Method of Estimating Pulse Response Using an Impedance Spectrum

• US 20100332165A1
• Filed: 06/11/2010
• Published: 12/30/2010
• Est. Priority Date: 06/11/2009
• Status: Active Grant

• Current Assignee: Battelle Energy Alliance LLC (Battelle Memorial Institute)
• Original Assignee: Montana Tech of the University of Montana (University of Montana System)
• Inventors: Morrison, John L., Morrison, William H., Motloch, Chester G., Christophersen, Jon P.
• Granted Patent: US 8,868,363 B2
• Time in Patent Office: Days
• US Class Current: 702/63
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

Electrochemical Impedance Spectrum (EIS) data are used directly to predict the pulse performance of an energy storage device. The impedance spectrum of the EIS is obtained in-situ using pre-existing techniques. A simulation waveform is configured such that the period of the pulse is greater than or equal to the lowest frequency of the impedance measurement. If the pulse is assumed to be periodic for analysis purposes, the complex Fourier series coefficients can be obtained. The number of harmonic constituents are selected so as to appropriately resolve the response, but the maximum frequency should be less than or equal to the highest frequency of the impedance measurement. In some cases, the measured frequencies of the impedance spectrum do not match the corresponding harmonic components of the simulated pulse wave. This is resolved by estimating the impedance measurements at the desired frequencies using linear interpolation, cubic spline fits, or other comparable methods. Using a current pulse as an example, the Fourier coefficients of the pulse are multiplied by the impedance spectrum at the corresponding frequency to obtain the Fourier coefficients of the voltage response to the desired pulse. The Fourier coefficients of the response are then summed reassemble to obtain the overall time domain estimate of the voltage using the Fourier series analysis. Thus, the response of an energy storage device to an anticipated or desired pulse can be estimated using low-level, charge neutral impedance measurements combined with Fourier series analysis.

Claims

1. A method of assessing the condition of an energy storage device by estimating a response to an excitation pulse, the method comprising the steps of:

a. measuring an impedance spectrum, the impedance spectrum comprising of at least a lowest frequency and at least a highest frequency;

b. configuring a simulated pulse, the simulated pulse comprising at least a low frequency;

c. decomposing the simulated pulse by Fourier analysis to obtain Fourier series coefficients, the Fourier series coefficients comprising at least a maximum frequency;

d. combining the Fourier series coefficients of the simulated pulse with the measured impedance spectrum to obtain an estimate response at each Fourier coefficient;

e. assembling the estimated response at each Fourier coefficients into an overall time response of the energy storage device; and

f. subtracting the assembled overall time response from a bias voltage of the energy storage device to estimate the response to the excitation pulse.

2. The method of claim 1, wherein said impedance spectrum is obtained offline over a broad frequency range.

3. The method of claim 2, wherein said impedance spectrum is obtained offline over a broad frequency range selected from the group consisting of a logarithmic frequency range, and a linearly-spread frequency range.

4. The method of claim 1, wherein said impedance spectrum is obtained online over a broad frequency range using techniques selected from the group consisting of Impedance Noise Identification, Compensated Synchronous Detection, Fast Summation Transformation, and other appropriate methods.

5. The method of claim 4, wherein said impedance spectrum is obtained in-situ.

6. The method of claim 1, wherein said simulated pulse is selected from the group consisting of a square wave, a triangle wave, a sawtooth wave, and other types of profiles.

7. The method claim 1, wherein said simulated pulse is configured from a constant current, a constant voltage, or constant power.

8. The method of claim 1, wherein said low frequency of said simulated pulse is greater than or equal to said lowest frequency of said impedance spectrum and wherein said maximum frequency used in said Fourier series coefficients is less than or equal to said highest frequency of said impedance spectrum.

9. The method of claim 1, wherein said measured impedance spectrum at said Fourier series coefficients is estimated through methods selected from the group consisting of linear interpolation, cubic spline, and other similar methods.

10. The method of claim 1, wherein the estimated response signal is smoothed through signal processing techniques to minimize or mitigate the Gibbs effect.