Fractional-order Modeling and Time Domain System Identification for Lithium-ion Battery on Electric Vehicle

Battery technology is critical to the development of electric vehicles. This paper presents a fractional-order model (FOM) for Lithium ion batteries with a constant phase element (CPE) in order to accurately describe the battery dynamics. To solve the fractional-order system control problem, the Oustaloup recursive approximation method was selected to model the fractional differentiation operator in integer order state-space form. The multi-swarm particle swarm optimization (MPSO) algorithm was implemented to identify the model parameters using time-domain battery test data. The model accuracy was measured by the average root-mean-squared error (RMSE) between the test datasets and the output from the optimized model. The validation result suggested that the FOM has better accuracy with smaller RMSEs compared with 1-RC model. With good accuracy, the derived FOM can be used in SOC estimation, battery aging analysis, etc.