Multi-time scale variable-order equivalent circuit model for virtual battery considering initial polarization condition of lithium-ion battery

An equivalent circuit model is developed for the virtual battery, which plays a key role in the application of the virtual battery. In this paper, a multi-time scale variable-order equivalent circuit model is proposed. The short and long time scale polarization characteristics are simulated respectively by the fractional-order model and the integer-order RC model, and a first-order RC model is used as the transition model between different time scales. Moreover, the time range for short-time scale model parameter identification is determined based on the electrochemical impedance spectroscopy acquired by the wavelet analysis. The evolution rule of short and long time scales model parameters under different initial polarization conditions and current rate is revealed. The model order changes in order of fractional order value, third-order and second-order. The voltage simulation result of the proposed model exhibits good agreement with current profile experiment, where the root mean square error (RMSE) is 2.838 mV. Under the power profile, compared to the conventional RC model, the RMSE of voltage and current simulation can be reduced by 79.65% and 79.27%.