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Příspěvek k analýze ustáleného chodu asynchronního stroje
Schreier, Luděk ; Bendl, Jiří ; Chomát, Miroslav
The paper deals with the problems associated with the estimation of the magnetizing current in generator operation of induction machines. According to some experts, the magnetizing current in generator operation is considerably bigger than in motor operation and this fact must be taken into consideration while designing the magnetic circuit. It is shown that this opinion is not in many cases quite justified and thus it is not necessary to overrate the magnetic circuit and an induction machine originally designed as a motor can be used as a generator without derating.
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O inversní Radonově transformaci
Chvála, František
A reconstruction of an image by application of the discrete inverse Radon transform realized by the function iradon of MATLAB may be unrealistic if the input data are represented by a small number of the image projections. To enhance the result, the set of input projections is extended, including additional virtual projections obtained from the former by a trigonometrical interpolation.
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Experiences in Matrix Converter Induction Motor Drive Implementation
Lettl, Jiří ; Bednář, M.
In this paper a special attention is paid to the indirect space vector modulation design based on the virtual DC-link concept. The entire converter is interpreted as a series connection of two matrix converters (rectifying virtual matrix converter and inverting virtual matrix converter). Thanks to this insight it is possible to compose the modulation strategy for the entire matrix converter from the rectifier and inverter part modulations.
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Aplikovatelnost nové metody pro lepší diskretizaci valmi malých hloubek vniku
Musil, Ladislav
The paper deals with tests of a new suggested method for an easier discretisation of thin layers of electromagnetic field penetrating into a conducting material. First the principle of the new method and its derivation is described. Comparison of computation with and without the transformation follows. The comparison is done on several very simple arrangements of induction heating of a ferromagnetic material. The computation were carried out by the FEM based professional code of FEMLAB supplemented with single purpose scripts written by the author in MATLAB and MATHEMATICA.
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Numerické modelování MHD jevu při čerpání tekutých kovů
Büllow, J. ; Doležel, Ivo ; Karban, P. ; Ulrych, B.
The paper deals with the numerical modeling of pumping molten metals based on the principle of the magnetohydrodynamic effect, i.e. force effect of an external stationary current field and magnetic field on an electrically conductive liquid. Described is the physical essence of the effect that represents the starting point for the formulation of its mathematical model. The theoretical analysis is illustrated on two examples. The first pump works with practically uniform electric field in a hydrodynamically less favorable channel of rectangular cross-section while the second one with nonuniform electric field in hydrodynamically more advantageous circular channel. The conclusion is devoted to the discussion about the possibilities of optimization of the device.
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Provozní parametry a charakteristiky aktuátorů s dilatačním prvkem
Doležel, Ivo ; Karban, P. ; Ulrych, B. ; Barglik, J. ; Pantelyat, M. ; Matyukhin, Y. ; Gontarowskiy, P.
In specific applications one needs actuators characterized by very high forces at small shifts. As actuators of classical constructions mostly cannot satisfy these requirements, the authors designed another arrangement with an inductively heated dilatation element. But huge mechanical strains and stresses of thermoelastic origin acting in its structural parts could lead to its damage or destruction. The paper deals with mathematical modeling of the device that is solved numerically in the combined formulation (while the electromagnetic field is solved independently, the thermal and thermoelastic effects are solved in the hard-coupled formulation). The algorithm is illustrated on a typical example whose results are discussed.
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Problémy konvergence při integrálním modelování 3D elektrostatických polí se singularitami
Hamar, R. ; Doležel, Ivo
Numerous electrostatic fields are characterized by the presence of singularities (for example, at the corners or along the edges of electrically conductive charged bodies). Solutions to the tasks involving such elements by classic low-order differential methods often lead to inaccurate results. One of the prospective methods seems to be the integral approach starting from finding the distribution of the charge using the system of the first-kind Fredholm equations. The paper shows an application of this approach to two electrically conductive cubes in a general position in space. Discretization of their surfaces is performed in several different ways and the results are compared with respect to their convergence.
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