Technical and economic feasibility of a regenerative braking system with on-board energy storage for freight trains

Abstract

This dissertation presents the technical and economic feasibility of a novel regenerative braking system (RBS) for the freight rail industry. A concept for a distributed RBS, integrated into the bogies of freight rail wagons, is proposed in a patent by Transnet SOC Ltd. The system allows for numerous RBSs to be installed on a single freight train, in a distributed manner, which collectively functions together to perform regenerative braking on the train with the goal of reducing the energy consumption of the train. The proposed system would, if implemented successfully, alleviate challenges and limitations with current RBS on diesel-powered freight trains. The patent also proposes that the RBS utilise mechanical energy storage by means of a high-speed flywheel which is connected to the train axles by a continuously variable transmission (CVT). The proposed RBS is conceptualised in this study by first establishing the requirements of the system from in-service train data, followed by the development of the subsystems to deliver workable concepts that would meet the requirements identified. A multi-domain, physical system simulation model is subsequently developed to establish the energy savings performance of each of the system concepts for typical freight train routes. The simulation results show that energy savings of between 10% and 24% can be realised by the feasible system concepts, depending on the configuration of the RBS concept and the duty-cycle of the specific train route. This proves the technical feasibility of the proposed system. Next, the proposed system and the candidate concepts are evaluated in economic terms. A cost-benefit analysis (CBA) is performed in which the cost and benefits over the life cycle of the RBS were combined into a single distribution and analysed. The decision criteria calculated in the CBA provide unanimous results as to which of the candidate concepts are economically feasible. It is shown that four of the candidate concepts, all utilising the same transmission topology incorporating a CVT with different flywheel configurations, are economically feasible. The RBS concepts show good return on investment and provide an internal rate of return (IRR) of 17% and a benefit-cost ratio (BCR) of 2.13. These results therefore indicate that the proposed distributed RBS for freight trains is economically feasible and would deliver favourable financial returns if pursued.