Battery SOC Estimation Switching Between Adaptive Filtering and Current Integration
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Solution Overview
Problem
Existing state-of-charge (SOC) estimation devices for secondary batteries face imprecision when the input current is constant and battery parameters change, as adaptive digital filter computing treatments struggle to follow these changes, leading to inaccurate SOC estimation, especially in lithium-ion batteries where internal resistance increases during discharge.
Innovation Solution
A state-of-charge estimating device that integrates current detection and terminal voltage detection, using a combination of adaptive digital filtering and current integration methods to estimate open-circuit voltage and SOC, with a second state-of-charge estimating part selecting the appropriate estimation method based on current stability to ensure precise SOC estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If adaptive digital filter computing treatment is used to estimate open-circuit voltage, then SOC estimation precision is improved under varying current conditions, but SOC estimation accuracy deteriorates when current is constant and battery parameters change
Solution Approach 1:
The system dynamically switches between adaptive digital filter computing treatment and current integration method based on real-time detection of current variation. When current varies, the adaptive digital filter is used; when current is constant, the current integration method is employed. This dynamic adaptation resolves the contradiction by ensuring appropriate methodology is selected for each operational condition.
Solution Approach 2:
The system changes the estimation parameter selection based on current characteristics. By detecting whether current is constant or varying, the system switches between two different estimation approaches (adaptive digital filter vs. current integration), thereby maintaining accuracy across different operating conditions despite parameter changes in the battery.
2Speed
If open-circuit voltage estimation is performed right after charge/discharge completion, then response time is improved, but estimation accuracy deteriorates due to voltage not yet leveling off
Solution Approach 1:
The system performs preliminary estimation using current integration method when charge/discharge is completed and current becomes constant. This allows SOC estimation to be performed immediately without waiting for voltage to level off, while maintaining accuracy through the alternative estimation approach designed for constant current conditions.
Solution Approach 2:
The current integration method serves as an intermediary approach that bridges the gap when voltage-based estimation cannot be performed accurately. Instead of waiting for voltage to stabilize, the system uses current integration as an alternative pathway to estimate SOC, thereby achieving both speed and accuracy.
3Device complexity
If a single SOC estimation method is used, then device complexity is reduced, but SOC estimation accuracy deteriorates under varying operating conditions
Solution Approach 1:
The system implements multi-functionality by incorporating both adaptive digital filter computing treatment and current integration method within a single SOC estimation device. The controller is designed to perform both estimation approaches and automatically select the appropriate one based on current characteristics, thereby achieving universal applicability across different operating conditions without requiring separate systems.
Data Source
AI summary
A state-of-charge (SOC) estimating device and method for a secondary battery that estimates the SOC of the battery with high precision when variation takes place in the parameters of the battery model, even if the input current is constant. A first SOC estimating part estimates the open-circuit voltage by estimating the battery parameters en bloc using an adaptive digital filter computing treatment from the measurement values of the current and the terminal voltage and computes a first estimated SOC of the secondary battery from the open-circuit voltage and a predetermined relationship between the open-circuit voltage and the SOC. A second SOC estimating part computes a second estimated SOC by means of current-integration. State-of-charge estimated value-selecting part selects the second SOC value as when the current is constant and otherwise selects the first SOC value.