Battery SOC Estimation Using Current-Based Dual Calculation Paths
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of batteries in electric vehicles, such as Coulomb counting and impedance measuring, face challenges with accuracy and computational efficiency, especially as the number of battery cells increases, leading to prolonged calculation times and increased memory usage.
Innovation Solution
A battery management system that employs a current sensor, relay, and main control circuit to measure battery current and cell voltages, selecting between two methods for estimating SOC based on current intensity, allowing for reduced calculation processes and memory usage by substituting current SOC values with previous values when changes are small, and using a representative value to estimate SOC deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the SOC of a plurality of battery cells is calculated by combining individual cell SOC values, then the accuracy of overall battery SOC estimation is improved, but the calculation time and memory usage increase significantly
Solution Approach 1:
The battery system is divided into multiple battery modules, each containing multiple battery cells. The SOC estimation is performed segmentally by first calculating representative values for each module, then combining module-level SOC estimates to obtain the overall battery SOC. This segmentation approach reduces the computational complexity compared to calculating individual cell SOC values and then combining them, as it aggregates data at the module level first, thereby reducing calculation time while maintaining acceptable accuracy.
2Measurement precision
If the SOC of a plurality of battery cells is calculated by combining individual cell SOC values, then the accuracy of overall battery SOC estimation is improved, but the memory space required increases
Solution Approach 1:
The battery system is divided into multiple battery modules, each containing multiple battery cells. The SOC estimation is performed segmentally by first calculating representative values for each module, then combining module-level SOC estimates to obtain the overall battery SOC. This segmentation approach reduces the computational complexity compared to calculating individual cell SOC values and then combining them, as it aggregates data at the module level first, thereby reducing calculation time while maintaining acceptable accuracy.
3Productivity
If Coulomb counting method is used to estimate SOC, then the SOC can be estimated based on discharged current measurement, but measuring errors accumulate over time reducing estimation accuracy
Solution Approach 1:
The system employs a dual-method approach that incorporates feedback mechanisms. The Coulomb counting method provides continuous SOC estimation based on current measurements, while the impedance measuring method provides periodic reference measurements of open circuit voltage. By comparing and adjusting the Coulomb counting results against the impedance method results, the system corrects accumulated errors while maintaining the efficiency of continuous monitoring.
4Measurement precision
If impedance measuring method is used to estimate SOC, then the SOC can be estimated based on open circuit voltage measurement, but the measurement process is time-consuming and reduces productivity
Solution Approach 1:
The system uses the impedance measuring method periodically rather than continuously. The open circuit voltage measurements are taken at specific intervals to provide reference SOC values, while the Coulomb counting method operates continuously for real-time monitoring. This periodic application of the more accurate but slower impedance method allows for error correction without significantly impacting overall system productivity.
Data Source
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AI summary
The present disclosure relates to a method for estimating a state of charge (SOC) of a battery and a battery management system applying the same. A method for estimating a SOC of a battery in a method for estimating a SOC of a battery module assembly including battery modules respectively including a plurality of battery cells includes: receiving a battery current from a current sensor; comparing the battery current and a threshold current, and selecting a method for estimating a first SOC or a method for estimating a second SOC according to a comparison result; estimating a SOC of the cells according to the selected method for estimating a state of charge; and estimating the SOC of the battery module assembly by combining the estimated SOC of the battery cells.