Battery Management System Cell Capacity Equalization
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Solution Overview
Problem
Existing battery management systems face challenges in accurately determining battery state of charge and predicting operational life in multi-cell batteries, leading to uneven cell aging and reduced warranty reliability due to internal thermal gradients and varying cell capacities.
Innovation Solution
The method involves calculating and dynamically adjusting cell-specific supporting currents to minimize capacity mismatches, using coulometric determination and current sensing to measure cell capacities, and implementing a temperature- and current-compensated algorithm to ensure all cells age at a comparable rate, thereby extending battery life and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cell capacity is determined by measuring current in each cell, then accurate state of charge determination is achieved, but measurement cost and difficulty increase significantly
Solution Approach 1:
The patent combines the measurement of battery charge/discharge current with cell charge current from DC/DC chargers to determine individual cell currents. By integrating these current measurements and summing them to obtain cell capacity, the system achieves accurate cell-level measurement without requiring separate complex measurement devices for each cell, thus reducing overall system complexity while maintaining precision.
2Reliability
If high quality accurately matched cells are used, then initial battery performance is optimized, but internal thermal gradients still cause uneven cell aging over time
Solution Approach 1:
The patent applies local quality by providing individual cell-specific supporting currents based on each cell's capacity relative to the weakest cell. Instead of uniform treatment, the system calculates and applies customized support currents to each cell to equalize their state of charge and aging rates, addressing the local variations in cell performance caused by thermal gradients and manufacturing tolerances.
Solution Approach 2:
The system proactively compensates for cell capacity differences before they lead to premature battery failure. By continuously monitoring cell capacities and applying supporting currents to weaker cells, the system prevents the development of significant capacity mismatches that would otherwise limit the battery pack's operational life, thus extending the duration of action.
3Productivity
If weak cells are not supported, then system simplicity is maintained, but effective battery capacity is limited by the weakest cell
Solution Approach 1:
The patent changes the current parameter applied to individual cells based on their capacity relative to the weakest cell. By dynamically adjusting cell-specific supporting currents according to each cell's state, the system enables the battery pack to deliver effective capacity beyond what the weakest cell could provide alone, thereby increasing productivity without requiring fundamental changes to the battery architecture.
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 enhances battery management by increasing effective capacity, extending operational life, and improving state of charge accuracy, reducing warranty liability and operational costs while maintaining consistent performance across all cells.
Implementation Method 1
a first DC/DC converter (7) connected across the first cell (3) and a second DC/DC converter (9) connected across the second cell (5)
Implementation Method 2
measuring means (11) for determining a cell capacity value for each of the battery cells
Data Source
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AI summary
A battery management system and a method for enhanced battery management of a battery containing a number of cells. The method and system measures the cell capacity of two or more of said cells, ranks the cells in order of their cell capacity values and calculates a value for a cell specific supporting current for the measured cell, for a given load, based upon the ranked cell capacity values. Calculated cell specific currents are then provided to the cells.