System for converting the DC traction substations into active substations

This paper is concerned with the possibilities of transformation the DC traction substations with uncontrolled rectifiers into active substation, being able to ensure both the braking energy recovery and active filtering function. There are a lot of approaches on the management of regenerative braking energy, most of them based on energy storage systems or the concept of reversible substation. Few references refer to the addition of complementary functions, such as harmonic filtering, and involve the adoption of specific structures without further argumentation. In this paper, the intention is to analyze and find argumentations on the possibilities of coupling a three-phase active power filter based on voltage source inverter topology in the power structure of a DC traction substation. The most used types of uncontrolled rectifiers, i.e. the three-phase bridge scheme and both 12-pulse parallel and series structures are taken into consideration. Based on correlation between the DC-line and AC-line voltages, it is shown that the active power filter can be connected directly in the secondary of the existing traction transformer only in the case of 12-pulse series rectifier. A dedicated recovery transformer is required for the other two schemes of rectifiers and some considerations and results on the compensating power and correlation between the active filtering performance and the voltage in the recovery transformer primary are presented.