Electric power conversion systems – Current conversion – With means to connect the input to diverse power sources
Reexamination Certificate
2000-11-15
2001-12-11
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
With means to connect the input to diverse power sources
C307S086000
Reexamination Certificate
active
06330176
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to power transfer apparatus and methods, and more particularly, to apparatus and methods for transferring power to a load from multiple alternative sources.
Computers, computer networks, telecommunications networks, medical equipment and other infrastructure often utilize redundant power sources to ensure that services and data are maintained in the event of loss or degradation of a primary power source, such as an AC utility line. For example, computers and network devices often are powered by uninterruptible power supplies (UPSs) that can maintain an AC supply from an alternative source, such as a battery-powered inverter.
In many applications, multiple sources of AC power may be available. For example, a load may be served from either a “preferred” source, such as an AC utility line, or from a less preferred secondary source, such as a motor-generator set. These multiple AC power sources may be supplied to a transfer switch that selectively connects the multiple AC power sources to a common AC power bus connected to the load. The transfer switch may operate automatically responsive to voltage or other conditions associated with the multiple AC power sources and/or the load. An example of such a transfer switch apparatus is described in U.S. Pat. No. 6,137,706 to Nesbitt et al.
SUMMARY OF THE INVENTION
According to embodiments of the invention, a power transfer apparatus for selectively transferring power to an AC power bus from first and second AC power sources is provided. The power transfer apparatus includes a first switch operative to couple and decouple the first AC power source to and from the AC power bus responsive to a first control signal and a second switch operative to couple and decouple the second AC power source to and from the AC power bus responsive to a second control signal. The apparatus also includes a first switch control circuit that generates the first control signal responsive to a first AC source voltage produced by the first AC power source and to a first inhibit signal and that generates a second inhibit signal responsive to a state of the first switch. The apparatus further includes a second switch control circuit that generates the second control signal responsive to a second AC source voltage produced by the second AC power source and to the second inhibit signal and that generates the first inhibit signal responsive to a state of the second switch.
According to some embodiments of the invention, the first switch control circuit includes a voltage detector circuit operative to generate an enable signal responsive to the first AC source voltage and a driver circuit operative to generate the first control signal responsive to the enable signal and the first inhibit signal. The first switch control circuit further includes an inhibit signal generator circuit operative to generate the second inhibit signal responsive to the first control signal.
For example, the first switch may include a relay including a switching element coupled to the AC power bus and configured to be coupled to the first AC power source and a coil operative to cause the switching element to couple and decouple the AC power source to and from the AC power bus responsive to a current in the coil. The driver circuit may include a relay driver circuit that controls the current in the coil responsive to the enable signal and the first inhibit signal. The inhibit signal generator circuit may include a current detector circuit operative to generate the second inhibit signal responsive to the current in the coil.
In other embodiments of the invention, the first switch control circuit is operative to cause the first switch to couple the first AC power source to the AC power bus when the first AC source voltage meets a first predetermined criterion and the first inhibit signal is deasserted. The first switch control circuit is also operative to cause the first switch to decouple the first AC power source from the AC power bus when the first AC source voltage fails to meet the first predetermined criterion. The first switch control circuit is further operative to cause the first switch to decouple the first AC power source from the AC power bus when the first inhibit signal is asserted. The second switch control circuit may operate in a similar fashion.
In still other embodiments of the invention, the first switch control circuit is further operative to assert the second inhibit signal when the first switch couples the first AC power source to the AC power bus, to maintain assertion of the second inhibit signal for a first predetermined interval following decoupling of the first AC power source from the AC power bus, and to deassert the second inhibit signal following the first predetermined interval. The second switch control circuit is further operative to cause the second switch to decouple the second AC power source from the AC power bus responsive to assertion of the second inhibit signal. The second switch control circuit may similarly generate the first inhibit signal to control operation of the first switch.
In yet other embodiments of the invention, the first switch control circuit is further operative to generate the first control signal responsive to the first AC source voltage, to the first inhibit signal and to a third inhibit signal. In such embodiments, the second switch control is further operative to generate the second control signal responsive to the second AC source voltage, to the second inhibit signal and to a fourth inhibit signal. The power transfer apparatus further includes a communications interface circuit configured to receive external signals on an external signal line and operative to generate the third and fourth inhibit signals responsive thereto. The first switch control circuit may be further operative to generate a first status signal that is indicative of a status of the first switch control circuit, and the second switch control circuit may be further operative to generate a second status signal that is indicative of a status of the second switch control circuit. The communications interface circuit may be configured to receive the first and second status signals and operative to transmit signals on the external signal line responsive to the first and second status signals.
According to other aspects of the invention, an uninterruptible power supply (UPS) system is provided. The UPS system includes an AC power bus, a first switch operative to couple and decouple a first AC power source to and from the AC power bus responsive to a first control signal, and a second switch operative to couple and decouple a second AC power source to and from the AC power bus responsive to a second control signal. The system also includes a first switch control circuit that generates the first control signal responsive to a first AC source voltage produced by the first AC power source and to a first inhibit signal and that generates a second inhibit signal responsive to a state of the first switch, and a second switch control circuit that generates the second control signal responsive to a second AC source voltage produced by the second AC power source and to the second inhibit signal and that generates the first inhibit signal responsive to a state of the second switch. The system further includes a UPS subsystem having a first input coupled to the AC power bus and a second input configured to be coupled to a DC power source. The UPS subsystem is operative to generate an AC output voltage from an AC voltage at the first input or a DC voltage at the second input.
In some embodiments of the invention, the first switch control circuit is operative to assert the second inhibit signal when the first switch couples the first AC power source to the AC power bus, to maintain assertion of the second inhibit signal for a first predetermined interval following decoupling of the first AC power source from the AC power bus, and to deassert the second inhibit signal following the first predetermined interval. In such embodi
Shah Dinesh
Thrap Guy C.
Berhane Adolf Deneke
Myers Bigel & Sibley & Sajovec
Powerware Corporation
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