CONTINUOUSLY OPERATING STANDBY A-C POWER SYSTEM

A continuously operating standby A-C power system which uses a single loop responsive to the system's input and output A-C voltages, the voltage of the battery included in the standby portion of the supply and the amplitude and frequency of the input A-C voltage for controlling the phase relationship between the input and output voltages. When the input A-C voltage is acceptable in both amplitude and frequency, the loop is closed. When the voltage becomes unacceptable, the loop opens. When the voltage returns to acceptability after a period of nonacceptability, circuitry is included in the system for slowly closing the loop.