Method and apparatus for measuring and analyzing electrical or electrochemical systems

• US 20030206021A1
• Filed: 05/21/2003
• Published: 11/06/2003
• Est. Priority Date: 07/25/1997
• Status: Abandoned Application

• Current Assignee: World Energy Labs Incorporated
• Original Assignee: World Energy Labs Incorporated
• Inventors: Brashear, Logan L., Laletin, William H., Salloux, Kurt
• Application Number:
  US10/443,230
• Publication Number:
  US 20030206021A1
• Time in Patent Office: Days
• US Class Current: 324/426
• CPC Class Codes: G01R 31/386 using test-loads

Abstract

A method and apparatus for creating a time-varying electrical excitation, delivering it to a system comprising at least one electronic or electrochemical element, and measuring and analyzing a time-varying electrical response developed within the system in response to the excitation. The response signal, and optionally the excitation signal, are sampled in a synchronous manner, and the sampled values are analyzed to determine various characteristics of the system, including State of Charge and State of Health. Additional analysis may be performed to: identify specific system defects; identify and quantify time-dependent processes; and, obtain values for elements of an equivalent electric circuit model. The method and apparatus may serve both as a measurement system as well as a control sub-system, and may be configured to operate in either an open-loop or closed loop manner. Furthermore, the method and/or apparatus may be used in conjunction with a power control system such as an electrical/electrochemical system test device, a battery charger, a battery conditioner, or a battery backup system or uninterruptible power supply. Alternate embodiments of the technique may be achieved by integration directly within a chip or chipset.

Claims

1. A method for measuring a time-varying response of an electric or electrochemical system, which system may comprise any combination of electrical elements and electrochemical cells, comprising the steps of:

exciting the system with a time-varying current excitation signal provided by an excitation means;

acquiring digital samples with a sampling means synchronized with said excitation means, and operating in accordance with a pre-determined sampling schedule, which samples are taken of the voltage present across the system during the duration of the excitation,

performing any combination of the operations of;

displaying some or all of the acquired samples;

storing some or all of the acquired digital samples;

performing at least one analysis of the digital samples to evaluate at least one characteristic of said system.

2. The method of claim 1, comprising the additional step of:

acquiring digital samples with a sampling means synchronized with said excitation means, and operating in accordance with a pre-determined sampling schedule, which samples are taken of the voltage present across a sensing element disposed to exhibit a voltage proportional to an excitation current.

3. The method of claim 1, wherein the excitation signal is adjustable.

4. The method of claim 1, wherein at the step of exciting, the excitation comprises a time-varying current signal which exhibits exactly one abrupt discontinuity, which discontinuity may be either:

an abrupt step-wise change in the amplitude of the excitation;

or

an abrupt step-wise change in the first time derivative of the amplitude of the excitation.

5. The method of claim 1, wherein the time-varying current excitation signal exhibits a plurality of abrupt discontinuities and comprises one or more waveforms, which waveform may be any of:

a rectilinear waveform, exhibiting a leading edge that constitutes an abrupt amplitude transition, followed by a substantially constant-amplitude portion, followed by another abrupt amplitude transition representing a trailing edge;

a ramping waveform comprising, in either order, an abrupt amplitude step representing an abrupt amplitude and a portion whose amplitude varies with time in a linear fashion, thus exhibiting a constant, but non-zero, first derivative with respect to time;

a triangle waveform comprising two distinct adjacent ramping segments each exhibiting a separate non-zero slope and whose adjacent ends are coincident at a point whereat the value of the slope of the waveform exhibits an abrupt transition;

6. The method of claim 1, wherein at the step of exciting, the excitation comprises a plurality of bipolar square waves, each comprising two part-cycles that have substantially identical duration, which part cycles have amplitudes that are substantially equal in magnitude but of opposite polarity.

7. The method of claim 1, wherein, over the course of a test event, the time average of the excitation current is non-zero so that either:

the DUT is excited with a net positive current representing charging;

or

the DUT is excited with a net negative current representing discharging.

8. The method of claim 1 wherein at the step of exciting, the excitation comprises a consecutive series of identical 50% duty cycle rectangular waveforms, each of which waveforms exhibits one of the following sets of characteristics:

a;

the waveform comprises one half-cycle representing a positive current pulse of a predetermined amplitude while the other of the half-cycle comprises a zero current rest period exhibiting the same duration as positive half cycle, which half-cycles can be arranged in either order;

b;

the waveform comprises one half-cycle representing a negative current pulse of predetermined amplitude while the other of the half-cycle comprises a zero current rest period exhibiting the same duration as positive half cycle, which half-cycles can be arranged in either order;

c;

the waveform comprises one half-cycle representing a positive current pulse of a first predetermined amplitude and another half-cycle representing a negative current pulse of a second predetermined amplitude exhibiting the same duration as the positive half cycle, which half-cycles can be arranged in either order, and which first and second predetermined may have either the same or different maximum amplitudes.

