Just as an orchestra needs a conductor, a battery management system (BMS) controls the power storage of an electric vehicle. However, up to now the monitoring is only based on the voltages, currents and temperatures of the individual battery cells. Their ageing or possible damage can only be checked externally using complex calculations. In the EU project Nemo, Graz University of Technology (TU Graz), the Vrije Universiteit Brussel and partners from industry have developed intelligent models and algorithms that enable the safety, service life and performance of batteries to be monitored directly in the vehicle's system.
Avoiding dangers
"The battery management system is an important tool for operating electric vehicles more safely and sustainably," says Christoph Drießen from the Vehicle Safety Institute at TU Graz. "If we recognise faults and damage to individual battery cells at an early stage via the BMS, many dangers can be avoided. And thanks to the monitoring of the ageing process of each individual cell, their service life can also be extended substantially through intelligent control."
The team at the Vehicle Safety Institute at TU Graz focused primarily on the safety aspects of the batteries. To this end, the researchers at the institute's Battery Safety Center examined battery cells that were mechanically deformed, for example to simulate parking damage. They used this laboratory data to train models and algorithms they had developed themselves so that the BMS can recognise damage independently and indicate when maintenance is required. In order to obtain the necessary data from inside the cell, the team is using new sensor technology known as electrochemical impedance spectroscopy (EIS), which measures the electrical resistance inside the cells in the vehicle.
Internal findings on ageing
In addition, the Graz researchers developed a model that predicts the change in physical volume of the cells during charging and discharging. As excessive expansion increases the mechanical pressure in the battery pack and can lead to cracks and deformations, this model helps to minimise the risk of internal short circuits and thermal peaks.
The algorithms and models pertaining to service life and ageing were developed at the Vrije Universiteit Brussel. Their implementation in the BMS offers clear advantages over previous models or external checks. "Up to now, a test only showed how much the capacity has decreased compared to the original battery condition," says Christoph Drießen. "But the new models also give us an insight into the changes within the cells as they age. This enables adjustments that are beneficial for performance, service life and safety."
Demonstrator as a model for series production
Despite the numerous new functions, the enhanced BMS would not be significantly larger or heavier than before. For the additional EIS measurements, however, additional sensors and a correspondingly adapted integration into the BMS are required.
In order to further demonstrate the developed technologies, a follow-up project will work on their continued development and transfer towards industrial application. A demonstrator at module level has already been set up for this in the current project.
The project was Co-funded by the European Union. Additional funding came from the Swiss State Secretariat for Education, Research and Innovation. In addition to TU Graz and the Vrije Universiteit Brussel, Infineon Technologies Austria, Ingenieurgesellschaft Auto und Verkehr (IAV) and the Centre Suisse d'Electronique et de Microtechnique (CSEM) were on board as hardware and software providers as well as TTTech for the cloud implementation and ICONS as partners.
