Battery Impedance Measurement for Accurate SOH Estimation
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Solution Overview
Problem
Conventional methods for determining the state of health (SOH) of secondary batteries, particularly in vehicles, face challenges due to variations in charge and discharge conditions, temperature effects, and noise interference, leading to inaccurate estimation of deterioration and discharge capability.
Innovation Solution
A method that estimates the deterioration level or discharge capability by calculating the impedance of a battery using a reference direct current value, eliminating the influence of superimposed charge/discharge currents through a relational expression involving exponential terms, and applying temperature correction using a specific temperature characteristic function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If battery voltage is measured to estimate SOC using linearity, then the estimation method is simple, but the accuracy is poor due to over-voltage effects and inability to obtain stabilized voltage
Solution Approach 1:
The patent changes the measurement parameter from battery voltage to battery impedance. By applying an AC signal and measuring the impedance response, the system obtains accurate SOC and SOH values without being affected by over-voltage or stabilization requirements, thus improving measurement precision while maintaining practical simplicity
Solution Approach 2:
The patent replaces the conventional voltage-based electrical measurement with an impedance-based electrical measurement. This substitution eliminates the problems associated with voltage measurement (over-voltage, stabilization time) while providing more accurate and reliable battery state information
2Reliability
If battery capacity is corrected based on deterioration level, then the method accounts for battery aging, but the accuracy remains insufficient due to lack of temperature and operational condition considerations
Solution Approach 1:
The patent introduces temperature as an additional parameter in the impedance measurement process. By measuring impedance at different temperatures and applying temperature correction, the system achieves accurate SOH determination across varying thermal conditions, thereby improving measurement precision while maintaining reliability
Solution Approach 2:
The patent employs a feedback mechanism where the measured impedance values are compared against reference values obtained under controlled conditions. The system continuously adjusts and corrects the SOH determination based on actual measurements, improving accuracy over time while accounting for deterioration
3Productivity
If AC signal is used to measure battery impedance, then the measurement can be performed during operation, but noise from alternator and load interferes with the measurement accuracy
Solution Approach 1:
The patent uses a high-frequency AC signal (vibration in the electrical domain) to measure battery impedance. The high frequency helps distinguish the measurement signal from low-frequency noise sources like alternator and load, enabling accurate measurements during operation while maintaining measurement precision
Solution Approach 2:
The patent introduces a signal processing intermediary that separates the measurement AC signal from noise components. By using band-pass filtering and synchronous detection, the system extracts the impedance information while rejecting operational noise, thus achieving both productivity and precision
4Adaptability or versatility
If impedance measurement is performed with superimposed charge/discharge currents, then the measurement reflects actual operating conditions, but the superimposed currents affect the accuracy of deterioration assessment
Solution Approach 1:
The patent applies a small AC signal on top of the existing DC charge/discharge current before performing the impedance measurement. This preliminary action ensures that the measurement is taken under actual operating conditions while the AC signal's effect is sufficient to determine impedance without being significantly affected by the DC component, thus maintaining both adaptability and precision
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
This approach allows for accurate determination of battery deterioration and discharge capability, ensuring reliable battery management by accounting for temperature and operational conditions, thereby improving the accuracy of SOH assessment.
Implementation Method 1
the storage battery supplies a power to each load during and after engine start and is charged by a charger as well, thereby being charged and discharged repeatedly
Implementation Method 2
Generally, since there is a strong correlation between an internal impedance or an internal resistance and an SOH of a secondary battery
Data Source
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AI summary
A method for detecting SOC and SOH of a storage battery includes: calculating an SOC value of the storage battery with use of an SOC calculation unit based on a measured voltage value or a measured current value of the storage battery and calculating an SOH value of the storage battery with use of an SOH calculation unit based on the SOC value; further calculating a new SOC value with use of the SOC calculation unit based on the SOH value and calculating a new SOH value with use of the SOH calculation unit based on the new SOC value, these further calculations of SOC value and SOH value being repeated a prescribed n times of at least one so as to obtain an nth calculated SOC value and an nth calculated SOH value; outputting the nth calculated SOH value as an SOH output value and outputting the nth calculated SOH value as an SOC output value; and storing the SOH output value into a memory.