Battery SOC Estimation Using Temperature-Dependent OCV Reference
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Solution Overview
Problem
Conventional methods for estimating the State of Charge (SOC) of batteries in electric vehicles are inaccurate due to the temperature-dependent open circuit voltage (OCV) and cannot account for dynamic battery patterns, leading to errors in measuring residual capacity.
Innovation Solution
A method that structures a comparative reference value by measuring open circuit voltages and residual capacities at various temperatures, using discharge capacity counting and OCV hysteresis to calculate an exact residual capacity, applicable to dynamic patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional OCV method is used to set initial SOC value, then the method is simple to implement, but the SOC estimation accuracy deteriorates due to temperature-dependent OCV changes
Solution Approach 1:
The patent changes the reference parameter from a single fixed OCV value to a temperature-dependent OCV table. By measuring and storing OCV values at multiple temperatures (e.g., -30°C to 60°C in 5°C intervals), the system selects the appropriate reference OCV based on current battery temperature, thereby maintaining high SOC estimation accuracy across varying thermal conditions while keeping the implementation relatively simple through pre-characterization.
Solution Approach 2:
The patent segments the continuous temperature range into discrete intervals by creating separate OCV reference values for different temperature ranges. This segmentation allows the system to handle temperature-dependent OCV variations by selecting the appropriate segment (temperature range) and its corresponding OCV reference, improving accuracy without requiring complex continuous modeling.
2Measurement precision
If discharge capacity counting is used for dynamic pattern batteries, then the residual capacity can be measured, but measurement errors increase due to apparatus errors and environmental variations
Solution Approach 1:
The patent implements a feedback mechanism where the measured terminal voltage during discharge is continuously compared against the temperature-compensated OCV reference values. The system calculates the voltage deviation and uses this feedback to correct the SOC estimation, thereby compensating for measurement errors and environmental variations in real-time during dynamic operation.
Solution Approach 2:
The patent replaces direct reliance on potentially error-prone current integration (Ah counting) with a voltage-based estimation method using OCV characteristics. By substituting the mechanical/electrical integration process with an electrochemical voltage measurement approach that accounts for temperature effects, the system achieves more reliable and consistent measurements under dynamic conditions.
3Stability of the object's composition
If OCV after sufficient relaxation is used as reference value, then the reference value is stable, but the method cannot be applied to batteries exhibiting dynamic patterns
Solution Approach 1:
The patent performs preliminary action by pre-measuring and storing OCV reference values at multiple temperatures before actual battery operation. This advance characterization creates a temperature-compensated reference table that can be quickly queried during dynamic operation, providing both the stability of relaxed OCV measurements and the adaptability needed for dynamic patterns.
Solution Approach 2:
The patent introduces dynamics by making the OCV reference value temperature-dependent rather than fixed. The system dynamically selects the appropriate OCV reference based on real-time battery temperature measurements, allowing the reference to adapt to changing operational conditions while maintaining the stability and accuracy of relaxed OCV measurements for each temperature condition.
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 accurate reference value for estimating SOC, reducing errors and enabling precise measurement of residual capacity in dynamic battery patterns.
Implementation Method 1
A lithium-ion polymer battery is much used as the battery for the electric vehicle
Implementation Method 2
it has been proved that the OCV is changed depending on the temperatures and the aging
Data Source
AI summary
Disclosed is a method for structuring a comparative reference value used to estimate a residual charge (SOC; State of Charge) of a battery. The method comprises comprising steps of: measuring open circuit voltages (OCV) and residual capacities (SOC) of a battery at various temperatures and tabling them according to the temperatures; measuring an open circuit voltage (OCV1) at a temperature before a test; carrying out a discharge capacity counting (Ah-counting) for the battery using a measurement apparatus while carrying out a dynamic pattern test; providing a sufficient relaxation time period for the battery after ending the dynamic pattern test; measuring an open circuit voltage (OCV2) at a temperature after the sufficient relaxation time period; obtaining residual capacity values of the battery corresponding to the measured open circuit voltages (OCV1, OCV2) from the table; assuming a difference between the above-obtained two residual capacity values as a δSOC and calculating an 1C-rated capacity based on the δSOC; and applying the calculated rated capacity as a denominator of the discharge capacity counting to calculate an exact residual capacity of the battery.