Battery Module Switching for State of Charge Estimation
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Solution Overview
Problem
Existing methods for determining the state of charge of a battery, such as using current sensors, voltage sensors, and cell behavior models, face issues like measurement drift, accuracy problems, and high costs, with the need for interrupting battery operation to measure open-circuit voltage.
Innovation Solution
A system with series current sensors and switching means to selectively disconnect modules, allowing for frequent correction of state of charge estimates using no-load voltage measurements without interrupting battery operation, and employing voltage sensors to calculate open-circuit voltage quickly or using a polarization drop law for robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage sensors measure open-circuit voltage to determine state of charge, then measurement precision is improved, but battery operation must be interrupted
Solution Approach 1:
The battery pack is divided into multiple series-connected modules. By disconnecting only one module at a time while keeping others connected, the system can perform open-circuit voltage measurements on the disconnected module without interrupting overall battery operation. This segmentation allows simultaneous measurement and operation, resolving the contradiction between measurement precision and operational continuity.
2Productivity
If current sensors are used to determine state of charge through integration, then battery operation can continue without interruption, but measurement precision deteriorates due to drift and bias
Solution Approach 1:
The system uses open-circuit voltage measurements from disconnected modules as feedback to correct the state of charge estimates obtained from current integration. This feedback mechanism eliminates drift and bias accumulated during continuous operation, maintaining high measurement precision while allowing uninterrupted battery operation through periodic correction cycles.
3Measurement precision
If modules are disconnected frequently to measure open-circuit voltage, then state of charge estimation precision is improved, but device complexity increases
Solution Approach 1:
The switching means are controlled dynamically based on battery power requirements and operational conditions. Modules are disconnected only when and where needed for measurement, with control logic that adapts to current battery demands. This dynamic control optimizes the balance between measurement precision and system complexity, performing disconnections strategically rather than continuously.
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 provides a precise and frequent estimation of battery state of charge, reducing measurement drift and operational interruptions, while being cost-effective and adaptable to cell wear.
Implementation Method 1
a sensor for the series current flowing through all the cells of the modules connected in series
Implementation Method 2
calculate the state of charge of the cells through which said series current flows from the integration of the series current
Implementation Method 3
voltage sensors across each of the cells of the disconnected module
Implementation Method 4
calculate the open-circuit voltage of each of the cells of the disconnected module from the voltage across the cell
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A system for estimating the charge status of a battery comprising at least two modules (1, 2, 3 and 4) each fitted with at least one cell (13-18, 19-24, 25-30 and 31-36), said system comprising a sensor (45) for sensing the series current traversing all the cells of the modules connected in series. This system further comprises: - switching means (37-44) capable of selectively disconnecting one of the modules, the other modules remaining connected in series; and -a calculation means (46) configured to calculate the charge status of the cells traversed by said series current from the integration of the series current and to calculate the charge status of each of the cells of the disconnected module from the no-load voltage of same.