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2.
Static model of temperature distribution in a photovoltaic module
Klemen Sredenšek, Sebastijan Seme, Gorazd Hren, 2021, izvirni znanstveni članek

Opis: The primary objective of this paper is to present a static model for calculating the temperature distribution in a photovoltaic module using the finite element method. The paper presents in more detail the theoretical background of solar radiation, heat transfer, and the finite element method. The results of the static model are evaluated using temperature measurements of a photovoltaic model, which were performed at the Institute of Energy Technology, Faculty of Energy Technology, University of Maribor. The results of the regression analysis show a good concurrence between the measured and modelled values of the temperature of the photovoltaic module, especially on days with a higher share of the direct component of solar radiation.
Ključne besede: photovoltaic module, temperature distribution, heat transfer, finite element method
Objavljeno v DKUM: 13.11.2023; Ogledov: 125; Prenosov: 5
.pdf Celotno besedilo (2,01 MB)
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3.
Experimental validation of a dynamic photovoltaic/thermal collector model in combination with a thermal energy storage tank
Klemen Sredenšek, Sebastijan Seme, Bojan Štumberger, Miralem Hadžiselimović, Amor Chowdhury, Zdravko Praunseis, 2021, izvirni znanstveni članek

Opis: The primary objective of this paper is to present a dynamic photovoltaic/thermal collector model in combination with a thermal energy storage tank. The added value of the proposed model is the use and integration of existing dynamic models for describing the entire photovoltaic/thermal system. The presented model was validated using measurements on the experimental system located at the Institute of Energy Technology, Faculty of Energy Technology, University of Maribor. The validation was carried out based on three different weather conditions—sunny, cloudy, and overcast. The validation results were evaluated using the normalized root mean square error and mean absolute percentage error for the temperature and output power of the photovoltaic/thermal collector and the temperature of the thermal energy storage tank. The model results concurred with the measurements, as the average mean absolute percentage error values for the temperature and output power of the photovoltaic/thermal collector and thermal energy storage tank temperature were 5.82%, 1.51%, and 7.58% respectively.
Ključne besede: photovoltaic/thermal collector, thermal energy storage tank, dynamic modeling, temperature distribution, output power
Objavljeno v DKUM: 13.11.2023; Ogledov: 123; Prenosov: 9
.pdf Celotno besedilo (8,22 MB)
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4.
Proportional-integral controllers performance of a grid-connected solar PV system with particle swarm optimization and Ziegler-Nichols tuning method
Klemen Deželak, Peter Braciník, Klemen Sredenšek, Sebastijan Seme, 2021, izvirni znanstveni članek

Opis: This paper deals with photovoltaic (PV) power plant modeling and its integration into the medium-voltage distribution network. Apart from solar cells, a simulation model includes a boost converter, voltage-oriented controller and LCL filter. The main emphasis is given to the comparison of two optimization methods-particle swarm optimization (PSO) and the Ziegler-Nichols (ZN) tuning method, approaches that are used for the parameters of Proportional-Integral (PI) controllers determination. A PI controller is commonly used because of its performance, but it is limited in its effectiveness if there is a change in the parameters of the system. In our case, the aforementioned change is caused by switching the feeders of the distribution network from an open-loop to a closedloop arrangement. The simulation results have claimed the superiority of the PSO algorithm, while the classical ZN tuning method is acceptable in a limited area of operation.
Ključne besede: photovoltaic power plant, optimization, PI controllers, distribution system
Objavljeno v DKUM: 10.11.2023; Ogledov: 186; Prenosov: 8
.pdf Celotno besedilo (3,36 MB)
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5.
Uporaba indikatorjev tehnične analize pri napovedi trendov na borznih in deviznih trgih
Urška Repušič, 2023, diplomsko delo

Opis: V diplomski nalogi ugotavljamo uporabnost indikatorjev tehnične analiz pri napovedi trendov na borznih in deviznih trgih, v zadnjem delu diplomske naloge ugotavljamo tudi uporabnost in pomen kombiniranja različnih indikatorjev tehnične analize. Vključili smo tudi pomen in uporabnost poznavanja tržnih struktur in njihovo kombiniranje z indikatorji tehnične analize. Investitorji na borznih in deviznih trgih si prizadevajo razumeti, katere indikatorje in katere tržne strategije v okviru posameznega indikatorja uporabiti z namenom obvladovanja prisotnih tveganj pri trgovanju na teh trgih in tudi za maksimiranje dobičkov. V diplomski nalogi so s teoretičnega in praktičnega vidika predstavljeni izbrani indikatorji tehnične analize, tržni trendi in strukture ter pomen in uporabnost kombiniranja različnih indikatorjev ter tržnih struktur. V diplomski nalogi smo ugotovili, da ima pri napovedih trenda na borznih in deviznih trgih veliko vlogo vsebinsko razumevanje posameznega indikatorja tehnične analize, branje grafikonov z vključenimi indikatorji in identificiranje signalov pri odločanju o trgovanju, pri določevanju vstopnih in izstopnih točk ter pri določanju kratkoročnih in dolgoročnih trendov. Iz praktičnim primerov, vključenih v diplomski nalogi se je ugotovilo, katere indikatorje je potrebno uporabiti za različne tržne strategije in katere kombinacije indikatorjev je smiselno uporabit za pridobitev dodatnih potrditev pravilnosti načrtovane strategije investiranja.
Ključne besede: MA, ADX, Parabolic SAR, MACD, RSI, stohastični oscilator, OBV, MFI, Accumulation/Distribution, pasovi bollingerja, ATR, Fibonacci nivoji.
Objavljeno v DKUM: 09.11.2023; Ogledov: 154; Prenosov: 8
.pdf Celotno besedilo (3,96 MB)

