The increasing adoption of power electronic devices may lead to large disturbance and destabilization of future power systems. However, stability criteria are still an unsolved puzzle, since traditional small-signal stability analysis is not applicable to power electronics-enabled power systems when a large disturbance occurs, such as a fault, a pulse power load, or load switching. To address this issue, this paper presents for the first time the rigorous derivation of the sufficient criteria for largesignal stability in DC microgrids with distributed-controlled DC-DC power converters. A novel type of closed-loop converter controllers is designed and considered. Moreover, this paper is the first to prove that the well-known and frequently cited Brayton-Moser's mixed potential theory (published in 1964) is incomplete. Case studies are carried out to illustrate the defects of Brayton-Moser's mixed potential theory and verify the effectiveness of the proposed novel stability criteria.Index Terms-large-signal stability criteria, power electronicsenabled power systems, distributed-controlled power converters, constant power loads, potential theory. I. INTRODUCTIONOWER systems are going through a paradigm shift from electric machine-based to power electronics-based, with a huge number of different players on the supply side [1]-[3]. Nowadays, thousands of distributed energy resources (DERs) are being integrated into power systems through power electronics components such as solar panels, wind turbines, and energy storage systems; however, the integration of numerous power electronic components and constant power loads (CPLs) destabilizes power systems and leads to critical oscillations. Consequently, one of the crucial challenges of this new paradigm is to keep the whole power system stable. The stability issues faced by DC microgrids are especially severe and urgent due to their unique properties. First, the low inertia of DC microgrids sharply weakens their stability; and second, owing to their advantage of smooth control, DC microgrids are unprecedentedly more promising than AC power systems given the increasing penetration of DERs. Therefore, the purpose of this paper is to solve the stability issues in power-converterdominated DC microgrids.Recent works related to stability analysis in DC microgrids can be categorized according to the type of disturbance and the number of converters, as shown in Table I. Most of the stability studies of DC microgrids are performed using small-signal and linearized models, especially for large-scale DC microgrids

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This study focuses on the problem of attack quantification in distribution automation systems (DASs) and proposes a quantitative model of attacks based on the common vulnerability scoring system (CVSS) and attack trees (ATs) to conduct a quantitative and systematic evaluation of attacks on a DAS. In the DAS security architecture, AT nodes are traversed and used to represent the attack path. The CVSS is used to quantify the attack sequence, which is the leaf node in an AT. This paper proposes a method to calculate each attack path probability and find the maximum attack path probability in DASs based on attacker behavior. The AT model is suitable for DAS hierarchical features in architecture. The experimental results show that the proposed model can reduce the influence of subjective factors on attack quantification, improve the probability of predicting attacks on the DASs, generate attack paths, better identify attack characteristics, and determine the attack path and quantification probability. The quantitative results of the model's evaluation can find the most vulnerable component of a DAS and provide an important reference for developing targeted defensive measures in DASs. these attack quantification results can also provide an important reference for security technicians to implement the DAS defense system.Quantification of the probability of an attack on a DAS directly affects the in-depth analysis of the system's security. Wang et al. [9] proposed a multilevel analysis and modeling method for a power system's communication network. Their case study showed that this method can be used to evaluate the static and dynamic relationships among power networks. Kateb et al. [10] developed an optimal structure tree method for risk assessment in a wide-area power system that can minimize the spread of network attacks. The authors in [9,10] provided a well-optimized evaluation of a specific power network. However, these evaluation neither reflected the attacker's behavior in terms of quantification of the probability of an attack nor provided suggestions for the protection of specific parts of the power system. The authors in [11] and the authors in [12] presented an attack assessment framework based on Bayes attributes-a stochastic game model and a fast modeling method for input data, respectively-which included network connection relationship and vulnerability information. However, the proposed methods were found to be inefficient when applied in DASs due to DAS architecture complexity and expansibility, and they could not generate attack path. The authors in [13] proposed a method for modeling network attacks with a multilevel-layered attack tree (MLL-AT), presented a description language based on the MLL-AT for attacks, and quantified the leaf nodes. This attack tree (AT) was found to be able to accurately model the attacks, especially multilevel network attacks, and can be used to assess system risks. However, the research is mainly based on cyberattacks, and there is no physical attacks involved. Besides, th...

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Mobile edge computing (MEC) effectively integrates wireless network and Internet technologies and adds computing, storage, and processing functions to the edge of cellular networks. This new network architecture model can deliver services directly from the cloud to the very edge of the network while providing the best efficiency in mobile networks. However, due to the dynamic, open, and collaborative nature of MEC network environments, network security issues have become increasingly complex. Devices cannot easily ensure obtaining satisfactory and safe services because of the numerous, dynamic, and collaborative character of MEC devices and the lack of trust between devices. The trusted cooperative mechanism can help solve this problem. In this paper, we analyze the MEC network structure and device-to-device (D2D) trusted cooperative mechanism and their challenging issues and then discuss and compare different ways to establish the D2D trusted cooperative relationship in MEC, such as social trust, reputation, authentication techniques, and intrusion detection. All these ways focus on enhancing the efficiency, stability, and security of MEC services in presenting trustworthy services.