Abstract
The lithium-ion batteries in the electric vehicles are nonlinear systems with complex electrochemical dynamics, and estimation of battery state-of-charge (SOC) is affected by factors such as environmental temperature and battery current. Considering the above problems, the accurate estimation of battery SOC has always been a difficult and the critical issue of battery management system (BMS). In this paper, the constant phase element (CPE) is introduced to the traditional time domain circuit model by analyzing the electrochemical impedance spectra of lithium-ion batteries. Accordingly, an equivalent circuit model based on electrochemical impedance is constructed by using fractional order theory, which has specific physical significant, leading to the improved estimation accuracy to represent battery voltage. Moreover, the polarization resistance in the model is replaced by Butler-Volmer (BV) equation, which can solve the problem caused by large current and temperature variation during the actual operation of electric vehicles. Next, based on the model, an $\text{H}\infty $ observer is designed for battery SOC estimation, and the proposed SOC observer is tested by real-time experimental data of battery. The efficiency of the proposed model and observer are validated by some simulations and experiment tests.
Highlights
With the promotion of renewable energy, more and more attention has been paid to electric vehicles [1], [2]
To accurate estimate the SOC of lithium-ion batteries in electric vehicles, an H∞ observer is proposed based on a novel equivalent circuit model of electrochemical impedance
The size of r1 determines the distance from the center of the arc to the real axis in the mid-frequency of the Electrochemical impedance spectroscopy (EIS) curve in Fig.1, and r2 determines the slope of the straight line in the low-frequency section of the curve [24]
Summary
With the promotion of renewable energy, more and more attention has been paid to electric vehicles [1], [2]. N. Chen et al.: Estimating the SOC of Lithium-Ion Battery Using an H-Infinity Observer method may not even be convergent with bad parameters selection when the training data cannot completely cover the present operating conditions [8]. Han et al [21] developed a simplified pseudo-two-dimensional (SP2D) model, which could simulate the battery efficiently without too much loss of accuracy Base on this model, an estimation algorithm using the Luenberger observer is proposed. To accurate estimate the SOC of lithium-ion batteries in electric vehicles, an H∞ observer is proposed based on a novel equivalent circuit model of electrochemical impedance. In the mid-frequency region, the EIS curve is a semi-circular curve segment, which is related to the double electric layer at the interface between the battery electrode and electrolyte This characteristic is described by parallel connection of a resistor and a CPE. The size of r1 determines the distance from the center of the arc to the real axis in the mid-frequency of the EIS curve in Fig., and r2 determines the slope of the straight line in the low-frequency section of the curve [24]
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