Computer controlled standby power supply system

摘要

A standby power supply system (SPS) is connected to supply power to a load by way of a transfer switch, to replace power from the AC lines, when the AC line fails to provide sufficient voltage to operate the load (e.g., 85% of nominal RMS voltage usually 120 VAC-RMS). The SPS has an inverter which switches voltage from a battery to generate AC power when the line fails. The inverter is controlled by varying the width of switching pulses in order to regulate the AC output voltage and compensate for reductions in battery voltage as the battery discharges. The AC output voltage is also synchronized with the line voltage when the line voltage returns (increases to greater than 85% of nominal value) so that on switch over back to the AC line, the AC waveform applied to the load does not change substantially before and after switch over. The inverter is controlled by a computer controller (microprocessor) directly in response to current in the inverter for regulating the output voltage without the need for sensing the output voltage, thereby avoiding sensing transformers and ancillary circuits connected to the AC lines. The microprocessor also functions as a variable frequency oscillator for synchronizing the inverter AC voltage with the line AC voltage thereby preventing output waveform discontinuities upon switch over from the inverter to the AC line.