CN109167379B

CN109167379B - Coordination control method for converter station and direct current circuit breaker of flexible direct current system

Info

Publication number: CN109167379B
Application number: CN201811097942.0A
Authority: CN
Inventors: 王顺亮; 舒稷; 刘天琪
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2018-09-20
Filing date: 2018-09-20
Publication date: 2020-01-07
Anticipated expiration: 2038-09-20
Also published as: CN109167379A

Abstract

The invention discloses a coordination control method of a converter station and a direct current breaker of a flexible direct current system, belonging to the field of relay protection of direct current transmission systems and comprising the following steps: when a fault occurs, cutting off a fault line by using a direct current breaker, and finding out an isolated converter station in an active power control mode; changing the active power reference value of the converter station control system to alpha times of the original rated value; after the voltage of the converter station is recovered to a rated value of a direct current system, changing an active power reference value of a control system into 0; reclosing the direct current breaker at the outlet of the converter station after the necessary insulation recovery time; detecting whether the fault continues to exist: if the fault still exists, reporting the system to be repaired, and if the fault is cleared, restoring the active power reference value of the control system to a rated value before the fault; the method can create conditions for the rapid reclosing of the direct current system, inhibit the impact current when the reclosing is in a fault clearing state, and is favorable for the stable and reliable operation of the direct current system.

Description

Coordination control method for converter station and direct current circuit breaker of flexible direct current system

Technical Field

The invention relates to a reclosing coordination control method for a converter station and a direct current breaker of a flexible direct current system, and belongs to the field of relay protection of direct current transmission systems.

Background

The flexible direct-current transmission system based on the voltage source type current converter develops rapidly in recent decades, and the establishment of the flexible direct-current transmission system is beneficial to gathering clean energy such as wind energy, light energy and the like distributed in various places and promoting the development and utilization of new energy. The flexible direct current power grid stably and reliably operates the protection system without disconnection, the Zhang north flexible direct current power grid which is built at present is the largest flexible direct current power grid in the world, an overhead line is adopted by the flexible direct current system to serve as a power transmission line, and a direct current breaker is utilized to disconnect direct current faults. With the use of overhead transmission lines, a large number of transient faults will occur. In order to improve the transmission stability, reclosing may be required after the disconnection fault.

The protection of the flexible dc power grid in the industry is mainly focused on the location and isolation of faults. And the research on the reclosing process after the fault line is cut off is less. After the faulty line has been cut off, all converter stations will not be blocked in order to achieve a fast reclosing. However, the removal of the faulty line may result in the isolated converter station in the constant active power control mode, and the voltage of the converter station will be out of control, possibly causing damage to the converter station.

Disclosure of Invention

The invention discloses a reclosing coordination control method of a flexible direct current system converter station and a direct current breaker, aiming at preventing the voltage of the direct current system converter station from being out of control before reclosing.

The coordination control method of the flexible direct current system converter station and the direct current circuit breaker. Which comprises the following steps:

A. when a fault occurs, the fault line is cut off by using the direct current circuit breaker immediately, and all converter stations are not locked.

B. After the fault line is cut off, the isolated converter stations in the fixed active power control mode are found out. In the two-end system, one end controls direct current voltage and the other end controls active power, so that a converter station controlling the active power is isolated inevitably after a line is cut; in a radiating multi-terminal dc network, the removal of a faulty line also results in the isolation of the converter station controlling the active power.

C. And changing the active power reference value of the converter station control system to alpha times of the original rated value, wherein the sign of the active power reference value is opposite to that of the original rated value. In order to quickly restore the voltage of the converter station to a rated value and prevent the voltage from violent fluctuation, the alpha value meeting the technical requirement is recommended to be-0.1 to-0.3;

D. after the voltage of the converter station is recovered to a rated value of a direct current system, changing an active power reference value of a control system into 0;

E. reclosing the isolated direct current breaker at the outlet of the converter station after waiting for the necessary insulation recovery time;

F. detecting whether the fault continues to exist: if the fault still exists, the direct current breaker is immediately switched off, the fault is judged to be a permanent fault, and the system maintenance is reported; and if the fault is cleared, immediately reclosing the direct current breaker at the other end of the fault line, restoring the active power reference value of the control system to the rated value before the fault, and restoring the normal operation of the line.

Further, the following criterion can be used to determine whether the fault still exists in step F: 1. detecting whether current flows through a reclosure direct-current breaker or not, if so, determining that the current is a permanent fault, and otherwise, determining that the fault is cleared; 2. detecting whether the voltage of a fault line is successfully established after reclosing, if the voltage is not established, determining that the fault is a permanent fault, otherwise, determining that the fault is cleared;

further, the necessary insulation recovery time in step E is 150- > 300 ms.

The invention achieves the following beneficial effects:

1. the method can effectively prevent the voltage of the direct current system converter station from being out of control after the fault line is cut off;

2. the method can create conditions for the rapid reclosing of the direct current system;

3. the method can inhibit the impact current when the reclosing is in a fault clearing state;

4. the method is beneficial to the stable and reliable operation of the direct current system.

