Secondary Cell Impedance Estimation from Transient Response Data
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Solution Overview
Problem
Conventional methods for estimating element parameters of secondary cells, such as lithium-ion batteries, are inaccurate due to the influence of inductive components.
Innovation Solution
An impedance detection device and method that calculates internal impedance and element parameters of secondary cells using current and voltage measurement data points during a transient response, employing an M-th degree equation based on an equivalent circuit model, thereby avoiding the influence of inductive components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Nyquist plot method is used to estimate element parameters, then the measurement process is simple, but the estimation accuracy is poor due to inductive component influence
Solution Approach 1:
The patent changes the approach from frequency-domain Nyquist plots to time-domain transient response analysis. By applying a step current or voltage and measuring the transient response, the method transforms the problem from frequency-based impedance measurement to time-based parameter estimation, thereby eliminating inductive component interference and improving accuracy
Solution Approach 2:
The patent segments the transient response into multiple discrete time points for measurement. By obtaining current or voltage data at I different time points (where I is a natural number greater than or equal to 2), the system can calculate multiple impedance data items and solve for element parameters through systematic calculation, improving accuracy while maintaining manageable complexity
2Measurement precision
If transient response measurement at multiple time points is performed, then element parameter estimation accuracy improves, but the measurement and calculation process becomes more complex
Solution Approach 1:
The patent uses I time points where I is greater than or equal to 2, which provides sufficient data for accurate parameter estimation without requiring excessive measurement points. This partial action approach achieves the necessary accuracy threshold while minimizing measurement and calculation time
Solution Approach 2:
The patent replaces complex iterative fitting methods with direct calculation using M-th degree equations. By formulating the relationship between transient response and element parameters as polynomial equations, the system achieves accurate parameter estimation through direct mathematical solution rather than iterative approximation, significantly reducing calculation time
Data Source
AI summary
An impedance detection device includes: an obtainer that obtains measurement data items on at least one of a current or a voltage at I time points in a transient response when a predetermined current or voltage is supplied to a secondary cell; and a calculator that calculates internal impedance based on the measurement data items. The calculator includes: a first calculator that calculates I impedance data items by using the measurement data items; and a second calculator that calculates an element parameter of an equivalent circuit model of the secondary cell, based on the I impedance data items and an M-th degree equation in which the internal impedance is represented by a linear combination of a plurality of terms. The M-th degree equation is an equation that is based on a theoretical value and is according to the predetermined current or voltage.