No. 4, 2006


Jan Hlina, Frantisek Chvala : On application of inverse Radon transform for diagnostics of asymmetric plasmatic radiation sources, pp. 317-325

The distribution of radiation intensity in plasma that cannot be considered as cylindrically symmetric is reconstructed from side-on radiation profiles by application of the inverse Radon transform. The side-on radiation profiles can be usually measured in a smaller number of projection planes than needed for obtaining sufficiently accurate results by usage of the relevant programme involved in the environment . Therefore, a method is proposed for completing the set of measured side-on profiles with a number of other side-on profiles obtained from the measured data by an interpolation. Some illustrative examples are presented.

Frantisek Vondrasek : The primary converter of traction drive with medium-frequency transformer, pp. 327-337

The work is a study of a converter proposed for direct connection to the contact wire of AC-fed traction vehicles. Its principle was explained in [1]. The system involves a new single-phase AC/AC-modular-multilevel-converter (M2LC) and a medium-frequency transformer. The single-phase converter consists of 4N identical submodules and of 4N identical storage capacitors. The calculation of the number N of submodules in one converter arm, as well as of the capacitance of the storage capacitors is proposed. In the conclusion, results of simulations are presented.

Karel Benes, Ivo Dolezel, Pavel Dvorak, Bohus Ulrych : Static characteristic of actuator working on principle of thermoelasticity, pp. 339-347

Electromechanical actuators transforming electromagnetic energy into unidirectional mechanical force play an important role in various industrial processes, control systems, robotics and a lot of other applications. They work on several different principles. In case that we require small shifts of their movable parts, it is possible to make use of thermoelastic displacements of a metal membrane produced by its induction heating. The paper presents a fundamental study of such a device that deals with its construction, operation parameters and optimisation. The mathematical model is solved in weakly coupled formulation. The theoretical analysis is illustrated on a typical example whose results are discussed.

Petr Filip, Jiri David, Radek Pivokonsky : Modelling of non-monotonous flow curves using empirical constitutive equations, pp. 349-362

A number of parameters appearing in the `classical' empirical constitutive equations usually oscillate between two and five. With the onset of new rheologically more complex materials exhibiting non-monotonous behaviour of flow curves this range (2-5) is no longer tenable and more additional parameters are required for a proper description of the flow curves. The present paper analyses this problem for the cases: shear viscosity vs. shear rate and shear viscosity vs. shear stress.

Petr Kokes, Radko Semerad : Regulation of an induction motor under broad changes in DC-link voltage, pp. 363-394

This paper deals with the control of an induction motor (IM) fed from a voltage source inverter (VSI) under conditions of a wide range and rapid changes in the DC-link voltage. Uncontrollable transients can arise in the IM due to a rapid voltage drop in the DC link. Two techniques which substantially increase the robustness of the IM control system under these rugged operating conditions are discussed in detail. They are the IM field-weakening and the IM torque limitation in case of the DC-link voltage drop. The field-weakening is studied in detail for the IM stator flux vector control method (SFVC). A simplification of the field-weakening structure has been designed with the use of the operating point trajectory analysis in a plane defined by stator flux space vector coordinates. In addition, an innovation of the maximum stator current limitation during IM field-weakening has been designed. We worked out a new control structure for the IM torque limitation based on the drive power balance. All mentioned solutions are theoretically discussed in detail and verified by computer simulations in the time domain and also by practical experiments with an 85 kW AC drive model.

Frantisek Durovsky, Ladislav Zboray : Presetting of rolling stand parameters by genetic algorithms, pp. 395-401

Bland-Ford mathematical model of rolling process is often used in metallurgy. The model allows to analyze rolling process according to data measured on the mill stand to get immeasurable variables for rolling control. The values obtained by modeling a currently rolled coil are used for mill presetting for the next coil. However, to achieve real-time rolling control, the Bland-Ford model is modified applying an artificial intelligence approach instead of analytical solution of a set of nonlinear differential equations. The genetic algorithm with hierarchical structure was used instead of classical iterative method.

Tomas Chraska : Transmission electron microscopy of plasma sprayed ceramic deposits, pp. 403-413

Microstructure of plasma sprayed deposits is usually very complex containing solidified lamellas, microcracks, unmelted particles and small voids. Internal structure of solidified lamellas is often composed of narrow columnar grains or can be amorphous. A powerful tool to study fine microstructures of the coatings and the complexities of the substrate/coating interfaces is the Transmission electron microscope. However, preparation of electron transparent foils, which require thickness below 500 mm, is very difficult especially in case of ceramic coatings on metal substrates. Traditional sample preparation techniques rely on extended ion-milling that tends to generate ion-induced artifacts in the samples. The modified wedge polishing technique introduced in the paper significantly reduces the time required for final ion-milling step. Several samples prepared by the wedge polishing method are documented.

Jaroslav Dudrik, Peter Dzurko : Arc welder with series-parallel resonant DC-DC converter, pp. 415-426

A resonant DC-DC high power converter operating above resonance frequency used as a dc current source for arc welding is described. The resonant dc-to-dc converter consists of input single-phase diode bridge rectifier, capacitor filter, high frequency series-parallel resonant inverter, high frequency power transformer and high frequency diode output rectifier. The experimental results of a 3 kW DC-DC converter working at switching frequency from 25 kHz to 50 kHz are presented.