UNINTERRUPTABLE A.C. POWER SUPPLY

摘要

1487049 Uninterruptable power supplies WESTERN ELECTRIC CO Inc 21 April 1976 [24 April 1975] 16216/76 Heading H2H An uninterruptable power supply comprises first and second power sources connected to terminals 13, 14 and 15, 16 respectively, voltage sensors 17, 18 for monitoring the voltage of the first source, an oscillator 25 coupled to the second source and circuitry including a switch 21 for selectively controlling the transfer of power from the first and second sources to output terminals 11, 12, the circuitry enabling the phase of the oscillator output to be aligned with the signal at the output terminals 11, 12 when the voltage of the first source has a first value and to be aligned with the first source when this source voltage has a second value. The first source is a mains supply and when it has its normal value, the sensor 18 causes a light emitting diode to trigger reverse parallel light activated thyristors in a gate 20. A load connected to the output terminals 11, 12 is therefore supplied with power via a transformer having a saturable core 56 and isolating magnetic shunts 50-53. The sensor 18 also supplies a signal to the switch 21 such as a semi-conductor bilateral switch arrangement to connect the output of a phase detector 28 to the oscillator 25. The detector 28 detects the zero crossings of the output signal at the terminals 11, 12 and constrains the oscillator to operate in phase with this signal. The oscillator controls an inverter 30, the output of which is in phase with the output signal at the terminals 11, 12 so that the inverter does not consume power from the second source such as a battery connected to the terminals 15, 16. If the voltage of the first source falls by 10 to 15%, the sensor 17 controls the switch 21 to connect a phase detector 19 to the oscillator 25 which is thus constrained to operate in phase with the first source. The power supplied to the load is therefore shared between the first source and the battery driven inverter. A further fall in the voltage of the first source is detected by the sensor 18 which controls the switch 21 to disconnect the oscillator 25 from the detectors 19, 28. The thyristors in the gate 20 are not triggered and the inverter 30 runs freely to supply all the power to the load. A circuit 24 monitors the battery voltage and inhibits operation of the inverter if the battery voltage falls below a predetermined level. When the first source voltage returns to normal, the thyristors in the gate 20 are triggered and the oscillator operates in phase with the output voltage at the terminals 11, 12.