Ultralocal Model-Free Adaptive Supertwisting Nonsingular Terminal Sliding Mode Control for Magnetic Levitation System
Jinsong Kang, Xiayi Huang, Chang Xia, Dongxiao Huang, Fengxiang Wang
Abstract
The magnetic levitation technology has attracted blooming attention from all walks of life thanks to its superiorities such as noncontact and active control. While the intrinsic features of open-loop instability and strong nonlinearity, along with the uncertain external disturbance make the levitation control particularly significant and difficult. For speeding up the convergence and obtaining a better stability and disturbance robustness, this article proposes an ultralocal model-free adaptive supertwisting nonsingular terminal sliding mode control strategy for the magnetic levitation system. Different from the conventional model-based control, ultralocal model-free control breaks the constraint of a precise system model. Therefore, an improved second-order ultralocal model is established for the magnetic levitation system. For the benefit of finite time convergence and nonsingularity, the nonsingular terminal sliding mode surface is chosen. As a second-order algorithm, supertwisting (ST) algorithm can fundamentally suppress the chattering effect of the sliding mode control. An adaptive ST algorithm is designed for the further improvement of the system dynamic response. The stability of the proposed scheme is strictly verified based on the Lyapunov stability theory. Simulation and experimental comparisons with the existing control methods validate the exceeding performance of the proposed strategy under various operating conditions.