Multi-Cell AC Impedance Circuit for Lower-Cost Battery Pack Sensing
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Solution Overview
Problem
The high implementation costs and complex communication chains associated with measuring the DC impedance of each battery cell in a battery pack for electric vehicles make it inefficient, particularly due to the need for multiple measurement circuits and nodes.
Innovation Solution
A multi-cell AC impedance measurement system that uses a single common measurement circuit to control an excitation current through multiple battery cells, receiving voltage signals, measuring the current, and calculating complex impedance using either one ADC per cell or two matched ADCs, allowing for efficient measurement of AC impedance in a single cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate measurement IC is used for each battery cell to measure DC impedance, then measurement accuracy is improved, but implementation cost and device complexity increase significantly
Solution Approach 1:
The patent combines multiple measurement functions into a single measurement IC that can measure impedance of multiple battery cells simultaneously. This single IC integrates excitation current generation, voltage measurement circuits, and impedance calculation capabilities, eliminating the need for separate measurement ICs for each cell and reducing the overall system complexity while maintaining measurement accuracy
Solution Approach 2:
The measurement IC is designed with universal functionality to handle multiple battery cells through a single interface. It can sequentially or simultaneously measure multiple cells by multiplexing the measurement circuits, allowing one IC to perform the work of multiple dedicated ICs while reducing communication nodes and implementation costs
2Productivity
If multiple measurement circuits are used to measure each battery cell simultaneously, then measurement speed is improved, but implementation cost and system complexity increase
Solution Approach 1:
The patent implements periodic measurement cycles where the single measurement IC sequentially measures multiple battery cells in rapid succession. By using periodic excitation signals and time-multiplexed measurement, the system achieves fast measurement of all cells without requiring parallel measurement circuits, thus maintaining high productivity while reducing device complexity
Solution Approach 2:
The measurement system dynamically switches between different battery cells during a measurement cycle using multiplexers and dynamic signal routing. This dynamic allocation of measurement resources allows the single IC to efficiently measure multiple cells in sequence, achieving parallel-like measurement speed without the hardware overhead of multiple dedicated circuits
Data Source
AI summary
A method for measuring a complex impedance of a plurality of battery cells in a battery pack comprises controlling an excitation current through the plurality of battery cells in the battery pack; receiving, in a single common measurement circuit, a plurality of voltage signals corresponding to the plurality of battery cells; measuring the excitation current; and calculating a complex impedance of each of the battery cells in the plurality of battery cells based on the plurality of voltage signals and the measured excitation current in a single measurement cycle using either one analog-to-digital converter (ADC) per battery cell or two matched ADCs per battery cell.