Circuit and Method for Battery Leakage Detection

• US 20160200209A1
• Filed: 01/13/2015
• Published: 07/14/2016
• Est. Priority Date: 01/13/2015
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Tabatowski-Bush, Benjamin A., Bilezikjian, John Peter
• Granted Patent: US 9,630,520 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B60L 2240/545 Temperature
• CPC Class Codes: B60L 2240/547 Voltage
• CPC Class Codes: B60L 2240/549 Current
• CPC Class Codes: B60L 3/0069 relating to the isolation, e.g. ground fault or leak current
• CPC Class Codes: B60L 3/12 Recording operating variables ; Monitoring of operating variables
• CPC Class Codes: B60L 50/16 with provision for separate direct mechanical propulsion
• CPC Class Codes: B60L 53/14 Conductive energy transfer
• CPC Class Codes: B60L 58/12 responding to state of charge [SoC]
• CPC Class Codes: B60L 9/00 Electric propulsion with power supply external to the vehicle electric propulsion for monorail vehicles, suspension vehicles or rack railways B60L13/00; in combination with batteries or fuel cells within the vehicle B60L50/53
• CPC Class Codes: G01R 27/14 Measuring resistance by measuring current or voltage obtained from a reference source G01R27/16, G01R27/20, G01R27/22 take precedence
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 10/7072 Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
• CPC Class Codes: Y02T 90/14 Plug-in electric vehicles

Abstract

A battery management system includes a switching element configured to selectively couple a resistive network in parallel with a capacitor that couples a voltage bus and a ground reference. A controller is programmed to, in response to activating the switching element for a predetermined time, output a diagnostic according to a leakage resistance that is based on a time associated with a predetermined change in a voltage across the capacitor. A time constant is derived from the voltage response and the leakage resistance is derived from the time constant.

Claims

1. A vehicle comprising:

a capacitor connected between a voltage bus and a chassis of the vehicle; and

at least one controller programmed to, in response to activating a switching element to couple a resistive network in parallel with the capacitor for a predetermined time, output a diagnostic according to a leakage resistance estimate that is based on a time associated with a predetermined change in a voltage across the capacitor.

2. The vehicle of claim 1 wherein the predetermined change is defined by a product of (1−

1/e), where e is Euler'"'"'s number, and a magnitude of a difference between an initial voltage across the capacitor and a final voltage across the capacitor.

3. The vehicle of claim 2 wherein the initial voltage is the voltage at a time immediately after activating the switching element.

4. The vehicle of claim 2 wherein the final voltage is the voltage at the predetermined time, and wherein the predetermined time is such that a rate of change of the voltage with respect to time is approximately zero at the predetermined time.

5. The vehicle of claim 1 wherein the leakage resistance estimate is further based on a capacitance of the capacitor.

6. The vehicle of claim 1 wherein the resistive network includes a current limiting resistor and a voltage measurement resistor connected in series, and wherein the voltage across the capacitor is proportional to a voltage across the voltage measurement resistor.

7. The vehicle of claim 1 wherein the leakage resistance estimate is a parallel combination of a first leakage resistance between a positive terminal of the voltage bus and the chassis of the vehicle and a second leakage resistance between a negative terminal of the voltage bus and the chassis of the vehicle.

8. The vehicle of claim 1 wherein the at least one controller is further programmed to output the diagnostic when the leakage resistance estimate is less than a predetermined resistance.

9. A battery management system comprising:

a switching element configured to selectively couple a resistive network in parallel with a capacitor that couples a voltage bus and a ground reference; and

at least one controller programmed to, in response to the selective coupling exceeding a predetermined time, output a diagnostic according to a leakage resistance estimate that is based on a time associated with a predetermined change in a voltage across the capacitor.

10. The battery management system of claim 9 wherein the resistive network includes a current limiting resistor and a voltage measurement resistor connected in series, wherein the voltage across the capacitor is proportional to a voltage across the voltage measurement resistor.

11. The battery management system of claim 9 wherein the predetermined change is defined by a product of (1−

1/e), where e is Euler'"'"'s number, and a magnitude of a difference between an initial voltage across the capacitor and a final voltage across the capacitor.

12. The battery management system of claim 11 wherein the initial voltage is the voltage at a time immediately after the coupling.

13. The battery management system of claim 11 wherein the final voltage is the voltage at the predetermined time, and wherein the predetermined time is such that a rate of change of the voltage with respect to time is approximately zero at the predetermined time.

14. The battery management system of claim 9 wherein the leakage resistance estimate is further based on a capacitance of the capacitor.

15. The battery management system of claim 9 wherein the at least one controller is further programmed to activate the switching element in response to a signal indicative of an end of an ignition cycle.

16. The battery management system of claim 9 wherein the leakage resistance estimate is based on a parallel combination of a first leakage resistance between a positive terminal of the voltage bus and the ground reference and a second leakage resistance between a negative terminal of the voltage bus and the ground reference.

17. The battery management system of claim 9 wherein the at least one controller is further programmed to output the diagnostic when the leakage resistance estimate is less than a predetermined resistance.

18. A method comprising:

coupling, by a controller, a resistor network in parallel with a capacitor that couples a voltage bus and a chassis of a vehicle for a predetermined time; and

outputting, by the controller, a leakage resistance value based on a time for a voltage across the capacitor to change by a predetermined amount.

19. The method of claim 18 wherein the predetermined amount is defined by a product of (1−

1/e), where e is Euler'"'"'s number, and a magnitude of a difference between an initial voltage and a final voltage.

20. The method of claim 19 wherein the final voltage is less than the initial voltage.