Collaborative compensation strategy of electrified railways and DFIG-based wind farm for suppressing voltage unbalance

Single-phase traction loads of electrified railways have aroused the worst voltage unbalance (VU) problem in a weak remote grid, where possesses a number of wind farms (WFs). To utilize the compensator capacity effectively, this paper focuses on VU compensation effort sharing for traction power supply system (TPSS) and WF. Firstly, to achieve the stable VU compensation of point of common coupling (PCC), a VU propagation model is proposed to reveal the VU contribution of TPSS and WF, which provides a compensation target. Then, in terms of the VU active compensation ability of double fed induction generotor (DFIG), a negative sequence current (NSC) optimal compensation model is established under constraints of stable operation limits. Furthermore, a collaborative control strategy with the objective of VU limit at PCC is presented to provide reference current for TPSS and WF. Finally, simulation results are carried out to verify the effectiveness of the proposed strategy, and the compensator capacity of TPSS can be reduced by 18% when the active compensation ability of WF is taken into account.