Indirect current control in active DC railway traction substations

This paper is focused on a practical solution to convert a classical DC railway traction substation with unidirectional power flow into a bidirectional substation having the capability of power quality improvement through the active filtering function. The case of 12-pulse parallel rectifier in the traction substation is taken into consideration and the new functions are performed by an IGBT-based voltage source inverter with interface passive circuits on both DC and AC sides, which is connected to the power supply through a dedicated transformer. The proposed control system handles the current at the active power filter output in indirect mode, with minimal sensed quantities, by regulating the voltage across the compensation capacitor. In order to verify the operation of the system and assess its performance, detailed computer simulation studies were conducted using the Matlab/Simulink package.