Implementation of State-of-Charge and State-of-Health Estimation for Lithium-Ion Batteries

An estimation method of the state-of-charge (SOC) and the state-of-health (SOH) for Li-ion batteries is implemented in this paper. For the proposed methods, we defined the ratio between the variations in voltage and the variations in current in each cell during the operation processes of battery modules as the dynamic impedance, which is used to determine the SOC of the battery. Any initial values are unnecessary in the proposed estimation methods, and the proposed dynamic impedance can better reflect the real electrical characteristics of Li-ion batteries than traditional estimation methods. Furthermore, real-time calculations can be achieved using the proposed methods. The SOH of Li-ion batteries decays as the batteries age, which also influences the value of the dynamic impedance. The projection technique is proposed to determine the SOH based on the dynamic impedance. In this study, a real time platform for estimating SOC and SOH is built, a MCU with a battery management system (BMS) is also integrated. The used BMS receives the related information to estimate the SOC and SOH, and comprises some protection devices to increase battery life spans. Some experimental results are presented to verify the accuracy and feasibility of the proposed theoretical predictions.