JPS5895935A - Control system for dc multiterminal transmission facility - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (a) Description of the Technical Field The present invention provides a DC multi-terminal power transmission system consisting of a plurality of converters, even if any converter is disconnected from the system due to an accident or the like. This invention relates to a control device for DC multi-terminal power transmission equipment that maintains a stable system.

(b) Description of Prior Art In order to further utilize the advantages of conventional two-terminal DC power transmission, there is a strong desire to develop technology for DC multi-terminal power transmission.

Figure @1 is a DC 4-terminal power transmission system diagram to which the present invention can be applied, where 1 to 4 are AC systems, 5 to 8 are conversion transformers, and 9 are
, 10 is a forward transformation device, 11° 11 is an inverse transformation device, JJ~
2a is a DC interrupter.

Compared to DC two-terminal power transmission, DC multi-terminal power transmission requires more advanced cooperative control between each conversion device. For this reason, in DC multi-terminal power transmission, mutual information between each converter is illustrated and collected at the central device via a dangerous transmission system and monitored, and based on this information, optimal operation commands are issued to each converter. It is necessary to increase the value by 4. On the other hand, in an emergency, it is necessary to use a control system that allows stable operating points for the DC voltage and current of each manipulating device without interfering with the central control unit and transmission system. Especially as DC interrupters were developed,
There is an increasing need for a control system that allows stable operation to continue even if a faulty location is disconnected at high speed.

Now, as a DC multi-terminal control method, the nutrient Ws43-
No. 8641 newsletter, No. 41 Kai111i51-66455 are known as Arashi. The one disclosed in Japanese Patent Publication No. 43-8641 expands the conventional two-terminal power transmission control method to multi-terminal power transmission, and its characteristic diagram is shown in Figure 2. , the forward converter 10 in FIG. Set the settings to summer rl, Idpr2 and actual R respectively.
ICJ vRECJ current value Idrl, !
art or I) JV i.

The current setting value of the constant current control circuit of INVJ is 14pH.

The current values that actually flow through Idpi2 and KINVi and INVIIIC are abbreviated as Idil and IdH. Now,
In FIG. 2, the operating point of each converter in the steady state is P, , P wealth, pm, p, i.e., RffiC
Determine J kami pressure, and other (D RECJ, INV J
, INV J performs constant current control. In order for this control method to operate stably, the following conditions must be satisfied.

(■srl+Idprri-(summerit+IjpH)-j
I≧0...■(l1rl + Idr2) x (Id
il +I! 12) -・=■ In other words, the sum of the current settings of the forward converter must be greater than the sum of the current settings of the inverse converter.In other words, the sum of the current settings of the forward converter must be Subtract the sum of the current setting values of the converter to obtain the margin value (hereinafter referred to as the current margin. In formula ■)! ) must be positive or zero.

Now, Hiro, this method has the following drawbacks. For example, if REC1, the voltage determining terminal, stops due to an accident, the stability condition equation 0 will no longer hold, and all conversion circuits will stop. It is a must. In other words,
An accident in the forward converter that results in a system shutdown.

Next, the characteristic diagram of JP-A No. 118g$1-66455 is shown in Figure 3 of Tuna.

In this method, each converter is equipped with constant voltage control in addition to constant current control, and in addition to the concept of current margin described above, the concept of voltage margin is introduced. If you decide on a terminal, the voltage setting value for constant voltage control of that converter will be smaller than the voltage setting values of all other converters by a predetermined voltage margin (hereinafter abbreviated as 4V). In addition, regarding the current setting value, the formula (2) is made to hold true.

Now, as before, if we assume that RECJ has an accident and is shut down, the system will come to a halt unless some sort of action is taken with this system. This is because the voltage determining terminal no longer exists. Also, as a matter of course, the formula (2) no longer holds true. Therefore, JP-A-51-66
Publication No. 455 proposes that a central control device be provided, and the information of all the converters can be collected and processed in this central control device. That is, in the previous example, if the RICj stops due to an accident, the information will be transmitted to the central control device, and the central control device will use that information to send the remaining conversion devices,
It is proposed to prevent the system from stopping by giving commands for new voltage and current settings.

