Battery SOH Estimation Using Complex Impedance Phase-Magnitude
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Solution Overview
Problem
Conventional methods for estimating the state of health (SOH) of energy storage devices, such as batteries, are inaccurate and slow, especially when battery conditions like State-Of-Charge (SOC) change, and do not effectively utilize the interrelationship between the magnitude and phase of complex impedance for precise SOH estimation.
Innovation Solution
A method and system that measure the complex impedance of energy storage devices over a range of frequencies and estimate SOH based on the interrelationship between the magnitude and phase, using graphical representations like phase-magnitude plots, and employ machine learning models to predict SOH and other parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacity-based methods are used to estimate SOH, then historical data can be stored and analyzed, but the estimation is slow and requires complete charge and discharge cycles
Solution Approach 1:
The patent replaces conventional capacity-based estimation methods (which require complete charge/discharge cycles) with impedance-based measurement. By measuring complex impedance at multiple frequencies and analyzing the phase-magnitude relationship, the system obtains SOH indicators rapidly without needing to subject the battery to full cycling, thus eliminating the time penalty while maintaining accuracy.
Solution Approach 2:
The patent transforms the approach by changing from measuring capacity (which requires time-consuming cycles) to measuring impedance parameters (magnitude and phase at different frequencies). This parameter substitution enables rapid SOH estimation because impedance measurements can be taken instantly at operational frequencies without requiring the battery to undergo complete charge/discharge transitions.
2Measurement precision
If IC-DV-based methods are used to estimate SOH, then voltage and current data can be utilized, but the accuracy is sensitive to voltage and current noise in the measurements
Solution Approach 1:
The patent substitutes IC-DV-based estimation (which directly uses noisy voltage and current measurements) with impedance-based estimation. By measuring complex impedance through dedicated impedance analysis at multiple frequencies, the system obtains data that is less sensitive to operational noise, as impedance measurements are performed under controlled excitation conditions that filter out typical operational disturbances.
Solution Approach 2:
The patent introduces impedance magnitude and phase as intermediary parameters between the raw voltage/current measurements and the final SOH estimation. These intermediary parameters serve as noise-filtered representations of battery state, as the phase-magnitude relationship captures essential degradation indicators while being less susceptible to the voltage and current noise that directly affect IC-DV methods.
3Ease of operation
If impedance-based methods using only DC or real component are used, then measurements can be simplified, but the applications are limited and accuracy is insufficient
Solution Approach 1:
The patent extends the measurement approach from one-dimensional (DC or real component only) to two-dimensional complex impedance measurement. By incorporating both magnitude and phase components across multiple frequencies, the system captures additional information dimensions that reveal more about battery degradation mechanisms, thereby improving accuracy while maintaining measurement simplicity through standardized impedance analysis procedures.
Solution Approach 2:
The patent segments the impedance measurement into multiple frequency points rather than using a single DC or real-component measurement. By analyzing the phase-magnitude relationship across different frequencies, the system extracts multiple independent indicators of battery health (such as resistance changes, capacitance changes, and time constant variations), each providing complementary information that collectively enhances SOH estimation accuracy.
4Measurement precision
If complex impedance values are used for SOH estimation, then more information can be utilized, but identifying accurate indicators and relationships is difficult and highly inaccurate when battery conditions change such as SOC
Solution Approach 1:
The patent changes the analysis approach by transforming complex impedance data into specific derived parameters (phase-magnitude relationship characteristics) that are inherently more stable across varying SOC conditions. By focusing on the relationship between phase and magnitude rather than absolute values, the system identifies indicators that reflect degradation mechanisms independent of charge state, thereby reducing complexity while improving accuracy.
Solution Approach 2:
The patent applies local quality analysis by examining specific features of the phase-magnitude relationship at different frequency regions. Different frequency ranges provide localized information about different battery components (electrolyte, electrodes, interfaces), and by analyzing the phase-magnitude characteristics in these localized frequency domains, the system identifies SOC-invariant degradation indicators without needing to process the entire spectrum uniformly, thus reducing overall complexity.
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
Provides accurate and rapid estimation of SOH, enabling timely adjustments and preventing potential failures by leveraging the unique indicators present in the phase-magnitude relationship, which conventional methods miss.
Implementation Method 1
measuring a complex impedance of an energy storage device for a range of frequency
Data Source
AI summary
Systems and method for determining State-of-Health (SOH) for energy storage devices are described herein. An example method includes measuring a complex impedance of an energy storage device for a range of frequency, and estimating a state of health (SOH) of the energy storage device based on an interrelationship between a magnitude and a phase of the complex impedance of the energy storage device.