Nonlinear control of a magnetic levitation system without premagnetization

A nonlinear model of an inertial wheel supported by active magnetic bearings is presented. A nonlinear controller based on input-output linearization is then derived to stabilize this model. This is contrasted to the typical practice of obtaining a linear model via premagnetization of the bearings through a bias current. Experimental results demonstrate that the rotor vibration and energy consumption of the bearings are lower when the nonlinear control method is used. A sliding mode control method is also proposed so that control is achieved with only two values of voltage input, in much the same manner as pulse width modulation. Simulations are also presented to test the robustness of the sliding mode control.