Control arrangement and method for high-speed source-transfer switching system

• US 6,331,798 B1
• Filed: 04/24/2000
• Issued: 12/18/2001
• Est. Priority Date: 04/29/1999
• Status: Expired due to Fees

• Current Assignee: S&C Electric Company
• Original Assignee: S&C Electric Company
• Inventors: Segredo, Anthony F., Ennis, Michael G., Ruta, Joseph W., OʼLeary, Raymond P.
• Primary Examiner(s): KIM, JUNG H
• Application Number:
  US09/556,261
• Time in Patent Office: 603 Days
• Field of Search: 307/127, 307/112, 307/18, 307/23, 307/29, 307/43, 307/64, 307/70, 307/80, 307/81, 307/85, 307/86, 307/87, 327/470, 327/472
• US Class Current: 327/470
• CPC Class Codes: H03K 17/0403 in thyristor switches
• CPC Class Codes: H03K 17/136 in thyristor switches
• CPC Class Codes: H03K 17/735 Switching arrangements with several input- or output-terminals, e.g. multiplexers, distributors H03K17/722 takes precedence; logic circuits H03K19/00; code converters H03M5/00, H03M7/00

Abstract

A control arrangement and method is provided for a power electronic system configured as a high-speed source-transfer switching systems (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.

Claims

1. A control arrangement for a source-transfer switching system of the type that includes first and second solid-state switches having respective first and second control inputs, input source connections and output connections, the output connections connected to a common load circuit connection, the control arrangement comprising:

transfer control means for controlling the first and second solid-state switches via the first and second control inputs so as to selectively supply the common load circuit connection via either the first or second solid-state switch, said transfer control means further comprising first means for selectively transferring control between the first and second solid-state switches when the incoming voltage differential across the solid-state switch to be turned on is sufficient to establish an initial current flow that is in opposition to the current flow in the solid-state switch to be turned off, and second means for selectively transferring control whenever it is possible to establish that the switch to be turned off will remain off.

2. The control arrangement of claim 1 wherein said first means comprises means for determining if there is sufficient time for the initial current flow to drive the current in the solid-state switch to be turned off to zero.

3. The control arrangement of claim 2 wherein the input source connections are connected to alternating-current sources.

4. The control arrangement of claim 2 wherein said first means further comprises means responsive to the inductance defined by the source.

5. The control arrangement of claim 1 wherein said first means further comprises third means responsive to a first transfer input for transferring control based on said incoming voltage differential.

6. The control arrangement of claim 1 wherein said second means comprises third means for measuring the voltage across the switch to be turned off.

7. The control arrangement of claim 1 wherein said second means comprises third means for predicting the occurrence of a current zero.

8. A method for controlling a source-transfer switching system of the type that includes first and second solid-state switches having respective first and second control inputs, input source connections and output connections, the output connections being connected to a common load circuit connection, the method comprising the steps of:

controlling the first and second solid-state switches via the first and second control inputs so as to selectively supply the common load circuit connection via either the first or second solid-state switch;

detecting predetermined conditions so as to make transfer between the first and second solid-state switches desirable;

transferring control between the first and second solid-state switches in response to a first category of predetermined conditions detected in said detecting step based on the incoming voltage differential across the solid-state switch to be turned on being sufficient to establish an initial current flow that is in opposition to the current flow in the solid-state switch to be turned off; and

transferring control between the first and second solid-state switches in response to a second category of predetermined conditions detected in said detecting step based on the input source connection to the solid-state switch to be turned off.

9. A method for controlling the transition from supplying a load from one switch to another switch, each of the switches including input and output connections, each input connected to a respective source connection, the method comprising the step of determining when appropriate conditions will be satisfied to perform the transfer as an open transition without paralleling the sources supplying the switches, said determining step further comprising the step of establishing when forced commutation conditions are met or establishing when the switch to be turned off will remain off when the switch to be turned on is turned on.