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Open AccessArticle

SOC Estimation of Multiple Lithium-Ion Battery Cells in a Module Using a Nonlinear State Observer and Online Parameter Estimation

1
Department of Electrical Engineering, Soongsil University, Seoul 06978, Korea
2
Department of Economics, Soongsil University, Seoul 06978, Korea
*
Author to whom correspondence should be addressed.
Energies 2018, 11(7), 1620; https://doi.org/10.3390/en11071620
Received: 2 June 2018 / Revised: 17 June 2018 / Accepted: 18 June 2018 / Published: 21 June 2018
(This article belongs to the Special Issue Power Electronics 2018)
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Abstract

In recent years, electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in electric vehicles (PEVs) have become very popular. Therefore, the use of secondary batteries exponentially increased in EV systems. Battery fuel gauges determine the amount of charge inside the battery, and how much farther the vehicle can drive itself under specific operating conditions. It is very important to provide accurate state-of-charge (SOC) information of the battery module to the driver, since inaccurate fuel gauges will not be tolerated. In this paper, a model-based approach is proposed to estimate the SOCs of multiple lithium-ion (Li-ion) battery cells, connected in a module in series, by using a nonlinear state observer (NSO) and an online parameter identification algorithm. A simple method of estimating the impedance and SOC of each cell in a module is also presented in this paper, by employing a ratio vector with respect to the reference value. A battery model based on an autoregressive model with exogenous input (ARX) was used with recursive least squares (RLS) for parameter identification, in an effort to guarantee reliable estimation results under various operating conditions. The validity and feasibility of the proposed algorithm were verified by an experimental setup of six Li-ion battery cells connected in a module in series. It was found that, when compared with a simple linear state observer (LSO), an NSO can further reduce the SOC error by 1%. View Full-Text
Keywords: state of charge estimation; lithium-ion battery; nonlinear state observer; online parameter estimation; ratio vector state of charge estimation; lithium-ion battery; nonlinear state observer; online parameter estimation; ratio vector
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Tran, N.-T.; Khan, A.B.; Nguyen, T.-T.; Kim, D.-W.; Choi, W. SOC Estimation of Multiple Lithium-Ion Battery Cells in a Module Using a Nonlinear State Observer and Online Parameter Estimation. Energies 2018, 11, 1620.

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