Battery Cell Aging Estimation via Equivalent Circuit Model
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Solution Overview
Problem
Existing methods for estimating the aging of accumulator battery cells, such as those used in electric vehicles, lack precision and reliability, fail to detect defective cells, and misinterpret reversible capacity variations as aging.
Innovation Solution
A method that models a battery cell as an electrical circuit with a perfect voltage source, resistors, and capacitors to accurately calculate the state of charge and maximum capacity, using a system of discrete equations and a state observer to estimate the variation of maximum capacitance, allowing for the detection of defective cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an extended Kalman filter is used to estimate battery charge level and maximum capacity, then the estimation process is simplified, but the precision and reliability of the estimation deteriorates
Solution Approach 1:
The patent transforms the electrochemical battery model into an equivalent electrical circuit model with changing parameters (resistors, capacitors, voltage sources) that represent different electrochemical phenomena. This allows using standard electrical circuit analysis methods while maintaining accuracy in estimating charge level and maximum capacity
Solution Approach 2:
The patent introduces an intermediary electrical circuit model that mediates between the complex electrochemical processes and the estimation algorithm. The circuit model with its resistors, capacitors, and voltage sources serves as a bridge, translating electrochemical behavior into electrical parameters that can be accurately estimated
2Productivity
If a simple estimation method is used, then the computational load is reduced, but the ability to detect defective cells is lost
Solution Approach 1:
The patent segments the battery into individual cells, each modeled by its own electrical circuit. This allows independent monitoring and detection of defective cells while maintaining overall system efficiency. Each cell's equivalent circuit can be analyzed separately to identify abnormalities
Solution Approach 2:
The patent uses time-varying parameters in the electrical circuit model (resistors, capacitors, voltage sources) that adapt to different operating conditions. This enables the system to maintain computational efficiency while accurately tracking cell-specific parameters for defect detection
3Device complexity
If traditional estimation methods are used, then the calculation process is simpler, but reversible capacity variations are misinterpreted as aging
Solution Approach 1:
The patent employs a dynamic electrical circuit model where resistors, capacitors, and voltage sources change their values based on operating conditions such as charge level, temperature, and current. This dynamic adaptation allows the model to distinguish between reversible capacity variations (due to operating conditions) and irreversible aging effects
Solution Approach 2:
The patent transforms static estimation parameters into dynamic ones that evolve with battery state. The equivalent circuit parameters (resistances, capacitances, voltages) are continuously updated to reflect current operating conditions, enabling accurate differentiation between temporary capacity changes and permanent aging
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 reliable and precise estimation of battery cell aging, enabling the detection of defective cells and avoiding misinterpretation of reversible capacity variations, thus improving the management of battery health and autonomy prediction.
Implementation Method 1
The perfect voltage source then models the electrochemical potential of the cell
Implementation Method 2
The resistance models the voltage drop induced by the cell connectors and the internal resistance of the cell
Implementation Method 3
the capacitor represents the double layer phenomenon at the electrode/electrolyte interfaces
Implementation Method 4
The other resistor and capacitor pairs connected in parallel model the phenomenon of diffusion of lithium ions in the cell
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a method for estimating the ageing of at least one cell of a storage battery, comprising the following steps: a) acquiring a voltage (Vcell) across the terminals of said cell and an amperage (I) passing through said cell, and b) calculating a maximum capacitance and a level of charge of said cell in accordance with the voltage and the amperage acquired in step a). According to the invention, in step b), the calculation is made by resolving: a system of discretised equations corresponding to a modelling of said cell as an electric circuit (42) comprising, in series, an ideal voltage source (Eeq), a resistor (RΩ), a first resistor (Rct) and capacitor (Cdl) pair connected in parallel, and at least one second resistor (Ri) and capacitor (Ci) pair connected in parallel; and a discretised equation for estimating the variation in the maximum capacitance of said cell.