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In this paper, we focus on an output secure consensus control issue for nonlinear multi-agent systems (MASs) under sensor and actuator attacks. Followers in an MAS are in strict-feedback form with unknown control directions and unknown dead-zone input, where both sensors and nonlinear characteristics of dead-zone in actuators are paralyzed by malicious attacks. To deal with sensor attacks, uncertain dynamics in individual follower are separated by a separation theorem, and estimation parameters are introduced for compensating and mitigating the influence from adversaries. The influence from actuator attacks are treated as a total displacement in a dead-zone nonlinearity, and an upper bound, as well as its estimation, is introduced for this displacement. The dead-zone nonlinearity, sensor attacks and unknown control gains are gathered together regarded as composite unknown control directions, and Nussbaum functions are utilized to address the issue of unknown control directions. A distributed secure consensus control strategy is thus developed recursively for each follower in the framework of surface control method. Theoretically, the stability of the closed-loop MAS is analyzed, and it is proved that the MAS achieves output consensus in spite of nonlinear dynamics and malicious attacks. Finally, theoretical results are verified via a numerical example and a group of electromechanical systems. [ABSTRACT FROM AUTHOR]

In this work, adaptive consensus control of leader-following fractional-order multi-agent systems whose each subsystem includes functional uncertainties, external disturbances, and unknown control directions is investigated utilizing neural networks and the Nussbaum function. The controller is synthesized within the framework of the backstepping algorithm, where the "explosion of complexity" problem is mitigated through the use of a command filter, and the adverse impact of filtered errors is decreased using compensation signals. The function uncertainties of each follower are approximated by neural networks, and a disturbance update law is developed to identify the boundary of the disturbance. Importantly, a general conclusion is provided to affirm the applicability of the Nussbaum function in addressing controller design for fractional-order systems with unknown control directions. Finally, the validity of the proposed approach is verified via two numerical examples. [ABSTRACT FROM AUTHOR]