Battery SOH Estimation via Voltage Variation Pattern
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Solution Overview
Problem
Existing methods for estimating the State Of Health (SOH) of batteries are inaccurate due to the IR drop effect and measurement errors, making it difficult to reliably determine internal resistance and SOH, which is crucial for maintaining battery health and preventing overcharging or overdischarging.
Innovation Solution
An apparatus and method that estimate SOH based on a battery voltage variation pattern, using a combination of Ampere counting and open-circuit voltage estimation, with a weighted mean convergence calculation to improve accuracy, incorporating a data storage unit, SOC estimating units, and a SOH estimating unit that uses correlations and look-up tables or functions to calculate the relative battery capacity degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If battery voltage and charging/discharging current are measured to indirectly calculate internal resistance according to Ohm's law, then internal resistance can be obtained, but measurement errors and IR drop effect cause insufficient reliability
Solution Approach 1:
The patent introduces open-circuit voltage (OCV) as an intermediary parameter to bridge the gap between measured voltage and actual battery state. By using OCV tables that map measured voltages to corrected values, the system eliminates IR drop effects and measurement errors from direct internal resistance calculations, thereby improving both measurement precision and reliability of SOH estimation.
Solution Approach 2:
The patent replaces the direct electrical measurement approach (Ohm's law using current and voltage) with a lookup table-based correction system. Instead of calculating internal resistance through electrical measurements that are prone to error, the system uses pre-generated OCV tables to determine battery state, substituting a complex measurement-based system with a data-driven correction approach.
2Measurement precision
If SOC is estimated by integrating charging/discharging currents, then SOC can be obtained, but measurement errors are continuously accumulated causing SOC accuracy to deteriorate over time
Solution Approach 1:
The patent implements feedback by continuously comparing the estimated SOC with open-circuit voltage measurements and using OCV tables to correct deviations. This feedback mechanism prevents error accumulation by periodically resetting and correcting the SOC estimate based on actual voltage measurements, thereby maintaining high accuracy over extended periods.
Solution Approach 2:
The patent performs preliminary action by pre-generating OCV tables that map measured voltages to corrected open-circuit voltages for various states of charge. These tables are created in advance through comprehensive testing, allowing the system to immediately correct measurement errors without needing to wait for error accumulation to manifest, thus preventing accuracy deterioration from the outset.
3Measurement precision
If battery voltage is used to estimate SOC while charged/discharged, then SOC can be obtained, but IR drop effect causes estimated voltage to be significantly different from actual voltage
Solution Approach 1:
The patent converts the harmful IR drop effect into a beneficial correction opportunity. By measuring the actual voltage during charging/discharging and using OCV tables to calculate the corresponding open-circuit voltage, the system transforms the voltage deviation caused by IR drop into accurate SOC estimation. The harmful voltage drop becomes the basis for identifying and correcting battery state, thereby eliminating the harmful effect's impact on measurement 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 significantly improves the accuracy of SOH estimation, allowing for precise monitoring of battery capacity degradation and preventing overcharging or overdischarging, thereby enhancing battery safety and longevity.
Implementation Method 1
when a battery is charged/discharged, the estimated voltage of a battery is significantly different from an actual voltage due to an IR drop effect
Data Source
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AI summary
An apparatus estimates SOH of a battery based on a battery voltage variation pattern. A data storing unit obtains and stores battery voltage, current and temperature data from sensors, at each SOH estimation. A first SOC estimating unit estimates first SOC by current integration using the battery current data. A second SOC estimating unit estimates open-circuit voltage from the voltage variation pattern, and calculates and stores second SOC corresponding to the open-circuit voltage and temperature using correlations between the open-circuit voltage/temperature and SOC. A weighted mean convergence calculating unit calculates and stores convergence value for weighted mean value of ratio of the second SOC variation to the first SOC variation. A SOH estimating unit estimates capacity corresponding to the weighted mean convergence value using correlation between the weighted mean convergence value and the capacity, estimates relative ratio of the estimated capacity to an initial capacity, and stores it as SOH.