Energy storage devices in hybrid railway vehicles: a kinematic analysis

Concerns over future energy security, energy costs, and competitiveness with other modes have prompted the railway industry to search for cost-effective energy efficient traction solutions which will ensure continuing business feasibility. For non-electrified routes, where the business case for electrification is unfavourable, traction is usually provided by diesel fuel combustion. Hybridization offers the potential to achieve a step change in energy efficiency. This article presents an analysis of the potential benefits of hybridization for rail vehicles. The performance requirements of the energy storage device in a hybrid rail vehicle which is storage device dominant are derived. A rail vehicle simulator has been developed in order to compute the drive train duty cycle in typical high-speed and commuter passenger services. The outputs from the simulator have been inputted into a series hybrid model, which has been optimized to preserve the state of charge of the energy storage device over a single typical rail journey. The analysis suggests the energy savings of up to 28 per cent for high-speed intercity vehicles and 35 per cent for commuter vehicles are achievable with practical system components. A sensitivity analysis exploring the effect of the inherent efficiency of the regenerative braking capability and the energy storage device revealed that primary energy savings are only realized with in/out storage efficiencies of greater than similar to 40 per cent.