JPH0227894B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-terminal DC power transmission device, and particularly to a control method for stopping some AC/DC converters.

FIG. 1 shows an example of the configuration of a conventional multi-terminal DC power transmission device. AC/DC converters 5, 6 and 7 are connected to the DC transmission line 1 via DC reactors 2, 3 and 4.
is connected. Note that a circuit breaker 8 is inserted between the DC reactor 4 and the AC/DC converter 7. The AC/DC converter 5 is operated as a forward converter, and the AC/DC converters ₆ and 7 are operated as inverse converters. ₂ , Id ₃ is flowing.

FIG. 2 is an operation time chart of the apparatus shown in FIG. The DC current Id ₁ of the AC/DC converter 5 is divided into a DC current Id ₂ of the AC/DC converter 6 and a DC current Id ₃ of the AC/DC converter 7. When stopping only the AC/DC converter 7 operating as an inverse converter from such an operating state, the command of stop command a (time t ₀ )
As a result, the DC current setting value given to the control system of the AC/DC converter 7 is gradually decreased to bring the DC current Id ₃ into a small state. In this state, as shown in b, the circuit breaker 8 is opened before and after the gate block (time t ₁ ) of the AC/DC converter 7, and the AC/DC converter 7 is stopped.

However, in such a conventional method, if the gate block is performed when the DC current Id ₃ has not been sufficiently reduced at time t ₁ , the AC/DC converter 7 will not only be unable to turn off the DC current Id ₃ , but also This may damage the circuit breaker 8 or cause a short circuit in the DC system.
There was a drawback in that the remaining AC/DC converter 5 operating as a forward converter and the AC/DC converter 6 operating as an inverse converter hindered the continuation of DC power transmission.

SUMMARY OF THE INVENTION An object of the present invention is to provide a stop control method for a multi-terminal DC power transmission device that eliminates the above-mentioned drawbacks and allows a part of AC/DC converters to be stopped smoothly without affecting other devices.

The present invention aims to reduce the current flowing through the AC/DC converters to be stopped when stopping some AC/DC converters of a multi-terminal DC power transmission device in which a plurality of AC/DC converters are connected to the main line of a DC system. After reducing the DC current to approximately zero and detecting that the DC current is intermittent, a gate block signal is applied to the AC/DC converter to stop it. At this time, the above object is achieved by lowering the DC voltage for a certain period of time in order to facilitate the occurrence of current interruption.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows the configuration of an AC/DC converter used in an embodiment of a multi-terminal DC power transmission device that implements the stop control method for a multi-terminal DC power transmission device according to the present invention. The thyristor elements 9 are connected in a three-phase bridge,
A DC current intermittent detection device 10 is connected in parallel to each thyristor element 9.

FIG. 4 shows a specific example of the configuration of the DC current intermittent detection device 10, and also shows an example of the configuration of a DC current interruption determination device that determines whether or not the DC current is interrupted. The output of the voltage waveform shaping circuit EP is input to a forward voltage detection circuit RED and a reverse voltage detection circuit IED. The output of the forward voltage detection circuit RED is input to the AND circuit AND ₁ and the OR circuit OR ₁ , and the output of the reverse voltage detection circuit IED is input to the OR circuit OR ₁ . The output of flip-flop circuit FF ₁ is a correction circuit ER that corrects the waveform.
is input to the AND circuit AND ₁ , and the correction circuit ER
The output of OR circuit OR ₁ is input to AND circuit AND ₂ . Such a DC current intermittent detection device 1
0 is voltage waveform shaping circuit EP, forward voltage detection circuit
RED, a reverse voltage detection circuit IED, a flip-flop circuit FF ₁ , and an AND circuit AND ₁ .
88443 gate pulse generator)
The flip-flop circuit _FF1 of the voltage detection section and this
Correction circuit ER that corrects the waveform of FF ₁ , OR circuit
It is constructed by adding an intermittent current detection section consisting of OR ₁ and AND circuit AND ₂ .

