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Investigations on the coupling LCL filter in active traction substations

The theoretical and experimental investigations presented in this paper are related to an LCL filter with damping resistance used to interface the voltage source inverter of an active DC-traction substation with the power supply. The case study of DC-traction system with six-pulse diode rectifier, as is the case of Bucharest subway substations, is taken into consideration. Starting from the configuration and the tasks of the system to be added to the existing transformer-rectifier group in order to ensure the functions of active filtering and regeneration, some design considerations and limits for the AC coupling passive filter of LCL type are made first. Then, the influence of the LCL filter's inductances on the system performance, in terms of harmonic distortion of the supply currents and fundamental power factor, is investigated in both simulation and experimental ways. A laboratory test bench of small scale with configurable coupling inductances, together with a control platform based on the DSP dSPACE 1103 board are used in the conducted experimental tests.