Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Patent
1997-08-26
1999-06-01
Wong, Peter S.
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
363 89, 363 56, 307 86, 307 87, 307 45, H02M 3335, H02H 7122, H02J 100
Patent
active
059093609
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to uninterruptible power supplies and in particular, though not necessarily, to uninterruptible power supplies for computers.
Uninterruptible power supplies are required for many applications where the loss of mains power has serious implications. For example, where computer systems are used to transfer large amounts of data over a network it is essential that a backup power supply is available in the event that mains power is lost in order to prevent the loss of valuable information.
Early uninterruptible power supplies were generally placed between a standard AC utility outlet and the AC input socket of an electrically powered device. Such power supplies typically included an AC to DC converter for converting received AC power into DC power to charge a battery and an DC to AC converter for reconverting the DC power back into AC power for supply to the AC input socket of the electrical device. This resulted in considerable duplication of circuitry as an AC to DC converter was also included in the integral power supply of the electrical device.
GB 2,120,474A describes a standby power supply system intended to be integrated into an internal power supply of an electrical device and which is intended to reduce the above noted duplication of circuitry which arose with previous uninterruptible power supplies. The system includes an AC to DC converter and an inverter circuit which is used to couple chopped DC power through a transformer into a set of secondary windings arranged to provide regulated DC output voltages for internal use by the electrical device. A battery is coupled via a tertiary winding of the transformer to the secondary windings and is arranged to provide electrical power to the secondary windings when the input AC voltage fails. However, the additional winding required to couple the battery to the secondary windings results in increased manufacturing costs and an increase in the overall size of the system.
EPO,243,061 describes a power supply system similar to that of GB2,120,474A where the battery is coupled to the tertiary winding via a diode. The circuit is arranged so that, under normal operating conditions the diode is reverse biased, isolating the battery from the tertiary winding. However, when the AC voltage drops, resulting in a corresponding drop in voltage across the tertiary winding, the diode becomes forward biased providing power from the battery to the tertiary winding.
Document WO 91/07803 describes an uninterruptible power supply in which the battery is coupled directly to one of the secondary windings of the transformer to couple power directly to the corresponding output. Power is also reflected through the transformer, from that secondary winding, to the other secondary windings to provide DC power to the other DC outputs. Whilst this power supply of WO 91/07803 results in a considerable simplification in the power supply circuitry, and to a reduction in the size of the supply, there remains a need to provide a simpler and cheaper power supply system.
It is an object of the present invention to overcome or at least mitigate certain of the disadvantages of known uninterruptible power supplies.
According to the present invention there is provided an uninterruptible power supply comprising:
an input for receiving AC utility power;
an AC to DC converter coupled to the AC input and arranged to generate DC power at an output of the converter;
a transformer;
an inverter coupled between the AC to DC converter and a primary winding of the transformer and arranged to supply a chopped DC voltage to the primary winding, so that a corresponding chopped DC voltage, having an amplitude V.sub.s, is generated across a secondary winding of the transformer coupled to said output;
an auxiliary power supply comprising energy storage means operable at a voltage V.sub.b ; and
diode isolation means coupled between a supply terminal of the energy storage means and said secondary winding, wherein the diode isolation means is arranged to be in a non-conductive state when
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Lavin James Vincent
Stanley Alastair
Magnum Power Solutions Limited
Patel Rajnikant B.
Roth Gregory L.
Wong Peter S.
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