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2. The impact of plug-in hybrid vehicles in low-voltage distribution systems using a Monte Carlo simulationEvica Smilkoska, Vasko Zdraveski, Jovica Vuletić, Jordančo Angelov, Mirko Todorovski, 2023, izvirni znanstveni članek Opis: The growing presence and randomness of renewable-based Distributed Generation, such as solar, photovoltaic, and wind power, and heavy Plug-in Hybrid Electric Vehicle loads in residential distribution grids result in both a higher degree of imbalance and a wide range of voltage fluctuations. When increasing the number of Plug-in Hybrid Electric Vehicles that are simultaneously charged, the additional unpredicted load may cause several problems to the current grid in terms of voltage deviations, thermal overloads, power losses, increased aging of transformers and lines, decreased quality of supply, and power outages. This paper proposes an approach that models Plug-in Hybrid Electric Vehicles’ behaviour and performs power flow analysis on CIGRE low voltage benchmark grid to investigate the impact on the current distribution grid. Ključne besede: plug-in hybrid electric vehicle, power quality, non-deterministic approach, voltage deviations, power losses, distribution systems Objavljeno v DKUM: 11.10.2023; Ogledov: 390; Prenosov: 5 Celotno besedilo (6,44 MB) Gradivo ima več datotek! Več... |
3. Energy consumption and grid interaction analysis of electric vehicles based on particle swarm optimisation methodKlemen Deželak, Klemen Sredenšek, Sebastijan Seme, 2023, izvirni znanstveni članek Opis: The widespread adoption of electric vehicles poses certain challenges to the distribution grid, which refers to the network of power lines, transformers, and other infrastructure that delivers electricity from power plants to consumers. This higher demand can strain the distribution grid, particularly in areas with a high concentration of electric vehicles. Grid operators need to ensure that the grid infrastructure can handle this additional load and prevent overloading and consequences in terms of additional losses. As part of the task, a methodology was developed for the assessment of the electricity consumption of battery electric vehicles in Slovenia. The approach used for the calculation includes the number of electric cars, average consumption, distance travelled and efficiency of the system. Additionally, the results of the modelling approach for an integrated distribution grid model in terms of steady-state simulations are presented. The regular situation of the power losses within the distribution grid is managed together with an optimal result. In this sense, an application of the particle swarm optimisation-based strategy is suggested to minimise reliance on grid systems. Ključne besede: electric vehicles, distribution grid, optimisation, power losses Objavljeno v DKUM: 10.10.2023; Ogledov: 309; Prenosov: 25 Celotno besedilo (2,22 MB) Gradivo ima več datotek! Več... |
4. Optimization of the distribution network operation by integration of distributed energy resources and participation of active elementsNevena Srećković, 2020, doktorska disertacija Opis: Distribution Networks (DNs) are evolving from a once passive to an active part of the electricity network. This evolution is driven by the current political and environmental decisions, Directives and Incentives, as well as the technological development, observed in the everincreasing integration of renewable energy resources, advanced network control and measurement devices, the upcoming energy exibility market, etc. This Doctoral Thesis deals with the problem of optimization of the technical aspects of a DN operation, enabled by the proliferated integration of the photovoltaic systems (PV) and other active devices. The main objective of the Thesis is the optimization of a DN operation in terms of minimization of electrical energy losses while ensuring the proper voltage profiles and preventing thermal overloadingof lines. Therefore, three Differential Evolution-based optimization procedures were developed and tested on real medium and low voltage DNs. The first methodology determines the optimal rooftop surfaces for the installation of PV systems, yielding minimum annual energy losses. It is based on the simultaneous consideration of high-resolution spatio-temporal solar and PV potential data, as well as long-term measured profiles of consumption and generation of electrical energy within the network of a given configuration. The second algorithm minimizes network losses in a time-discrete operation point, by determining the optimal operation of the following active elements: PV systems capable of cooperation in reactive power provision, On-Load Tap Changer equipped transformer substations and remotely controlled switches for network reconfiguration. The final algorithm was developed by a proper consolidation of the first two approaches, yielding the synergistic effects expressed as the increase of loss reduction and network exibility. The results of the performed case studies show that the locations of the highest suitability for PV installation with respect to the solar energy availability, are not necessarily the best choice from the network operation standpoint. Therefore, both standpoints should be considered simultaneously when choosing the rooftop surfaces for PV installation. Furthermore, by determining optimal hourly operation of the considered active elements, not only the additional reduction of annual network losses was achieved, but also increased accommodation of the PV systems that doesn't violate operation constraints. Ključne besede: distribution network, optimization of operation, active network elements, PV system placement, minimization of losses Objavljeno v DKUM: 11.06.2020; Ogledov: 1791; Prenosov: 414 Celotno besedilo (44,58 MB) |
