Combined battery SOC/SOH estimation using a nonlinear adaptive observer

Abstract

This work presents a modeling and estimation techniques for State of Charge and State of Health estimation for Li-ion batteries. The analysis is done using an adaptive estimation approach for joint state and parameter estimation and by simplifying an existing nonlinear model previously obtained from experiments tests. A switching mechanism between two observers, one for the charging phase and one for the discharging phase, is done to avoid transients due to the discontinuity of model's parameters. Simulations on experimental data show that the approach is feasible and enhance the interest of the proposed estimation technique

Real-Time Implementation of an Extended Kalman Filter and a PI Observer for State Estimation of Rechargeable Li-Ion Batteries in Hybrid Electric Vehicle Applications—A Case Study

“…The main factors that affect the Li-Ion battery dynamics in realistic operating conditions are summarized with more details in [18]. Amongst these factors, we highlight the following:…”

“…The electrical circuit model is relatively accurate to capture the dynamic circuit characteristics of a battery cell, such as the open-circuit voltage, terminal voltage, transient response, and self-discharge. However, this model is unable to capture the nonlinear capacity behaviors, such as the rate capacity effect and recovery effect of the battery due to the use of a constant capacitance to represent the remaining usable capacity of the battery [18,19]. Nevertheless, considering the modeling errors, capacity variation, and the additional output sensor noise, the 2RC EMC Li-Ion battery model whose dynamics is given by the Equations (5) and (6) is not sufficient to model the entire dynamics of the Li-Ion battery.…”

“…The "excessive currents or a high ambient temperature will cause the battery cell temperature to rise and the resulting expansion of the active chemicals will in turn cause the internal pressure in the battery cell to rise. Overcharging also causes a rise in temperature, but more seriously, overcharging can also cause the release of gases resulting in an even greater build up in the internal pressure", as is stated in [18]. An increased pressure tends to magnify the effects of high temperature by increasing the rate of the chemical actions in the battery cell.…”

“…The thumb rule is that "for every 10 • C increase in temperature the reaction rate doubles". Thus, an hour at 35 • C is equivalent to two hours at 25 • C in battery life, thus the heat is one of the strongest enemy for the battery; even small increases in temperature have a great impact on battery performance [18].…”

On-Board State-of-Charge Estimation of Li-Ion Battery in Hybrid Electric Aircraft Vehicles Using State Estimators – Case Study

“…The first estimator, detailed also in [8], is an improved version of an extended Kalman filter (EKF), well documented in [4][5][6] and suggested also in [10], such that to estimate the Li-Ion battery SOC much accurately. The second SOC estimator is a nonlinear observer described in detail in [9] that is more simple to be implemented in real-time compared to the one described in [13].…”