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A systematic differentiator-based adaptive backstepping control methodology is proposed for a class of sandwich-like nonlinear system with unknown state-dependent deadzone nonlinearity and parametric uncertainties. The novelty of our approach is that a high-order sliding mode differentiator is utilized to estimate the nonstrict feedback coupling term resulting from the sandwiched deadzone, and all the outputs of the differentiator are integrated into the backstepping procedure based on Lyapunov functions with flat zone recursively. By this approach, all the unknown parameters are estimated online, the discontinuity of the virtual input caused by bound estimations is avoided. It is shown that the ultimate boundedness of all the closed-loop signals is achieved and the output tracking error converges to a preset set. Simulation is performed to verify the theoretical findings. [ABSTRACT FROM AUTHOR]

In this paper, we study a robust disturbance attenuation problem that arises when applying the Artstein–Kwon–Pearson reduction transformation for a class of uncertain Lipschitz nonlinear systems with input delay and external disturbances. A conventional predictor-based feedback controller is adopted with the control gain matrix carefully identified by solving a couple of sufficient conditions in terms of linear matrix inequalities. Lyapunov–Krasovskii functionals are constructed to guarantee that the robust disturbance attenuation problem can be solved by the proposed controller. A numerical example is included to validate the performance of the proposed controller. [ABSTRACT FROM AUTHOR]

This paper deals with the leader-follower consensus problem of Lipschitz nonlinear systems under fixed directed communication networks. Both state and output feedback control are proposed based on state and output measurements of neighbouring agents, respectively. Laplacian matrix features are explored for the stability analysis, and the sufficient conditions are derived to solve the consensus problem. Finally, simulation results are included to demonstrate the effectiveness of the output-based consensus controller. [ABSTRACT FROM PUBLISHER]

This study deals with the fixed‐time stabilisation of a class of non‐linear systems. A non‐linear controller, based on sliding mode, is proposed to ensure the fixed‐time stabilisation of a non‐holonomic system in chained form. An upper bound of the settling time, independent of the initial system state, is estimated. Then, a distributed switched strategy, based on local information, is introduced to solve the fixed‐time consensus problem for multiple non‐holonomic agents. Using Lyapunov functions, the switching times are explicitly given and only depend on the controller gains and the Laplacian matrix. Simulation results highlight the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

This brief addresses an output feedback control design for Lipschitz nonlinear systems in the presence of input delay. A nonlinear observer is introduced to estimate the system states. A truncated predictor state feedback, which is the conventional predictor state feedback law with the distributed term dropped, is implemented with the estimated states. Lyapunov–Krasovskii functionals are constructed to establish conditions under which this observer-based truncated predictor feedback law asymptotically stabilizes the system at the origin. The effectiveness of the proposed method is demonstrated on Chua's circuit. [ABSTRACT FROM AUTHOR]

This paper is devoted to investigating the finite-time consensus problem for a multi-agent system in networks with undirected topology. A new class of global continuous time-invariant consensus protocols is constructed for each single-integrator agent dynamics with the aid of Lyapunov functions. In particular, it is shown that the settling time of the proposed new class of finite-time consensus protocols is upper bounded for arbitrary initial conditions. This makes it possible for network consensus problems that the convergence time is designed and estimated offline for a given undirected information flow and a group volume of agents. Finally, a numerical simulation example is presented as a proof of concept. [ABSTRACT FROM PUBLISHER]

This paper investigates the fixed-time cooperative output regulation (FTCOR) problem with unknown exosystem of second-order nonlinear multiagent systems. To solve this problem, it is necessary to ensure that each agent can obtain the reference trajectory originating from an unknown exosystem and reconstruct the solution of the regulator equation containing the exogenous signal and unknown parameter vectors within a fixed time, and the unknown exosystem makes it difficult to solve these two problems with existing tools. By using auxiliary filtering variables, we propose a fixed-time adaptive distributed observer (FTADO) and design a fixed-time distributed internal model (FTDIM) based on this FTADO. These two new tools ensure the solvability of the two problems just mentioned. Then, based on these two tools, we transform the problem into a fixed-time stabilization problem of a so-called augmented system. Through the backstepping technique, we propose a distributed controller that solves this fixed-time stabilization problem while relaxing the assumptions of similar references. • More general and difficult controlled objects and research problem are considered. • A fixed-time adaptive distributed observer for an unknown leader system is designed. • A compensator is designed to reconstruct the ideal value of the system in fixed time. • Additional assumption for similar work is avoided. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a nonlinear robust controller is proposed to deal with the flight mode transition control problem of tail-sitter aircrafts. During the mode transitions, the control problem is challenging due to the high nonlinearities and strong couplings. The tail-sitter aircraft model can be considered as a nominal part with uncertainties including nonlinear terms, parametric uncertainties, and external disturbances. The proposed controller consists of a nominal H ∞ controller and a nonlinear disturbance observer. The nominal H ∞ controller based on the nominal model is designed to achieve the desired trajectory tracking performance. The uncertainties are regarded as equivalent disturbances to restrain their influences by the nonlinear disturbance observer. Theoretical analysis and simulation results are given to show advantages of the proposed control method, compared with the standard H ∞ control approach. [ABSTRACT FROM AUTHOR]