The DC current intermittent determination device 11 includes the AND circuit
OR circuit OR ₂ where the output of AND ₂ is input and this
Flip-flop circuit to which the output of OR ₂ is input
It consists of FF ₂ . In addition, 12 to 18 in the figure
indicates an input or output terminal.

FIG. 5 is a time chart showing the operation waveforms of each part of the DC current intermittent detection device 10 and determination device 11 shown in FIG. 4, and shows the detection operation when the DC current is interrupted. The voltage waveform B between the anode and cathode (hereinafter referred to as voltage waveform between A and K) of the three-phase bridge-connected thyristor 9 shown in FIG.
input to EP, and the output of the same circuit EP to the forward voltage detection circuit
Input to RED and reverse voltage detection circuit IED. In response to this input, the forward voltage detection circuit RED outputs a waveform F on the forward voltage side of the A-K voltage waveform B. Further, the reverse voltage detection circuit IED outputs a waveform G on the reverse voltage side of the A-K voltage waveform B. This waveform F and G
is input to the OR circuit _OR1 , which outputs _the waveform H to the AND circuit _AND2 .

On the other hand, an automatic pulse phase shift control device (not shown)
APPS (hereinafter referred to as APPS) on-pulse signal C
is sent to terminal 13, and off-pulse signal D is sent to terminal 14.
The flip-flop circuit _FF1 outputs a signal E with a period _T1 . Now, if the weight _angle of _the commutation current in the three _- phase bridge circuit shown in FIG. This signal E is input to the correction circuit ER, and this circuit ER receives the signal E.
Since the output terminal is configured to block the output of time T ₂ from time t _{0 to t 1 in}
A signal I of time T ₃ is output, and this signal I
is input to the AND circuit AND ₂ . As mentioned above, in addition to this signal I, this AND circuit AND ₂ also has the following signals:
A signal H obtained by shaping the voltage B between A and K of the thyristor 9 and combining the forward voltage detection signal F and the reverse voltage detection signal G is input.

Symbol A indicates a DC current waveform when the DC current is intermittent between times t ₂ and _{t 4} (time T ₄ ) during the conduction period T ₁ in the thyristor 9 . Now, when an intermittent occurs in the waveform A of this DC current, the forward voltage in the voltage waveform B between A and K of the thyristor 9 increases at time T6 from time _t3 to _t4 of the conduction period _T1 , and again from _{time t2 to} time T6. t ₃
A reverse voltage occurs at time _T5 . At this time, the forward voltage detection circuit RED outputs a signal for this forward voltage at time _T6 between times _t3 and _t4 , as shown by waveform F in the figure.
Similarly, the reverse voltage detection circuit EID outputs a signal at time _T5 between times _t2 and _t3 in waveform G. As mentioned above, waveform F and waveform G are synthesized by OR circuit OR ₁ , so the output waveform H of OR circuit OR ₁ is as follows.
A signal is output at time _T4 from time _t2 to _t4 .

Now, one cycle of the AC frequency of thyristor 9 is measured as time.
Assuming that _t0 to _t6 (time _T7 ), the output signal H of the OR circuit _OR1 at time _T7 is input to the AND circuit _AND2 . However, since the output signal I of the correction circuit ER is input to the AND circuit from time t ₁ to _{t 5} (time T ₃ ), the AND circuit AND ₂ inputs the output signal I of the correction circuit ER during the conduction period T ₁ of the thyristor 9 mentioned above. Time t ₃ ~ t ₄
(time T ₆ ) forward voltage detection signal F and time t ₂ to _{t 3} (time
The combined signal J of the reverse voltage detection signal G of _T5 ) is
It is output to the terminal 16 from time t ₂ to _{t 4} (time T ₄ ).
Needless to say, this signal J is a current interruption detection signal when interruption occurs during the conduction period _T1 of the thyristor 9.

