Abstract: An uninterruptible power supply is provided that is capable of turning off an AC switch made up of thyristors as quickly as possible by using a power converter. A power is supplied from the utility power supply 3 to the load 9 through the AC switch 1 made up of antiparallelly connected thyristors. Under this condition, in the event that the power failure detection means 12 detects a power outage, if the current detection means 11a detects a current of a positive polarity, the reference sinusoidal voltage generation circuit 11 generates the high synchronous sinusoidal voltage Vref2 which is higher, by the voltage difference command value &Dgr;V, than the synchronous sinusoidal voltage Vref1 in phase with the utility power supply.

Abstract: An uninterruptible power supply is provided that is capable of turning off an AC switch made up of thyristors as quickly as possible by using a power converter. A power is supplied from the utility power supply 3 to the load 9 through the AC switch 1 made up of antiparallelly connected thyristors. Under this condition, in the event that the power failure detection means 12 detects a power outage, if the current detection means 11a detects a current of a positive polarity, the reference sinusoidal voltage generation circuit 11 generates the high synchronous sinusoidal voltage Vref2 which is higher, by the voltage difference command value &Dgr;V, than the synchronous sinusoidal voltage Vref1 in phase with the utility power supply.

Abstract: A parallel operation-type uninterruptible power system capable of preventing one of uninterruptible power systems from being extremely increased in load sharing ratio without having to operate each uninterruptible power system while watching operation of the remaining uninterruptible power systems. The uninterruptible power systems each are constituted by an inverter circuit and an inverter circuit control device. The inverter circuit control device includes a PWM control signal generating means. The PWM control signal generating means generates a PWM control signal so as to gradually reduce an output voltage of the inverter circuit as supply active power increases and until a judging means judges that the supply active power has reached a predetermined level and so as to reduce the output voltage at a reduction ratio increased as compared with before to keep it from falling into an overload condition when the judging means judges that the supply active power has reached the predetermined level.

Abstract: A parallel operation-type uninterruptible power system capable of preventing one of uninterruptible power systems from being extremely increased in load sharing ratio without having to operate each uninterruptible power system while watching operation of the remaining uninterruptible power systems. The uninterruptible power systems each are constituted by an inverter circuit and an inverter circuit control device. The inverter circuit control device includes a PWM control signal generating means. The PWM control signal generating means generates a PWM control signal so as to gradually reduce an output voltage of the inverter circuit as supply active power increases and until a judging means judges that the supply active power has reached a predetermined level and so as to reduce the output voltage at a reduction ratio increased as compared with before to keep it from falling into an overload condition when the judging means judges that the supply active power has reached the predetermined level.