JPH0332289B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a DC multi-terminal power transmission system with three or more terminals in which a DC switch is inserted in each section of a DC transmission line, in particular, a method for switching and closing DC transmission sections at branch points of the DC transmission line. A DC multi-terminal power transmission system is equipped with a central control device that adjusts the current command value of each terminal, etc., and transmits the minimum necessary information such as load distribution coordination commands to adjacent terminals at high speed. Regarding the control method.

Conventionally, high-voltage DC power transmission has been limited to two-terminal power transmission, but as the development of DC switches that have the ability to cut and cut load current under the full voltage of the DC system has progressed, in the future, this type of DC switching DC multi-terminal power transmission is becoming more practical.

By the way, when putting DC multi-terminal power transmission into practical use by using a DC switch, it is desirable to selectively disconnect only the faulty section when a power transmission line fails, and continue transmitting power to the remaining healthy lines as much as possible. In addition, when changing the system due to a fault, _the I _dp
may require rapid changes.

In general, the converter control method at each terminal is such that only one terminal determines the DC system voltage _Ed , and all remaining terminals are subject to constant current control. In this case, the current at the voltage determining terminal is determined from the sum of the currents at the constant current terminals. In other words, the voltage determining terminal is a "wrinkle absorber" for current, and the actual current I _d is the current setting value I _dp
The current margin ΔI is increased with respect to the current margin ΔI.
Here, to simplify the explanation of the above relationship, a case of two-terminal power transmission will be described as an example. In other words,
If the voltage determining terminal is the power receiving end (INV), the first
As shown in FIG. 1A, ΔI>0, and in the case of the power transmission end (REC), ΔI<0 as shown in FIG. 1B. Therefore, as is clear from Figure 1, if this current margin ΔI is lost, the operating equilibrium point A will be lost and power transmission will become impossible, so it is important to always maintain the current margin ΔI in multi-terminal power transmission. is also a necessary condition. This relationship can be expressed as a general formula as follows. However, in this formula, ΔI>0.

(ΣI _dp ) _REC − (ΣI _dp ) _INV = ΔI …(1) Therefore, when putting a DC multi-terminal power transmission system into practical use, the current setting value I _dp of each terminal must be adjusted, especially when changing the system due to a failure. Always do the above even if you change
It is necessary to consider cooperative control for I _dp so as to satisfy equation (1).

Currently, the control method for DC multi-terminal power transmission systems is to install a central control device, collect the necessary information from each terminal, and then set the current at each terminal to satisfy equation (1) above. There is a centralized control method that issues control commands to each terminal again after determining the value I _dp . However, this control method has the disadvantage that it is highly dependent on the transmission system because information must be exchanged between each terminal and the central control device.

Here, we will consider the case where the above-mentioned centralized control method is adopted in a DC multi-terminal power transmission system as shown in FIG. 2. In the DC multi-terminal power transmission system shown in Figure 2, DC switches S1 to S5 are inserted in each section of the transmission line DL, and when a transmission line fault occurs, only the faulty section is selected and disconnected, and the remaining healthy terminals are 1) It is desirable to continue operation as much as possible by coordinating equations. Also, regarding the failure section, after a short period of time (for example, 1
seconds), turn on the DC switch, and if the fault is cleared, return to previous operation. Although such high-speed reclosing of a DC transmission line is relatively simple, it involves a rapid change in the current setting. If such control is performed using the centralized control method described above, information will be sent back and forth between each terminal and the central control device, and the amount Σ (amount of information) x (transmission distance) will be used as a measure of transmission dependence. Considering this, the dependence on transmission is high. Here, the information includes a current setting value I _dp of each terminal, a direct current, a disconnection open/close signal, and the like.
Therefore, as the dependence on transmission increases, it naturally becomes disadvantageous in terms of system reliability, high speed control and protection, and transmission system cost.

