Abstract: A ground power unit capable of no-break power transfer includes a rectifier for converting power from commercial mains to direct current, a switching circuit, a power transformer, and a pattern generator for controlling the operation of the switching circuit. Voltage and current sensors monitor whether the phase of the ground power unit is leading or lagging the phase of the aircraft power bus at the tinge of power transfer. The frequency and phase of the pattern generator converter is adjusted to bring the two systems into alignment quickly, well before the power transfer operation is completed. The ground power unit limits the power transfer between the two systems to prevent the overloading of either.

Abstract: An electrical power supply for providing an electrical power signal of substantially constant voltage when the current level of the power signal is less than a predetermined value and for reducing the voltage of the power signal below said predetermined level when the power signal current level exceeds the predetermined value includes a ferroresonant transformer. A saturable reactor provides a current responsive impedance connected to the primary of the ferroresonant transformer for reducing the voltage supplied to the primary winding. The maximum current level in the secondary circuit of the ferroresonant transformer is adjusted by adjusting the effective impedance of the saturable reactor. A rectifier may be connected in the secondary circuit of the ferroresonant transformer to provide direct current electrical power signal.