Wyniki 1-10 spośród 11 dla zapytania: authorDesc:"Damijan MILJAVEC"

Study of the behaviour of a doubly-fed induction machine supplied with scalar open-loop control DOI:10.15199/48.2019.05.06

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Introduction Doubly-fed induction machine (DFIM) is usually used in large-power variable-speed drives with limited range of speed in the vicinity of the synchronous speed using bidirectional power converter [1-5], e. g. wind turbines, large pumps etc. Stator is connected directly to the public network (400 V and 50 Hz in Europe), whereas rotor is connected to the same network via power converter with adjustable voltage and frequency (Fig. 1). Fig.1. Power flow in the drive system with DFIM and power converter If power converter (rotor voltage source) allows only unidirectional power flow (Fig. 1), i. e. from the network to the machine (diode rectifier at the input side instead of the transistor bridge), then the operational area is limited to the supersynchronous speeds [6-7], assuming that the machine operates as a motor (Fig. 2). The power rating of the rotor voltage source is a fraction of the total power and it increases with increasing speed range [8-10]. In the steady-state motor operation, the rotor rotates in the supersynchronous area with the mechanical speed, which is defined as the sum of the rotational frequency of the stator and rotor rotating magnetic field, divided by the number of pole pairs: (1) p ω ω Ω 1 2 + = where: Ω - mechanical speed in [1/s], ω1/ω2 - angular frequency of the stator/rotor voltage in [1/s], p - number of pole pairs. Fig.2. Supersynchronous motor operation area (grey) Simulated drive system The two-dimensional finite-element-method (FEM) model (Fig. 3) with analytically calculated resistances and end-winding leakage inductances was built in order to obtain as accurate results as possible. The machine data are given in Table 1. The scalar open-loop control with variable voltage-to-frequency ratio (U/f control) has been used for the rotor voltage source in the simulations. Namely, the U/f control it is one of the simplest, easy-to-design and low-cost m[...]

Analyses and tests of interlamination short-circuits

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Since the interlamination short-circuits in stator cores can cause major damage to electrical machine a great emphasis is placed to detect such faults. ELCID (Electromagnetic Core Imperfection Detector) test is nowadays often used for testing of interlamination insulation in stator cores of large electrical machines. To investigate this relatively young method a laboratory model of stator core was built, which enables measurements and analyses of intentional short-circuits in the core. Interlamination faults were also simulated and analysed using FEM. Streszczenie. Ponieważ zwarcia międzywarstwowe w rdzeniach stojanów mogą spowodować istotne awarie maszyn elektrycznych jest sprawą wielkiej wagi detekcja takich zwarć. Test detektorem uszkodzeń rdzeni magnetycznych jest współcześnie często używany dla testowania izolacji międzywarstwowej w rdzeniach stojana dużych maszyn elektrycznych. Do zbadania tej relatywnie nowej metody zbudowany został laboratoryjny model rdzenia stojana, który umożliwia pomiary i analizę celowych zwarć w rdzeniu. Uszkodzenia międzywarstwowe były także symulowane i analizowane za pomoca MES. (Analizy i testy zwarć międzywarstwowych) Keywords: ELCID, fault diagnostics, interlamination short-circuit, stator core. Słowa kluczowe: detector uszkodzeń rdzenia elektromagnetycznego, zwarcia międzywarstwowe, rdzeń stojana Introduction A traditional method for detection of interlamination faults is the High Flux Ring Test, often referred to as a Thermal Loop Test. The rotor is removed from the machine and the stator core is magnetically excited by a high voltage high current temporary winding. Magnetic flux produced in stator yoke should be near to that normally applied in service. Hot spots are detected by a variety of means including thermal cameras. Because of the required dismantling of the machine, high voltage excitation winding, high power source, that method is not very convenient. One of contemporary methods is ELC[...]

