In this paper, we present a control design framework wherein an adaptive-based corrective signal is augmented to the output of the nominal controller in order to suppress or counteract the effect of malicious actuator attacks. Due to the unavailability of full-state measurements, a nonminimal controllable realization of the nominal closed-loop system is used to design the corrective signal predicated on partial state information. Two illustrative numerical examples are given to demonstrate the efficacy of the proposed adaptive control architecture.
KEYWORDSactuator attacks, adaptive control, cyber-physical systems, output feedback
INTRODUCTIONCyber-physical systems (CPSs) have different meanings to different researchers and practitioners. The common thread in CPSs is the fact that they involve the integration of computation, communication, and physics working together in order to achieve required control objectives. These systems usually consist of networked agents, which include actuators, sensors, communication devices, and control processing units. 1 Since communication and computation devices are becoming cheaper and smaller, they are extensively used to interact directly with the physical environment, and hence, the use of these devices is becoming ubiquitous. Therefore, sensors and actuators, which collect, exchange, and use data in a CPS, are designed such that they can be interfaced with network and communication devices. The main reason of the advent of CPSs is the tight integration of the physical processes they control and computational resources and communication capabilities that exist in modern engineering systems. 2 The CPS architectures are being used in many different applications such as power systems, transportation systems, process control systems, large-scale manufacturing systems, ecological systems, and health care systems. Many of these applications involve safety-critical systems, and hence, any failures or cyber-attacks can cause catastrophic damage to the physical system being controlled resulting in drastic societal ramifications.Due to the open communication and computation platform architectures of CPS, one of the most important challenges in these systems is their vulnerability to malicious cyber-attacks. Cyber-attacks can severely compromise system stability, performance, and integrity. In particular, malicious attacks in feedback control systems can compromise sensor measurements as well as actuator commands to severely degrade closed-loop system performance and integrity. Cyber-attacks are continuously becoming more sophisticated and intelligent, and hence, it is vital to develop algorithms that can suppress their effects on CPSs. 3 Depending on the a priori system knowledge and the available resources of the attacker, different malicious attacks can be injected into CPSs. 4 The available resources of the attacker can be generally categorized as disclosure and disruption Int J Adapt Control Signal Process. 2019;33:943-955.wileyonlinelibrary.com/journal/acs