An Accurate Lithium-Ion Battery Gas Gauge Using Two-Phase STC Modeling

The lithium-ion (Li-ion) battery is a time-varying, nonlinear component. Its discharge characteristic is dependent on discharge current, loading change scheme, ambient temperature, and initial state-of-charge (SoC), and hence its remaining time can vary with the discharge operating conditions in a manner of nonlinear relationship. The non-linearity behavior makes the accurate gas-gauge of Li-ion battery very difficult. This paper presents an efficient scheme to simplify the estimation of battery service time with high-degree of accuracy. According to the typical discharge characteristic of Li-ion batteries, we applied a two-phase single-time-constant (STC) model for the gas-gauging strategy and parameterize the discharge operating conditions in terms of the first-phase gradient, the knee voltage, and the second-phase gradient, instead of using complex curve-fitting equations. As shown in the experimental results, the accuracy of predicted remaining time is less than 1% for constant current cases, and 10% for loading change cases.