Controller Design for Large-Gap Control of Electromagnetically Levitated System by Using an Optimization Technique

In this paper, design and implementation of an optimized controller for a single magnet-based electromagnetic levitation system (EMLS) where an electromagnet of 2.6-kg mass is levitated over a large gap under a fixed ferromagnetic guide-way has been discussed. EMLS is inherently unstable and strongly nonlinear in nature. A single position controller (lead type) along with an outer proportional-integral (PI) controller has been designed that will stabilize the EMLS represented mathematically by three different plants corresponding to three different operating points. An optimization technique utilizing the random search method with interval reduction, proposed by Luus and Jaakola, has been used for designing the controller. A "model matching control" design procedure has been utilized for the design of outer PI controller. The inner controller stabilizes the three unstable plants, whereas the outer PI control action is used to modify the three position outputs as per the desired model response. The combined control action provides good stability and satisfactory performance (like fast response, less overshoot, and zero steady-state error) for the different operating zones of EMLS. Stability has been confirmed by Kharitonov-Nyquist enclosure diagrams. The simulated controllers have been successfully implemented, thus validating the modeling and controller design procedure.