Bartosz Rozegnał

Soft switching systems in three-phase voltage source inverters usually require the use of additional elements, such as transistors, capacitors and inductors. Contrary to the existing solutions, in the proposed soft switching system, the danger of an abrupt discharge of the capacitors through the conductive transistor does not occur. Moreover, there is no risk of interruption of the inductor current, which usually causes damage to the transistors. In the paper principles of the system operation are described in detail and rules of component selection are presented. Laboratory tests were performed for different operating conditions. The test results have confirmed the operation correctness of the three-phase voltage source inverter with the proposed soft switching system.

Zmniejszenie strat przełączania w trójfazowych falownikach napięcia można uzyskać, stosując układy łagodnego przełączania, które nie tylko wpływają na zwiększenie sprawności falownika, ale również pozwalają ograniczyć gabaryty układów chłodzących elementy półprzewodnikowe, co w napędach trakcyjnych ma istotne znaczenie. Zdecydowana większość istniejących układów łagodnego przełączania ma pewne mankamenty mogące zagrozić bezawaryjnej pracy falowników w przypadku wystąpienia zakłóceń w układzie sterowania. W artykule skrótowo opisano strukturę, zasady działania oraz wyniki badań laboratoryjnych proponowanego układu łagodnego przełączania tranzystorów. Szczególną uwagę zwrócono na alternatywne wersje proponowanego układu, które pozwalają polepszyć parametry eksploatacyjne układu podstawowego. 

Reduction of the switching losses in three-phase voltage source inverters can be achieved by using of soft switching systems that not only increase the efficiency of the inverters, but they also reduce the size of the semiconductor cooling circuits, that is especially important in traction vehicles. The majority of existing soft  switching systems have some drawbacks that could be danger for inverter operation in the case of disturbances in control systems. The paper briefly describes the structure, operation principles and results of laboratory tests of the proposed soft switching system. Particular attention has been paid to the specific features of alternative versions of the proposed soft switching system, that allow to improve operating parameters of the basic system.

This paper presents an attempt to detect short circuits in double sourced electrical lines by discrete wavelet transform. First part of this talk describes a database preparation which is created by dynamic simulation base on model of double sourced transmission line. In order to choose the right model a comparison of two different represent of line has been made. In first one, transmission line is represented by two four-poles, and the second one is represented by n-four poles. Steady state’s analyses of different kinds of short-cuts show that two four-poles model line with acceptable precision. Simulation’s results for all kinds of short-cuts create a vast database. The database can be used to project detection algorism based on discrete wavelet transformation.

This paper presents an analysis of short circuit signals by discrete wavelet transform. The signals are obtained by simulation on two four-pole UHV transmission line’s model. Both efficacy of short circuit detection and sensibility to other system’s faults are discussed. An important part of the article is to consider the great influence of well adjusted wavelet function and decomposition level on correctness and speed of short circuit detection. The adequate selection of detection algorism’s parameters based on database including the signal’s samples shows a possibility of practical use of this kind of information in real transmission lines.

The efficiency of three-phase voltage source inverters depends mainly on power losses that occur in semi-conductor elements. Total losses in these elements are a sum of conduction losses and switching losses. The switching losses are dependent on the supply voltage, load current, operating frequency and on the dynamic parameters of the switching elements; these losses can be limited with the use of soft switching methods. This paper discusses the switching loss dependence on the above mentioned factors. An analysis was carried out on power losses in voltage source inverters which generate the output voltage in the form of a rectangular wave and losses in these inverters operating with pulse width modulation. A comparison of switching losses was performed for two voltage source inverters with different nominal power ratings.

This paper presents the process of the development of the real life laboratory model of the five node power system of closed loop structure. The model was built using ‘power’ scaling and taking into consideration the parameters of the 400 kV lines built in the Polish National Power system. After the three-year development of the model, the parameters of the elements of this model were gained or obtained using classic identification procedures. During this part of the research, some differences between the parameter values given by the manufacturers and those obtained through identification procedures were reported and analyzed. The Matlab/Simulink model of the laboratory setup was then built to emulate the system behavior during dynamic states. The comparison of the currents, voltages and generator speeds proved to be simple tasks since the shape of the short-circuit current waveforms, for example, depends not only on parameter values but also on the time of the fault occurrence with respect to system voltages. Thus, the time responses of the laboratory and Simulink models were compared to evaluate time constants of the post fault processes.