Impedance based simulation models for energy storage devices in advanced automotive power systems

The demands on vehicle electric power systems are rapidly increasing. Apart from modifications and optimizations of the existing systems, the introduction of a higher dc voltage level and new supply architectures is discussed. Especially the demands on the energy storage devices will drastically change. In the future, storage devices have to be fully included into the computer-based development process of the vehicle electric systems. Hence, powerful simulation models are required, representing a good compromise between simulation precision and computation time. This thesis reveals that non-linear lumped-element equivalent-circuit models meet the above described demands in the most promising manner. The power of this modeling concept is demonstrated for supercapacitors, lithium-ion and VRLA batteries. To determine suitable equivalent-circuit topologies as well as to parameterize the models, the method of electrochemical impedance spectroscopy is employed. Sets of impedance spectra are systematically measured. In addition, for a meaningful interpretation of the acquired impedance data, the most important aspects of the theory of the modeled energy storage devices are briefly reviewed. After this, the proposed simulation models are fully parameterized, implemented into a time domain simulation tool and finally thoroughly verified. Impedance-based simulation models of VRLA batteries are currently being successfully employed by the research department of a large car manufacturer. Due to its unique versatility, the impedance-based modeling approach can easily be adapted to other storage technologies in the future.