Investigation of control strategies for hybrid energy storage systems in hybrid electric vehicles

The current developments of energy storage systems do not offer an adequate solution for hybrid electric vehicles. Both battery as well as capacitor do not meet the given demands. The present paper deals with the combination of both components building a vehicular hybrid energy storage system. From several linking possibilities of the storage system a proper topology including DC-converter was derivated. In this way, an additional degree of freedom occurs in purpose of the storage's inside power split, which can be used by a control strategy. Here three strategies are defined focusing different target variables like loss reduction, leveling the component's state of charge or optimizing the system's operating points. These control strategies are verified by dint of several typical driving cycles within a vehicle simulation system. It can be shown that even a simple control strategy enables efficient energy savings in the hybrid vehicle.