Abstract: A microprocessor based uninterruptible power supply generates an AC electrical output power from an AC input source when the AC input source is within settable voltage limits and from an auxiliary source of DC power when the AC input source is outside said the voltage limits. The microprocessor provides monitoring of the AC input voltage to determine its amplitude and frequency, and uses this information to set the magnitude and frequency of the AC output voltage and to select the source of the AC output power. A power factor improvement circuit boosts the selected source to a high DC voltage which is inverted by a chopper circuit to produce a high frequency AC voltage is rectified and sent to a PWM inverter to produce the AC output power. An average current feedback loop provides the output voltage regulation and utilizes current limiting to provide output current limiting for protection against short circuits and overloads.

Abstract: An uninterruptible power supply for supplying a load with AC output power generates the AC output power from an AC input source when the AC input source is within settable voltage limits and transfers to generating the AC output power from an auxiliary source of DC power when the AC input source is outside the voltage limits. A microprocessor provides monitoring and sampling of the AC input voltage to determine its amplitude and frequency, and uses this information to set the magnitude and frequency of the AC output voltage by generating a sine reference signal to control the AC output frequency and voltage phase angle. The microprocessor maintains a voltage phase relationship between the AC input power and AC output power to eliminate voltage and current transients at transfer times between the AC and DC input sources that would be present if the AC output suddenly had a drastic, voltage phase angle change.