A vehicle power system includes a battery bus between a traction battery and voltage converter, a high-voltage bus between the voltage converter and an inverter, and a controller. The controller, responsive to a contactor between the traction battery and voltage converter opening, controls an engine to maintain a speed of a generator electrically coupled with the inverter within a predefined range, controls the voltage converter to drive a measured voltage of the battery bus toward a first commanded value based on a first difference between the first commanded value and measured voltage of the battery bus, and controls the generator to drive a measured voltage of the high-voltage bus toward a second commanded value different than the first commanded value based on the first difference and a second difference between the second commanded value and the measured voltage of the high-voltage bus.