JPH0218018B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a branch line closing control method in a DC multi-terminal power transmission system, and particularly to a DC multi-terminal power transmission system suitable for connecting a branch line in a branch type DC multi-terminal power transmission system. Related to branch line closing control method.

Direct current power transmission is used for high-power long-distance transmission, etc., because the construction cost of lines is low and it is particularly advantageous for cable power transmission. DC power transmission generally consists of a forward converter station, a DC line, and a reverse converter station. Power transmission methods include a DC two-terminal power transmission method in which two AC systems are connected to a DC connection, and a DC multi-terminal power transmission method in which three or more AC systems are connected to a DC connection. The present invention relates to this DC multi-terminal power transmission, and next, a conventional DC multi-terminal power transmission system will be explained.

FIG. 1 shows a configuration diagram of a branch type DC multi-terminal power transmission system consisting of three converter stations. In the figure, power transmission systems 1, 2, and 3 constituting one power transmission system include AC/DC converters 11, 12, which convert alternating current to direct current or direct current to alternating current, respectively.
13, DC reactor 21 for smoothing DC current,
22, 23, branch lines 41, 4 which are DC transmission lines
2, 43, a high-speed disconnector or DC breaker 31 that connects or disconnects the branch lines 41, 42, 43 according to a command;
32, 33, 34, 35, 36, AC/DC converter 1
A control device 5 that controls the operating states of 1, 12, and 13.
1, 52, and 53 are provided. In addition to the above-mentioned system, a control device 54 is provided which controls on/off of high-speed disconnectors 34, 35, and 36 provided at the branch points of the branch lines 41, 42, and 43. Furthermore, the control device 54 and the systems 1, 2,
3 includes signal transmission devices 61, 62 for transmitting control commands from each of the control devices 51 to 54 and status signals indicating the operation and operating status of each part of each system 1, 2, and 3 to each of the control devices 51 to 54; 63 and 64 are provided.

In such a branch type DC multi-terminal power transmission system, when performing normal multi-terminal power transmission, all high-speed disconnectors 31 to 36 are turned on and systems 1, 2,
An operation is performed in which DC power is transmitted and received between the two. However, if one converter station is out of operation, for example if the AC/DC converter 13 is out of operation, the high speed disconnectors 33 and 36 are opened and the branch line 43 is stopped.
is separated from the branch point, and the AC/DC converters 11 and 12 are operated. And AC/DC converter 13
When restarting or restarting the switch, first turn on the high-speed disconnector 36 at the branch point and then turn on the high-speed disconnector 33, or reverse the order in which the high-speed disconnectors 36 and 33 are turned on. Above, a method of starting the AC/DC converter 13 at the optimum phase has been considered.

However, when the high-speed disconnector 33 or 36 is turned on using this method, there is a potential difference between the branch lines 41 and 42 that are transmitting power and the branch line 43 that should be turned on.
A step DC voltage is applied to the branch line 43. Therefore, this voltage causes vibration between the inductance of the branch line 43, the inductance of the DC filter, and the capacitance of the DC filter, etc., and overvoltage occurs on the branch line 43 and the DC power transmission side of the AC/DC converter. There is a risk of damaging the AC/DC converter. Especially when the branch line is a long-distance power transmission line or consists of a cable transmission line, the value of overvoltage becomes large. An example of this overvoltage is shown in FIG.

FIG. 2 shows voltage waveform diagrams at various parts of the branch line when the high-speed disconnectors 33 and 36 are turned on and the AC/DC converter 13 is additionally activated. 2a, b, and c are voltage waveform diagrams at the high-speed disconnectors 31, 32, and 33, and d in FIG. 2 is a voltage waveform diagram at the DC side output end of the AC/DC converter 13. Then, when the AC/DC converter 13 is additionally activated at time t ₁ , after time t ₂ (approximately 5 mS), the AC/DC converter 1
Voltage at high speed disconnector 31, 32 at the output end of 3
An example in which an overvoltage approximately 2.46 times higher than E ₁ and E ₂ occurred is shown in Figure d.

As described above, in the conventional DC multi-terminal power transmission system, when an AC/DC converter that is stopped is connected to a branch line that is transmitting power, an overvoltage may be generated in the branch line that is being connected, and the AC/DC converter may be damaged.

The present invention has been made in view of the above problems,
The purpose is to provide a branch line closing method in a DC multi-terminal power transmission system that can prevent generation of overvoltage due to branch line closing.

