Guest editorial: Secure and resilient operations of cyber-physical urban energy systems

Security and resilience of energy systems have become major concerns in energy engineering. Several recent power grid attacks, including the first known devastating cyber-attack in 2015 and the first US ‘denial of service’ attack to the western power grid in March 2019, remind us of the global challenge represented by energy system attacks launched through the cyber-communication network. Meanwhile, attacks on energy systems are growing in number, causing severe impacts on public health and national security.

Resilience is playing an essential role in operating a dynamic cyber-physical energy system, such as microgirid. Thus, it is necessary to systematically understand the operation mechanism of a dynamic energy system, to implement proper strategies to improve its resilience subject to disturbances or attacks. To advance those fields, scientific research is needed to study and develop novel technologies, including but not limited to resilience study, resilient control, attack detection, defense strategies, machine learning, and data analytics.

This Special Issue of IET Energy Systems Integration focuses on Secure and Resilient Operations of Cyber-Physical Urban Energy Systems. Brief descriptions of each of the three papers in the Special Issue are provided below. We encourage the readers to refer to the papers for more details.

In “Resilience Assessment Methodologies and Enhancement Strategies of Multi-Energy Cyber Physical Systems of the Distribution Network”, Yang et al. introduced an extensive review on the state-of-the-art-research of power systems resilience. They give a definition of the Multi-Energy Cyber Physical Systems resilience and summarise its related characteristics, and the models of extreme disasters and equipment vulnerability are analysed. The qualitative resilience assessment curve, indexes and process of the Multi-Energy Cyber Physical Systems are developed. They present the key improvement measures for the planning and operation of MECPSs resilience and the focus of future research.

In “Attack and Defence methods in cyber-physical power system (CPPS)”, Yang and Liu focus on dealing with the attacks against complex CPPS, by profiling the structure of CPPS and the potential threats, conducting an in-depth analysis of CPPS attack modes from the cyber and physical subsystems, and summarising the three-level security defense methods for CPPS in detail. The future technological development prospects of CPPS security research are explicitly addressed, which will provide technical support for building reliable, safe, and robust energy systems. Overall, this paper analyses and summarises the typical attack patterns and multi-dimensional defense methods of CPPS and presents four problems that need to be deeply studied and solved in CPPs defense, so as to provide a reference for the subsequent technical development. First, the existing research studies on CPPS security are based on the attacks that have been detected or have been intercepted, but there is a lack of effective research on the identification and defense against unknown attacks. Therefore, the identification and active defense without a priori information of unknown attacks are of great significance to improve the security of CPPS. Second, Coordinated Cyber-Physical Attacks (CCPA) is more destructive and stealthier than network attacks due to the diversity of attack combinations and the difficulty of attack detection. However, there is little research on CCPA, so the new defense methods against CCPA are the interesting topic worth exploring. Third, with the development of the new generation of artificial intelligence technology, represented by deep learning and reinforcement learning, it has shown powerful and good application effects in the field of CPPS attack detection and security defense. It is necessary to establish a comprehensive information collection mechanism and a unified CPPS attack sample database. It can be collaboratively shared among countries around the world. Fourth, the off-line simulation is mainly used to study the dynamic process of CPPS attack and defense, but it hardly demonstrates the complex and fast dynamic evolution of both cyber and physical sub-systems in CPPS. Therefore, there is an urgent need to establish a real experimental field, which will play an extremely important role in promoting CPPS system risk analysis, chain fault propagation, resource deployment and dynamic arming.

In “Vulnerability Analysis of Secondary Control System when Microgrid Suffering from Sequential DoS Attacks”, Wang et al. proposed a vulnerability assessment method when the microgrid suffering denial-of-service (DoS) attacks. The sequence model of the attack actions and ‘N-1’ contingency actions are proposed to find the traversal expression. With the traversal method, vulnerable factors of the microgrid can be interpreted by the proposed comprehensive vulnerability metric which provides an intuitive and easy way to understand the vulnerability of microgrid secondary control system. The metric is composed by four basic indicators which concern not only final states of the microgrid when a DoS attack ends, but also the dynamic process of the microgrid. To test the proposed metric, two mitigation methods with the purpose of mitigating the impact on the physical system caused by the DoS attacks are also proposed: the self-adaptive coefficient method and the fault tolerance method. Finally, a 33-node microgrid platform with 8 DGs has been built to test the proposed vulnerability assessment method. The study results show that the nodes with high cyber degree are the vulnerable nodes and the fault-tolerance method can provide a better mitigation result with the average metric 9.41 than the self-adaptive coefficient method with 9.03.