The present invention has been made in view of the above circumstances, and its purpose is to provide a DC multi-terminal power transmission system,
If a DC switch can be used to protect against transmission line failures or converter station failures, it is mainly used for self-end control protection, and at branch points of DC transmission lines, adjustment of the current setting value of each terminal as the DC transmission section opens and closes. A central control device with a central control function is installed to check the coordination of current settings, and when it is necessary to change the current settings, the minimum necessary information is transmitted to adjacent terminals. By doing so, we aim to provide a highly reliable control system for a DC multi-terminal power transmission system with low transmission dependence.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows the configuration of the present invention using a DC three-terminal system as an example. In FIG. 3, 1 and 2 are the power transmitting end, 3 is the power receiving end, and these terminals 1, 2, and 3 are connected to converters 11 and 12, 21 and 22,
31 and 32 are provided, and the converters 11, 2
1 and 31 constitute positive poles, and converters 12, 22, and 32 constitute negative poles, respectively, forming a bipolar system as a whole. Reference numeral 7 denotes a DC transmission line between the power transmission end 1 and the power reception end 3, and a T-branch from the middle of these to the power transmission end 2. This DC transmission line 7 is connected between the positive end converters 11, 21, and 31 of each terminal Positive power transmission line 71, 7 connecting
4, 77 and negative polarity converters 12, 22, 32 at each terminal
Negative power transmission lines 73, 76, 79 connecting between them and both converters 11 and 12, 21 and 22, 31 and 3 at each terminal
Neutral wires 72, 75, 78 connecting each connection of 2
It consists of Further, 13 and 15 are DC switches inserted into the respective lines 71 and 73 on the power transmission end 1 side, and 23 and 25 are the respective lines 77 and 79 on the power transmission end 2 side.
33 and 35 are the DC switches inserted in the power receiving end 3
A DC switch inserted into each side line 74, 76,
16, 18, 26, 28, 36, 38 are the lines 71, 73, 77, 79, 74 at the T junction,
76, respectively. On the other hand, 10, 20, 30 are terminal control devices provided corresponding to the respective terminals 1, 2, 3, and these terminal control devices 10, 20, 30 are connected to the positive and negative electrode converters 1.
For 1 and 12, 21 and 22, and 31 and 32, the current setting value I _dp is increased or decreased and the firing angle is controlled. In addition, 5 is a first central control device, and this first central control device 5 is used for normal converter starting and stopping, changing the load of each terminal during steady operation, and controlling the paralleling or disconnection of terminals to the operating system. Such operation commands with sufficient time are given to the terminal control devices 10, 20, and 30 of each terminal via the transmission lines 51 to 53. Furthermore, 6 is a second central control device provided corresponding to the T-junction of the DC power transmission line 7, and this second central control device 6 is similar to the first central control device, although the details will be described later. Check the coordination of the current setting values of each terminal by inputting the command value of the normal current setting value I _dp from 5 and the open/close information of the DC switch inserted in each line at the T branch point. If it is necessary to change the current setting value due to the opening of the DC switch due to a fault in the line, a command to change the current setting value I _dp is given to the terminal control device of the adjacent terminal.

Note that there are DC switching lines 16, 26, 36, 18, 28, 3 at branch points for each line of the DC transmission line 7.
8 is provided, and a current transformer, etc. for line protection (not shown) is also provided, so it corresponds to the switchyard of the AC system, and therefore, T
It is possible to arrange a second central control unit as described above at the branch point.

FIG. 4 shows, as an example, DC switches 16, 26, 36 inserted into positive transmission lines 71, 74, 77 in the second central control unit 6 provided corresponding to the T-junction of the DC transmission line 7. Among these, the functions for the DC switch 16 are mainly shown, and the configuration of each part corresponding to that in FIG. 3 is shown with the same symbol attached to the corresponding part. In FIG. 4, 91 and 92 are DC switches 13, 1
93 and 94 are time-limiting circuits attached to these current differential _relays 91 and 92; and 96 open the DC switches 13 and 16 when a trip command is applied from the current differential relays 91 and 92;
It is also an opening/closing control circuit that recloses the DC switches 13 and 16 when the operation outputs of the time limit circuits 93 and 94 are input. On the other hand, the second central controller 6 checks the steady state current setting I _dp transmitted from the first central controller 5 via the cyclic digital telemeter 97, the transmission circuit 51, and the cyclic digital telemeter 98. function to send an I _dp command to the terminal control device 10, 20, 30 of each terminal,
DC switch 1 output from current differential relay 92
Due to the trip command of 6, the power transmitting end 1 and the power receiving end 3
The current setting value I _dp of the positive electrode and negative electrode converters 11, 12, 31, 32 for the terminal control devices 10, 30 of
A function to send changes and reverse converter firing angle control commands (β advance), a function to judge the success or failure of reclosing of the DC switch 16, and a function to determine the success or failure of reclosing of the DC switch 16. For the terminal control devices 10 and 30, positive and negative terminal converters 11, 12, 31,
It has a function to send a command to return the current setting value I _dp of 32 and the firing angle control of the inverter to the previous state, and in the case of failure to reclose, it is determined to be a permanent failure and the result is displayed. The data is sent to the first central control unit 5. Such various functions can be easily obtained by processing information using, for example, a microcomputer.

