Linearizing control of magnetic suspension systems

In many applications, magnetic suspension systems are required to operate over large variations in air gap. As a result, the nonlinearities inherent in most types of suspensions have a significant impact on performance. Specifically, it may be difficult to design a linear controller which gives satisfactory performance, stability, and disturbance rejection over a wide range of operating points. One way to address this problem is through the use of nonlinear control techniques such as feedback linearization. For most common designs of magnetic suspensions the governing equations are in the so-called companion form, lending themselves to feedback linearization. A single degree of freedom magnetic suspension has been designed and constructed in order to compare the performance of linear and nonlinear digital control schemes in a well-controlled experimental environment. We demonstrate the superiority of nonlinear controllers over conventional controllers for systems with large variations in operating point via experiments on our system.