Method for predicting the loading capability of an electrochemical element

• US 20030001581A1
• Filed: 05/29/2002
• Published: 01/02/2003
• Est. Priority Date: 06/01/2001
• Status: Active Grant

• Current Assignee: VB Autobatterie GmbH
• Original Assignee: VB Autobatterie GmbH
• Inventors: Meissner, Eberhard, Laig-Horstebrock, Helmut
• Granted Patent: US 6,909,261 B2
• Time in Patent Office: Days
• US Class Current: 324/433
• CPC Class Codes: G01R 31/3647 for determining the ability of a battery to perform a critical function, e.g. cranking
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements

Abstract

A method for predicting the loading capability of an accumulator by measuring the current I, voltage U and temperature T of the accumulator, and comparing the measured values with the corresponding values of the response of an equivalent circuit diagram of the accumulator, the parameters of the components of the equivalent circuit diagram and the state variables are varied so that a match with the measured values is obtain. The loading capability is deduced from the matched parameters and state variables determined in this way. The equivalent circuit diagram has the form -Uo-R-C_S- and the input voltage U′ of the equivalent circuit diagram is a voltage that is corrected with respect to the measured battery voltage U, the correction function containing as variables only the current I, the voltage U and the temperature T and as a nonlinear term a logarithmic dependency on I. By using the equivalent circuit diagram, the instantaneous loading capability, i.e., the response of the battery under a hypothetical load with an assumed current value I, is predicted by imposing this current value I on the equivalent circuit diagram with the found parameters and evaluating the voltage response calculated.

Claims

1. A method for predicting loading capability of a battery comprising:

measuring current I, voltage U and temperature T of the battery;

forming an equivalent circuit with an equivalent circuit diagram -Uo-R-C_S-, wherein Uo is voltage at t=o, R is resistance and CS is capacitance;

correcting input voltage U′

of the equivalent circuit diagram with respect to measured battery voltage U, the correcting containing as variables only current I, voltage U and temperature T and as a nonlinear term a logarithmic dependency on I;

varying parameters of components of the equivalent circuit diagram and state variables;

comparing measured values with corresponding values of responses of the equivalent circuit diagram of the battery; and

determining the loading capability from matched parameters and state variables.

3. The method as claimed in claim 1, wherein correcting the input voltage is achieved with a correction function:

u=û

*1n(i), wherein û

is a fixed parameter and I is current.

4. The method as claimed in claim 3, wherein the battery is a lead-acid battery, and û

lies in the value range of from about 5 to about 50 mV per cell.

5. The method as claimed in claim 3, wherein the battery is a lead-acid battery, and û

lies in the value range of from about 10 to about 30 mV per cell.

6. The method as claimed in claim 1, wherein correcting the input voltage is achieved with a correction function:

u=û

₁*1n(i)+û

₂*1n(î

), wherein û

₁ and û

₂ are fixed parameters, i is current, and i represents current information filtered from current i with a time constant τ

₂=a₂*Q/i, wherein Q is storage capacity of the battery and a₂ is a constant.

8. The method as claimed in claim 6, wherein the battery is a lead-acid battery and the constant a₂ for calculating the time constant τ

₂=a₂*Q/i lies in the value range of from about 0.05 to about 2.0, and wherein the parameters û

₁ and û

₂, respectively, lie approximately in the value range of from about 3 to about 30 mV per cell.

10. The method as claimed in claim 6, wherein the battery is a lead-acid battery and the constant a₂ for calculating the time constant τ

₂=a₂*Q/i lies in the value range of from about 0.1 to about 0.5, and wherein the parameters û

₁ and û

₂, respectively, lie approximately in the value range of from about 5 to about 2 mV per cell.

15. The method as claimed in claim 1, wherein the battery is a lead-acid battery and only such measured values are used as occur at operating times of operation in which either a charge quantity of at least about 3%, of the capacity of the lead-acid battery has discharged since last charging, or during which a matched quantity C_S is greater than a limit value of at least about 18 Ah/V/cell of 100 Ah.

17. The method as claimed in claim 1, wherein determined quantity Uo is an indication that the battery has previously been drained, and wherein if Uo falls below a threshold value Ulimit, depending on the temperature T, during discharge or exceeds it during charging, this is displayed.

