SYSTEM FOR DETERMINING BATTERY IMPEDANCE

• US 20130307334A1
• Filed: 05/18/2012
• Published: 11/21/2013
• Est. Priority Date: 05/18/2012
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: MIDDLETON, Justin Dale, Kwok, Wellington Ying-Wei
• Granted Patent: US 9,018,913 B2
• Time in Patent Office: Days
• US Class Current: 307/31
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• 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: H02J 7/00712 the cycle being controlled or terminated in response to electric parameters

Abstract

A method for real-time characterization of a battery includes providing electric power to one or more electrical power loads, charging and discharging the battery based on power needs of the one or more electrical power loads, and monitoring for a circumstance where charging and discharging of the battery results in terminal voltage of the battery substantially equaling open-circuit voltage of the battery and recording the measured terminal voltage as a first measured voltage. The method may also include monitoring for a subsequent circumstance subsequent when charging and discharging the battery results in battery current larger than a predetermined value and recording an existing terminal voltage as a second measured voltage. The method may also include using the first and second measured voltages to determine a measured internal impedance of the battery. These actions may be performed between startup and shutdown of the power system.

Claims

1. A method for real-time characterization of a battery in a power system, the method comprising:

between startup and shutdown of the power system, operating the power system by;

providing electric power to one or more electrical power loads of the power system,

charging and discharging the battery based on power needs of the one or more electrical power loads,

with at least one information-processing device, monitoring for a circumstance where the charging and discharging of the battery based on the power needs of the one or more electrical power loads results in a terminal voltage of the battery substantially equaling an open-circuit voltage of the battery and recording the measured terminal voltage as a first measured voltage,

with the at least one information-processing device, monitoring for a circumstance subsequent to the terminal voltage substantially equaling the open-circuit voltage when charging and discharging the battery based on the power needs of the electrical power loads results in battery current larger than a predetermined value and recording an existing terminal voltage as a second measured voltage, and

with the at least one information-processing device, using the first measured voltage and the second measured voltage to determine a measured internal impedance of the battery.

2. The method of claim 1, wherein monitoring for a circumstance where the charging and discharging of the battery based on the power needs of the one or more electrical power loads results in a terminal voltage of the battery substantially equaling an open-circuit voltage of the battery and recording the measured terminal voltage as first measured voltage includes:

with the at least one information-processing device, monitoring for a circumstance where battery current has remained smaller than a reference value for a reference period; and

when battery current has remained smaller than the reference value for the reference period, recording with the at least one information-processing device the terminal voltage of the battery as the first measured voltage.

3. The method of claim 2, further comprising using the measured internal impedance of the battery to estimate with the at least one information-processing device a value indicative of a state of health of the battery.

4. The method of claim 3, further comprising, subsequent to estimating the value indicative of the state of health of the battery, repeatedly reestimating with the at least one information-processing device the internal impedance of the battery based on the estimated value indicative of the state of health of the battery and at least one of a measured temperature of the battery, a measured terminal voltage of the battery, or a measured battery current magnitude.

5. The method of claim 4, further comprising determining with the at least one information-processing device a limit for a magnitude of battery current based on voltage limits for the battery and the estimated internal impedance.

6. The method of claim 1, further comprising using the measured internal impedance of the battery to estimate with the at least one information-processing device a value indicative of a state of health of the battery.

7. The method of claim 6, further comprising, subsequent to estimating the value indicative of the state of health of the battery, repeatedly reestimating with the at least one information-processing device the internal impedance of the battery based on the estimated value indicative of the state of health of the battery and at least one of a measured temperature of the battery, a measured terminal voltage of the battery, or a measured battery current magnitude.

8. The method of claim 7, further comprising determining with the at least one information-processing device a limit for a magnitude of battery current based on voltage limits for the battery and the estimated internal impedance.

9. The method of claim 6, further comprising using the value indicative of the state of health of the battery to determine with the at least one information-processing device whether the battery has reached an end of its useful life.

10. The method of claim 6, further comprising using the value indicative of the state of health of the battery to estimate with the at least one information-processing device how much remaining life the battery has.

11. A power system, comprising:

a battery;

one or more electrical power loads; and

power-system controls configured to coordinate operation of the power system between startup and shutdown of the power system, including

controlling supply of electric power to the electrical power loads,

controlling charging and discharging of the battery based on power needs of the one or more electrical power loads,

monitoring for a circumstance where the charging and discharging of the battery based on the power needs of the one or more electrical power loads results in battery current remaining smaller than a reference value for a reference period, and when this circumstance occurs, recording a terminal voltage of the battery as a first measured voltage,

monitoring for a circumstance subsequent to the terminal voltage substantially equaling the open-circuit voltage when charging and discharging the battery based on the power needs of the electrical power loads results in battery current larger than a predetermined value and recording an existing terminal voltage as a second measured voltage, and

using the first measured voltage and the second measured voltage to determine a measured internal impedance of the battery.

12. The power system of claim 11, wherein the power-system controls are further configured to use the measured internal impedance of the battery to estimate a value indicative of a state of health of the battery.

13. The power system of claim 12, wherein the power-system controls are further configured to repeatedly reestimate the internal impedance of the battery based on the estimated value indicative of the state of health of the battery and at least one of a measured temperature of the battery, a measured terminal voltage of the battery, or a measured battery current magnitude.

14. The power system of claim 13, wherein the power-system controls are further configured to use the estimated internal impedance of the battery to determine a limit for a magnitude of battery current based on voltage limits for the battery and the estimated internal impedance.

15. The power system of claim 11, wherein the power-system controls are further configured to use the measured internal impedance of the battery to estimate a value indicative of a state of health of the battery.

16. The power system of claim 15, wherein the power-system controls are further configured to repeatedly reestimate the internal impedance of the battery based on the estimated value indicative of the state of health of the battery and at least one of a measured temperature of the battery, a measured terminal voltage of the battery, or a measured battery current magnitude.

17. The power system of claim 15, wherein the power-system controls are further configured to use the value indicative of the state of health of the battery to determine with the at least one information-processing device whether the battery has reached an end of its useful life.

18. A method of operating a power system with a battery, the method comprising:

estimating an internal impedance of the battery with at least one information-processing device;

determining with the at least one information-processing device a first current magnitude based on voltage limits for the battery and the estimated internal impedance;

comparing with the at least one information-processing device the first current magnitude and a second current magnitude to determine which of the first and second current magnitudes is smaller, the second current magnitude being a limit for a magnitude of current for at least one component of the power system; and

calculating with the at least one information processing device a charging or discharging power limit for the battery based on whichever of the first and second current magnitudes is smaller.

19. The method of claim 18, wherein:

the method further comprises monitoring for a circumstance where a terminal voltage of the battery substantially equals an open-circuit voltage of the battery and recording the measured terminal voltage as a measured open-circuit voltage of the battery; and

estimating the internal impedance of the battery with the at least one information-processing device includes estimating the internal impedance based at least in part on the measured open-circuit voltage.

20. The method of claim 18, wherein:

the method further comprises monitoring for a circumstance where a terminal voltage of the battery substantially equals an open-circuit voltage of the battery and recording the measured terminal voltage as a measured open-circuit voltage of the battery; and

estimating the internal impedance of the battery with at least one information-processing device includes estimating the internal impedance based at least in part on the measured open-circuit voltage and a terminal voltage of the battery measured during subsequent charging or discharging of the battery.