Untersuchung eines von Doppelschichtkondensatoren unterstützten Zweispannungsbordnetzes für Mikro-Hybrid-Fahrzeuge

Abstract

Micro-hybrid-vehicles are an attractive alternative to the more complex mild or full-hybrid vehicles because of the low cost of manufacture. They too, offer the ability of regenerative breaking, start/stop the combustion engine and even boosting the combustion engine though to a limited extent only. But there are not only benefits. The start/stop functionality results in a significantly higher relative charge exchange. Also batteries are limited in their ability to take up and provide bursts of high power during events such as regenerative breaking and start-up the combustion engine. This will cause a reduced cycle life of the battery. To handle these drawbacks a second energy storage with a high cycle lifetime to support the battery is beneficial. Especially ultra-capacitors can easily deliver such high power peaks without noticeable aging. The system design of micro-hybrids benefits from the use of ultracapacitors as a second energy store achieving a better on-board net stability and from capturing more regenerative braking energy. In the thesis a simulation of a complete micro hybrid drivetrain and the electrical on-board net with ultra-capacitor assistance is shown. The adaptive controller results in additional fuel savings and a significantly reduced charge/discharge load of the battery which results in a higher lifetime. The optimal ultra-capacitor size is determined with an offline optimization done with dynamic programming and the Bellmann/Dijkstra algorithm. Two different vehicles were examined, one with a Diesel engine and a second one with a gasoline engine. The complete system consisting of an ultra-capacitor and a DC/DC-converter is integrated in a test vehicle. The results have shown, that for the NEDC the fuel consumption can be lowerd up to 12.5 %. Additionally the charge exchange of the battery can be reduced by 90 % to achieve a higher cycle lifetime and a better voltage stability.