Modified AC/DC Unified Power Flow and Energy-Saving Evaluation for Urban Rail Power Supply System With Energy Feedback Systems
Wei Liu, Jian Zhang, Hui Wang, Tuojian Wu, Ying Lou, Xiaowen Ye
Abstract
Energy feedback systems (EFSs) have been widely applied in urban rail transit, and a power flow algorithm and energy-saving evaluation of urban rail power supply systems with EFSs are studied in this paper. First, trains, the reflux system, and traction substations with EFSs are modeled, and the multimode transitions are analyzed, including the maximum power state of the EFS. Then, a modified AC/DC unified power flow algorithm for the DC power supply system, which simplified the DC reflux system is proposed, and a field case study based on a multiple train scenario is presented to validate the algorithm. Furthermore, system-level energy-saving evaluation indexes are applied according to system power flow analysis. When the headway time decreases, the proposed indexes decrease in general mainly as there is more regenerative braking energy absorbed by adjacent trains. The higher the load rates of the step-down substations are, the more daily feedback energy is utilized. When the start voltage of the EFS ranges from 1650 V to 1770 V, the maximum energy-saving rate reaches 11.9%, which occurs when the start voltage is 1670 V. When the no-load voltage is relatively high, the start voltage should not be higher than 1750 V to keep the system running in high efficiency. These results can provide advice for the design and operation of traction power supply systems with EFSs.