Yang, Jia Di; (2025) Developing Cell-Level Testing Protocols and Mass Estimation Models for Fuel Cell Hybrid Electric Vehicles. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

With an increasing focus on decarbonisation of the transport sector, it is imperative to consider routes to electrify ground vehicles beyond the use of Li-ion technology. This thesis presents a comprehensive analysis of tools and experimental systems of Proton Exchange Membrane Fuel Cell (PEMFC) and lithium-ion battery (LiB) systems integrated into fuel cell hybrid electric vehicles (FCHEVs), focusing on component sizing, synergy between PEMFC and LiBs, electrochemical degradation characterisation, and degradation analysis using X-Ray computed tomography (CT). Both parallel and fuel cell range extender (FCREx) architecture were taken into consideration. Through the collection and analysis of electrochemical degradation data, such as polarisation curves, cyclic voltammetry (CV), linear sweep voltammetry (LSV), capacity fade, and electrochemical impedance spectroscopy (EIS), the study identifies degradation modes under various operating scenarios and their implications for long-term performance and durability. X-ray CT techniques were used to further probe the LiB degradation as a form of physical characterisation. To stress-test the PEMFCs and LiBs under realistic driving behaviour, a drive cycle endurance testing protocol was formulated for both the PEMFC and LiB counterparts. Additionally, the thesis explores the effect of hybridisation degree on system mass and performance across different vehicle types, including light-duty vehicles, Class 8 heavy goods vehicles, and buses. By modelling these scenarios and varying the operating conditions such as hybridisation degree and cell operating power of the PEMFC stack and battery pack, the research highlights the benefits and potential hindrances of hybridisation in terms of weight, packaging, durability, and cost-effectiveness. A vehicle sizing tool was programmed in MATLAB Simulink from the ground up to achieve this. The model has a novel system weight feedback loop that enhances accuracy in vehicle mass and performance estimation, offering a valuable tool for vehicle design. This model focuses more on sizing, weight analysis, and hybridisation degree, rather than energy management systems (EMS), which is already abundant in the literature. By combining insights on electrochemical degradation, physical degradation, hybridisation impacts, and the application of drive cycles, this research helped develop tools and experimental systems to improve the optimisation of FCHEVs, contributing to the advancement of sustainable ground-vehicle transportation.

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