In order to achieve the above-mentioned object, the present invention provides a method for connecting AC/DC converters that are to be connected in order before connecting them to a branch line that is currently transmitting power, when other AC/DC converters that are stopped are connected to a branch line that is currently transmitting power. Starts up as a converter and charges the branch line to be turned on. After the voltage at the switch end of the branch line to be turned on is charged to a voltage that is approximately equal to the voltage at the switch point of the branch line during power transmission, the branch line of the AC/DC converter to be turned on is turned on. I did it like that. However, when the AC/DC converter is operated as an inverse converter, the AC/DC converter that was charging the branch line to be turned on when the branch line is turned on is switched from operating as a forward converter to operating as an inverse converter. In this way, the present invention is characterized in that no potential difference occurs between the voltage of the branch line during power transmission and the voltage of the branch line to be turned on.

Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 3 shows a configuration diagram showing an embodiment of a system to which the present invention is applied. In this example,
Unlike the conventional system shown in FIG.
2 and 73 are provided, and these detection signals are supplied to the signal transmission device 64, and the configurations of the respective control devices 51, 52, 53, and 54 are different. A configuration diagram of a control device 53 as one of these control devices is shown in FIG. In FIG. 4, the control device 53 includes a command value generation circuit 5.
00, constant current control circuit 501, constant voltage control circuit 5
02, constant margin angle control circuit 503, minimum voltage selection circuit 504, changeover switch 505, automatic pulse phase shifter 506, changeover switch 507, addition circuit 50
8. Control angle calculation circuit 509, first-order delay circuit 510
It is composed of.

The command value creation circuit 500 receives the signal transmitted from the signal transmission device 63 and converts the AC/DC converter 13
Create the signals necessary for the operation of AC/DC converter 1
A current command value Idp that commands the current flowing in the branch line 3 is given to the constant current control circuit 501, a voltage command value Vdp that commands the DC output voltage of the AC/DC converter 13 is given to the constant voltage control circuit 502, and The value of the voltage value Ve at is given to the adding circuit 508.
Further, switching signals C ₁ , C ₂ , and C ₃ are applied to the switching switches 505 and 507 and the first-order lag circuit 510 . Constant current control circuit 501 is AC/DC converter 13
The constant voltage control circuit 502 supplies a control signal to the minimum voltage selection circuit 504 to set the current to the current command value Idp, and the constant voltage control circuit 502 applies a control signal to the minimum voltage selection circuit to set the DC output voltage of the AC/DC converter 13 to the voltage command value Vdp. 5
Give it to 04. The constant margin angle control circuit 503 creates a control angle for maintaining the margin angle necessary for the AC/DC converter 13 to perform stable operation during inverter operation, and sends a control signal based on the creation to the minimum voltage selection circuit 5.
Give it to 04. The minimum voltage selection circuit 504 selects the minimum voltage suitable for operation of the AC/DC converter 13 from among the control signals of the constant current control circuit 501, constant voltage control circuit 502, and constant margin angle control circuit 503, and switches the selection signal to a changeover switch. Give to 505. This signal is
During normal startup and startup after branch line charging, the pulse is directly applied to the automatic pulse transfer device 506 via the changeover switch 505.
The signal is output as a gate pulse signal to control the AC/DC converter 13.

Note that the changeover switch 505 is connected to the AC/DC converter 1
3 is additionally activated or restarted, the switching signal _C1 from the command value generation circuit 500 switches to select the signal of the first-order delay circuit 510.

Further, the changeover switch 507 is connected to the AC/DC converter 13.
This is a switch for selecting a predetermined voltage at the time of startup, and is set to the R side when the AC/DC converter 13 is in rectifier operation according to the switching signal _C2 of the command value generation circuit 500, and to the I side when it is in inverter operation. Can be switched. The voltage supplied to the R side and the I side corresponds to the voltage ΔVe corresponding to the voltage drop of the branch line from the branch point to the converter station, and the voltage of ΔVe is applied to the R side, and -ΔVe is applied to the I side. voltage is applied. The voltage selected by the changeover switch 507 is applied to an adder circuit 508, added to the voltage Ve at the branch point of the branch line, and supplied to the control angle calculation circuit 509. The control angle calculation circuit 509 is the AC/DC converter 1
3 input or output AC voltage e ₂ and addition circuit 508
A control voltage Vα corresponding to the control angle α is output based on the output value of .

Vα=K ₁ cos ⁻¹ {(Ve±ΔVe)/e ₂ } Here, K ₁ is a constant (voltage/control angle).
Control voltage Vα is applied to first-order lag circuit 510.
The first-order delay circuit 510 is the command value creation circuit 50.
When activated in accordance with the starting command C3 from 0, the output of the first-order lag circuit slowly rises from 0 to the value of the control voltage Vα with a certain time constant, and is supplied to the changeover switch 505.

Here, the effect when the AC/DC converter 13 is additionally activated by rectifier operation will be explained. First, when the AC/DC converter 13 is operated as a rectifier, the changeover switch 507 is switched to the R side by the changeover signal _C2 from the command value generation circuit 500. Then, in the control angle calculation circuit 509, a control voltage Vα based on the following equation is calculated.
The following calculations are performed.

