Na Wang

All real control systems are subject to uncertainties and disturbances, so feedback controllers have to be designed such that closed-loop systems possess the desired dynamic and steady-state responses in the presence of any allowable uncertainties and disturbances. It is common practice to address the effects of uncertainties and disturbances via bounding techniques and the almost disturbance decoupling approach, respectively. Linear, affine, and power growth conditions on uncertainties are required for almost disturbance decoupling. However, when these conditions are not satisfied, almost disturbance decoupling is not possible. A new concept called weak disturbance decoupling is introduced to mitigate the effects of disturbances. A weak disturbance decoupling problem is to find a feedback controller so that the close-loop system has the weak disturbance decoupling performance, that is, the closed-loop system is stable and the norm of the output is not greater than the sum of a positive constant and the product of the norm of the disturbance and a positive constant.

This article considers a weak disturbance decoupling control problem for strict-feedback systems with unmodeled dynamics and disturbances. Utilizing a series of inequalities, the unmodeled dynamic is approximated. Using an adaptive backstepping control method, a weak disturbance decoupling controller is constructed to stabilize the closed-loop system. The primary objective of this paper is to design an adaptive controller that effectively attenuates the impact of disturbances in scenarios where such disturbances are present, while ensuring the bounded stability of system states in the absence of disturbances. Simulation and experiment results are presented to verify the effectiveness of the proposed weak disturbance decoupling strategy.

This article addresses a neural adaptive finite-time tracking control problem for n-th order strict feedback systems. By utilizing the backstepping design method, neural networks technology and finite-time stability theory, a tracking controller is constructed step by step. In contrast to the previous results, a (n−j)-th order differentiable piecewise function is introduced at step j so that the corresponding virtual controller is differentiable up to the order of n−j, all known terms in the original system and the derivatives of virtual controllers are treated as known and linear terms are introduced in virtual controllers and actual controllers. The proposed control strategy guarantees that all the closed-loop system variables remained bounded and the reference trajectory is well tracked in finite time. Finally, the efficacy of the proposed controller is verified by comparative experimental results for a 6-degree-of-freedom robotic manipulator. Test results confirm that the tracking controller with linear terms, virtual control derivatives and known terms has higher control accuracy.

Volatile organic compounds exist widely in building interior decoration materials. In order to reduce the health effects of this substance, this paper is devoted to the tracking control problem and almost disturbance decoupling problem for determining volatile organic compounds in a climate chamber control system. According to backstepping technology and implicit function theorem, a state feedback controller is designed. The variables that are unpredictable are regarded as disturbances and are handled by using the almost disturbance decoupling approach. The effectiveness of the control strategy is proved by stability analysis and two simulation examples.

Many practical control systems contain unknown terms and parameters, and are required to complete a control task at prescribed time and operate for an infinite-time interval. This article considers a prescribed-time (PT) tracking control problem for strict feedback systems with unmodeled dynamics (UDs). A PT adjustment function is designed, which is sufficiently differentiable for an infinite-time interval. By applying the PT adjustment function, a modified PT dynamic signal is first introduced to dominate the impact of UDs. Utilizing a series of inequalities, the UDs are approximated. By using the backstepping design method and PT stability theory, a tracking controller is constructed. With the proposed control strategy, both PT and infinity-time tracking performance are guaranteed, and the output tracking error enters a neighborhood of the origin at PT, whose size can be made small enough. Finally, comparative simulation and experiment results are provided to illustrate the effectiveness of the proposed controller.

Summary: It is well known that all practical control systems are subject to external disturbances. Therefore, a feedback controller should be designed so that the closed‐loop system has some desired properties such as stability, good tracking performance, at the same time, the impact of external disturbances on the performance of the closed‐loop system is attenuated to some degree. On the other hand, almost all models for real fully actuated systems, which are derived based on the physical laws, are described by a set of high order differential equations. The traditional method for controlling these fully actuated systems is to convert the high order differential equations to first order differential equations, which are called the state equations, and then to design feedback controllers by using the state‐space design methods. Such conversion causes some inconveniences. To overcome such inconveniences, a high‐order fully actuated (HOFA) design method has been proposed to control HOFA systems. The main goal of this paper is to design a weak disturbance decoupling controller for HOFA nonlinear systems to guarantee the stability and desired output tracking performance of the closed‐loop system and to attenuate the impact of disturbances.