Forming a genetic record of cylindrical magnetic separator structures

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A possibility of realization of structural genetic algorithm (SGA) for synthesis of separators magnetic systems structural varieties is demonstrated taking basic Species of cylindrical longitudinally-symmetric y-oriented ones as an example. The veracity of synthesis results is proved by means of comparison of the synthesis results with the data of patent information research. A forecasted component of the synthesis results is determined. Streszczenie. W artykule przedstawiono możliwa realizację strukturalnego algorytmu genetycznego do syntezy magnetycznych separatorów. Jako przykładu takiej syntezy użyto separatora cylindrycznego z symetrią wzdłużną. Wiarygodność wyników syntezy wykazano przez porównanie wyników syntezy z danymi, pochodzącymi z informacji patentowej. Przewidywany składnik wyników syntezy został określony. (Formowanie zapisu genetycznego struktur z cylindrycznymi separatorami magnetycznymi). Keywords: chromosome set, generating structure, genetic model, structural genetic algorithm. Słowa kluczowe: zespół chromosomów, struktura generacyjna, model genetyczny, strukturalny algorytm genetyczny Introduction Expansion of the sphere of magnetic separators application in modern conditions and increasing diversity of magnetic separation devices, connected with it, result in large percent of search design procedure in their designing [1]. In practice, search and synthesis of new structural variants are mainly of a heuristic character and based on the use of designer’s intuition and personal experience. In such conditions research oriented to determination of the regularities of magnetic separators structure forming processes and development of methodological instruments providing realization of a directed search and synthesis of their new structural varieties is topical. Research methodology substantiation Determination of Species variety and development of genetic systematics of a class of open working area magnetic [...]

A novel control strategy for the switched reluctance generator

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The paper proposes a novel switching strategy that increases the efficiency of the energy conversion and reduces the noise level produced by the generator. The technique redistributes the three switching stages of the converter within one working cycle. Such technique is viable when the generator operates below its base speed. Here, the back electromagnetic force is always lower than the DC-link voltage, hence the phase current is controlled at a desired value. The proposed control method is validated using a commercially available four phase 8/6 switched reluctance generator. Streszczenie. W artykule zaproponowano nową strategię przełączania generator reluktancyjnego. Metoda zwiększa skuteczność konwersji energii I redukuje szumy. W jednym cyklu realizuje się trzy etapy przełączeń. Metoda jest zalecana gdy generator operuje poniżej bazowej szybkości. (Nowa strategia sterowania generatorem reluktancyjnym) Keywords: acoustic noise, asymmetric bridge converter, current control, efficiency, switched reluctance generator. Słowa kluczowe: generator reluktancyjny, przełączanie, szumy Introduction To enable energy conversion, the switched reluctance (SR) machine utilizes variable inductance enabled by laminated salient poles on its stator and rotor. As rotor carries no windings or permanent magnets its size is small with low inertia. The stator poles are equipped with concentrically wound phase windings, thus simplifying the manufacture. As there is no winding distribution between the different stator slots, each winding is electrically independent for which reason the mutual coupling between phases is negligible. Consequently, an electrical fault in one of the phases does in general not affect the other phases. Because of the sequential energizing of the stator phases, there is a need for the SR machine to use a controllable converter for its operation. Hence, the SR machines are used in variable-speed drive systems and because of their [...]

Brush-less Direct Current Machine Coupled with Internal Combustion Engine

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The development and prototype design of a brush-less direct current (BLDC) machine with an external rotor and a control unit coupled with internal combustion engines (ICE) is presented. The main goal was to fulfill all ICE starting demands, regardless temperature and inflexibly limited voltage supply net. Stringent starting torque demands, electrical machine geometry limitations and a wide rotat[...]

