Battery testing and modelling lead to energy optimization

As listed numerous times, the relatively limited operating range is one of the major deal breakers, when it comes to people choosing an electric vehicle over an ordinary car. In the JOSPEL project, we are looking to improve the energy consumption of the vehicle and the battery efficiency – the goal is to get more available energy for mobility and consume less energy from the grid.

In the JOSPEL project, the development of a novel energy efficient climate system for electric vehicles is stealing most of the headlines. But in fact, we are doing extensive research in the field of battery analysis and modelling, as the battery is what will be powering the other sub-systems in the vehicle as well as provide the extended operating range. The Fraunhofer Institute for Solar Energy Systems, who is a partner in the project, is carrying out the battery tests at their Department of Electrical Energy Storage in Freiburg, Germany.

Battery models mirror reality

What they are doing is making very detailed analyses by testing numerous properties of the EV battery cells. With these analyses, they can develop battery cell models that represent the electric, thermal and aging behaviour of the real cells.

With the test results, we are able to evaluate the battery cells and design the new battery system according to their performance, explains Maximilian Bruch, Project Manager for Team Battery Engineering in the Department of Electrical Energy Storage at the Fraunhofer Institute for Solar Energy Systems.

So far, the tests have been very successful and enlightening, and the Battery Engineering team was able to gather the necessary model parameters and subsequently verify the models to some extent with additional tests. The Battery Engineering team recently compiled a report where they explain the battery cell models that they use. Here, they also document the first results of the tests along with the model parameters.

Later on in the project, these battery cell models are also needed to reliably calculate the usable energy stored in the battery and offer a lifetime prediction.

Extensive testing offers valuable insights about performance

The overall goal of the battery testing and modelling has been to increase the performance of the battery system. However, when carrying out these types of tests, the main challenge is to make good, representative simulation models for the battery and the EV, and then find the optimal operation conditions – the so-called sweet spot. When this is done, the most important challenge is to translate the findings into a working prototype that applies the benefits.

But after having tested the battery cells, the Battery Engineering team now knows in which temperature range the EV batteries perform well – and they have also investigated in which temperatures they age faster. This behaviour has been transferred to a model that simulates the whole lifetime of an electric vehicle, and the simulation achieved the goal of increasing battery performance by combining different strategies and operational parameters. These strategies included pre-cooling and -heating of the EV battery when the vehicle is still connected to the grid (i.e. thermal preconditioning), reasonable cooling during standby at a high efficiency, and finally a flexible charging time. In fact, the simulation revealed that these strategies could to reduce the energy consumption of the battery system with more than 12 % and increase the battery lifetime by 15 %.

Consequently, all the functions and information of the battery are monitored and coordinated with the central vehicle computer via the Battery Management System. That way, the JOSPEL project has ended up with an operational management that decreases the energy consumption AND increases the battery lifetime.