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1
Content available Mathematical and simulation modeling of dual active bridge
Barlik Roman, Grzejszczak Piotr, Koszel Mikołaj
Bulletin of the Polish Academy of Sciences. Technical Sciences
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2022
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Vol. 70, nr 5
art. no. e142653
EN
The paper is a structured, in-depth analysis of dual active bridge modeling. In the research new, profound dual active bridge converter (DAB) circuit model is presented. Contrary to already described idealized models, all critical elements including numerous parasitic components were described. The novelty is the consideration of a threshold voltage of diodes and transistors in the converter equations. Furthermore, a lossy model of leakage inductance in an AC circuit is also included. Based on the circuit equations, a small-signal dual active bridge converter model is described. That led to developing control of the input and output transfer function of the dual active bridge converter model. The comparison of the idealized model, circuit simulation (PLECS), and an experimental model was conducted methodically and confirmed the high compatibility of the introduced mathematical model with the experimental one. Proposed transfer functions can be used when designing control of systems containing multiple converters accelerating the design process, and accurately reproducing the existing systems, which was also reported in the paper.
2
Content available Extremal properties of linear dynamic systems controlled by Dirac’s impulse
Białas Stanisław, Górecki Henryk, Zaczyk Mieczysław
International Journal of Applied Mathematics and Computer Science
|
2020
|
Vol. 30, no. 1
75--81
EN
The paper concerns the properties of linear dynamical systems described by linear differential equations, excited by the Dirac delta function. A differential equation of the form an x(n) (t) + ∙∙∙ a1 x’(t) + a0 x(t) = bm u (t) + ∙∙∙ + b1 u’(t) + b0 u(t) is considered with ai, bj >0. In the paper we assume that the polynomials Mn(s) = ansn + ∙∙∙ + a1s + a0 and Lm(s) = bmsm + ∙∙∙ + b1s + b0 partly interlace. The solution of the above equation is denoted by x(t, Lm, Mn). It is proved that the function x(t, Lm, Mn) is nonnegative for t ∊ (0, ∞) , and does not have more than one local extremum in the interval (0, ∞) (Theorems 1, 3 and 4). Besides, certain relationships are proved which occur between local extrema of the function x(t, Lm, Mn), depending on the degree of the polynomial Mn(s) or Lm(s) (Theorems 5 and 6).
3
Content available remote Wykrywanie zwarć zwojowych w transformatorze energetycznym przy użyciu metody SFRA
Lewandowski K., Morańda H.
Przegląd Elektrotechniczny
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2018
|
R. 94, nr 10
118--121
PL
W artykule przedstawiono wyniki badań odpowiedzi częstotliwościowej transformatora bez zwarcia oraz ze zwartymi wybranymi cewkami uzwojenia górnego napięcia. Do pomiarów zwierano od jednej do pięciu pierwszych cewek uzwojenia fazy L3. Pomiary wykonywano jednym z czterech sposobów: pomiar odpowiedzi danego uzwojenia przy rozwartych i zwartych zaciskach pozostałych uzwojeń oraz pomiar międzyuzwojeniowy indukcyjny i pojemnościowy. Z przeprowadzonych badań wynika, że najskuteczniejszym układem pomiarowym do wykrywania zwarcia zwojowego w transformatorach jest pomiar odpowiedzi częstotliwościowej przy pozostawieniu pozostałych zacisków na potencjale swobodnym.
EN
The article presents the results of the transformer frequency response investigations without and with shorting the selected upper voltage winding coils. For measurements first coils, from one to five, of the L3 phase winding, were shorted. The measurements were carried out in one of four ways: measurement of the frequency response of a selected winding with open and closed terminals of the remaining windings, measurement in an induction inter-winding system and measurement in a capacitive inter-winding system. The conducted tests show that the most effective measurement method for detecting of a winding short-circuit in transformers is to measure the frequency response with the remaining terminals on the floating potential.
4
Content available Zasady poprawnego wykonywania pomiarów transformatorów energetycznych przy użyciu metody SFRA
Lewandowski K.
