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Opis: This paper examines the controllability of the stator and rotor magnetic flux linkages of doubly fed induction machines (DFIMs), considering small-signal oscillations and their relationship with electromagnetic machine design. To this aim, we first analyze 66 sets of lumped parameters from the dynamic model of a DFIM. Based on this, we classify DFIMs into three categories based on their modal parameters, namely, two for wind applications and one for pumped-hydro applications. Additionally, we identify reciprocal relationships between the damping of both identified oscillatory modes and the largest eigenvalues of the stator and rotor controllability Gramian matrices. Among the different lumped parameters, the winding resistances are found to influence these relationships the most. All analyzed DFIMs for wind applications were found to be less controllable and to exhibit better damping of oscillatory modes than DFIMs for pumped-hydro applications. Furthermore, based on the results of the controllability analysis, we selected three objective function candidates suitable for an optimization procedure aimed at minimizing the energy required to control the rotor flux linkages. An example objective function was evaluated in a multi-objective DFIM design process for wind applications that enables the design of more controllable machines that provide the desired damping of oscillations, which can consequently contribute to improving grid resilience.
Ključne besede: contorollability, design optimization, doubly fied indusction generators, modal analysis
Objavljeno v DKUM: 14.01.2026; Ogledov: 0; Prenosov: 2
Celotno besedilo (4,52 MB)

Opis: 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.
Ključne besede: trifazni transformator, matematično modeliranje, vklopni pojav
Objavljeno v DKUM: 23.09.2025; Ogledov: 0; Prenosov: 30
Celotno besedilo (7,52 MB)

Opis: 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.
Ključne besede: virtual synchronous generator, inertia constant, damping coefficient, small-signal stability, multi-objective optimization, genetic algorithm
Objavljeno v DKUM: 12.08.2025; Ogledov: 0; Prenosov: 12
Celotno besedilo (5,26 MB)

Opis: 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.
Ključne besede: distributed generation, fault current injection, voltage support, distance protection, transmission network faults
Objavljeno v DKUM: 16.06.2025; Ogledov: 0; Prenosov: 11
Celotno besedilo (1,39 MB)
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Opis: 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.
Ključne besede: power system, synchronous generators, oscillations, local modes, eigenvalue analysis
Objavljeno v DKUM: 27.03.2025; Ogledov: 0; Prenosov: 20
Celotno besedilo (4,17 MB)
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