Papers by Bogdan Tomoiaga
Electric Power Systems Research 104, 216-225 , Aug 1, 2013
The reconfiguration of a power distribution system, by exchanging the functional links between it... more The reconfiguration of a power distribution system, by exchanging the functional links between its elements, represents one of the most important procedures to improve the performance in the operation of a distribution system. The optimization through reconfiguration (or optimal reconfiguration) of a power distribution system is not a new problem but still represents a difficult one and is specified in some strategies for smart grids. The paper addresses this problem as a single objective one, where, as main criterion, active power losses have been chosen. There is no unique acceptance regarding which approach (based on heuristics, meta-heuristics, genetic algorithms, etc.) is the most proper to use in order to solve this problem. The most important thing is how the specific knowledge of the problem domain is used and modeled in the implementation. Moreover, the indices which can quantify the quality of a reconfiguration method consist in runtime and the obtained solution and these indices can be confirmed only by experimental results. In order to solve the problem (to search and find the optimal solution) an original genetic algorithm based on connected graphs is proposed. Comparative tests performed on some test systems demonstrated the accuracy and the promptness of the proposed algorithm.
Advanced Engineering Forum 8-9, 185-194, Jun 27, 2013
The concept of microgrid was first introduced in 2001 as a solution for reliable integration of d... more The concept of microgrid was first introduced in 2001 as a solution for reliable integration of distributed generation and for harnessing their multiple advantages. Specific control and energy management systems must be designed for the microgrid operation in order to ensure reliable, secure and economical operation; either in grid-connected or stand-alone operating mode. The problem of energy management in microgrids consists of finding the optimal or near optimal unit commitment and dispatch of the available sources and energy storage systems so that certain selected criteria are achieved. In most cases, energy management problem do not satisfy the Bellman's principle of optimality because of the energy storage systems. Consequently, in this paper, an original fast heuristic algorithm for the energy management on stand-alone microgrids, which avoids wastage of the existing renewable potential at each time interval, is presented. A typical test microgrid has been analysed in order to demonstrate the accuracy and the promptness of the proposed algorithm. The obtained cost of energy is low (the quality of the solution is high), the primary adjustment reserve is correspondingly assured by the energy storage system and the execution runtime is very short (a fast algorithm). Furthermore, the proposed algorithm can be used for real-time energy management systems.
Energies 6(3): 1439-1455, Mar 6, 2013
Reconfiguration, by exchanging the functional links between the elements of the system, represent... more Reconfiguration, by exchanging the functional links between the elements of the system, represents one of the most important easures which can improve the operational performance of a distribution system. The authors propose an original method, aiming at achieving such optimization through the reconfiguration of distribution systems taking into account various criteria in a flexible and robust approach. The novelty of the method consists in: the criteria for optimization are evaluated on active power distribution systems (containing distributed generators connected directly to the main distribution system and microgrids operated in grid-connected mode); the original formulation (Pareto optimality) of the optimization problem and an original genetic algorithm (based on NSGA-II) to solve the problem in a non-prohibitive execution time. The comparative tests performed on test systems have demonstrated the accuracy and promptness of the proposed algorithm.
Experimental evaluation of a real time energy management system for stand-alone microgrids in day-ahead markets
Applied Energy 106, 365-376, Mar 6, 2013
A Microgrid (MG) Energy Management System (EMS) is a vital supervisory control to make decisions ... more A Microgrid (MG) Energy Management System (EMS) is a vital supervisory control to make decisions regarding the best use of the electric power generation resources and storage devices within this MG. This paper presents an operational architecture for Real Time Operation (RTO) of an islanded MG. This architecture considers two different parts including Central Control Unit (CCU) and MG Testbed. CCU implements an EMS based on Local Energy Market (LEM) to control a MG. In order to reach this objective, this unit executes Day Ahead Scheduling (DAS) and Real Time Scheduling (RTS). Regarding DAS, a Modified Conventional EMS (MCEMS) based on LEM (MCEMS−LEM) algorithm has been proposed to find out hourly power set-points of Distributed Energy Resources (DERs) and customers. LEM is also presented in MCEMS−LEM to obtain the best purchasing price in Day-Ahead Market (DAM), as well as to maximize the utilization of existing DER. With regard to RTS, it must update and feedback the power set-points of DER by considering the results of DAS. The presented architecture is flexible and could be used for different configurations of MGs also in different scenarios. Simulations and experimental evaluations have been carried out using real data to test the performance and accuracy of the MG testbed. This paper aims to operate the MG in islanded mode, ensuring uninterruptable power supply services and reducing the global cost of generated power. Results demonstrate the effectiveness of the proposed algorithm and show a reduction in the generated power cost by almost 8.5%.
