ANALYSIS OF EMERGENCY MODES OF TRACTION INDUCTION ELECTRIC DRIVE

Abstract

The operation process of the traction asynchronous electric drive of the rolling stock may be accompanied by the occurrence of emergency modes, which are characterized by current overloads and may lead to damaging power electric circuits or mechanical part of the electric drive. Therefore, studying electromagnetic processes that occur in emergency modes of operation is relevant, in particular, for developing systems aimed at diagnosing and protecting traction equipment. Ukrainian and foreign studies of emergency modes in an asynchronous electric drive were analyzed. The most frequent causes of emergency modes are failures in static converters, therefore it is advisable to conduct an analysis of electromagnetic processes specifically in autonomous inverters. Using Matlab/Simulink software environment a simulation model of the vector control system of the traction asynchronous electric drive with spatial vector pulse width modulation was developed, and the short-circuit modes of the power switch of the autonomous voltage inverter and the disappearance of the supply voltage were simulated. The oscillograms of electromagnetic processes in these modes were shown and compared with the nominal mode of operation. The simulation results show that the analyzed emergency modes, even with a short duration of less than 0.5 s, can lead to significant damage to the electric drive. Both cases lead to significant current overloads: in the case of a short circuit of the power switch, a three-fold excess of the phase current is observed, during recovery after a supply voltage failure, the phase currents increase to the starting level, as well as an almost instantaneous increase in the supply voltage on the input filter capacitor occurs. The Fourier analysis of the phase A current in the above emergency modes shows an increase in the coefficient of nonlinear distortions by 65 %, a decrease in the amplitude of the main harmonic to 60 %, and the appearance of a significant number of subharmonics. In the case of a short circuit, the amplitudes of the subharmonics even exceed the fundamental harmonic. In addition, the process of returning from the emergency mode to normal at the first moment of time was characterized by a reduced moment of resistance (20 % of the nominal), and then by an exit to the nominal parameters.