Active discharging high voltage direct current bus system and method for a vehicle

1. A discharge control system of a vehicle, comprising:

a traction power inverter module (TPIM) configured to convert a first direct current (DC) voltage output by a first battery to alternating current (AC) power and to apply the AC power to an electric motor;

an accessory power module (APM) configured to convert the first DC voltage into a second DC voltage of a second battery,

wherein the second DC voltage is less than the first DC voltage;

a voltage calculation module configured to, when the first DC voltage is less than an operation threshold voltage of the APM, determine the second DC voltage based on a function of the first DC voltage and the operation threshold voltage;

a diagnostic module configured to indicate whether a discharge fault is present; and

a discharge control module configured to, when the discharge fault is present, based on at least one of the first DC voltage and the second DC voltage, selectively control operation of at least one of (i) the TPIM and (ii) the APM.

2. The discharge control system of claim 1 wherein the discharge control module is configured to, when the first DC voltage is greater than a first high voltage (HV) threshold and the discharge fault is present, at least one of:

operate the TPIM to apply the AC power to windings of the electric motor; and

operate the APM to convert the first DC voltage into the second DC voltage.

3. The discharge control system of claim 2 wherein the discharge control module is configured to, when the first DC voltage is less than the first HV threshold and greater than a second HV threshold and the discharge fault is present, at least one of:

operate the TPIM to apply the AC power to windings of the electric motor; and

operate the APM to convert the first DC voltage into the second DC voltage.

4. The discharge control system of claim 3 wherein the discharge control module is configured to, when the first DC voltage is less than the second HV threshold and greater than a third HV threshold and the discharge fault is present, operate the APM to convert the first DC voltage into the second DC voltage and not operate the TPIM to apply the AC power to windings of the electric motor.

5. The discharge control system of claim 1 wherein the discharge control module is configured to, when the second DC voltage is greater than a first low voltage (LV) threshold and the discharge fault is present, at least one of:

operate the TPIM to apply the AC power to windings of the electric motor; and

operate the APM to convert the first DC voltage into the second DC voltage.

6. The discharge control system of claim 5 wherein the discharge control module is configured to, when the second DC voltage is less than the first LV threshold and greater than a second LV threshold and the discharge fault is present, at least one of:

operate the TPIM to apply the AC power to windings of the electric motor; and

operate the APM to convert the first DC voltage into the second DC voltage.

7. The discharge control system of claim 6 wherein the discharge control module is configured to, when the second DC voltage is less than the second LV threshold and greater than a third LV threshold and the discharge fault is present, operate the APM to convert the first DC voltage into the second DC voltage and not operate the TPIM to apply the AC power to windings of the electric motor.

8. The discharge control system of claim 1 wherein the discharge control module is configured to:

when the first DC voltage is greater than a first high voltage (HV) threshold and the discharge fault is present:

operate the TPIM to apply the AC power to windings of the electric motor; and

operate the APM to convert the first DC voltage into the second DC voltage; and

when the second DC voltage is greater than a first low voltage (LV) threshold and the discharge fault is present:

operate the TPIM to apply the AC power to windings of the electric motor; and

operate the APM to convert the first DC voltage into the second DC voltage.

9. The discharge control system of claim 8 wherein the discharge control module is configured to:

when the first DC voltage is less than the first HV threshold and greater than a second HV threshold and the discharge fault is present:

operate the TPIM to apply the AC power to windings of the electric motor; and

operate the APM to convert the first DC voltage into the second DC voltage; and

when the second DC voltage is less than the first LV threshold and greater than a second LV threshold and the discharge fault is present:

operate the TPIM to apply the AC power to windings of the electric motor; and

operate the APM to convert the first DC voltage into the second DC voltage.

10. The discharge control system of claim 9 wherein the discharge control module is configured to:

when the first DC voltage is less than the second HV threshold and greater than a third HV threshold and the discharge fault is present, operate the APM to convert the first DC voltage into the second DC voltage and not operate the TPIM to apply the AC power to windings of the electric motor; and

when the second DC voltage is less than the second LV threshold and greater than a third LV threshold and the discharge fault is present, operate the APM to convert the first DC voltage into the second DC voltage and not operate the TPIM to apply the AC power to windings of the electric motor.

11. The discharge control system of claim 1 wherein the discharge control module is further configured to, when the first DC voltage is less than the operation threshold voltage and the discharge fault is present, maintain operation of the APM for a second predetermined period.

12. The discharge control system of claim 11 wherein the discharge control module is further configured to, when the second DC voltage is less than the operation threshold voltage and the discharge fault is present, maintain operation of the APM in current mode for a third predetermined period.

13. The discharge control system of claim 12 wherein:

the second predetermined period is less than eight seconds; and

the third predetermined period is greater than eight seconds.

14. The discharge control system of claim 12 wherein the APM is further configured to, when the second DC voltage falls below a predetermined voltage for less than a fourth predetermined period and subsequently becomes greater than the fourth predetermined period, provide current to the TPIM for the third predetermined period.

15. The discharge control system of claim 12 wherein the discharge control module is further configured to, when the second DC voltage falls below a predetermined voltage for less than a fourth predetermined period and subsequently becomes greater than the fourth predetermined period, wake-up the TPIM.

16. A discharge control method for a vehicle, comprising:

by a traction power inverter module (TPIM), converting a first direct current (DC) voltage output by a first battery to alternating current (AC) power and applying the AC power to an electric motor;

by an accessory power module (APM), converting the first DC voltage into a second DC voltage of a second battery,

wherein the second DC voltage is less than the first DC voltage;

when the first DC voltage is less than an operation threshold voltage of the APM, determining the second DC voltage based on a function of the first DC voltage and the operation threshold voltage;

indicating whether a discharge fault is present; and

when the discharge fault is present, based on at least one of the first DC voltage and the second DC voltage, selectively controlling operation of at least one of (i) the TPIM and (ii) the APM.

17. The discharge control method of claim 16 further comprising, when the first DC voltage is greater than a first high voltage (HV) threshold and the discharge fault is present, at least one of:

operating the TPIM to apply the AC power to windings of the electric motor; and

operating the APM to convert the first DC voltage into the second DC voltage.

18. The discharge control method of claim 17 further comprising, when the first DC voltage is less than the first HV threshold and greater than a second HV threshold and the discharge fault is present, at least one of:

operating the TPIM to apply the AC power to windings of the electric motor; and

operating the APM to convert the first DC voltage into the second DC voltage.

19. The discharge control method of claim 18 further comprising, when the first DC voltage is less than the second HV threshold and greater than a third HV threshold and the discharge fault is present, operating the APM to convert the first DC voltage into the second DC voltage and not operating the TPIM to apply the AC power to windings of the electric motor.

20. The discharge control method of claim 16 further comprising, when the second DC voltage is greater than a first low voltage (LV) threshold and the discharge fault is present, at least one of:

operating the TPIM to apply the AC power to windings of the electric motor; and

operating the APM to convert the first DC voltage into the second DC voltage.