Battery Pack State of Charge Observer Module
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Solution Overview
Problem
Current methods for determining the state of charge (SOC) of battery packs in electric vehicles are inaccurate due to small voltage changes in lithium battery cells and inaccuracies in electric current integration, necessitating improved methods for monitoring and controlling SOC.
Innovation Solution
A method using an observer module with an influence factor that combines measured voltage, current, and temperature values with a cell model to accurately determine and control the SOC, employing a Kalman filter to update the SOC value and account for measurement and model errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If voltage-based state of charge estimation is used, then the measurement process is simple, but the estimation accuracy deteriorates due to small voltage changes in lithium battery cells
Solution Approach 1:
The patent combines multiple measurement methods (voltage-based estimation, current integration, and temperature compensation) into a unified state of charge determination system. The controller integrates these different approaches to compensate for their individual limitations, particularly using current integration to correct voltage-based estimation errors in lithium battery cells with small voltage changes.
Solution Approach 2:
The patent introduces temperature as an additional parameter to improve state of charge estimation accuracy. By measuring temperature and using temperature-compensated voltage thresholds, the system adapts to varying operating conditions that affect battery voltage characteristics, thereby improving measurement precision without sacrificing operational simplicity.
2Duration of action of moving object
If current integration method is used, then the state of charge can be tracked over time, but accuracy deteriorates due to integration errors and drift
Solution Approach 1:
The patent implements a feedback mechanism where the controller continuously monitors the battery voltage and compares it against expected values based on the integrated current. When discrepancies are detected (indicating integration drift), the system uses voltage-based estimation to correct the integrated state of charge value, thereby maintaining accuracy over extended tracking periods.
Solution Approach 2:
The system performs periodic calibration by comparing the integrated state of charge with voltage-based estimates at regular intervals or when specific conditions are met. This periodic correction prevents cumulative integration errors from deteriorating accuracy over time, while maintaining continuous tracking capability.
3Device complexity
If a simple voltage threshold method is used, then the device complexity is low, but the reliability deteriorates due to inability to account for measurement and model errors
Solution Approach 1:
The patent applies a filtered version of the state of charge estimation rather than using raw calculated values. By implementing smoothing filters and gradual updates, the system reduces the impact of transient measurement errors and model inaccuracies, improving reliability without requiring excessively complex error correction mechanisms.
Data Source
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AI summary
The invention relates to a method for determining the state of charge (SOC) of a chargeable battery pack (5) comprising at least one battery cell (5a, 5b, 5c), said method comprising the steps of: providing an initial state of charge value (SOC1) for said battery pack (5); estimating a battery cell voltage value (Vest) using a cell model (7b) based on input values representing at least a measured voltage (Vmeas) of said battery pack (5); comparing said estimated battery cell voltage value (Vest) with said measured battery cell voltage value (Vmeas) for said at least one battery cell (5a, 5b, 5c); and determining an estimated state of charge value (SOCest) to update the state of charge (SOC) from the initial state of charge value (SOC1), based on said comparing step and by using an observer module (7a). According to the invention, the observer module (7a) comprises an influence factor, said influence factor representing errors in the state of charge (SOC) based on the parameterization of said cell model (7b). The invention also relates to an arrangement for determining the state of charge (SOC) of a battery pack (5).