Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device
Reexamination Certificate
2000-04-24
2001-12-18
Kim, Jung Ho (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing three or more electrode solid-state device
C307S087000, C307S127000
Reexamination Certificate
active
06331798
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to high-speed source-transfer switching systems and more particularly to a control arrangement and method that controls the transfer of a load from one source to another in a desirable fashion to minimize transfer delays while also avoiding undesirable current flow between the sources.
2. Description of Related Art
High-speed source-transfer switching systems (HSSTSS) for electrical power distribution systems provide reliable, continuous power delivery to a load by transferring the supply of the load from a first source to a second independent source when undesirable characteristics are sensed in the first source. To achieve high-speed transfer operation, one type of HSSTSS utilizes solid-state switches formed by thyristors, one solid-state switch for each of the sources. These high-speed switches are also known as static transfer switches. To control the transfer operations, the HSSTSS utilizes control arrangements to provide appropriate control signals to control the operation of the thyristors of each solid-state switch via the gate of each thyristor. The control arrangements sample the voltage waveforms of each source to detect when transfer between the sources is necessary, e.g. sensing outages and momentary interruptions as well as voltage sags and swells based on the source supplying the load being above or below preset levels. Under certain circuit conditions, transfer between sources by the control arrangements can introduce undesirable transfer delays and/or permit undesirable current flow between the sources. The arrangement in U.S. Pat. No. 5,808,378 avoids undesirable current flow between sources by delaying transfer until a polarity comparison is satisfied that ensures that the current will flow in the incoming source after transfer will be in opposition to the current flowing in the outgoing source before transfer. Undesirable transfer delays are also minimized by establishing a forced commutation condition before transfer between sources, i.e. transfer is delayed until the incoming source voltage differential and the outgoing current establish an initial change in current flow in opposition to current flow in the switch to be turned off.
SUMMARY OF THE INVENTION
Accordingly, it is a principal object of the present invention to provide a control arrangement and method for high-speed source-transfer switching systems that provides open-transition transfers to avoid the paralleling of sources and undesirable current flow.
It is another object of the present invention to provide a control arrangement and method for high-speed source-transfer switching systems that minimizes undesirable transfer delays by establishing appropriate conditions before performing the transfer between sources.
It is a further object of the present invention to provide a control arrangement for solid-state transfer switches that inhibits the transfer of a load from one source to another if the transfer condition is initiated by a downstream fault.
It is yet another object of the present invention to provide a control arrangement for high-speed source-transfer switching systems that both avoids undesirable current flow between sources via either the establishing of forced commutation conditions or by waiting before issuing control signals to perform the transfer between sources.
These and other objects of the present invention are efficiently achieved by the provision of a control arrangement and method for a power electronic system configured as a high-speed source-transfer switching system (HSSTSS). The HSSTSS supplies an electrical load with alternating current from either a first source or a second source via respective first and second solid-state switches. The HSSTSS also includes a controller that samples the voltage waveforms of each of the first and second sources to detect when transfer between the sources is desirable, e.g. outages or voltage that is either too low or too high. The controller provides appropriate control signals to control operation of the solid-state switches and transfer supply of the load therebetween. The control arrangement avoids undesirable current flow between sources via a comparison of the voltages of the sources and current in the outgoing source, i.e. a polarity comparison to ensure that the current that will flow in the incoming source after transfer will be in opposition to the current flowing in the outgoing source before transfer. Thus, the transfer is delayed until the polarity comparison is satisfied. Additionally, the control arrangement minimizes undesirable transfer delays by establishing appropriate transfer conditions before issuing control signals to perform the transfer between sources, i.e. the transfer to turn on the incoming switch is delayed until after appropriate conditions establish that the outgoing source is off or can be effectively turned off. One form of appropriate conditions include the establishing of forced commutation conditions, preferably established by the incoming source voltage differential and the outgoing current being of the same polarity such that the voltage differential across the solid-state switch that is being turned on is sufficient to establish an initial change in current flow in opposition to the current flow in the solid-state switch to be turned off. The appropriate forced commutation is established by the voltage differential between the two sources being of sufficient magnitude to force the outgoing current to zero. Additionally, under certain conditions, the transfer is accomplished by awaiting the next current zero.
REFERENCES:
patent: 5808378 (1998-09-01), O'Leary
patent: 6023193 (2000-02-01), Ierymenko
patent: 6137191 (2000-10-01), O'Leary et al.
Ennis Michael G.
O'Leary Raymond P.
Ruta Joseph W.
Segredo Anthony F.
Kim Jung Ho
Lapacek James V.
S&C Electric Company
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