Parametrization and validation of lithium ion battery cell models: Poster presented at 8. Internationale Fachtagung "Kraftwerk Batterie" 2016, Münster, 26. - 27. April 2016

Abstract

Li‐Ion battery cells are basic components of the power train of Electric Vehicles. Their behaviour is controlled by battery management systems (BMS). As part of the IKEBA project [1], we create a prototype of a virtual simulation platform for BMS. This platform allows to verify the suitability and the interaction between selected hardware components (Li‐Ion batteries and semiconductor circuits for battery monitoring), and the software of a battery management system (BMS) by means of simulation. The electronic system level (ESL) behavioural languages SystemC and SystemC AMS were used for modelling. In this context, models of battery cells are essential. The cells were modelled by equivalent circuit models (ECM) that consist of a series connection of a voltage source, an internal resistance and two parallel connections of resistances (R) and capacitances (C). The components of the ECM cell model depend on temperature and state of charge (SOC). These dependencies can be described by one‐ and two‐dimensional lookup tables (LUT). Because of effort and uncertainties of material parameters, we resigned to determine ECM model parameter tables based on geometry and low level electrochemical behaviour simulations. Therefore, the data points that establish the tables were determined on the base of current interruption technique (CIT) measurements for a special battery cell type. For more details see [2]. The evaluation of cell voltages delivers the corresponding ECM parameter values. A special challenge is to derive the unique R und C values from observed time constants. For this purpose, only small changes from one CIT period to the next were accepted. We could approve the CIT measurement results by simulation with the parametrized cell model as expected. For better validation, we used a current profile that describes charging and discharging a battery based on the New European Drive Cycle (NEDC). Simulation and measurement results were in very good accordance. Only for a measurement with a SOC of 20% at the beginning, small deviations were detected. That means in our opinion, that the presented approach is a good choice for BMS simulations in the design process.References:[1] IKEBA - Integrierte Komponenten und integrierter Entwurf energie‐effizienter Batteriesysteme. Available: http://www.iam.kit.edu/awp/ikeba/[2] Boxia Lei et al., Comparison of calorimetric studies on 18650 lithium‐ion cells and equivalent circuit model‐based simulation applied to driving cycles (this conference)