Perturbation Observer-Based Robust Control Using a Multiple Sliding Surfaces for Nonlinear Systems with Influences of Matched and Unmatched Uncertainties

This paper presents a lumped perturbation observer-based robust control method using an extended multiple sliding surface for a system with matched and unmatched uncertainties. The fundamental methodology is to apply the multiple surfaces to approximate the unknown lumped perturbations simultaneously influencing on a nonlinear single input–single output (SISO) system. Subsequently, a robust controller, based on the proposed multi-surface and the approximated values, is designed to highly improve the control performance of the system. A general stability of the lumped perturbation observer and closed-loop control system is obtained through the Lyapunov theory. Results of a numerical simulation of an illustrative example demonstrate the soundness of the proposed algorithm.

Observer-Based Consensus of Higher-Order Nonlinear Heterogeneous Multiagent Systems with Unmatched Uncertainties: Application on Robotic Systems

SUMMARYThe consensus of higher-order nonlinear heterogeneous multiagent systems with matched and unmatched uncertainties is studied in this paper. The distributed observer-based controllers for multiagent systems are achieved using a fixed-time sliding mode controller based on the disturbance observer. For this purpose, the disturbance observers are designed for finite-time estimation of matched and unmatched uncertainties. Using the estimated values, the fixed-time distributed sliding mode controllers are designed and the consensus protocol is achieved. In this regard, a theorem is proved, which guarantees the fixed-time convergence of consensus errors. The effectiveness of the proposed distributed controllers has been validated through simulations for two robotic multiagent systems and a numerical example.

Three-dimensional integrated guidance and control for strap-down missiles considering seeker’s field-of-view angle constraint

This paper investigates a novel three-dimensional (3D) integrated guidance and control (IGC) method for skid-to-turn (STT) missiles with strap-down seeker. Firstly, a nonlinear IGC model considering seeker’s field-of-view (FOV) constraint is built by employing the strap-down decoupling model, based on which the strict feedback state equation with matched and unmatched uncertainties is derived. Secondly, to handle the FOV angle and the roll angle constraints, an IGC law is proposed by combining dynamic surface control (DSC) approach with integral barrier Lyapunov function (iBLF), by which an adaptive law is employed to estimate the square of the disturbance bound. Finally, the uniform ultimately boundedness of the closed-loop system is proved strictly based on the Lyapunov stability theory, and the effectiveness and robustness of the proposed IGC scheme are illustrated with numerical simulations.

Robust Output Regulation of a Class of Nonlinear Systems Via Disturbance Observer in the Presence of Matched and Unmatched Uncertainties

The purpose of this paper is to propose a controller for nonlinear systems to achieve robust asymptotic tracking of a class of reference signals, in the presence of matched and unmatched disturbances and model uncertainties. The disturbances and reference signals are generated using two linear exosystems. In the proposed controller, instead of using the upper bound of disturbances in the design process, their instantaneous values are estimated disturbance observer. Therefore, disturbance observer-based control (DOBC) methods are less conservative with respect to conventional approaches. In addition to the DOBC design, a new stepwise procedure based on backstepping technique and sliding mode control is proposed. In the proposed approach, in each step, estimations of disturbances and the upper bound of model uncertainties are used to compose virtual control laws; these virtual control laws compose the final control law. Finally, numerical and practical examples are simulated to show the efficiency of the proposed technique and also to verify the theoretical results.

A Novel Disturbance Observer for Multiagent Tracking Control with Matched and Unmatched Uncertainties

In this paper, multiagent tracking control problem of second-order multiagent systems with unknown leader acceleration, input saturation, and matched and unmatched disturbances is investigated. An auxiliary system is constructed to approximate system position states, and a novel sliding mode disturbance observer is designed to estimate matched and unmatched uncertainties. A sliding mode disturbance observer-based control protocol is proposed by constructing a novel sliding mode manifold based on the sliding mode disturbance observer outputs. In addition, the input saturation and the unknown leader acceleration become a part of lumped uncertainties by using mathematic transformation. The lumped uncertainties estimated by the sliding mode disturbance observer are compensated by the sliding mode disturbance observer-based control protocol. Stability of the second-order multiagent systems is guaranteed via Lyapunov method. Finally, a simulation example is proposed to exhibit advantages and availability of the developed techniques.