Kuno Janson

AC-DC converter with parametric reactive power compensation

Resonant converters of 50 (60) Hz AC-DC are described, where each half cycle of network voltage the capacitor and inductor of an oscillatory circuit are switched from series into parallel and vice versa. The duration of series and parallel connection and also the transformer ratio are parametrically dependent on load. In the case of short circuit, only the parallel oscillating circuit operates. This restricts sharply the output current. The reactive power of the capacitor and the inductor compensate each other, both in the cases of series and parallel connection. Therefore, the power factor is very high from no load to short circuit. This converter fits very well for supplying arc furnaces, and there is no need for the costly and fast reactive power compensator and filter circuits. The operating principle of the converter, design principles, and a real operating converter rated 5.4 MW supplying a steel-melting arc furnace are described.

Analyses of supply voltage quality, power consumption and losses affected by shunt capacitors for power factor correction

This paper is focused on active power consumption and losses in industrial and commercial facilities, depending upon supply voltage quality parameters. The shunt capacitors for power factor correction affect directly supply voltage level and harmonic distortions of supply voltage and current and hence affect power losses in industrial facilities, particularly in induction motors. In the paper practical measurement methods are described for estimating power losses when power factor correction capacitors are used. The impact of capacitors upon supply voltage level and harmonic distortions is discussed. Measurement results of voltage and current harmonics spectrum in industrial 0,4 kV power systems are shown.

Load-resonant converter with changing resonant tank topology for welding applications

In this paper a new approach and corresponding converter based on varying resonant tank topology for supplying DC loads like welding arc is presented. In order to describe suggested topology the circuitry of proposed converter and some design aspects are discussed in relation to typical load conditions during welding process. Simulation and first experimental data are also provided and analyzed. The obtained natural characteristic of this converter has a constant power mode in the range of welding currents and inherent parametrical short-circuit limitation. Also, its fast “natural” response to change of load conditions could probably yield in better arc stability and more even weld bead quality.

Reactive power compensation for spot welding machine using thyristor switched capacitor

High-power industrial spot-welding machines make use of transformers that have very high reactive power consumption. Simple reactive power compensation schemes cannot be used however, because of the cyclic nature of the spot welding transformer operating. This paper describes the development of a simple reactive power compensator solution for the spot-welding machines. Focus is also put on the transformer saturation and current transients that can emerge from deployment of such reactive power compensation methods.

EMC education and related problems at Tallinn Technical University

Taking into account the importance of electromagnetic compatibility (EMC), modern electrical education requires more attention to give future electric and electronic engineers with good EMC knowledge. The purpose of this paper is to present the current situation with EMC educational and lab activities, as well as plans for the future at Tallinn University of Technology, Estonia. The paper describes the existing course and contents of creating courses in EMC given in the Department of Electric Machines and Fundamentals of Electrical Engineering. The aim and proposed effect of the courses are outlined.

New theoretical approach to input current shaping in ac-dc power converters

A new method for an input current waveform correction in typical power converters is described. It assumes an implementation of the so-called virtual transformer with a fast-changing voltage ratio. Theory and calculations are presented to confirm the method validity. Practical implementation is left out of the scope of the given paper due to size limitations.

Economical feasibility of off-grid hybrid power supply for estonian remote areas—part 2: Determination of breakeven grid extension distances

The paper considers the implementation of an off-grid hybrid power supply as an alternative to construction of a grid connection in sparsely populated remote areas in Estonia. In the previous part, the proper configurations of the off-grid hybrid system and component sizes were determined through optimization procedures at different typical meteorological conditions including coastal and inland ones. In this part, levelized costs of energy (LCOEs) were found for a newly built grid connection under the same load demands and interest rates. They were compared with the LCOEs for the off-grid systems in order to find breakeven grid extension distances. As a result, the recommendations on the expedience of off-grid hybrid power supply were obtained for different regions of Estonia.

Supply voltage level optimization in industrial low voltage networks

This paper is focused on measurement and analysis of supply voltage level in low voltage industrial power systems in Estonia. A practical method for analysis of supply voltage quality parameters implementing stochastic theory is discussed. Measurement results of supply voltage quality parameters - voltage magnitude, voltage level and voltage sags in industrial 0.4 kV power systems of Estonia are shown. The impact of shunt capacitors for power factor correction upon supply voltage level is discussed.

Wind power generation impact on Sõrve peninsula network operation in Saaremaa

There is rapidly increasing wind generation capacity in Estonia. The main wind areas are located near sea coastal line where wind parks can often be connected only to relatively weak medium-voltage distribution power grids. The aim region of investigation was wind-rich Sõrve peninsula of Saaremaa island. The impact of existing wind farms on levels of voltages, losses and consumption has been preliminarily investigated. A way to decrease voltage deviations has been proposed.

New practical approach to input current shaping in AC-DC power converters

In principle, a distortion of a waveform shape of AC/DC converter current could be corrected by use of a fast-controlled impedance-matching transformer. Changes in the converter input impedance can be eliminated by means of the varying transformation ratio of this transformer. The paper considers a practical performance of the fast-controlled impedance-matching transformer on a basis of a non-conducting converter. It is found that the shape of current waveform can be made sinusoidal if the instant power passing through a converter is proportional to the squared instant value of the supply voltage and/or the output voltage and the output current of the converter are in inverse proportion. A non-conducting converter with alternating of parallel and series resonance meeting requirements is considered. The converter topology, an operating principle and output voltage control are described. The basics of the converter calculation and the converter current waveform modeled on computer are presented.