Abstract
The deterioration of lithium-ion batteries has been detected by an increase in the battery impedance by means of an alternating current method or a battery capacity test. These methods require an interruption of the operation because the battery has to be removed. A method estimating equivalent circuit parameters of a lithium-ion battery during operation is proposed in this article. The increase in the internal impedance has a close relation to the deterioration of the battery. The circuit is expressed by a resister and an RC parallel circuit connected in series. The parameters can be estimated by applying a convolution technique to the voltage and current fluctuation of the battery during operation. A diagnosis circuit using a microcomputer is developed using a simple algorithm employing z-transformation in the parameter estimation. The estimated parameters depend on its state of charge (SOC) and ambient temperature. The SOC dependency is solved by estimating timing, and the temperature dependency is corrected by a function derived in this article. The deterioration diagnosis of the battery can be applied to a solar power generation system, and the feasibility is discussed in this article.
Highlights
Lithium-ion batteries are used with various apparatus due to their remarkable features, such as high energy density [1]
Using convolution technique and z-transformation is proposed in this article
The effectiveness of the deterioration diagnosis method using the time-domain convolution method shown in Equation (3) is described
Summary
Lithium-ion batteries are used with various apparatus due to their remarkable features, such as high energy density [1]. Sustainable power generations using natural energies such as solar and wind have been introduced to prevent global warming. The lithium-ion battery is used with the power generation systems for stabilizing generated power [2,3]. Its operating voltage, current, and temperature have to be kept within its specification. The battery is led to thermal runaway or over-charge/discharge, and it may result in a burst [4]. Almost all the lithium-ion batteries are used with BMS (battery management system), which monitors the voltage, current, and temperature of the battery [5,6]. Most BMSs do not have the deterioration diagnosis feature
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