LFP Battery SOC Correction Using Voltage Hysteresis
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of lithium iron phosphate (LFP) batteries are limited by the small change in open circuit voltage (OCV) during usage, leading to inaccuracies in SOC estimation, and current integration methods accumulate errors over time.
Innovation Solution
A vehicle control apparatus and method that utilizes the hysteresis characteristic of charge and discharge voltages to correct SOC estimates by comparing voltage parameters and identifying points where the change rate of the voltage parameter is 0, updating the profile based on battery information, and correcting SOC values accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If current integration method is used to estimate SOC, then real-time SOC estimation is achieved, but error accumulates over time reducing accuracy
Solution Approach 1:
The patent uses OCV measurements as feedback to correct the SOC estimation. The controller periodically measures OCV and compares it with the SOC value obtained from current integration, then adjusts the SOC estimation accordingly to eliminate accumulated errors.
Solution Approach 2:
The patent changes the estimation parameter from solely relying on current integration to using both current integration and OCV characteristics. By utilizing the relationship between OCV and SOC (especially the hysteresis characteristic), the system achieves more accurate SOC estimation.
2Measurement precision
If voltage measurement method using OCV-SOC curve is used, then SOC estimation is achieved, but LFP batteries show limited accuracy due to small OCV change
Solution Approach 1:
The patent applies local quality by considering the charging/discharging state separately. It uses different OCV-SOC relationships for charging and discharging processes, leveraging the hysteresis characteristic to improve accuracy in each specific local condition rather than using a single universal curve.
Solution Approach 2:
The patent dynamically adjusts the SOC estimation by detecting whether the battery is charging or discharging and selecting the appropriate OCV-SOC relationship accordingly. This dynamic approach adapts to changing battery states to maintain high accuracy.
3Measurement precision
If hysteresis characteristic of OCV is utilized, then LFP battery SOC estimation accuracy is improved, but measurement and calculation complexity increases
Solution Approach 1:
The patent performs preliminary action by pre-storing the OCV-SOC relationship data (including hysteresis characteristics) in memory. During operation, the controller simply retrieves and applies the appropriate pre-calculated relationships, avoiding complex real-time calculations while maintaining high 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
Improves the accuracy of SOC estimation for LFP batteries by correcting errors in current integration methods and addressing the limitations of OCV-based estimation, providing more precise SOC information to users.
Implementation Method 1
calculate a voltage parameter and an SOC according to a hysteresis characteristic of a charge voltage and a discharge voltage
Data Source
AI summary
A vehicle control apparatus identifies information of a battery, estimates a first state of charge (SOC) of the battery at a first time point and a second SOC of the battery at a second time point, calculates a voltage parameter and an SOC so as to determine a profile of the battery, determines a first result for whether the first voltage parameter increases or decreases to the second voltage parameter, calculates a third voltage parameter, calculates a fourth voltage parameter, determines a second result for whether the third voltage parameter increases or decreases to the fourth voltage parameter, and compares the first result with the second result to correct the SOC.