Research of rnergy processes in circuits containing iron in saturation condition

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Problems of application of instantaneous power theory theses to the analysis of electromagnetic and energy processes in nonlinear ferromagnetic circuits at different degrees of its saturation have been considered. Results confirm the necessity to revise the conventional methods and approaches to analyze the nonlinear circuits in saturation conditions. Streszczenie. Rozważono problemy związane z teorią mocy chwilowej zastosowaną do analizy elektromagnetycznych i energetycznych procesów w nieliniowych obwodach ferromagnetycznych w różnym stopniu nasyconych. Wyniki analiz potwierdzają konieczność rewizji metod konwencjonalnych i podejść do analizy obwodów nieliniowych w stanie nasycenia. (Badania procesów energetycznych w obwodach zawierających żelazo w warunkach nasycenia) Keywords: magnetic saturation, magnetic material, energy processes, iron losses. Słowa kluczowe: nasycenie magnetyczne, materiał magnetyczny, process energetyczny, straty w żelazie Introduction Changes of the state of electro-technical and electromechanical magnetic systems during their operation cause the problem of diagnostics regarding their electrical and magnetic properties topical. In this case it is often necessary to solve the problems connected with accurate measurements of the magnetic system parameters and characteristics. The influence of devices with changes in their magnetic system on electromagnetic compatibility to the supply system is another important issue. Problem statement In the course of long-term operation and repairs of electro-technical and electromechanical devices with magnetic system, made of laminated electro-technical steel, deterioration of its properties occurs. It shows in the change of magnetic characteristics, increase of iron losses and higher degree of magnetic saturation. Change of magnetic system state results in increased level of its saturation. Consequently, the considered devices present a nonlinear load for the supply[...]

Nonlinear reluctance model of transverse flux motor

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The aim of this paper is to present parametric nonlinear reluctance model of outer rotor permanent magnet transverse flux machine (TFM). Main and leakage magnetic flux paths of TFM are studied and modelled with reluctances using mean length and cross area approximation which divide the model into simple solids. General propose circuit simulator is used to solve the model. The main goal of the model is to provide the results of machine performances with sufficient accuracy and quick enough to use them in optimization procedures. Streszczenie. Celem artykułu jest prezentacja nieliniowego reluktancyjnego modelu maszyny elektrycznej z poprzecznym strumieniem i z zewnętrznym wirnikiem i magnesem trwałym. Strumienie magnetyczne, główny i rozproszenia, modelowane są z reluktancjami przy użyciu średnich długości i przekrojów, które dzielą model na proste obiekty. Zadaniem symulatora obwodowego jest rozwiązanie modelu. Głównym celem modelowania jest dostarczenie wyników działania maszyny z dostateczną dokładnością i wystarczająco szybko do wykorzystania w procedurach optymalizacyjnych. (Nieliniowy model reluktancyjny silnika z poprzecznym strumieniem). Keywords: finite element method, nonlinear reluctance model, transverse flux machine Słowa kluczowe: metoda elementów skończonych, nieliniowy model reluktancyjny, naszyna ze strumieniem poprzecznym Introduction The development of soft magnetic composite materials (SMC) increase the interest in electromagnetic structures with 3-D guided magnetic flux, such as transverse flux machine (TFM) [1, 2] shown in Fig. 1. Model of TFM is composed of inner stator made from soft magnetic composite material and outer rotor composed of yoke and permanent magnets. The three phase coils are in form of ring and positioned in the stator slot. The rotor magnets are shifted for 120 electrical degrees circumferentially regarding each phase. Fig.1. 3-D model of 1/36 transverse flux motor Further, the paper proposes a[...]

Determination of power indices for a three-phase induction motor with a phase-wound rotor through particular losses components

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A method of determination of power indices for a three-phase induction motor with a phase-wound rotor through particular losses components in the function of their integral and instantaneous values is developed. The adequacy of the method is confirmed. The prospect of its use is grounded for the situation when the state of structural assemblies and motor elements changes in the process of long-term operation and after repair. Streszczenie. Przedstawiona została metoda określenia wskaźników trójfazowego silnika indukcyjnego z wirnikiem uzwojonym poprzez poszczególne składniki strat w funkcji ich integralnych i chwilowych wartości. Odpowiedniość metody została potwierdzona. Perspektywa stosowania tej metody oparta jest ukierunkowana na sytuacje kiedy konstrukcyjny montaż i elementy silnika zmieniły się w procesie długotrwałego działania oraz po remoncie. (Określenie wskaźników mocy dla trójfazowego silnika indukcyjnego z uzwojonym wirnikiem poprzez poszczególne składniki strat). Key words: induction motor, phase-wound rotor, losses components, power indices. Słowa kluczowe: silnik indukcyjny, wirnik uzwojony, składniki strat, wskaźniki mocy. Introduction In a competitive market, which is especially acute during crisis years, the industrial production aims at considerable decrease of various kinds of expenditure influencing the prime cost of manufactured goods. For most enterprises of metallurgic, chemical and other adjacent industries electric power costs, coming to 30-35 % in the total cost, are considerable. This poses the problem of optimization of power costs in control of various technological objects and processes at an enterprise. It is possible to optimize power consumption in an electric drive by means of control systems estimating real power conditions of electric machines operation and their efficiency. The prospect of the use of such systems is determined by availability of reliable methods of finding power and moment on[...]

