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Summary: This paper studies the problem of model reference safety‐critical adaptive control for a class of nonlinear and switched systems with nonlinear reference models. An adaptive law is designed to estimate unknown parameters, while an energy function is proposed to guarantee the boundedness and safety of nonlinear systems. Also, a model reference safety‐critical adaptive control framework is established to ensure that the state trajectory of nonlinear systems is always within the safe set in the presence of unknown parameters. Moreover, the results obtained are extended to switched uncertain nonlinear systems under arbitrary switchings. A switched adaptive controller is designed to reduce the conservativeness caused by adoption of a common update law for all subsystems. Also, the safety of switched systems under arbitrary switchings is guaranteed as well as the boundedness of the error states between the switched nonlinear systems and the switched reference models by utilizing the common Lyapunov function method. Finally, two illustrative numerical examples are given to demonstrate the effectiveness of the proposed control architecture. [ABSTRACT FROM AUTHOR]

Summary: In this work, an adaptive feedback linearized model predictive control (AFLMPC) scheme is proposed to compensate system uncertainty for a class of nonlinear multi‐input multi‐output system. Initially, a feedback linearization technique is used to transform the nonlinear dynamics into an exact linear model, thereafter, a model predictive control scheme is designed to obtain the desired tracking performance. A suitable constraint mapping algorithm has been developed to map input constraints to the new virtual input of the proposed control scheme. The proposed control scheme utilizes multiple estimation model and the concept of second‐level adaptation technique Pandey et al. (2014) to handle the parametric uncertainty in real‐time. Hence, the adaptive term in the control scheme is used to counteract the effect of model uncertainties and parameter adaptation errors. The effectiveness of the proposed AFLMPC control algorithm has been verified successfully in simulation as well as the experimental setup of the TRMS model. The unavailable states of the nonlinear system have been estimated using an extended Kalman filter based state observer. The performance of the proposed control algorithm has been compared with other existing nonlinear control techniques in simulation and experimental validation. [ABSTRACT FROM AUTHOR]

This paper proposed an adaptive nonlinear model predictive control approach for a 2‐DoF helicopter model with both parametric uncertainties and input–output constraints. In the proposed control technique, the nonlinear helicopter model is linearized along the prediction horizon using a state and parameter‐dependent state‐space model. Furthermore, a linear quadratic objective function with constraints is carried out using the developed linearized model. Here, the multiple estimation model and the concept of second‐level adaptation are used to handle the parametric uncertainty of the nonlinear system. To ensure the boundedness of the estimated parameter within a predefined compact region, a projection based adaptive law is used. The adaptive tuning laws for the unknown parameters are derived by Lyapunov stability analysis. An ensemble Kalman filter has been used to observe the unavailable states of the 2‐DoF helicopter model. The effectiveness of the proposed control algorithm has been verified successfully in simulation as well as real‐time experimental setup of 2‐DoF of helicopter model and results are documented in tabular form to show superiority with an existing approach. [ABSTRACT FROM AUTHOR]

Summary: This article explores the impact of regular perturbations (ie, small terms) in input constrained optimal control problems for nonlinear systems. In detail, it is shown that perturbation terms of magnitude ε appearing in the dynamics or the cost function lead to a variation of magnitude Kε2 in the optimal cost. The scale factor K can be estimated from the nominal (ε=0) solution and the analytic expressions of the perturbations. This result extends existing results that have been established in the absence of input constraints. Technically, the result is proven by means of interior penalties which allow constructing a sequence of suboptimal feasible solutions. Two numerical examples serve as illustration. [ABSTRACT FROM AUTHOR]

The problem of robust tracking and model following is considered for a class of uncertain non‐linear systems with any time‐varying delays and completely unknown dead‐zone input non‐linearity. Here, time‐varying delays are assumed to be any continuous and bounded non‐negative functions, and any information on their derivatives need not known. In the study, the system uncertainties assumed to be any continuous and bounded non‐linear functions, and their non‐linear upper bounds do not need also to be known. Based on Wu inequality, a novel design method is presented by which some simple and direct robust tracking control schemes can be easily constructed. It is shown that the tracking error between the output of an actual dynamical system and the dynamical signals of the given reference model can be guaranteed to be uniformly exponentially bounded. A numerical example is also given to describe the design procedure of the presented method, and the simulations of this numerical example are implemented to demonstrate the validity of the theoretical results. [ABSTRACT FROM AUTHOR]