This current intermittent detection signal J is output by the operation of each DC current intermittent detection device 10 installed in each arm in the AC/DC converter constituted by the three-phase bridge circuit shown in FIG. If the DC current intermittent detection device 10 outputs the signal J, these signals are input to the OR circuit OR ₂ via the input terminal 17 of the determination device 11 in FIG. k ¹ , k ² …k ⁶ →k ¹ …
Outputs the signal. The flip-flop circuit FF ₂ is set by the input of the first signal K, determines that an interruption has occurred in the DC current of the AC/DC converter having a three-phase bridge configuration, and outputs the signal L to the output terminal 1.
Output to 8. The voltage waveform shaping circuit ED, the forward voltage detection circuit RED, the reverse voltage detection circuit IED, and the flip-flop circuit FF ₁ perform the current intermittent detection operation described above, and also detect the gate of the thyristor 9 including the AND circuit AND ₁ . It also performs the operation of outputting a signal to the output terminal 15. However, this operation is described in the gate pulse generator of the aforementioned Japanese Patent No. 53-88443, and is not directly related to the present invention, so its explanation will be omitted.

6 and 7 show an embodiment of a multi-terminal DC power transmission device using the DC current intermittent detection device 10 described above and applying the stop control method for a multi-terminal DC power transmission device of the present invention. .

In the example of FIG. 6, AC/DC converters 23, 24, and 25 are connected to the DC power transmission line 19 via DC reactors 20, 21, and 22. These AC/DC converters 23, 24, and 25 have a DC current intermittent detection device (same as the DC current intermittent detection device 10) 2
6, 27, and 28 are connected, and these DC current intermittent detection devices are further connected to DC current intermittent determination devices (same as the DC current intermittent determination device 11) 29, 30, and 3.
Connected to 1. In addition, terminals 32, 33 and 34 are in the AC system, and commutating transformers 35 and 3 are connected respectively.
AC/DC converters 23, 24 and 2 via 6 and 37
5. Note that the reference numeral 38 indicates the earth. The AC/DC converters 23, 24, and 25 of each AC system are 6 in the 3-phase bridge circuit shown in FIG.
This is a case of phase operation, and it is assumed that the AC/DC converter 23 is operated as a forward converter and the AC/DC converters 24 and 25 are operated as inverse converters.

In the example of FIG. 7, AC/DC converters 23, 24, and 25 are connected to the DC transmission line 19 via DC reactors 20, 21, and 22, but in this embodiment, AC/DC converters 39, 40, and 41 is connected. These AC/DC converters 39, 40 and 41 are connected to DC current intermittent detection devices 42, 43 and 4.
4, these DC current intermittent detection devices 4
2, 43 and 44 are DC current intermittent determination devices 29,
30 and 31. Further, the terminals 32, 33 and 34 of the AC system are connected to DC current intermittent detection devices 42, 43 and 44 via commutating transformers 45, 46 and 47, respectively. The other configurations are the same as the example shown in FIG. 6, but the AC/DC converters 23, 39 and AC/DC converters 24, 4
Each of the 0 and AC/DC converters 25, 41 is operated in a 12-phase configuration with a pair of 3-phase bridges.

Next, the operation of the above embodiment will be explained, but since the operation is the same in both examples, the following explanation will be made using the example shown in Fig. 6. I will only explain about. 6th
In the figure, the AC/DC converter 23 is now under constant current control.
It is assumed that the AC/DC converter 24 is a forward converter based on ACR, the AC/DC converter 24 is an inverse converter based on constant voltage control AVR, and the AC/DC converter 25 is an inverse converter based on constant current control ACR. In this case, the following DC current settings are made in the control system (constant current control ACR) of each AC/DC converter. The AC/DC converter 23 has a DC current setting value i _dp1 to which a current margin Δi _dp1 has been added.
However, the DC current setting value i _dp2 in the AC/DC converter 24 is
Further, a DC current setting value i _dp3 is given to the AC/DC converter 25, and the relationship between these setting values is i _dp1 > i _dp2
+i _dp3 is used.

