Battery Charge-Discharge Curve Estimation for Real-Time Efficiency Diagnosis
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Solution Overview
Problem
Existing methods for estimating the charge-discharge efficiency of lithium ion batteries are not suitable for real-time operation in aggregates, as they require long constant current periods and are not adaptable to the varied conditions of batteries with different types, manufacturers, and reuse histories.
Innovation Solution
An economic efficiency estimation apparatus and method using a charge-discharge curve, which includes a function derivation unit, charge and discharge units, a measurement unit, a state estimation unit, and an estimation arithmetic processing unit. This system derives an approximate curve of the open-end voltage and impedance functions, corrects them using a Kalman filter and Gaussian function, and estimates the charge-discharge curve to calculate economic efficiency indices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pOCV or GITT methods are used to estimate OCV and Z values, then measurement precision is improved, but the method becomes unsuitable for real-time operation in battery aggregates due to long constant current periods and varied battery conditions
Solution Approach 1:
The patent changes the measurement parameters from traditional pOCV/GITT methods to a dynamic estimation approach using terminal voltage, current, and temperature data during normal charge-discharge operations. This allows accurate OCV and Z value estimation without requiring long constant current periods, making it adaptable to varied battery conditions in aggregates.
Solution Approach 2:
The patent replaces the mechanical/electrical measurement system (pOCV/GITT with constant current charging-discharging) with a computational estimation system using algorithms that process terminal voltage, current, and temperature data. This substitution enables real-time estimation during normal operations without disrupting battery usage.
2Measurement precision
If traditional charge-discharge efficiency estimation methods are used, then measurement precision is improved, but productivity deteriorates due to inability to perform real-time estimation during normal operations
Solution Approach 1:
The patent enables continuous estimation of charge-discharge efficiency during normal charge-discharge operations by using terminal voltage, current, and temperature data that are continuously available. This eliminates the need to stop operations for specialized measurements, maintaining continuous productive use of the battery aggregate.
Solution Approach 2:
The patent makes the battery system self-diagnostic by using its own operational data (terminal voltage, current, temperature) to estimate efficiency parameters. This eliminates the need for external specialized measurement equipment and procedures, enabling real-time monitoring during normal operations.
3Reliability
If comprehensive efficiency degradation diagnosis is performed on battery aggregates, then reliability is improved, but device complexity increases due to need for multiple diagnosis functions
Solution Approach 1:
The patent creates a universal estimation system that simultaneously provides capacity degradation diagnosis, efficiency degradation diagnosis, and charge-discharge curve estimation using the same set of measurements (terminal voltage, current, temperature) and algorithms. This multi-functional approach improves reliability without proportionally increasing device complexity.
Solution Approach 2:
The patent merges multiple diagnosis functions (capacity degradation, efficiency degradation, charge-discharge curve estimation) into a single integrated system that processes the same measurement data through unified algorithms. This combination reduces the need for separate measurement systems and simplifies the overall diagnostic apparatus.
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 accurate estimation of economic efficiency and efficiency degradation for various rechargeable batteries, including reused ones, by using the charge-discharge curve, thus optimizing energy use and reducing energy loss in battery aggregates.
Implementation Method 1
a state estimation unit configured to estimate state parameters including a value of a charging rate, and a polarization voltage and an internal impedance of the secondary battery using an algorithm of a Kalman filter
Implementation Method 2
calculate a posterior estimation value by correcting the open-end voltage value and the impedance value in accordance with a correction expression using a Gaussian function having a predetermined learning rate L and a correction width σ as terms
Data Source
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AI summary
An economic efficiency estimation apparatus derives an approximate curve of an initial open-end voltage function and an initial impedance function, sets a prior estimation function, and measures a charge-discharge voltage and a charge-discharge current. A state estimation unit estimates state parameters including an SOC value, and a polarization voltage and an internal impedance using a Kalman filter. The apparatus obtains an estimation error between a prior estimation voltage and an actually measured voltage, calculates a posterior estimation value by a correction expression using a Gaussian function having a learning rate and a correction width as terms which are set for the estimation error and current value, corrects the prior estimation function based on the posterior estimation value, sets a new prior estimation function, estimates a charge-discharge curve, and estimates an economic efficiency index based on a charge-discharge power amount of the secondary battery estimated from the curve.