Active Cell Balancing Circuit for Low-SOC Battery Cells
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Solution Overview
Problem
Existing passive battery balancing technologies waste electrical energy by draining it to load resistors, leading to inefficient balancing and premature battery degradation due to out-of-balance conditions, particularly when cells have varying self-discharge rates.
Innovation Solution
A system that actively balances batteries by selectively charging individual cells with a current-limited power supply, using voltage sensors and switches controlled by a controller to equalize state of charge (SOC) without converting energy to heat.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive balancing is used to equalize cell SOCs, then battery balance is restored, but electrical energy is wasted as heat in load resistors
Solution Approach 1:
Instead of draining energy from high SOC cells to balance the battery (passive approach), the patent inverts the approach by actively charging low SOC cells to match the highest SOC cell. This is achieved by connecting individual cells to a power supply through switches, allowing selective charging of cells with lower SOC until all cells reach the target SOC level, thereby eliminating energy waste in resistors.
2Reliability
If passive balancing drains all cells to the lowest SOC level, then complete balance is achieved, but battery capacity is reduced
Solution Approach 1:
The patent inverts the traditional balancing approach by not draining cells to the lowest SOC level, but instead charging low SOC cells up to the highest SOC level. This preserves the overall battery capacity while achieving balance, as no energy is discarded and the minimum usable capacity of the battery is maintained.
3Productivity
If individual cell charging is implemented, then balancing efficiency is improved, but system complexity increases
Solution Approach 1:
The patent segments the battery system into individually controllable cells, with each cell equipped with its own switch (e.g., MOSFET) that can be independently controlled by a microcontroller. This segmentation allows selective charging of specific cells based on their SOC status, enabling efficient active balancing while using simple, readily available electronic components.
Solution Approach 2:
The patent introduces a microcontroller as an intermediary that monitors cell voltages and controls the switches to enable selective charging. This intermediary manages the complexity by providing intelligent control logic that determines which cells need charging and when to terminate charging, thereby achieving efficient balancing without requiring complex hardware circuits.
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
Effectively maintains battery balance by efficiently adding energy to cells with lower SOC, preventing premature degradation and extending battery life, especially in cases of leaky cells.
Implementation Method 1
The power supply 141 can provide a current source to the cells (101, 102, 103, 104). When the power supply 141 is active and one pair of switches is closed, current flows from the positive terminal 143 of the power supply 141 to one of cells (101, 102, 103 or 104)
Implementation Method 2
Voltage sensors (111, 112, 113, 114) are connected in parallel to each cell (101, 102, 103, 104). The controller 131 also receives data from the voltage sensors (111, 112, 113, 114) via one or more voltage sensors data lines 134
Data Source
AI summary
An apparatus and method of balancing cells in a battery using an isolated power supply and pairs of switches to direct power to cells at a lower state of charge to bring them into balance with cells at a higher state of charge.