Here, the AC/DC converter 2 being operated as an inverse converter.
5, first decrease the DC current setting value i _dp3 of the converter and reduce the DC current of the converter.
Decrease Id ₃ to near zero current. In this case, the DC current setting value i _dp1 of the AC/DC converter 23 also decreases as the DC current setting value i _dp3 decreases, so the DC current Id ₁ of the AC/DC converter 23 becomes the DC current Id flowing to the AC/DC converter 24. There will only be ₂ . DC current of the AC/DC converter 25 operating as the above-mentioned inverse converter
When Id ₃ is reduced to near zero, intermittent currents occur in the DC current. The DC current intermittent detection device 28 detects this DC current interruption as explained in FIGS. 4 and 5 above. DC current intermittent detection device 28
When detecting intermittent DC current, it operates the DC current intermittent determination device 31 to gate block the AC/DC converter 25 and partially stop the AC/DC converter 25 from the operating mode of the multi-terminal DC power transmission device. . FIG. 8 is a diagram illustrating such an operation in more detail.

FIG. 8 shows a specific example of the multi-terminal DC power transmission device, which is the embodiment shown in FIG. FIG. 9 is a time chart explaining the operation. The input signal from the stop command switch 48 is input to the DC current setting device 49 of the AC/DC converter 25, and the output of this DC current setting device 49 is sent to the constant current control device 5.
0, and the output of this constant current control device 50 is input to the AC/DC converter 25. AC/DC converter 2
A DC voltage transformer 51 is attached to 5.
The output of the DC voltage transformer 51 is input to the DC current intermittent detection device 28, and the output of the DC current interruption detection device 28 is input to the DC current interruption determination device 31. The output of the DC current intermittent determination device 31 is input to the DC current setting device 49 and is also output to the terminal 52 which is the output terminal of the gate block signal of the AC/DC converter 25. Now, when disconnecting the AC/DC converter 25 from the DC power transmission system and stopping it, at time t ₀ of the operation time chart shown in FIG. 9, give a stop command A from the stop command switch 48 to the DC current setting device 49, Decrease the DC current setting value i _dp3 of the setting device 49.
The constant current control device 50 gradually lowers the DC current Id ₃ of the AC/DC converter 25 over time, following the decrease in the set value i _dp3 . Eventually, this DC current Id ₃ will change to the DC current setting value i _dp3 when time t ₁ is reached.
Intermittentness occurs because the amount of time becomes small. The occurrence of this discontinuity is introduced to the DC current discontinuity detection device 28 by the DC voltage transformer 51 connected to each arm of the AC/DC converter 25. In FIG. 8, six phases are collectively shown as a DC voltage transformer 51.

At this time, the DC current intermittent detection device 28 performs the operations explained in FIGS. 6 and 7, and immediately outputs _{the DC} current interruption detection signal J to the DC current interruption determination device 31. , an output signal L is obtained at the same time t ₁ when the intermittent DC current Id ₃ is started.
This signal L is outputted to the terminal 52 as a block signal of the gate signal of the AC/DC converter 25. On the other hand, this signal L is inputted to the DC current setting device 49 in order to further force this intermittent state when the DC current Id ₃ starts to be interrupted. Then,
The DC current setting device 49 operates so that the DC current setting value i _dp3 , which was gradually decreased between time t ₀ and t ₁ due to the stop command A, is rapidly reduced to zero at time t ₁ . Through the above-described operating procedure, some of the AC/DC converters 22 in the multi-terminal DC power transmission device shown in FIGS. 6 and 7 can be smoothly stopped.

FIG. 10 is a block diagram showing another specific example of the embodiment shown in FIG. 6 in more detail, and FIG. 11 is a time chart illustrating its operation. 1st
The block diagram of FIG. 0 is almost the same as the specific example shown in FIG. The voltage is input to a constant voltage control device 54, and the output of this constant voltage control device 54 is outputted to a terminal 55. Since the other configurations are the same as those shown in FIG. 8, their explanation will be omitted. Note that the terminal 55 is connected to the control voltage applied to the APPS (not shown) of the AC/DC converter that controls the voltage of the DC system.
This is the EC output terminal.

