Battery State of Charge Computation Using Voltage and Current Integration
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Solution Overview
Problem
Existing state of charge computation systems for secondary batteries face inaccuracies due to low accuracy in estimating battery impedance voltage, leading to significant errors in calculated state of charge, especially as batteries deteriorate and open voltage becomes unreliable.
Innovation Solution
A state of charge computation system that integrates current measurements with error limits and battery capacity, using multiple estimated state of charge calculations based on open voltage and current integration, to select the most accurate state of charge value within a predetermined cycle, thereby reducing accumulated errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If state of charge is calculated only by integration of charging/discharging current, then calculation is simple, but current detection error accumulates and accuracy deteriorates over time
Solution Approach 1:
The patent combines two different calculation methods: current integration method and open voltage estimation method. The control unit calculates state of charge using both methods simultaneously and selects the more accurate result based on comparison, thereby merging the advantages of both approaches to maintain accuracy while managing complexity.
Solution Approach 2:
The system uses feedback by comparing results from two different calculation methods. The control unit continuously monitors both current integration results and open voltage estimation results, and uses this comparison feedback to determine which method provides more accurate results under current conditions, thereby correcting accumulated errors.
2Measurement precision
If battery open voltage is used to calculate state of charge, then current integration error is corrected, but accuracy is low when battery impedance voltage estimation is inaccurate
Solution Approach 1:
The system dynamically switches between calculation methods based on real-time conditions. The control unit determines which method (current integration or open voltage estimation) is more reliable under current battery conditions and uses that method, making the calculation approach adaptive rather than static.
Solution Approach 2:
The patent changes the calculation parameters based on battery state. When battery impedance is high or open voltage estimation is unreliable, the system switches to current integration method. When open voltage estimation is reliable, it uses that method instead, thereby changing the calculation parameters adaptively to maintain accuracy.
3Measurement precision
If multiple estimated state of charge values are calculated and compared, then accuracy is improved, but device complexity increases
Solution Approach 1:
The patent segments the state of charge calculation into two independent calculation paths: current integration path and open voltage estimation path. Each path is calculated separately and then compared, allowing the system to maintain multiple calculation methods without creating a monolithic complex system.
Data Source
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AI summary
The disclosed charging-rate computation system outputs a first estimated charging rate on the basis of the estimated open-circuit voltage of a secondary cell, outputs a second estimated charging rate on the basis of the cell capacity of the secondary cell and the results of integrating the measured current of the secondary cell as well as the upper error bound thereof over a predetermined cycle, outputs a third estimated charging rate on the basis of the cell capacity and the results of integrating the measured current as well as the lower error bound thereof over the predetermined cycle, and outputs a fourth estimated charging rate on the basis of the cell capacity and the results of integrating the measured current over the predetermined cycle. In the time period within the predetermined cycle, the abovementioned fourth estimated charging rate is output as the charging rate, and at the endpoint of the predetermined cycle: when the first estimated charging rate is a value of an estimated charging rate between the second estimated charging rate and the third estimated charging rate, the first estimated charging rate is considered the charging rate; when the first estimated charging rate is a value that is at least the second estimated charging rate, the second estimated charging rate is considered the charging rate; and when the first estimated charging rate is less than or equal to the third estimated charging rate, the third estimated charging rate is considered the charging rate.