Battery Pack SOC Estimation Using Cell-Specific Thermal and Electrochemical Models
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Solution Overview
Problem
Current battery management systems face inaccuracies in estimating State of Charge (SOC), uptime, and capacity due to cell-to-cell variations in parameters like capacity, resistance, and temperature within battery packs, leading to erroneous user expectations and potential equipment shutdowns.
Innovation Solution
A model combining equivalent circuit, electrochemical, and thermal models is used to accurately estimate SOC, uptime, and capacity by considering cell-specific parameters such as voltage, current, and temperature, allowing for real-time or pre-discharge cycle analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If coulomb counting is used for determining SOC of the battery pack, then the estimation process is simple, but the accuracy of SOC estimation deteriorates due to cell-to-cell variations
Solution Approach 1:
The patent divides the battery pack into individual cell units, where each cell's parameters (capacity, resistance, temperature, SOC) are monitored and estimated separately. This segmentation allows the system to account for cell-to-cell variations by treating each cell as an independent entity with its own characteristics, thereby improving overall SOC estimation accuracy while maintaining computational efficiency through modular processing.
2Measurement precision
If cell-to-cell variations in parameters are considered, then the accuracy of SOC and capacity estimation is improved, but the complexity of the estimation model increases
Solution Approach 1:
The patent dynamically adjusts key parameters (capacity, resistance, temperature, SOC) for each individual cell based on real-time measurements and historical data. By allowing these parameters to change and adapt rather than assuming fixed values, the model accurately captures cell-to-cell variations and their evolution over time, improving estimation precision while using efficient algorithms to manage computational complexity.
3Device complexity
If the cell with lowest capacity is used to determine remaining capacity, then the calculation is simplified, but the accuracy deteriorates due to faster discharge of higher capacity cells
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors the actual discharge behavior of each cell and compares it with the estimated remaining capacity. When discrepancies are detected (such as when higher capacity cells discharge faster than expected), the system adjusts the remaining capacity calculation by incorporating real-time current measurements and cell-specific discharge rates, ensuring accurate estimation without requiring complex iterative calculations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides precise estimates of battery pack uptime, remaining capacity, and chargeable capacity, enhancing reliability and user experience by accounting for individual cell variations and thermal dynamics.
Implementation Method 1
electrochemical model for estimating the State of Charge (SOC), capacity and voltage of the cells
Implementation Method 2
thermal model for estimating the temperature of the cells
Implementation Method 3
equivalent circuit model for estimating the State of Charge (SOC), capacity and voltage of the cells
Data Source
AI summary
Methods and electronic devices for estimating state of charge (SOC) of a battery pack. Various embodiments provide a model comprising an (electrical) equivalent circuit model, an electrochemical (thermal) model, and a (convective) thermal model. The model estimates parameters pertaining to each cell of the battery pack individually, and determines the variations in the values of the parameters among each of the cells of the battery pack. The parameters include capacity, temperature current, voltage, and SOC. The parameters are computed based on at current drawn by the battery pack, electrochemical parameters, thermal parameters, and cell internal and connection resistances of the individual cells. Various embodiments compute battery pack uptime, chargeable capacity of the battery pack and SOC of the battery pack, based on the values of the parameters.