It is true that this method seems to have no problems in theory, but when manufacturing actual equipment using this method,
There are various problems.

The first problem is that transmission lines that can transmit large amounts of information at very high speeds are essential. Such a transmission line is not desirable for our future FF11 due to problems such as poor location. In addition, in other countries, the highly reliable micro@wires currently used in Japan are not used, and low-reliability and low-speed power line transmission is common.
& Therefore, it is difficult to require reliable, high-speed transmission lines.

The second problem is related to the reliability of the central control device. That is, if a problem occurs in the central control device, the system may stop, so
This central control device must have very high reliability, which leads to very high costs.

The third problem is related to commutation failure.

There are many factors that can cause commutation failures, such as voltage drop in the AC system connected to the inverter, waveform distortion, etc. Keep in mind that commutation failures will always occur with a non-negligible probability. According to 0M/foreign literature, which is clear from past operating results of two-terminal power transmission, this has occurred at a rate of Kana p. Commutation failure is not a scary accident in two-terminal power transmission, and is usually resolved as a single commutation failure. Even if it occurs continuously, do not stop the converter, for example. In the Hokkaido-Ihonshu DC power transmission facility, a method is adopted in which the inverter is operated as pie spare (hereinafter abbreviated as BPP) for a short period of time and then automatically returns to normal operation. Normally, it is treated as a minor or major failure. however,
Commutation failure at multiple DC terminals may lead to system shutdown. For example, in Fig. 1, when all converters are operating at their rated values, if 1Nv1 (inverse converter JJ) fails in commutation, REC1, RIC!
' all the current flows into INV J, so INV
J is not an overcurrent value of 200-, and INV J is 0 problem a, which causes no-load operation, and is not an overcurrent value of 200-.

(It is sufficient to design the converter in advance so that it can be overloaded for a short period of time, and if the converter is operated for a short period of time, it becomes a problem in terms of cost.) In other words, for example, if the previous commutation failure is caused by a temporary AC system voltage If it is 6 due to a drop, we want to return to the steady state immediately after the AC system voltage recovers, but INV 1 is
It can no longer be started. In other words, since the 2001C) current is flowing, the commutation heavy angle increases significantly, and the margin angle is insufficient and commutation is not possible.In this case, in order to ensure a sufficient margin angle, If the control lead angle is increased, there is a possibility that commutation can be achieved, but this will result in so-called zero power factor operation where the voltage is almost zero, and the problem will not be solved at all. Considering that 9 commutation failures are minor failures in the first case, but they are not serious failures in the case of DC multi-terminals, and that commutation failures occur with a frequency of about 1,000, This means that there is a risk that the system will stop working.

(4+) Purpose of the Invention The purpose of the present invention was to eliminate such drawbacks, and to prevent accidental stoppage of the converter comprising the converter from causing a system stoppage, and to prevent transmission lines and central control equipment from being stopped. It is an object of the present invention to provide a new control device for DC multi-terminal power transmission equipment that can reduce dependence as much as possible and further prevent system stoppage due to commutation failure.

(-) Structure of the invention Hereinafter, the present invention will be explained with reference to the drawings.

4 and 5 are control block diagrams showing one embodiment of the present invention. FIG. 4 is a control block diagram of a forward transform device, and FIG. 5 is a control block diagram of an inverse transform device.

