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For the adversarial attacks on the communication links from the controller to the actuators, most of the existing attack-resilient control results focus on denial-of-service attacks. Unlike the existing results, this paper studies the observer-based attack-resilient control problem for linear systems with false data injection attacks and process disturbances. Due to limited resources, the malicious attacker is assumed to only manipulate a certain number of communication links from the controller to the actuators. A novel control architecture is proposed, which consists of an attack-resilient state observer, a controller gain scheme, and a supervisory switching strategy. The observer is developed based on the maximin strategy, and state estimation will be used to construct the controller. The switching strategy is designed to pick an appropriate controller gain and prevent the attack signals from entering the plant automatically. It is shown that the closed-loop system is stable with an attack-resilient performance.Finally, to verify the effectiveness of the proposed controller, simulation results on a linearized reduced-order aircraft system and an IEEE six-bus power system are provided. KEYWORDSattack-resilient control, cyber-physical systems, observer, supervisory switching strategy INTRODUCTIONCyber-physical systems (CPSs) integrate physical processes, computational resources, and communication capabilities 1 and merge the cyber-world with the physical world. CPSs have become prevalent in multifarious real-wold systems, including communication systems, power systems, and aerospace systems. Since CPSs are increasingly connected to the intranet and internet for remote monitoring and control, they become more vulnerable to malicious cyberattacks. For this reason, security issues of CPSs subject to cyberattacks have attracted considerable attention in the last decades. [2][3][4] In a networked control system, cyberattacks to the communication links can be broadly divided into two categories: denial-of-service (DoS) attacks and deception attacks. DoS attacks refer to obstructing/blocking the communication between networked agents 5,6 and causing packet losses. Deception attacks (including false data injection [FDI] attacks, 7,8 sparse attacks, 9 replay attacks, 10 zero-dynamic attacks, 11 etc) are intended to manipulate transmitted data packages and result in false feedback information. 8 For the immense field of CPSs' application, various problems have been investigated, eg, sensor scheduling, 12,13 secure state estimation, 14-16 and secure control. 17 4382It is also worth noting that there are many research challenges toward achieving a secure control objective, as argued in the work of Cardenas et al. 17 During recent years, some researchers have tried to solve the challenging secure control problem for CPSs.Related works on secure control: The secure estimation and control problem was addressed in the work of Fawzi et al 18 for the discrete-time systems with FDI sensor attacks. The main idea is to first design ...

Summary This paper investigates the attack‐resilient state estimation problem for linear systems with adversarial attacks and unknown inputs, where the upper bound of the unknown inputs is unknown. It is assumed that the attacker has limited resources and can only manipulate a certain number of sensors. In most of the existing observer design approaches for the systems with unknown inputs even in the absence of attacks, the observer matching condition should be satisfied. To overcome this restriction, a novel switched observer is proposed, where the matched unknown inputs will be completely compensated by means of the outputs and the mismatched part will be suppressed in terms of L2‐gain rejection property. Meanwhile, the observer can provide an attack‐resilient state estimation. Compared with the existing results, the proposed observer can guarantee that the resulting observer error system is stable with unknown input attenuation level γ that can be optimized. Finally, a simulation example of an unmanned ground vehicle is provided to show the effectiveness of the proposed approach.