Battery Pack Full Charge Capacity Update via OCV Ratio
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Solution Overview
Problem
Existing methods for determining the full charge capacity (FCC) of stacked rechargeable battery cells are complex and require continuous monitoring of each cell, making it difficult to adjust updating conditions effectively.
Innovation Solution
A method and battery management system that periodically measure open-circuit cell voltage (OCV) and current values, process coulomb counting, estimate state of charge (SOC), and update FCC based on a predefined end-of-discharge condition, allowing for simplified and effective FCC calculation without the need for continuous monitoring or calibrating data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If continuous monitoring of each cell is performed to determine FCC, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple cell monitoring into pack-level monitoring by measuring total pack voltage and current, then calculating FCC at the pack level rather than individually for each cell. This merging approach maintains measurement precision while significantly reducing device complexity.
Solution Approach 2:
The monitoring system is designed to serve multiple functions: it tracks state of charge (SOC), determines full charge capacity (FCC), and monitors pack health status. By making the monitoring system universal, the patent avoids the need for separate dedicated FCC monitoring mechanisms for each cell, thereby reducing overall system complexity while maintaining precision.
2Reliability
If continuous monitoring of each cell is performed to determine FCC, then reliability is improved, but ease of operation deteriorates
Solution Approach 1:
The system automatically determines FCC during normal discharge operations without requiring manual intervention or calibration. The BMS continuously monitors pack voltage and current, automatically calculates SOC, and updates FCC when discharge termination conditions are met. This self-service approach maintains high reliability while greatly improving ease of operation.
Solution Approach 2:
The system performs preliminary calculations of SOC and discharge capacity during normal operation, preparing the data needed for FCC determination in advance. When discharge termination conditions are met, the FCC is already calculated and ready for updating, eliminating the need for complex real-time decision-making or manual calibration procedures.
3Manufacturing precision
If FCC updating conditions are strictly checked for each cell, then manufacturing precision is improved, but productivity decreases
Solution Approach 1:
Instead of requiring complete discharge of each individual cell to determine FCC, the patent uses partial discharge monitoring at the pack level. By monitoring the aggregate discharge characteristics of the pack and applying the discharge termination condition to the total pack capacity, the system achieves sufficient calibration precision without the excessive time required for complete cell-by-cell discharge, thereby improving productivity.
Data Source
AI summary
A method of searching for full charge capacity of stacked battery cells in a rechargeable battery pack and a battery management system based on the method are disclosed. The method includes the steps of: predefining an end-of-discharge condition as a ratio of change of open-circuit cell voltage to change of state of charge; providing a full charge capacity for a rechargeable battery pack assembled of several stacked battery cells; charging the rechargeable battery pack until it is fully; discharging the rechargeable battery pack; measuring current values and open-circuit cell voltages periodically; processing coulomb counting based on the measured current values and zeroing a sum of coulomb counting values when a new discharging cycle begins; estimating state of charge during discharging periodically; calculating a running ratio; and updating the full charge capacity by the current sum of the coulomb counting values when the running ratio is equal to or greater than the end-of-discharge condition.