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In the battery management system, the state of charge (SOC) forecast is the most basic and most important part. The precise estimation of SOC is not only able to provide users with battery power supply situation, it is also the foundation of charging-discharging management and balance control in battery management system.Therefore, how to accurately predict the value of SOC is great significance.Prevention at lithium-ion battery level, this paper is to research the forecasting algorithm of SOC. By the analysis of lithium-ion battery working principle, the emergence and change mechanism of electric quantity can be understood, based on this the battery charge and discharge characteristics was studied and in the process how do the battery current, temperature and other factors effecting on SOC was considered which lay the foundation for estimate of SOC, in the end with analysis of other factors which affect SOC algorithm like self-discharge rate, cycle number and working conditions, This paper describes a new method that by dividing battery into three states, the different algorithm, extended Kalman filter algorithm, open-circuit voltage method and Ah counting method were combined to predict SOC, through the analysis of battery charge-discharge efficiency and regularity for change of the voltage curve, a computing method which was about dynamic changing capacity and accumulation capacity based on coulomb efficiency was gave to improve the Ah counting, then based on this, a more accurate battery-space model was established. Thus the calculation of SOC was completed.In the end, the actual charge-discharge test based on SE60AHA type lithium batteries was accomplished in this paper. During the experiment, the method proposed in this paper was compared with the traditional method under three kinds of conditions, making normal charging and discharging experiment, increasing noise interference on current and changing the value of the SOC initial, in the results, the method used in this paper can not only improve the SOC precision, but also can suppress the noise and correct the initial error.
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