Battery State of Charge Determination via Internal Resistance and Temperature
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Solution Overview
Problem
Existing methods for determining the state of charge of batteries, such as current integration and battery rest voltage measurement, are either inaccurate or require specific conditions, and are not applicable to all battery chemistries like lithium iron phosphate due to flat characteristic curves.
Innovation Solution
A method that uses a characteristic curve field to determine the state of charge based on internal resistance and temperature, allowing for continuous and precise monitoring of battery state across various conditions and chemistries, by measuring current temperature and internal resistance and using a predetermined selection method to equate state of charge values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If current integration method is used to determine state of charge, then the method can be applied continuously under load, but the accuracy deteriorates over time due to error accumulation
Solution Approach 1:
The patent employs feedback by continuously comparing the determined state of charge with reference measurements and correcting deviations. The system uses measured terminal voltage, current, and temperature data to continuously update and correct the state of charge determination, preventing error accumulation over time while maintaining continuous monitoring capability.
Solution Approach 2:
The patent changes the measurement parameters from relying solely on current integration to using a combination of terminal voltage, current, temperature, and their derivatives. By incorporating multiple parameters and their relationships through differential equations, the system maintains accuracy while enabling continuous determination under various load conditions.
2Measurement precision
If open-circuit voltage measurement method is used to determine state of charge, then high precision can be achieved, but the method requires specific conditions (fully charged battery or open-circuit voltage conditions) that limit its applicability
Solution Approach 1:
The patent creates a universal determination method that works across multiple conditions by using a unified mathematical model incorporating terminal voltage, current, temperature, and their derivatives. The system can determine state of charge during charging, discharging, and rest periods without requiring separate calibration procedures, making it applicable to all battery types and operating conditions.
Solution Approach 2:
The patent performs preliminary characterization of the battery system by storing differential capacity curves and other reference data obtained from prior measurements. These pre-acquired characteristics are then used during operation to enable accurate state of charge determination without requiring the battery to be in specific pre-conditioned states, thus eliminating the need for frequent recalibration.
3Measurement precision
If recalibration methods are used to correct state of charge errors, then accuracy can be restored, but the methods depend on specific environmental and system conditions such as fully charged battery or open-circuit voltage conditions
Solution Approach 1:
The patent implements self-service by enabling the battery management system to automatically perform continuous calibration and correction during normal operation. The system uses real-time measurements of voltage, current, and temperature to continuously update the state of charge determination without requiring external intervention or specific calibration conditions, thus maintaining both accuracy and operational flexibility.
4Measurement precision
If methods based on voltage differential or capacity determination are used, then state of charge can be determined with better accuracy, but these methods can only be performed in specific situations such as alternating between charging and discharging
Solution Approach 1:
The patent ensures continuity of useful action by implementing a determination method that continuously calculates state of charge during all operating phases including charging, discharging, and rest periods. The mathematical model using differential equations and stored capacity curves enables uninterrupted monitoring without requiring the battery to undergo specific cycles or transitions, thus maintaining both accuracy and universal applicability.
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
Enables accurate and continuous determination of battery state of charge in virtually any situation, independent of battery chemistry or condition, with no situational restrictions, and can be applied to any battery type, including lithium iron phosphate batteries.
Implementation Method 1
a characteristic field is provided which indicates an internal resistance for a specific battery type for various predetermined temperature ranges as a function of the state of charge
Data Source
Figure 1~2
AI summary
The invention relates to a method for determining a current state of charge (SOC0, SOC1, SOC2) of a battery (14) of a specific battery type, wherein a characteristic curve field (22) is provided which specifies an internal resistance (Ri) for the specific battery type for various predetermined temperature ranges (ΔT) as a function (26) of the state of charge (SOC) for the specific battery type, a current temperature (T) of the battery (14) is measured, a current internal resistance value (Ri0, Ri1) of the battery (14) is determined, and on the basis of the current temperature (T) and the current internal resistance value (Ri0, Ri1), the current state of charge value (SOC0, SOC1, SOC2) of the battery (14) is determined using the characteristic curve field (22).