Today´s modern vehicle energy distribution networks have high requirements with regards to both boardnet stability and power availability. Even though 48V systems are emerging slowly, the industry´s main focus is still on 12V applications. The ongoing electrification and addition of new features drives both common energy storages and system architectures to their limits. In the last few years, many architectures were developed to encounter the typical problems of the increasing number of high-power consumers. These architectures use DC/DC converters and/or multiple energy storage devices to ensure voltage stability and also increase energy regeneration to reduce fuel consumption. The main challenge is to develop a solution which provides both reliable electrical performance over a wide temperature range and, most importantly, cost efficiency. In order to optimize electrical performance, a hybrid energy storage, based on a standard 12V lead-acid battery and a 15V ultracapacitor module, were evaluated. A LN3 AGM battery is used as a reference and is a common choice in modern start-stop vehicles. Starting with an extensive simulation study carried out by a well-known European system house, the initial configuration went through several iteration loops to optimize and streamline the design. The main focus was set to cranking performance of various starter devices; comparing standard starters with enhanced starters and belt-driven starter generators. Cold cranking and warm cranking was evaluated in the temperature range of -30°C to +65°C. Based on the simulation results, an optimum energy storage solution was configured. A 12V LN3 AGM battery was used as a reference. The goal of the program is to define and design an energy storage solution with equivalent or improved performance. Cold-cranking, self-discharge and charge acceptance tests were conducted in our laboratories to compare the behavior of the new prototypes and the reference batteries. The resulting 12V hybrid energy storage shows similar performance to a comparable AGM battery, which combines a 40Ah LN0 enhanced flooded lead-acid battery and a corresponding ultracapacitor module with 320F, packaged in a standard form factor. The new combination can enable additional high-power features like start-stop operation at lower temperatures, active suspension, e-steering or even electrical turbo chargers. The experiments are still running and will be completed until eehe takes place in 2017.

Autor: Stefan Werkstetter
Co-Autor: Dr. Priya Bendale
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