A vehicle propulsion system comprising: a first bi-directional DC-DC converter coupled to a first DC bus (36, 80); an energy storage system comprising at least one energy storage unit coupled to the first bi-directional DC-DC converter; a first DC-to-AC inverter coupled to the first DC bus (36, 80); a first electromechanical device coupled to the first DC-to-AC inverter; and a controller programmed to: determine a real-time operating speed of the first electromechanical device; determine a scheduled speed of the first electromechanical device from a voltage scheduling look-up table based on a real-time torque of the first electromechanical device and the real-time voltage of the first DC bus (36, 80); and compare the real-time operating speed of the first electromechanical device to the scheduled speed of the first electromechanical device; characterized in that the controller is programmed to control the DC-DC converter to: shift the voltage of the first DC bus (36, 80) by a predetermined voltage interval; increase the voltage of the DC bus (36, 80) by the predefined voltage interval if the scheduled speed of the first electromechanical device is less than the real-time operating speed of the first electromechanical device; and decrease the voltage of the DC bus (36, 80) by the predefined voltage interval if the scheduled speed of the first electromechanical device is greater than the real-time operating speed of the first electromechanical device.. a first bi-directional DC-DC converter coupled to a first DC bus (36, 80); an energy storage system comprising at least one energy storage unit coupled to the first bi-directional DC-DC converter; a first DC-to-AC inverter coupled to the first DC bus (36, 80); a first electromechanical device coupled to the first DC-to-AC inverter; and a controller programmed to: determine a real-time operating speed of the first electromechanical device; determine a scheduled speed of the first electromechanical device from a voltage scheduling look-up table based on a real-time torque of the first electromechanical device and the real-time voltage of the first DC bus (36, 80); and compare the real-time operating speed of the first electromechanical device to the scheduled speed of the first electromechanical device; characterized in that the controller is programmed to control the DC-DC converter to: shift the voltage of the first DC bus (36, 80) by a predetermined voltage interval; increase the voltage of the DC bus (36, 80) by the predefined voltage interval if the scheduled speed of the first electromechanical device is less than the real-time operating speed of the first electromechanical device; and decrease the voltage of the DC bus (36, 80) by the predefined voltage interval if the scheduled speed of the first electromechanical device is greater than the real-time operating speed of the first electromechanical device.. determine a real-time operating speed of the first electromechanical device; determine a scheduled speed of the first electromechanical device from a voltage scheduling look-up table based on a real-time torque of the first electromechanical device and the real-time voltage of the first DC bus (36, 80); and compare the real-time operating speed of the first electromechanical device to the scheduled speed of the first electromechanical device; characterized in that the controller is programmed to control the DC-DC converter to: shift the voltage of the first DC bus (36, 80) by a predetermined voltage interval; increase the voltage of the DC bus (36, 80) by the predefined voltage interval if the scheduled speed of the first electromechanical device is less than the real-time operating speed of the first electromechanical device; and decrease the voltage of the DC bus (36, 80) by the predefined voltage interval if the scheduled speed of the first electromechanical device is greater than the real-time operating speed of the first electromechanical device.. shift the voltage of the first DC bus (36, 80) by a predetermined voltage interval; increase the voltage of the DC bus (36, 80) by the predefined voltage interval if the scheduled speed of the first electromechanical device is less than the real-time operating speed of the first electromechanical device; and decrease the voltage of the DC bus (36, 80) by the predefined voltage interval if the scheduled speed of the first electromechanical device is greater than the real-time operating speed of the first electromechanical device..