Performance Plus Range: Combined Battery Concept for Plug‑In Hybrid Vehicles 2013-01-1525

PlugIn Hybrid Electric Vehicles (PHEV) offer the opportunity to experience electric driving without the risk of vehicle break-down due to a low battery charge state. Thus, PHEV's represent an attractive means of meeting future CO2-legislation.

PHEV batteries must fulfill a divergent list of requirements: on the one hand, the battery must supply sufficient energy to ensure it can be driven an appropriate distance in EV-mode. On the other hand, even with a low state-of-charge (SOC), the battery must supply sufficient power to assist the engine in vehicle acceleration or to recuperate on deceleration. This leads to a compromise in terms of cell selection. Fundamentally, high energy cells cannot provide high charge and discharge rates and high power cells cannot provide sufficient energy. Consequently, the battery can either be provided with the required energy content by switching many power cells in parallel, or it can meet the power requirements with the help of a very large energy battery with a low discharge rate. Neither solution is optimal in terms of the packaging, weight and cost aspects.

This paper presents an innovative and cost-efficient battery concept including customized set-up of the battery through combination of the energy and power modules. The current flow from the battery's energy pack to the power pack and back is realized through a cost-efficient current controller. The combined battery utilizes a predefined current, offering advantages in terms of predicted service life in comparison with conventional batteries. The combined battery provides cost advantages of 12% and weight advantages of 18% compared with conventional battery technology. The current controller offers the flexibility of combining different energy sources which, in turn, permits modular systems to be generated for a wide range of applications with potential scaling effects.

Within this paper, the requirements for PHEV batteries are described along with the concept of the combined battery, the mechanical and electrical layout, as well as the test results of the battery concept on basis of a specific application example.