SOC Estimation via Surface Stress Correction
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Solution Overview
Problem
Existing secondary battery systems face challenges in accurately estimating State of Charge (SOC) due to hysteresis in SOC-OCV curves, particularly when using active materials with large volume changes during charging and discharging, as they do not adequately account for surface stress effects.
Innovation Solution
A secondary battery system and method that utilize correspondence relations between SOC and OCV, incorporating surface stress calculations based on use history to correct estimated OCV values, thereby improving SOC estimation accuracy by considering hysteresis effects caused by surface stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SOC estimation methods using SOC-OCV curves are used, then the estimation process is simple, but SOC estimation accuracy deteriorates due to hysteresis effects
Solution Approach 1:
The patent pre-calculates and stores correspondence relations between surface stress and OCV change amounts in a lookup table before actual SOC estimation. This preliminary action allows the estimation process to simply query the table with calculated surface stress values, avoiding complex real-time calculations while achieving high accuracy by compensating for hysteresis effects
Solution Approach 2:
The patent introduces surface stress as an intermediary parameter that mediates between the battery's charge state and OCV measurements. By calculating surface stress from use history and using it to correct OCV values through pre-stored correspondence relations, the system accurately accounts for hysteresis effects without requiring complex real-time modeling
2Quantity of substance
If active materials with large volume changes are used, then battery capacity increases, but SOC estimation accuracy deteriorates due to increased surface stress effects
Solution Approach 1:
The patent converts the harmful effect of surface stress (which causes hysteresis and estimation errors) into a beneficial correction mechanism. By calculating surface stress from use history and using pre-stored correspondence relations to determine OCV correction amounts, the system transforms the stress-induced OCV deviations into accurate SOC estimates, enabling high-capacity materials to be used without sacrificing estimation accuracy
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 enables highly accurate SOC estimation even with active materials exhibiting large volume changes, reducing computational resource requirements and enhancing estimation precision.
Implementation Method 1
a correspondence relation between the surface stress and an amount of change in the OCV with reference to OCV in the case where the surface stress is the reference stress, the amount of change in the OCV being caused by the surface stress of the active material
Implementation Method 2
a hysteresis appears in the relation between an SOC and an OCV due to a surface stress
Data Source
AI summary
A secondary battery system includes: a secondary battery having an electrode containing an active material; and an electronic control unit configured to execute an SOC estimation process of estimating an SOC of the secondary battery. The electronic control unit is configured to: i) calculate the surface stress from a use history of the secondary battery; ii) calculate the amount of change in OCV from the calculated surface stress iii) correct an estimated OCV with the use of the amount of change in OCV; the estimated OCV being estimated from a voltage value and current value of the secondary battery; and iv) estimate an SOC corresponding to the corrected estimated OCV as the SOC of the secondary battery.