear approximation around the operating point is employed, but the obtained linearized model cannot express the exact behavior of the system at any other operating points. In this paper, we discuss the wide area stabilization of magnetic bearings using the exact linearization approach. First, we derive a nonlinear mathematical model for a magnetic bearing, then we show that this nonlinear system belongs to a class of exactly linearizable nonlinear systems. Next, by using the exact linearization method, we transfer the nonlinear model of a magnetic bearing to a linear time-invariant state model in spite of change of the operating point and the rotational speed of the rotor. Then we construct the state feedback control system by the conventional LQ method. Finally, we evaluate the validity of our proposed method by experiments.