In FIG. 4, numerals 21 to 23 are adders, into which various fixed values and detected values are input. 24 is a constant voltage control circuit (hereinafter referred to as
It is abbreviated as mu■. ) 25 is a first constant current control circuit (hereinafter abbreviated as CRJ); 26 is a second constant current control circuit (hereinafter abbreviated as ACRJ); and 21 is a maximum value selection circuit. 28 is a circuit that automatically selects the output signal of the control circuit with the larger control delay angle (hereinafter abbreviated as α), and 28 is the output signal of the control circuit with the smaller α. The minimum value selection circuit 2p automatically selects 2
The maximum value selection circuit 30, which is the same as 1, is a level detector that receives a DC voltage as an input and detects when the value becomes less than or equal to a predetermined value. Further, JJ and JJ are switches, which respond to the output signal of the level detector, and when the output signal becomes a logic level "1", that is, the level detector When a drop in voltage is detected, the switch J1 switches to O.
FF, switch J2 is turned on. Fig. 5 also has almost the same configuration as Fig. 4, JJ~35 is an adder, 7g is M, Jl is ACRJ, za is MCR2, 3# is a maximum value selection circuit, and 40 is a minimum value selection circuit. A constant margin angle control 41 (hereinafter abbreviated as CICR) for controlling the margin angle to a constant value is further provided on the inverse conversion device side shown in the circuit. Also, V
dpr and Vdr indicate the voltage setting value and voltage detection value of the forward converter, Vdpi and Vdl respectively indicate the voltage setting value and voltage detection value of the inverse converter, and Isr.

Idpr'p Idr is the forward conversion device's module C.
The current setting value of RJ, the current setting value of ACRj, and the current detection value are shown, and the current setting value of the inverter 0ACRJ, the current setting value of Mu CRj, the current product, The output value vAC is the AC system voltage. The output signal of the switch 31 or 770O in FIG. 4 and the output signal of the minimum value selection circuit 40 in FIG. 5 are sent to the phase control circuit for firing/? Rus is determined.

Now, it's configured like this! The operation of the III control circuit will be explained below.

First, in Fig. 4, in the steady state, Mu CR
For example, the current t-1
000 m, l1pr of ACRl is 1
At this time, the Vdpr of the VR is set to the optimum value for flowing 000 μm, for example, the rated value is 250 μm.
Set to perform constant voltage control at %230kV with respect to kVg. Furthermore, l1pr- of muCR2 is, for example, 10(
) to perform constant current control. If you set f' as shown above, the output of A■ will be the set value of 230 kV.
On the other hand, since the detected value is 250 kV, it is negative. is selected. Next, the output of ACR2 is set to 100.
Since the detected value is 1000 mm for the system, the output of the minimum value selection circuit Za will be The output of MCRJ is selected, and the maximum value selection time yr
The output of MUCRj is selected as the output of zs.

In steady state II (rated voltage), the level detector 30 is inactive, so the switch J1 is on and the switch J2 is off, so the O converter is eventually operated by the mu CR1. . In such a state, if some kind of accident occurs and the DC voltage drops, the level detector 30 will operate, switch J2 will be turned on, and switch 11 will be turned on.
turns off, and in turn MuORj operates, controlling the DC current to 100 Mu in the previous example.

be controlled.

Since the same concept can be applied to FIG. S, the explanation will be omitted.

(・y Function of the Invention Now, FIG. 6 shows a characteristic diagram when FIGS. 4 and 5 are applied to the DC 4-terminal power transmission shown in FIG. 1.

That is, it corresponds to FIGS. 2 and 4.

The steady-state MIO operating point in FIG. 6 is indicated by Pi-'-P. From FIG. 6, the following can be seen.

(1) The converter that determines the voltage is RECJ. That is, RECJ performs AVR rolling, and the remaining converters perform ACRJ operation.

(2) Regarding the current setting value and the current value flowing through each converter, the above-mentioned equations 0 and 0 hold true.

Now, consider the case where fi RECj stops due to an accident.0
For example, a ground fault occurs at point y in Figure 1.

This is a case where RKCj can be stopped by interrupting the DC interrupter 15. In this case, the operating point becomes PHe P#P4 shown in the characteristic diagram of FIG. That is, in FIG. 7, the voltage determining terminal shifts to INV J K, and RICCJ
, INV j will perform an ACR1 rollover.

At this time, regarding the current setting value in FIG. 7, the above-mentioned equation 9(2) holds true, but equation 0 no longer holds true. However, this system can be operated stably. The applicant has already demonstrated by digital printing that a system having the control characteristic diagram shown in Figure 7 operates stably. The reason for this will be explained below.

