Output signals from ground power units can be combined to supply more energy for aircraft to use for starting a jet engine. The combining can be possible when the outputs from the ground power units are synchronized. In a synchronization process, a first ground power unit may be started so that its first output signal serves as a reference for the synchronization. Then, an interconnect on a second ground power unit can be toggled to start and stop the generation of a second output signal at different times until the signals are in phase (i.e., synchronized).

Output signals from ground power units can be combined to supply more energy for aircraft to use for starting a jet engine. The combining can be possible when the outputs from the ground power units are synchronized. In a synchronization process, a first ground power unit may be started so that its first output signal serves as a reference for the synchronization. Then, an interconnect on a second ground power unit can be toggled to start and stop the generation of a second output signal at different times until the signals are in phase (i.e., synchronized).