Secondary Battery SOC Estimation via Dynamic Method Switching
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of secondary batteries, particularly in hybrid vehicles, face challenges due to varying conditions and temperature effects, leading to inaccuracies in estimating remaining capacity, especially when internal resistance changes and relaxation times are not adequately considered.
Innovation Solution
A device and method that detect input/output current, output voltage, and battery temperature, using characteristic storage and stable state determination to estimate SOC accurately by switching between methods based on stability and temperature, employing a battery model when current integration errors are detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If current integration method is used to estimate SOC continuously, then real-time SOC estimation is achieved, but estimation accuracy deteriorates due to current detection offsets and integration errors
Solution Approach 1:
The patent implements periodic switching between current integration method and open circuit voltage method for SOC estimation. The controller alternates between these two methods based on predetermined conditions, such as when the vehicle is stopped or when estimation accuracy requirements are not met by current integration alone. This periodic switching allows the system to maintain real-time estimation capability while periodically correcting accumulation errors through the OCV method, thereby resolving the contradiction between real-time speed and estimation accuracy.
2Measurement precision
If open circuit voltage method is used to estimate SOC, then high estimation accuracy is achieved, but response time increases due to relaxation time requirements
Solution Approach 1:
The patent dynamically selects between current integration method and open circuit voltage method based on real-time operating conditions. When the vehicle is moving and real-time response is critical, the current integration method is used. When the vehicle is stopped or during periods when accuracy is prioritized, the OCV method is employed. This dynamic switching strategy allows the system to optimize between response time and estimation accuracy according to actual operational needs, resolving the contradiction between these two parameters.
3Duration of action of stationary object
If current integration method is used under varying temperature conditions, then continuous monitoring is maintained, but estimation accuracy deteriorates due to temperature-dependent internal resistance changes
Solution Approach 1:
The patent incorporates temperature compensation by switching to open circuit voltage method under specific temperature conditions. When temperature varies significantly or exceeds predetermined thresholds, the system transitions from current integration to OCV-based estimation, as OCV is less sensitive to temperature effects. This parameter-based switching allows the system to maintain continuous monitoring while adapting to temperature variations, thereby preserving estimation accuracy across different thermal conditions.
Data Source
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AI summary
A method of estimating charged state of a secondary battery (10) provided with a detector (30, 32, 34) capable of detecting input/output current (Ib), an output voltage (Vb) and battery temperature (Tb),characterized in that it comprises: a first estimating step (S200) of estimating the remaining capacity (SOC) of said secondary battery by calculating an amount of change in said remaining capacity based on an integrated value of said input/output current; a second estimating step (S220) of estimating the remaining capacity of said secondary battery based on a battery model using said input/output current, said output voltage and said battery temperature as input variables; a time measuring step (S 120, S210, S230) of measuring duration (Tcnt) of continuous execution of the estimation of remaining capacity by said first estimating step; and a selecting step (S 160, S 170) of selecting one of said first and second estimating steps of estimating said remaining capacity, based on determination as to whether said input/output current is within a prescribed range (125) that allows use of the battery model or not and on said duration of continuous execution obtained by said time measuring step.