Cell Balancing Current Control for Flat-Cable Resistance Variation
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Solution Overview
Problem
The use of flat cables in cell-to-BMS connections in multi-series batteries results in varying resistance values based on cable length, leading to unequal cell balancing currents and reduced efficiency.
Innovation Solution
A cell balancing current control device and method that adjusts the on/off duty ratio of a switching module based on the resistance value of the flat cable length to optimize the cell balancing current for each individual cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat cable is used to connect each cell to the BMS, then the connection structure is simplified and ease of manufacture is improved, but the resistance value varies based on cable length causing unequal cell balancing currents and reducing cell balancing efficiency
Solution Approach 1:
The patent applies local quality by setting different resistance values for balancing resistors corresponding to different cell positions. Specifically, balancing resistors are configured with resistance values that compensate for the varying cable lengths - cells farther from the BMS have balancing resistors with lower resistance to compensate for higher cable resistance, ensuring uniform balancing current distribution across all cells
Solution Approach 2:
The patent changes the resistance parameter of balancing resistors based on cable length. The BMS calculates and sets specific resistance values for each balancing resistor according to its corresponding cable length, transforming a uniform system into a non-uniform one where each component's parameter is optimized for its specific position and conditions
2Device complexity
If a uniform cell balancing current is applied to all cells, then the control system is simple, but cells with different cable lengths experience different actual currents due to varying resistance, reducing balancing accuracy
Solution Approach 1:
The patent implements local quality by configuring each balancing resistor with a position-specific resistance value. The BMS stores and applies different resistance parameters for different cell positions, ensuring that each cell receives the appropriate compensating resistance to achieve uniform actual balancing current despite varying cable lengths
Solution Approach 2:
The BMS measures the actual cell voltages and balancing currents, then calculates and adjusts the duty cycle of switching modules based on the pre-stored resistance values corresponding to each cable length. This feedback mechanism ensures that the system adapts to actual conditions while maintaining uniform balancing effectiveness across all cells
3Productivity
If the cable length to each cell is made equal, then resistance values would be uniform and cell balancing efficiency would improve, but the physical layout and device complexity increase
Solution Approach 1:
Instead of changing the physical cable lengths to achieve uniformity, the patent changes the electrical parameter (resistance value) of balancing resistors to compensate for the inherent differences in cable lengths. This approach maintains the flexible physical layout while achieving uniform balancing current through parameter adjustment
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
Improves cell balancing efficiency by ensuring each cell receives an appropriate balancing current based on its specific cable resistance, thereby enhancing overall battery performance.
Implementation Method 1
a difference in cell voltage occurs during charging and discharging, a cell balancing operation is performed... a resistance value depending on a length of the flat cable which connects each cell of a multi-series battery and a battery management system (BMS)
Data Source
AI summary
A cell balancing current control device and method for a battery pack are capable of reflecting a resistance value depending on a length of a flat cable which connects each cell of a multi-series battery and a battery management system (BMS) (that is, cell to BMS connection) to control an on/off duty ratio of a switching module for applying a cell balancing current to be different for each individual cell, and a battery pack. Cell balancing current control is based on an on/off duty of a switching module calculated by reflecting the resistance value depending on the length of the flat cable.