Abstract
Nowadays emissions and fuel efficiency are crucial performance indicators for any vehicle. The diminishing oil resources along with climate changes are pushing car makers towards more eco-friendly solutions. Hybrid electric vehicles seem to be a necessary step towards zero-emissions cars. The contribution of this dissertation focuses on the analysis and the energy management of hybrid energy storage systems, consisting of a battery and a supercapacitor, for hybrid electric vehicles and electric vehicles. This PhD is funded as part of the European FP7 project AUTOSUPERCAP, which aims to develop high energy and high power density supercapacitors for vehicle applications. Therefore, the objective of this PhD is the assessment of the potential benefit deriving from the adoption of hybrid energy storage systems, rather than the conventional solution based on battery only. This target is achieved through a series of modelling, simulation and validation activities, based on different case study vehicle applications (e.g. micro-hybrid electric vehicle, through-the-road parallel hybrid electric vehicles, parallel hybrid electric vehicles and fully electric vehicles). In parallel, different novel algorithms for the power split within hybrid energy storage systems are investigated. The results of this work show that the adoption of a supercapacitor stack within a hybrid energy storage system is very promising in terms of reduction of battery current and extension of the battery life. In particular, the simulated results, over a selection of driving cycles, indicate a reduction of the root mean square and peak value of the battery current by respectively 77% and 93% for a parallel-through-the road hybrid electric vehicle when compared to the battery only case. These results are achieved with the adoption of a control strategy based on the optimal control theory. Moreover, the hybrid storage pack can be optimally designed, which means that the size (i.e. weight) of the system can be reduced. This, together with the higher power density of supercapacitors, can be beneficial in terms of energy efficiency. A 3% of fuel savings are achieved when the hybrid energy storage system is adopted within a novel parallel hybrid electric vehicle.