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. 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.
1. A method of monitoring bus isolation using bus leakage resistances exhibited by first and second buses in an electrified vehicle, comprising:
measuring first and second leakage-related currents for the first and second buses by sequentially connecting each bus to chassis ground via respective detector circuits each comprising a respective limiting resistance and a respective sense resistance selectably connected between the respective bus and the chassis ground;
estimating each 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 currents; selecting a bus isolation value according to a smaller one of the estimated bus leakage resistances, including balanced and unbalanced leakage resistances; and
estimating a balanced leakage resistance by selecting a larger one of the estimated bus leakage resistances.
2. The method of claim 1 further comprising the step of:
estimating an unbalanced leakage resistance according to a formula:
R
unbal
=
R
lp
·
R
l
m
R
lp
-
R
l
m
where R lp and R lm are the estimated bus leakage resistances.