Voltage Unbalance Management for High-Speed Railway Considering the Impact of Large-Scale DFIG-Based Wind Farm

The worst voltage unbalance (VU) problems are aroused by single-phase 25-kV traction power supply systems (TPSSs) of high-speed railways (HSRs) in a three-phase grid, especially when connected to a weak remote grid which is around a number of large-scale wind farms. Implementing VU management for HSRs, including limit government and compensation for VU, is an important approach to ensure the network operates securely. In this article, to portray the power performance of Double-fed induction generators (DFIGs) under the unbalance condition, a complex voltage unbalance factor (CVUF) is introduced to establish a clear mathematical relationship between the VU and output power. Furthermore, employing the consumption capability of DFIGs for unbalance power, a VU limit pre-assessment approach for HSRs is developed, which provides an objective for VU compensation of TPSSs. To arrive the compensation target and optimize the traction substation (TSS) capacity, a uniform VU propagation model integrating the TPSS, wind farm, and grid is established to provide a reference current for the TPSS. Compared with the initial compensation result, TSS capacity can be reduced by 22%. The effectiveness of the VU limit pre-assessment method and compensation approach for TPSSs is verified by a case study.