Implementation of Switching Fallback Control to Expand Availability under Cyber-attacks

Industrial control systems (ICSs) require system design and operation under cyber-attacks. As a control method for ICSs under cyber-attacks, fallback control is required to continue minimum control with limited functions. This study aims to design and implement a method of switching multiple fallback control that enables both safe operation continuity and control performance against cyber-attacks. To prevent system deadlock and ensure availability, the current researchers model the fallback control operation as a discrete event system (DES) based on the system’s controllability via supervisory control.The modeling targets are Factory Automation (FA) systems consisting of Supervisory Control And Data Acquisition (SCADA), Programmable Logic Controllers (PLCs) for a robot arm and conveyors, and a fallback PLC. In this study, we divide the supervisor functions and implement an abnormality detection function in SCADA and a fallback switching function in the fallback PLC, respectively. To verify the effectiveness of these functions, we conduct two types of fallback control switches under two attack scenarios involving tampering with the conveyor speed values.As a result, we were able to achieve the optimal selection and switching of fallback control based on the severity of the attacks. This makes it possible to realize a control system with both controllability and availability against cyber-attacks.