نوید رضایی

DC microgrids are attaining more attraction in the smart grids on account of major characteristics such as reactive power removal, low power losses and high reliability, stability, controllability and energy efficiency. A suitable peer-to-peer (P2P) local electricity market is very essential to ensure the prosperity of networked DC microgrids in the sustainment of increasing penetration of renewable energy resources. The P2P energy trading provides a beneficial platform so that the peers including the distributed generators, end-use consumers and prosumers can buy or sell electrical energy directly with each other. This paper presents an optimization model of P2P energy trading for interconnected multiple DC microgrids coordinated via an energy management system (EMS) to maximize the total profit of participants. Each DC microgrid includes several photovoltaic arrays and wind turbines, residential loads, and electric vehicles (EVs). In the proposed framework, the permissible value of power losses is considered that reflects the limitation of power exchange between the peers and significantly influences the objective value.

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.

In the light of the emergence of smart grids, the functions associated with this type of grids in the blocks of the energy management system require the adoption of robust strategies in order to provide a higher level of control and protection. Under-frequency load shedding (UFLS) sheds load blocks when the frequency drop is below the threshold limit. In adaptive UFLS, in an advanced telecommunications platform, the main quantities of the system are measured at each hour and in real-time; besides, the optimal amount of load is shed according to frequency deviation. In this paper, an hourly framework using Mixed-Integer Linear Programming (MILP) is proposed for an optimal design of an adaptive UFLS in smart networks. The goal is to provide a more systematic adaptive UFLS that is less dependent on trial and error. Here, the under-frequency relay is set for each hour in regard to operating conditions and uncertainties resulting from contingencies, to renewable energy sourses (RES), and to load fluctuations at that hour. The simulations are performed on the IEEE 39-bus test system over a 24-hour time horizon.

Recently, environmental, economic and reliability oriented motivations facilitate cellular operation of smart power systems in the light of microgrid paradigm. Obviously, due to low inertia stack, high variety of generation units with various technical characteristics and different islanded and grid-connected operational modes, make the protection and control structures become new challenges. On the other hand, by integration of advanced metering and communication infrastructures in the microgrids, differential protection as the most reliable relaying logic, play a vital role in the protection structure of the microgrids. Owing to nature of occurring faults in the microgrids, high resistance faults have created a major problem in applying differential protection and directional fault. In this paper is used a new method for quick and accurate detection of fault in DC micro-grid, so that it detected internal fault from external fault, the performance of this new algorithm is also shown for increasing the fault resistance and compared with the conventional differential protection. The basis of new method is to use the Fault Component Current of the two sides of the study line and plot them on the  plan to identify the type of fault. In this paper simulation of internal and external fault in EMTP-ATP for different values of fault resistance is done and the implementation of the new algorithm and conventional differential protection is done in MATLAB. The simulation results indicate the accuracy and high speed of the operation of the new expressed method.

The present study aims to synthesis and characterization of spinel coating for spark plug aero-engine application. At first spinel coatings were synthesized by mechanical alloying. The different spinel coatings with spinel different composition and modulation were applied on alumina substrate. The phase content of the samples was characterized by X-ray diffraction (XRD) method. The microstructure and thickness of the coatings were analyzed by scanning electron microscopy. Nano-hardness and Young’s modulus of the coating were measured by nano-indentation method. The electrical resistance of the coating was studied at different temperatures. The electrical wear resistance of the coating was evaluated by spark method. The XRD method confirmed the synthesis of copper based spinels. The coatings had a thickness of 19-22 μm with proper density. The average nano-hardness of the coatings was 10 GPa. The wear rate after 140000 of spark was less than 1% of coating weight. It was also found that the optimum modulation of the multilayer coating is 4 successive layers composed of CuFe2O4+CuCr2O4, followed by two layer of CuCr2O4 and again CuFe2O4+CuCr2O4 layer. The ratio of the components in the composite layers were 50:50 wt.%

This paper proposes a flexible distributed energy management system for the coordinated operation of networked microgirds (MGs). Each MGs are considered as distinct entities with local objectives to optimize their own operation costs and power exchanges. The networked MGs are connected by a common bus, which can exchange electrical powers in this way. A two-level algorithm is used to coordinate the operational planning of these MGs. The first level is for the economic operation of each microgrids and the second level is to optimize the power exchanges. The planning of the MGs is simulated by taking into account the power flow equations and voltage constraints in a multi-MG system in a 24-hour period. A penalty price is also defined to control the power exchanges among MGs. The results of simulation indicate that using the proposed energy management system increases the performance and improves the reliability in each of the MGs.

One of the important issues in coordination of protective relays is minimization of the time interval between the operation of main and backup overcurrent (OC) relays. Overcurrent relays coordination problem due to the large number of variables and the nature of the objective functions can be introduced as a complex optimization problem that necessitates the need for an efficient optimization method with appropriate accuracy and speed. Given that for the realization of protective purposes including increased relays operation speed, selectivity, support, reliability and stability, different objective functions can be described, therefore, providing a multi-objective mathematical problem in optimizing protective problems may be necessary. In this regard, this article due to the capabilities of the MOPSO, proposes a multi-objective optimization structure, in which the SQP by increasing the speed and not increasing the search space is added to MOPSO. In this paper, several objective functions are proposed based on protection goals and optimal adjustment points have been extracted using the proposed multi-objective MOPSO-SQP. The simulations have been implemented and carefully analyzed on several typical power systems. The simulation results confirm the efficiency of the proposed algorithm in ensuring the optimal coordination of protective overcurrent relays in power system.