Lithium Phosphate Battery State of Charge Estimation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods fail to accurately estimate the state of charge of electrochemical elements with lithium phosphate-type electrodes, particularly between 30% and 90% charge, due to minimal voltage variation, leading to inaccuracy in energy availability assessment.
Innovation Solution
A method that optimizes state of charge estimation by defining charge profile zones based on voltage and charge limits, using calibration relationships and coulometry to adjust and refine state of charge measurements, especially in 'flat' voltage zones, and accounts for measurement errors to prevent overloading or overdischarging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If voltage measurement is used to estimate state of charge in lithium phosphate elements, then the measurement method is simple, but the measurement precision deteriorates in the 30-90% charge range due to minimal voltage variation
Solution Approach 1:
The charge profile is divided into multiple zones (first zone: 0-30% SOC, second zone: 30-90% SOC, third zone: 90-100% SOC) with different voltage characteristics. Each zone is handled by a dedicated estimation algorithm, allowing precise measurement in each segment while maintaining overall system simplicity
Solution Approach 2:
The estimation method dynamically switches between different algorithms based on the current operating zone. In the flat voltage zone (30-90% SOC), the system transitions from voltage-based estimation to coulometry-based estimation, adapting the measurement approach to the local voltage characteristics
2Measurement precision
If coulometry is used continuously to improve state of charge measurement precision, then measurement precision improves, but device complexity and computational requirements increase
Solution Approach 1:
Coulometry is applied partially - only in the specific charge range (30-90% SOC) where voltage measurement is insufficient. In other ranges, the simpler voltage-based method is used, avoiding unnecessary computational complexity while maintaining precision where needed
Solution Approach 2:
The system uses an intermediate zone (30-90% SOC) where coulometry acts as a mediator between the two extreme zones. This intermediate approach compensates for voltage measurement limitations without requiring full coulometric monitoring, balancing precision and complexity
3Use of energy by moving object
If the element operates in the flat voltage zone (30-90% SOC), then energy availability is maximized, but state of charge detection becomes difficult leading to potential overloading or overdischarging
Solution Approach 1:
The system implements feedback through continuous monitoring of charge quantity and comparison with zone boundaries. When the estimated SOC approaches 30% or 90% thresholds, the system provides feedback signals to adjust operation, preventing overdischarging or overloading while maintaining operation in the optimal energy availability zone
Solution Approach 2:
The system performs preliminary estimation of state of charge using coulometry before operating in the flat voltage zone, establishing accurate baseline values. This preliminary action ensures reliable detection is in place before the element enters the 30-90% SOC range where voltage measurement would be insufficient
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 precise determination of the state of charge between 30% and 100% and between 0% and 10%, preventing overloading and overdischarging, and allows for partial adjustments in 'flat' voltage zones, ensuring accurate energy availability assessment.
Implementation Method 1
Electrical energy is produced by electrochemical reactions during an element discharge
Implementation Method 2
the voltage of the element varies very slightly depending on its state of charge. for a state of charge between about 30 and about 90%
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The method involves measuring voltage of an electrochemical element (E11). Adjusted charge state of the element is determined when value determined from a calibration relationship of voltage as a function of charge state is assigned to the adjusted state and zero value is assigned to a parameter corresponding to cumulative error in charge state obtained by coulometry, or coulometry determined value is assigned to the adjusted state. Cumulative measurement error for measurement of the charge state between time periods is determined. Independent claims are also included for the following: (1) a system for estimating charge state of an electrochemical element (2) an estimation system assembly (3) a computer program product having a set of instructions for estimating charge state of an electrochemical element (4) a computer-readable data carrier having a set of instructions for estimating charge state of an electrochemical element.