Battery State of Charge Estimation via Terminal Voltage
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Solution Overview
Problem
Existing battery state of charge (SOC) estimation methods for electric vehicles are either imprecise when using overall battery measurements or overly complex and costly when measuring each cell individually, failing to accurately account for cell imbalance.
Innovation Solution
A method that determines the minimum and maximum cell voltages and calculates a weighted average voltage based on these values, using an equation that weights the maximum cell voltage when the state of charge increases and the minimum cell voltage when the state of charge decreases, allowing for precise SOC estimation without the need for individual cell voltage measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If individual cell voltage measurements are used to estimate SOC, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The invention extracts only the essential information needed for SOC estimation by using a single battery terminal voltage measurement combined with current integration, rather than measuring all individual cell voltages. This extraction approach maintains sufficient precision while reducing measurement system complexity and cost.
Solution Approach 2:
Instead of measuring all cell voltages (excessive action), the invention uses a partial measurement approach by measuring only the battery terminal voltage and combining it with current data. This partial action provides sufficient information for accurate SOC estimation without the full complexity of individual cell measurements.
2Measurement precision
If individual cell voltage measurements are used to estimate SOC, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The invention extracts only the essential information needed for SOC estimation by using a single battery terminal voltage measurement combined with current integration, rather than measuring all individual cell voltages. This extraction approach maintains sufficient precision while reducing measurement system complexity and cost.
Solution Approach 2:
The invention replaces expensive individual cell voltage measurement systems with a simpler, more economical approach using terminal voltage measurement and computational algorithms. This substitution uses cheaper measurement components while achieving comparable SOC estimation accuracy.
3Device complexity
If global battery measurements are used to estimate SOC, then device complexity is reduced, but measurement precision deteriorates due to cell imbalance
Solution Approach 1:
The invention changes the measurement parameters by using terminal voltage combined with current integration data, rather than relying solely on individual cell voltage measurements or simple average calculations. This parameter change enables accurate SOC estimation that accounts for cell imbalance while keeping the system simple.
Solution Approach 2:
The invention substitutes physical individual cell voltage measurements with a computational approach using terminal voltage and current integration. This substitution replaces complex mechanical/electrical measurement infrastructure with simpler sensors and algorithmic processing.
4Measurement precision
If sophisticated models like Kalman filter are used for each cell, then measurement precision is improved, but device complexity and computational requirements increase
Solution Approach 1:
The invention extracts only the essential information needed for SOC estimation by using a single battery terminal voltage measurement combined with current integration, rather than measuring all individual cell voltages. This extraction approach maintains sufficient precision while reducing measurement system complexity and cost.
Solution Approach 2:
The invention changes the measurement parameters by using terminal voltage combined with current integration data, rather than relying solely on individual cell voltage measurements or simple average calculations. This parameter change enables accurate SOC estimation that accounts for cell imbalance while keeping the system simple.
Data Source
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AI summary
The invention relates to a method for estimating the state of charge (SOCBAT ) of a battery comprising a plurality of cells (C1,...CN) connected in series, characterized by the determination, at a given time, of the minimum cell voltage (UCmin ) and of the maximum cell voltage(UCma x) from among the cell voltages, and the calculation of a physical quantity (Ump) analytically depending on the minimum (UCmin ) and maximum (UCmax ) cell voltages according to an equation including weighting elements ensuring that the weight associated with the maximum cell voltage (UCmax ) increases when the state of charge of the associated cell increases, and the weight associated with the minimum cell voltage (UCmin ) increases when the state of charge of the associated cell decreases.