Including the Impact of Bus Bar Design and Weld Quality
Electrochemical Cell Model and Current Distribution Busbar Model
Authors: Yaxing Ren, W. Dhammika Widanage, James Marco
WMG, University of Warwick
- We have developed a module scale model of the different electrical pathways within a commercially representative busbar design for cells connected in series and parallel.
- The model links cell performance (current flow, heat generation) with degradation and will help support the transition from cell to pack engineering.
- This work is being undertaken with Jaguar Land Rover as a case study for the methodology being developed.
Background & Motivation
- The capacity and resistance differences of cells amplify the inhomogeneity at a system level and results in accelerated aging and degradation.
- For the module design, where many cells are in parallel, the BMS typically does not have access to individual cell currents and temperatures.
- We aim to predict current, state of health and temperature of each cell in the module (or pack) via modelling the interaction between cell and busbar and weld quality.
- The traditional Pseudo two Dimensional (P 2 D) model and the Single Particle Model with electrolyte SPMe are difficult to implement for real time optimisation and control.
- The simplified electrochemical model after model order reduction and linearisation needs to be parameterised using experimental data of a three electrode cell.
- The result shows that the developed electrochemical model based observer can be used within real time control applications to detect the anode potential in real time to avoid battery degradation caused by lithium plating.
- In order to demonstrate the current distribution in the busbar, we have designed three 1 D equivalent circuits with different levels of complexity.
- The simple model connects all cells in parallel, the second model considers the weld resistance pathways, and the full/complex model considers the impact of weld resistance and the geometry of the busbar.
- From the initial current distribution results, the complex equivalent circuit model matches the best with the 3D model results derived from our industrial partner.
Impact / Next Steps
- We have derived a simplified electrochemical model of Li ion cell for real time implementation suitable for fast charge research.
- We are working with Jaguar Land Rover to find the optimized busbar model to predict current distribution and module performance.
- The next step will be the validation of the busbar model in experimental tests together with real cells and higher fidelity cell models.
- Design the optimised charge management strategy for the battery module by predicting the load current, state of health, temperature, and degradation of each cells from the model during fast charge operation.
- Li L, Ren Y, O’Regan K, Koleti UR, Kendrick E, Widanage WD, Marco J. Lithium ion battery cathode and anode potential observer based on reduced order electrochemical single particle model . Journal of Energy Storage. 2021 Dec . 2021 Dec 1;44:103324.
- Hosseinzadeh E, Arias S, Krishna M, Worwood D, Barai A, Widanage D, Marco J. Quantifying cell to cell variations of a parallel battery module for different pack configurations . Applied Energy. 2021 Jan 15;282:115859.
- Pastor Fernández C, Bruen T, Widanage WD, Gama Valdez MA, Marco J. A study of cell to cell interactions and degradation in parallel strings: implications for the battery management system. Journal of Power Sources. 2016 Oct 15;329:574-85.
Yaxing is a Faraday Institution Research Fellow at the University of Warwick, working on the Multi Scale Modelling project. His research interests are on mathematical modelling and control system design with a particular focus on sustainable energy and electric vehicles.
This project brings together world-leading battery experts with a broad set of skills to build the critical bridge between science and engineering, working innovatively alongside UK industry to deliver impact. The team is creating new methodologies and techniques to measure electrolyte properties, characterise the 3D structure of cells and parameterise models. The project is delivering a portfolio of exceptional, world-leading research of strategic importance for the UK.
By conducting experiments to measure the battery voltage at various SoCs and temperatures it is possible to develop phenomenological models that relate the applied current and the voltage. An equivalent circuit model (ECM) is one such phenomenological model most widely used in industry to simulate the voltage response for subsequent Battery Management System control and state estimation.