Voltage dips represent a significant power quality problem. The main cause of voltage dips and short-term interruptions is an electrical short circuit that occurs in transmission or distribution networks. Faults in the power system are stochastic by nature and the main cause of voltage dips. As faults in the transmission system can affect more customers than faults in the distribution system, to reduce the number of dips, it is not enough to invest in a small part of the transmission or distribution system. Only targeted investment in the whole (or a large part of the) power system will reduce voltage dips. Therefore, monitoring parts of the power system is very important. The ideal solution would be to cover the entire system so that a power quality (PQ) monitor is installed on each bus, but this method is not economically justified. This paper presents an advanced method for determining the optimal location and the optimal number of voltage dip measuring devices. The proposed algorithm uses a monitor reach area matrix created by short-circuit simulations, and the coefficient of the exposed area. Single-phase and three-phase short circuits are simulated in DIgSILENT software on the IEEE 39 bus test system, using international standard IEC 60909. After determining the monitor reach area matrix of all potential monitor positions, the binary bat algorithm with a coefficient of the exposed area of the system bus is used to minimize the proposed objective function, i.e., to determine the optimal location and number of measuring devices. Performance of the binary bat algorithm is compared to the mixed-integer linear programming algorithm solved by using the GNU Linear Programming Kit (GLPK).

Abstract:The integration of distributed energy sources transforms passive distributed grid, in which the energy flows only in one direction (from the source to the consumer), in an active one, in which energy flows in both directions. To maximize positive impacts, which distributed generation (DG) can provide to the distribution network, it is necessary to determine the optimal allocation of distributed generation. The optimal allocation can be determined by using the optimization method. There are two main categories: exact methods (traditional) and heuristic (non-traditional) methods. Exact methods search for global optimum while heuristic methods achieve satisfactory solutions with greater computation speed. This paper gives a brief review of non-traditional methods used for determining optimal location and optimal power of DG with the aim to reduce real power losses and to improve voltage characteristics. Also, there is a review of the application of those methods in determining the optimal power, optimal location and optimal cycle of charging/discharging of electrical energy storage systems.

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Abstract:Modern society has a growing need for the electricity. To protect the environment, future energy demand must be met with more environmentally friendly technologies, such as renewable energy sources. Because of its vast availability, solar radiation has been used for decades to generate electricity through photovoltaic systems (PV) for residential, educational, and commercial buildings. However, the growth of distributed generation (and renewable energy sources) across power systems in industrialized countries has created new challenges. Random renewable generation causes an imbalance between electricity production and consumption, so smart grids and microgrids may be solutions. In this article, we investigate improving the energy efficiency in the Faculty of Electrical Engineering building in Osijek by using a microgrid. To do so, we compared the total electricity consumption of the building and the production of a 10 kWp photovoltaic power plant on that building. The improvement in energy efficiency of the building produced a maximum savings of up to 10% of the building's total electricity consumption.Keywords: distributed generation; renewable energy sources; energy efficiency; microgrid; PV power plant POBOLJŠANJE ENERGETSKE UČINKOVITOSTI U ZGRADARSTVU POMOĆU MIKROMREŽA Sažetak: Moderno društvo ima sve veću potrebu za električnom energijom. Kako bi se zaštitio okoliš, buduća potražnja će morati biti pokrivena s više ekološki prihvatljivih tehnologija, poput obnovljivih izvora energije. Zbog svoje visoke dostupnosti, Sunčevo zračenje se već desetljećima koristi za proizvodnju električne energije putem fotonaponskih sustava (PV) na stambenim, obrazovnim ili poslovnim zgradama. Prodor distribuirane proizvodnje (i obnovljivih izvora energije) u elektroenergetske sustave industrijaliziranih zemalja stvara nove izazove. Nestalna proizvodnja obnovljivih izvora električne energije stvara neravnotežu između proizvodnje i potrošnje, a kao moguće rješenje općenito je prihvaćen koncept napredne mreže i mikromreže. Ovaj članak istražuje mogućnosti povećanja energetske učinkovitosti pomoću mikromreže u zgradi Elektrotehničkog fakulteta Osijek. Uspoređuje se ukupna potrošnja električne energije u zgradi Fakulteta s proizvodnjom od 10 kWp fotonaponske elektrane ETFOS 1, koja se nalazi na krovu iste zgrade. Usporedba navedenih rezultata pokazala je poboljšanje energetske učinkovitosti zgrade u obliku maksimalne uštede, koja doseže i do 10 % ukupne potrošnje.