9. The method of claim 1, wherein at the step of exciting, the excitation comprises a plurality of rectangular current waveform cycles, at least one of which cycles may differ from any of the others with respect to at least one parameter, which parameters include:

amplitude value of either or both part cycles, which amplitude value may be positive, negative or zero;

cycle duration;

duty cycle ratio.

10. The method of claim 1, wherein the excitation current comprises a constant or slowly-varying component constituted to perform charging or discharging, coupled with a relatively rapidly varying component constituted according to claim 3, samples of which rapidly varying component may be synchronously acquired according to a pre-determined sampling schedule.

11. The method of claim 1, wherein the amplitude of at least a portion of the excitation applied during a test event is constituted to insure that no irreversible changes will be wrought on the DUT.

13. The method of claim 1, wherein the excitation means corresponds to a controlled current source that is disposed to provide either unipolar or bipolar current output, comprising one or a combination of:

a bipolar transistor operative within the feedback loop of an operational amplifier configured to control the current sourced by the transistor, in accordance with a separate controlling signal provided to the operational amplifier;

or

a field effect transistor operative within the feedback loop of an operational amplifier configured to control the current sourced by the transistor, in accordance with a separate controlling signal provided to the operational amplifier;

or

at least one operational amplifier configured to provide a controlled current output in accordance with a separate controlling signal provided to the at least one operational amplifier.

14. The method of claim 13, wherein the output of the controlled current source representing the excitation signal may be interrupted by means of an intervening, controllable switch means.

15. The method of claim 1, wherein the synchronous sampling means comprises an analog to digital converter equipped with a sampling clock control input connected to a synchronizing clock means.

16. The method of claim 1, wherein the synchronizing clock is provided by one of:

a controller means;

or

a waveform generator means;

or

an external clock signal source.

17. The method of claim 1, wherein the sampling schedule may be constituted as any one or combination of:

at least one set of time delay values have linearly increasing offsets with respect to a previously pre-determined point in time, which point may either represent the instant at which a test event commences, or represent the instant at which a waveform part-cycle commences;

at least one set of time delay values have exponentially increasing offsets with respect to a previously pre-determined point in time, which point may either represent the instant at which a test event commences, or represent the instant at which a waveform part-cycle commences;

at least one set of time delay values have parametrically increasing offsets with respect to a previously pre-determined point in time, which point may either represent the instant at which a test event commences or represent the instant at which a waveform part-cycle commences, and which set of values set need not correspond to a simple mathematical series.

18. The method of claim 1, wherein, irrespective of the amplitude of the excitation at the instant the test event commences, synchronous sampling commences concurrently with the beginning of the test event such that samples are acquired according to a predetermined set of time delay values.

19. The method of claim 1, wherein, irrespective of the amplitude of the excitation at time following the final abrupt transition in a test event, synchronous sampling may commence concurrently with said abrupt excitation transition and proceed according to a predetermined set of time delay values.

20. The method of claim 1, wherein synchronous sampling may commence concurrently with any abrupt excitation transition and proceed according to a predetermined set of time delay values.

21. The method of claim 1, wherein the sampling schedule is prestored.

22. The method of claim 1, wherein, during any portion of a test event, synchronous samples may be acquired from either the time-varying voltage response signal, or the excitation signal, or both.

24. The method of claim 1;

wherein the samples acquired by the synchronous sampler are stored in a memory means.

25. The method of claim 1, where at the step of evaluating, an analysis is performed on the sampled response data to determine the time constant of at least one component of the time-dependent voltage response emitted by the electrochemical system, and optionally thereafter, performing an additional analysis to determine the relative voltage amplitude coefficient associated with the process corresponding to said time constant.

