Reactive-power control apparatus and reactive-power compensator using the same

• US 20080157728A1
• Filed: 06/25/2007
• Published: 07/03/2008
• Est. Priority Date: 08/04/2006
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: Kono, Yoshiyuki, Takeda, Masatoshi, Temma, Koji, Toki, Naohiro
• Granted Patent: US 7,688,043 B2
• Time in Patent Office: Days
• US Class Current: 323/210
• CPC Class Codes: H02J 3/1864 wherein the stepless control of reactive power is obtained by at least one reactive element connected in series with a semiconductor switch
• CPC Class Codes: Y02E 40/10 Flexible AC transmission systems [FACTS]

Abstract

In a conventional reactive-power compensator using a static reactive-power compensator (SVC), there are many cases in which the SVC is operating in a state in which it generates an amount of reactive power equivalent to a large part of its capacity. When an unforeseen large voltage fluctuation occurs in this state, the SVC can not sufficiently generate the amount of reactive power required to mitigate the voltage fluctuation. In some cases, such a voltage fluctuation can not be brought under control. To address this situation, a reactive-power compensator utilizes a reactive-power control apparatus that includes a comparison voltage generator for generating, for a control target voltage and to mitigate voltage fluctuation, a comparison voltage restricted within predetermined limits and obeying a predetermined time-lag characteristic. A differential voltage generator generates a differential voltage that is the difference between the comparison voltage and the control target voltage. A reactive-power control device controls, in response to the differential voltage, control-target reactive power generated by an SVC, at a time-related characteristic faster than the time-lag characteristic for the comparison voltage.

Claims

1. A reactive-power control apparatus, comprising:

a comparison voltage generator for generating, for a control target voltage as a target, to mitigate voltage fluctuation, a comparison voltage restricted within predetermined limits and obeying a predetermined time-lag characteristic;

a differential voltage generator for generating a differential voltage that is the difference between the comparison voltage and the control target voltage; and

a reactive-power control device for controlling, in response to the differential voltage, control-target reactive power generated by a static reactive-power compensator, at a time-related characteristic faster than the time-lag characteristic for the comparison voltage.

2. The reactive-power control apparatus according to claim 1, further comprising:

a first reactive-power-compensation device controller for controlling operation of a reactive power compensation device as a control target, in situations in which the reactive-power control device is not operating and in which reactive power generated by the static reactive-power compensator has deviated from the predetermined limits, so as to bring the reactive power generated by the static reactive-power compensator within the predetermined limits.

3. The reactive-power control apparatus according to claim 2, further comprising:

a second reactive-power-compensation device controller for controlling operation of a reactive power compensation device as a control target, in situations in which the reactive-power control device and the first reactive-power-compensation device controller are not operating and in which a voltage at a predetermined voltage-observation point has deviated from the predetermined limits, so as to bring the voltage within the predetermined limits.

4. The reactive-power control apparatus according to claim 1, further comprising:

a static-VAr-compensator-generated reactive-power coordinating unit for setting reactive power generated by the static reactive-power compensator to a predetermined value, in situations in which the differential voltage is smaller than a predetermined value and in which the control target voltage is within the predetermined limits.

5. A reactive-power compensator, comprising:

a static reactive-power compensator, connected to a busbar, for generating reactive power in response to voltage fluctuation at the busbar;

a comparison voltage generator for generating, for the voltage at the busbar as a control target voltage, a comparison voltage restricted within predetermined limits and obeying a predetermined time-lag characteristic;

a differential voltage generator for generating a differential voltage that is the difference between the comparison voltage and the control target voltage; and

a reactive-power control device for controlling, in response to the differential voltage, reactive power generated by said static reactive-power compensator, at a time-related characteristic faster than the time-lag characteristic for the comparison voltage.

6. The reactive-power compensator according to claim 5, further comprising:

a first reactive-power-compensation device controller for controlling operation of a reactive power compensation device as a control target, in situations in which the reactive-power control device is not operating and in which reactive power generated by the static reactive-power compensator has deviated from the predetermined limits, so as to bring the reactive power generated by the static reactive-power compensator within the predetermined limits.

7. The reactive-power compensator according to claim 6, further comprising:

a second reactive-power-compensation device controller for controlling operation of a reactive power compensation device as a control target, in situations in which the reactive-power control device and the first reactive-power-compensation device controller are not operating and in which a voltage at a predetermined voltage-observation point has deviated from the predetermined limits, so as to bring the voltage within the predetermined limits.

8. The reactive-power compensator according to claim 5, further comprising:

a static-VAr-compensator-generated reactive-power coordinating unit for setting reactive power generated by the static reactive-power compensator to a predetermined value, in situations in which the differential voltage is smaller than a predetermined value and in which the control target voltage is within the predetermined limits.