A novel model of the initial state of charge estimation for LiFePO4 batteries

Abstract The State-of-Charge (SOC) is an important performance parameter and evaluation index in rechargeable battery energy storage systems. Here, a novel smart estimation method based on coulomb counting is proposed in order to enhance estimation accuracy. Firstly, an enhanced model for the initial SOC (SOC 0 ) estimation based on dynamic multi-parameter method is investigated, because SOC 0 plays a key role in calculating real SOC in-time. All the design limits, such as voltage, temperature, are used as its constraints. And more importantly, the relaxation effect also is considered. The SOC 0 with the main parameters satisfies Gauss function. Secondly, the quantitative relations of the energy efficiencies are measured and analyzed under the moderate discharging situation. The results show a negative quadratic correlation between energy efficiency and rate, and exhibit a reduction in energy efficiency as rate increases. Lastly, a test with several consecutive hybrid pulse power characteristic test profiles is carried. The experimental results indicate that the correction of SOC 0 can efficiently limit the error below 4%, and also exhibit that considering on the effect of energy efficiency can further reduce its estimation error.