Analytic Estimation of Three-dimensional Variables for SOC in Iron Phosphate Lithium-ion Battery

Abstract A three-dimensional variable analysis method for the estimation of state of charge (SOC) in iron phosphate lithium-ion battery is proposed. The 100Ah/3.6V iron phosphate lithium-ion battery is regarded as the research object. The relationship between SOC and single factor was got by using the control variable method, and the specific expression was got by using the way of data fitting. Then the situation when multiple factors work together is analyzed, and the function between SOC and the three factors—temperature(T),charging voltage(U) and charging current(I) was got by using the way of data fitting. The feasibility of this method is tested with experimental data, and the error analysis has been done. The results indicate that the SOC estimation error of this method is less than 2%. The two-dimensional surface and contour curve is given when charging voltage(U) is 3.3V and under the condition of different charging current and temperature.