Lithium Battery Initial SOC Estimation Using DCIR Mapping
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Solution Overview
Problem
Lithium batteries face challenges in accurately setting the initial state of charge (SOC) due to a flat region in Open Circuit Voltage (OCV) variation with SOC, leading to increased errors in SOC estimation, especially in 12V lithium batteries, which affects battery management and endurance.
Innovation Solution
A vehicle system that includes a sensor to detect current, voltage, and temperature, a controller to calculate SOC using a direct current internal resistance (DCIR) map, and an alternator to adjust the SOC range based on actual charge current differences, ensuring accurate SOC estimation and endurance management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If Open Circuit Voltage (OCV) is used to estimate initial SOC of lithium battery, then the estimation process is simple, but the estimation precision deteriorates due to flat OCV region in 12V lithium batteries
Solution Approach 1:
The patent changes the estimation parameter from Open Circuit Voltage (OCV) to Direct Current Internal Resistance (DCIR). By measuring DCIR at different SOC levels and creating a DCIR-SOC map, the system achieves accurate SOC estimation in the flat OCV region where voltage-based methods fail. This parameter substitution resolves the contradiction by maintaining estimation simplicity while dramatically improving precision.
2Measurement precision
If DCIR map method is used to estimate initial SOC, then the estimation precision is improved, but the device complexity increases due to additional measurements and calculations
Solution Approach 1:
The system uses the battery's own operational characteristics (voltage and current measurements during normal charging/discharging) to calculate DCIR values. By leveraging existing sensor data and the battery's self-response to load changes, the method avoids requiring separate dedicated measurement equipment, thus improving precision while limiting complexity increase to algorithmic rather than hardware additions.
3Ease of operation
If inaccurate initial SOC is used, then the system operation is simple, but the SOC estimation error increases leading to reduced battery endurance
Solution Approach 1:
The patent implements preliminary DCIR-based SOC estimation before normal battery operation begins. By establishing an accurate initial SOC value through DCIR measurement and map lookup prior to charging cycles, the system ensures reliable starting conditions for subsequent SOC tracking. This preliminary action prevents error accumulation throughout battery usage, maintaining both operational simplicity and long-term reliability.
Data Source
AI summary
A vehicle includes a vehicle battery; a vehicle sensor configured to detect a current, a voltage and a temperature of the vehicle battery; and an alternator configured to output a target voltage to the vehicle battery. A controller is configured to calculate state of charge (SOC) estimation based on the current, voltage and temperature of the vehicle battery, calculate an initial SOC based on a direct current internal resistance (DCIR) map and apply the initial SOC to the SOC estimation, when an open circuit voltage (OCV) is maintained in a predetermined range after engine-off, and adjust an available SOC range based on a difference between an actual battery charge current amount, to which the initial SOC is applied, and the calculated SOC estimation.