In-Situ State of Health Analysis and Simulation of Electric Vehicle Battery Packs Using Conventional Charging Infrastructure

The authors propose and compare two in-situ methods for the state of health estimation of an electric vehicle battery pack, without the requirement of dismantling the battery from the vehicle. Using the conventional charging infrastructure, the authors achieved a reproducible and comparable testing environment that allows cost efficient state of health observation over the vehicles life time. Pulse and constant current testing methods have been used to identify the internal resistance, available capacity and open circuit voltage of the battery. The obtained data were implemented into a RINT battery simulation model for verification purposes. The simulation was performed to verify the data sets obtained using the two different methods against data from real world drives, as well as to compare the two against each other. Comparison of the simulation model results against 30 unique real world drives has shown, that the state of health defining parameters "internal resistance" and "available capacity" have been properly estimated using the two methods and that usability could be verified. In comparison against each other, the pulse charge testing has shown to provide better results than the constant current testing, while also requiring less time to perform the test. A detailed explanation of the used methods is given in the full paper.