Battery State of Health Estimation via Partial Discharge
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Solution Overview
Problem
Existing methods for estimating the state of health of Lithium Iron Phosphate batteries are limited by the need for precise sub-millivolt no-load voltage measurements, which are challenging due to low voltage variations, and cannot completely discharge the battery to measure remaining capacity, making it difficult to assess health without completely discharging the source.
Innovation Solution
A method involving discharging the battery by a predetermined amount, measuring the open-circuit voltage, and comparing it to a threshold value to estimate the state of health, leveraging the characteristic offset in no-load voltage evolution with respect to the state of charge, allowing for precise estimation without full discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sub-millivolt no-load voltage measurements are used to estimate state of health, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent changes the measurement parameter from no-load voltage to discharge capacity. By measuring the actual capacity through controlled discharge and comparing it to the rated capacity, the system achieves accurate state of health estimation without requiring complex sub-millivolt voltage measurement circuits.
2Measurement precision
If the battery is completely discharged to measure remaining capacity, then measurement accuracy is improved, but battery reliability deteriorates
Solution Approach 1:
The patent applies partial discharge action by discharging the battery to a predetermined state of charge (e.g., 3.0V per cell) rather than complete discharge. This partial measurement approach provides sufficient capacity data for state of health estimation while preserving enough charge to maintain the battery's protective function during power outages.
3Reliability
If the battery is not completely discharged to maintain protective role, then battery reliability is preserved, but measurement precision deteriorates
Solution Approach 1:
The patent implements feedback by measuring actual discharge capacity and using this information to calculate state of health through comparison with rated capacity. The system continuously monitors discharge characteristics and uses this feedback to provide accurate state of health estimation without requiring complete battery depletion.
4Measurement precision
If multiple parameters (temperature, cycles, humidity) are considered for state of health estimation, then estimation accuracy is improved, but device complexity increases
Solution Approach 1:
The patent extracts the essential measurement from complex environmental parameter monitoring by focusing solely on discharge capacity measurement. This extraction approach isolates the most critical factor for state of health determination, eliminating the need for multiple temperature, humidity, and cycle counters while maintaining estimation accuracy.
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 simple and precise estimation of the state of health by measuring open-circuit voltage with reduced precision needs, determining if the battery's state of health is satisfactory or unsatisfactory, and identifying the necessary discharge quantity to assess remaining capacity, thus extending battery life without complete discharge.
Implementation Method 1
An electrical energy storage source is an electrochemical device subject to aging
Data Source
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AI summary
The invention relates to a method for estimating the state of health (SOH) of an electrical energy storage source, said method comprising the following steps: - discharging (50) of said electrical energy storage source of a predetermined quantity of energy (Qe) while said source is charged; - measuring (51) an open-circuit voltage (OCV) of said electrical energy storage source; - comparing (52) between said open-circuit voltage (OCV) and a threshold value (Vs); and - estimating the state of health (SOH) as a function of said comparison (52).