SOC Calculation Using Variable Reference Capacity
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Solution Overview
Problem
The accuracy of state of charge (SOC) calculation in energy storage devices like lithium ion batteries deteriorates due to changes in the correlation between open circuit voltage (OCV) and residual capacity over time, leading to errors in SOC estimation, especially in high capacity regions.
Innovation Solution
An energy storage device management apparatus with a voltage sensor, memory for storing OCV-residual capacity correlations, and an information processing unit that calculates SOC based on a reference capacity less than full charge, allowing for accurate SOC determination even as the device deteriorates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the SOC is calculated using the OCV method assuming the correlation between OCV and residual capacity remains unchanged, then the calculation is simple, but the accuracy of SOC calculation deteriorates due to battery deterioration
Solution Approach 1:
The patent applies preliminary action by pre-storing multiple OCV-residual capacity correlation data sets corresponding to different battery states (initial state, deteriorated states at different cycle hours) in memory. When SOC calculation is needed, the system proactively selects the appropriate correlation data set based on battery cycle history before performing the calculation, rather than attempting to detect deterioration in real-time. This allows the simple OCV method to maintain high accuracy by using pre-prepared correction data.
2Ease of operation
If the reference capacity is set to the full charge residual capacity, then the SOC calculation follows the conventional definition, but errors increase especially in high capacity regions due to battery deterioration
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the reference capacity parameter based on battery deterioration level. Instead of using a fixed reference capacity equal to full charge residual capacity, the system selects reference capacity values from stored correlation data sets that correspond to the battery's actual state. This parameter adjustment compensates for deterioration effects and maintains accurate SOC calculation in high capacity regions where errors traditionally occur.
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 accurate SOC estimation and prediction of deterioration, improving the calculation of electric vehicle travelable distance and preventing battery depletion, while reducing errors due to manufacturing variations and capacity changes.
Implementation Method 1
a voltage sensor that detects a voltage of an energy storage device
Data Source
AI summary
Based on a voltage of a secondary battery detected by a voltage measurement unit, a residual capacity is acquired from a correlation between the voltage and the residual capacity of the secondary battery stored in a memory, and a state of charge (SOC) which is a ratio of the residual capacity to a reference capacity is obtained. The reference capacity is set to a prescribed amount less than a residual capacity at full charge. Further, an information processing unit determines an abnormality of a module based on a comparison between the SOC and an SOC obtained by another method.