Method for detecting battery thermal events via battery pack isolation monitoring

• US 8,168,315 B1
• Filed: 08/23/2011
• Issued: 05/01/2012
• Est. Priority Date: 08/23/2011
• Status: Active Grant

• Current Assignee: Tesla Inc.
• Original Assignee: Tesla Motors Incorporated (Tesla Inc.)
• Inventors: Hermann, Weston Arthur
• Primary Examiner(s): Ridley, Basia
• Assistant Examiner(s): Cullen, Sean P
• Application Number:
  US13/216,127
• Time in Patent Office: 252 Days
• Field of Search: 429/50, 429 90- 93, 324/500, 324/525
• US Class Current: 429/92
• 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 2250/10 by alarm
• CPC Class Codes: B60L 3/0046 relating to electric energy storage systems, e.g. batteries or capacitors
• CPC Class Codes: B60L 3/0069 relating to the isolation, e.g. ground fault or leak current
• CPC Class Codes: B60L 3/04 Cutting off the power supply under fault conditions protective devices and circuit arrangements in general H01H; H02H
• CPC Class Codes: B60L 50/64 Constructional details of batteries specially adapted for electric vehicles
• CPC Class Codes: B60L 58/21 having the same nominal voltage
• CPC Class Codes: B60L 58/25 by controlling the electric load
• CPC Class Codes: B60L 58/26 by cooling
• CPC Class Codes: G01R 31/1263 of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 10/486 for measuring temperature
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

A method for detecting cell failure within a battery pack based on variations in the measured electrical isolation resistance of the battery pack is provided. The method includes the steps of monitoring the isolation resistance; determining when the isolation resistance falls below a preset value; and performing a predetermined response when the isolation resistance falls below the preset value. The method may include additional steps such as (i) determining how long the isolation resistance remains below the preset value; (ii) determining the rate of change in the isolation resistance; (iii) determining how long it takes for the electrical isolation resistance to recover; (iv) determining when the isolation resistance falls below a third preset value, wherein this step is performed after the isolation resistance recovers to greater than the second preset value; and (v) monitoring for a secondary effect associated with cell failure.

Claims

1. A method of detecting and responding to a cell failure of at least one cell of a plurality of cells comprising a battery pack, the method comprising the steps of:

periodically monitoring an electrical isolation resistance of said battery pack;

comparing said electrical isolation resistance to a preset resistance value;

determining when said electrical isolation resistance falls below said preset resistance value, wherein said electrical isolation resistance falling below said preset resistance value is indicative of said cell failure;

monitoring a battery pack temperature;

determining when said battery pack temperature exceeds a preset temperature;

determining if said electrical isolation resistance falling below said preset resistance occurs within a preset time period of said battery pack temperature exceeding said preset temperature; and

performing a predetermined cell failure response if said electrical isolation resistance falling below said preset resistance value occurs within said preset time period of said battery pack temperature exceeding said preset temperature.

2. The method of claim 1, further comprising the step of setting said preset resistance value to a percentage of an initial electrical isolation resistance of said battery pack.

3. The method of claim 2, wherein said percentage is selected from a range of 25% to 50%.

4. The method of claim 2, wherein said percentage is selected from a range of 10% to 25%.

5. The method of claim 1, wherein said step of performing said predetermined cell failure response further comprises a step of activating a visual warning indicator.

6. The method of claim 1, wherein said step of performing said predetermined cell failure response further comprises a step of activating an audible warning indicator.

7. The method of claim 1, wherein said step of performing said predetermined cell failure response further comprises a step of reducing an electrical load on said plurality of cells of said battery pack.

8. The method of claim 1, wherein said step of performing said predetermined cell failure response further comprises a step of minimizing an electrical load on said plurality of cells of said battery pack.

9. The method of claim 1, wherein said step of performing said predetermined cell failure response further comprises a step of increasing cooling applied to said battery pack by a battery pack cooling system.

10. The method of claim 1, wherein said step of performing said predetermined cell failure response further comprises a step of activating a fire containment system.

11. The method of claim 1, wherein said step of performing said predetermined cell failure response further comprises a step of recording date and time information corresponding to said electrical isolation resistance falling below said preset resistance value.

12. The method of claim 1, wherein said step of performing said predetermined cell failure response further comprises a step of transmitting a notification message via a communication and notification subsystem.