In the figure, 99 to 102 are cyclic digital telemeters for transmitting commands from the second central controller 6 to the power transmitting end 1 and the power receiving end 3.

The functions of the second central control device 6 described above are for the case where it corresponds to the DC switch 16, but also when it corresponds to other DC switches 26, 36, 18, 28, 38, commands to each terminal are provided. It has exactly the same functions as the above, only the content is different.

In addition, in FIG. 4, the main circuit and command system to terminal 2 are omitted because terminal 2 is the power transmission end, and in the case of a failure of power transmission line 71,
This is because power transmission can be continued without changing the I _dp directive.

Next, to describe the operation, first, referring to FIG. 3, a case where, for example, a ground fault occurs in the positive power transmission line 71 will be explained based on FIG. 4. Now, if there is no failure in the DC power transmission line 7, the second central control device 6
The normal I _dp transmitted from the central controller 5 of
Based on the command value, a command to control the operation of the positive and negative bipolar converters 11 and 12, 21 and 22 at the power transmission ends 1 and 2 at current setting values I _dp10 and I _dp20 is transmitted to the terminal control devices 10 and 20 at both ends. The terminal control device 30 sends a command to control the operation of the positive and negative bipolar converters 31 and 32 at the power receiving end 3 at a current setting value I _dp30 .
is given through the transmission line. In such a state, if a ground fault occurs in the positive power transmission line 71, the current differential relays 91 and 92 output a trip command, and the switching control devices 95 and 96 open the DC switches 13 and 16. , At the same time, the time limit circuits 93 and 94 are energized to prepare for re-closing. Further, the trip command for the current differential relay 92 at the T-junction is inputted to the second central control unit 6 as a warning signal for opening the DC switch 16. Then, according to the function displayed within the dotted line frame, the positive polarity converter P of the power transmission end 1 is
For 111, the current minimum value I _dnio and the negative polarity converter P
For 212, set the current setting value I _dp10 × K (for example, K = 1.5) to the cyclic digital telemeter 10.
1, 102 and the transmission line 61 to the terminal control device 10, and the positive polarity converter P of the receiving electrode 3.
131, the current setting value I _dp30 - I _dp10 , and the negative polarity converter P232, the firing angle β advance command is sent to the cyclic digital telemeters 99, 10.
0 and the terminal control device 30 via the transmission line 63
to be transmitted. Therefore, even if the positive power transmission line 71 is separated from the grid and the power transmitted at the power transmission end 1 is lost, the terminal control device 1 is directly connected to the second central control device 6.
0, 30, and decrease the current setting value I _dp of the positive converter 31 for the power receiving end 3 to maintain the relationship of equation (1).
Power transmission can continue on the healthy side except for section 1. In this case, it goes without saying that the negative side can continue power transmission without being affected by a failure in the positive power transmission line, but it is also possible that the power will be overloaded for a short period of time, so this example shows such a case. . That is, in order to transfer the power transmitted from the positive pole of the power transmitting end 1 to the negative pole side in the above-mentioned failure, the current setting value I _dp of the negative pole converter 12 is temporarily increased by 1.5 times, and the current setting value I dp of the negative pole converter 32 of the power receiving end 3 is For this purpose, firing angle β advance control is simultaneously performed. Such short-term (for example, 1 to 2 seconds) overload control is possible for the converter, and the power reduction in the event of a single-pole failure can be reduced.

When a certain period of time (for example, 1 second) has elapsed since the current setting value I _dp was changed or the firing angle β was advanced in accordance with a command from the second central controller, the time limit circuits 93 and 94 are activated. As a result, the switching control circuits 95 and 96 reclose the DC switches 13 and 16. At this time, the second central controller 6 determines whether the re-closing has been successful based on the presence or absence of a trip command for the current differential relay 92, and if it is determined that the re-closing has been successful, the function displayed within the dotted line frame is used to Return to power transmission. In other words, the positive and negative bipolar converter 11 at the power transmission end 1,
12, the current setting value I _dp10 and the receiving end 3
The terminal control devices 10 and 3 at each end issue commands such as resetting the current setting value I _dp30 for the positive polarity converter 31 and resetting the firing angle β advancement for the negative polarity converter 32.
Give to 0. Furthermore, when the DC switches 13 and 16 are opened again due to a permanent failure due to the operation of the current differential relays 91 and 92, and the re-closing fails, the result is transmitted to the cyclic digital telemeter 98, transmission line 51, and cyclic digital telemeter 97. via the first central control unit 5.

Note that the terminal 2 is the power transmission end, and the positive power transmission line 7
In the case of 1 failure, power transmission can be continued without changing the I _dp command, so in this example, especially at the power transmission end 2
No instructions are required.