Measurement of electric discharge machining bearing currents in brush-less direct-current motors

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The paper deals with electric discharge machining bearing currents in brush-less direct-current electric motors. The shunt resistor as a current sensor was analyzed regarding appropriateness for measurement of high-frequency bearing currents. The circuit model of electric discharge machining current’s circuit was built to determine the influence of insulation sleeves and bypass bridge to the initial system. Parameters of the model were estimated with simplex algorithm. The measurements and investigations of bearing-currents’ trend line were performed. Streszczenie. Artykuł dotyczy zagadnienia prądów występujących przy elektrycznym rozładowaniu maszynowym (ang. Electrical Discharge Machining) w łożyskach bezszczotkowej maszyny DC. Rolę czujnika prądu spełnił równolegle dołączony rezystor. W celu określenia wpływu tulei izolacyjnych oraz bocznika na warunki początkowe, dokonano analizy modelu zjawiska. Stworzono obwód elektryczny, którego odpowiednie parametry estymowano przy pomocy algorytmu simpleksowego. Przedstawiono wyniki pomiarów i analiz. (Pomiary prądów elektrycznego wyładowania maszynowego w łożyskach bezszczotkowej maszyny DC). Keywords: bearing currents, trend line, current sensor, equivalent circuit model. Słowa kluczowe: prądy łożyskowe, linia trendu, czujnik prądu, obwód równoważny. Introduction Bearing currents are parasitic phenomena, especially prominent in electric motors, supplied by inverters, like brush-less direct-current (BLDC) motors. Bearing life could be significantly reduced due to flow of electric current. Inverter-induced bearing currents can be divided into four groups, namely capacitive currents, electric discharge machining (EDM) currents, high-frequency circulating currents and bearing currents, due to currents between the motor and the load [1]. In low-power motors EDM currents are especially prominent, therefore this paper focuses on them. Shaft voltage builds up in motor due to common mo[...]

Taking stator cores properties into account when induction motors vibration parameters are calculated

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Problems of induction motor stator core condition influence on the general pattern of magnetic field distribution, magnetic tension tensor space distribution and the value of electromagnetic vibroexcitating force are researched. The necessity of taking into account different changes of properties of steel of yoke and teeth zone, as well as nonuniform distribution of stator core teeth zone properties, when vibration electromagnetic component is calculate, is substantiated. Streszczenie. Badano wpływ rozkładu pola magnetycznego I wibracji na warunki pracy twornika silnika indukcyjnego. W szczególności uwzględniono zmianę właściwości stali rdzenia. (Badanie właściwości materiału twornika przy projektowaniu silnika indukcyjnego z uwzględnieniem wibracji) Key words: induction motor, stator core, vibration electromagnetic component, magnetic properties. Słowa kluczowe: silnik indukcyjny, wibracje, właściwości materiału magnetycznego Introduction During long-term induction motor (IM) usage, alternating with a number of repairs, the properties of stator laminated core interlamination insulation change [1]. It results in occurrence of local shorted circuits randomly distributed along the length and across the volume of the core. The mentioned phenomenon causes winding overheating at local sections and increased vibration of the electric machine (EM). Neglect of taking into account the change and irregularities in distribution of stator core properties prevents one from correct estimation of admissible EM operating conditions. The consequence of this is their quicker failures due to stator winding overheating and vibration. There are a number of efficient calculation methods to determine thermal condition of such IM. At the same time the problem of estimation of the magnetic system properties change influence on IM vibration parameters remains uninvestigated. Problem statement The purpose of the paper consisted in substantiation of the p[...]

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