Print Email Facebook Twitter A Practical Circuit-based Model for State of Health Estimation of Li-ion Battery Cells in Electric Vehicles Title A Practical Circuit-based Model for State of Health Estimation of Li-ion Battery Cells in Electric Vehicles Author Lam, L. Contributor Bauer, P. (mentor) Faculty Electrical Engineering, Mathematics and Computer Science Department Electrical Power Engineering Programme Electrical Power Processing Date 2011-08-23 Abstract In this thesis the development of the state of health of Li-ion battery cells under possible real-life operating conditions in electric cars has been characterised. Furthermore, a practical circuit-based model for Li-ion cells has been developed that is capable of modelling the cell voltage behaviour under various operating conditions. The Li-ion cell model can be implemented in simulation programs and be directly connected to a model of the rest of the electronic system in electric vehicles. Most existing battery models are impractical for electric vehicle system designers and require extensive background knowledge of electrochemistry to be implemented. Furthermore, many models do not take the effect of regenerative braking into account and are obtained from testing fully charged cells. However, in real-life applications electric vehicles are not always fully charged and utilise regenerative braking to save energy. To obtain a practical circuit model based on real operating conditions and to model the state of health of electric vehicle cells, numerous 18650 size LiFePO4 cells have been tested under possible operating conditions. Capacity fading was chosen as the state of health parameter, and the capacity fading of different cells was compared with the charge processed instead of cycles. Tests have shown that the capacity fading rate is dependent on temperature, charging C-rate, state of charge and depth of discharge. The obtained circuit model is capable of simulating the voltage behaviour under various temperatures and C-rates with a maximum error of 14mV. However, modelling the effect of different temperatures and C-rates increases the complexity of the model. The model is easily adjustable and the choice is given to the electric vehicle system designer to decide which operating conditions to take into account. By combining the test results for the capacity fading and the proposed circuit model, recommendations to optimise the battery lifetime are proposed. Subject LiFePO4battery modelcapacity fadingelectric vehiclelithium-ion batterybattery degradation To reference this document use: http://resolver.tudelft.nl/uuid:a7446a0a-4c29-4c68-bbe2-273f68f85ed7 Embargo date 2011-10-12 Part of collection Student theses Document type master thesis Rights (c) 2011 Lam, L. Files PDF MScthesis_LongLamv3.pdf 4.92 MB Close viewer /islandora/object/uuid:a7446a0a-4c29-4c68-bbe2-273f68f85ed7/datastream/OBJ/view