The essence of intelligence lies in the acquisition/learning and utilization of knowledge. However, how to implement learning in dynamical environments for nonlinear systems is a challenging issue. This article investigates the deterministic learning (DL) control problem for uncertain pure-feedback systems by output feedback, which achieves the human-like learning and control in a simple way. To reduce the complexity of control design and analysis, first, by combining an appropriate system transformation, the original pure-feedback system is transformed into a simple normal nonaffine system. An observer is then introduced to estimate the transformed system states. Based on the backstepping and dynamic surface control techniques, a simple adaptive neural control scheme is first developed to guarantee the finite time convergence of the tracking error using only one neural network (NN) approximator. Second, through DL, the exponential convergence of the NN weights is obtained with the satisfaction of partial persistent excitation condition. Thus, locally accurate approximation/learning of the transformed unknown system dynamics is achieved and stored as constant NNs. Finally, by utilizing the stored knowledge, an experience-based controller is constructed and a novel learning control scheme is further proposed to improve the control performance without any further adaptation online for the estimate neural weights. Simulation results have been given to illustrate that the proposed scheme not only can learn and memorize knowledge like humans but also can utilize experience to achieve superior control performance.
K E Y W O R D Sadaptive control, deterministic learning, neural networks, pure-feedback nonlinear systems
INTRODUCTIONOver the past decades, a number of approximation-based adaptive neural/fuzzy control approaches have been developed for uncertain nonlinear systems based on the concepts of backstepping design. [1][2][3][4] However, in contrast to the strict-feedback systems with affine form, 5-8 only a few results have been obtained for nonaffine pure-feedback systems since lack of mathematical tools, which possess a more general system form and can represent many practical applications, such as Duffing oscillator, 9 mechanical systems, 10 continuous stirred tank reactor (CSTR) system, 11 the system to Int J Robust Nonlinear Control. 2020;30:2701-2718. wileyonlinelibrary.com/journal/rnc