SOC Estimation Algorithm for Lithium Iron Phosphate Batteries
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Solution Overview
Problem
Current battery state of charge (SOC) estimation methods, particularly in lithium iron phosphate batteries, face inaccuracies due to voltage sensing errors and temperature variations, leading to inconsistent charge termination and energy delivery.
Innovation Solution
An algorithm that calculates the change in state of charge (dSOC) for a given voltage change (dSOC/dV) at a specific temperature, creating an array of voltages and determining the maximum dSOC to set a signal indicating whether the data is usable, thereby improving SOC accuracy and consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage-based SOC estimation is used in lithium iron phosphate batteries, then SOC can be determined, but large errors occur in regions where small voltage changes correspond to large SOC changes
Solution Approach 1:
The system pre-calculates and stores the relationship between voltage changes and SOC changes (dSOC/dV) across the entire operating range before actual SOC estimation. This allows the system to identify problematic regions in advance and avoid using voltage measurements from these regions, preventing errors rather than correcting them afterward
Solution Approach 2:
The patent introduces an intermediate parameter (dSOC/dV ratio) that mediates between the raw voltage measurement and the final SOC estimation. By calculating this intermediate ratio and comparing it against threshold values, the system can determine whether a voltage measurement is reliable before using it for SOC estimation, thus filtering out erroneous data
2Productivity
If voltage sensing and SOC estimation are performed continuously, then real-time monitoring is achieved, but errors propagate in regions with high dSOC/dV
Solution Approach 1:
The system implements a feedback mechanism where the calculated dSOC/dV ratio is continuously compared against pre-established threshold values. When the ratio exceeds the threshold (indicating a problematic region), the system flags the measurement as unusable and can switch to alternative SOC estimation methods or wait for better measurements, thus preventing error propagation while maintaining continuous monitoring
3Measurement precision
If compensation for battery current and temperature is applied, then voltage reading accuracy is improved, but system complexity increases
Solution Approach 1:
The patent pre-calculates compensation values and correction factors for various temperature and current conditions before operation. These pre-computed values are stored in lookup tables or pre-defined relationships, allowing the system to apply compensations by simple indexing and interpolation rather than performing complex real-time calculations, thus maintaining accuracy while reducing computational complexity
Data Source
AI summary
Systems and methods for improvements in battery state of charge accuracy, charge termination consistency, capacity estimation, and energy delivery consistency. More specifically, embodiments herein detail systems and methods using an algorithm to calculate the change in state of charge for a given voltage change (dSOC/dV) at a given temperature in a region around the present voltage measurement or estimation and to set a signal indicating when the measurement should not be used due to potential error.