Abstract
This paper deals with optimal charging versus aging minimization for lithium-ion batteries. The optimal charging strategy proposed involves charging controllers whose design relies on a battery model. The model, especially designed for automotive battery management systems applications, is recalled in this paper. It provides the voltage response of a cell to an input current. It also models side reactions that produce degradation mechanisms and thus decrease battery performance. Side reaction modelling involves taking into account the temperature cell variations, which are thus also modelled. The association of the three above-mentioned sub-models leads to an electro-thermal battery aging model used to design an optimal charging strategy that simultaneously takes into account the minimization of charging time and maximization of battery lifetime. Thus, to achieve a charging controller that manages battery health, an appropriate charging trajectory was computed by solving an optimization problem minimizing aging. Then, a charge control loop was designed. The nonlinear behavior of the battery was taken into account through the linearization of the electro-thermal aging model in different operating conditions. To take into account the resulting linear model family, the CRONE design methodology was used. The principles of this methodology are recapped and the design of the charging control loop is explained. The efficiency of the resulting charge controller is illustrated by several simulations.
Highlights
A long lifetime is a very important requirement for the design of electric and hybrid-electric vehicles.To meet this requirement, battery lifetime must be optimized
To the best knowledge of the authors, the physics-based battery model proposed in this study, which takes into account degradation mechanisms as a function of State of Charge (SOC), temperature and C rate, is unprecedented in the literature
The fast charging strategy developed in this paper, which can be integrated in a battery management system (BMS), is described globally by Figure 2
Summary
A long lifetime is a very important requirement for the design of electric and hybrid-electric vehicles. In [17], a nonlinear MPC was used for the energy management of a power-split hybrid electric vehicle to improve battery aging while maintaining the fuel economy at a reasonable level In all these closed loop charging strategies, in spite of their valuable contribution, the MPC approach does not ensure robustness with respect to rapid variations in state variables (for instance, anode potential). This magnitude is, known to greatly aggravate battery aging Referring to this state of the art in the field of lithium-ion fast charging strategies and using a physics-based model of the cell, this paper addresses the following main challenges:. The design of these controllers is based on a family of models that capture the nonlinear behaviour of the cell around several operating points.
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