DC voltage setting device 53 and constant voltage control device 54
The other devices, except for the above, operate exactly the same as in the case described in FIG. 8 and stop the AC/DC converter 22, so their explanation will be omitted. On the other hand, the DC voltage setting device 5
3 and the constant voltage control device 54 contribute to controlling the voltage of the DC system using the residual AC/DC converter 24 in reverse converter operation without partial shutdown.
The DC voltage setting device 53 performs a control operation to reduce the DC current Id ₃ and an operation to detect the discontinuation of the current Id ₃ , but since these operations are the same as those described in FIG. 8, the explanation will be omitted. I will omit this and mention it as necessary.

In the example of FIG. 10, when the stop command A shown in FIG. 11 is given by the stop command switch 48 to the DC current setting device 49 and the DC voltage setting device 53 at time _t0 , the DC current setting device 49 The DC current Id ₃ of the AC/DC converter 25 is gradually decreased. Then, the DC current Id ₃ is interrupted, and the gate block signal L of the AC/DC converter 25 is outputted to the terminal 52. This signal L is used as a gate block for the AC/DC converter 25, and voltage control of the DC system is also used to ensure that the AC/DC converter 25 is stopped by inputting this gate block signal. .

Further, to explain _the above _- mentioned stopping operation according to _{FIG .}
, decrease the voltage setting v _dp to v _dp ′. This reduction in the set value is caused by the control operation of the DC voltage setting device 53, which causes the AC/DC converter 24 operating as an inverse converter to reduce the voltage El of the DC system to the voltage El'.
The voltage drop control of the DC system at this time T ₁ is as follows:
For the AC/DC converter 25 that partially stops, time t ₁
AC/DC converter 25 in the operation of the gate block
Since the relationship with the DC voltage E _d25 becomes E _d25 > El′,
DC current of AC/DC converter 25 performing inverse converter operation at time _t1 when gate block signal is input
ID ₃ can be easily turned off. That is,
As is well known, the voltage V _d on the DC output side of the converter is expressed as follows, where e ₂ is the AC voltage of the converter, I _d is the DC current, I d is the commutation reactance, and α is the control delay angle.
It is expressed by equation (1).

V _d = ke ₂ (cosα−I _d X/2) ...(1) where k is a constant.

Now, if e ₂ and I _d are kept constant and V _d is decreased, α increases from equation (1). The magnitude of the ripple in the DC current changes in proportion to sinα, and α with an upper limit of π/2.
becomes larger as . When the magnitude of ripple in the DC current increases, the DC current tends to cross the zero point. In other words, current interruption is likely to occur.
Generally, when the converter is stopped, I _d is controlled to a small value. Therefore, the voltage drop due to the reactive power of the converter becomes smaller, and e ₂ becomes higher. Due to changes in both I _d and e ₂ , α becomes larger from equation (1), and therefore I _d becomes more likely to be interrupted. From the above, adding voltage control to the DC system of the remaining AC/DC converter 24 means that the AC/DC converter 25
This means that the system can be stopped reliably.

In the explanation so far, the case where the AC/DC converter 25 operates as an inverse converter has been described. However, when operating as a forward converter, the voltage El of the DC system is controlled by the DC voltage of the AC/DC exchanger 25.
By changing E _d25 to the relationship E _d25 < El′, the AC/DC converter 2 operating as a forward converter can be
The direct current Id ₃ of 5 can be easily turned off in the same way as when operating as the inverter described above.

In the example of FIG. 7, two AC/DC converters, for example AC/DC converters 23 and 45, are used in each AC system.
Although it has the function of a 12-phase operation mode, consideration must be given to the case where one unit in each AC system is stopped and DC power is transmitted in a 6-phase operation mode. Therefore, in this embodiment, each AC/DC converter 23,
24, 25, 39, 40 and 41, DC current intermittent detection devices 26, 27, 28, 42, 43 and 44
The configuration is such that it connects. However, in any case, DC power is transmitted in a 12-phase operation mode, and 6
If the phase operation mode is not adopted, the above-described stopping operation can be satisfactorily performed without providing the DC current intermittent detection devices 42, 43, and 44 shown by broken lines in FIG.

