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Open access

A. Sikorski and A. Kuźma

Cooperation of induction squirrel-cage generator with grid connected AC/DC/AC converter

The paper presents a squirrel-cage induction machine operating as a generator principally designed for use in small wind and hydroelectric power stations. The main advantages of such a generator are its high reliability, low price and costs of operation and maintenance. The asynchronous generator coupled to the grid through the AC/DC/AC converter is capable of generating energy even at low turbine speed. The results of investigations on the AC/DC and DC/AC converters controlled by linear and nonlinear current regulators are also discussed.

Open access

A. Sikorski and M. Korzeniewski

AC/DC/AC converter in a small hydroelectric power plant

The article discusses application of AC/DC/AC converter cooperating with an induction generator in small hydroelectric power plants. The induction generator works with power grid or a separated group of receivers, enabling to generate power even at low speeds of the turbine. The article provides also results of the investigation concerning the functioning of the generator coupled with AC/DC/AC converter in steady and transient states during start-up and voltage decay.

Open access

K. Kulikowski and A. Sikorski

Efficiency improvement due to direct torque and flux three levels three areas control method applied to small hydroelectric power plant

The paper presents a description of a new DTFC3L3A (direct torque and flux control three levels three areas) control method of induction machine as well as its comparison with the DTC method. The basis for the comparison is the switching frequency of described methods. The proposed method is optimized to reduce number of switchings (which is proportional to switching power losses) in static state, as well as it takes into account the δ angle which makes it possible to obtain a sinusoidal shape of flux within range of low angular frequencies of an asynchronous machine. The paper includes the results of experiments performed on a three level DC/AC inverter for both control methods.

Open access

Krzysztof Dmitruk, Marek Korzeniewski and Andrzej Sikorski

Abstract

Frequency based methods developed to detect an islanding condition in modern power grid structures have been discussed. The condition may occur in power grid lines to which additional energy sources with power electronic converters have been connected such as solar panels or wind turbines. It is a hazardous operating state for grid workers and devices connected to the islanded part of the grid. Such a state results from the inability to control amplitude and frequency of basic harmonic of the grid voltage. An islanding problem in a power grid with additional small energy sources has been discussed. A basic passive and active islanding detection method have been presented and compared with known frequency based algorithms, namely active frequency drift and active frequency drift with a positive feedback algorithm. Finally, a laboratory test of the proposed islanding detection methods in a three- -phase grid with an AC-DC converter has been conducted. To demonstrate differences between the tested methods, total harmonic distortion injected into the output converter current and detection time of islanding state have been measured.

Open access

A. Sikorski, K. Kulikowski and M. Korzeniewski

Abstract.

This paper describes two modern direct torque and flux control methods of an induction machine supplied by a three-level inverter. Additionally, it presents a comparison of the methods both in static and dynamic states. The methods, in a specific way, make use of an increased number of active vectors of the three-level inverter in order to improve control quality and reduce switching frequency. The two methods modify the DTC method by using its advantages and eliminating, at the same time its drawbacks.

In static states the comparison was based on the results of investigations performed for two different load values and three set values of angular speed, whereas in dynamic states the comparison was focused on the behavior of the machine at startup.

The results of the investigations have shown that both methods give very good performance. They are characterized by both sinusoidal shape of flux and low current deformations even at low angular speeds i.e. less than 10% of the nominal value. The presented methods also allow to generate nominal flux for set zero angular speed in order to achieve excitation of the induction machine. The switching frequencies for both methods are very similar in almost the whole range of control but the methods have shown some differences in control quality, particularly for higher torque values.

Open access

A. W. Demiaszkiewicz, G. Polańczyk, B. Osińska, A. M. Pyziel, I. Kuligowska, J. Lachowicz and A. Sikorski

Abstract

In 2011-2013 1588 samples of dogs’ blood were examined for dirofilariosis using Knott method, as well as the Kingston and Morton method. The species of microfilariae was determined on the basis of morphometric characteristics. Samples were also examined using the Canine Heartworm Antigen Test. Positive samples were examined using a multiplex PCR assay for species confirmation. Microfilariae belonging to the species D. repens were found in the blood samples of dogs from all the provinces of Poland. The mean prevalence of this species observed in Poland was 11.7%. The range of intensity of infection was counted using the number of microfilariae found in 60 μl of blood amounted to between 1 and 158, and the mean intensity was 18 microfilariae. Microfilariae and antigens of D. immitis were not found in any examined blood samples.