Modular and smart Li-ion battery system

Background

Common battery packs are replaced and either disposed of or recycled at the end of their service life. The in series and in parallel connected cells of a battery pack age with different speeds and would partially still be usable.

Instead of disposing of them, more and more attempts are being made to prepare the battery packs for a second-life application. For this purpose they are disassembled and the state of each cell is characterized. This process is very costly and often not economically viable. In order to simplify the process, a battery system is to be developed that allows characterization during operation and easy replacement of individual battery cells.

Goals

Development of a battery system based on battery cells of the 18650 type and with the following characteristics and functions:

• Robust, modular design
• Easy replacement of modules and cells, also during operation ("hot swap")
• Integrated protection functions
• Determination of state of battery cells during operation
• Measurement of current, voltage and temperature of each cell and logging of the data
• Integrated battery management system
• Disconnect and connect each individual cell with an el. switch
  

Results

The developed battery block consists of a 19-inch rack with backplane, a control module and up to twelve battery modules. The modules in Eurocard format can be easily inserted into the battery block. On the backplane the parallel and serial connections of the battery modules can be configured and thus the voltage of the battery block can be defined.

Each battery module can be equipped with up to six parallel battery cells. Current, voltage and temperature of each cell are continuously monitored and logged. The cells can be individually connected to the module via electronic switches.

The control module monitors the battery modules and controls the voltage balancing of parallel modules. It stores the measured data on a memory card and enables communication with a computer. A battery management system also monitors the total current of the battery block and the charging and discharging process.