Battery SOC Estimation Using Temperature-Based Capacity References
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Solution Overview
Problem
Current battery management systems face challenges in accurately estimating the state of charge (SOC) of automotive batteries due to variations in capacity with temperature and differences in Open Circuit Voltage (OCV) depending on the charged, discharged, and deteriorated states of the battery.
Innovation Solution
An apparatus and method that simulate the use amount of an automotive battery in engine-on/off states by creating test conditions based on vehicle driving information, including specific charging and discharging cycles, to estimate the battery's state of charge, lifespan, and aging, using a computer and tester to determine the SOC, SOH, DOD, and energy use amount.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a method of estimating SOC through coulomb counting using a nominal capacity reference is used, then the SOC can be determined, but an error occurs because the actual capacity reference changes with temperature
Solution Approach 1:
The patent changes the reference capacity parameter from a fixed nominal value to a dynamic value that varies with temperature. The system stores multiple capacity references corresponding to different temperature ranges and selects the appropriate reference based on the current battery temperature, thereby compensating for temperature-induced capacity variations and improving SOC estimation accuracy.
2Measurement precision
If a method of detecting SOC by finding the relationship between SOC and factors such as internal resistance, temperature, and discharged current is used, then SOC can be detected, but it is difficult to measure accurate SOC because there is a difference in characteristic depending on charged state, discharged state, and degree of deterioration
Solution Approach 1:
The patent segments the battery's operational characteristics by dividing the temperature range into multiple intervals, each with its own capacity reference. This segmentation allows the system to account for different battery behaviors at different temperatures, improving the accuracy of SOC detection across various operating conditions.
Solution Approach 2:
The patent makes the capacity reference dynamic by selecting different references based on real-time temperature measurements. Instead of using a static nominal capacity, the system adapts the capacity reference to match current operating conditions, thereby accounting for variations in charged state, discharged state, and deterioration level.
3Measurement precision
If a durability test is performed to estimate battery lifespan, then accurate SOC and aging estimation can be achieved, but the test requires a long duration
Solution Approach 1:
The patent changes the test parameters by applying accelerated stress conditions, specifically temperature cycling and repeated charge-discharge cycles at elevated temperatures. These parameter changes accelerate the aging process, allowing the system to obtain lifespan and SOC estimation data in a significantly reduced time frame while maintaining measurement accuracy.
Solution Approach 2:
The patent performs preliminary characterization of the battery's capacity-temperature relationship before conducting the durability test. This preliminary action establishes the foundation for accurate SOC estimation during the accelerated test, enabling the system to track aging and SOC changes accurately even under compressed test conditions.
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 accurate estimation of battery state of charge and aging by simulating real-world conditions, allowing for a short duration durability test and improving the accuracy of battery management systems.
Implementation Method 1
a battery that stores and releases energy
Implementation Method 2
a method of estimating an SOC uses a nominal capacity reference
Data Source
AI summary
An apparatus for estimating a battery state of charge includes a computer that determines a lifespan of a battery by creating test conditions for the battery by reflecting predetermined driving information of a vehicle and then performing the test conditions; and a tester that performs charging according to predetermined charging conditions and discharging according to predetermined discharging conditions on the battery in accordance with the test conditions.