In Japanese Patent Publication No. 43-8641, the concept of current margin was introduced in order to ensure stability conditions, but the above-mentioned formula (2) was indispensable for stability. In other words, if the above equation (2) no longer holds true, it means that the forward converter cannot supply the current value required by the inverter, and the inverter automatically lowers its own voltage to obtain the required current. This is because the system's DC voltage eventually drops to zero in an attempt to ensure the same. In other words, all converters, whether forward or inverse converters, perform constant current control and are operated with completely uncoordinated current setting values.

Next, in JP-A-51-6641) S, the concept of voltage margin is added to the concept of current margin, but if you compare the control characteristic diagrams Figures 2 and 3, As you can see, they are essentially the same thing. That is, in Fig. 2, the secondary voltage of the converting transformer at the terminal (RKCJ) that determines the voltage is controlled by tap, so that it is higher than the secondary voltage of the converting transformer at all other terminals. Although the stain pressure determining terminal is determined by making the voltage smaller, the voltage setting value of the terminal (RECj) that determines the voltage is determined by setting the voltage setting value of the terminal (RECj) that determines the voltage by providing a constant voltage control circuit instead of using tap control in Fig. 3. Since the voltage setting value of all terminals must be made smaller than the voltage setting value of all terminals, the stain pressure determination terminal is determined.
6455 also makes the system unstable for the same reason as in Japanese Patent Publication No. 43-8641. 4G Kaisho 51-66
The difference between Publication No. 455 and Publication No. 11fi 43-8641 is that normal tap control takes several seconds to operate one tap, but it is said that high-speed control can be achieved by centralizing control using a transmission line. The point is that

However, in the present invention, since the voltage setting values of each terminal are different, as is clear from the characteristic diagram in FIG. 7, even if the voltage determining terminal (REC2) stops due to an accident,
In order for Vz to automatically become a voltage determining terminal and perform constant voltage control,
It is stable at 6, in which all the converters do not perform constant current control based on completely uncoordinated current setting values, as in Japanese Patent No. 66455.

This means that in the control device of the present invention, an accidental stoppage of the converter, etc., does not lead to a system stoppage, a high-speed transmission line is not necessarily required, and there is no possibility that the system will stop due to a malfunction in the central control device. It means many things.

Next, we will consider commutation failure. Now, in FIG. 1, it is assumed that the voltage of the AC system 3 connected to the inverter J J (INV J ) has decreased for some reason, and as a result, INV 1 has failed in commutation. At this time, as mentioned above, Japanese Patent Publication No. 43-8641, Japanese Patent Application Laid-Open No. 51-
In the method of Publication No. 66455, the currents of RECJ and REC1 all flow into INV J, and INV J becomes an overcurrent, and even if the voltage of AC system 3 is restored, the current of
VJ becomes unable to start. However, in the present invention, IN'v1 can be activated without any problem.

The reason for this will be explained using the control characteristic diagram shown in FIG. I
When NV J fails in commutation, the currents of REC1 and REC1 all flow into INV J, but since commutation failure is the same as a DC short circuit, the DC voltage is zero. This means that in the control characteristic diagram of FIG. 6, all converters shift to ACR1 operation, the DC voltage becomes zero at tl, and INV J has a maximum of 11pr'1 and Idp.
This means that only a current equal to the sum of r'2 flows. Therefore, if small values are set in advance for Ipr'l and Idpr'2 to prevent the current from intermittent,
When the voltage of the AC system J is restored, K INV J can be activated. That is, since the current value is small, the commutation overlap angle is small, and therefore a sufficient margin angle can be secured. This also applies to d and INVJ.

This is the same as starting the system from a state where no current is flowing, except for the condition that a small current is flowing, that is, starting the system for the first time, so it starts without any delay. be able to.

In addition, the straight lines ■ and ■ with the lower right corner in FIG. 6 are due to the minimum value limiter of α, which is not shown in FIG. 4, and the straight lines ω and ■ are due to constant margin angle control. It is.

