Capacitor Voltage Balancing Circuit for Fast Cell Equalization
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Solution Overview
Problem
Existing voltage balancing circuits for series-connected power storage devices suffer from high power consumption, large size, high cost, and slow voltage equalization speed, particularly when dealing with a large number of devices.
Innovation Solution
A voltage balancing circuit using N single-pole double-throw switches and N capacitors, where the switches are connected to the power storage devices and capacitors, with a switch controller controlling the switches to facilitate direct charge transfer between devices, eliminating the need for discharge resistance and heavy magnetic components, and allowing quick voltage balancing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If voltage balancing is performed by transferring charge between adjacent battery cells, then voltage balancing is achieved, but the balancing speed is slow due to sequential processing
Solution Approach 1:
The voltage balancing circuit divides the battery pack into multiple groups, with each group containing adjacent battery cells. Each group has its own balancing circuit that can independently transfer charge between cells within that group. This segmentation allows parallel processing of balancing operations across multiple groups simultaneously, dramatically increasing balancing speed compared to sequential processing of individual cells.
Solution Approach 2:
The balancing circuit transfers charge not only between immediately adjacent cells but also between cells that are separated by one or more cells within the same group. This partial skipping of cells allows faster redistribution of charge across the battery pack while still maintaining the parallel group structure, achieving excessive action beyond simple adjacent-cell balancing.
2Productivity
If switching elements are inserted between all adjacent battery cells to enable parallel balancing, then balancing speed increases, but the number of switching elements becomes excessively large
Solution Approach 1:
Instead of placing switching elements between every adjacent cell pair in the entire battery pack, the circuit segments cells into groups where switching elements are only inserted between adjacent cells within the same group. This reduces the total number of switching elements from O(N²) to O(N/G) where N is total cells and G is number of groups, while still enabling parallel balancing operations across multiple groups.
Solution Approach 2:
Each switching element within a group serves multiple functions: it enables charge transfer between adjacent cells, allows skipping of intermediate cells for faster balancing, and works in conjunction with other switching elements in the same group to achieve various balancing configurations. This multi-functionality reduces the need for dedicated switching elements for each possible cell pair.
3Device complexity
If charge is transferred by directly connecting positive terminal of one cell to negative terminal of adjacent cell, then simple circuit structure is achieved, but voltage polarity mismatches prevent effective charge transfer
Solution Approach 1:
The balancing circuit introduces asymmetric connections within each group by connecting positive terminals to positive terminals and negative terminals to negative terminals of cells, rather than the symmetric adjacent polarity connection. This asymmetric polarity-matching approach ensures that voltage differences between cells can be effectively utilized for charge transfer, regardless of the cells' positions in the battery pack sequence.
Solution Approach 2:
The circuit uses intermediate connection points and switching elements that act as mediators to properly connect cells with matching polarities. These intermediaries enable the circuit to overcome the direct adjacent-cell polarity mismatch problem by routing charge through appropriate terminal connections, ensuring reliable charge transfer while maintaining circuit functionality.
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 circuit achieves low power loss, reduced size, and lower cost while enabling fast voltage equalization across multiple series-connected power storage units, suitable for large numbers of devices without the need for bulky magnetic components or complex sensors.
Implementation Method 1
a capacitor is inserted between a positive terminal of the i-th battery cell and a positive terminal of the j-th battery cell, or between a negative terminal of the i-th battery cell and a negative terminal of the j-th battery cell, so that a voltage difference between the battery cells is balanced by charge transfer from a capacitor
Data Source
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Figure 3A~3B
AI summary
A voltage balancing circuit is applied to a power supply system. The power supply system comprises N power storage devices. The voltage balancing circuit comprises: N switches, N capacitors and a controller; the N switches are respectively connected to the N serial power storage devices; the N switches are respectively connected to the first terminals of the N capacitors; the second terminals of the N capacitors are connected to a common neutral line; the controller is connected to the N switches through a control line to control the switching of the N switches. The voltage balancing circuit avoids power loss when balancing the voltage of a plurality of serial power storage devices, and is small in size and low-cost, and balances voltage quickly.