Voltage Stability in Traction Power Systems
Introduction of new electric vehicles in the rail network has the recent years often caused problems related to oscillations in the power supply due to repetitive controller actions and feedback loop effects. New inverter vehicles are also more sensitive to voltage variations than older vehicles with AC series motors. This gives challenges related to optimizing control system design in both vehicles and feeding stations. A short presentation of some of the problems and the consequences is given in [1]. For improvement of the present traction power supply related to feeding capacity and economical optimization, different systems for reducing the line impedance are considered. This may also allow centralized feeding by fewer and bigger converter stations. A significant increase in use of power electronic technology is expected both on supply and load side. Experiences from other countries have shown that this may cause new power system stability problems, for example as described in [2].Theoretical analysis
The strong coupling between railway vehicles and railway infrastructure makes compatibility problems to an issue within all technical fields, but the complexity of the electrical power system gives special challenges for optimized interaction. Stability is one of these compatibility topics and experiences have shown that an unstable power system can give consequences for both:
̣€¢ Train operator (e.g. train doṇ€™t run as expected or at all),
̣€¢ Infrastructure manager (e.g. installation damages due to over voltages, equipment and component stressing and protective actions or shutdowns) and
̣€¢ Third-party (e.g. voltage fluctuations in utility grid).