1. Practical approaches to the control of milk fermentation with kefir grainsJožef Ritonja, Andreja Goršek, Darja Pečar, Darius Andriukaitis, Boštjan Polajžer, 2024, independent scientific component part or a chapter in a monograph Abstract: In the chapter, milk fermentation for kefir production is studied. The traditional
kefir production process based on inoculating kefir grains into milk is considered. The
quality and quantity of the produced kefir also depend on the dynamics of the fermentation process. The chapter presents the design and synthesis of the closed-loop
control system in which changing the bioreactor’s temperature is used to control the
time course of the concentration of dissolved CO2. In the chapter: (1) a nonlinear
dynamic mathematical model of the fermentation process, which allows evaluating
the influence of the bioreactor’s temperature on the dynamics of the fermentation
process, is presented; (2) the design and synthesis of a conventional linear control
system with constant parameters are carried out; (3) an adaptive control system that
enables the tracking of the courses of the quantities of the fermentation process to the
desired reference trajectories without the time-consuming preliminary identification
of the parameters of the fermentation process model is developed. The numerical,
experimental, and analytic outcomes of the study are presented.
Keywords: milk fermentation, batch biorector, mathematical modeling, control system design and synthesis, linear control, model reference adaptive control
Published in DKUM: 08.01.2026; Views: 0; Downloads: 2
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2. Izpeljava, programska implementacija in eksperimentalna validacija matematičnega modela energetskega transformatorja : magistrsko deloStela Ugrinčić, 2025, master's thesis Abstract: Magistrsko delo obravnava matematično modeliranje trifaznega energetskega transformatorja z diferencialnimi enačbami s skoncentriranimi parametri. Cilj naloge je bil izpeljava in programska implementacija matematičnega modela, ki upošteva nelinearne lastnosti magnetnega jedra. Namenjen je analizi stacionarnega obratovanja in prehodnih pojavov. Model je bil implementiran v odprtokodnem programskem jeziku Python in validiran z uporabo programskega orodja DIgSILENT PowerFactory ter z meritvami na laboratorijskem transformatorju. Rezultati potrjujejo delovanje in uporabnost modela za stacionarne in dinamične simulacije energetskih transformatorjev, ki opisujejo delovanje transformatorja, hkrati pa razkrivajo omejitve pri upoštevanju nelinearnosti magnetnega jedra ter nakazujejo možnosti za nadaljnji razvoj.
Keywords: trifazni transformator, matematično modeliranje, vklopni pojav
Published in DKUM: 23.09.2025; Views: 0; Downloads: 26
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3. Načrtovanje in implementacija regulacijskega sistema za dušenje nihanj mostnega žerjava : diplomsko deloNiki Zmazek, 2025, undergraduate thesis Abstract: Namen diplomske naloge je sistematični pristop k izdelavi protinihajnega sistema mostnega žerjava. Opisane so osnovne konstrukcijske izvedbe in splošno delovanje mostnih žerjavov. Predstavljene so težave, povezane z nihanjem bremena, ki jih poskušamo zmanjšati z razvojem namenskega protinihajnega sistema. V nalogi je izpeljan nelinearni matematični model mostnega žerjava, izvedena je linearizacija tega modela in določitev lineariziranega modela odstopanj. Na podlagi lineariziranega modela je izvedena sinteza z regulatorjem stanj. Realiziran protinihajni sistem je preizkušen na mostnem žerjavu. Rezultati potrjujejo pravilnost in uspešnost predstavljenega pristopa.
Keywords: mostni žerjav, protinihajni sistem, matematično modeliranje, načrtovanje regulacijskega sistema, regulator stanj
Published in DKUM: 22.09.2025; Views: 0; Downloads: 21
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4. Controllability-oriented method to improve small-signal response of virtual synchronous generatorsAntonija Šumiga, Boštjan Polajžer, Jožef Ritonja, Peter Kitak, 2025, original scientific article Abstract: This paper presents a method for optimizing the inertia constants and damping coefficients of interconnected virtual synchronous generators (VSGs) using a genetic algorithm. The goal of optimization is to find a balance between minimizing the rate of change of frequency (RoCoF) and enhancing controllability. Five controllability-based metrics are tested: the minimum eigenvalue, the sum of the two smallest eigenvalues, the maximum eigenvalue, the trace, and the determinant of the controllability Gramian matrix. The approach includes the oscillatory modes’ damping ratio constraints to ensure the small-signal stability of the entire system. The results of optimization on the IEEE 9-bus system with three VSGs show that the proposed method improves controllability, reduces RoCoF, and maintains the desired oscillation damping. The proposed approach was tested through time-domain simulations.
