Battery Cell Charge Balancing via Target Depth of Discharge
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Solution Overview
Problem
Existing battery management systems face inefficiencies in balancing the states of charge across multiple battery cells, leading to unnecessary energy losses due to differences in cell capacities caused by production variations and aging, especially in hybrid and electric vehicles.
Innovation Solution
A method that determines individual cell capacities and states of charge, calculates a target depth of discharge and state of charge for each cell, and iteratively discharges cells with significant deviations from their targets, optimizing energy balance without requiring additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional resistive cell balancing is used to equalize states of charge, then charge balance is achieved, but energy is lost as heat and efficiency deteriorates
Solution Approach 1:
The patent replaces the traditional resistive balancing mechanism with a capacitive balancing mechanism. Instead of dissipating energy as heat through resistors, the system uses capacitors to store and transfer energy between cells, substituting a energy-dissipating mechanical/thermal process with an energy-conserving electrical storage process.
Solution Approach 2:
The patent changes the fundamental parameter of the balancing approach from resistive (energy-dissipating) to capacitive (energy-storing). By altering the physical mechanism from resistance-based to capacitance-based, the system transforms the energy loss problem into an energy conservation solution while maintaining the charge balancing function.
2Power
If individual battery cells are connected in series to increase voltage and energy content, then overall battery performance improves, but cells with different capacities cause the lowest capacity cell to limit the overall charge
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors the state of charge of each individual cell and uses this information to control the capacitive balancing process. The system adjusts energy transfer based on real-time cell status, ensuring that cells with different capacities are balanced appropriately without compromising overall battery performance.
Solution Approach 2:
The patent segments the battery management into individual cell-level control, monitoring and balancing each cell separately rather than treating the battery as a single unit. This segmentation allows the system to address capacity differences between cells while maintaining the series connection benefits for overall power output.
3Loss of energy
If capacitive or inductive balancing methods are used instead of resistive balancing, then energy can be exchanged between cells with limited efficiency, but hardware complexity increases
Solution Approach 1:
The patent designs the capacitive balancing system to serve multiple functions: it balances cells with different capacities, maintains charge uniformity, and can operate in conjunction with the existing series connection architecture. The same capacitive elements serve both as energy storage devices and as balancing components, reducing the need for separate dedicated balancing hardware.
Data Source
AI summary
A method for balancing states of charge of battery cells of a battery includes determining the individual cell capacities of the cells. A k-th cell having the smallest cell capacity, the individual states of charge, the depth of discharge, a target depth of discharge, and a target state of charge are determined. The deviation of the state of charge of a cell from the target state of charge (ΔSOCtarget,n) and the minimum deviation of the state of charge of a cell from the target state of charge (ΔSOCmin) are determined. At least one of the cells, to which ΔSOCtarget,n−ΔSOCmin>X applies, where X≧0, is discharged. If ΔSOCtarget,n−ΔSOCmin≦X applies to all cells, the method ends. If this condition does not apply to all cells, the individual states of charge are determined again and the method is repeated.