Hierarchical control optimization of AC systems in urban rail stations for regenerative energy use with start-stop constraints

To overcome the inefficiencies in regulating air conditioning (AC) systems in urban rail stations, which limit the effective absorption of megawatt-level regenerative braking energy (RBE) from the traction power supply system (TPSS), this paper introduces a robust and feasible hierarchical optimization control framework. The framework incorporates minimum start-stop time constraints while minimizing communication costs. At the cluster layer, response mechanisms for each AC are developed to maximize RBE utilization. At the aggregation layer, tailored regulation plans are designed to mitigate peak-to-valley variations in the energy supplied by the power grid to the AC loads. Finally, at the device layer, AC units strictly adhere to their individualized control plans, reducing switching frequency, optimizing RBE utilization, and minimizing energy fluctuations from the power grid. Case studies demonstrate that the proposed approach enhances RBE utilization by 17 % and reduces the standard deviation of grid-supplied energy to the AC systems by 33 %, thereby significantly contributing to energy savings in urban rail systems.