Design and Functional Demonstration of a 100 A Battery Testing Unit with Minimal Power Supply Load

For minimizing the fire hazard of lithium-ion cells becoming defective in operation, the state of health (SoH) of such batteries can be estimated by prior testing. In those tests, the battery is charged and discharged again while observing its condition. When charging batteries, power supply requires high power from the grid. The stored energy is often converted into heat during discharging phase. For tackling such problems, a system is proposed for transferring energy from one battery to another while either current or power in one battery is held constant. The concept incorporates a DC link interconnecting all system components for power transmission, a programmable logic controller (PLC) for test sequencing, and DC/DC converters for controlling current flow and voltage levels within the cross-charging-discharging system. Additionally, a switched-mode power supply (SMPS) and a DC link chopper are responsible for balancing the total energy stored in the system. Reduced grid load is the result of interleaving charging and discharging processes. This paper addresses design and dimensioning issues as well as a control strategy for proper operation. The working principles of the system is explained by defining example operational states and a small scale functioning model demonstrates operation with a single battery cell. Finally, suggestions for improvements and further development are made.