Objective In the DC traction power supply system of urban rail transit equipped with inverter feedback devices, electrical loops can be formed between the inverter feedback devices and rectifier devices in the substation or between adjacent substations via AC/DC buses. This can easily induce inter-substation circulating currents, leading to ineffective power circulation, increased equipment losses, and reduced overall efficiency. Therefore, it is necessary to conduct an in-depth investigation into the formation mechanism, influencing factors and occurrence patterns of inter-substation circulating currents from the perspective of traction power supply system design.

Method An AC/DC integrated equivalent circuit model is established covering traction substations, inverter feedback devices, trains and the traction network, to analyze the generation paths and power balance relationships of inter-substation circulating currents under typical operation scenarios. The circulating current probability is proposed as a quantitative index to evaluate the occurrence likelihood of circulating currents. In the case study of an actual metro line, a simulation model is built by combining its power supply topology, train operation parameters and equipment characteristics to validate the accuracy of the above-mentioned circuit model.

Result & Conclusion  The formation of inter-substation circulating currents depends on the matching relationship between the capacity of inverter feedback devices and the adjacent AC load, and is closely related to the real-time distribution of traction power and braking power of the trains on the line. From the perspective of operation organization, the probability of inter-substation circulating currents generally first increases and then decreases as the train headway grows. For a given headway, the duration and occurrence probability of circulating currents are significantly affected by the departure time difference between up-bound and down-bound trains.