LFP Battery SOC Calibration Using Internal Resistance Thresholds
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Solution Overview
Problem
The current integration method for estimating the state of charge (SOC) of lithium iron phosphate (LFP) batteries is inaccurate due to measurement errors from current sensors, and the small changes in open circuit voltage (OCV) within the optimal use range make OCV-SOC curve estimation unsuitable for these batteries.
Innovation Solution
A battery management apparatus that measures voltage, current, and optionally temperature, calculates average values over time, determines internal resistance, and calibrates the SOC to a reference value when the internal resistance meets a threshold, using a lookup table for temperature corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the current integration method is used to estimate SOC, then the SOC can be determined continuously over time, but the measurement accuracy deteriorates due to accumulated errors from current sensor inaccuracies
Solution Approach 1:
The patent implements a feedback mechanism by periodically calibrating the current integration method with OCV-SOC curve measurements. The system compares the SOC estimated by current integration with the SOC derived from OCV measurements, and uses this feedback to correct accumulated errors, thereby maintaining long-term accuracy while preserving continuous monitoring capability
Solution Approach 2:
The patent employs periodic calibration actions where the system switches between current integration method and OCV-SOC curve method at predetermined intervals or conditions. This periodic alternation allows the system to reset accumulated errors regularly, maintaining measurement precision over extended operation periods
2Measurement precision
If the OCV-SOC curve method is used to estimate SOC, then the measurement accuracy can be improved, but the method becomes unsuitable for LFP batteries due to minimal OCV changes in the optimal use range
Solution Approach 1:
The patent applies local quality by using different estimation methods for different SOC ranges. For LFP batteries, it uses current integration method for the optimal use range (30%-95% SOC) where OCV changes are minimal, and switches to OCV-SOC curve method or other calibration techniques at extreme SOC levels where voltage changes are more pronounced, thereby achieving both accuracy and adaptability
3Ease of operation
If the current sensor measurement values are used directly, then the system operation is simple, but the accumulated error becomes significant over time
Solution Approach 1:
The patent introduces an intermediary calibration mechanism that mediates between the simple current sensor measurements and the accurate but complex OCV-SOC curve method. The system uses readily available voltage and temperature measurements as intermediaries to periodically correct the current integration results, maintaining system simplicity while improving long-term 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
Accurately calibrates the SOC of LFP batteries, reducing errors from continuous current sensor measurement inaccuracies and providing precise capacity estimation.
Implementation Method 1
calculate an average internal resistance value of the LFP battery for the predefined time based on the average voltage value and the average current value
Data Source
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AI summary
Disclosed is a battery management apparatus and method for calibrating the state of charge (SOC) of a lithium iron phosphate (LFP) battery. The battery management apparatus according to an embodiment of the present disclosure calculates, when going into calibration mode, an average voltage value of voltage values received from a voltage measuring unit for a predefined time, calculates an average current value of current values received from a current measuring unit for the predefined time, calculates an average internal resistance value of the LFP battery for the predefined time based on the average voltage value and the average current value, determines if the average internal resistance value is equal to or larger than a preset reference resistance value, and when the average internal resistance value is equal to or larger than the reference resistance value, calibrates the current SOC to a preset reference SOC.