The calculation Vα=K ₁ ·cos ⁻¹ {(Ve+ΔVe)/e ² } is performed and provided to the first-order lag circuit 510. Switching command for additional start at this time
C1 switches the changeover switch 505 to the output side of the first-order lag circuit 510. As a result, the AC/DC converter 13 is activated and charging of the branch line 43 is started. This charging voltage gradually increases so that the DC side output voltage of the AC/DC converter 13 reaches a value of (Ve+ΔVe). It is assumed that at this time, the high-speed disconnector 33 of the AC/DC converter 13 is naturally turned on by a control signal from the control device 53.

Insertion point (branch point) of branch lines 41 and 42 during power transmission
When the voltage at the switching end of the branch line 43 to be switched on (in this case, the voltage at the branching point) becomes almost equal, the control device 53 passes the signal to the high-speed disconnector 36 on the branching point side via the signal transmission device 63. command is output. After the high-speed disconnector 36 is turned on by this command, the closing of the branch line 43 is completed by carrying out partial activation at the normal multi-terminals.

On the other hand, when the AC/DC converter 13 is additionally started by inverter operation, if the branch line to be turned on is charged in the same manner as in the operation described above, the polarity of the DC voltage of the AC/DC converter 13 will be reversed. As in the conventional case, an overvoltage will occur when the high-speed disconnector is turned on.

Therefore, when the AC/DC converter 13 is operated by an inverter, the high speed disconnector 33 is configured to be capable of switching between two systems, as shown in FIG. 5, and the direction of current flow in the AC/DC converter 13 is reversed. It is necessary to make a connection for this purpose. In this way, the polarity of the DC voltage at the branch point and the polarity of the DC voltage applied by the inverter operation will match. The control voltage Vα' in this case has a value expressed by the following equation.

Vα′=K*cos ⁻¹ {(Ve−ΔVe)/e ₂ } Calculation based on the control voltage Vα′ is executed in the control angle calculation circuit 509, and the AC/DC converter 13
The DC side output voltage of is controlled to a value of approximately (Ve - ΔVe). And the branch line 43 to be inserted
When the voltage at the branch point becomes approximately equal to the voltage at the branch point, a control signal from the control device 53 outputs a command to close the high-speed disconnector 36 on the branch point side. Note that if the connection for switching the polarity of the high-speed disconnector 33 is made again when the branch line has been turned on, normal partial activation of the AC/DC converter 13 can be performed.

As described above, according to this embodiment, even when the AC/DC converter is additionally started or restarted by rectifier operation or inverter operation, charging of the branch line to be turned on is performed before turning on the branch line at the branch point. The branch point is turned on when the voltage at the branch point and the voltage of the branch line to be turned on become almost equal. Therefore, no overvoltage will occur in the branch line, and the AC/DC converter and the branch line will not be damaged by the overvoltage.

FIG. 6 shows a configuration diagram of a control device as another embodiment of the present invention.

In this embodiment, the voltage setting value of the constant voltage control circuit 502 is set to be equal to the voltage at the branch point, so that the constant voltage control circuit 502 can control charging of the branch line. In this embodiment, unlike the case shown in FIG. 4, the switching circuit 511 is configured so that either the voltage command value Vdp from the command value generation circuit 500 or the output signal of the adder circuit 508 is given to the constant voltage control circuit 502. It is provided. This switching circuit 511 selects the signal of the voltage command value Vdp during normal operation, and selects the signal of the adder circuit 508 during branch line charging such as during additional startup. This switching is performed by a switching signal C ₁ from the command value generation circuit 500.

As described above, the constant voltage control circuit 502 controls the control angle so that the DC output voltage of the AC/DC converter 13 becomes equal to the command value. That is, when the AC/DC converter 13 performs rectifier operation, control is performed so that the DC output voltage of the AC/DC converter 13 becomes Ve + ΔVe, and when the AC/DC converter 13 performs inverter operation, control is performed so that the DC output voltage becomes Ve - ΔVe. Let's do it.

The method of operating the high-speed disconnector, etc., and the method of charging the branch line when the AC/DC converter 13 performs inverter operation are the same as in the case described above, and in this embodiment as well, the branch line is not turned on. No overvoltage occurs. Furthermore, this embodiment has the advantage of simplifying the control apparatus because only a circuit for creating a voltage setting value needs to be added to the control apparatus during normal operation.

Next, an embodiment of the present invention is shown in FIG. In this embodiment, unlike the case shown in FIG. 3, the voltage at the branch point is determined from the detected values of a DC voltage detector 81 and a DC current detector 91 provided at the converter station. The configuration is the same as in Figure 3,
Identical components are given the same reference numerals and their explanations will be omitted. Note that the DC voltage detector 81 and the DC current detector 91 are also provided in a normal converter station, and similar devices are also provided in other converters stations. The control device in this embodiment is configured as shown in FIG. That is, the control device 53 in this embodiment is the control device 53 shown in FIG.
In addition, a function generating circuit 512 is provided, and the other configurations are the same as those shown in FIG. The function generating circuit 512 calculates the voltage at the branch point from the current value Idf and voltage value Vdf detected by the DC voltage detector 81 and the DC current detector 91 according to the following formula.
This is to calculate Ve′.

