Evaluation of Different Methods for Voltage Sag Source Detection

This paper compares and evaluates three different methods for voltage sag source detection. First method (method I) is based on the assumption, that the energy flow at the monitoring point increases during downstream events and decreases during upstream events. Second and third method (methods II and III) are both based on the assumption that currents measured at the monitoring point increase during downstream events and decrease during upstream events. The slope of a current-voltage trajectory is investigated in method II, while a real current component is observed within method III. Both current-based methods (II and III) require fundamental harmonic components of sampled voltages and currents, which are extracted using discrete orthogonal series expansion, such as Fourier or Walsh. Algorithms of this type are especially appropriate for studying steady-state and periodically repeating conditions. Voltage sags are, on the contrary, transient disturbance events. Thus, usage of the discussed algorithms may not be appropriate. Furthermore, criteria within methods II and III are checked for each phase individually. In the cases of asymmetrical voltage sags exact interpretation of the obtained results, therefore, might not be possible. Method I is, on the contrary, based on instantaneous values of line voltages and currents, while three-phase criterion is used. An exact interpretation of the results obtained by this method is, therefore, also possible in cases of asymmetrical voltage sags. All the discussed methods for voltage sag source detection have been tested by applying extensive simulations and field tests. The results for ground faults, asymmetrical voltage sags, upstream events and motor starting have been analyzed in order to evaluate all the discussed methods. The obtained results show that all discussed methods are very successful in cases of heavy motor starting and other symmetrical voltage sags. In cases of asymmetrical voltage sags the methods II and III do not work well, especially for those originating from the upstream side, while the method I is not successful only in particular cases of voltage sags due to upstream ground faults. Based on the performed evaluation it can be concluded, that further development is still needed to increase the degree of confidence in the discussed methods

Pregled hibridnih termoelektričnih sistemov

The primary objective of this paper is to review state-of-the-art hybrid photovoltaic/thermal systems and their performance analysis. The paper is designed to facilitate the comparison and evaluation of results obtained by other authors. The review was carried out for different types and designs of photovoltaic/thermal modules in indoor and outdoor conditions, as well as for different cooling types and materials.Cilj prispevka je pregled stanja hibridnih termoelektričnih sistemov in njihove učinkovitosti delovanja. Struktura prispevka je tematsko zasnovana tako, da olajša primerjavo in ovrednotenje rezultatov med drugimi študijami. Pregled je izveden za različne tipe in oblike termoelektričnih modulov, ter za različne vrste hlajenja in uporabljenih materialov

Optimal sun-tracking of a photovoltaic system considering the electric drive losses

