Feedback linearization of an active magnetic bearing with voltage control

In this paper, 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 mu -synthesis to guarantee a beam compliance performance specification. A common problem associated with voltage control in magnetic suspensions, coil resistance variation, is successfully handled via augmenting the feedback linearized plant with a structured uncertainty. Experimental results demonstrate that the mu controller with feedback linearization achieves the performance specified during design for the nonlinear plant independent of the disturbance force level or displacement incurred.