Battery State Estimation via AC Impedance Frequency Analysis
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Solution Overview
Problem
Conventional methods struggle to accurately estimate the state of charge and discharge of batteries, particularly when voltage-based methods are insufficient, and fail to recognize battery health, leading to potential accidents like overcharging, overdischarging, solution leakage, and explosions.
Innovation Solution
A method and system that estimate the state of charge and discharge by analyzing the frequency dependency of complex impedance and direct-current resistance, using alternating-current impedance measurements and pulse loads, and compare these with known states to control charging and discharging, while also evaluating battery health through complex impedance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If voltage measurement is used to estimate state of charge, then the method is simple and widely applicable, but it fails when voltage-based estimation is insufficient for certain battery types
Solution Approach 1:
The patent changes the measurement parameter from voltage to internal resistance (through AC impedance measurement). By measuring the real part of impedance at multiple frequencies and comparing frequency dependency characteristics, the system achieves accurate SOC estimation for battery types where voltage-based methods fail, while maintaining broad applicability across different battery chemistries.
2Reliability
If conventional voltage-based monitoring is used, then the system is simple to operate, but it cannot detect battery health degradation and prevent serious accidents
Solution Approach 1:
The AC impedance measurement system performs multiple functions simultaneously: it estimates state of charge (real part of impedance), evaluates battery health (changes in impedance characteristics over time), and detects degradation patterns. This multi-functional approach enhances safety without requiring separate monitoring systems for each function.
Solution Approach 2:
The system continuously monitors impedance characteristics and provides feedback on both SOC and battery health status. By comparing measured impedance values against reference data and tracking changes over time, the system can alert operators to degradation trends and potential safety issues before they become critical.
3Measurement precision
If AC impedance measurement is performed at multiple frequencies, then state of charge estimation accuracy is improved, but measurement time and system complexity increase
Solution Approach 1:
The patent measures impedance at multiple frequencies (including Warburg frequency and lower frequencies) to capture the frequency dependency characteristics needed for accurate SOC estimation. By selecting specific frequency points that provide the most diagnostic information, the system achieves high measurement accuracy while minimizing the total number of measurements required.
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
Enables accurate estimation and management of battery state and health, preventing accidents by effectively controlling charging and discharging, and early detection of health degradation such as short circuits, thus ensuring safe battery operation.
Implementation Method 1
determining complex impedance between positive and negative electrodes of a battery at a plurality of frequencies
Implementation Method 2
comparing frequency dependency of Warburg impedance of the determined complex impedance with frequency dependency of Warburg impedance corresponding to a known state of charge or depth of discharge
Implementation Method 3
Secondary batteries are widely used in a household stationary electrical storage device, an electric vehicle power source
Implementation Method 4
a battery in which ionic liquid is used as electrolytic solution
Data Source
AI summary
It is intended to recognize the state of charge or depth of discharge of the battery more accurately than conventional technologies and to recognize health of a battery appropriately. Complex impedance between positive and negative electrodes of the battery is determined at a plurality of frequencies, and the state of charge or depth of discharge of the battery is estimated by comparing frequency dependency of Warburg impedance of the determined complex impedances with frequency dependency of Warburg impedance corresponding to a known state of charge or depth of discharge of the battery. Similarly, complex impedance is determined, and the health of the battery is evaluated by using the real part of the complex impedance at a point where the imaginary part of the complex impedance is zero on a line obtained by extending a part, which indicates frequency dependency of Warburg impedance, of a complex impedance characteristic curve representing a correlation relationship between the real and imaginary parts of the determined complex impedance.