A Novel Real-Time State-of-Health and State-of-Charge Co-Estimation Method for LiFePO4 Battery**Supported by the Guangdong Innovation Team Project under Grant No 2013N080, and the Peacock Plan of Shenzhen Science and Technology Research under Grant No KYPT20141016105435850.

Abstract

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 LiFePO4 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 (Rs), parallel resistance (Rp) and parallel capacity (Cp), are identified from a real-time experimental test. Finally we find that Rp and Cp could be utilized to make a judgement on the SOH. More importantly, the linear relationship between Cp and the SOC is established to make the estimation of the SOC for the first time.