Witold Mazgaj

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.

Artykuł dotyczy anizotropowych właściwości typowych blach prądnicowych. Przyczyną anizotropii magnetycznej takich blach jest występowanie w nich pewnych tekstur. Krótko scharakteryzowano typy tekstur najczęściej występujące w tych blachach. Dla kilku wybranych blach prądnicowych przedstawiono wartości typowych parametrów magnetycznych dla różnych kierunków magnesowania. Zaproponowano metodę uwzględnienia anizotropowych właściwości blach prądnicowych w obliczeniach zmian indukcji podczas przemagnesowania osiowego i obrotowego. Specjalnie dobrana funkcja rozłożenia ziaren w danej blasze pozwala uwzględnić anizotropowe właściwości w obliczeniach zmian indukcji. Przykłady zmian indukcji podczas przemagnesowania osiowego i obrotowego przedstawiono w końcowej części artykułu.

Calculation of power losses in transformer steel sheets is still a significant problem. In some places of cores of a three-phase transformer the flux density is not parallel to the rolling direction; it especially refers to the so-called T-points of the transformer cores. In these places magnetization curves differ from the curve measured for the rolling direction. The paper deals with hysteresis losses, eddy current and excess losses and their dependences on the direction of magnetization processes. Analysis is performed for several frequencies of the magnetization process. Measured power losses of the selected transformer steel sheets are compared with results obtained on the basis of the analytical formulas.

This article deals with the methodological aspects of the modelling and field analysis of machines with surface mounted permanent magnets on the rotor, taking into account the anisotropic properties of the stator core. These considerations are intended to show the effect of anisotropy on the structure of the mathematical model of the machine and answer the question of whether if based on classical modelling, it is possible to take into account the rotational magnetization phenomena. The results explain the question, how the magnetic anisotropy effect at rotational magnetization is important from an exploitation point of view.

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.

In typical dynamo steel sheets, the magnetization process can have a two-fold character. In parts of the dynamo sheets which refer to the stator core of induction motors the magnetization process has a rotational character. On the other hand, the axial magnetization occurs mainly in the stator teeth. This paper discusses the specific power loss of typical dynamo sheets and its dependence on the magnetization frequency and on the maximum value of the flux density in dynamo sheets. Anisotropic properties of these sheets were taken into consideration. Special attention was given to understanding the dependency of the magnetization direction on specific power loss. The measured specific power losses of two selected dynamo sheets were compared with results obtained on the basis of analytical formulas.

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.