Summary: The objective of this paper is to develop performance‐based fault detection (FD) and fault‐tolerant control (FTC) schemes for a class of nonlinear systems. To this end, the representation forms of nonlinear systems with faults and the controller parameterization forms are studied first with the aid of the nonlinear factorization technique. Then, based on the stable kernel representation and the stable image representation of the faulty nonlinear system, the stability performance of the closed‐loop system is addressed, respectively. The so‐called fault‐tolerant margin is defined to evaluate the system fault‐tolerant ability. On this basis, two performance‐based FD schemes are developed aiming at detecting the system performance degradation caused by system faults. Furthermore, to recover the system stability performance, two performance‐based FTC strategies are proposed based on the information provided by the FD unit. In the end, a numerical example and a case study on the three‐tank system are given to demonstrate the proposed results. [ABSTRACT FROM AUTHOR]

This study is to estimate the bounds for the maximum allowable sampling interval (MASI) and the coarsest quantisation density (CQD) that guarantee the stability of non‐linear systems with multi‐input signals sampled and logarithmic quantised. First of all, hybrid feedback systems are proposed to describe the non‐linear control systems. Then a sufficient condition is provided to ensure that the systems are uniformly globally exponentially stable. A crucial step is to find a novel Lyapunov function to verify the stability conditions in the sense of the hybrid framework. Meanwhile, explicit bounds for the MASI and CQD are obtained to guarantee stability. Furthermore, in the case of no quantisation or no sampling, some special stability criteria can be also obtained. Finally, some examples are given to illustrate the effectiveness of the proposed theorem. [ABSTRACT FROM AUTHOR]

Summary: An unpredictably maneuvering speedy target travels in a plane, which also hosts a team of fully actuated robots whose velocities and accelerations are upper‐bounded in magnitude. The robots should approach the target and then follow it at a prespecified distance. They also should achieve an even self‐distribution around the target and a given angular velocity of rotation about the target. Every robot has access to the relative position of the target and other robots (in the latter case, within a finite "visibility" range) and to the angular speed of its own pure rotation; access to the coordinates of its own linear velocity in its own local frame is also employed in some cases. The robots are not equipped with communication facilities and cannot distinguish among one another; assignment of different roles to various robots is infeasible. Necessary conditions for the mission feasibility are first obtained. A distributed control law is then presented, and its global convergence and collision avoidance property are rigorously justified under slight enhancement of the just mentioned necessary conditions. The performance of the control law is illustrated by computer simulations. [ABSTRACT FROM AUTHOR]

Summary: This paper develops novel fault‐tolerant integral sliding mode control allocation schemes for a class of an overactuated affine nonlinear system. The proposed schemes rely on an existing baseline controller, and the objective is to retain the nominal (fault‐free) closed‐loop performance in the face of actuator faults/failures by effectively utilizing actuator redundancy. The online control allocation reroutes the control effort to healthy actuators using the knowledge of actuator effectiveness level estimates. One of the proposed schemes is tested in simulation using a well‐known high‐fidelity model of a large civil transport aircraft (B747) from the literature. Good simulation results show the efficacy of the scheme. [ABSTRACT FROM AUTHOR]

Summary: In this paper, the global stabilization problem of a class of cascaded systems with upper‐triangular structures is considered. On the basis of the forwarding technique, a series of virtual controllers are recursively constructed for the driving subsystem. According to the mild assumption imposed on the driven subsystem, a partial‐state feedback controller is obtained for the entire cascaded nonlinear system by developing a delicate design fashion. It is shown that the obtained state feedback controller will render the entire cascaded nonlinear system globally asymptotically stable. Numerical examples are conducted to validate the proposed control scheme. [ABSTRACT FROM AUTHOR]

The by-now standard formulation of interconnection and damping assignment passivity-based control (for input-affine systems) proposes the solution of a partial differential equation (PDE) that defines the assignable energy functions and computes the control using the input matrix pseudo-inverse. However, in its original formulation-a more general design procedure was proposed, which was essentially abandoned because of the difficulties in solving the PDE. In this note, a new family of interconnection and damping assignment passivity-based controls is proposed by extending this method in the following directions: (i) It allows the desired interconnection and damping matrices to depend on the control signal, giving the possibility to shape the PDE to ensure its solvability; (ii) the PDE directly generates the control signal that have, in general, simpler expressions; and (iii) it is applicable for general nonlinear systems possibly not affine in the control. The technique is illustrated with three examples, including the well-known boost power converter for which it yields a simple, high-performance controller. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A solution to the stabilization problem of a compact set by means of the Interconnection and Damping Assignment Passivity-Based Control methodology, for an affine nonlinear system, was introduced. To this end, we expressed the closed-loop system as a Port Hamiltonian system, having the property of almost all their trajectories asymptotically converge to a convenient limit set, except for a set of measure zero. It was carried out by solving a partial differential equation (PDE) or single matching condition, which allows the desired energy level or limit set E to be shaped explicitly. The control strategy was tested using the magnetic beam balance system and the pendulum actuated by a direct current motor (DC-motor), having obtained satisfactory results. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]