19. The method as claimed in claim 1, wherein a magnitude |dP/dq| of rate of change of one of matching parameters P (P=Uo,R,Cs) with a transferred charge quantity q exceeds a limit value is an indication that the battery has previously been drained, and wherein whenever |dP/dq| exceeds a threshold value |dP/dq| limit, this is displayed.

2. A method for predicting loading capability of a battery comprising:

measuring current I, voltage U and temperature T of the battery;

forming an equivalent circuit with an equivalent circuit diagram -Uo-R-C_S-, wherein Uo is voltage at t=o, R is resistance and CS is capacitance;

correcting input voltage U′

of the equivalent circuit diagram with respect to measured battery voltage U, the correcting containing as variables only current I, voltage U and temperature T and as a nonlinear term a logarithmic dependency on I′

, and I′

is obtained from I by low-pass filtering;

varying parameters of components of the equivalent circuit diagram and state variables;

comparing measured values with corresponding values of responses of the equivalent circuit diagram of the battery; and

determining the loading capability from matched parameters and state variables.

7. The method as claimed in claim 2, wherein correcting the input voltage is achieved with a correction function:

u=û

₁*1n(i)+û

₂*1n(i), wherein û

₁ and û

₂ are fixed parameters, i is current, and i represents current information filtered from current i with a time constant τ

₂=a₂*Q/i, wherein Q is storage capacity of the battery and a₂ is a constant.

9. The method as claimed in claim 7, wherein the battery is a lead-acid battery and the constant a₂ for calculating the time constant τ

₂=a₂*Q/i lies in the value range of from about 0.05 to about 2.0, and wherein the parameters û

₁ and û

₂, respectively, lie approximately in the value range of from about 3 to about 30 mV per cell.

11. The method as claimed in claim 9, wherein the battery is a lead-acid battery and the constant a₂ for calculating the time constant τ

₂=a₂*Q/i lies in the value range of from about 0.1 to about 0.5, and wherein the parameters û

₁ and û

₂, respectively, lie approximately in the value range of from about 5 to about 2 mV per cell.

12. The method as claimed in claim 2, wherein the logarithmic dependency is determined from u=û

₁*1n(î

₁)+û

₂*1n(î

₂), wherein û

₁ and û

₂ are fixed parameters, î

₁ and î

₂ represent current information filtered from current i with time constants τ

₁=a₁*Q/î

₁ and τ

₂=a₂*Q/î

₂, wherein Q is storage capacity of the battery and a₁ and a₂ are constants.

13. The method as claimed in claim 12, wherein the battery is a lead-acid battery and a₁ of the time constant τ

₁=a₁*Q/î

₁ lies in the value range of from about 0.005 to about 0.2, and the parameter a₂ of the time constant τ

₂=a₂*Q/î

₂ lies in the value range of from about 0.05 to about 2, and wherein the parameters û

₁ and û

₂, respectively, lie approximately in the value range of from about 3 to about 30 mV per cell.

14. The method as claimed in claim 12, wherein the battery is a lead-acid battery and a₁ of the time constant τ

₁=a₁*Q/î

₁ lies in the value range of from about 0.005 to about 0.2, and the parameter a₂ of the time constant τ

₂=a₂*Q/î

₂ lies in the value range of from about 0.05 to about 2, and wherein the parameters û

₁ and û

₂, respectively, lie approximately in the value range of from about 5 to about 20 mV per cell.

16. The method as claimed in claim 2, wherein the battery is a lead-acid battery and only such measured values are used as occur at operating times of operation in which either a charge quantity of at least about 3%, of the capacity of the lead-acid battery has discharged since last charging, or during which a matched quantity C_S is greater than a limit value of at least about 18 Ah/V/cell of 100 Ah.

18. The method as claimed in claim 2, wherein determined quantity Uo is an indication that the battery has previously been drained, and wherein if Uo falls below a threshold value Ulimit, depending on the temperature T, during discharge or exceeds it during charging, this is displayed.

20. The method as claimed in claim 19, wherein the battery is a lead-acid battery, parameter P involving parameter R, and |dR/dq| limit for the lead-acid battery is at least approximately 3 times as great as an original value of |dR/dq| for the battery when fully charged.