The state of charge(SOC) and state of health(SOH) are two of the most important parameters of Li-ion batteries in industrial production and in practical applications.The real-time estimation for these two parameters is crucial to realize a safe and reliable battery application.However,this is a great problem for LiFePO_4 batteries due to the large constant potential plateau in the charge/discharge process.Here we propose a combined SOC and SOH co-estimation method based on the experimental test under the simulating electric vehicle working condition.A first-order resistance-capacitance equivalent circuit is used to model the battery cell,and three parameter values,ohmic resistance(R_s),parallel resistance(R_p) and parallel capacity(C_p),are identified from a real-time experimental test.Finally we find that R_p and C_p could be utilized to make a judgement on the SOH.More importantly,the linear relationship between C_p and the SOC is established to make the estimation of the SOC for the first time.
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