Device and a method for voltage control in an electric transmission network

• US 20040052015A1
• Filed: 10/07/2003
• Published: 03/18/2004
• Est. Priority Date: 11/30/2000
• Status: Active Grant

• Current Assignee: ABB Power Grids Switzerland AG (Hitachi, Ltd.)
• Original Assignee: ABB AB (ABB Limited)
• Inventors: Thordvaldsson, Bjorn, Angquist, Lennart
• Granted Patent: US 6,984,962 B2
• Time in Patent Office: Days
• US Class Current: 361/22
• CPC Class Codes: H02J 3/1835 with stepless control
• CPC Class Codes: Y02E 40/10 Flexible AC transmission systems [FACTS]
• CPC Class Codes: Y02E 40/30 Reactive power compensation

Abstract

A device for control of a compensator (SVC), connected to a polyphase electric transmission network (NW), for reactive electric power in dependence on a voltage (V^abc) sensed in the transmission network has a voltage controller (7, 8) which, in dependence on the difference of a reference value (V, ref) for said voltage and its sensed value, forms a reference value (QCR) for a reactive power flow (QC) through the compensator. The device comprises transformation means (3, 4, 11, 12, 13) which represents the sensed voltage as a voltage vector (V^dq) in a rotating two-phase system of coordinates and form a compensation signal (Sc) in dependence on a sensed change of the angular position of the voltage vector in the two-phase system of coordinates. The device further comprises summation means (9) for forming the reference value for reactive power flow through the compensator in dependence on the compensation signal.

Claims

1. A device for control of a compensator (SVC), connected to a polyphase electric transmission network (NW), for reactive electric power in dependence on a voltage ({overscore (V)}^abc) sensed in the transmission network, the device having a voltage controller (7, 8) which, in dependence on the difference of a reference value (V,ref) for said voltage and its sensed value, forms a reference value (QCR) for a reactive power flow (QC) through the compensator, characterized in that the device comprises transformation means (3, 4, 11, 12, 13), which represent the sensed voltage as a voltage vector ({overscore (V)}^dq) in a rotating two-phase system of coordinates and forms a compensation signal (Sc) in dependence on a sensed change of the angular position of the voltage vector in the two-phase system of coordinates, and further comprises summation means (9) for forming the reference value for reactive power flow through the compensator in dependence on the compensation signal.

2. A device according to claim 1, characterized in that said transformation means comprise phase-correcting means (12, 13) which dynamically influence the angular position of the voltage vector relative to said system of coordinates and amplitude-correcting means (11) for influencing the amplitude of the compensation signal.

3. A device according to claim 2, characterized in that said phase-correcting means comprise a phase-locked circuit (13) and a transforming member (12), whereby the transforming member forms the voltage vector ({overscore (V)}^dq) in said rotating two-phase system of coordinates in dependence on the phase-locked circuit and on the voltage sensed in the transmission network.

4. A device according to claim 3, characterized in that said phase-correcting means form the voltage vector ({overscore (V)}^dq) in said rotating two-phase system of coordinates such that, under stationary conditions, the voltage vector coincides with a first axis in the system of coordinates and that said transformation means form the compensation signal in dependence on a component (V_d) of the voltage vector which coincides with a second axis in the system of coordinates, perpendicular to the first one.

5. A device according to any of the preceding claims, characterized in that the compensator comprises a thyristor-controlled reactor (1) and that the reference value (B,ref) for the susceptance of the thyristor-controlled reactor is formed in dependence on said reference value of the reactive power flow through the compensator.

6. A method for control of a compensator (SVC), connected to a polyphase electric transmission network (NW), for reactive electric power in dependence on a voltage ({overscore (V)}^abc) sensed in the transmission network, whereby a voltage controller (7, 8) is supplied with a reference value (V,ref) for said voltage and, in dependence on the difference of the reference value and the sensed value of the voltage, forms a reference value (QCR) for a reactive power flow (QC) through the compensator, characterized in that

a voltage vector ({overscore (V)}^dq) is formed which represents the sensed voltage in a rotating two-phase system of coordinates,

a compensation signal (Sc) is formed in dependence on a sensed change of the angular position of the voltage vector in the two-phase system of coordinates, and that

the reference value for reactive power flow through the compensator is formed in dependence on the compensation signal.

7. A method according to claim 6, characterized in that

the angular position of the voltage vector relative to said system of coordinates is dynamically influenced by means of phase-correcting means (12, 13), and that

the amplitude of the compensation signal is influenced by means of amplitude-correcting means (11).

8. A method according to claim 7, characterized in that the voltage vector ({overscore (V)}^dq) in said rotating two-phase system of coordinates is formed in dependence on a transforming means (12) and a phase-locked circuit (13) and on the voltage sensed in the transmission network.

9. A method according to claim 8, characterized in that

the voltage vector ({overscore (V)}^dq) is formed in said rotating two-phase system of coordinates such that, under stationary conditions, the voltage vector coincides with a first axis in the system of coordinates, and that

the compensation signal is formed in dependence on a component (V_d) of the voltage vector which coincides with a second axis in the system of coordinates, perpendicular to the first one.

10. A method according to any of claims 6-9, wherein the compensator comprises a thyristor-controlled reactor (1), characterized in that the reference value (B,ref) for the susceptance of the thyristor-controlled reactor is formed in dependence on said reference value for the reactive power flow through the compensator.