Keywords: virtual synchronous generator, inertia constant, damping coefficient, small-signal stability, multi-objective optimization, genetic algorithm
Published in DKUM: 12.08.2025; Views: 0; Downloads: 11
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5. Električni in elektromehanski pretvorniki : zapiski predavanjIvan Zagradišnik, Jožef Ritonja, 2025 Abstract: V publikaciji so predstavljene osnove elektromehanske pretvorbe in štirje osnovni električni stroji: transformator, asinhronski stroj, sinhronski stroj in komutatorski stroj. Publikacija je razdeljena v pet poglavij. V nadaljevanju je predstavljena vsebina posameznih poglavij. Uvod: magnetno polje, vzbujanje navitij, induciranje napetosti, sile in vrtilni moment (navor), pretvarjanje električne moči v električno ali mehansko, izgube, izkoristek, segrevanje in hlajenje. Transformator: elementi gradnje, idealni in realni enofazni transformator, trifazni transformator, posebne izvedbe transformatorjev. Asinhronski stroj: opis gradnje z navitji in način delovanja, zagoni motorjev in spreminjanje hitrosti vrtenja ter vrtilnega momenta, asinhronski generator, enofazni asinhronski motorji. Sinhronski stroj: opis gradnje in način delovanja, obratovanje na togem omrežju, približna obravnava nasičenega stroja, vzbujalni sistemi in uporaba trajnih magnetov za vzbujanje, ter sinhronski motorji s trajnimi magneti. Komutatorski stroj: opis gradnje in način delovanja, reakcija kotve, problemi komutacije, elektronska komutacija, karakteristike različnih električnih vezav statorja in rotorja, spreminjanje hitrosti vrtenja, izmenični (univerzalni) komutatorski stroji.
Keywords: osnove elektromagnetike, transformator, asinhronski stroj, sinhronski stroj, komutatorski stroj
Published in DKUM: 16.07.2025; Views: 0; Downloads: 192
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6. Power-based concept for current injection by inverter-interfaced distributed generations during transmission-network faultsBoštjan Polajžer, Bojan Grčar, Jernej Černelič, Jožef Ritonja, 2021, original scientific article Abstract: This paper analyzes the influence of inverter-interfaced distributed generations’ (IIDGs)
response during transmission network faults. The simplest and safest solution is to switch IIDGs
off during network faults without impacting the network voltages. A more elaborate and efficient
concept, required by national grid codes, is based on controlling the IIDGs’ currents, involving
positive- and negative-sequence voltage measured at the connection point. In this way the magnitude
and phase of the injected currents can be adjusted, although the generated power will depend on the
actual line voltages at the connection point. Therefore, an improved concept is proposed to adjust
IIDGs’ fault current injection through the required active and reactive power, employing the same
voltage characteristics. The proposed, i.e., power-based concept, is more definite than the currentbased one, since the required power will always be generated. The discussed concepts for the fault
current injection by IIDGs were tested in different 110-kV networks with loop and radial topologies,
and for different short-circuit capabilities of the aggregated network supply. Based on extensive
numerical calculations, the power-based concept during transmission networks faults generates
more reactive power compared to the current-based concept. However, the voltage support by IIDGs
during transmission networks faults, regardless of the concept being used, is influenced mainly
by the short-circuit capability of the aggregated network supply. As regards distance protection
operation, it is influenced additionally by the network topology, i.e., in radial network topology, the
remote relay’s operation can be delayed due to a largely seen impedance.
Keywords: distributed generation, fault current injection, voltage support, distance protection, transmission network faults
Published in DKUM: 16.06.2025; Views: 0; Downloads: 8
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7. Use of a heating system to control the probiotic beverage production in batch bioreactorJožef Ritonja, Andreja Goršek, Darja Pečar, 2021, original scientific article Abstract: Fermentation is a crucial bioengineering process, existentially important for modern society.
The most commonly used production unit for this process is the batch bioreactor. Its main advantage
is unsophisticated construction, which unfortunately results in its incapability of controlling the
transient state of the fermentation process. Control of the fermentation can significantly improve
the quality of the product and the economy of the process; therefore, it is useful for bioreactors to
be equipped with a control system. Based on the experimental results, we used an optimization
method to identify a mathematical model that describes the impact of the bioreactor’s temperature
on the fermentation’s transient process. The obtained model was applied for the design and synthesis
of the closed-loop control system. Simulations and experiments confirmed the effectiveness of the
proposed control system. In this way, we can ensure the consistent quality of the produced probiotic
product, increase the amount of the product, and shorten the fermentation time. The original results
display the feasibility of the closed-loop control of the batch bioreactor’s fermentation process by
changing the temperature. So far, the process has been carried without a closed-loop control system.
