Nonlinear adaptive control of magnetic levitation system using terminal sliding mode and integral backstepping sliding mode controllers.

Magnetic levitation (MagLev) system is an unstable, highly non-linear and dynamically fast. These characteristics make it challenging task to design a suitable controller to ensure any object to stay at a certain distance from the electromagnet with negligible error. It can be achieved by generating the required flux with the help of a control input. This suspension of ferromagnetic object in air is achieved by balancing the forces of attraction of gravity and electromagnetic. This makes the system highly vulnerable to external disturbances and parametric uncertainties. The controller must be able to adapt the changing electrical resistance and be robust if the mass of the levitating object for MagLev changes. In this paper, three nonlinear controllers: adaptive terminal sliding mode control (AT-SMC), adaptive backstepping sliding mode (ABS-SMC) and adaptive integral backstepping sliding mode (AIBS-SMC) based controllers have been proposed for tracking the air gap to desired value while maintaining the momentum and flux to desired values. Lyapunov theory has been used for proving the global asymptotic stability of the proposed controllers. For performance analysis, simulations have been carried out using Matlab/Simulink environment, where the proposed controllers have been compared with each other. Among the proposed controllers, AT-SMC gives better performance in terms of transient and overall dynamical response. The effect of parametric variations/uncertainties on all of the proposed controllers has also been examined by varying parametric values, by adding noise and disturbance in the system. Moreover, simulation results for the proposed controllers have also been compared with recently proposed controllers in literature. The physical realization of proposed AT-SMC has been examined with the help of a comparison between simulation results and the controller hardware in loop (C-HIL) experimental results.