Uninterruptible Power Supplies

Abstract

A power train of an uninterruptible power supply selectively transforms its load from a primary source of power to a reserve source of power under control of a stored program control operating in real time. A microprocessor operating in conjunction with a prioritized interrupt controller and a plurality of external counters monitors and responds to signal conditions existing at various points of the power supply. In particular, the amplitude of a primary AC voltage source is sampled at precise angles of the sinusoidal waveform in response to a comb pulse waveform generated to conform to the actual period of the primary AC voltage. The frequencies range is determined by comparing a count interval to the period of the primary AC voltage. Relative power flow from the primary AC voltage source and a reserve AC voltage signal is controlled by relative phasing of the two signals. The reserve AC voltage signal is adjusted in phase during normal operation when all power is supplied by the primary AC voltage source by comparison to an AC output signal of the power supply to either null power dissipation in the generator of the reserve AC voltage signal or to supply charging current to its energizing DC voltage source.