Novel topology for correction of unbalanced load in single phase electric traction systems

Railway traction loads present large single phase loads to the supply system. Typically zero sequence components are removed using a phase to phase transformer connection, however a large negative sequence component remains. As the amount of rail traffic increases and the use of regenerative braking becomes higher, the issue of negative sequence becomes more critical. This paper presents a novel active filter approach to negative sequence compensation using single phase compensators at the track side of the system. The compensators for two separate track sections share a common DC bus, which allows power transfer between the sections. A control algorithm based on synchronous reference frame theory is proposed, with modified transformations to reflect the two phase nature of the system. The topology and control algorithm are verified using simulation and results are shown.