A single dof magnetic levitation system using time delay control and reduced-order observer

Magnetic levitation systems are required to have a large operating range in many applications. As one method to solve this problem, Time Delay Control (TDC) is applied to a single-axis magnetic levitation system in this paper. A reduced-order observer is utilized to estimate states excluding measurable states in the control law. The system consists of a square air-core solenoid and a circular permanent magnet attached on a plastic ball. Theoretical magnetic forces of the system are obtained on the basis of the location of the magnet around the solenoid. The magnetic levitation force is obtained by the experiment, and then compared with the theoretical one. As the results of the control experiments, the nonlinear controller (TDC : 1–2 mm) has a larger operating range than the linear controller (PD control: 1–1.4 mm), and is superior to linear control in the robustness to the modeling uncertainty and the performance of the disturbance rejection.