Abstract

The use of equivalent circuit models for simulating the operating behavior of lithium-ion batteries is well established in the automotive and the renewable energy sector. However, finding the correct parameter set for these models is still a challenging task. This manuscript proposes a comprehensive methodology for estimating the required, temperature dependent simulation parameters from battery measurements. Based on a specific load current and prior system knowledge, an algorithm first analyses the correlation between current steps and the measured terminal voltage. Second, a combination of particle swarm optimization and Gauss–Newton algorithm fits the initially estimated parameters from the first algorithm to the measurement data. Finally, the dependency of each simulation parameter on both the state of charge and the battery temperature is determined. As this contribution aims at modeling reversible effects of lithium-ion batteries, ageing effects are neglected. The validation against measurement data proves that the generated parameter set enables the user to accurately reproduce and investigate the operating behavior of the chosen battery. Applied to a lithium-iron-phosphate cell, the comparison between measurements and simulations in standardized real-life automotive driving cycles (Artemis, FTP75 and WLTC) shows a terminal voltage error of less than 1.09% within the typical operational window between state of charge 0.15 and 0.95.

Highlights

  • The use of equivalent circuit models for simulating the operating behavior of lithium-ion batteries is well established in the automotive and the renewable energy sector

  • T HE use of mathematical- or electrical equivalent circuit (EEC) models for simulating the operating behaviour of different types of batteries is already well-established in the automotive and the sustainable energy sector [1]–[8]

  • A high number of different approaches is found in this review, while only one author [11] proposes the use of a Particle Swarm Optimisation (PSO) method for identifying EEC parameters, in this case for online diagnostics

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Summary

MODELING AND SIMULATION

T HE use of mathematical- or electrical equivalent circuit (EEC) models for simulating the operating behaviour of different types of batteries is already well-established in the automotive and the sustainable energy sector [1]–[8]. In their work Reuter et al [17] compare different optimisation methods In this comparison the GN is found to be very accurate for estimating the parameters of a Lithium-Ion battery but can be rather slow or requires high computational power, respectively. Shen et al [18] proofed this method to be suited for battery parameter estimation by combining a PSO with a Levenberg-Marquardt algorithm to gain electrochemical parameters like potential and current density. In their model they neglect the temperature dependency of the parameters, which is one of the main innovations of this work.

EQUIVALENT CIRCUIT MODELS
BATTERY MEASUREMENT
ALGORITHM FOR PARAMETER ESTIMATION
Correlation Between Terminal Voltage and Current
Particle Swarm Optimisation
Gauss-Newton Algorithm
Comparison of the Optimisation Algorithms
Temperature Dependency of the Parameters
VALIDATION
Findings
CONCLUSION AND OUTLOOK

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