Uninterruptible power supply with AC and DC power inputs

Details Uninterruptible power supply with AC and DC power inputs Uninterruptible power supply with AC and DC power inputs

1996-12-30

1998-07-14

Wong, Peter S.

Electric power conversion systems

Current conversion

Including an a.c.-d.c.-a.c. converter

363 17, 307 64, 307 66, H02M 545, H02M 3335, H02J 700

Patent

active

057814228

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

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 computer installations such as network file servers, telecommunications equipment or other applications where a sudden loss of power would create an unacceptable and costly occurrence. Such occurrences include the loss of data during a data transfer or the shutdown of an entire business as a result of the loss of a computer.
Presently available uninterruptible power supplies are placed between the AC utility socket and the AC utility input for the computer or other electrical device which must receive continuous electrical power. The power supply includes a battery providing electrical energy in the event of a power failure, an AC to DC converter and an inverter converting electrical energy back from DC to AC. The electrical device's internal power supply then receives the AC output from the uninterruptible power supply and in turn converts this to the various regulated and unregulated voltages required for the device.
The AC to DC converter of the conventional uninterruptible power supply converts the AC power to DC power at approximately the battery voltage with a trickle charge being available to ensure that the battery, generally a lead acid battery, remains charged at all times. The inverter then reconverts the DC energy From the DC battery voltage back to an AC power supply approximating standard utility AC power. In the event of a power failure, the internal DC voltage from the AC to DC converter drops below the battery output voltage. This is sensed and causes the battery to begin supplying the DC power to the inverter in place of the DC to AC converter. The battery continues to supply power until AC utility power is restored or the battery is discharged.
While such arrangements work satisfactorily, they are relatively expensive and inefficient. They must work at relatively high power levels, typically two hundred to three hundred watts, and are typically only 75 to 85 percent efficient. Consequently, substantial amounts of power must be dissipated within the uninterruptible power supply and large and expensive components are required.
In addition, the AC to DC converter, the inverter, and corresponding control circuits must be duplicated within the conventional power supply of the device being powered and the customer must therefore in effect purchase two power supplies; a standard device power supply and an uninterruptible power supply.
For the above reasons, uninterruptible power supplies are used only in relatively expensive devices where device size is not a consideration.
There is disclosed in WO 91/07803 an uninterruptible power supply which incorporates the functions of a standard, internal, power supply and which substantially eliminates the duplication of components which occurs with standard uninterruptible power supplies. This power supply is only arranged, however, to receive AC input power and makes no provision for receiving DC input power.


SUMMARY OF THE INVENTION

It is an object of the present invention to overcome or at least mitigate the disadvantages of known uninterruptible power supplies.
It is a second object of the present invention to provide an uninterruptible power supply which is cheap, compact and energy efficient and which can receive DC input power.
It is a third object of the present invention to provide an uninterruptible power supply which incorporates the functions of a standard internal power supply but which substantially avoids the duplication of major components.
According to a first aspect of the present invention there is provided an uninterruptible power supply comprising first and second inputs for receiving AC and DC power respectively, first and second switching circuits coupled to corresponding ones of the inputs, an additional auxiliary power supply coupled to said first and second inputs, and selection means for se

REFERENCES:
patent: 4564767 (1986-01-01), Charych
patent: 4672228 (1987-06-01), Swoboda
patent: 4719550 (1988-01-01), Powell et al.
patent: 5289045 (1994-02-01), Lavin et al.
patent: 5319249 (1994-06-01), Frank et al.

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