System and method for high voltage system isolation resistance measurement

• US 9,720,049 B2
• Filed: 07/08/2015
• Issued: 08/01/2017
• Est. Priority Date: 07/22/2014
• Status: Active Grant

• Current Assignee: Robert Bosch Battery Systems LLC (Robert Bosch GmbH), Robert Bosch GmbH
• Original Assignee: Robert Bosch Battery Systems LLC (Robert Bosch GmbH), Robert Bosch GmbH
• Inventors: Anzicek, Joshua
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US14/793,804
• Publication Number:
  US 20160025816A1
• Time in Patent Office: 755 Days
• Field of Search: 320116, 320117, 320119, 320121, 324430, 324433, 324434
• CPC Class Codes: G01R 27/025 Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• 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
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]

Abstract

A circuit that measures isolation resistance in a battery pack that is associated with a load includes four resistors. Two resistors are connected between terminals of the battery pack and another two resistors are connected in the load in parallel to the resistors in the battery pack. A controller operates two contactors to disconnect the battery from the load and measure first and second voltages in the battery pack and one of the two resistors. The controller operates the two contactors to connect the battery to the load and measures third and fourth voltages in the battery pack and one of the two resistors. The controller identifies the isolation resistance with reference to resistance values of the four resistors and the first, second, third, and fourth measured voltages.

Claims

1. A battery isolation resistance measurement circuit comprising:

a first plurality of resistors connected in parallel to a plurality of battery cells in a battery cell pack;

a second plurality of resistors in a load that receives power from the battery cell pack;

a first contactor configured to connect and disconnect a first terminal of the battery cell pack from a first terminal of the load; and

a controller operatively connected to the first contactor, the controller being configured to;

operate the first contactor to disconnect the battery cell pack from the load;

identify a first voltage and a second voltage in the first plurality of resistors within the battery cell pack while the battery cell pack is disconnected from the load;

operate the first contactor to connect the battery cell pack to the load;

identify a third voltage and a fourth voltage in the first plurality of resistors within the battery cell pack while the battery cell pack is connected to the load; and

identify an isolation resistance of the battery cell pack with reference to the first, second, third, and fourth voltages and predetermined resistance values of the first plurality of resistors and the second plurality of resistors.

2. The circuit of claim 1 further comprising:

a second contactor configured to connect and disconnect a second terminal of the battery cell pack from a second terminal of the load; and

the controller being operatively connected to the second contactor, the controller being further configured to;

operate the first contactor and the second contactor to disconnect the battery cell pack from the load;

identify the first voltage and the second voltage in the first plurality of resistors within the battery cell pack while both the first contactor and the second contactor disconnect the battery cell pack from the load;

operate the first contactor and the second contactor to connect the battery cell pack to the load; and

identify the third voltage and the fourth voltage in the first plurality of resistors within the battery cell pack while the first contactor and the second contactor connect the battery cell pack to the load.

3. The circuit of claim 2, the controller being further configured to:

operate the first contactor to disconnect the first terminal of the battery cell pack from the load;

operate the second contactor to connect the first terminal of the battery cell pack from the load;

identify a fifth voltage and a sixth voltage in the first plurality of resistors within the battery cell pack while the first contactor is disconnected from the load and the second contactor is connected to the load; and

identify an isolation resistance of the load with reference to the fifth voltage, the sixth voltage, the isolation resistance of the battery cell pack, and the predetermined resistance values of the first plurality of resistors and the second plurality of resistors.

4. The circuit of claim 1 further comprising:

a first voltmeter configured to measure voltage across a first resistor in the first plurality of resistors, the first resistor being connected to the first terminal of the battery cell pack;

a second voltmeter configured to measure voltage across the first terminal and the second terminal of the battery cell pack; and

the controller being operatively connected to the first voltmeter and the second voltmeter, the controller being configured to;

identify the first voltage in the first plurality of resistors with reference to a first voltage measurement from the first voltmeter while the battery cell pack is disconnected from the load;

identify the second voltage in the first plurality of resistors with reference to a second voltage measurement from the second voltmeter while the battery cell pack is disconnected from the load;

identify the third voltage in the first plurality of resistors with reference to a third voltage measurement from the first voltmeter while the battery cell pack is connected to the load;

identify the fourth voltage in the first plurality of resistors with reference to a fourth voltage measurement from the second voltmeter while the battery cell pack is connected to the load.

5. The circuit of claim 1, the controller being further configured to:

identify an isolation voltage of the battery cell pack with reference to the isolation resistance of the battery cell pack, third and fourth voltages, and the resistance values of the first plurality of resistors.

6. The circuit of claim 1 wherein a low voltage ground is connected between a first resistor and a second resistor in the first plurality of resistors.

7. A battery isolation resistance measurement circuit comprising:

a battery cell pack including a plurality of battery cells including a first terminal and a second terminal;

a first sensing resistor connected to the first terminal of the battery cell pack;

a second sensing resistor arranged to form a series connection with the first sensing resistor and to the second terminal of the battery cell pack;

a first resistor connected to the series connection between the first sensing resistor and second sensing resistor and the first resistor being connected to a switching device, the switching device being further connected to the second terminal of the battery cell pack; and

a controller operatively connected to the switching device, the controller being configured to;

operate the switching device to disconnect the first resistor from the second terminal of the battery cell pack;

identify a first voltage between the first terminal and the second terminal of the battery cell pack and a second voltage across the first sensing resistor and the second sensing resistor while the first resistor is disconnected from the second terminal of the battery cell pack;

operate the switching device to connect the first resistor to the second terminal of the battery cell pack;

identify a third voltage between the first terminal and the second terminal of the battery cell pack and a fourth voltage across the first sensing resistor and the second sensing resistor while the first resistor is connected to the second terminal of the battery cell pack; and

identify an isolation resistance of the battery cell pack with reference to the first voltage, the second voltage, the third voltage, the fourth voltage, and predetermined resistance values of the first sensing resistor, the second sensing resistor, and the first resistor.

8. The circuit of claim 7, wherein the switching device is an n-channel MOSFET.

9. The circuit of claim 7 further comprising:

a load connected to the first terminal and the second terminal of the battery cell pack, the load further comprising;

a second resistor connected in series with a third resistor, the second resistor being further connected to the first terminal, the third resistor being further connected to the second terminal, and a connection between the second and third resistors being connected to between the first sensing resistor and the second sensing resistor and to the first resistor; and

the controller being further configured to identify the isolation resistance of the battery cell pack with reference to predetermined resistance values of the second resistor and the third resistor in a configuration with the load being connected to the battery cell pack.