Battery Impedance Measurement Using Multiplexer and ADCs
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Solution Overview
Problem
The high cost and complexity of measuring the impedance of multiple battery cells in a battery pack, due to the need for a large number of integrated circuits (ICs), pose a challenge in battery management applications, especially in electric vehicles where the number of cells is significant.
Innovation Solution
The use of a multiplexer to connect multiple analog-to-digital converters (ADCs) to a single battery cell, allowing each ADC to measure voltage and current, and implementing digital post-processing to compensate for ADC mismatches, reduces the number of required ICs and minimizes measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If N integrated circuits are mounted on N in-series connected battery cells to monitor impedance, then measurement precision is improved, but device complexity and cost increase due to high number of required ICs
Solution Approach 1:
Multiple battery cells are electrically connected in parallel to form a combined battery unit, which is then monitored by a single integrated circuit. This merging approach reduces the total number of ICs required while maintaining measurement capability through the parallel configuration that preserves impedance characteristics.
Solution Approach 2:
A single integrated circuit is designed to monitor multiple battery cells simultaneously through the parallel connection configuration. The IC performs universal monitoring functions for impedance, voltage, and current across multiple cells, eliminating the need for dedicated ICs for each individual cell.
2Measurement precision
If N integrated circuits are mounted on N battery cells to monitor impedance, then measurement precision is improved, but manufacturing cost increases due to high number of required ICs
Solution Approach 1:
Multiple battery cells are electrically connected in parallel to form a combined battery unit, which is then monitored by a single integrated circuit. This merging approach reduces the total number of ICs required while maintaining measurement capability through the parallel configuration that preserves impedance characteristics.
Solution Approach 2:
The patent uses voltage and current measurements from the parallel-connected battery unit to derive impedance information that represents individual cell characteristics. By copying the measurement approach from equivalent circuit theory, the system achieves accurate impedance monitoring without requiring physical separation of measurement circuits for each cell.
3Measurement precision
If multiple ADCs are used to measure voltage and current for impedance calculation, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The voltage measurement circuit and current measurement circuit are integrated within a single integrated circuit, combining multiple measurement functions into one device. This reduces the total number of separate components while maintaining the capability to perform both voltage and current measurements for impedance calculation.
Solution Approach 2:
The patent introduces a differential amplifier as an intermediary component that processes both voltage and current signals within the single IC. This intermediary element enables the integration of multiple measurement functions by providing a common signal processing path that handles both voltage and current inputs for impedance derivation.
Data Source
AI summary
In some examples, a device can be used for measuring the impedance of a first battery cell. The device includes a first analog-to-digital converter (ADC) and a second ADC. The device also includes a multiplexer configured to connect the first ADC to the first battery cell in a first instance and to connect the second ADC to a current sensor in the first instance. The current sensor is configured to sense current through the first battery cell. The multiplexer is also configured to connect the first ADC to the current sensor in a second instance and to connect the second ADC to the first battery cell in the second instance or in a third instance.