A method for controlling an electrically-powered torque machine of a powertrain system includes determining a predicted torque command to control the torque machine. A flux command is determined responsive to the predicted torque command. The flux command is a flux level providing a fast torque reserve that is responsive to the predicted torque command. The fast torque reserve is a prescribed minimum rate of change in torque output from the torque machine responsive to the predicted torque command. An inverter controller controls flux of the torque machine responsive to the flux command.