Battery Degradation Diagnosis Using Temperature-Compensated Cell Metrics
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing battery degradation diagnosis methods based on state of charge (SOC) variation and positive electrode potential are prone to erroneous diagnosis due to temperature fluctuations and usage modes, leading to inaccurate assessment of battery health.
Innovation Solution
A battery system that includes a control device with a parameter calculation unit to repeatedly calculate SOC variation and positive electrode potential, a comparison unit to compare these parameters with thresholds, and a diagnosis unit to determine battery degradation based on the slope of count values over cumulative usage or travel distance, adjusting thresholds based on temperature variation to reduce erroneous diagnosis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If degradation diagnosis is based on SOC variation among cells, then degradation can be detected, but erroneous diagnosis occurs when temperature variation among cells is large
Solution Approach 1:
The patent changes the diagnostic parameter from simple SOC variation to a composite parameter that incorporates temperature variation compensation. Specifically, it calculates a temperature-compensated SOC variation by subtracting the expected SOC variation due to temperature differences from the actual SOC variation, thereby isolating the degradation-related component.
Solution Approach 2:
The patent introduces temperature as an intermediary variable to mediate the relationship between cell conditions and SOC variation. By measuring temperature at each cell and using it to calculate expected SOC variation, the system can distinguish between temperature-induced SOC differences and degradation-induced SOC differences.
2Measurement precision
If degradation diagnosis is based on positive electrode potential, then degradation can be detected, but erroneous diagnosis occurs depending on usage mode
Solution Approach 1:
The patent makes the diagnosis threshold dynamic by adjusting it according to usage mode and temperature conditions. Instead of using a fixed threshold for positive electrode potential, the system adapts the threshold based on real-time operating conditions, allowing accurate degradation detection across different usage scenarios.
Solution Approach 2:
The patent changes the diagnostic approach by combining multiple parameters (SOC variation, positive electrode potential, temperature) into a comprehensive diagnostic model. This multi-parameter approach allows the system to differentiate between temporary potential drops due to usage mode and permanent degradation.
3Device complexity
If simple threshold comparison is used for degradation diagnosis, then diagnosis process is simple, but diagnosis accuracy decreases due to temperature and usage mode variations
Solution Approach 1:
The patent segments the degradation diagnosis process into multiple independent calculation steps: temperature measurement, expected SOC variation calculation, actual SOC variation measurement, temperature-compensated SOC variation calculation, and final degradation determination. This segmentation allows each step to be optimized independently while maintaining overall accuracy.
Solution Approach 2:
The patent implements feedback mechanisms where temperature measurements and usage mode information continuously feed into the diagnosis algorithm. The system uses real-time feedback from temperature sensors and usage mode detection to dynamically adjust the diagnostic parameters and thresholds, improving accuracy without significantly increasing complexity.
Data Source
AI summary
A battery system includes a monitoring unit configured to detect voltages, currents, and temperatures of cells included in a battery. An ECU increments a count value when an SOC variation among the cells becomes larger than a threshold, based on the detection results of the monitoring unit. The ECU increments a count value when a positive electrode potential of the cell becomes lower than a threshold, based on the detection result of the monitoring unit. The ECU diagnoses that the battery is degraded when the amount of change in any of the count values becomes equal to or larger than a predetermined value.