Transformer-Based Bidirectional Battery Balancing Circuit
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Solution Overview
Problem
Existing battery balancing systems, particularly for Li-ion batteries in high voltage applications, face inefficiencies and higher costs due to the need for bulky active balancing circuitry, with passive balancing being cost-effective but inefficient, and active balancing being costly.
Innovation Solution
A battery apparatus and balancing circuit that uses a transformer with multiple windings and transistors to facilitate bidirectional charge transfer between batteries, allowing selective connection of cell batteries to a balancing circuit for charge balancing without requiring dedicated buffer batteries or DC-DC converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If passive balancing is used to discharge cells with higher voltage, then cost is reduced, but efficiency and performance deteriorate
Solution Approach 1:
The patent introduces a buffer battery as an intermediary component that facilitates active balancing between series-connected battery cells. The buffer battery temporarily stores excess charge from cells with higher voltage and transfers it to cells with lower voltage, achieving efficient balancing while avoiding the need for expensive DC-DC converters or transformers for each cell pair.
Solution Approach 2:
The balancing circuit designed in the patent serves multiple functions: it performs active balancing for series-connected cells, charges the buffer battery when cells have excess energy, and can discharge the buffer battery to supplement cells needing charge. This multi-functional approach improves efficiency compared to passive balancing while keeping costs lower than dedicated active balancing circuits for each cell.
2Productivity
If active balancing with DC-DC converters and transformers is used, then efficiency is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges multiple balancing operations into a single unified circuit that handles balancing for multiple series-connected cells simultaneously. Instead of requiring separate DC-DC converters or transformers for each cell pair, one balancing circuit with a buffer battery can service the entire string, dramatically reducing device complexity and size while maintaining high efficiency.
Solution Approach 2:
The buffer battery acts as a central intermediary that simplifies the balancing architecture. Rather than needing complex point-to-point conversion circuits between each cell pair, the buffer battery provides a single intermediary storage point that all cells can interact with, reducing the overall system complexity while achieving efficient energy transfer.
3Power
If multiple Li-ion cells are connected in series for high voltage applications, then voltage support is improved, but the need for bulky active balancing circuitry increases
Solution Approach 1:
The patent segments the balancing function by separating the buffer battery from the series-connected cell string. This segmentation allows the balancing circuit to operate independently with a single buffer battery rather than requiring proportional balancing circuitry for each cell in the series string, significantly reducing the volume of balancing circuitry needed while supporting high voltage applications.
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 solution enables efficient and cost-effective bidirectional charge transfer, improving the performance and reducing the size and cost of battery balancing systems compared to traditional active and passive methods, while maintaining high voltage isolation.
Implementation Method 1
A transformer with a first winding coupled with the first battery, a second winding coupled with a second battery
Data Source
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AI summary
Disclosed examples include battery apparatus and balancing circuits (200) for transferring charge between one or more of a plurality of first battery cells and a second battery, in which the first battery cells are coupled with a first winding (W1) of a transformer (300), and the second battery is coupled with a second winding (W2). A first transistor (Q1) is turned on to allow current flow in the first winding (W1) to discharge the first battery cells, and then the first transistor (Q1) is turned off. The resulting induced voltage in the second winding (W2) turns on a second transistor (Q2) to provide flyback active charge balancing to charge the second battery. A signal from a third winding (W3) allows detection of low or zero current flow in the second winding (W2) for a controller (314) to begin subsequent charge transfer cycles for full isolation between the first and second batteries.