Modular battery design for reliable, flexible and multi-technology energy storage systems

With large scale battery systems being more and more used in demanding applications regarding lifetime, performance and safety, it is of great importance to utilize not only cells with a high cyclic and calendric lifetime but also to optimize the whole system architecture. The aim of this work is therefore, to highlight the benefits of a modular system architecture allowing the use of hybrid battery systems combining high power and high energy cells in a multi-technology system. To achieve an optimized performance, efficiency and lifetime for an electric vehicle the complete drive train topology has to be taken into account instead of optimizing one of the components individually. Consequently, the topic will be analyzed from the system's point of view, addressing in particular the modularization of the battery as well as the power electronics needed to do so. It will be shown that a highly flexible battery system can be realized by dc-to-dc converters between a modular, hybrid battery system and the drive inverter. By the dc-to-dc converters the battery output voltages and the inverter input voltages are decoupled. Hence, the battery's topology can be chosen unrestrictedly within a wide range and easily be interconnected to a common dc-link of a different voltage. The benefits of this flexibility will be analyzed in detail showing especially how the lifetime of the battery system can be improved and the impact on system weight.