Abstract
The issue of interfering influence of traction vehicles on railway traffic control systems is a serious problem posing a threat to railway traffic safety. This issue is gaining in importance as more and more vehicles equipped with traction inverters are put into service. Current harmonics generated by traction vehicles equipped with voltage source inverters can be controlled in such a way that they do not exceed the limits imposed by railway operators. One of the current harmonic control techniques, proposed by the authors, is the use of a combination of SHE (Selective Harmonic Elimination) and SHM (Selective Harmonic Mitigation) techniques to control the traction voltage source inverter. In this article, the author present the results of investigations on the influence of supply voltage fluctuations on the efficiency of shaping techniques of the current harmonic spectra taken from the DC network by VSI traction drive system, using the SHE and SHM modulation techniques. Regarding the fact that in 3 kV DC electric traction systems, fluctuations of the vehicle's supplying voltage are accepted in a wide range, it is necessary to determine the influence of voltage changes on the proposed modulation techniques. The research object is a simulation model of traction drive which consisting of an asynchronous motor fed by a voltage source inverter. The simulation model was verified by the means of measurements performed at a low scale laboratory stand. Analysis of the tested techniques when supplying voltage is fluctuating, allows to evaluate their usefulness in real operating conditions. The results obtained for SHE and SHM techniques were compared with SPWM modulation.
Highlights
The modern traction vehicles are commonly equipped with power electronics devices to provide fluent and dynamic control over torque of traction motors
In previous works [7, 8, 11] the Author presented the possibility of application of selective harmonic elimination (SHE) and selective harmonic mitigation (SHM) techniques to eliminate or control chosen current harmonics generated by traction drive to fulfil limits from Fig. 1
The issue presented in this paper is to prove that change of supplying voltage can be compensated with change of modulation index of voltage waveform generated by traction inverter with sustained control of chosen current harmonics bellow assumed limits
Summary
The modern traction vehicles are commonly equipped with power electronics devices to provide fluent and dynamic control over torque of traction motors This type of devices are known to be the significant source of current harmonics which may occur as the distortion for railway signalling system. This frequency band is known to be critical because of high level of current harmonics generated by traction drives and relatively low attenuation of vehicle's input filter This was the motivation for the author to take this frequency band under consideration. The current Icat can be recalculated to current If (Fig.2), using formula (1) where impedances of the choke ZLf(jω) and the capacitor ZCf(jω) are taken under consideration This formula is correct only for high frequencies where impedance of input filter can be assumed linear: I f
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