# Reliability Assessment of Cyber-Physical Distribution Systems Considering Cyber Disturbances
## 1 Introduction  
With the wide application of information technology, the traditional distribution network has gradually developed into a highly integrated cyber-physical system (CPS), in which energy support is provided for the cyber system by the physical system, while the cyber system provides 3C (communication, computation, control) technical support for the physical system to achieve collaborative interaction between information flow and energy flow [1, 2]. However, compared with the traditional distribution network reliability assessment, the physical system in the distribution network CPS is highly dependent on the cyber system, which makes it face many new challenges in the system reliability assessment [3]. On the one hand, the interaction mechanism of CPS is more ambiguous, which significantly increases the complexity of the distribution network CPS analysis. On the other hand, cyberattacks and information component failures will have a potential negative impact on the reliability of CPS operation in distribution networks, with a strong dependence on the cyber-physical infrastructure. In recent years, malicious cyberattacks have been occurring, affecting the operational status of the system and subsequently the economic and social stability of the city [4]. The failure to make prompt decisions and take reasonable action in response to changes in the system status is the cause of severe losses. Consequently, there is an urgent need to analyze the impact of various types ofcyber disturbances, such as external and internal threats, on the reliability of CPSs in distribution networks. In Table 1, a comparative review of the available research works in the area of the reliability assessment of distribution network CPSs is presented. In the field of reliability assessment methods, available reliability assessments are divided into three main categories according to the different methods used for cyber systems and physical systems [5]: analytical methods for both cyber systems and physical systems, analytical methods for cyber systems and simulation methods for physical systems, and simulation methods for both cyber systems and physical systems. The simulation method is mainly based on probability and statistics, using computers for simulation [6]. For instance, reference [7] improves the sampling method of the Monte Carlo method. The improved important sampling algorithm realizes the optimization of the state probability distribution for the power system. The non-sequential Monte Carlo method is used in [8] to assess the reliability of the system. However, the computational efficiency problem and sampling difficulty of the simulation method are increasingly highlighted due to the increase in the scale of the system and the diversity of various component states. The main principle of the analysis method is to accurately calculate the reliability indices of the system in accordance with the parameters of each system component by analyzing the logical relationship between each component and the system [9]. Reference [10] uses the analytical method to calculate the availability of protection and monitoring functions and equates them to the corresponding physical components, which contribute to increasing the effectiveness of the CPS reliability assessment. In the field of reliability modeling, a fault tree analysis represents the logical relationships between systems and components by diagrams [11]. A fault tree analysis has been used in [12; 13; 14] to assess system reliability. However, certain application bottlenecks of the fault tree analysis method are reflected in the problem of space explosion in calculations with the increasing system scale [15]. Therefore, the method of solving the minimum cut set by using fault trees is only applicable to simple distribution networks, and the calculation is too complicated to be applied to the reliability index calculation of distribution network CPSs.