Railway electrification provides faster and reliable train journeys, but requires a substantial investment for the railway infrastructure. Therefore, many branch lines with moderate traffic will still be operated by diesel trains, with raising concerns about journey time, pollution and noise. Hydrogen is an environmentally friendly alternative to diesel and could be used by a fuel cell to produce electrical power for the traction motors of the trains, achieving a performance similar to that of standard electric trains. The UK is currently exploring possible ways of replacing the existing diesel fleets with independently powered electric trains and a Class 379 Electrostar battery train has been recently tested for passenger service with success. Due to the limited range of batteries, long recharge times and limited lifetime, it is expected that hybrid trains with fuel cells and batteries will be the best candidate to replace diesel trains.
Due to the large power requirements, the powertrain of hydrogen trains is likely to be formed by multiple fuel cell stacks and battery banks that need a suitable power conversion system and energy management. The power conversion system has to be capable of regulating the torque and speed of traction motors for the entire speed range and load of the train, as well as being modular, reliable and highly efficient. Power converters based on multilevel technology have the potential to satisfy these requirements and offer the possibility of integrating fuel cell stacks and energy storage in one system, removing the need of external cables and protections. These new converters have also large flexibility on the energy management between the fuel cell and the battery and are tolerant to either fuel cells, battery or semiconductor faults.
This project investigates new advanced topologies of boost multilevel converters supplied by a combination of fuel cells and energy storage, guaranteeing temperature management of the different stacks and state of charge balancing of the storage. The research will be based on modelling of the converter and the control, numerical simulations of the entire power train and experiments on a small-scale laboratory demonstrator.