(1) Modified Example FIG. 8 shows the inverse conversion device 11 (INV J
) is a control 4G behavior diagram in the case where the constant voltage control (Mu VR) operation is performed and all the remaining conversion devices are operated by the first constant current control (Muell 1 ). The operating points are points P1 to P4. It is clear that even in such a case, the same effect as described above will be obtained.

In addition, although the explanation has been given using the DC 4-terminal power transmission system diagram shown in Figure 1, the present invention is not limited to DC 4-terminal power transmission systems, and is generally applicable to multi-terminal system configurations. It goes without saying that it is also applicable to 2-terminal power transmission with converters connected.

Furthermore, it is also applicable to conventional two-terminal power transmission.

This advantage means that the present invention is very effective when considering the construction process of multi-terminals.

Furthermore, in FIG. 4, various methods can be considered as means for selecting MuCRJ when the DC voltage drops below a predetermined value.For example, the switch JIt12, the maximum value selection circuit 29, etc. are not provided. There is also a method of applying a bias to the adders zx, xx in the direction in which α becomes larger when a decrease in the DC voltage is detected. In any case, since the gist of the present invention is to realize the control characteristics as shown in FIG. 6, the means for realizing the same is not limited to the above embodiment.

(f) A General Effect As explained above, according to the present invention, all the converters are provided with the first and second constant current control circuits and the constant voltage control circuit, and furthermore, the inverse converter is provided with the first and second constant current control circuits and the constant voltage control circuit. , a constant margin angle control circuit is added, and the voltage setting value of the constant voltage control circuit of all converters other than the converter that is unable to perform constant voltage control is smaller than the voltage setting value of the converter that performs constant voltage control. and each voltage setting value is set to a different value from each other,
By configuring the second constant current control circuit to operate at least at a DC voltage value lower than the DC voltage value in a steady state, it is possible to prevent a system stoppage due to an accidental stoppage of the converter. .

■Direct current interrupters can be used effectively.

■Transmission (2) Reduces dependence on lines.

■Reliance on centralized control equipment can be reduced.

■System stoppage due to commutation failure can be prevented.

It has many remarkable effects.

[Brief explanation of drawings]

1st WJ is a DC 4-terminal power transmission system diagram, FIG. 2 is a conventional control characteristic diagram, FIG. 3 is another conventional control characteristic diagram, and FIGS. 4 and 15 are an example of the present invention. A control block diagram showing
FIG. 6, FIG. 7, and FIG. 8 show control characteristic diagrams of the present invention. 1-4... AC system, 5-8... Conversion transformer, 9
~10... Forward conversion device, 11-12... Inverse conversion device, 13-20... DC interrupter, 21-2J... Adder, 24... Constant voltage control circuit, 25- 26... Constant current control circuit, 21-... Maximum value selection circuit, 2#... Minimum value selection circuit, xm-... Maximum value selection circuit, 10...
Level detection circuit, 31.32... switch, 31~s
i・-adder, S#...constant voltage control circuit, JF~J#
...constant current control circuit, 3ft...maximum value selection circuit,
40--Minimum value selection circuit, 41... Constant margin angle control circuit. Figure 1 Figure 2 (RECl) [RFe5) (INVl)
[INV2) Figure 3 (RECl) (RFe5) (INVII
[INV2] Figure 4 Figure 5 Figure 6 [REC1] (REC2] (INVII
[INV21 No. 70 [REC1] [REC2] (INVI)
[INV21 Figure 8

Claims (1)

[Claims] (1) In a DC multi-terminal power transmission facility consisting of multiple converters, all converters are each equipped with a constant voltage control device, and the minimum value of the constant voltage setting value of the converter operating as a forward converter is reversely converted. The maximum value of the constant voltage setting value of the converter that operates as a converter is also set to a large value, and the converter that operates as a forward converter is set so that the current is set to the first constant current setting for a voltage lower than the constant voltage setting value. a first constant current control device that controls the current so that it does not exceed a second constant current setting value; and a first constant current control device that controls the current so that the current does not fall below a second constant current setting value for voltages that are higher than the constant voltage setting value and below a predetermined DC voltage value. A DC multi-terminal power transmission equipment 6 control device that is equipped with a second constant current control device that performs the following.