Bus leakage resistance estimation for electrical isolation testing and diagnostics

Patent metadata

Field	Value
Publication number	US-9758044-B2
Application number	US-201414504588-A
Country	US
Kind code	B2
Filing date	Oct 2, 2014
Priority date	Oct 2, 2014
Publication date	Sep 12, 2017
Grant date	Sep 12, 2017

Abstract

Electrical bus isolation is detected for an electrified vehicle having a DC power source connected to positive and negative buses. The positive bus is connected to chassis ground, and a resulting first current is sensed that flows through a negative bus leakage resistance and a balanced leakage resistance. The negative bus is connected to chassis ground, and a resulting second current is sensed that flows through a negative bus leakage resistance and a balanced leakage resistance. The positive and negative bus leakage resistances are estimated in response to respective ratios of the first and second currents. An isolation value is compared to a threshold, wherein the isolation value is responsive to a voltage of the DC power source and a smaller one of the positive and negative bus leakage resistances. An atypical isolation is signaled when the isolation value is less than the threshold.

First claim

What is claimed is:

1. An electrified vehicle comprising:
a positive bus connectable to a positive output of a DC power source;
a negative bus connectable to a negative output of the DC power source;
a chassis ground distributed within the vehicle;
a first detector circuit comprising a first limiting resistance and a first sense resistance selectably connected between the positive bus and the chassis ground in order to sense a resulting first current flowing through a negative bus leakage resistance and a balanced leakage resistance;
a second detector circuit comprising a second limiting resistance and a second sense resistance selectably connected between the negative bus and the chassis ground in order to sense a resulting second current flowing through a positive bus leakage resistance and the balanced leakage resistance; and
a control circuit identifying the positive and negative bus leakage resistances in response to respective ratios of the first and second currents.

2. The vehicle of claim 1 wherein the detector circuits include respective sampling switches closed by the control circuit.

3. The vehicle of claim 1 wherein the control circuit is configured to disconnect the positive and negative buses from the DC power source when an isolation value is less than a threshold, the isolation value being determined using a smaller one of the positive and negative bus leakage resistances.

4. The vehicle of claim 1 wherein the control circuit is configured to detect a fault condition when an isolation value is less than a threshold, the isolation value being determined using a smaller one of the positive and negative bus leakage resistances.

5. The vehicle of claim 1 wherein the positive bus leakage resistance is identified according a formula:

R
lp

=

V
b

I
RSP

-

R
C

⁡

(

1
+

I
RSM

I
RSP

)

where R lp is the positive bus leakage resistance, V b is a voltage from the DC power source, I RSP is the second current, I RSM is the first current, and R C is the combined sense circuit resistance.

6. The vehicle of claim 1 wherein the negative bus leakage resistance is identified according a formula:

R
lm

=

V
b

I
RSM

-

R
C

⁡

(

1
+

I
RSP

I
RSM

)

where R lm is the negative bus leakage resistance, V b is a voltage from the DC power source, I RSM is the first current, I RSP is the second current, and R C is the combined sense circuit resistance.

7. The vehicle of claim 1 wherein the control circuit identifies a balanced leakage resistance as a higher one of the positive and negative bus leakage resistances, and wherein the control circuit monitors changes over time of the balanced leakage resistance to identify a potential malfunction of the vehicle.

8. The vehicle of claim 1 wherein the control circuit identifies an unbalanced resistance according to a formula:

R
unbal

=



R
lp

·

R
lm

R
lp

-

R
lm



where R lp and R lm are the positive and negative bus leakage resistances, respectively, and wherein the control circuit monitors changes over time of the unbalanced resistance to identify a potential malfunction of the vehicle.

9. A method of detecting bus isolation for an electrified vehicle, the vehicle having a DC power source connectable to a positive bus and a negative bus and a chassis ground distributed within the vehicle, the method comprising the steps of:
connecting a first fixed resistance between the positive bus and chassis ground;
sensing a resulting first current flowing through a negative bus leakage resistance and a balanced leakage resistance;
connecting a second fixed resistance between the negative bus and chassis ground;
sensing a resulting second current flowing through a positive bus leakage resistance and a balanced leakage resistance;
estimating the positive and negative bus leakage resistances in response to respective ratios of the first and second currents;
comparing an isolation value to a threshold, wherein the isolation value is responsive to a voltage of the DC power source and a smaller one of the positive and negative bus leakage resistances; and
signaling an atypical isolation when the isolation value is less than the threshold.

10. The method of claim 9 wherein the signaling of an atypical isolation includes disconnecting the DC power source from the positive and negative buses.

11. The method of claim 9 further comprising the step of measuring the voltage of the DC power source, wherein the measured voltage is used in determining the isolation value.

12. The method of claim 9 wherein the voltage used in determining the isolation value is comprised of a predetermined constant.

13. The method of claim 9 wherein the positive bus leakage resistance is estimated according a formula:

R
lp

=

Assignees

• Ford Global Tech Llc

Inventors

• Gale Allan R
• Kautz Richard W

Classifications

• B60L3/0069 Primary

  relating to the isolation, e.g. ground fault or leak current · CPC title

• G01R31/007

  using microprocessors or computers · CPC title

• G01R27/025

  Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters · CPC title

• Y02T10/7241

  Cross-Sectional Technologies · mapped topic

• Y02T10/7022

  Cross-Sectional Technologies · mapped topic