Stackable Bi-Directional Battery Balancer
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Solution Overview
Problem
Existing battery balancing systems are inefficient in terms of time and energy, as they often involve passive energy dissipation, unidirectional charge transfer, and are not capable of simultaneous balancing of multiple cells connected in series, limiting the total useful capacity and longevity of battery packs.
Innovation Solution
A bi-directional battery balancing system using transformer connections that allows for simultaneous balancing of multiple cells in a stack, with each cell within a sub-stack being balanced independently and efficiently, using a single serial port for control, enabling charge transfer between adjacent sub-stacks to equalize state of charge across all cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive balancing is used to discharge cells with higher SOC, then cell voltage equality is achieved, but energy is dissipated as heat causing high energy loss
Solution Approach 1:
An intermediary energy storage element (capacitor or inductor) is introduced to temporarily store energy from cells with higher SOC and transfer it to cells with lower SOC. This mediator enables direct energy transfer between cells without dissipating energy as heat, resolving the contradiction between achieving cell voltage equality and minimizing energy loss.
Solution Approach 2:
Instead of discarding excess energy from overcharged cells as heat (passive balancing), the system recovers this energy by transferring it to undercharged cells through active balancing circuits. The energy that would have been wasted is now reused, simultaneously achieving cell equality and energy conservation.
2Device complexity
If unidirectional balancing systems are used, then charge transfer is simplified, but balancing effectiveness is reduced as cells cannot both add and withdraw charge
Solution Approach 1:
The balancing system transitions from a static unidirectional charge transfer approach to a dynamic bidirectional approach. Power electronic switches (such as MOSFETs or IGBTs) enable the system to dynamically reverse charge flow direction, allowing cells to both add and withdraw charge as needed. This dynamic capability improves balancing effectiveness while maintaining manageable system complexity through intelligent control.
3Device complexity
If sequential balancing of cells is performed, then circuit complexity is reduced, but balancing time increases significantly
Solution Approach 1:
The battery pack is segmented into multiple independent balancing circuits, each capable of operating autonomously on a specific cell or cell group. This segmentation allows parallel balancing operations across multiple cells simultaneously, dramatically reducing total balancing time while keeping each individual circuit relatively simple and manageable.
Solution Approach 2:
The system enables continuous balancing action across all cells by operating multiple balancing circuits in parallel rather than sequentially. All cells undergo balancing simultaneously without idle time between operations, maximizing the utilization of balancing resources and minimizing total balancing time while maintaining reasonable circuit complexity.
4Power
If series connected cells are used to achieve high voltage, then power density increases, but the total useful capacity is limited by the weakest cell
Solution Approach 1:
A feedback mechanism continuously monitors the state of charge and voltage of each cell in the series connection. Based on this real-time feedback, the balancing system actively adjusts charge distribution to ensure all cells operate within their optimal capacity ranges. This feedback control prevents the weakest cell from limiting the overall pack capacity, allowing the battery system to fully utilize the capacity of all cells while maintaining high voltage and power density.
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 approach reduces balancing time and energy wastage, extends battery life by ensuring all cells operate within a balanced state of charge, and allows for the support of a theoretically unlimited number of cells through a single communication port, enhancing power efficiency and capacity utilization.
Implementation Method 1
A first cell balancer of the plurality of cell balancers may include a transformer having a primary winding and a secondary winding
Data Source
Figure 1~2b
Figure 3
Figure 4
AI summary
A battery balancing system includes at least one sub-stack, each sub-stack comprising a plurality of cells connected in series. The system also includes a balancing module for each sub-stack comprising an independent bidirectional balancer for each cell in the sub-stack. The system includes a daisy chained stackable serial port. The balancing system senses a state of charge (SOC) of each cell in each sub-stack. The average SOC of the sub-stack is determined. For a weak cell, additional charge is provided from its respective sub-stack during the discharging of the battery. For a strong cell, additional charge is removed and provided to its respective sub-stack during discharging of the battery. Any number of sub-stacks can be stacked in series while maintaining the same serial control, allowing a theoretically unlimited number of cells to be supported from a single communication port without the need for additional digital isolators.