26. The method of claim 1, where during the step of evaluating, at least one of the following analyses is performed:

a. determining the time constant of at least one component of the time-dependent voltage response emitted by the electrochemical system;

b. determining the relative amplitude coefficient associated with the process corresponding to a determined time constant;

c. analyzing the upper envelope-extrema comprising the set of maximum amplitude values attained by the response voltage during a plurality of successive response waveform cycles;

d. analyzing the lower envelope-extrema comprising the set of minimum amplitude values attained by the response voltage during a plurality of successive response waveform cycles;

e;

performing a non-linear curve fitting analysis of at least one portion of at least one response cycle to extract information regarding the time constants and relative amplitudes of a set of exponential curves which can be added together to approximate the sampled data to an arbitrary degree of accuracy;

f;

performing any integral transform method of analysis applied to the sampled data from one or more consecutive response cycles, whereby frequency domain data is developed from the sample time domain data;

g. computing the first time derivative for at least one pair of data points representing consecutive response samples;

h. computing the second time derivative for at least one triplet of data points representing consecutive response samples;

i. performing an analysis whereby the shape of at least one response waveform portion is characterized, thereby allowing pattern recognition and other correlation-based methods to be employed to extract information about the electrochemical system;

j. the sampled data is decimated to reduce the effective sampling rate, which decimated data may then be subject to any analysis.

27. The method of claim 1, further comprising, after the step of evaluating, the step of utilizing the information developed during the step of evaluating to characterize the electrochemical system by at least one of the following methods:

a. the extraction of information regarding the electrochemical system is achieved by comparing the results of at least one previous analysis to suitable benchmark data;

b. the extraction of information regarding the electrochemical system is achieved by performing a secondary analysis on information derived from the results of at least two previous analysis, the output of which secondary analysis is compared to suitable benchmark data;

c. the extraction of information from results of at least one previous analysis, allowing a characterization of the state of charge of the electrochemical system;

d. the extraction of information from results of at least one previous analysis, allowing a characterization of the state of health of the electrochemical system;

e. the extraction of information from results of at least one previous analysis, allowing a characterization of the electrochemical system as either severely depleted and/or defective.

f. the extraction of information from results of at least one previous analysis, allowing a characterization of at least one specific defect and/or failure mechanism in the electrochemical system;

g. the extraction of information from results of at least one previous analysis, allowing a characterization of the passivation state of the electrochemical system;

h. the extraction of information from results of at least one previous analysis, allowing a characterization of at least one underlying electrochemical process that occurs within the electrochemical system in response to the excitation;

i. the extraction of information from results of at least one previous analysis, allowing a characterization of at least one equivalent circuit model that describes the underlying electrochemical system;

j. the extraction of information from results of at least one previous analysis, allowing a determination of the rechargeability of the electrochemical system;

k;

the extraction of information according to a fuzzy logic means applied either directly from the sampled data, or from the results of at least one previous analysis, which information may be used to determine the state of charge or state of health of the DUT;

l. the extraction of information according to a neural network means applied either directly from the sampled data, or from the results of at least one previous analysis results of at least one previous analysis, which information may be used to determine the state of charge or state of health of the DUT;

m. calculating the values of elements of an equivalent circuit model;

n. deriving by graphical means, the characteristics of at least one electrochemical process;

28. The method of claim 1, wherein at the step of acquiring, a parametric-by-pulse sampling schedule is employed whereby digital samples are acquired within each part-cycle, in a synchronous manner according to a pre-determined set of time delay values, which set need not correspond to a simple mathematical series, which delay values are synchronized with respect to the beginning of said part-cycle.

29. The method of claim 1, further comprising the step of:

performing a batch mode test processes, whereby a plurality of exciting/acquiring/evaluating test events are performed in consecutive order.

30. The method of claim 1, wherein the excitation amplitude provided during any part-cycle is either:

a;

of a sufficiently small magnitude to ensure linear response within the cell/battery of cells;

or

a;

of a sufficiently small magnitude to ensure that the changes effected within the cell or battery of cells during the first part-cycle of an excitation waveform are fully reversed during the second part-cycle of said waveform;

or

c. of a sufficiently large amplitude that the condition of the cell or battery of cells is changed, so that changes effected within the cell during the first part-cycle of an excitation waveform are not fully reversed during the second part-cycle of said waveform.

31. The method of claim 1, where in the number of sampled data points obtained during at least one half cycle corresponds exactly to an integral power of 2.

32. The method of claim 1, where the amplitude of each excitation pulse, corresponding to a part-cycle, is parametrically adjustable, and can, therefore, be changed to any value for any part-cycle.

45. The method of claim 1, wherein at the step of exciting, the excitation corresponds to a periodic signal comprising at least one sine wave.

47. The method of claim 1, wherein a sinusoidal excitation is employed, and synchronous sampling may commence at any time during the excitation, which point in time corresponds to a predetermined point in the current sine wave cycle and thereupon proceed according to a predetermined set of time delay values.

