Zmodyfikowany filtr wejściowy przekształtnikowych napędów trakcyjnych

New fully controlled semiconductor power switches make considerable increase of operation frequency of converters in traction drives possible. Considering undesirable consequences of pulse current flow in the supply source and in the traction network, the increase of the converter's operation frequency allows to significant decrease of the capacitance and inductance of the input filter's components. However, the decrease of the parameter values of these components can be unacceptable due to instable operation of the drive system, which results in appearance of low-frequency undamped oscillations in the current and voltage waveforms of the input filter's capacitor. Various methods of damping these oscillations presented in the literature, for example increasing of the capacitance of the filter's capacitor, inserting an additional resistor or specific control strategies have some disadvantages and are not always effective. A method to limit the unstable region of operation of the traction drive through appropriate solution of the input filter system assuming that the mass and dimensions of the filter components are not bigger and the cost is not higher than in case of commonly applied LC filter has been suggested in the paper. Results of research of the features of the modified input filter and the results of comparison analysis between this filter and the LC type Γ filter have been presented. Special attention was paid to the stable operation region and to fluctuations of current and voltage in the filter system. The research was carried out using the IsSpice simulation program and the Maple computer algebra system.