Battery SOC Estimation via Nominal Volume and Pressure Changes
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Solution Overview
Problem
Current methods for estimating the state-of-charge (SOC) of batteries, particularly lithium-ion batteries, are inaccurate due to non-linear battery dynamics and dependence on various factors, leading to SOC estimation drift and challenges in resetting the SOC without damaging the battery.
Innovation Solution
A system and method that uses a sensor to measure changes in the nominal volume or pressure of the battery, constructing charging and discharging curves to estimate SOC, allowing for a more accurate and independent estimation of battery state through characteristic features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If open circuit voltage is used to estimate SOC, then the estimation method is simple to implement, but the estimation accuracy deteriorates due to voltage being influenced by temperature, charging history, and other factors
Solution Approach 1:
The patent introduces an intermediary physical quantity (battery dimension or pressure) that mediates between the battery's charge state and the estimation system. Instead of directly using voltage which is influenced by multiple factors, the system uses dimension/pressure changes as an intermediate indicator that more directly reflects SOC, thereby improving estimation accuracy while maintaining implementation simplicity
Solution Approach 2:
The patent changes the measurement parameter from electrical (voltage) to mechanical (dimension or pressure). This parameter transformation allows the system to estimate SOC based on physical expansion/contraction of the battery, which is less susceptible to temperature and charging history effects, thus resolving the accuracy problem while keeping the method simple
2Speed
If current integration method is used to estimate SOC, then the estimation can be performed in real-time, but the SOC drifts away from the real value over time requiring periodic resetting
Solution Approach 1:
The patent implements a feedback mechanism where dimension or pressure measurements are continuously used to correct and reset the SOC estimation. The characteristic curve of dimension/pressure versus SOC provides feedback information that allows the system to periodically reset the estimated SOC to match the actual SOC, preventing drift accumulation while maintaining real-time estimation capability
Solution Approach 2:
The battery's own physical expansion and contraction during charging and discharging serve as a self-indicating mechanism. The system leverages the battery's natural physical behavior (volume change with SOC) to provide self-correction information, eliminating the need for external calibration procedures or full charge/discharge cycles to reset SOC
3Reliability
If lithium-ion batteries are used to maintain voltage level, then the battery performance is improved, but the SOC estimation becomes significantly more challenging due to minimal voltage change from 20% to 80% SOC
Solution Approach 1:
The patent transitions from measuring SOC in the electrical dimension (voltage) to the mechanical dimension (dimension or pressure). Since lithium-ion batteries maintain stable voltage across a wide SOC range, the system switches to measuring physical expansion/contraction, which provides detectable changes in a different dimension, thereby solving the detection difficulty while preserving battery performance
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
This approach provides a more reliable and accurate SOC estimation that is less dependent on temperature and other factors, enabling periodic resetting of electrical SOC estimates and improving battery management in electric vehicles.
Implementation Method 1
Lithium-ion based batteries maintain their voltage level for a long time even as the SOC drops. The voltage of a lithium ion battery will not change significantly in a range from about 20% to 80% SOC.
Data Source
AI summary
A system and method for monitoring a state-of-charge (SOC) of a battery, where the system includes a sensor and a controller. The sensor provides a measurement signal that can track changes of a nominal volume of the battery by either measuring a size or pressure of the battery, where the nominal volume is the volume that the electrolyte, anode, cathode and current collectors would occupy if unconstrained. The controller is programmed to use a function to estimate the SOC from the measurement signal. The function can be established after constructing and finding a repeatable charging and discharging curve of the battery that graphs the measurement signal compared to the SOC of the battery.