نشریه فناوری های نوین مهندسی برق در سیستم انرژی سبز
سال سوم شماره 1 (پیاپی 9، بهار 1403)

Due to the expansion and increasing penetration level of distributed generation units which are usually inertialess or low inertia, new challenges have arisen in power system studies. Thus, in power system studies, microgrids which may have numerous distributed generation units should be modelled and simulated that is very time consuming and complex. Therefore, dynamic equivalencing of microgrids in order to reduce computation burden and complexity is inevitable. In this paper, a new method for dynamic equivalencing of microgrids that includes inverter-based generation units and DSTATCOMs is proposed. The proposed equivalent model is a physical one which includes components such as equivalent converter, controller, resistance, reactance and equivalent load. Using the measurement data at the point of common coupling and utilizing optimization procedure, the parameters of the equivalent model will be identified. The proposed method is applied to IEEE 33-bus test system to show its accuracy and effectiveness.

Providing electricity to critical electrical loads in all conditions is one of the important goals facing designers and operators of power systems. On the other hand, power systems are always exposed to various events and disasters. The ability to face these events and disasters in power systems is brought up with the concept of resilience. In this article, improving the resilience of distribution networks is pursued. For this purpose, the expansion of fixed and portable energy storage systems in distribution networks has been carried out to keep distribution networks resilience. Due to the importance of providing the critical loads, meeting the critical loads is considered as the main resilience criterion. The proposed model is formulated as a mixed integer linear optimization problem. Minimization of costs is considered as the objective function and fulfillment of restrictions in normal and resilience conditions of the network are considered as the constraints of the problem. In this model, the distribution network is divided into several separate zones and the fulfillment of critical loads in the zones is followed by the available resources and energy storage systems. The results of studies on the test network show the ability of portable energy storage systems to meet the requirements of network resilience.

The increasing growth of natural disasters and cyber-physical attacks has made developing resilience enhancement strategies for distribution networks become a significant challenge for researchers. Hence, in this paper, a black-start strategy based on multi-microgrids capability is presented in two layers of preventive and corrective measures within a hierarchical centralized energy management framework. The preventive measures layer is based on the regulation of black-start bilateral contracts between the active distribution network operator and the multi-microgrids owner, as well as the regulation of demand response contracts between the multi-microgrids owner and the microgrid response loads. The corrective measures layer includes islanding of microgrids during events, calling of responsive loads, and finally economic-resilient operational planning of the active distribution network in order black-start the distribution system. The developed model is formulated in the framework of hierarchical centralized energy management using an LP-metric-based multi-objective optimization approach, then it is solved by the DICOPT solver in the GAMS package. The effectiveness of the proposed black-start strategy is investigated by evaluating the supplied load as a resilience index on the modified IEEE 33-bus distribution network. The recovery of all the curtailed load of the distribution system after utilizing the proposed strategy indicates the efficiency of the proposed strategy indicates the effectiveness of the proposed black-start strategy.

The increasing use of distributed generation sources in microgrids causes problems when a fault occurs, including an increase in the level of short-circuit current in the microgrid and consequently it causes disturbances in the system after fixing the fault. In this paper, using a novel method, the installation location and the optimal resistance value of the resistive superconducting fault current limiter in the microgrid are determined by considering the energy losses in the resistive superconducting fault current limiter, the requirements of low voltage ride through of the doubly fed induction generator and the interrupting capacity of circuit breakers. Also, a mathematical model of resistive superconducting fault current limiter is presented, which by simulating and placing it in the microgrid and applying various types of faults in different points of the microgrid, the effectiveness of the proposed resistive superconducting fault current limiter in reducing the short circuit current level of the microgrid, the impact of simultaneous use of resistive superconducting fault current limiter and auto recloser in significant decreasing of disturbances after Fixing the fault and improving the requirements of low voltage ride through of the doubly fed induction generator are approved. Finally, the analytical comparison of the proposed method with other studies conducted in this field is examined and proves its effectiveness.

This article introduces a two-stage linear model designed for the coordination of networked microgrids, aimed at optimizing energy management and enhancing profitability through proactive and corrective strategies. Initially, the first stage involves day-ahead hourly planning for microgrids, executed in a deterministic environment without accounting for uncertainties. Subsequently, the second stage addresses these uncertainties in real-time network operation through a stochastic programming approach. The model's objective function quantifies and incorporates the variations resulting from both the proactive and corrective phases. To handle uncertainties in wind and solar energy production as well as load demand, probability distribution functions derived from Monte Carlo simulations are utilized. From these, representative scenarios are chosen using a scenario reduction technique. Specifically, the K-means algorithm is employed for scenario clustering, with the Davies-Bouldin (DB) index facilitating automatic clustering. Additionally, load management is conducted via a demand response program. The proposed model stipulates that, within microgrids, only non-critical load levels can be modulated based on the network's economic benefit. This optimization model, formulated as mixed integer programming, is simulated and resolved in the GAMS software environment. The primary goal of this two-stage model is to achieve optimal energy management by balancing economic efficiency with robust network performance. The results obtained validate the model's effectiveness.

Instant messengers have been popularized by users for private and business communication as an alternative to the cheap short message system in mobile phones with limited computing power. However, until recently, most mobile messaging applications did not protect the confidentiality or integrity of messages. Due to reports of communications being intercepted by intelligence services such as the NSA, people have been motivated to look for alternative messengers to maintain the security and privacy of their communications on the Internet. Initially, with Facebook's purchase of the popular messaging app WhatsApp, other apps claiming to offer secure communications gained significant new users. One messaging app that claims to offer secure instant messaging features and has garnered a lot of attention is TextSecure Messenger. Next, Signal Messenger, which is considered the successor of TextSecure, uses the protocols available in this messenger to exchange text messages. Considering that the WhatsApp messenger is based on the signal protocol, in this article a complete description of the encryption complexity of the signal protocol is presented. In the following, a security analysis of the three main components of this protocol including: key exchange, key extraction and authentication in encrypted messages is described. It has also been shown that the process of sending and displaying messages in this protocol can achieve most of the security goals. Finally, the role of quantum attacks that resulted from the computing power of quantum computers in solving classical asymmetric cryptography problems in the security of the key agreement protocol used in the Signal was checked. It is also shown that the use of Post-Quantum key exchange cryptographic protocols can secure the key agreement part of the Signal protocol against attacks by quantum algorithms.