Battery Management Unit Cell Balancing Strategy
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Solution Overview
Problem
Conventional battery management systems fail to effectively suppress voltage dispersion in assembled batteries, particularly in plug-in hybrid vehicles that infrequently undergo external charging, leading to inefficient cell-balancing and reduced battery capacity.
Innovation Solution
A battery management unit that records the lowest voltage cell during full charge and uses this as a target voltage for cell-balancing, even if it's not the lowest at the time of balancing, and sets an upper limit for cumulative balancing time based on electric current and capacity difference, ensuring balancing occurs only under low load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If cell-balancing is performed based on the lowest voltage cell at the time of balancing, then the voltage dispersion is reduced at that moment, but the voltage dispersion increases after the battery is fully charged again due to individual cell charging-discharging characteristics
Solution Approach 1:
The system performs preliminary identification of the lowest voltage cell during full charge and stores this information in advance. This preliminary action allows the control unit to later balance voltages based on the originally identified lowest cell rather than the current lowest cell, preventing voltage dispersion increase after subsequent charging cycles.
Solution Approach 2:
The control unit continuously monitors cell voltages and compares current voltages against the stored lowest voltage cell information. This feedback mechanism enables the system to adjust balancing operations dynamically, discharging specific cells based on their original lowest voltage status rather than current status, thereby maintaining long-term voltage stability.
2Stability of the object's composition
If cell-balancing is performed frequently to maintain voltage equality, then voltage dispersion is suppressed, but energy consumption increases due to discharging cells during balancing
Solution Approach 1:
Instead of continuously balancing all cells, the system performs partial balancing only on cells identified as having higher voltages than the stored lowest voltage cell. This partial action approach reduces energy consumption while still maintaining acceptable voltage dispersion levels by targeting only the necessary cells for balancing.
Solution Approach 2:
The system changes the balancing parameter from continuous monitoring and balancing to periodic balancing based on stored full-charge voltage data. This parameter change reduces the frequency of balancing operations, thereby reducing energy consumption while maintaining voltage stability through strategic timing of balancing actions.
3Stability of the object's composition
If cell-balancing takes a long time to equalize all cell voltages, then complete voltage equality is achieved, but the vehicle experiences power shortage and reduced efficiency
Solution Approach 1:
The system extracts and stores the identity of the lowest voltage cell during full charge, separating this critical information from continuous real-time balancing operations. This extraction allows the system to perform faster, targeted balancing on specific cells rather than continuously monitoring and balancing all cells, thereby reducing balancing time while maintaining voltage equality.
Solution Approach 2:
By performing the identification of the lowest voltage cell in advance during full charge and storing this information, the system eliminates the need for time-consuming real-time analysis during balancing operations. This preliminary action enables faster balancing decisions and reduces the overall time required to achieve voltage equality, improving vehicle efficiency.
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 reduces voltage dispersion and maintains battery capacity by targeting the original lowest voltage cell for balancing, even when it's not the current lowest, and optimizes energy usage by limiting balancing time, enhancing fuel and electric efficiency.
Implementation Method 1
Electric power is transferred from cells having high voltages to cells having low voltages using electromagnetic induction
Data Source
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AI summary
The battery management unit for a vehicle includes a charger (14) mounted on the vehicle (10) for charging an assembled battery (13) including a plurality of cells (9) with electric power from an external power source; a memory (1) that records which cell is a lowest cell having the lowest voltage when the assembled battery (13) is fully charged; and a cell-balancer (5) that carries out cell-balancing on the voltage of the assembled battery (13) by discharging, when the charger (14) is not charging the assembled battery (13), one or more cells (9) each having a voltage higher than a current voltage of the lowest cell (9) to the current value of the lowest cell (9). Thereby, it is possible to suppress an increase in dispersion of voltages and reduction in battery capacity.