Assembled Cell Charging Method with Voltage-Based Current Control
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Solution Overview
Problem
The challenge in charging assembled cells with multiple secondary batteries connected in series is the fluctuation in voltage due to differences in capacity and state of charge, leading to overcharging and reduced cycle service life, which existing methods like constant-current constant-voltage charging struggle to manage effectively, especially as the number of cells increases, resulting in reliability issues and potential safety hazards.
Innovation Solution
A charging method that detects cell voltages and adjusts the charging current setting value when a cell reaches a predetermined charge termination upper limit voltage, lowering the current and stopping the charge if the lowest cell voltage falls below a limit, ensuring all cells are protected from overcharging and preventing internal short-circuiting and overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If constant-current constant-voltage charging method is used, then charging speed is improved, but cell overcharging occurs due to voltage fluctuation between cells
Solution Approach 1:
The patent segments the charging control into two independent parts: (1) overall charging control based on assembled cell voltage, and (2) individual cell voltage monitoring with independent overcharge protection. This segmentation allows the system to maintain high charging speed while preventing any single cell from overcharging, even when voltage fluctuations occur between cells.
Solution Approach 2:
The patent implements a feedback mechanism where each cell's voltage is monitored in real-time, and when any cell reaches its upper limit voltage, the charging current is automatically reduced or stopped for that cell. This feedback loop prevents overcharging while allowing the overall charging process to continue at high speed for cells that have not reached their limit.
2Reliability
If feedback control is implemented for all cells to prevent overcharging, then cell protection is improved, but control circuit complexity increases
Solution Approach 1:
The control system is segmented into a simple main controller that manages overall charging based on assembled cell voltage, and individual cell monitoring units that independently track each cell's voltage. This segmentation allows comprehensive cell protection without requiring the main controller to process complex feedback from all cells simultaneously, thereby reducing overall control circuit complexity.
Solution Approach 2:
Each cell is equipped with its own voltage monitoring and protection mechanism that operates independently. When a cell reaches its voltage limit, it automatically triggers protection for itself without requiring complex centralized control, thereby simplifying the overall control circuit while maintaining reliable cell protection.
3Temperature
If number of series connections is increased to achieve high voltage, then power supply voltage is improved, but voltage fluctuation between cells increases
Solution Approach 1:
The patent segments the voltage monitoring and control into individual cell-level operations. Each cell's voltage is monitored and controlled independently, which prevents voltage fluctuations in one cell from affecting the charging status of other cells. This segmentation allows the system to maintain stable overall voltage even when numerous cells are connected in series.
Solution Approach 2:
The patent applies different voltage limits and control strategies to different cells based on their individual characteristics. Each cell has its own upper and lower voltage limits tailored to its specific properties, allowing the system to accommodate voltage fluctuations between cells while maintaining overall system stability and achieving the desired high power supply voltage.
Data Source
AI summary
According to one embodiment, a charging method for an assembled cell including a plurality of secondary batteries connected in series is disclosed. The method can detect the cell voltages. The method can set a charging current setting value so as to lower the charging current setting value of the assembled cell, if at least one of the detected cell voltages reaches a predetermined charge termination upper limit voltage. The method can control the charging current of the assembled cell according to the charging current setting value. In addition, the method can stop the charge, when a lowest cell voltage is lower than a predetermined charge termination lower limit voltage at a time when at least one of the cell voltages detected reaches the charge termination upper limit voltage.