This paper focuses on the control problem of time-delay nonlinear high-order fully actuated (HOFA) systems with unmodeled dynamics and unknown dead-zone input. The primary objective of this paper is to design an adaptive controller by using the HOFA systems approach. To do so, we need to tackle some technical obstacles. Firstly, in order to deal with unmodeled dynamics in the HOFA systems, the technique of changing the supply rate is combined with the HOFA systems approach. Secondly, an adaptive dead-zone inverse is constructed to compensate for the influence of the unknown asymmetrical dead-zone input nonlinearity. Then, the controller is designed by the HOFA systems approach, and it is proved that all states of the systems converge to a bounded region based on the Lyapunov-Krasovskii functions. Finally, the simulation results demonstrate the effectiveness of the designed adaptive controller.
K E Y W O R D Sadaptive controller designs, dead-zone input, fully actuated nonlinear systems, time-delay systems, unmodeled dynamics
INTRODUCTIONIn recent years, the HOFA systems approach has received much attention, 1-7 which has been proven to be very effective and simple in dealing with the analysis and control problems of second-order or higher-order nonlinear systems such as Lagrangian systems, angular momentum, inverted pendulum systems, and so forth. A significant advantage of this approach is that a linear constant closed-loop system with an arbitrary assignable eigenstructure can be obtained, and all the design degrees of freedom existing in the closed-loop system are provided. Therefore, the feature helps to deal with many nonlinear system control problems, such as robust control, 3 adaptive control, 4 robust adaptive control, 5 disturbance attenuation 6 and disturbance decoupling. 7 On the basis of the study above, Liu 8 investigated the control problem of HOFA nonlinear systems with time-varying delays in the discrete-time domain. The problem of adaptive control for a class of time-delay systems was studied by the HOFA systems approach, 9 and a continuous adaptive controller was designed for the system. However, among the above results, it should be pointed out that there is still content for development based on the HOFA systems approach to deal with nonlinear problems such as nonlinear time-delay, unmodeled dynamics and dead-zone input, and so forth. It is well known that time-delay is widespread in the practical control systems, such as electrical power systems, communication systems, teleoperation systems, chemical reactor systems, and so forth. [10][11][12] Besides, as we all know, many systems cannot be accurately modeled due to certain factors when dealing with the control problems of practical physical systems, so we often encounter nonlinear systems with unmodeled dynamics. The existence of time-delay