Charge Transfer EIS Measurement for Battery Impedance Analysis
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Solution Overview
Problem
Existing battery management systems require significant equipment and incur energy losses when performing electrochemical impedance spectroscopy (EIS) measurements, especially on high-capacity batteries with low excitation frequencies.
Innovation Solution
A method and apparatus that wire accumulator cells in series, allowing charge transfer between two groups of cells to determine impedance values with reduced equipment and energy loss, using a DC/DC converter for charge offset without external energy storage, and employing synchronous rectification to minimize switching elements and energy storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an external energy store (capacitor/inductor) is used to generate excitation signals for EIS measurements, then excitation can be provided to the battery, but the energy store must be dimensioned to store the energy quantity of the greatest excitation signal, leading to large size and high cost especially for large batteries and low frequencies
Solution Approach 1:
The battery system uses itself as the energy store by dividing its cells into two groups that charge and discharge alternately. This self-service approach eliminates the need for external energy storage components, as the battery's own cells provide the necessary energy for excitation signals during EIS measurements.
Solution Approach 2:
The battery is segmented into two groups of cells (first number and second number of accumulator cells) that operate in alternating phases. One group charges while the other discharges, providing the excitation signal without requiring external energy storage. This segmentation allows the system to generate its own excitation signals using its internal structure.
2Ease of operation
If active balancing circuits are provided for each cell to transfer charge between adjacent cells, then charge transfer can be achieved, but this is associated with relatively high equipment outlay
Solution Approach 1:
The EIS measurement function and the charge transfer function are merged into a single process. The same charge transfer between cell groups that provides excitation signals also serves as the active balancing mechanism, eliminating the need for separate balancing circuits and reducing equipment complexity.
Solution Approach 2:
The charge transfer mechanism serves multiple functions simultaneously: it generates excitation signals for EIS measurements, performs active balancing between cell groups, and enables impedance spectroscopy. This multi-functionality reduces the overall equipment requirements and simplifies the system architecture.
3Device complexity
If charge is transferred back and forth between cell groups to generate excitation signals, then EIS measurements can be performed with reduced equipment outlay, but energy loss must be minimized
Solution Approach 1:
The charge transfer between the two cell groups occurs periodically, with each group alternating between charging and discharging phases. This periodic action allows energy to be efficiently transferred back and forth between the groups, minimizing losses by keeping the energy within the battery system rather than dissipating it externally.
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 enables efficient EIS measurements with reduced equipment outlay and minimal energy loss, allowing for continuous monitoring of batteries during normal operation with low energy consumption.
Implementation Method 1
using a DC/DC converter for charge offset
Implementation Method 2
employing synchronous rectification to minimize switching elements and energy storage
Data Source
AI summary
Subjecting batteries with a plurality of cells to a balancing is known. Active balancing is carried out between adjacent cells or cell groups by means of a bus across uninvolved cells. Using this charge transfer for electrochemical impedance spectroscopy is known. The problem is to provide a system and method with which EIS measurements can be carried out on a battery using significantly less equipment outlay, with as little energy loss as possible, on batteries with high capacity and also on those with low excitation frequencies. The problem is solved in that charge is transferred back and forth between a first number of accumulator cells and a second number of accumulator cells during determination of at least one voltage value. The first and second numbers of accumulator cells are wired in series, and the first and second number is at least two.