Battery Cell Balancing During Sleep Mode Without Overheating
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Solution Overview
Problem
Conventional cell balancing methods in electric vehicle batteries are inefficient and cannot effectively balance cells during long parking phases or when the vehicle is asleep, leading to reduced usable capacity and range, as they often cause overheating or over-discharge.
Innovation Solution
A stand-alone cell balancing method using a main management unit and multiple stand-alone slave devices, where cells are grouped and connected to resistors with unique parity identifiers, allowing for efficient balancing without overheating or over-discharging by selecting non-adjacent resistors and setting a predetermined threshold for balancing eligibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional dissipative balancing is used during vehicle operation, then cell charge dispersion is reduced, but the total usable capacity decreases and the balancing is insufficient for long parking phases
Solution Approach 1:
The patent performs balancing operations in advance during vehicle operation when the BMS is active, preparing the cell charges to be as balanced as possible before the vehicle is parked. This preliminary action reduces the imbalance that would otherwise accumulate during long parking phases, allowing the vehicle to maintain optimal capacity and range even when balancing cannot occur during sleep mode
2Reliability
If stand-alone balancing is implemented during vehicle sleep mode, then cell balancing continues during parking phases, but overheating or over-discharge may occur
Solution Approach 1:
The patent applies partial balancing during sleep mode by selectively discharging only the most charged cells (those above a threshold voltage) rather than attempting to balance all cells. This partial action is sufficient to maintain acceptable charge distribution across the battery pack without generating excessive heat or causing over-discharge, as the balancing current is limited and applied only where needed
Solution Approach 2:
The patent changes the balancing parameters during sleep mode by using a higher voltage threshold (e.g., 4.2V or 4.25V) compared to normal operation, and by limiting the balancing current to a lower value. These parameter changes ensure that balancing occurs safely during sleep mode without causing overheating or over-discharge, while still maintaining adequate cell charge distribution
3Productivity
If balancing current is increased to balance more ampere-hours during driving phases, then balancing efficiency improves, but the risk of overheating and over-discharge increases
Solution Approach 1:
The patent dynamically adjusts the balancing current based on real-time cell voltage measurements and operating conditions. During vehicle operation, the BMS can apply higher balancing currents when needed, while during sleep mode it switches to lower currents. This dynamic adjustment optimizes balancing speed while preventing overheating and over-discharge by adapting the current level to the specific operational context
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 method enables optimal cell balancing during vehicle sleep mode without overheating or over-discharging, maintaining battery health and extending the vehicle's range by ensuring cells are balanced efficiently and effectively.
Implementation Method 1
discharging the cells into a resistor to a target state of charge
Data Source
AI summary
A method for controlling the cell balancing of a battery of electrical accumulators of an electrical system includes balancing, for each subgroup, the cell having the largest amount of electrical charge to be balanced with selected cells.