Drawings

FIG. 1 is a flow chart of the operation of the coordinated control method;

FIG. 2 is a topology structure diagram of a two-terminal flexible DC system;

FIG. 3 is a topology structure diagram of a five-terminal flexible DC system;

FIG. 4 is converter station voltage after a fault without a coordinated control method;

FIG. 5 is a converter station voltage after a fault when the coordinated control method is employed;

FIG. 6 is a fault line reclosing current without the coordinated control method;

FIG. 7 is a fault line reclosing current when the coordinated control method is employed;

Detailed Description

The following detailed description is made with reference to the accompanying drawings:

the coordination control method disclosed by the invention mainly aims to ensure that the voltage of the converter station after the flexible direct current system fails is not out of control, and inhibit the impact current of reclosure during transient failure.

Fig. 1 is an operation flowchart of the coordination control method.

In a flexible direct current power grid, a direct current breaker can cut off a fault line immediately after a direct current transmission line fails, and a converter station for controlling active power can be isolated under certain conditions.

As shown in fig. 2, in the two-terminal dc system, one terminal of the converter station 2 controls dc voltage, and one terminal of the converter station 1 controls active power. The converter station 1 is isolated after the line fault has been removed. As in the five-terminal dc system shown in fig. 3, the

converter stations

3 and 4 control the active power and are connected in a radiating manner to the main network. After the line 14 or the line 23 has been cut off, the converter station 4 or the converter station 3 will be isolated from the system.

Since the isolated converter station is controlling the active power, the voltage of the station will lose control after being isolated. Fig. 4 shows the voltage change condition of the converter station after the two-end system transmission line 1.0s in fig. 2 is failed and cut off, and it can be seen that the voltage of the converter station 1 rapidly rises to the maximum value after the failure is cut off. The maximum value is a maximum limit value for the maximum voltage that is set in order to prevent damage to the components of the converter station. The direct reclosing of the faulty line without a coordinated control strategy to suppress the overvoltage of the converter station, an overcurrent is still generated even in the state where the reclosing has been cleared.

Immediately after the converter station controlling the active power is isolated, the reference value of the active power in the control system of the converter station is changed to a times the previous nominal value. In order to allow the converter station voltage to recover quickly and to prevent severe fluctuations in the voltage, a is recommended to meet the technical requirements of-0.1 to-0.3. The active power reference value of the control system is restored to the nominal value after the converter station voltage is restored.

And after the reclosing time preset by the protection system is up, reclosing the direct current breaker at the outlet of the converter station, and detecting the voltage and current signals to judge whether the fault still exists. And if the fault is cleared, reclosing the direct current breaker at the other end of the line, and recovering the normal operation of the direct current system. And if the fault still exists, immediately switching off the reclosure direct current breaker, judging that the fault is a permanent fault, and reporting to system maintenance. The following criteria can be used for judging whether the fault still exists: 1. detecting whether current flows through a reclosure direct-current breaker or not, if so, determining that the current is a permanent fault, and otherwise, determining that the fault is cleared; 2. detecting whether the voltage of a fault line is successfully established after reclosing, if the voltage is not established, determining that the fault is a permanent fault, otherwise, determining that the fault is cleared;

fig. 5 shows a voltage change condition after the two-terminal system converter station shown in fig. 2 has a transient fault at 1.0s and recloses in a fault clearing state at 1.3s after the coordination control method is adopted. It can be seen from the figure that this coordinated control method effectively suppresses overvoltage of the converter station 1. Therefore, the voltage difference of the converter stations at two ends of the fault line before reclosing can be effectively restrained by adopting the coordination control method, and therefore overcurrent after normal reclosing can be reduced.

Fig. 6 shows the fault line reclosing current when the coordinated control method is not used, and fig. 7 shows the fault line reclosing current after the coordinated control method is used. The comparison shows that the coordination control method effectively inhibits the overcurrent after the reclosing is normal.

The above examples are merely illustrative, illustrative and not restrictive of the methods of the present invention. All such modifications and variations are intended to be included herein within the scope of this disclosure.

Claims

1. A coordination control method for a converter station and a DC circuit breaker of a flexible DC system is characterized by comprising the following steps:

A. when a fault occurs, a direct current breaker is used for cutting off a fault line immediately, and all converter stations are not locked;

B. finding out an isolated converter station in an active power control mode;

C. changing the active power reference value of the converter station control system to alpha times of the original rated value, wherein the sign of the active power reference value is opposite to that of the original rated value; alpha is-0.1 to-0.3;

E. reclosing the direct current breaker at the outlet of the converter station after waiting for the necessary insulation recovery time;

F. detecting whether the fault continues to exist: if the fault still exists, the direct current breaker is immediately switched off, the fault is judged to be a permanent fault, and the system maintenance is reported; and if the fault is cleared, immediately reclosing the direct current breaker at the other end of the fault line, and restoring the active power reference value of the control system to the rated value before the fault.

2. The method for coordination control of a converter station and a dc breaker of a flexible dc system according to claim 1, wherein the following criteria can be used for determining whether the fault still exists in step F:

a. detecting whether current flows through a reclosure direct-current breaker or not, if so, determining that the current is a permanent fault, and otherwise, determining that the fault is cleared;

b. and detecting whether the voltage of the fault line is successfully established after reclosing, if the voltage is not established, the fault is regarded as a permanent fault, otherwise, the fault is regarded as cleared.