EV Battery Fade Estimation Using Cathode Voltage and Kalman Updates
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Solution Overview
Problem
Existing methods fail to accurately determine the fade state of Lithium Manganese rich batteries in electric vehicles, which is crucial for assessing the remaining capacity and life of the battery, due to variations in the thermodynamic relationship between equilibrium potential and material state over the battery's life.
Innovation Solution
A method involving the measurement of terminal voltage during charging, updating battery models using a Kalman filter, determining maximum cathode voltage, and calculating the state of lithiation based on a selected relation between cathode voltage and lithiation state to accurately assess the battery's fade state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional voltage measurement methods are used to determine battery fade state, then the measurement process is simple, but the measurement precision is insufficient due to thermodynamic relationship variations
Solution Approach 1:
The patent implements a feedback mechanism where terminal voltage measurements during charging are continuously fed back to update the battery model parameters (such as open-circuit voltage, hysteresis voltage, and ohmic resistance). This updated model then provides more accurate fade state determination, creating a closed-loop system that improves measurement precision through iterative refinement.
Solution Approach 2:
The patent introduces a battery model as an intermediary between the terminal voltage measurements and the fade state determination. This model acts as a mediator that translates raw voltage data into accurate fade state information by accounting for thermodynamic relationship variations, thereby improving measurement precision without directly modifying the measurement process itself.
2Measurement precision
If the battery model is updated continuously during charging operation, then the fade state determination accuracy is improved, but the computational complexity increases
Solution Approach 1:
The patent applies partial action by updating only the necessary model parameters (open-circuit voltage, hysteresis voltage, ohmic resistance) during charging operation rather than performing a complete model re-identification. This selective updating approach maintains accuracy while reducing computational complexity compared to full model updates.
Solution Approach 2:
The patent focuses on changing specific model parameters (such as open-circuit voltage and hysteresis voltage) based on terminal voltage measurements during charging, rather than redesigning the entire battery model. This parameter-specific adjustment approach improves fade state determination accuracy while minimizing computational overhead.
3Measurement precision
If maximum cathode voltage is determined after charging operation, then the lithiation state calculation is accurate, but the time required for measurement increases
Solution Approach 1:
The patent performs preliminary actions by continuously monitoring and recording terminal voltage data during the charging operation itself, rather than waiting until after charging completes. This preliminary data collection reduces the post-charging measurement time while maintaining accuracy, as the necessary voltage data is already captured during the charging process.
Solution Approach 2:
The patent maintains continuity of useful action by continuously measuring terminal voltage throughout the charging operation, ensuring that the data collection process is ongoing and uninterrupted. This continuous measurement approach eliminates idle time between charging and measurement, reducing the total time required while preserving measurement accuracy.
Data Source
AI summary
A vehicle includes a system that performs a method for operating the vehicle. A processor obtains an initial voltage fade state of a battery of the vehicle and a model of an initial state of the battery of the vehicle, commences a charging operation of the battery, measure a terminal voltage of the battery while charging, updates the model during the charging operation using the terminal voltage, ends the charging operation, obtains measurements of a cathode voltage after the charging operation has ended, determines a maximum cathode voltage from the measurements, determines an updated voltage fade state of the battery based on the maximum cathode voltage, selects a relation between cathode voltage and lithiation state based on the updated voltage fade state, calculates a state of lithiation of a cathode from the maximum cathode voltage using the selected relation, and operates the vehicle based on the updated voltage fade state.