Feedback linearization of an active magnetic bearing with voltage control

A feedback linearization controller is presented for a single-degree-of-freedom (DOF) magnetic bearing test rig. The feedback linearization controller is derived from a detailed nonlinear electromagnet model using both analytic relationships and experimental calibration data. The controller is implemented on the test rig in voltage mode, and measured open-loop transfer functions are used to demonstrate the effectiveness of the feedback linearization controller in transforming the nonlinear system to a linear plant. Next, a high-performance controller for the feedback linearized plant is designed with μ-synthesis to guarantee a beam compliance performance specification. A common problem associated with voltage control in magnetic suspensions and coil resistance variation, is successfully handled by augmenting the feedback linearized plant with a structured uncertainty. Experimental results demonstrate that the μ controller with feedback linearization achieves the performance specified during design for the nonlinear plant independent of the disturbance force level or displacement incurred