Redundant multiphase power supplies for common load device

Details Redundant multiphase power supplies for common load device Redundant multiphase power supplies for common load device

2000-11-09

2001-11-13

Berhane, Adolf Doneke (Department: 2838)

Electric power conversion systems

Current conversion

Having plural converters for single conversion

C363S070000

Reexamination Certificate

active

06317346

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method and apparatus for improving reliability in a multiphase power supply arrangement. More specifically, the invention relates to SCR-controlled, multi-phase power sources that supply a common load in a manner that reduces or eliminates a “single point of failure.”
BACKGROUND OF THE INVENTION
Faults in an AC power supply may exist as a phase loss, an under-voltage condition, an over-voltage condition, or other condition. Such faults may result from a variety of reasons including breaker trips, fuse loss, inverter faults, shorted turns in a transformer, and ground faults. Frequency or phase errors may also occur when the AC power frequency falls outside of specified ranges. Power supply faults have deleterious impact on electrical equipment, and in many applications cannot be tolerated.
Achieving reliability by using multiple power sources to supply a single-phase or DC load device is relatively simple. Multiple sources, for example, can be connected in parallel with the load device so that a failure of one source will not shut down the load. For single-phase AC supplies, this works fine, provided the phases of the respective sources are, maintained in substantial synchronism. Other precautions, however, must be taken if the difference between the respective phases become significant. Connecting a single-phase AC load device to multiple single-phase AC sources does not require precise phase alignment because most load devices can tolerate minor phase differences. Using two or more multiphase AC sources to power a multiphase load, however, presents certain challenges. While it is possible to connect multiphase sources in parallel, a failure of any phase usually results in a failure in another phase or in the other source. Furthermore, prior systems cannot handle multiphase AC power sources in parallel to supply high performance loads where high reliability is essential.
SUMMARY OF THE INVENTION
To address the above and other problems, an embodiment of the present invention comprises respective silicon controlled rectifiers (SCRs) connected in parallel to respective phases of at least two multiphase AC power sources for supplying power to a common load. A first group of SCRs connects a first power source to the load and a second group of SCRs connects a second power source to the load. During normal operation, the SCRs are switched at or near zero crossings of the respective phases in a bridge rectifier fashion to allow source current from each AC power source to supply the load. Upon detection of a fault, a controller issues gating signals to selected SCR(s) to effectively remove the “defective” phase from the load, thereby permitting the corresponding phase of the other source to seamlessly continue powering the common load without interruption. The controller may optionally issue an alarm upon detection of a fault.
According to another embodiment of the invention, the topology of a paralleling SCR circuit comprises an input for a first multi-phase power source, a first 3-pole in-line input disconnect device, a first SCR group and a second in-line output disconnect device. A first multiphase power source connects to a first 3-pole in-line disconnect device which, in turn, connects a first group of silicon controlled rectifiers to second group of in-line output disconnect devices. The paralleling circuit also includes an input for second multiphase power source, a similarly connected third disconnect devices, and a similarly connected fourth disconnect devices. This scenario may be repeated for additional multiphase power sources. The topological structure of the paralleling circuit still further includes a paralleling output that combines the outputs of the first an second plurality of silicon controlled rectifiers so that they may power a common source.
Another embodiment of the invention includes a method of supplying continuous uninterruptible power to a common load using a power paralleling circuit that effectively combines separate and independent power sources. SCRs of first and second groups are connected to at least first power and second power sources, respectively. The method comprises providing respective gating signals to the first group of SCRs at or near zero crossing points of each phase of the multi-phase power source, and providing respective gating signals to the second group of SCRs at or near zero crossing points of the multi-phase power source, thereby alternately firing the respective SCRs at appropriate times during their AC cycles. The method additionally includes monitoring fault conditions in the respective phases of the power sources and controlling the SCR gating signals to isolate a phase or source from the load upon detection of a fault, thereby seamlessly supplying the load with uninterrupted power. The method optionally includes issuing an alarm upon detection of a fault.
Other objects, features, and advantages of the present invention will become apparent when considered in conjunction with the accompanying drawings. The invention, though, is pointed out with particularity by the appended claims.


REFERENCES:
patent: 5319536 (1994-06-01), Malik
patent: 5796601 (1998-08-01), Yamamoto
patent: 6081437 (2000-06-01), Chen et al.

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