Abstract
Keywords - Boardnet Architecture, Supercap, Li-Ion-Battery, Standby Time, Plug&Play
Lead acid batteries have been the exclusive vehicle energy storage for more than a century. Driven by the introduction of new safety, control, and comfort functions, the overall energy requirements are continually rising, driving lead acid battery technology to its limits.
New Boardnet extensions and topologies are under development or entering the market, mainly driven by existing issues like insufficient supply stability, short standby times or the need to improve fuel efficiency.
The all present cost pressure has so far limited the development of an integrated energy management approach, excluding the 12V Boardnet from technical progress and development methods now used in hybrid vehicle applications.
Based on hybrid topologies a new Boardnet concept has been developed , superior in energy density, life time, weight and volume, improving cold start capability and start/stop functions. Provisions are made to support eDrag (dropping the alternator during acceleration) and regenerative braking for further improved fuel economy.
Unlike a conventional lead acid system the new concept is based on the separation of energy storage and the allocation of electrical power. An energy management efficiently controls the energy flow, supervising the charge/discharge processes while monitoring the state of charge and health of battery and DLC. Energy transfer between the storage devices and the electrical system is established by means of high efficiency DC/DC converters based on a modular concept. Fuel consumption and standby power losses are reduced by means of efficient energy storage, a dedicated architecture and combined recuperation and start/stop strategy. Double Layer capacitors, Lithium Polymer batteries and lead acid battery are re arranged for improving both vehicle cold start performance and stop phase supply.
A simulation of the vehicle´s longitudinal dynamic, along with a proposed E/E-architecture on equivalent circuit level reduces development time significantly. Special is taken to reduce fuel consumption while maintaining engine start ability. This can be realized in an elegant manner just by separating energy storage and the allocation of electrical power.
First prototypes, combining Double Layer capacitors and lead acid batteries or Lithium Polymer batteries were developed and successfully tested along with a new energy management system. Everything is packaged into the shape of a standard starter battery, offering easy adaptation and implementation into existing vehicles with minimum modifications, making it a plug&play battery replacement even for the after market. Compared to a conventional electrical system the new storage system leads to 65% weight reduction while extending vehicle standby time up to 25%.