A two-stage coordinated power allocation strategy for onboard hybrid energy storage systems in urban rail transit oriented toward comprehensive operating cost

Abstract

To address the dual challenges of enhancing energy efficiency and mitigating lithium-ion battery (LiB) degradation in onboard hybrid energy storage systems (HESS) under grid-connected operation, this paper proposes a novel two-stage coordinated power allocation strategy. The approach minimizes a comprehensive operating cost that integrates both traction energy consumption and LiB degradation. First, an electro-thermal-aging coupled model for the LiB is developed and integrated into a DC traction power supply system (TPSS) model with onboard HESS, enabling real-time quantification of both system power flows and battery degradation dynamics. Subsequently, a two-stage hierarchical power coordination framework is introduced to manage multi-source power interactions between the HESS and the traction network (TN), leveraging the complementary characteristics of the storage devices. This architecture decouples the optimization problem, significantly reducing computational burden. In Stage I, a Dynamic Programming–Dual-Mode Fuzzy Logic Control (DP–DFLC) method schedules supercapacitor (SC) power by combining offline optimal trajectory generation with online adaptive correction. In Stage II, a unified economic metric is innovatively formulated to express both energy consumption cost and degradation cost in a common monetary dimension, thereby avoiding empirical weight tuning in multi-objective optimization. Based on this metric, a cost-aware model predictive control (MPC) method is developed to allocate the smoothed residual power between the LiB pack and TN, while enhancing both interpretability and real-time applicability. Finally, hardware-in-the-loop (HIL) simulations validate the effectiveness and real-time feasibility of the proposed strategy, suggesting its promising potential for cost-efficient HESS control under grid-connected rail operation.