Accurate Remaining Available Energy Estimation of LiFePO 4 Battery in Dynamic Frequency Regulation for EVs with Thermal-Electric-Hysteresis Model

Zhihang Zhang, Languang Lu, Yalun Li (), Hewu Wang () and Minggao Ouyang
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Zhihang Zhang: School of Vehicle and Mobility, Tsinghua University, Beijing 100084, China
Languang Lu: School of Vehicle and Mobility, Tsinghua University, Beijing 100084, China
Yalun Li: School of Vehicle and Mobility, Tsinghua University, Beijing 100084, China
Hewu Wang: School of Vehicle and Mobility, Tsinghua University, Beijing 100084, China
Minggao Ouyang: School of Vehicle and Mobility, Tsinghua University, Beijing 100084, China

Energies, 2023, vol. 16, issue 13, 1-28

Abstract: Renewable energy power generation systems such as photovoltaic and wind power have characteristics of intermittency and volatility, which can cause disturbances to the grid frequency. The battery system of electric vehicles (EVs) is a mobile energy storage system that can participate in bidirectional interaction with the power grid and support the frequency stability of the grid. Lithium iron phosphate (LiFePO 4 ) battery systems, with their advantages of high safety and long cycle life, are widely used in EVs and participate in frequency regulation (FR) services. Accurate assessment of the state of charge (SOC) and remaining available energy (RAE) status in LiFePO 4 batteries is crucial in formulating control strategies for battery systems. However, establishing an accurate voltage model for LiFePO 4 batteries is challenging due to the hysteresis of open circuit voltage and internal temperature changes, making it difficult to accurately assess their SOC and RAE. To accurately evaluate the SOC and RAE of LiFePO 4 batteries in dynamic FR working conditions, a thermal-electric-hysteresis coupled voltage model is built. Based on this model, closed-loop optimal SOC estimation is achieved using the extended Kalman filter algorithm to correct the initial value of SOC calculated by ampere-hour integration. Further, RAE is accurately estimated using a method based on future voltage prediction. The research results demonstrate that the thermal-electric-hysteresis coupling model exhibits high accuracy in simulating terminal voltage under a 48 h dynamic FR working condition, with a root mean square error (RMSE) of only 18.7 mV. The proposed state estimation strategy can accurately assess the state of LiFePO 4 batteries in dynamic FR working conditions, with an RMSE of 1.73% for SOC estimation and 2.13% for RAE estimation. This research has the potential to be applied in battery management systems to achieve an accurate assessment of battery state and provide support for the efficient and reliable operation of battery systems.

Keywords: frequency regulation; electric vehicles; remaining available energy; thermal-electric-hysteresis coupling model; state of charge (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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