US 6,002,238 AGranted

Method and apparatus for measuring complex impedance of cells and batteries

OwnerKeith S. Champlininventor

Life of this patent

Estimating the term…

Loading patent…

Abstract

A periodic time-varying current with smallest period 1/f.sub.1 excites a cell/battery and provides a timing reference. Linear circuitry produces two signals, one proportional to the excitation current, the other proportional to the responding time-varying voltage. These signals are processed with identical frequency-limiting filters to attenuate higher-order harmonics and noise. Using the timing reference for synchronization, a microprocessor/microcontroller commands analog to digital converters to sample the frequency-limited current and voltage signals at equally-spaced times over a period and accepts the digitized samples as inputs. The digital samples are averaged over multiple periods and employed to calculate averaged Fourier coefficients of in-phase and quadrature components of frequency-limited current and voltage at frequency f.sub.1. By numerically combining these Fourier coefficients, the microprocessor/microcontroller determines real and imaginary parts of the cell/battery's complex impedance at frequency f.sub.1.

Claims42

Dependent claims

Apparatus for evaluating impedance of an electrochemical cell or battery at a discrete frequency comprising:

current excitation circuitry adapted to be coupled to said cell or battery and adapted to pass a periodic current through said cell or battery, said periodic current characterized by a smallest period equal to the reciprocal of said discrete frequency;
current sensing and processing circuitry coupled to said current excitation circuitry and adapted to provide a current signal in response to said periodic current;
voltage sensing and processing circuitry coupled to said cell or battery and adapted to provide a voltage signal in response to a periodic voltage across said cell or battery;
current sampling and converting circuitry coupled to said current sensing and processing circuitry and adapted to provide digital representations of sampled values of said current signal, said sampled values obtained at discrete current sampling times synchronized with said periodic current and uniformly distributed in time over half-period or full-period intervals of said smallest period of said periodic current;
voltage sampling and converting circuitry coupled to said voltage sensing and processing circuitry and adapted to provide digital representations of sampled values of said voltage signal, said sampled values obtained at discrete voltage sampling times synchronized with said periodic current and uniformly distributed in time over half-period or full-period intervals of said smallest period of said periodic current;
and,
computation and control circuitry coupled to said current excitation circuitry, to said current sampling and converting circuitry, and to said voltage sampling and converting circuitry, said computation and control circuitry adapted to initiate said current sampling times, to initiate said voltage sampling times, and to numerically combine said digital representations of said sampled values of said current signal and said digital representations of said sampled values of said voltage signal to evaluate said impedance.

4 more elements

Apparatus for measuring impedance of an electrochemical cell or battery at a discrete frequency comprising:

current excitation circuitry adapted to be coupled to said cell or battery and adapted to pass a periodic current through said cell or battery, said periodic current characterized by a smallest period equal to the reciprocal of said discrete frequency;
current sensing circuitry coupled to said current excitation circuitry and adapted to produce a current signal proportional to said periodic current;
voltage sensing circuitry coupled to said cell or battery and adapted to produce a voltage signal proportional to a periodic voltage developed across said cell or battery;
filtering circuitry coupled to said current sensing circuitry and to said voltage sensing circuitry, said filtering circuitry characterized by a frequency response characteristic and adapted to provide a frequency-limited current signal in accordance with said frequency response characteristic and a frequency-limited voltage signal in accordance with the same said frequency response characteristic;
and,
evaluating circuitry coupled to said filtering circuitry and to said current excitation circuitry and adapted to provide values of said impedance of said electrochemical cell or battery in accordance with said frequency-limited current signal and said frequency-limited voltage signal.

3 more elements

A method for measuring impedance of an electrochemical cell or battery at a discrete frequency comprising the steps of:

exciting said cell or battery with a periodic time-varying current characterized by a smallest period equal to the reciprocal of said discrete frequency;
sensing a current signal proportional to said periodic time-varying current and a voltage signal proportional to a time-varying response voltage across said cell or battery;
processing said current signal and said voltage signal with identical frequency response functions to obtain a frequency-limited current signal and a frequency-limited voltage signal;
and,
combining said frequency-limited current signal and said frequency-limited voltage signal to determine said impedance of said electrochemical cell or battery.

2 more elements

Dependencies are inferred from the claim text.