Modular and intelligent battery control system for electric vehicles and stationary storage systems

Intelligent networking of stationary energy storage systems, electric vehicles, or uninterruptable power supply systems for data centers enables the integration of renewable and fluctuating power sources to higher extents. For economically operation of the increasing number of storage components it becomes essential to maintain unequally aged or deteriorate battery cells. Aged batteries from electric vehicles may have unsufficient capacity and therefore need to be replaced, but they might be still suitable in so called “second life” for stationary storage. Then, cells or modules can be combined, while the control systems enables maximum available system capacity, which results from the maximum capacity of the individual cells or modules. Therefore, each cell module has been equipped with an integrated control device and a power electronic active balancing circuit to exactly control discharge and charge properties and optimize the stack power or energy capability. State of charge and state of health data are monitored over the whole battery life time and stored into the internal memory of the module controller. Due to the internal control and monitoring system, calculation of the remaining storage capability of aged cells, the status and reliability of each cell and the whole battery stack becomes available online at any time. Furthermore, the lifetime of the cells is being extended due to adjusted an optimized charging and discharging processes for each module. The paper describes the results of a recently conducted research project of three industrial and one academic partners. A real operating prototype has been built and successfully tested in the laboratory. In addition, the requirements of a grid connected battery system have been tested with the system. A bidirectional power converter was controlled by a data communication interface, which provides the power demand of a distribution grid in real time, while the battery system communicates its ability to deliver power back to the grid control system. Figure 1 shows the charge and discharge power converters, which contain a centralized power electronic system and additional module integrated converters and controllers. A critical requirement for the project was the overall efficiency and reliability of the system. Finally, the control system of each battery cell module has been integrated into an application specific circuit (ASIC) which was very important regarding cost and efficiency.