Control strategy of advanced 25 kV-50 Hz electrified railway systems

Technological innovation has been largely involved in the general modernisation of electrified railway systems in the last few decades. Better quality performances of supply and electrification subsystems are thus expected, which have until now made less recourse to electronic and automation techniques than other technological sections of the system. A method is proposed for compensating voltage and current unbalances in single-phase 25 kV-5OHz railway power supply, based on a new configuration of the traction substation. Two Scott-connected transformers are coupled with an impressed voltage two-phase inverter, to obtain stabilisation of load voltages to rated values. Satisfactory power factor and reduction of network disturbances, as well as nonlinear load effects of the load, can also be reached. The full compensation of load unbalances and a substantial inherent protection against disturbances, even under changing conditions of power parameters, are obtained through a nonlinear control system, based on the variable structure system theory. Numerical simulations codirm the high performance of the compensation method with respect to fast response time, steady-state accuracy, and very low sensitivity to disturbances.