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LiFePO4 Battery Calculation Model for EV

Though LiFePO4 battery has the property of better safety and longer lifetime, the number of charge/discharge cycle has significant impact on the lifetime and power quality of LiFePO4 battery. Therefore, we also investigate the relationship between voltage variation and state-of-charge (SoC) and storage time and cycle number. The creative point of this research is that the developed mathematical model with dual exponential terms not only represents the characteristics of two RC networks in the modified Thevenin circuit, but also explains the electrochemical reactions, based on Butler-Volmer kinetics. The parameters of exponential terms are calculated by fitting the discharging curve (voltage VS SoC) which are highly related to the battery storage time and cycle number since the batteries with different conditions are used for measurements. Finally, this model satisfactorily captures the discharging behaviors of most tested batteries with an RMSE of less than 0.002. In addition, this method can also be used to distinguish batteries under various conditions without the need to perform complicated calculations.

 

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使用於電動車之磷酸鋰鐵電池模型

LiFePO4電池為電動車重要的零組件之一，具有更好的安全性和更長的壽命的性質，充電/放電循環的次數對LiFePO4電池的壽命和能量具有顯著的影響。因此，我們研究了電壓和充電狀態（SoC）、儲存時間和循環次數三者之間的關係。本研究的創新在於：開發具有雙指數項的數學模型不僅代表了在改進的Thevenin電路中的兩個RC網絡的特性，而且解釋了基於Butler-Volmer動力學的電化學反應。通過擬合與電池儲存時間和循環數高度相關的放電曲線（電壓V.S SoC）來計算指數項的參數，因為具有不同條件的電池用於測量。最後，該模型令人滿意地捕獲大多數測試電池的放電行為，RMSE小於0.002。此外，該方法還可以用於在各種條件下區分電池，而不需要執行複雜的計算。

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