The problem is current and has not yet been solved sufficiently. There are many attempts published;
one of the last shows the possibility of controlling the fermentation process by changing the oxygen
supply, which is more complex and expensive for realization than the solution from our study.
Keywords: probiotic bewerages, fermentation, modelling, identification, control implementation
Published in DKUM: 16.06.2025; Views: 0; Downloads: 7
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8. Analysis of synchronous generators’ local mode eigenvalues in modern power systemsJožef Ritonja, Boštjan Polajžer, 2022, original scientific article Abstract: New energy sources, storage facilities, power electronics devices, advanced and complex
control concepts, economic operating doctrines, and cost-optimized construction and production of
machines and equipment in power systems adversely affect small-signal stability associated with local
oscillations. The objective of the article is to analyze local oscillations and the causes that affect them in
order to reduce their negative impact. There are no recognized analyses of the oscillations of modern
operating synchronous generators exposed to new conditions in power systems. The basic idea is to
perform a numerical analysis of local oscillations of a large number of synchronous generators in
the power system. The paper represents the local mode data obtained from a systematic analysis of
synchronous generators in the Slovenian power system. Analyzed were 74 synchronous generators
of the Slovenian power system, plus many additional synchronous generators for which data were
accessible in references. The mathematical models convenient for the study of local oscillations
are described first in the paper. Next, the influences of transmission lines, size of the synchronous
generators, operating conditions, and control systems were investigated. The paper’s merit is the
applicable rules that have been defined to help power plant operators avoid stability-problematic
situations. Consequently, boundaries were estimated of the eigenvalues of local modes. Finally,
experiments were performed with a laboratory-size synchronous generator to assess the regularity of
the numerically obtained conclusions. The obtained results enable the prediction of local oscillations’
frequencies and dampings and will be useful in PSS planning.
Keywords: power system, synchronous generators, oscillations, local modes, eigenvalue analysis
Published in DKUM: 27.03.2025; Views: 0; Downloads: 15
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9. Electrical and Electromechanical Converters : Lecture NotationsIvan Zagradišnik, Jožef Ritonja, 2025 Abstract: The publication is divided into five chapters: Introduction: magnetic field, excitation of windings, induction of voltage, forces and torque, conversion of electrical power into electrical or mechanical power, losses, efficiency, heating and cooling. Transformer: construction elements, ideal and real single-phase transformer, three-phase transformer, special transformer designs. Induction machine: description of construction with windings and mode of operation, starting motors and varying speed and torque, induction generator, single-phase induction motors. Synchronous machine: description of construction and operation, operation on a rigid grid, approximate treatment of a saturated machine, excitation systems and the use of permanent magnets for excitation, and permanent magnet synchronous motors.
Keywords: fundamentals of electromagnetics, transformer, induction machine, synchronous machine, commutator machine
Published in DKUM: 17.01.2025; Views: 0; Downloads: 46
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10. Izvedba vodenja čistilnega stroja turbinskega vtokaLuka Širec, 2024, undergraduate thesis Abstract: Namen diplomske naloge je bil posodobitev krmilnega sistema avtomatiziranega čistilnega stroja na turbinskem vtoku MHE Melje. Čistilni stroj ima dvoje čistilnih grabelj, ki drsijo po rešetkah navzgor in odstranjujejo naplavine. Grablje poganja hidravlični agregat in s pomočjo elektromagnetnih ventilov upravlja stroj. Vodenje je izvedeno s pomočjo programirljivega logičnega krmilnika. V okviru posodobitve vodenja smo zamenjali strojno in programsko opremo. Programirljivi logični krmilnik Siemens Simatic S7-200 smo zamenjali s Siemens Simatic S7-1200. V programskem okolju TIA Portal V16 smo napisali uporabniški program na osnovi lestvičnega diagrama. Za vnos in prikaz informacij o delovanju stroja smo izdelali tudi grafični vmesnik HMI.
Keywords: Elektrarna, čistilni stroj na turbinskem vtoku, programirljivi logični krmilnik, S7-1200, TIA Portal V16, vmesnik HMI.
Published in DKUM: 20.09.2024; Views: 0; Downloads: 57
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