A new hybrid SVC scheme with Scott transformer for balance improvement

Due to the dynamic characteristics of traction load and unevenly train dispatch schedule, the unbalances currents are generally presented at point of common coupling (PCC). To suppress the degree of unbalance, a specially connected transformer or/and reactive power compensation device can be applied. Traditionally, a phase-shifted Scott transformer type SVC was installed in front of Scott connection transformer to improve the voltage fluctuation which is caused by high speed railway (HSR) systems. However, this solution is the most effective only in case that the power factor angle of each phase load equals /spl pi//6 lagging; otherwise, a quite severe negative sequence current still presented at PCC. In this investigation, a new hybrid SVC scheme is proposed to improve this disadvantage. The results show that the proposed scheme can effectively restrict the negative sequence current to zero no matter what power factor of traction load.