Application of Voltage Amplification Circuit for Improving State Estimation Accuracy of LiFePO₄ Batteries

LiFePO4 (LFP) batteries are gaining a large market share in the electric vehicle and energy storage system markets due to their high cycle characteristics, excellent price competitiveness, and superior stability. However, the flat open circuit voltage (OCV) characteristics over a wide state of charge (SOC) range limit the application of conventional SOC estimation methods that use OCV levels. Recently, high-accuracy ICs for battery management systems have been developed to address this issue. However, the change in OCV with respect to SOC is only a few mV, which causes difficulty in accurately estimating the state of LFP batteries. This study proposes a voltage amplification circuit using an OP-Amp to improve the state estimation accuracy of LFP batteries. For validation, SOC estimation based on an extended Kalman filter was performed using data collected through the proposed circuit. Experimental results confirm that the accuracy of the measured voltage and SOC estimation have improved compared with those using the conventional circuit.