According to this embodiment, the DC current Id ₃ of the AC/DC converter 25 to be stopped is reduced, and the interruption of the current that occurs due to the decrease in Id ₃ is detected by the DC current interruption detection device 28. At the same time, the DC current intermittent determination device 31 generates a signal for gate blocking the AC/DC converter 25, and stops the AC/DC converter 25 when the DC current is cut off. Since the timing of gate blocking can be properly determined, it is possible to completely prevent any effects on other devices connected to the DC transmission line 19 or short circuits in the DC system. This has the effect of smoothly stopping only the AC/DC converter 25. In addition, the DC current intermittent detection device 28 prevents the first point in time when the DC current Id ₃ is interrupted, and the AC/DC converter 25
This has the effect of preventing unnecessary overvoltage of the AC/DC converter 25 that would occur if the gate block was performed several to tens of seconds after the timing when the interruption occurred. .
Furthermore, in the embodiment shown in FIG. 10, since the DC current intermittent detection method is combined with the DC system voltage control method, there is an effect that the AC/DC converter 25 can be reliably stopped.

As described above, according to the stop control method for a multi-terminal DC power transmission device of the present invention, some AC/DC converters can be stopped smoothly without affecting other devices.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of a conventional multi-terminal DC power transmission device, Fig. 2 is a time chart showing the operation of the device shown in Fig. 1, and Fig. 3 is a stop control of the multi-terminal DC power transmission device of the present invention. FIG. 4 is a circuit diagram showing an example of the configuration of an AC/DC converter equipped with a DC current intermittent detection device for realizing the method, FIG. 4 is a block diagram showing an example of the configuration of the DC current intermittent detection device shown in FIG. Fig. 4 is a time chart showing the operation of the DC current intermittent detection device, and Fig. 6 shows an example of a multi-terminal DC power transmission device in a six-phase operation mode to which the stop control method for a multi-terminal DC current device of the present invention is applied. 7 is a block diagram showing another embodiment of a multi-terminal DC power transmission device in a 12-phase operation mode to which the stop control method for a DC power transmission device of the present invention is applied, and FIG. 8 is similar to FIG. 6. A block diagram showing a partial detailed example of the multi-terminal DC power transmission device shown in FIG. 9, a time chart showing the operation of the device shown in FIG. 8,
FIG. 10 is a block diagram showing another detailed example of the multi-terminal DC power transmission device shown in FIG. 6, and FIG. 11 is a time chart showing the operation of the device shown in FIG. 19...DC transmission line, 23, 24, 25, 3
9, 40, 41... AC/DC converter, 26, 27, 2
8, 42, 43, 44...Direct current intermittent detection device, 29, 30, 31, 45, 46, 47...Direct current intermittent determination device, 48...Switch, 49...
...DC current setting device, 50...constant current control device,
53...DC voltage setting device, 54... Constant voltage control device.

Claims (1)

[Claims] 1 Acts as a forward or inverse converter 3
In a stop control method for a multi-terminal DC power transmission device in which more than one AC/DC converter is connected to one DC system, each of the AC/DC converters is provided with a DC intermittent signal that detects intermittent DC current flowing through the AC/DC converter. A detection device is provided, and in response to a stop command for the AC/DC converter to be stopped, it reduces the DC current flowing through the AC/DC converter to be stopped, and also controls other AC/DC converters operating as inverse converters at a constant voltage. Controlled by the device, the voltage of the DC system is brought to a state lower than the DC voltage of the AC/DC converter that should be stopped, and the AC/DC converter that should be stopped is stopped in such a state. Stop control method for multi-terminal DC power transmission equipment.