Battery Impedance Calibration Using a Series Reference Resistor
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Solution Overview
Problem
Existing battery monitoring systems face measurement errors due to phase shifts in wiring systems, leading to inaccurate impedance calculations in lithium-ion batteries, which can result in dangerous conditions like overheating and explosion.
Innovation Solution
A battery monitoring device and system that includes a reference resistor connected in series with the battery, a measurement calculation unit to measure impedance, and a calibration unit to correct gain and phase errors using the impedance of the reference resistor, ensuring accurate impedance measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If impedance measurement is performed using conventional methods, then measurement can be conducted, but measurement accuracy deteriorates due to phase shifts in wiring systems
Solution Approach 1:
A reference resistor is introduced as an intermediary component connected in series with the battery. This reference resistor serves as a mediator to capture the phase shift and gain error introduced by the wiring system. By measuring the voltage across this known reference resistor, the system can calculate the actual current flowing through the battery and use this information to correct the impedance measurement, thereby eliminating the measurement errors caused by wiring phase shifts.
Solution Approach 2:
The system implements a feedback mechanism where the measured voltage across the reference resistor is used to calculate the actual current, and this calculated current is then fed back to correct the impedance measurement. The calibration unit uses the reference resistor measurements to determine correction factors for gain and phase, which are applied to subsequent battery impedance measurements, creating a continuous feedback loop that ensures accurate measurements despite wiring variations.
2Measurement precision
If calibration using reference resistor is implemented, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The reference resistor serves multiple functions simultaneously: it acts as a current sensing element, a phase reference, and a calibration standard. The same hardware component (reference resistor) is used for both normal operation current measurement and for calibration purposes, eliminating the need for separate calibration hardware and reducing overall system complexity despite the enhanced measurement capabilities.
Solution Approach 2:
The system performs self-calibration using the reference resistor, which provides its own known impedance characteristics as a built-in reference standard. The calibration process is automated through the calibration unit that automatically calculates correction factors based on measurements taken during normal operation, eliminating the need for external calibration equipment or manual calibration procedures.
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 enables precise impedance measurement of batteries, enhancing battery control and reliability by correcting for measurement errors caused by wiring phase shifts, thereby improving safety and performance.
Implementation Method 1
PTL 1 suggests employing an alternating current (AC) impedance method for measuring the impedance of a battery by measuring voltage and current while causing the battery to sweep an AC signal.
Implementation Method 2
a calibration unit configured to correct a gain and a phase of the impedance of the battery that has been measured, using the impedance of the reference resistor that has been measured
Data Source
AI summary
A battery monitoring device includes: a reference resistor connected to a cell stack in series; a measurement calculation unit (a voltage measurement unit, a current measurement unit, and an impedance calculation unit) configured to measure impedance of each of cells in the cell stack and impedance of the reference resistor; and a calibration unit configured to correct a gain and a phase of the impedance of each of the cells that has been measured, using the impedance of the reference resistor that has been measured.