Design and performances of the separating circuit in regeneration and filtering system for active DC-traction substations

In the regeneration and filtering systems used in DC-traction substations, a separating circuit, between the catenary and the voltage source inverter, is necessary. It interacts with the compensating capacitance only in the regeneration mode of the system and affects the quality of the active power transfer resulted in the braking mode. The phenomena that occur are complex because the inverter operates in switching mode, as a current source. Starting from the Simulink model analysis, it was developed the mathematical model of the separating circuit, for the worst case in terms of the current switching. The circuit operation analysis led to finding some design expressions which use the imposed values for the voltage ripple across the compensating capacitor and for the current ripple through the catenary line. The identified expressions were particularized for an active DC-traction substation with 12-pulse parallel rectifier, and then the performances were determined based on the complete virtual model, in closed loop.