Secondary Battery Deterioration Estimation via Frequency-Filtered Impedance
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Solution Overview
Problem
Existing methods for estimating the deterioration state of secondary batteries in vehicles face accuracy issues due to decreased Fourier transform accuracy when certain conditions are met, leading to inaccurate impedance calculation and subsequent deterioration state estimation.
Innovation Solution
A method involving a controller that acquires and stores voltage and current values, performs frequency conversion, and determines whether specific conditions are met to decide on impedance component calculation, excluding data that satisfies certain conditions to improve accuracy, and considers current, temperature, and SOC variations to reflect dependencies in impedance calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Fourier transform is performed on current values to calculate impedance components for each frequency, then the deterioration state can be estimated, but the accuracy decreases when specific current value conditions are met
Solution Approach 1:
The patent applies preliminary action by checking whether specific conditions (first condition and second condition) are satisfied for current values before performing Fourier transform. This pre-check prevents performing transform on data that would yield inaccurate results, thereby maintaining measurement precision while avoiding reliability issues.
Solution Approach 2:
The patent extracts and excludes current value data that satisfies the problematic conditions (first condition: current in first frequency range > first reference value; second condition: current in second frequency range < second reference value) from the Fourier transform process. By removing this problematic data subset, the overall accuracy of impedance calculation is improved.
2Measurement precision
If impedance components are calculated for all frequency ranges, then comprehensive deterioration estimation is achieved, but calculation time increases
Solution Approach 1:
The patent applies partial action by selectively calculating impedance components only for frequency ranges where the current values do not satisfy the problematic conditions. Instead of performing Fourier transform on all data, it performs transform only on valid data subsets, reducing calculation time while maintaining comprehensive deterioration estimation through multi-frequency analysis.
3Measurement precision
If current variation width, temperature variation width, and SOC variation width are considered in data selection, then impedance calculation accuracy is improved, but the complexity of the estimation method increases
Solution Approach 1:
The patent applies parameter changes by introducing variation width parameters (current variation width, temperature variation width, SOC variation width) as selection criteria for valid data. By setting permissible thresholds for these parameters, the method improves impedance calculation accuracy while managing complexity through systematic parameter-based filtering.
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 enhances the accuracy of secondary battery deterioration state estimation by avoiding data with high current variations and significant changes in current, temperature, and SOC, thereby improving the reliability of impedance calculation and deterioration assessment.
Implementation Method 1
performing frequency conversion of each of the plurality of voltage values and each of the plurality of current values of the secondary battery that are stored in the memory to calculate a voltage value and a current value of the secondary battery for each frequency
Data Source
AI summary
The first step includes performing FFT for a voltage and a current of a battery a plurality of times to thereby calculate the voltage and the current for each frequency. The second step includes determining whether or not the first condition and the second condition are satisfied for the current of the battery that is calculated for each frequency. The third step includes calculating an impedance component of the battery for each frequency range when at least one of the first condition and the second condition is not satisfied, and not calculating the impedance component of the battery for each frequency range when each of the first condition and the second condition is satisfied. The first condition shows that the current in a low frequency range is greater than a reference value. The second condition shows that the current in a frequency range is less than a reference value.