Optimizing Train Speed Profiles to Improve Regeneration Efficiency of Transit Operations

With reduced environmental impact becoming an increasingly important benefit of the rail transportation mode, continual improvement in efficiency and reduced energy consumption has become a major concern to rail transit operators. For electrified rail transit operations, regenerative braking is one practical way for saving energy because it enables the kinetic energy of a train to be transmitted via the overhead catenary wire or third rail for use by adjacent trains. Although various regeneration technologies have been introduced, work is still needed to improve energy recovery efficiency. This paper focuses on energy recovery efficiency from an operational point of view. In a mass transit system, there are two operating modes for two consecutive trains: the following train either systematically applies the same speed profile as the leading train, or the following train adjusts its speed to a different speed profile according to the position, speed and regeneration potential of the leading train. With operations synchronized to reuse energy, the latter mode achieves better energy recovery efficiency than the former one. Based on the above understanding, the objective of this paper is to develop the optimal speed profile for a following train in order to minimize pantograph voltage fluctuations and improve energy recovery efficiency. Dynamic programming is applied to this problem in order to optimize the speed profile for a set of given infrastructure and train characteristics. Simulation results with Visual C++ demonstrate that the algorithm can provide an optimal operational strategy with better energy performance while satisfying safety constraints and comfort criteria. Based on this work, energy optimization potentials with different headways are discussed in the case study. This research will facilitate development of on-board train control system logic or system energy analysis that will reduce energy consumption and provide rail transit operators with operational cost savings.