An Equivalent Circuit Model of Lithium-Ion Batteries for Commercial Charging Strategy: Application to Step Charge

Lithium-ion batteries represent a complex and nonlinear voltage behaviour on various time scales. Battery models are needed to analyze and estimate the battery behaviour and determine their suitability for practical applications. Battery model simulations in previous studies were mainly based on pulse charge and discharge cases. The current amplitude used in the test cases was limited, and the temperature factor of the battery model was neglected. The simulation conditions above were significantly different from those in practical applications. In this paper, an equivalent circuit model considering the temperature factor is developed to simulate the practical applications of lithium-ion batteries. Experimental tests for parameterization are applied to the commercially available 189 Ah lithium iron phosphate battery cells under a wide range of experimental conditions. The parameters are obtained through experimental tests and are used to build the equivalent circuit model of the battery. The parameterized model is modified to fix the voltage error in both low and high state-of-charge levels before model verification. Constant-current charge test and step charge test are both applied to the proposed model and the comparative model without temperature factor to verify and compare the model accuracy. Simulation results are compared against laboratory experimental results under the same conditions. For most of the state-of-charge levels, the voltage error of the proposed model lies below 0.5% for the constant-current charge test and 1% for the step charge test. Compared with the model without the temperature factor, the proposed model demonstrates the average reductions in RMSE and MAE of 49.89% and 47.74% under constant-current charge test, and 59.72% and 71.04% under step charge test, respectively. Increased accuracy is obtained for practical applications compared with previous studies.