The above explanation is about changing the current setting value I _dp for each terminal when a ground fault occurs in the positive power transmission line 71. However, when a ground fault occurs in the positive power transmission line 74, the DC switch 33, By opening 36, both the positive electrode converters 11 and 21 of the power transmitting ends 1 and 2 become unloaded, and if this continues, the positive electrode power of the power receiving end 3 becomes zero, and the power as a terminal becomes only the negative electrode power, so that it is halved. Therefore, in such a case, the second central controller 6 selects the negative polarity converter 1 which is a healthy polarity.
A command to increase the current setting value I _dp of 2 and 22 is transmitted. In addition, after confirming failure recovery by re-closing the DC switch 36, the current setting value of the positive polarity converters 11 and 21 is set.
Return I _dp from the minimum value to the previous value, and at the same time set the current setting value I _dp of negative polarity converters 12 and 22 during overload operation.
A command is transmitted to restore the original state. Furthermore, even in the event of a ground fault in the positive power transmission line 77, by inputting the open/close information of the DC switch 26 at the T-junction to the second central controller 6, the current setting value for each terminal can be set.
It is possible to transmit an I _dp change command. In this case, the functions of the second central control device 6 are exactly the same as those described above, but the only difference is the display portion within the dotted line frame.

The above explanations are based on the positive electrode transmission lines 71, 74,
77, but also when a ground fault occurs in any of the negative transmission lines 73, 76, 79, the DC switches 18, 28,
38, the second central controller 6 depending on the closing information
A command to change the current setting value I _dp necessary to maintain the relationship of equation (1) described above may be transmitted to the corresponding terminal via the transmission line. For example, when a ground fault occurs in the negative power transmission line 73, the function display within the dotted line frame in the second central control unit 6 shown in FIG.
Similar to the above, a command can be transmitted to a terminal that requires a change in the current setting value I _dp .

In this way, this method focuses on self-end control protection when DC switches can be used to protect against transmission line failures and converter station failures in DC multi-terminal power transmission systems.
In addition, a second central controller 6 with a central control function that adjusts the current setting value of each terminal as the DC transmission section opens and closes is installed at the branch point of the DC transmission line to coordinate the current setting value. If it is necessary to change the current setting value, the minimum necessary information is transmitted to the adjacent terminal, so the necessary information from each terminal can be stored in one place, unlike the centralized control method. Compared to the case where the commands are collected and determined and commands are sent to each terminal again, the dependence on transmission can be relatively lowered, and the system is superior in terms of reliability, high speed control and protection, and transmission system cost. This makes it compatible with technological trends in DC multi-terminal power transmission, and can be expected to be a method that will be highly effective in the practical application of multi-terminal DC power transmission in the future.

Although an example of a DC multi-terminal power transmission system has been described above to explain the system of the present invention, the system can also be applied to the following system configuration in the same manner as described above.

(1) Although the system configuration shown in Figure 3 is for one bipolar line, it can also be applied to two bipolar lines in the same manner as described above. In other words, in the case of a bipolar two-line circuit, there are two bipolar configurations as the DC main circuit, which are exactly the same as shown in Figure 3, and they operate independently of each other at all times, and only in the event of a failure open the faulty section and connect it to the other bipolar healthy line. This is a parallel method. Therefore,
In the case of such a bipolar two-line circuit, it is possible to continue power transmission without changing the current setting value I _dp of each terminal of the failed pole, but even for such a system configuration, a second central control at the T-junction By installing the device 6, commands can be issued directly to each terminal for opening and closing the parallel switch, resulting in an excellent high-speed operation.

(2) Figure 5 shows an example of a three-terminal always-parallel method for two bipolar lines. That is, FIG. 5 uses the same concept as the two-line AC power transmission line operation, and in the event of a failure, if one line is disconnected, power is transferred to the healthy line, so there is no need to change the current setting value I _dp . Therefore, if there is no problem with the switching capacity of the DC switch, there is no need for a parallel switch, which simplifies the system. In such a case, a second central controller 6 similar to that shown in FIG. If provided, it will be advantageous for high-speed control. Especially T like this
In a branched three-terminal system, the transmission lines to each terminal are concentrated at the branch point, so it is possible to directly know when a transmission line is open or closed in the event of a failure, and the load status of each transmission line can be determined at its own end. Therefore, the current setting value I _dp of each terminal
Adjustment or overload control of healthy poles is also required.
It is relatively easy to command each terminal at high speed.

