Monitoring and battery management are crucial for a safe, reliable and long-living operation time of battery packs in all kinds of operation. This paper describes the general functional units of battery management systems in a systematic way and discusses the battery monitoring. The battery management system comprises the battery monitoring, battery diagnosis, electrical and thermal management, and the cell balancing system. The battery management is a consultant to the vehicle energy management system. It helps the energy management to find optimum operating strategies. The basic structure of the battery management systems is quite similar for lithium-ion batteries and super caps. Beside the general functionality a focus is on the OCV effects in this paper. OCV is used in most algorithms for long-term stabilisation of current counters and for capacity loss calculations. Therefore this paper puts a focus on experimental results and interpretation of OCV of different lithium-ion battery products with different materials. Results show, that SOC errors occurring from OCV deviations from the real equilibrium and can be significant for LiFePO4 where as standard NMC and NCA materials show a fast relaxation to the equilibrium voltage. In the report are shown several impact factors on the equilibrium voltage measurement. Deviations from the real OCV depend on the relaxation time and hysteresis effects. In fact for the application the occurring error due to deviations from the real OCV are of relevance. They determine the error in SOC determination. The calculated error due the OCV deviations as a function of time following the last charging or discharging event is shown.
Monitoring and state-of-charge diagnostics of lithium-ion batteries and supercapacitors
2011
16 Seiten, 18 Bilder, 1 Tabelle, 2 Quellen
Conference paper
English
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