Development of efficient and sustainable power management strategies for hybrid vehicles

Abstract

The descarbonization of the transport sector has taken great interest and has become one of the main objectives of government and organizations, aiming to reduce the greenhouse gas (GHG) emissions caused by the road transport. Different alternatives have been explored to replace fossil fuel vehicles by vehicles propelled using alternatives fuels. One of the options that has been gaining acceptance among consumers are Battery Electric Vehicles (BEVs). However, the acceptance of these vehicles has been compromised due to their limited autonomy and their high cost compared to conventional combustion vehicles. Another option gaining attention in the automotive market are the Hybrid Electric Vehicles (HEVs). Although these vehicles solve the problem of autonomy, they still emit direct emissions into the environment, because of the hybridization with fossil fuels. Hydrogen has appeared as an alternative to the fossil fuels. Hydrogen produces zero direct emissions, and can be considered as a combustible with zero indirect emissions, if it is produced through renewable energies. The use of hydrogen as fuel has pushed the development of Fuel Cell Electric Vehicles (FCEVs). FCEVs contain a Fuel Cell (FC), which takes advantage of the electrochemical reaction between the hydrogen and the oxygen to generate electricity. Despite the advantages of these vehicles, the reduced number of hydrogen refuelling stations around the world and the problems that still persist in the production of hydrogen, has hindered their popularity in the automotive market. A solution that has gained interest in the recent years is the hybridization of the FCEVs, through the addition of an energy storage element (battery or super capacitor), giving birth to Fuel Cell Hybrid Electric Vehicles (FCHEVs). In the first part of this Thesis, two hybrid powertrain models are presented: Plug-in Fuel Cell Hybrid Vehicle (FC-PHEV) and Range Extended Fuel Cell Hybrid Vehicle (FC-EREV). A novel approval test procedure is proposed to measure the emissions, autonomy and energy consumption of both powertrain configurations. The proposed test allows a fair comparison between the different powertrains models. Taking as a starting point the behavior imposed by the test for each powertrain model, an Energy Management System (EMS) that implements xiii a Rule-Based Strategy (RBS) has been proposed. This proposal considers configurable input parameters to fulfill different objectives. Parameter selection is carried out using a sweepbased approach, where the parameters are selected from a discrete set of values. Selection is performed to offer the best vehicle performance in terms of distance traveled, emissions and energy consumption. An extensive evaluation through simulations is performed, using parameters taken from a commercial vehicle, achieving ranges between 665 km and 830 km depending on the driving profile used. In addition, it is demonstrated that the performance of the vehicle heavily depends on the controller parameters. The second part of this Thesis contemplates the inclusion of the hydrogen available in the vehicle tank, in the decision rules of the EMS. This is done by dividing the hydrogen tank in levels, and the selecting a different set of parameters for each level. By defining these sets of parameters, two new EMSs are proposed, single (EMS type 1) and multi-level (EMS type 2). Because of the high number of parameters to be adjusted, a new Particles Swarm Optimization (PSO)-based parameter selection is proposed. This considers the specifics of the problem to be solved. The EMSs have been tested for different driving conditions, where improvements between 9 % and 12 % in the distance traveled are accomplished compared to the RBS-based EMS with sweep-based parameter selection. Specifically, ranges between 758 km and 934 km were achieved, when the powertrain implements the EMS type 2 configuration. In regard of the energy consumption, when the RBS with sweep-based selection is employed, the results match the ones reported in the literature and with respect to commercial vehicles. However, the multi-level approach, together with the PSO-based parameter selection, achieves a reduction in the energy consumtion between 7 % and 11 % for the same driving conditions. Additionally, a redution of emissions per per kilometer traveled is achieved thanks to the proposed EMSs and parameter selection methods. Finally, this Thesis contributes to the advance in the EMS design for hybrid hydrogen propelled vehicles. Among the findings and knowledge obtained from this research, the potential of hydrogen hybrid propelled systems stands out, contributing to the development and implementation of efficient and sustainable transport solutions.