Poznan University of Technology Academic Journals. Electrical Engineering
|
2018
|
No. 95
163--174
PL
W artykule zaprezentowano podstawowe zasady wykonywania pomiarów transformatorów energetycznych z wykorzystaniem metody SFRA. Przedstawiono sposoby podłączania przewodów pomiarowych, które zostały opisane w [1]. Zaprezentowano praktyczne aspekty pomiarów z uwzględnieniem dobrej praktyki pomiarowej, które pozwalają uzyskać wiarygodne i powtarzalne wyniki pomiarów, nadające się do porównywania z przebiegami wzorcowymi, uzyskanymi np. u producenta transformatora. Przeanalizowano wpływ sprzętu pomiarowego, sposobu podłączenia przewodów pomiarowych oraz innych czynników, które koniecznie należy uwzględnić podczas wykonywania pomiarów. Ponadto, autor przedstawił kilka przykładowych wyników błędnie wykonanych pomiarów, zrealizowanych na rzeczywistych transformatorach energetycznych o mocy 16 MVA oraz 630 kVA.
EN
The article presents the basic principles of performing of SFRA measurements method on power transformers. Methods of connecting test leads are described, as shown in the standard [1]. Practical aspects of measurements, including good measurement practice, are presented, which allow to obtain reliable and reproducible measurement results, suitable for comparison with fingerprint waveform obtained, for example, from the manufacturer of transformer. The influence of measuring equipment, methods of connecting test leads and other factors, which must be taken into account during the measurements, are analyzed. Moreover, the author presented a few examples of incorrectly performed measurements, carried out on a real 16 MVA and 630 kVA power transformers.
5
Content available The role of parameter constraints in EE and OE methods for optimal identification of continuous LTI models
Byrski W., Byrski J.
International Journal of Applied Mathematics and Computer Science
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2012
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Vol. 22, no. 2
379-388
EN
The paper presents two methods used for the identification of Continuous-time Linear Time Invariant (CLTI) systems. In both methods the idea of using modulating functions and a convolution filter is exploited. It enables the proper transformation of a differential equation to an algebraic equation with the same parameters. Possible different normalizations of the model are strictly connected with different parameter constraints which have to be assumed for the nontrivial solution of the optimal identification problem. Different parameter constraints result in different quality of identification. A thorough discussion on the role of parameter constraints in the optimality of system identification is included. For time continuous systems, the Equation Error Method (EEM) is compared with the continuous version of the Output Error Method (OEM), which appears as a special sub-case of the EEM.
6
Content available Comparison of transfer functions using estimated rational functions to detect winding mechanical faults in transformers
Bigdeli M., Vakilian M., Rahimpour E.
Archives of Electrical Engineering
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2012
|
Vol. 61, nr 1
85-99
EN
As it is found in the related published literatures, the transfer function (TF) evaluation method is the most feasible method for detection of winding mechanical faults in transformers. Therefore, investigation of an accurate method for evaluation of the TFs is very important. This paper presents three new indices to compare the transformer TFs and consequently to detect the winding mechanical faults. These indices are based on estimated rational functions. To develop the method, the necessary measurements are carried out on a 1.3 MVA transformer winding, under intact condition, as well as different fault conditions (axial displacement of winding). The obtained results demonstrate the high potential of proposed method in comparison with two other well-known indices. Additionally, two important methods for describing TFs by rational functions are studied and compared in this paper.
7
Content available Ocena uszkodzeń uzwojeń transformatorów na podstawie odpowiedzi częstotliwościowej wyznaczanej metodą impulsową
Furgał J., Kuniewski M.
Elektrotechnika i Elektronika
|
2009
|
T. 28, z. 1--2
1-6
PL
Ocena stanu technicznego transformatorów energetycznych ma istotne znaczenie ze względu na funkcje, jaką transformatory spełniają w sieciach elektrycznych, oraz na ich koszt. Dlatego transformatory są poddawane szczegółowym badaniom diagnostycznym. Badania obejmują między innymi stan techniczny uzwojeń. W tym celu stosowana jest metoda analizy odpowiedzi częstotliwościowej, umożliwiająca wykrywanie uszkodzeń uzwojeń. Podstawą analizy są charakterystyki częstotliwościowe funkcji przenoszenia transformatorów. Są one wyznaczane przy zastosowaniu różnych metod. Obecnie prace badawcze w tej dziedzinie są prowadzone w celu doskonalenia kryteriów rozpoznawania charakteru i zakresu zniekształceń uzwojeń badanych metodą analizy odpowiedzi częstotliwościowej. W artykule przedstawiono badania wybranych uszkodzeń uzwojeń transformatorów energetycznych na podstawie analizy odpowiedzi częstotliwościowej wyznaczanej metodą impulsową.