Electrical and Power Engineering (EPE), 2012 International Conference and Exposition on , Oct 2012
The reliability of a distribution system can be considered from the point of view of a particular... more The reliability of a distribution system can be considered from the point of view of a particular customer or from the entire supply system, e.g. average interruption frequency (SAIFI) and system average interruption duration (SAIDI). The reliability indices which are referring at the interruption frequency are mainly influenced by the adopted operational configuration and the minimization in operation of SAIFI represents an important aim. A substantial change in the power distribution systems behavior appears because of the large-scale introduction of distributed generation as distributed generators connected directly to the main distribution system or inside of microgrids which are also connected to the main distribution system. In the paper, authors propose an original fuzzy based method for the estimation of the average interruption frequency on distribution smart grids.
Modern Power Systems (MPS), 2011 4th International Conference on, May 2011
Modern power systems are in the process of entering in a new stage of development where will be f... more Modern power systems are in the process of entering in a new stage of development where will be fundamentally different from classical ones, which implies new challenges and approaches. By carrying out of command, control, protection, automation, metering and power quality monitoring complex systems, the prerequisites for an electricity distribution network to become intelligent ("smart grid") are created. However, a set of issues remains related to how such an infrastructure is used in order to maximize consumer supply safety, minimize losses of active power, optimize power quality indices etc. The central idea is that a "smart grid" must be an optimized network. In this paper, the authors present their vision on the issue of optimizing the operation of an electric distribution network.
Balkan Power Conference 2008, Sep 2008
In an open electricity market environment, dispersed generation is predicted to play an important... more In an open electricity market environment, dispersed generation is predicted to play an important position. A high level of penetration and dispersion with distributed generators of an electric network imposes some additional problems; among them, of significant importance is the reconfiguration. The problem of reconfiguration has become more difficult because the customers ask more and more quality in power supply and reliability. The paper presents an original algorithm, aiming to find out the optimal open-looped points of electrical distribution networks with dispersed generation in order to obtain optimal radial configurations using Pareto optimality and evolution strategies.
The essential attributes of interruptions in the power supply of the consumers are the frequency ... more The essential attributes of interruptions in the power supply of the consumers are the frequency and the duration. While the durations are predominantly influenced by the electrical network structure and the existent automations, the frequency is powerfully influenced by the functioning schema adopted. For electrical distribution networks working in a radial configuration, the frequency of interruptions may be minimised by the suitable choice of the loop opening points. The authors propose an original method for the minimization of the system average interruption frequency index (SAIFI) in power supply, which contains besides the technological restrictions also the restriction regarding the resistive power loss.
Energetica 53 (2), 51-54, Feb 2005
Calculul indicatorilor de fiabilitate pentru sisteme complexe impune determinarea parametrilor ec... more Calculul indicatorilor de fiabilitate pentru sisteme complexe impune determinarea parametrilor echivalenţi (intensităţi de defectare λe şi de reparare/înlocuire μe/υe) ataşaţi diagramelor bloc ce descriu comportarea acestor sisteme. Literatura de specialitate prezintă formulele de calcul pentru λe şi μe (υe) în cazul diferitelor scheme conţinând combinaţii de elemente conectate în serie şi/sau paralel. Totuşi, aceste relaţii sunt greu de aplicat, în special în cazul sistemelor complexe, cu caracter general, în care pot apărea n elemente serie (de acelaşi tip sau diferite) cu m elemente paralel, în diverse combinaţii. Autorii propun modelarea elementelor componente ale schemelor bloc prin tipuri abstracte de date cu doi parametri (λ şi μ), pentru care se definesc o serie de operaţii. Odată cu realizarea acestei modelări, toate elementele diagramelor bloc vor fi tratate ca obiecte de tip „parametru de fiabilitate“ urmând ca obţinerea parametrilor echivalenţi (λe şi μe), precum şi a indicatorilor de fiabilitate, să se realizeze în urma evaluării unor expresii simplificate.
Energetica 52 (10), 458-462, Oct 2004
Datorita tendintelor actuale de simplificare a instalatiilor de conexiuni ale statiilor electrice... more Datorita tendintelor actuale de simplificare a instalatiilor de conexiuni ale statiilor electrice, se pune problema dezvoltarii unei metode sistematice, pe baza careia sa se poata stabili structura optima a acestora, în conditii de siguranta în functionare. Lucrarea prezinta un algoritm original, care, pe baza determinarii echipamentelor critice - sisteme de bare colectoare, (auto)transformatoare, linii electrice -, indica structura minimala a instalatiilor de conexiuni ale statiilor SEN, care asigura continuitatea în alimentarea cu energie electrica.
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Papers by Bogdan Tomoiaga