• Investigate the VVC issue of urban power grids with integrated FTPSSs for the first time. • A hierarchical distributed VVC framework coordinates the hour-level and second-level timescales. • A reactive power capacity optimization method for FTSSs enables sustained reactive power support. • A parallel ADMM algorithm tailored to vertically layered grids achieves threefold acceleration. • A real-time voltage control strategy facilitates communication-free equitable reactive power sharing. Flexible DC traction power supply systems (FTPSSs) have been increasingly deployed in urban rail transit. The high converter-level flexibility enables them to supply subway power while simultaneously contributing to volt/var control (VVC) in urban power grids. However, their practical application is hindered by fluctuating reactive power capacity and the complexity of coordinating with other devices. To overcome these issues, a reactive power optimization method exploiting the overload capability of flexible traction substations (FTSSs) is developed to ensure sustained long-term reactive support, and a hierarchical distributed VVC framework is proposed to manage these VVC devices across two timescales. At the upper layer, a parallel alternating direction method of multipliers (ADMM) algorithm is designed to achieve a threefold acceleration in hourly optimization, whereas at the lower layer, second-level real-time control with adaptive power sharing enables communication-free coordination among FTSSs. Case studies on the Beijing Changping District power grid and Beijing Subway system demonstrate that the proposed strategy reduces network losses by 6.6%, suppresses 67.6% of cable-induced reverse reactive power flow, and preserves voltage stability at second-level timescales. The fully distributed architecture further ensures low communication overhead and high computational efficiency, highlighting its practical applicability for modern urban power grids.
Shilong et al. (Sun,) studied this question.