An equivalent circuit model for state of energy estimation of lithium-ion battery

For a Li-ion battery based energy storage system, the state of energy is a key index for the energy management and operation optimization. In the actual Li-ion batteries based energy storage system in building environment, the varying load current will lead to the estimated battery's residual energy deviated from the real value. To solve this problem, an equivalent circuit model is presented for the Li-ion battery's state of energy estimation during and after discharging process. The state of energy is introduced in the proposed approach to replace the traditional index SOC, to describe the electrical behaviors and the residual energy of the Li-ion battery under dynamic load current conditions, so that the battery's internal energy loss on its internal resistance and during the electrochemical reaction processes, as well as the effects of the decrease of the OCV during discharging are taken into consideration. Experimental data of the previous study regarding energy efficiency of Li-ion batteries used as energy storage devices in building is utilized in the present study. Finally, the simulation results on 20 Ah LTO batteries indicate that the proposed equivalent circuit is competent to predict the state of energy accurately. What's more, state of energy appears an improvement over SOC in terms of accuracy in capturing battery's energy changes. Thus, this study provides a viable solution for estimating Li-ion battery's SOE and capturing the battery's energy behaviors under dynamic loads.