A method of controlling a powertrain of a hybrid vehicle includes comparing an operating efficiency of a motor-generator-inverter to an upper MGI efficiency threshold when a boost operating mode is selected. When the operating efficiency of the motor-generator-inverter is equal to or greater than the upper MGI efficiency threshold, the motor-generator-inverter is controlled to operate in the boost operating mode. The operating efficiency of the motor-generator-inverter is compared to a lower MGI efficiency threshold when a regenerative operating mode is selected. When the operating efficiency of the motor-generator-inverter is equal to or greater than the lower MGI efficiency threshold, the motor-generator-inverter is controlled to operate in the regenerative operating mode.