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One way to improve the unification of the casting structure may be the application of forced convection of liquid metal during the crystallization in the mould or continuous casting mould. This paper presents the results describing the influence of selected parameters of rotate electromagnetic field enforcing the movement of liquid metal in the mould on the morphology of graphite in grey cast iron. Different form of flake graphite was obtained in conditions of changes in the rate of liquid metal solidification in the range of pouring and liquidus temperature TZALTL and casting with the influence of electromagnetic field.

The paper reports on design, simulation and development of a test bed prototype for microfabricated, chip-integrated inductor developed by Tyndall National Institute, Cork, Ireland. A test circuit is developed for a buck DC/DC converter topology. The device is powered from Li-Ion battery or with use of a similar source (approximately 3.6 V) and should be able to deliver approximate 0.5 W with output voltage of 1.0-1.2 V. The main issue is to achieve high switching frequency-between 5 MHz and 15 MHz.

A system designed for the control of overhead crane motion is described in the paper. The control system keeps the motion of the crane centred, eliminating its bevel at the same time. The motion of the crane outside the centre and with the nonzero bevel is the result of nonsymmetry disposition of the horizontal loads, geometrical imperfections of the construction and the phenomenon of wheels side reflection. The centring and elimination of the bevel angle is realised by a single controller, subordinated to the speed controller. The behaviour of the crane has been simulated based on a mathematical model which reflects all the above-mentioned essential phenomena occurring in the crane. The measurement of the crane position in relation to the centre of the runway and the measurement of bevel angle, which could be done in the proposed system by means of only two distance sensors, plays a key role in the described system. The results gained in the work can be a starting point for experimental research based on microprocessor control realisation.

The subject of the paper is the basic topology of a Class E inverter. The influence of the inverter parameters on its characteristics is analysed in the paper. The characteristics of the inverter are given by its efficiency /spl eta//sub Z/ and the relative input resistance r/sub _DC/. They are delivered as a function of the switching frequency, the inductance and the load resistance. The analysis is carried out by means of the method based on the idealised model of the inverter which reflects turn-on loss. The results obtained theoretically are compared with the results of laboratory measurements. The laboratory measurements are for a 1 MHz, 200 W inverter.

The paper is focused on a toroidal superconducting transformer with cold magnetic core. The transformer was developed aiming at the solution where magnetic core could operate immersed in LN2, not having much higher power losses than a core operating in room temperature. The second aim is concerned to the perpendicular component of the magnetic flux. It was assumed that it should be minimized. The third aim is required maximal coupling coefficient between windings. Magnetic material METGLAS 2605 SA1 (Metglas Ltd) was selected as the best taking electrical and mechanical properties into account. Numerical analysis of the transformer was carried using ANSYS software. It was assumed that magnetic core could be put inside windings and/or outside of it. The analysis and measurements yield that the best solution is the transformer with magnetic core put inside the windings. Such a construction reduces significantly perpendicular component of the magnetic field in HTS wire. Because outer winding is put on the inner one it gives maximal possible coupling coefficient. The primary and the secondary have the same number of turns. It means bifilar way of winding. The described transformer has the following constructional data: i) diameter of the main circle: 144 mm, ii) maximal diameter: 208 mm, iii) diameter of the small cross-section of the transformer (without external magnetic core): 50 mm and it results with the following parameters: output power 1.59 kVA, power density 700 VA/kg, efficiency: 99.5, coupling coefficient 0.99 at 100 ARMS of input current and maximum flux density 1.2 T.

SUMMARY The main aim of this paper is to show that well known definition of integral square error /ISE/ may be a criterion of comparative analysis of modulation procesees. The effect of analysis of ISE property is that the comparison of pulse signal with model signal by their integrals gives an estimation of shape of the signal which is aiequate to current on the output of inverters. Simultaneously, this ISE is the measure which is corresponding to additional losses in an inverter load caused by deformation of current. As an example of the application of this criterion the results of numerical calculations of ISE versus amplitude of the first harmonic for choosed forms of modulation are given in the paper. The possibility of making synthesis of pulse modulation by minimizing the ISE is also pointed.

The subject of this paper is the refinement of a sinusoidal gate driver (SGD). This driver is devoted to the Class DE inverter as the driver of MOSFETs. The load of the inverter has variable parameters. In order to ensure the optimum mode of operation of the Class DE inverter, its switching frequency and relevant commutation angle are automatically adjusted as the load parameters change. The SGD driver is based on the Class D inverter. The driver and the inverter operate in a frequency range of 1 MHz. The PLL system, together with a relevant delay and a properly shaped amplitude-frequency characteristic of the driver's output voltage, maintain the optimum mode of the Class DE inverter. The SGD driver has been built and tested. This paper contains a short description of the Class DE inverter and the optimum conditions for its operation. Next, the concept behind the operation of the driver is presented. Then, technical data for the laboratory driver and the Class DE inverter are described. An example of measured waveforms and a photograph of the laboratory system are presented. Finally, the design considerations are given.