| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 105 === Lithium ion batteries possess many advantageous characteristics, like of great power density、portable and having excellent cycle life, and are becoming widely used in electric vehicles (EV). In this study we use a numerical analysis software – Dymola, which is famous in Europe automobile industry, to build a lithium iron phosphate (LFP) battery model. The battery model can be combined with other system engineering model like power train system model in Dymola so that it can help us to enter the automobile market in Europe. Generally, the temperature of LFP batteries rises while discharging. If the battery operates beyond the appropriate temperature range, it will lead to a shorter cycle life of the battery. Moreover, as in many applications the cost of batteries pertains to a significant portion of the total cost, battery lifetime is critical for profitability. However some experiments, such as ageing, are expensive and time consuming and cannot be done comprehensively for every control parameters. Hence, this study aims to develop an accurate model to facilitate the analysis of battery performance. Besides, the safety issue for Li-ion battery is also what people always concerned. Nail penetration into a battery pack, resulting in a state of short-circuit and subsequent burning, is likely to occur in electric vehicle collisions. Therefore in this study, a reliable model to describe the thermal behavior for battery nail penetration test is also developed.
In our battery model, we choose the equivalent circuit model (ECM) framework which resembles the physical processes of a battery with equivalent circuits such that it reduces the complexity of analysis. To prove the reliability of the model, we analyzes the 40138 LFP batteries produced by PSI by simulating the discharge curve and temperature evolution at different C-rate (0.5C, 1C, 2C,5C) of single cells and battery packs. The simulation results under various operation conditions are validated with experimental results. Moreover, we build an ageing model which can predict the long-term battery cycle behavior based on the short-term discharge cycle test of various depth of discharge.
To describe the battery thermal behavior while nail penetrating, we build a heat transfer model by Ansys workbench. This model can capture the temperature evolution trend induced by internal short-circuit and thermal run away. Also, this nail penetration model is validated against a benchmark model for its reliability.
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