Battery OCV Estimation via Logarithmic Inflection Detection
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Solution Overview
Problem
Existing methods for estimating the open-circuit voltage (OCV) of electrochemical batteries in vehicles require long relaxation times, often exceeding one hour, which is impractical for real-time applications due to limited opportunities during automotive use, and existing adaptive methods are computationally complex.
Innovation Solution
A method for estimating OCV using a logarithmic representation of the voltage signal during battery relaxation, detecting an inflection point to calculate OCV symmetrically, which can be done in a few tens of seconds with minimal computational resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the battery system is charged to high voltage (above 4.2V) to increase energy density, then the energy storage capacity is improved, but the risk of electrolyte decomposition and battery damage increases
Solution Approach 1:
The patent applies preliminary action by pre-charging the battery at a reduced voltage (first charging voltage below 4.2V) before applying the full charging voltage. This preliminary charging step forms a protective layer on the electrode surface, preventing electrolyte decomposition when the battery is subsequently charged to high voltage (above 4.2V), thus resolving the contradiction between energy density and electrolyte stability
Solution Approach 2:
The patent changes the charging voltage parameter dynamically by implementing a two-stage charging process: first charging at a lower voltage (below 4.2V) and then charging at the higher voltage (above 4.2V). This parameter change allows the battery to achieve high energy density while the initial low-voltage charging protects against electrolyte decomposition, resolving the technical contradiction
2Loss of time
If the open-circuit voltage is measured immediately after charging to save time, then the measurement speed is improved, but the voltage reading is inaccurate due to ongoing chemical reactions
Solution Approach 1:
The patent applies preliminary action by performing a rest period wait time (5-30 minutes) after charging before measuring the open-circuit voltage. This preliminary waiting allows chemical reactions to stabilize and cease, ensuring that the voltage measurement taken afterward is accurate, thus resolving the contradiction between measurement speed and accuracy
Solution Approach 2:
The patent implements feedback by using the measured open-circuit voltage to determine the state of charge and control the charging process. The system waits for the voltage to stabilize (feedback condition met) before taking the measurement, ensuring accuracy while minimizing wait time through optimized feedback control
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 real-time estimation of OCV with improved accuracy and reduced computational demands, suitable for embedded applications in vehicles and other systems with power and computing constraints.
Implementation Method 1
a lookup table storing a relationship between open-circuit voltages and states of charge at a fully charged temperature is used to estimate the open-circuit voltage of the battery pack based on a terminal voltage of the battery pack and a state of charge of the battery pack
Data Source
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Figure 3a~3b
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AI summary
The invention relates to a method for determining the open-circuit voltage of an electrochemical accumulator. The method comprises the steps of continuously measuring (202) a voltage signal, continuously calculating (203) a logarithmic signal of the voltage depending on said voltage signal as a function of the value in logarithmic form of time, checking (205) whether the logarithmic signal contains a point of inflection and, in the event of detecting at least one point of inflection at a second time, estimating (207a) the open-circuit voltage parameter symmetrically about the point of inflection as a function at least of the value of the logarithmic signal at the second time. The invention is applicable in particular to the management of motor vehicle drivetrain battery systems.