Abstract
Ambient temperature affects the performance of a battery power system and its accuracy in state-of-charge (SOC) estimation for electric vehicles and smart grid systems. This paper proposes a battery model that considered ambient temperature, cell temperature, hysteresis voltage and thermal aging on capacity due to multiple charging and discharging. The SOC is then estimated using an extended Kalman filter. Several forms of validation were tested on an actual cell battery under specific ambient temperatures to verify the battery cell model, terminal voltage and SOC estimation performance. The SOC estimation results show an improvement in root-mean-squared error as compared to Extended Kalman Filter (EKF) without considering the temperature dependency. The proposed battery temperature-dependent model gave a smaller root-mean square error in SOC and terminal voltage at 5 °C, 15 °C and 45 °C.
Highlights
Lithium iron phosphate (LiFePO4 ) batteries have become popular for renewable energy storage devices, electric vehicles [1,2,3] and smart grids [4,5,6]
There have been many efforts in recent years to enhance the accuracy of the SOC estimation in a battery management system (BMS) [7]
The results of pulse-relaxation discharge in the electrochemical thermal model [28] describe the dynamic change of Lithium-ion concentration distribution in phases that were useful for analyzing the polarization of the battery
Summary
Lithium iron phosphate (LiFePO4 ) batteries have become popular for renewable energy storage devices, electric vehicles [1,2,3] and smart grids [4,5,6]. The results of pulse-relaxation discharge in the electrochemical thermal model [28] describe the dynamic change of Lithium-ion concentration distribution in phases that were useful for analyzing the polarization of the battery Another pseudo-two dimensional electrochemical thermal model [29] showing the battery pack application was developed for the electric vehicle battery pack and thermal management system to maintain the temperature uniformity and decrease the maximum temperature of the cells. A unified lithium-ion battery model that includes the ambient temperature, cell temperature, thermal aging effect on capacity, hysteresis voltage and its impact on state-of-charge (SOC)-open-circuit voltage (OCV) relationship, hysteresis voltage dynamics and terminal voltage is proposed and validated by an actual experimental test.
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