Electrical transmission or interconnection systems – Plural supply circuits or sources – Substitute or emergency source
Reexamination Certificate
1999-06-14
2001-01-16
Ballato, Josie (Department: 2836)
Electrical transmission or interconnection systems
Plural supply circuits or sources
Substitute or emergency source
C363S034000
Reexamination Certificate
active
06175166
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of power distribution, and more particularly to systems for mitigating voltage disturbances and interruptions.
BACKGROUND OF THE INVENTION
Power outages and voltage disturbances can cause extensive damage to industrial processes and data loss in information systems. Momentary disturbances (e.g., disturbances with a duration of less than 5 seconds) account for the large majority of interruptions or voltage sags experienced on utility feeders.
Solutions for providing sag or interruption mitigation on utility feeders have been proposed. For example, it has been proposed to protect an entire utility feeder with a system in which an inverter and power electronics continuously supply power to the critical load to be protected. These solutions entail high costs, and several of them only provide sag mitigation as opposed to sag and interruption mitigation. They are therefore unable to prevent critical load outages in which the utility feeder opens, or in which sags occur coincident with a large phase angle offset as is normally the case for voltage disturbances resulting from transmission line faults.
Accordingly, a goal of the present invention is to provide a cost-effective solution for reliably mitigating voltage disturbances and interruptions.
SUMMARY OF THE INVENTION
The present invention provides a low cost solution that takes advantage of the brevity of the phenomenon (i.e., voltage interruption, outage, sag or disturbance) it is required to mitigate. The invention makes use of several unique properties of power semiconductor devices working together to accomplish the mitigation task in an optimum and cost effective way. The invention also reduces the continuous power loss inherent in systems that continuously process the full load power via power conversion/inversion processes. The inventive approach saves energy as compared to other approaches by not continuously processing the full load power but instead inserting full load power conversion in the system only during the brief voltage disturbance interval. The power processing inverters are run continuously but in a no load, low loss condition, thus improving the reliability of the entire system.
A system in accordance with the present invention mitigates disturbances and interruptions in unregulated, disturbance-prone electrical input power for energizing a load coupled to an output terminal. The system comprises at least one back-up energy module comprising a DC energy source coupled to a charging circuit and a DC-AC inverter. The system also comprises a first electronically controllable switch for conducting current from an input terminal to the load, a second electronically controllable switch for conducting current from the back-up energy module to the load, and a system control module. The control module controls the operation of the first and second switches and the back-up energy module so that current may be delivered from the input terminal to the load during normal operations and from the back-up energy module to the load during an occurrence of an interruption or disturbance of a short duration in the unregulated input power.
Other features of the present invention are described below.
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ABB Power T&D Company Inc.
Ballato Josie
DeBeradinis Robert L.
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
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