Battery State of Charge Determination Using Weighted Sensor Fusion
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Solution Overview
Problem
Determining the state of charge (SOC) and state of health (SOH) of rechargeable batteries is challenging due to complex degradation mechanisms and the need for robust, cost-sensitive designs that do not interfere with charging or discharging processes, especially in applications with fluctuating load profiles and partial recharge cycles.
Innovation Solution
A method involving two distinct processes to determine the SOC, one through charge counting by integrating input and output currents and another through voltage evolution measurement, with a weighted average calculation to derive a robust SOC value, using loss factors and trustworthiness coefficients to account for measurement reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single charge counting process is used to determine state of charge, then the measurement is simple and cost-effective, but the accuracy and robustness are insufficient due to complex degradation mechanisms and fluctuating load profiles
Solution Approach 1:
The patent combines multiple different processes (charge counting, voltage evolution measurement, and other SOC estimation methods) into a unified framework that calculates a final SOC value as a weighted combination of results from all processes. This merging approach improves measurement accuracy by leveraging the strengths of each individual method while compensating for their weaknesses through the weighted averaging mechanism.
Solution Approach 2:
The patent creates a universal SOC determination method that can accommodate multiple different measurement processes and adapt to various battery types and application scenarios. The framework is designed to be flexible, allowing different processes to be weighted differently based on their reliability under specific conditions, making it applicable to diverse battery systems including those with fluctuating load profiles and partial recharge cycles.
2Reliability
If robust state of charge determination is implemented, then the state of health assessment improves, but the cost and complexity of the control system increase
Solution Approach 1:
The patent enables the battery management system to self-assess its own state of health by utilizing the determined SOC values and comparing them against expected performance characteristics. The system automatically identifies degradation patterns and updates its internal models without requiring external intervention or complex additional hardware, allowing the battery to essentially monitor and assess its own health status through intelligent algorithms.
Solution Approach 2:
The patent changes the approach from direct complex measurements to using SOC determination as an intermediate parameter that indirectly provides state of health information. By monitoring how SOC values evolve over time and comparing measured discharge capacities against rated capacities, the system can assess battery degradation and health status through parameter analysis rather than direct complex measurements.
3Measurement precision
If multiple measurement processes are combined to improve accuracy, then the state of charge determination becomes more robust, but the computational complexity and processing time increase
Solution Approach 1:
The patent implements a flexible weighting system where not all measurement processes need to be equally weighted or fully processed at all times. The system can adjust the weighting factors to emphasize more reliable processes under specific conditions while reducing the computational burden from less reliable processes. This partial action approach allows the system to achieve robust SOC determination by focusing computational resources on the most effective measurement methods for given operating conditions.
Data Source
AI summary
Determining a state of charge (SOC) of a rechargeable battery includes using a first process to determine a first value for the SOC of the battery and using a second process to determine a second value for the SOC of the battery and deriving the SOC as a weighted average of the first value for the SOC and the second value for the SOC. During a charging cycle of the battery an input charge of the battery is determined from an input current flowing into the battery and a charging time. During a discharging cycle an output charge of the battery is determined from an output current flowing out of the battery, a discharging time and an actual capacity of the battery is the sum of the input charge over charging cycles minus the sum of the output charge over discharging cycles.