String resistance detector

• US 7,212,934 B1
• Filed: 03/06/2006
• Issued: 05/01/2007
• Est. Priority Date: 03/06/2006
• Status: Expired due to Fees

• Current Assignee: National Aeronautics and Space Administration US Government As Represented By The Administrator of The, United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Davies, Francis J., Hall, A. Daniel
• Primary Examiner(s): Bui; Bryan
• Application Number:
  US11/370,379
• Time in Patent Office: 421 Days
• Field of Search: 702/65, 702/66, 702/75, 702/76, 702/189, 324/322, 324/426, 324/600, 333/17.3, 333/32
• US Class Current: 702/76
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health
• CPC Class Codes: G01R 31/396 Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery

Abstract

Method and system are disclosed for determining individual string resistance in a network of strings when the current through a parallel connected string is unknown and when the voltage across a series connected string is unknown. The method/system of the invention involves connecting one or more frequency-varying impedance components with known electrical characteristics to each string and applying a frequency-varying input signal to the network of strings. The frequency-varying impedance components may be one or more capacitors, inductors, or both, and are selected so that each string is uniquely identifiable in the output signal resulting from the frequency-varying input signal. Numerical methods, such as non-linear regression, may then be used to resolve the resistance associated with each string.

Claims

1. A method of determining individual string resistance in a network of resistive strings, each resistive string having a unique preselected impedance connected thereto, comprising the steps of:

applying a frequency-varying input signal to said network such that portions of said frequency-varying input signal propagate through each resistive string of said network;

recording an output signal from said network, said output signal resulting from said portions of said frequency-varying input signal propagating through said resistive strings of said network; and

determining a resistance for each resistive string in said network based on said frequency-varying input signal, said unique preselected impedance of each resistive string, and said output signal, wherein said step of determining comprises relating said frequency-varying input signal, said unique preselected impedance for each resistive string, said resistance for each resistive string, and said output signal to each other in one or more mathematical equations and curve-fitting said one or more mathematical equations to a plot of said output signal.

2. The method according to claim 1, wherein at least two resistive strings in said network have different resistances.

3. The method according to claim 1, wherein said frequency-varying input signal has a known step slope or transient waveform.

4. The method according to claim 1, wherein said frequency-varying input signal has an alternating waveform, further comprising sweeping said frequency of said alternating waveform through a predetermined range of frequencies.

5. The method according to claim 1, further comprising arranging said unique preselected impedance for each resistive string so that said network has a high or low impedance only for certain frequencies of said frequency-varying input signal.

6. The method according to claim 1, wherein said step of curve-fitting comprises using non-linear regression to curve fit said one or more mathematical equations to said plot of said output signal.

7. A computer-readable storage medium encoded with instructions for causing a computer to perform the method according to claim 1.

8. A method of determining individual string resistance in a network of resistive strings, each resistive string having a unique preselected impedance connected thereto, comprising the steps of:

applying a frequency-varying input signal to said network such that portions of said frequency-varying input propagate through each resistive string of said network;

recording an output signal from said network, said output signal resulting from said portions of said frequency-varying input propagating through said resistive strings of said network; and

determining a resistance for each resistive string in said network based on said frequency-varying input signal, said unique preselected impedance of each resistive string, and said output signal, wherein said step of determining comprises analyzing peaks in a plot of said output signal to determine said resistance for each resistive string as a curve-fit parameter derived from a nonlinear regression.

9. The method according to claim 8, wherein said plot of said output signal is an amplitude plot.

10. The method according to claim 8, wherein said plot of said output signal is a phase plot.

11. A computer-based system for determining individual string resistance in a network of resistive strings, each resistive string having a unique preselected impedance connected thereto, comprising:

a computing unit;

a waveform generator controllable by said computing unit to generate a frequency-varying input signal, said waveform generator connected to said network such that said frequency-varying input signal propagates through each resistive string of said network; and

a microcontroller controllable by said computing unit to record an output signal from said network, said output signal composed of said frequency-varying input signal propagating through said resistive strings of said network;

wherein said computing unit is programmed to determine a resistance for each resistive string in said network based on said frequency-varying input signal, said unique preselected impedance for each resistive string, and said output signal.

12. The system according to claim 11, wherein said network is a battery module and said resistive strings are battery cells of said battery module.

13. The system according to claim 11, wherein said network is a thermistor network and each resistive string is an individual thermistor.

14. The system according to claim 11, wherein said system is part of a battery charger application.

15. The system according to claim 11, wherein said network is a fuel cell and said resistive strings are single cells of said fuel cell module.

16. The system according to claim 11, wherein said network are multiple strain gauges and said resistive strings are single strain gauges of said network.

17. The system according to claim 11, wherein said resistive strings are in parallel with one another and said frequency-varying input signal is a voltage signal.

18. The system according to claim 11, wherein said resistive strings are in series with one another and said frequency-varying input signal is a current signal.

19. The system according to claim 11, wherein said unique preselected impedance for each resistive string is capacitive impedance.

20. The system according to claim 11, wherein said unique preselected impedance for each resistive string is inductive impedance.

21. The system according to claim 11, wherein said unique preselected impedance for each resistive string includes a capacitive impedance and inductive impedance combination that functions as a filtering circuit at certain frequencies of said frequency-varying input signal.

22. A method of resolving a resistance of an individual string, said individual string part of a either a parallel string network or a series string network, using a single input signal and a single output signal of said parallel or said series string network, comprising the steps of:

connecting a frequency-varying impedance component with known electrical characteristics in series with each individual string for said parallel string network or in parallel with each individual string for said series string network, or using multiple frequency-varying impedance components with known electrical characteristics both in parallel and series with each individual string for either said parallel or said series string network, wherein said electrical characteristics of said frequency-varying impedance component are based on network size, resistance resolution accuracy, and impedance characteristics needs;

applying said single input signal to said parallel or said series string network, said single input signal being a voltage signal for said parallel string network and a current signal for said series string network;

generating a symbolic representation of said single output signal as a function of said single input signal, said frequency-varying impedance component of each individual string, and said resistance of each individual string;

curve-fitting said symbolic representation to a plot of said single output signal resulting from application of said single input signal to said parallel or said series string network using non-linear regression, wherein said resistance for each individual string is a curve-fit parameter derived from said nonlinear regression; and

correlating said unique predetermined electrical characteristics of each frequency-varying impedance component to said resistance for each individual string to thereby identify a location of said individual string.