Development of a control strategy accounting for the battery ageing and state of health for hybrid electric vehicles

The hybridization degree of the vehicles is getting bigger due to the felt need to fight and reduce tail pipe emissions. Internal combustion engine efficiency-oriented optimization on its own is not effective in reducing fuel consumption to respect increasingly stringent regulatory restrictions. Hybrid powertrains represent a viable solution. The ever-growing hybridization degree of the powertrain requires also bigger electrochemical system to store the electrical energy on board. Battery compartment is more and more solicited and plays an increasingly central role in this transition toward renewable energy for vehicles propulsion. Also battery represents an important cost in the total cost of the vehicle and it is clear why an health-conscious management of the electrochemical system is crucial in achieving the best possible benefit. Furthermore battery performances change over time and as the time goes on they decrease inexorably. Besides the "operative" reactions, within the battery there are some side, undesirable, reactions which deplete battery performance. Complex aging mechanisms take place inside the battery involving different battery areas. These aging mechanisms are strictly related to the battery operating conditions and severely restrict battery characteristics in operation. This work proposes an innovative way of looking at the on-board energy management problem. An ageing model has been parametrized and developed in the first section of the thesis and used to solve the optimization problem in the second part. The strength of this model is to be found in its intrinsic simplicity and reliability. Unlike conventional energy management strategies, the proposed strategy is careful to the health of the battery. The proposed strategy attempts to find an optimal solution both in terms of fuel consumption and battery degradation in time. It is interesting to notice that the battery life increases in front of a not significant increase in fuel consumption.