Pre-charge via bi-directional DC/DC converter and auxiliary battery

1. A vehicle power system comprising:

a traction battery;

a bi-directional DC/DC converter;

main contactors configured to electrically connect the traction battery and bi-directional DC/DC converter when closed;

a DC link capacitor electrically between the main contactors and bi-directional DC/DC converter, wherein the bi-directional DC/DC converter is configured to charge the DC link capacitor to a target value before all of the main contactors are closed and without use of a resistor being in parallel with one of the main contactors; and

one of more controllers programmed to

specify the target value according to a voltage of the traction battery and a stored offset calibration constant,

obtain measured voltage values of the traction battery and DC link capacitor before and after the main contactors are closed, and

update the offset calibration constant based on the measured voltage values.

2. The vehicle power system of claim 1 , wherein the one or more controllers includes a battery controller programmed to update the offset calibration constant based on the measured voltage values.

3. The vehicle power system of claim 1 , wherein the one or more controllers includes a DC/DC controller programmed to update the offset calibration constant based on the measured voltage values.

4. The vehicle power system of claim 1 further comprising an auxiliary battery, wherein the bi-directional DC/DC converter is further configured to charge the DC link capacitor with energy from the auxiliary battery.

5. A method comprising:

following a request to activate a vehicle and prior to closing a main contactor to electrically connect a traction battery with a DC link capacitor, operating a bi-directional DC/DC converter to charge the DC link capacitor to a target voltage with energy from an auxiliary battery without electrically connecting a resistor in parallel with the main contactor;

specifying the target voltage according to a voltage of the traction battery and a stored offset calibration constant;

obtaining measured voltage values of the traction battery and DC link capacitor before and after the main contactors are closed; and

updating the offset calibration constant based on the measured voltage values.

6. The method of claim 5 further comprising after the DC link capacitor achieves the target voltage, closing the main contactor.

7. A power control arrangement for a vehicle, comprising:

a bi-directional DC/DC converter; and

one or more controllers programmed to,

after a request to activate the vehicle, command the bi-directional DC/DC converter to charge a DC link capacitor electrically between main contactors and the bi-directional DC/DC converter to a target value without connecting a resistor in parallel with one of the main contactors and before closing all of the main contactors,

specify the target value according to a voltage of a traction battery and a stored offset calibration constant,

obtain measured voltage values of the traction battery and DC link capacitor before and after the main contactors are closed, and

update the offset calibration constant based on the measured voltage values.

8. The power control arrangement of claim 7 , wherein the one or more controllers includes a battery controller programmed to update the offset calibration constant based on the measured voltage values.

9. The power control arrangement of claim 7 , wherein the one or more controllers includes a DC/DC controller programmed to update the offset calibration constant based on the measured voltage values.