Device and a method for voltage control in an electric transmission network
View Patent ↗A device for control of a compensator connected to a polyphase electric transmission network for reactive electric power in dependence on a voltage sensed in the transmission network. A voltage controller, in dependence on the difference of a reference value for the voltage and its sensed value, forms a reference value for a reactive power flow through the compensator. A transformation element represents the sensed voltage as a voltage vector in a rotating two-phase system of coordinates and forms a compensation signal in dependence on a sensed change of the angular position of the voltage vector in the two-phase system of coordinates. A summation element forms the reference value for reactive power flow through the compensator in dependence on the compensation signal.
1. A device for control of a compensator, connected to a polyphase electric transmission network, for reactive electric power in dependence on a voltage sensed in the transmission network, the device having a voltage controller which, in dependence on the difference of a reference value for said voltage and its sensed value, forms a reference value for a reactive power flow through the compensator, wherein the device comprises transformation means, which represent the sensed voltage as a voltage vector in a rotating two-phase system of coordinates and forms a compensation signal 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 for forming the reference value for reactive power flow through the compensator in dependence on the compensation signal.
2. The device according to claim 1 , wherein said transformation means comprise phase-correcting means which dynamically influence the angular position of the voltage vector relative to said system of coordinates and amplitude-correcting means for influencing the amplitude of the compensation signal.
3. The device according to claim 2 , wherein said phase-correcting means comprise a phase-locked circuit and a transforming member, whereby the transforming member forms the voltage vector 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. The device according to claim 3 , wherein said phase-correcting means form the voltage vector 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 of the voltage vector which coincides with a second axis in the system of coordinates, perpendicular to the first one.
5. The device according to claim 1 , wherein the compensator comprises a thyristor-controlled reactor and wherein the reference value 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, connected to a polyphase electric transmission network, for reactive electric power in dependence on a voltage sensed in the transmission network, whereby a voltage controller is supplied with a reference value for said voltage and, in dependence on the difference of the reference value and the sensed value of the voltage, forms a reference value for a reactive power flow through the compensator, wherein
a voltage vector is formed which represents the sensed voltage in a rotating two-phase system of coordinates,
a compensation signal is formed in dependence on a sensed change of the angular position of the voltage vector in the two-phase system of coordinates, and
the reference value for reactive power flow through the compensator is formed in dependence on the compensation signal.
7. The method according to claim 6 , wherein
the angular position of the voltage vector relative to said system of coordinates is dynamically influenced by means of phase-correcting means, and
the amplitude of the compensation signal is influenced by means of amplitude-correcting means.
8. A The method according to claim 7 , wherein
the voltage vector in said rotating two-phase system of coordinates is formed in dependence on a transforming means and a phase-locked circuit and on the voltage sensed in the transmission network.
9. The method according to claim 8 , wherein
the voltage vector 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
the compensation signal is formed in dependence on a component of the voltage vector which coincides with a second axis in the system of coordinates, perpendicular to the first one.
10. The method according to claim 6 , wherein the compensator comprises a thyristor-controlled reactor, and wherein the reference value for the susceptance of the thyristor-controlled reactor is formed in dependence on said reference value for the reactive power flow through the compensator.