Secondary Battery SOH Estimation via SOC-OCV Model Updates
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Solution Overview
Problem
Existing secondary battery state estimation methods face difficulties in accurately estimating the state of health (SOH) due to changes in SOC-OCV characteristics over time, especially in regions with greater negative effects, leading to incorrect calculations and uncertainty about the battery's state.
Innovation Solution
A secondary battery state estimation device that measures terminal current and voltage, calculates internal resistance, and uses SOC-OCV characteristic models to estimate SOC and SOH, with differential and integrated calculations to update models and adjust for varying OCV thresholds, ensuring accurate estimation and learning across different SOC regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SOC-OCV characteristic models are used to estimate SOH, then estimation can be performed, but accuracy deteriorates in regions with greater negative effects where SOC-OCV characteristics change over time
Solution Approach 1:
The patent divides the SOC range into multiple regions (first SOC region with greater negative effects, second SOC region with smaller negative effects) and applies different estimation strategies to each region. This segmentation allows accurate SOH estimation by using appropriate methods for each SOC region, resolving the contradiction between overall estimatability and regional accuracy.
2Ease of operation
If equalized charging is implemented based on SOC transition, then battery balance is improved, but SOH estimation becomes inaccurate when SOC-OCV characteristics change
Solution Approach 1:
The patent implements a feedback mechanism where SOC transition information is continuously monitored and used to update SOH estimation. The system records SOC transitions during equalized charging and uses this feedback to correct SOH estimation, maintaining both operational capability and estimation accuracy despite SOC-OCV characteristic changes.
3Stability of the object's composition
If SOH is estimated only in regions with small SOC-OCV changes, then estimation stability is improved, but the ability to know battery state in all regions is reduced
Solution Approach 1:
The patent adds a temporal dimension to SOH estimation by tracking SOC transitions over time and using cumulative SOC change information. This allows the system to estimate SOH across all SOC regions by integrating information from multiple charging/discharging cycles, not just static single-point measurements, thereby expanding coverage while maintaining stability.
Data Source
AI summary
A secondary battery state estimation device includes: a state measurer configured to measure state variables including a terminal current and a terminal voltage of a secondary battery; an internal resistance calculator configured to calculate internal resistance of the secondary battery; an estimated open-circuit-voltage (OCV) calculator configured to calculate an estimated OCV; an estimated state-of-charge (SOC) calculator configured to calculate an estimated SOC, by using an SOC-OCV characteristic model; a differential estimated SOC calculator configured to calculate a differential estimated SOC; an integrated terminal current calculator configured to calculate an integrated terminal current; and a state-of-health (SOH) calculator configured to calculate an SOH. The SOH that the SOH calculator has calculated in a high SOC state where at least the estimated OCV is equal to or above a first threshold value is entered into an SOH estimation model used to estimate the SOH to update the SOH estimation model.