Capacitive AC-Link Battery Equalizer for Multi-Cell Balancing
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Solution Overview
Problem
Existing battery equalization technologies, such as DC-DC converters with selective switches (DCSS) and multiport circuits (MC), face challenges in efficiently balancing battery voltages across multiple cells, requiring complex control circuits and multiple active components, which increases cost and complexity.
Innovation Solution
A battery equalizer using a capacitively-coupled ZETA-derived converter with a single active switch and a shared AC link, eliminating the need for selection switches and reducing the number of magnetic components, allowing for autonomous equalization of multiple cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC-DC converters with selective switches (DCSS) are used for battery equalization, then battery cell voltage balancing can be achieved, but the number of switches and control circuits increases significantly
Solution Approach 1:
The patent combines multiple battery equalization functions into a single DC-DC converter circuit. Instead of using separate switches for each battery cell selection, the invention uses one converter with capacitive coupling to simultaneously equalize multiple battery cells, merging what would traditionally require multiple discrete components into a unified circuit architecture.
Solution Approach 2:
The DC-DC converter is designed to perform multiple functions: it serves as both the voltage conversion element and the equalization mechanism for multiple battery cells. The single converter circuit universally handles equalization across all connected battery cells through its capacitive coupling architecture, eliminating the need for cell-specific control circuits.
2Device complexity
If multiport circuits are used to replace converter and selective switches, then the number of active components is reduced, but transformer design becomes challenging with many cells
Solution Approach 1:
The patent extracts the transformer component from the equalization circuit entirely. Instead of using a multiport circuit with a complex multi-winding transformer that would require one winding per battery cell, the invention removes the transformer and uses a DC-DC converter with capacitive coupling, thereby eliminating the manufacturing challenges associated with designing and implementing large-scale transformers.
Solution Approach 2:
The invention replaces the magnetic coupling mechanism (transformer) with an electrostatic coupling mechanism (capacitive coupling). This substitution eliminates the need for physical transformer windings and magnetic cores, replacing them with capacitor-based energy transfer that is simpler to manufacture and scale with the number of battery cells.
3Device complexity
If DCSS with one output is used, then the circuit structure is simple, but only one battery can be equalized at a time requiring selector switches
Solution Approach 1:
The patent merges multiple equalization channels into a single DC-DC converter output. Instead of having separate equalization paths for each battery cell that would require selector switches, the invention combines all equalization functions through one converter with capacitive coupling, allowing simultaneous equalization of multiple batteries without requiring switching between channels.
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 solution reduces circuit size, weight, and cost while simplifying control, enabling efficient and simultaneous equalization of multiple battery cells with reduced complexity and active components.
Implementation Method 1
An AC side of the AC/DC converter is capacitively-coupled to the AC link at the input end of the cell circuit
Data Source
AI summary
A battery equalizer for a series-connected battery string. The battery equalizer contains a plurality of cell circuits, an AC link, and a DC/AC converter. The plurality of cell circuits at their input ends is connected in parallel with each other and to the AC link. Each cell circuit at its output end is adapted to connect to a corresponding battery cell of the battery string. The DC/AC converter connects to the AC link. Each of the cell circuits contains an AC/DC converter, and an AC side of the AC/DC converter is capacitively-coupled to the AC link at the input end of the cell circuit. As the current taken from the first stage is common to all battery cells, charging or discharging of individual battery cells is autonomously determined by the output current of the second stage.