Extraction of thevenin-based equivalent circuit of multi-cell lead acid battery pack and SoC estimation

Year 2024, Volume: 3 Issue: 1, 93 - 100, 30.06.2024

Hayri Arabacı , Kemal Erdoğan

Abstract

Lead acid batteries are widely used in UPS due to their cheapness. In case of mains power failure, the length of the operating period powered by the battery depends on the energy capacity of the battery. In this case, predicting the remaining time depending on usage is important for the healthy operation of the system. Determining the remaining time can be done by monitoring the SoC of the batteries. SoC monitoring can be done using equivalent circuit models of the battery. In systems where a single battery cell is used, the equivalent circuit is generally taken into account for a single cell. Nowadays many serially connected batteries are used in UPS. In this case, it becomes difficult to make calculations in the equivalent circuit created by connecting the single cell equivalent circuit in series. In this study, the approach of using a single equivalent circuit model to be created for the entire system is proposed. In the study, the Thevenin equivalent circuit model of an uninterruptible power supply battery group, in which 8 batteries (12V) are connected in series, was created with only three parameters. The accuracy of the created equivalent circuit was ensured by comparing it with the values calculated using the current counting method. First, the discharge curve of the battery was obtained. SoC-Open Circuit Voltage graph was created from these curves. Equivalent circuit parameters were calculated from the dynamic behavior of the battery. During the process of fully discharging the battery, the values of SoC corresponding to the battery voltage were determined by counting the current. The values of SoC obtained as a result of the current counting process were compared with the values calculated through the equivalent circuit. As a result of the comparisons, an average accuracy rate of 99.85% was achieved in estimating the SoC. These results show that the proposed method can be used to estimate the SoC in systems using serially connected batteries.

Keywords

Battery Equivalent Circuit Model, Energy Storage, Lead Acid Battery, Parameter Estimation, SoC, State of Charge

Ethical Statement

As the authors of this study, we declare that all ethical standards have been complied with.

Supporting Institution

This study was supported by Panoteknik Generator Electricity and KOSGEB within the scope of project number 359846.

EXTRACTION OF THEVENIN-BASED EQUIVALENT CIRCUIT OF MULTI-CELL LEAD ACID BATTERY PACK AND SoC ESTIMATION

Abstract

Lead acid batteries are widely used in UPS due to their cheapness. In case of mains power failure, the length of the operating period powered by the battery depends on the energy capacity of the battery. In this case, predicting the remaining time depending on usage is important for the healthy operation of the system. Determining the remaining time can be done by monitoring the SoC of the batteries. SoC monitoring can be done using equivalent circuit models of the battery. In systems where a single battery cell is used, the equivalent circuit is generally taken into account for a single cell. Nowadays many serially connected batteries are used in UPS. In this case, it becomes difficult to make calculations in the equivalent circuit created by connecting the single cell equivalent circuit in series. In this study, the approach of using a single equivalent circuit model to be created for the entire system is proposed. In the study, the Thevenin equivalent circuit model of an uninterruptible power supply battery group, in which 8 batteries (12V) are connected in series, was created with only three parameters. The accuracy of the created equivalent circuit was ensured by comparing it with the values calculated using the current counting method. First, the discharge curve of the battery was obtained. SoC-Open Circuit Voltage graph was created from these curves. Equivalent circuit parameters were calculated from the dynamic behavior of the battery. During the process of fully discharging the battery, the values of SoC corresponding to the battery voltage were determined by counting the current. The values of SoC obtained as a result of the current counting process were compared with the values calculated through the equivalent circuit. As a result of the comparisons, an average accuracy rate of 99.85% was achieved in estimating the SoC. These results show that the proposed method can be used to estimate the SoC in systems using serially connected batteries.

Keywords

Battery Equivalent Circuit Model, Energy Storage, Lead Acid Battery, Parameter Estimation, SoC, State of Charge

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