Inter-module Balance Circuit for Lithium-ion Battery Voltage Equalization
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Solution Overview
Problem
Lithium ion secondary batteries using olivine type cathodes face challenges in achieving balance between modules due to small voltage differences and capacity variations, making equalization difficult, especially over long cycles.
Innovation Solution
An inter-module balance circuit is implemented that divides the charge necessary for eliminating voltage differences into 10 or more parts, allowing for efficient charge transfer between modules, eliminating the need for transformers and ensuring the withstand voltage of switching elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a common transformer and switching circuit are used for multiple power storage modules, then device complexity is reduced, but wiring becomes complicated and the number of connections increases significantly
Solution Approach 1:
The patent divides the common transformer into separate transformers for each power storage module. Each module has its own transformer and switching circuit, eliminating the need for complex star-like wiring connections. This segmentation resolves the contradiction by increasing device complexity locally while dramatically improving ease of operation and wiring simplicity.
2Ease of operation
If uniform voltage control is applied to all cell groups, then control simplicity is maintained, but the ability to transmit power from high voltage to low voltage cell groups is lost
Solution Approach 1:
The patent implements dynamic control where each module's transformer and switching circuit can be independently controlled based on voltage conditions. The control unit adjusts switching operations dynamically to enable bidirectional power flow between modules with different voltages, resolving the contradiction by making the system adaptable while maintaining operational simplicity through automated control.
3Device complexity
If a common coil and switching element are provided on the secondary side of the transformer, then device complexity is reduced, but the withstand voltage requirement for the switching element becomes difficult to ensure
Solution Approach 1:
The patent assigns separate transformers and switching elements to each power storage module. This segmentation ensures that each switching element only needs to withstand the voltage of its own module rather than the total voltage of all series-connected modules, thereby ensuring reliability while maintaining reasonable device complexity.
4Productivity
If charge is transferred in a single operation to eliminate voltage differences, then productivity is improved, but manufacturing precision and balance control become difficult with small voltage differences
Solution Approach 1:
The patent implements periodic charge transfer operations where charge is divided into multiple segments and transferred in repeated cycles. The control unit monitors voltage differences and performs incremental charge transfers, allowing precise balance control even for small voltage differences while maintaining overall productivity through automated periodic operation.
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
The inter-module balance circuit effectively balances voltage between modules, even with small differences, reducing variability and ensuring stable charge and discharge performance over long cycles, while simplifying wiring and reducing the size of the inductor circuit.
Implementation Method 1
a flyback transformer is caused to operate, thereby electric charge is transferred from the high-voltage power storage module to the low-voltage power storage module
Data Source
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AI summary
Provided is a power storage apparatus, including: series circuits, the series circuits being formed of first coils and first switching elements, the first coils and the first switching elements being connected to a plurality of battery units in parallel; second coils electromagnetically coupled to the first coils; second switching elements connected to the second coils in series; a capacitor inserted between two common power source lines for commonly supplying voltage to both ends of the series circuits of the second coils and the second switching element related to the plurality of battery units; and a control unit that supplies a control pulse signal to the first switching element and the second switching element for equalizing voltage of each of the plurality of battery units, in which an amount of charge obtained by dividing an amount of transferred charge necessary for eliminating a voltage difference between the first battery unit and the second battery unit into 10 or more is transferred by switching operations of the first and second switching elements.