Cell Voltage Measurement Using Periodic Switching
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Solution Overview
Problem
Measuring cell voltages in series-connected accumulator cells often leads to unbalanced loading, reducing the effective capacity of battery packs due to existing methods.
Innovation Solution
A method and device using series-connected measuring resistors and switches to measure cell voltages relative to a common reference potential, allowing for balanced voltage determination across cells by calculating the difference in voltage drops across two terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional voltage measurement methods are used to measure individual cell voltages, then cell voltage measurement is achieved, but the individual cells become unbalanced due to different loading levels during measurement
Solution Approach 1:
The measurement process is performed periodically by sequentially switching between different cells in groups. Instead of measuring all cells simultaneously (which causes unbalance), the system measures cells in alternating cycles, allowing previously measured cells to recharge while others are being measured, thus maintaining cell balance while achieving accurate voltage measurements.
Solution Approach 2:
The system performs preliminary actions by pre-charging certain cells through parallel connection during periods when they are not being measured. This ensures that when a cell is selected for measurement, it is already in a balanced state, preventing the unbalance problem that occurs with conventional simultaneous measurement methods.
2Loss of information
If individual cell voltages are measured simultaneously, then complete voltage data is obtained, but the effective capacitance of the battery pack is reduced due to unbalance
Solution Approach 1:
The system obtains complete voltage data through periodic sequential measurement of all cells. By measuring cells in alternating cycles and using a capacitor to store voltage information, the system achieves complete data collection without simultaneously loading all cells, thus preserving effective capacitance while maintaining data completeness.
Solution Approach 2:
A capacitor is introduced as an intermediary element to store the voltage information of cells during the periodic measurement process. This capacitor allows the system to capture complete voltage data from all cells sequentially without requiring simultaneous measurement, thereby avoiding the unbalance issue while maintaining data completeness.
3Measurement precision
If measuring resistors are connected in parallel to cells during measurement, then voltage measurement is enabled, but loading unbalance occurs between cells
Solution Approach 1:
The measuring resistors are connected in parallel to cells periodically rather than simultaneously. The switching mechanism connects measuring resistors to different cells in alternating cycles, allowing cells to be measured one at a time while others remain unloaded or are recharging, thus enabling voltage measurement capability while maintaining loading balance.
Solution Approach 2:
The connection state of measuring resistors is made dynamic rather than static. The switching mechanism dynamically connects and disconnects measuring resistors from different cells based on the measurement cycle, allowing the system to adapt the loading distribution over time and maintain balance while enabling voltage measurements when needed.
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 minimizes unbalance, enhancing measuring precision, interference immunity, and response time, while maintaining accuracy across various cell counts.
Implementation Method 1
A number of series-connected measuring resistors matching the number of the cells to be measured, as well as a number of switches between the measuring resistors and the cells by means of which, upon closing, one of the measuring resistors can be parallel-connected to one of the cells
Data Source
AI summary
The invention relates to a method and a device for measuring cell voltages of accumulator cells in a plurality of series-connected accumulator cells in a battery pack or cell pack including an Li-Ion cell pack. The method and the device are characterized in that no unbalancing of the battery pack is caused by the measurements of the cell voltages on the individual accumulator cells.