12. The method of claim t, wherein the amplitude of at least a portion of the excitation applied during a test event is constituted to insure that at least one irreversible change will be wrought on the DUT.

23. The method of claim f, wherein the samples acquired by the synchronous samplers are provided as input to a controller means.

33. An apparatus is provided that comprises:

a means of providing a time-varying current excitation to a system representing a DUT;

a means of acquiring synchronous samples of the voltage present across the system;

a means suitable for performing any combination of;

the display of some or all of the acquired samples;

the storage of some or all of the acquired digital samples;

at least one analysis of the digital samples to evaluate at least one characteristic of said system.

34. The apparatus of claim 33, further comprising a means of acquiring synchronous samples of the voltage present across a shunt element, which voltage is developed in response to the passage of an excitation current through said shunt element.

35. The apparatus of claim 33, wherein the connections between the apparatus and a DUT represent a Kelvin connection, comprising separate connections for:

a current driver means;

a current receiver means; and

both inputs of a sensor means.

36. The apparatus of claim 33, wherein a controlled current source constitutes the excitation driver means, which current source is disposed to provide either unipolar or bipolar current output, comprising one or a combination of:

a bipolar transistor operative within the feedback loop of an operational amplifier configured to control the current sourced by the transistor, in accordance with a separate controlling signal provided to the operational amplifier;

or

a field effect transistor operative within the feedback loop of an operational amplifier configured to control the current sourced by the transistor, in accordance with a separate controlling signal provided to the operational amplifier;

or

at least one operational amplifier configured to provide a controlled current output in accordance with a separate controlling signal provided to the at least one operational amplifier.

37. The apparatus of claim 33, wherein a current receiver means is provided to receive a current signal from a DUT, which current receiver may comprise either:

a voltage controlled voltage source;

or

an electrically conductive member disposed, by virtue of a connection to the local ground circuit of the test device, to maintain a potential of substantially zero volts when receiving an excitation current signal.

38. The apparatus of claim 33, wherein the excitation is adjusted to exhibit either:

a net positive current, to achieve a charging function for the DUT;

or

a net negative current, to achieve a discharging function for the DUT

39. The apparatus of claim 33, where in the excitation comprises a composite signal exhibiting either a net positive or net negative aspect and which excitation includes portions characterized by abrupt transitions suitably disposed for eliciting a time-varying polarization response that may be synchronously sampled to yield samples that are analyzed to provide an evaluation of at least one characteristic of said system.

40. The apparatus of claim 33, wherein the excitation signal is modulated by feedback signal developed according to at least one evaluated characteristic, which modulation can take the form of:

a variation in any of the amplitude, duration or duty-cycle characteristics of the time varying waveform component of the excitation;

an alteration variation in a constant or slowly time-varying component of the excitation, which component may confer a net bias upon the excitation.

46. The apparatus of claim 33, wherein the excitation signal is modulated according to a control signal received from either a communications port or a local interface, which modulation can take the form of:

a variation in any of the amplitude, duration or duty-cycle characteristics of the time varying waveform component of the excitation;

an alteration variation in a constant or slowly time-varying component of the excitation, which component may confer a net bias upon the excitation.

41. An apparatus, representing a preamplifier, is provided comprising:

at least one sense amplifier equipped with two differential input that are disposed to receive a differentially sensed input signal and produce an output that is a scaled replica of said differentially applied input signal, the potential of which output is referenced to common ground;

an inverting integrator means equipped with two differential inputs and providing an output that signal represents the inverse of the time integral of a differential input voltage provided across its two inputs, one of which is connected to a fixed potential and the other of which is connected to the output of said sense amplifier;

a inverting unity gain buffer amplifier, provide with an output, and an input that is connected to the output of said integrator;

a feedback connection between output of the inverting integrator and the non-inverting input of the sense amplifier and a feedback connection between the output of the buffer to the inverting input of the sense amplifier;

which feedback connections jointly represent a offsetting signals which serve to keep the average value of the output of the sense amplifier at a potential of zero volts.

42. The apparatus of claim 41 wherein the buffer amplifier comprises an operational amplifier having a non-inverting input representing the input of the buffer, and an inverting input connected to a fixed potential of the same value as the fixed potential provided to the integrator means.

43. The apparatus of claim 41, wherein the fixed potential provided to the integrator means is a potential of zero volts, equivalent to a connection to common ground, and thereby the output of the integrator means appears referenced to common ground.

44. The apparatus of claim 41, where the time constant of the integrator is predetermined, and is substantially longer than the longest period of any time-varying response signal that may be presented to the inputs of the associated sense amplifier.