EN
Estimation of technical state of power transformers have essential meaning with regard on the function of transformers in electrical networks and their costs. Therefore transformers are investigated in detail at exploitation conditions. Investigations include among others technical state of windings. To detection of winding failures the frequency response analysis method is used. As a base of analysis the frequency characteristics are used. They are determined by use of different methods. Nowadays scientific investigations in this area are made in purpose to improvement the criterions of character and range of winding deformations by use of the frequency response analysis method. The investigations of selected failures of windings of power transformers on the base of analysis of frequency response determined by use of impulse method are presented in the paper.
8
Content available remote Rozpoznawanie uszkodzeń uzwojeń na podstawie funkcji przenoszenia transformatorów
Florkowski M., Furgał J.
Przegląd Elektrotechniczny
|
2007
|
R. 83, nr 12
60-63
PL
Metody badań diagnostycznych transformatorów są obecnie systematycznie rozszerzane i doskonalone. Do wykrywania uszkodzeń uzwojeń coraz szerzej jest stosowana metoda analizy odpowiedzi częstotliwościowej. Jej podstawą są zależności częstotliwościowe funkcji przenoszenia transformatorów. Jednocześnie jest ona ciągle doskonalona. W artykule przedstawiono metodę identyfikacji uszkodzeń uzwojeń przy wykorzystaniu charakterystyk częstotliwościowych transformatorów. Podano kryteria pozwalające odróżnić różne typy uszkodzeń takie jak zwarcia międzyzwojowe czy przesunięcia uzwojeń.
EN
Nowadays methods of diagnostic investigations of power transformers are systematically developed. The frequency response analysis method is more frequently used for detection of winding failures. Its base constitute frequency dependencies of transformer transfer function. This method is sistematicaly developed. The identification method of winding failures by use of transformer frequency characteristics is presented in the paper. The criteria for discrimination between varoius types of defect have been provided, for example winding movements or turn-to-turn faults.
9
Content available remote Optimal approximation, simulation and analog realization of the fundamental fractional order transfer function
Djouambi A., Charef A., Besançon A. V.
International Journal of Applied Mathematics and Computer Science
|
2007
|
Vol. 17, no 4
455-462
EN
This paper provides an optimal approximation of the fundamental linear fractional order transfer function using a distribution of the relaxation time function. Simple methods, useful in systems and control theories, which can be used to approximate the irrational transfer function of a class of fractional systems for a given frequency band by a rational function are presented. The optimal parameters of the approximated model are obtained by minimizing simultaneously the gain and the phase error between the irrational transfer function and its rational approximation. A simple analog circuit which can serve as a fundamental analog fractional system is obtained. Illustrative examples are presented to show the quality and usefulness of the approximation method.
10
Content available remote Robust performance of a class of control systems
Wang L.
Control and Cybernetics
|
2004
|
Vol. 33, no 1
71-83
EN
Some Kharitonov-like robust Hurwitz stability criteria are established for a class of complex polynomial families with nonlinearly correlated perturbations. These results are extended to the polynomial matrix case and non-interval D-stability case. Applications of these results in testing of robust strict positive realness of real and complex interval transfer function families are also presented.
11
Content available remote Identification of Low-Order Continuous-Time Models Via Discrete-Time Trends of Measurements
Janiszowski K. B.
International Journal of Applied Mathematics and Computer Science
|
1999
|
Vol. 9, no 4
839-853
EN
The paper deals with the problem of continuous-time (CT) identification of parameters in transfer functions for low-order linear systems, based on recorded discrete-time (DT) data. Algorithms for direct estimation of CT parameters are developed from rules for transformation of a CT transferfunction controlled via a zero-order sampling-and-hold unit into a DT representation.Two schemes are derived and tested: the first is based on the Goodwin transformation and the other is derived from the modified Tustin transformation. Both the approaches result in relations which can be used for direct estimationof CT parameters in a model of the investigated system. The numerical schemes contain some expressions that are reminiscent of DT differences and consequently they may magnify disturbances. Therefore the results of extensively testing both the schemes including different types of disturbances, measurement noise, slow varying drifts, measurement resolution errors together with changes in the sampling time are presented. A model of a pneumatic servomechanism system was used as a test plant.
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