Bus leakage resistance estimation for electrical isolation testing and diagnostics
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. A larger one of the estimated bus leakage resistances is selected as a balanced leakage resistance. Failure of a device connected to a bus (such as a wiring cable or a fuel cell) is predicted in response to predetermined decreases in the estimated balanced leakage resistance over time.
1. A method of fault prediction in an electrified vehicle, comprising:
measuring first and second leakage-related currents for first and second buses connected to a DC source by sequentially connecting each bus to ground using a first detector circuit and a second detector circuit, wherein the first detector circuit comprises a first limiting resistance and a first sense resistance selectably connected between the first 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, and wherein the second detector circuit comprises a second limiting resistance and a second sense resistance selectably connected between the second 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;
estimating each of the positive bus leakage resistance and the negative bus leakage resistance in response to 1) a bus voltage present during the measuring step divided by the respective first and second leakage-related currents and 2) respective ratios of the first and second leakage-related currents;
selecting a larger one of the estimated bus leakage resistances as an estimated balanced leakage resistance; and
predicting a failure of a device connected to the buses according to predetermined decreases in the estimated balanced leakage resistance over time.
2. The method of claim 1 further comprising:
estimating an unbalanced leakage resistance according to a formula:
R
unbal
=
R
lp
·
R
lm
R
lp
-
R
lm
where Ri lp and R lm are the estimated positive and negative bus leakage resistances; and
predicting a failure of another device connected to the buses according to predetermined decreases in the unbalanced leakage resistance over time.
3. The method of claim 1 wherein the step of predicting a failure is comprised of:
comparing the estimated balanced leakage resistance to a predetermined threshold; and
generating a predicted failure notification in response to the balanced leakage resistance falling below the predetermined threshold.