Study on Optimization of Return Current Nodes in Active Return Traction Power System

The rail potential and stray current in urban rail transit are mitigated by the active return traction power system (AR-TPS) by transferring the running rail current to the return cables through the return current node (RCN). To improve the mitigation performance of the AR-TPS, an optimization layout method of RCNs was proposed. First, a two-layer distributed parameter model and an RCN current transfer model were established to reveal the influence laws of RCN number and layout position on the current transfer capability. Then, based on engineering constraints and node functions, the number of RCNs was simplified to two, and the layout positions were optimized near the midpoint of the section with the optimal mitigation performance as the objective. Finally, a simulation verification was conducted based on the typical train operation curve. The results indicate that the outer RCN working in coordination with the active resistance converter is the primary path for transferring the return current to the return cables. The mitigation performance of the AR-TPS continuously improves as the RCN approaches the midpoint of the section. When the conventional traction power system is adopted, the maximum rail potential is 34.86 V; the maximum stray current is 2.89 A, and the total leakage charge is 134.00 C. When the AR-TPS with uniformly distributed RCNs before optimization is adopted, the above indicators are reduced to 14.84 V, 0.94 A, and 55.70 C, and the suppression rates are 57.42%, 67.47%, and 58.43%, respectively, compared with the conventional traction power system. When the AR-TPS optimized by the proposed method is adopted, the above indicators are further reduced to 8.66 V, 0.66 A, and 38.67 C, and the suppression rates are increased to 75.16%, 77.16%, and 71.14%.