Adaptive parameter identification and State-of-Charge estimation of lithium-ion batteries

Abstract

Estimation of the State of Charge (SOC) is a fundamental need for the battery, which is the most important energy storage in Electric Vehicles (EVs) and the Smart Grid.Regarding those applications, the SOC estimation algorithm is expected to be accurate and easy to implement. In this paper, after considering a resistor-capacitor (RC) circuit-equivalent model for the battery, the nonlinear relationship between the Open Circuit Voltage (Vod and the SOC is described in a look up table obtained from experimental tests. Assuming piecewise linearity for the Voc -SOC curve in small time steps, a parameter identification technique is applied to the real current and voltage data to estimate and update the parameters of the battery at each step. Subsequently, a reduced-order linear observer is designed for this continuously updating model to estimate the SOC as one of the states of the battery system. In designing the observer, a mixture of Coulomb counting and Voc algorithm is combined with the adaptive parameter-updating approach and increases the accuracy to less than 5% error. This paper also investigates the correlation between the SOC estimation error and the observability criterion for the battery model, which is directly related to the slope of the V oc-SOC curve.

Validation of eAircraft battery simulation approach using field measurement data

“…Theoretically, all parameters vary with current, temperature, SoH, SoC, etc [4], [8]. Battery model using such topology can be effectively identified to provide parameters as multivariable nonlinear functions [2], [4], [8].…”

“…Battery model using such topology can be effectively identified to provide parameters as multivariable nonlinear functions [2], [4], [8]. However, in the described model the priority of some parameter considerations are boosted, others are decreased or totally neglected in respect of the application and regarding the model operation on battery pack level defined as in [1].…”

“…The number of RC pairs can be chosen to fit to the experimental data, but at the cost of greatly increased time for the identification process of the model parameters. The 2-RC branch model is widely accepted as the practically best trade-off between model accuracy and complexity [2], [3], [8]. So the envelopes of the model discharge curves fit to the measurement data while the cost of the identification process is kept acceptably low.…”

“…(1) where i c is positive when the cell is charged and negative when discharged. The series resistor, R 0 , accounts for the ohmic losses in the cells and the two RC pairs, R 1 C 1 and R 2 C 2 account for the diffusive, in other words, transient losses [3], [6], [7], [8]. The number of RC pairs can be chosen to fit to the experimental data, but at the cost of greatly increased time for the identification process of the model parameters.…”

Examination of the effect of sensor properties on the secondary battery model in simulation environment

“…There are several methods available for determining the U OC -SOC diagram [4], [6]. Open circuit voltage-time diagram is shown in Fig.…”