Doktorska disertacija obravnava optimalno sledenje fotonapetostnega sistema soncu, pri čemer upoštevamo električne izgube pogonskega sklopa. Sledenje fotonapetostnega sistema soncu omogoča, da pri tem na sončne module pade čim več razpoložljive energije sončnega sevanja. Pogonski sklop, ki omogoča sledenje, predstavlja za fotonapetostni sistem porabo električne energije. Idealni izplen pretvorbe razpoložljive energije sončnega sevanja bi bil dosežen ob zveznem sledenju sledilnega sistema poti sonca. Ker imajo pogonski sklopi konstantno hitrost in diskreten način sledenja, se lahko idealnemu izplenu energije sončnega sevanja le približajo. V doktorski disertaciji je predstavljeno, kako diskretno slediti poti sonca, da na sončne module pade čim več razpoložljive energije sončnega sevanja, pri čemer so upoštevane električne izgube pogonskega sklopa. Za dosego želenega cilja so potrebne čim bolj natančne vrednosti o razpoložljivi energiji sončnega sevanja pri tleh v danem trenutku. Zato je v okviru doktorske disertacije razvit model za napoved celotnega in difuznega sončnega sevanja v obliki časovno odvisne funkcije za jasne dni. Model je potrjen s primerjavo med izmerjenim in napovedanim sončnim sevanjem za jasne dni. Napoved sončnega sevanja v obliki časovno odvisne funkcije in izgube pogonskih sklopov, kot funkcije naklona in azimuta, so uporabljeni za določitev optimalnih trajektorij sledilnega sistema. Za iskanje rešitve nelinearnega in omejenega problema je uporabljena stohastična metoda, imenovana Diferenčna evolucija. Tovrstni pristop za iskanje maksimalnega izplena fotonapetostnega sistema še ni bil raziskan v nobeni literaturi. Uporablja se točno določena kriterijska funkcija, ki je minimalna v optimizacijskem postopku glede na optimizacijske meje. S tem je zagotovljena največja možna pretvorba energije sončnega sevanja, upoštevajoč uporabljen model fotonapetostnega sistema, porabe sledilnega sistema, napovedi sončnega sevanja in lastnosti optimizacijskega postopka. Uporaba drugačnih in bolj naprednih modelov fotonapetostnega sistema, porabe sledilnega sistema ali napovedi sončnega sevanja lahko privede tudi do drugačnih optimalnih trajektorij sledilnega sistema. Vendar to nikakor ne zmanjša teže predlagane metode. Predlagana metoda daje maksimalni izplen fotonapetostnega sistema za uporabljene modele in podatke.Doctoral thesis deals with optimal sun-tracking of a photovoltaic system considering the electric drive losses. The Sun tracking PV system assures that the highest possible share of the available solar radiation reaches the surface of the PV modules. The electric drive which enables tracking is considered as the loss of the energy produced in the PV system. The maximum of the energy produced in the PV system is achieved by the continuous tracking of the PV system. Since the electric drives are determined by constant speed and time, and angle quantization the maximum of the energy produced can only approximate. The doctoral thesis presents a new method for determining such trajectories of the PV modules that change the position of the PV modules in such a way that the production of the electric energy in the given time interval of the observation reaches its maximum. The goal is to determine the maximum efficiency of the PV tracking system considering the tracking system energy consumption. To achieve this, exact values of the available solar energy are needed for a given moment. To do this, a new method for predicting direct and diffuse solar radiation on the Earth’s surface, in the form of the time dependent function, is developed. The method is confirmed by the comparison of the measured and the predicted solar radiation for clear days. The developed method for predicting the solar radiation in the form of the time dependent function and energy consumption of the tracking system, given as the functions of the azimuth and tilt angle change, are applied together to determine those trajectories of the PV module, where the PV system energy production, gives the maximum. To find a solution of the nonlinear and bounded optimization problem, a stochastic search algorithm called Differential Evolution is applied. The approach for determining the maximum of the energy produced in the PV system has not been researched yet. The explicitly defined objective function, which is minimized in the optimization procedure considering the optimization bounds, is used. Thus it is assured the maximum of the possible energy produced in the PV system, considering the applied model of the PV system, tracking system consumption, predicted solar radiation, and the properties of the applied optimization method. The use of the different and more advanced models of the PV system, the sun tracking system consumption or prediction of the solar radiation, can lead to the different optimal trajectories of the sun tracking system. However, this cannot reduce the importance of the proposed method. The proposed method gives the maximum of the possible energy produced in the discussed PV system, considering the applied models and data

Analiza porabe energije in interakcija omrežja z električnimi vozili na podlagi metode optimizacije z rojem delcev

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

Statični model temperaturne porazdelitve v fotonapetostnem modulu

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.Glavni cilj tega prispevka je predstavitev statičnega modela za izračun temperaturne porazdelitve v fotonapetostnem modulu po metodi končnih elementov. V prispevku je podrobneje predstavljeno teoretično ozadje sončnega sevanja, prenosa toplote in metode končnih elementov. Rezultati statičnega modela so ovrednoteni z meritvami temperature fotonapetostnega modela, ki so bile izvedene na Inštitutu za energetiko (Fakulteta za energetiko Univerze v Mariboru). Rezultati regresijske analize med izmerjenimi in izračunanimi vrednostmi temperature fotonapetostnega modula prikazujejo dobro ujemanje predvsem v dnevih z večjim deležem neposredne komponente sončnega sevanja

Comparison of experimentally and by the finite element method determined magnetically nonlinear iron core characteristics applied in the dynamic model of a single phase transformer

This paper deals with comparison of experimentally and by the finite element method determined magnetically nonlinear iron core characteristics. The obtained characteristic were used in the dynamic model of a single phase transformer. The comparison of the measured and by the dynamic model calculated results is given for the case of transformer steady state operation at rated load and for the case of switch-on of unloaded transformer