6.
Use of active elements for providing suitable voltage profiles and prevent overloads in radial distribution networks
Marko Vodenik, Matej Pintarič, Gorazd Štumberger, 2022, izvirni znanstveni članek

Opis: The article deals with the issue of providing suitable voltage profiles and preventing congestion of network elements in distribution networks. Active network elements and network users’ energy flexibility services are used to provide a suitable voltage profile and prevent congestion in distribution networks. The discussed active network elements include a transformer with on-load tap changer, reactive power compensation devices, energy storage systems, distributed energy resources, and network users’ energy flexibility services, where the active consumers adjust their consumption, production and storage of energy. Based on the Backward Forward Sweep load flow computation method, the case studies are performed for the discussed low voltage distribution network, where the measurement results were available. The case studies for preventing overload of the distribution transformer are performed using a battery energy storage system and network users’ energy flexibility services. The case studies for providing suitable voltage profiles are performed using all listed active elements and a combination of different active elements. In addition, to provide suitable voltage profiles, the existing conductors are replaced with conductors of a larger cross-section. Technically acceptable solutions that can provide a suitable voltage profile and prevent the overloading of network elements in the most demanding operating conditions are presented in this article.
Ključne besede: voltage profile, radial distribution network, load flow calculations, active network elements, energy flexibility
Objavljeno v DKUM: 30.10.2023; Ogledov: 321; Prenosov: 4
.pdf Celotno besedilo (5,24 MB)
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7.
The use of differential evolution to determine maximum generation and load values in the distribution network
Eva Tratnik, Janez Ribič, Matej Pintarič, Miran Rošer, Gorazd Štumberger, Miloš Beković, 2022, izvirni znanstveni članek

Opis: By integrating renewable energy sources into the existing distribution network, the characteristics and local stability of the network is highly impacted. The network, which was built with the goal of a directed energy flow from large conventional sources connected to the transmission network via the distribution network to consumers, can change the direction of the energy flow. The adoption of environmental commitments and directives encourages the integration of local dispersed energy sources, which can worsen voltage conditions in the distribution network. To avoid excessive local production, distribution network operators must limit the installation of new generati on units, as it is necessary to take into account the quality of power supply by monitoring its network parameters, such as the appropriate voltage profi le and the rati o between acti ve and reacti ve power. On the other hand, excessive loads due to the mass transiti on of household heati ng and transport towards electricity can also pose a problem for high-quality electricity supply due to the excessive voltage drop. The arti cle presents an algorithm for determining the maximum size of unit producti on and the maximum load at a node in the distributi on network. Also demonstrated is the use of variable tap transformer technology, which adjusts the tap of the transformer to provide an appropriate voltage profi le in the network. The enti re analysis was performed on a model of a real medium-voltage network, in which solar and hydropower plants are already included. The model was verifi ed by comparing its calculated values with actual measurements. The goal was to determine the size of the unit’s maximum producti on, as well as the size of the maximum load, by using the diff erenti al evoluti on algorithm, while keeping voltage profi les within the permissible limits. The results of the analysis are presented in the article.
Ključne besede: distribution network, renewable energy sources, optimisation method, voltage profile
Objavljeno v DKUM: 30.10.2023; Ogledov: 233; Prenosov: 9
.pdf Celotno besedilo (1,63 MB)
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8.
The Impact of coal and CO2 emission coupon market-driven prices on the economic operation of thermal power plants
Martin Bricl, Jurij Avsec, 2022, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: heat capacity peak, first-order phase change, domain size distribution, averaging
Objavljeno v DKUM: 27.10.2023; Ogledov: 110; Prenosov: 4
.pdf Celotno besedilo (14,78 MB)
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9.
Thermal analysis of a coreless axial flux permanent magnet machine
Franjo Pranjić, Marko Pezdevšek, Peter Virtič, 2022, izvirni znanstveni članek

Opis: The article deals with numerical analysis of a double sided coreless axial flux permanent magnet machine with two rotor disks and a coreless stator. Coreless stator represents copper windings which are held together by epoxy raisin, therefore a special focus has to be given to the stator temperature. In this article a numerical analysis is presented, which is based on the copper losses, namely the I2R product, where the resistance of the copper windings was both calculated as well as measured in the prototype machine.
Ključne besede: axial flux, CFD, coreless, permanent magnet, temperature distribution
Objavljeno v DKUM: 27.10.2023; Ogledov: 155; Prenosov: 9
.pdf Celotno besedilo (1,23 MB)
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10.
The impact of plug-in hybrid vehicles in low-voltage distribution systems using a Monte Carlo simulation
Evica 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: 220; Prenosov: 5
.pdf Celotno besedilo (6,44 MB)
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