Lithium Ion Battery Cell Charge Equalization via Dynamic Shunt Current Control
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Solution Overview
Problem
Lithium ion battery cells from a common production lot do not have perfectly matched parameters, leading to divergent charge states over multiple charge cycles, resulting in significant portions of battery capacity being forfeited as traditional charging systems cannot simultaneously establish maximum charge states for all cells.
Innovation Solution
A device and method that continuously equalizes charge states by measuring cell voltage and shunt current, calculating adjusted voltages, determining the lowest adjusted voltage, and calculating new shunt currents to balance charge states across all cells, using a battery management unit with control circuitry that adjusts shunt currents to ensure all cells reach maximum voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional end-of-charge cell balancing techniques are used, then the cell with the highest potential is addressed, but the majority of cells do not reach maximum charge state, resulting in significant portions of battery capacity being forfeited
Solution Approach 1:
The system continuously monitors individual cell voltages and shunt currents during charging, using feedback control to dynamically adjust shunt currents for each cell. This real-time feedback mechanism ensures all cells reach maximum charge state simultaneously, maximizing battery capacity utilization while maintaining charge state equality across all cells
Solution Approach 2:
The system dynamically changes the shunt current parameter for each cell based on its individual charge state and impedance characteristics. By continuously adjusting these parameters during the charging process rather than applying fixed balancing at the end, the system achieves both high capacity utilization and equal charge states across all cells
2Ease of manufacture
If battery cells with unmatched parameters are used to reduce manufacturing cost, then production cost decreases, but cell charge states diverge over multiple charge cycles, resulting in significant portions of battery capacity being forfeited
Solution Approach 1:
The system applies individualized charging and balancing strategies to each cell based on its specific parameters such as capacity and impedance. By tailoring the charging approach for each cell rather than using a uniform approach, the system can effectively utilize batteries made from cells with varied parameters, maintaining high capacity utilization without requiring expensive perfectly-matched cells
3Productivity
If continuous cell equalization is implemented, then all cells can reach maximum charge state simultaneously, but device complexity increases due to additional control circuitry and calculations
Solution Approach 1:
The control circuitry performs multiple functions simultaneously: it monitors cell voltages, measures shunt currents, calculates adjusted voltages, determines the lowest adjusted voltage, and computes new shunt currents all within a single integrated system. This multi-functionality reduces the need for separate dedicated components for each function, thereby managing device complexity while achieving continuous cell equalization and maximum capacity utilization
Data Source
AI summary
A method of equalizing charge states of individual cells in a battery includes measuring a previous cell voltage for each cell, measuring a previous shunt current for each cell, calculating, based on the previous cell voltage and the previous shunt current, an adjusted cell voltage for each cell, determining a lowest adjusted cell voltage from among the calculated adjusted cell voltages, and calculating a new shunt current for each cell.