5. Analytical modelling of achieving energy efficiency with green wallsDejan Tasić, 2019, magistrsko delo Opis: In the last years, energy efficiency has become an important issue for the EU and Slovenia, who both strive for more sustainable use of energy in buildings. As an innovative approach to such matter, green walls are vertical structures that can serve both as a façade or an insulation layer as well as an aesthetic design for building application. This thesis contains calculated annual heat (transmission) losses through different wall assemblies with and without a constructed green wall in front of them. The goal is to compare values of heat losses between those wall assemblies and the explanation of such results which will determine if green walls present a viable energy-efficient structure for buildings. Ključne besede: energy efficiency, green wall, heat losses, modelling Objavljeno v DKUM: 18.11.2019; Ogledov: 1929; Prenosov: 145 Celotno besedilo (3,83 MB) |
6. A new somatic cell count index to more accurately predict milk yield lossesJanez Jeretina, Dejan Škorjanc, Drago Babnik, 2017, izvirni znanstveni članek Opis: Intramammary infection and clinical mastitis in dairy cows leads to considerable economic losses for farmers. The somatic cell concentration in cow's milk has been shown to be an excellent indicator for the prevalence of subclinical mastitis. In this study, a new somatic cell count index (SCCI) was proposed for the accurate prediction of milk yield losses caused by elevated somatic cell count (SCC). In all, 97238 lactations (55207 Holstein cows) from 2328 herds were recorded between 2010 and 2014 under different scenarios (high and low levels of SCC, four lactation stages, different milk yield intensities, and parities (1, 2, and _>3). The standard shape of the curve for SCC was determined using completed standard lactations of healthy cows. The SCCI was defined as the sum of the differences between the measured interpolated values of the natural logarithm of SCC (ln(SCC)) and the values for the standard shape of the curve for SCC for a particular period, divided by the total area enclosed by the standard curve and upper limit of ln(SCC)=10 for SCC. The phenotypic potential of milk yield (305-day milk yield - MY305) was calculated using regression coefficients estimated from the linear regression model for parity and breeding values of cows for milk yield. The extent of daily milk yield loss caused by increased SCC was found to be mainly related to the early stage of lactation. Depending on the possible scenarios, the estimated milk yield loss from MY305 for primiparous cows was at least 0.8 to 0.9 kg day -1 and for multiparous cows it ranged from 1.3 to 4.3 kg day-1. Thus, the SCCI was a suitable indicator for estimating daily milk yield losses associated with increased SCC and might provide farmers reliable information to take appropriate measures for ensuring good health of cows and reducing milk yield losses at the herd level. Ključne besede: dairy cows, milk production, lactation intervals, milk yield losses, somatic cell count index Objavljeno v DKUM: 24.10.2017; Ogledov: 1542; Prenosov: 475 Celotno besedilo (317,33 KB) Gradivo ima več datotek! Več... |
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10. Flow-pressure analysis of loop gas networksJurij Krope, Peter Trop, Darko Goričanec, 2011, izvirni znanstveni članek Opis: This paper proposes a mathematical model underlying a computer program for flow-pressure analysis of loop gas pipe networks. The method is used on a test case with four nodes. The HAPN application for flow-pressure analyses of low pressure gas pipe networks is completely designed in object-oriented programming technology. The equations, which describe the physical flow-pressure conditions through every cross point are assumed to be continuous and the energy of every closed loop of analyzed network conserved. The system of non-linear equations was linearized by LTM (Linear Theory Method). The algorithm for numerical module LTM and the method for solution of sparse matrix are developed at the Faculty of Chemistry and Chemical Engineering, University of Maribor, Slovenia. Ključne besede: fluid mechanics, gas pipe networks, linear method, non-linear programming, pressure losses Objavljeno v DKUM: 01.06.2012; Ogledov: 2368; Prenosov: 33 Povezava na celotno besedilo |