Secondary Battery Impedance Estimation via Stability-Checked Fourier Transform
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Solution Overview
Problem
Existing methods for estimating the deteriorated state of secondary batteries in vehicles lack accuracy due to variations in current, temperature, and state of charge during data acquisition, which can lead to inaccurate impedance calculations and reduced estimation precision.
Innovation Solution
A method involving a control device that obtains and stores voltage and current data over a prescribed period, calculates changes in current, temperature, and state of charge, and only performs Fourier transform when conditions are stable, allowing for accurate impedance component calculation for each frequency bandwidth, thereby improving estimation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage and current data are obtained for a prescribed period to calculate impedance through Fourier transform, then impedance calculation is performed, but current, temperature, or SOC may vary during data acquisition leading to inaccurate impedance values
Solution Approach 1:
The system performs preliminary checks on current, temperature, and SOC values before initiating Fourier transform calculation. By evaluating whether these parameters remain within acceptable variation ranges during the data acquisition period, the system determines in advance whether the collected data is suitable for accurate impedance calculation, thus preventing inaccurate results from unstable conditions
Solution Approach 2:
The system continuously monitors current, temperature, and SOC values during data acquisition and uses this feedback to determine whether to proceed with impedance calculation. When parameter variations exceed thresholds, the system adjusts by selecting alternative time periods or adjusting acquisition conditions, ensuring that impedance calculations are only performed when reliability conditions are met
2Measurement precision
If data is collected over a longer prescribed period to improve Fourier transform accuracy, then impedance calculation precision improves, but the likelihood of current, temperature, or SOC variation increases
Solution Approach 1:
The system dynamically adjusts the data acquisition period length based on real-time monitoring of current, temperature, and SOC stability. When conditions are stable, longer acquisition periods are used to improve Fourier transform accuracy. When conditions become unstable, the system shortens the acquisition period or adjusts parameters, creating a dynamic adaptation that balances precision requirements with operational stability
3Productivity
If impedance calculation is performed continuously to monitor battery deterioration, then real-time deterioration tracking is achieved, but computational load and processing time increase
Solution Approach 1:
The system performs impedance calculation selectively rather than continuously - only when stability conditions for current, temperature, and SOC are satisfied. This partial action approach achieves effective real-time monitoring by capturing deterioration at appropriate moments without the excessive computational burden of continuous calculation at all times
Solution Approach 2:
The system extracts and evaluates specific stability criteria (current variation range, temperature variation range, SOC variation range) from the overall impedance calculation process. By separating the stability verification step from the Fourier transform calculation, the system reduces processing complexity while maintaining monitoring effectiveness
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures that impedance calculations reflect the actual conditions of the battery more accurately, enhancing the precision of secondary battery state estimation and enabling more effective monitoring of deterioration.
Implementation Method 1
calculating, by subjecting voltage values and current values of the secondary battery obtained the plurality of times and stored in the memory to frequency conversion (Fourier transform), an impedance component for each frequency bandwidth of the secondary battery
Data Source
AI summary
A method of estimating a deteriorated state of a battery includes steps S102 to S110. S102 is a step of obtaining a voltage and a current of the battery a plurality of times for a data acquisition period. S104 is a step of calculating an amount of change in current, an amount of change in temperature, and an amount of change in SOC during the data acquisition period. S106 is a step of obtaining an allowable amount of change in current, an allowable amount of change in temperature, and an allowable amount of change in SOC based on an average temperature. S110 is a step of calculating an impedance component for each frequency bandwidth based on the voltage and the current by subjecting the voltage and the current to Fourier transform when all amounts of change are smaller than the allowable amounts of change.