Battery SOC Estimation Using Pattern-Weighted Current and Voltage Fusion
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of batteries in electric motor vehicles face challenges in accuracy, particularly at low temperatures and due to complex internal resistance characteristics, leading to errors in SOC calculation.
Innovation Solution
A battery control device that calculates SOC by combining current-based and voltage-based methods using a feature amount indicating the charging/discharging pattern, with a weighting coefficient adjusted based on the discharging count rate to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If polarization characteristics are modeled with high accuracy to improve SOC estimation at low temperature, then SOC estimation accuracy is improved, but device complexity and calculation load increase
Solution Approach 1:
The patent divides the battery operation into distinct states based on temperature ranges and charging/discharging patterns. Instead of using a single complex polarization model for all conditions, the system segments the operating space and applies simplified appropriate models or correction factors for each segment, thereby reducing overall system complexity while maintaining accuracy where needed.
Solution Approach 2:
The patent changes parameters such as internal resistance values and open-circuit voltage characteristics based on temperature and charging/discharging state. By adjusting these parameters dynamically according to operating conditions rather than using fixed complex models, the system achieves accurate SOC estimation without the computational burden of sophisticated polarization modeling.
2Device complexity
If current integration method is used to calculate SOC, then calculation process is simplified, but SOC error accumulates over time due to current reading errors
Solution Approach 1:
The patent implements feedback mechanisms where the SOC calculated by current integration is continuously compared with SOC estimates from voltage-based methods. When deviations exceed thresholds, the system applies correction factors or switches to alternative calculation methods, thereby preventing error accumulation while maintaining the simplicity of the current integration approach during normal operation.
Solution Approach 2:
The patent combines multiple SOC calculation methods (current integration, voltage-based estimation, and polarization correction) into a composite approach. Each method contributes its strengths: current integration provides continuous monitoring with low computational load, while voltage-based methods and polarization corrections are applied periodically or conditionally to correct accumulated errors, achieving both simplicity and accuracy.
3Device complexity
If voltage-based SOC method is used, then SOC can be calculated without current integration, but internal resistance estimation accuracy decreases especially at low temperature
Solution Approach 1:
The patent performs preliminary actions by pre-characterizing the battery's internal resistance and polarization behavior at various temperatures and states of charge. These pre-acquired characteristics are stored and used to select appropriate parameters or correction factors during operation, eliminating the need for real-time complex measurements while maintaining accuracy even at low temperatures where dynamic measurement would be challenging.
Data Source
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AI summary
Provided are a battery control device which can estimates an SOC of a battery with a high accuracy, and an electric motor vehicle system. The battery control device (190) includes a feature amount calculation unit (152) which calculates a feature amount indicating a charging/discharging pattern of the battery, a first charging state amount calculation unit (151-1) which calculates a first charging state amount (SOCi) of the battery on the basis of a first battery state amount, a second charging state amount calculation unit (151-2) which calculates a second charging state amount (SOCv) of the battery on the basis of a second battery state amount, and a third charging state amount calculation unit (151-3) which calculates a third charging state amount (SOC(t)) on the basis of the feature amount, the first charging stage amount, the second charging stage amount.