High-order nonsingular fast terminal sliding mode control of electromagnetic linear actuator based on dual disturbance observers

Abstract

To improve position tracking of an electromagnetic linear actuator (ELA) under simultaneous mismatched and matched disturbances, an improved composite control framework based on conventional sliding-mode control (SMC) is proposed by integrating adaptive dual disturbance observers (DDOs) with a third-order nonsingular fast terminal sliding-mode controller (3rd-NFTSMC). A third-order nonlinear ELA model with displacement, velocity, and current as the state variables is established, and the improved LuGre model is employed to describe nonlinear friction. Nonlinear friction and other mechanical disturbances are incorporated into the mismatched disturbance, whereas electrical parameter variations are incorporated into the matched disturbance. The DDOs separately estimate the two disturbances with gains adjusted by adaptive laws, and their estimates are introduced through their respective compensation paths. The 3rd-NFTSMC constructs a third-order nonsingular fast terminal sliding-mode surface from the displacement, velocity, and estimated acceleration errors, thereby avoiding singularity. A power-integral reaching law with a smooth sigmoid function accelerates convergence and alleviates chattering. Practical finite-time stability is established through Lyapunov analysis. Simulation and experimental results under various operating conditions demonstrate that, compared with the other control methods considered in this paper, the proposed method more effectively suppresses the influence of matched and mismatched disturbances, achieving faster dynamic response and higher control accuracy.