SOC estimation algorithm for the multiple lithium-ion batteries

초록

Lithium-Ion batteries are being popularly used in hybrid electric vehicles (HEVs), plug in electric vehicles (PEVs) and electric vehicles (EVs) due to its advantages such as high energy density, long cycle life and low self-discharge. Since the battery module is composed of many cells connected in series and parallel, it is important to get the accurate state information of each cell. In this paper a model-based approach to estimate the State-of-Charge (SOC) of multiple battery cells in a module by using a nonlinear state observer and online parameter identification is proposed. The battery impedance is calculated from the dynamic fraction of the battery voltage and it is used for the SOC estimation by a nonlinear state observer. A simple method to estimate the impedance and SOC of each cell in a module by employing a ratio vector with respect to the reference value is also presented. The variation in the battery parameters is considered by using an online parameter identification with Auto Regressive with eXogenous input (ARX) to guarantee the reliable estimation results under the various operating condition. The validity and feasibility of the proposed algorithm is verified by the experimental results.