Joint Estimation of SOC and SOH for Lithium-Ion Batteries via Adaptive Variable Structure Observers

Abstract

A new method for obtaining the state of charge (SOC) and state of health (SOH) in real time for lithium-ion batteries is proposed on a two-order battery mode of rewritten mode equations. The mode equations are being rewritten to solve the difficulties of obtaining the error of state variable required for the observer feedback. Four adaptive variable structure observers (AVSOs) collaborate to estimate the four state variables to get SOC. Two AVSOs calculate SOH by estimating the battery’s internal resistance and capacity. In addition, to lessen the presence of the switching term of sliding mode observer (SMO) that causes chattering, a “trans” function is used in AVSOs. To ensure that the gain is appropriate, an adaptive gain is concurrently constructed in AVSOs. Finally, the experiments show that its average values of mean absolute error and root mean square error in three temperatures are lower 3.2% and 4.7% for SOC and 0.7% and 0.9% for SOH compared to the terminal SMO.