Multi-Cell Battery Voltage Balancing via Threshold Control
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Solution Overview
Problem
Conventional battery balancing methods for electric vehicles fail to optimize energy usage and extend battery life due to voltage imbalances among cells with different characteristics, leading to reduced driving range and premature cell damage.
Innovation Solution
A method that measures and balances the voltage of each parallel group of cells by controlling charging and discharging energy, using threshold voltages and normalized values to ensure all cells reach a defined state-of-charge, thereby optimizing energy usage and accommodating cells with varying capacities and voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional battery balancing methods are used, then the battery system can operate, but voltage imbalances among cells lead to reduced driving range and premature cell damage
Solution Approach 1:
The system performs preliminary voltage measurement and balancing determination after charging but before the vehicle starts moving. This preliminary action identifies voltage imbalances among parallel cell groups and pre-calculates the energy that needs to be dissipated, allowing the system to optimize the discharge phase by preventing premature termination due to imbalanced cells
Solution Approach 2:
The battery system is segmented into multiple parallel groups of cells, with each group's voltage measured and balanced independently. This segmentation allows the system to identify and address voltage imbalances in specific cell groups without affecting the entire battery system, thereby maximizing the usable energy from all cell groups
2Quantity of substance
If cells with different characteristics are used to extend battery system capacity, then the battery system can provide more energy, but voltage imbalances occur among cells
Solution Approach 1:
The system applies local quality control by measuring and balancing the voltage of each parallel cell group individually rather than treating the entire battery system uniformly. This allows cells with different characteristics to be accommodated by addressing the specific voltage needs of each cell group, maintaining overall system stability while preserving the benefits of using diverse cells for increased capacity
3Reliability
If the battery system is discharged to the lowest allowable state of charge of the parallel group with the lowest state of charge, then cell damage is prevented, but unused energy remains in other parallel groups
Solution Approach 1:
The system performs preliminary voltage measurement and balancing determination after charging but before the vehicle starts moving. This preliminary action identifies voltage imbalances among parallel cell groups and pre-calculates the energy that needs to be dissipated, allowing the system to optimize the discharge phase by preventing premature termination due to imbalanced cells
Solution Approach 2:
The system deliberately dissipates (discards) excess energy from cell groups with higher voltage through controlled resistive loading during the balancing phase. This discarding of excess energy enables the system to later utilize all cell groups fully during the discharge phase, converting the previously wasted energy into useful driving range
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 ensures safe and efficient charging and discharging, maximizing usable energy and extending battery life by maintaining optimal voltage balance across mismatched cells, even after cell replacement, thus enhancing the driving range and longevity of electric vehicles.
Implementation Method 1
the energy needed for driving is stored electrochemically in these cells
Implementation Method 2
continuously lose a small amount of their stored energy over time by unwanted internal leakage
Data Source
Figure 1
Figure 2a~2b
Figure 3
AI summary
A method for balancing voltage for a multi-cell battery system, in which the battery system includes at least two parallel groups of cells connected in series and in which the parallel group of cells includes at least one battery cell, includes: charging the battery system by keeping the voltage of all parallel groups of cells less than or equal to a second threshold voltage value, while at least the voltage of one group of parallel cells is less than or equal to a first threshold voltage; and while at least the voltage of one group of parallel cells is less than or equal to a second threshold voltage; and while the charging current is above a predefined minimal current. The method further includes measuring the voltage of each parallel group of cells while electrical loads are shut off and dissipating energy in each of the parallel group of cells of the amount that is represented by the voltage difference between the individual parallel group of cells and the parallel group of cells with the lowest voltage.