(3) Figure 6 shows an example of applying the present invention to a four-terminal system without branch transmission lines. In FIG. 6, each of the terminals 1 to 4 consists of a converter 11, 21, 31, 41, respectively, and only the positive electrode is shown for simplicity. Furthermore, since the terminals 2 and 3 each correspond to a T-junction, the second central control devices 6 and 6' are actually provided at the same location as the terminal control devices 20 and 30, respectively, and the first The relationship between the central control device 5 and the second central control device 6 and the relationship between the first central control device 5 and the terminal control devices 10, 20, 30, and 40 are as shown in FIGS. 3 and 4. The same is true.

Therefore, in a DC multi-terminal power transmission system as shown in FIG.
The current setting value of terminals 2, 3, and 4 is calculated by the power supply dropout.
It is necessary to cover this by adjusting I _dp and maintain the relationship expressed by equation (1) above. Therefore, since the second central controller 6 is directly connected to the power receiving end 2, it reduces the current setting value I _dp of its own end to compensate for part of the power supply dropout, and commands the remaining adjustment to the terminals 3 and 4. do. Therefore, the unadjusted portion of the current setting value I _dp is commanded to the second central control unit 6' via the transmission line 67. The second central control device 6' is connected to the sending end 3
Since the current setting value I _dp of the power receiving end 4 is directly connected to the current setting value I dp of the power receiving end 4 , it commands an increase in the current setting value I _dp of the power receiving end 4 or a reduction of the current setting value I dp of the power receiving end 4 via the transmission line 63 and responds to the command.

Next, in the case of a failure in the transmission line 74, the DC switches 33 and 36 are opened and the system is separated into two two-terminal systems, so each combination is as described above.
If necessary, the second central controller 6, 6' issues a command to change the current setting value I _dp of each terminal so that the relationship in equation (1) holds true.

Although FIG. 6 shows the case of single-pole power transmission for simplicity, overload control in the case of bipolar power transmission can be performed in the same manner as described in FIG. 4.

(4) In addition, the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with various modifications without changing the gist thereof.

As described above, according to the present invention, in a DC multi-terminal power transmission system with three or more terminals in which a DC switch is inserted in each section of a DC transmission line, switching of a DC transmission section is performed at a branch point of the DC transmission line. We installed a central control device that adjusts the current setting value of each terminal due to the current setting, and transmitted the minimum necessary information such as current setting value to adjacent terminals at high speed, reducing transmission dependence. It is possible to provide a control method for a DC multi-terminal power transmission system that can be made relatively low in cost and excellent in terms of system reliability, high speed control protection, and transmission system cost.

[Brief explanation of the drawing]

Figure 1 a and b show a two-terminal DC transmission system,
Diagram showing the voltage-current characteristics of the power transmitting end and power receiving end, 2nd
The figure is a schematic diagram for explaining the case where each terminal is controlled by a centralized control method in a DC multi-terminal power transmission system, Figure 3 is a system configuration diagram for explaining an embodiment of the present invention, and Figure 4 is a diagram for explaining the system configuration diagram for explaining an embodiment of the present invention. In the same example,
FIGS. 5 and 6 are block diagrams showing detailed examples of specific examples for explaining the functions of the second central control device, and are for explaining an example in which the present invention is applied to different DC multi-terminal power transmission systems. FIG. 1-4...terminal, 5...first central control device, 6,
6'...Second central control device, 7...DC power transmission line, 7
1 to 79...DC transmission lines in each section, 10, 20, 3
0, 40...Terminal control device, 11, 12, 21, 2
2, 31, 32, 41...Converter, 13-18, 2
3-28, 33-38, 43, 331...DC switch, 51-53, 61-63, 67...Transmission line.

Claims (1)

[Claims] 1. In a DC multi-terminal power transmission system with three or more terminals in which a DC switch is inserted in each section of a DC transmission line, normal converter start-up and stop, load changes at each terminal during steady operation, and changes to the operating system. a first central control device that provides timely information such as parallelization or uncoupling of terminals to a terminal control device provided at each terminal; and a first central control device provided at a branch point of the DC transmission line; A central control function that inputs the normal current setting value given from the central control device and the opening/closing information of each DC transmission section and adjusts the current setting value of each terminal as the DC transmission section opens and closes. If a failure occurs in any of the DC power transmission sections, the second central control device checks the coordination of current setting values in the converters of each terminal and adjusts the current settings. If the value needs to be changed, a command to change the current setting value is given directly to the terminal control device of the adjacent terminal, and if the failure is recovered within the scheduled time, the current setting value is returned to the original value. A control method for a DC multi-terminal power transmission system, characterized in that a command to return is given.