An AHP Approach for the Optimal Sizing of On-Board Energy Storage in DC Rail Transit Systems

Energy Storage Systems (ESSs) are widely recognized as highly effective solutions for enhancing the efficiency of electric rail transit systems. Both wayside and on-board storage solutions significantly improve energy recovery during train braking phases. This paper specifically focuses on on-board storage devices, addressing the question: 'How to determine the optimal size of on-board storage devices?' Answering this question is not simple, as oversized systems unnecessarily increase mass and volume, whereas undersized systems might lead to ineffective energy savings. In this regard, the present study introduces a novel procedure for sizing on-board storage devices, based on a multi-objective optimization framework formulated as a constrained linear least squares problem. The effectiveness of this approach is evaluated through numerical analyses, focusing on a typical scenario in a DC rail metro system.