Integrated Energy Storage Systems to Optimize Payback Period of Hybrid Vehicles

Enhancements of today's Micro-Hybrids based on stop-start systems with and without coasting and energy recuperation show a positive cost-benefit and a much shorter payback period compared to more complex and expensive Full-Hybrid concepts. However, improved Micro-Hybrid functionalities have a higher demand on the vehicle's electrical power network, which cannot be covered with traditional topologies alone. To enable the advanced Micro-Hybrid features, additional energy storage elements like second lead acid batteries, double-layer capacitors or lithium-ion cell based storage systems will be integrated into the power network. This will stabilize the network and provide a reliable source of energy. To apply even further reaching measures like creeping (also called crawling), and high power recuperation, a dual voltage power network will be required. This can be achieved by adding a second voltage level to the traditional 12V power network. In order to connect power networks with different voltage levels, DC/DC converters are required. This paper will discuss the constraints of a cost-optimum topology for each power class of DC/DC converter from Micro- up to Mild-Hybrid applications and present solutions to overcome these limitations. Furthermore, the different topologies are compared in regards of their economic benefit using the total cost of ownership model.