Ve′=K ₂ *(Vdf±Idf・Re) where K ₂ : Constant (voltage/voltage) Re : Resistance of the DC transmission line from the branch point to the converter station where the current/voltage detector is installed The sign is When the sign is +, it is used when the converter station operates as a rectifier, and when the sign is -, it is used when the converter station performs inverter operation.

The output of the function generating circuit 512 is supplied to the adding circuit 508 in the same way as the voltage Ve shown in FIG.
Therefore, in this embodiment as well, control similar to that shown in FIG. 4 is performed, and it is possible to prevent overvoltage from occurring when the branch line is turned on. Furthermore, this embodiment is more economical than the case of FIG. 3 because the voltage at the branch point can be detected using a DC current detector and a DC voltage detector that are normally provided.

Further, in the case of this embodiment, the same operation can be performed using the configuration shown in FIG. In this case, the aforementioned voltage Ve' is used instead of the voltage Ve shown in FIG.

As explained above, according to the present invention, when a stopped converter station is restarted or restarted, the branch line to be turned on is charged before the branch line is turned on,
By this charging, the branch line is turned on after the voltage at the turning point of the branch line reaches a value almost equal to the voltage at the turning point of the branch line that is transmitting power, and when the branch line is turned on, overvoltage occurs in the branch line. Since this can be prevented, the branch line can be stably input without damaging equipment at the converter station.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a conventional DC multi-terminal power transmission system, a to d in Fig. 2 are voltage waveform diagrams of various parts when the system shown in Fig. 1 is additionally activated, and Fig. 3 is A configuration diagram showing an embodiment of the present invention, FIG. 4 is a configuration diagram for explaining the configuration of the control device shown in FIG. 3, and FIG. 5 is a configuration diagram showing the conversion shown in FIG. 3. Figure 6 is a diagram for explaining the charging method when additionally starting the battery by inverter operation.
A configuration diagram for explaining the configuration of a control device as another embodiment of the present invention, FIG. 7 is a configuration diagram showing another embodiment of the present invention, and FIG. 8 is shown in FIG. FIG. 2 is a configuration diagram for explaining the configuration of a control device. 11, 12, 13... AC/DC converter, 31, 3
2, 33, 34, 35, 36...high speed disconnector, 4
1, 42, 43...branch line, 51, 52, 53, 5
4... Control device, 61, 62, 63... Signal transmission device, 70, 71, 72, 73, 81... DC voltage detector, 91... DC current detector.

Claims (1)

[Scope of Claims] 1. A plurality of AC/DC converters are connected in parallel and in a branched manner via branch lines, and a turn-on switch is connected to each branch point, and DC power is transferred between these AC/DC converters. In a DC multi-terminal power transmission system that transmits and receives DC power, some AC/DC converters in the system transmit and receive DC power, and an AC/DC converter that is stopped is connected to a branch line that is transmitting power via a branch line. When turning on the AC/DC converter, the AC/DC converter to be added is activated as a forward converter, and the branch line connected to the AC/DC converter is charged. After the voltage is charged to a voltage approximately equal to the voltage at the branch line input switch point of the branch line that is transmitting power, if the AC/DC converter of the branch line to be additionally input operates as an inverter, the conversion operation is switched. , when operating as a forward converter, by turning on the input switch of the branch line to be input as is,
A branch line input control method in a DC multi-terminal power transmission system characterized by input to a branch line during power transmission. 2. Claim 1, characterized in that the voltage across the closing switch of the branch line to be additionally connected is determined from the detected value of a voltage detector installed near both ends of the closing switch of the branch line to be additionally connected. A branch line closing control method in the DC multi-terminal power transmission system described above. 3. The voltage across the closing switch of the branch line to be connected is determined from the detected values of a voltage detector and a current detector provided in the AC/DC converter that is additionally connected. Branch line closing control method in DC multi-terminal power transmission system. 4 When the additional AC/DC converter is operated as a forward converter, the voltage drop due to the additionally connected branch line is added to the voltage at the input point of the branch line that is started as the forward converter and is transmitting power. When the branch line to be turned on is turned on after charging the branch line to be turned on until the voltage becomes approximately equal to the applied voltage, and the AC/DC converter to be added is operated as an inverter, the AC/DC converter is activated as a forward converter and charges the branch line to be turned on to a voltage approximately equal to the voltage at the turning point of the branch line currently transmitting power minus the voltage drop of the branch line to be added, and 2. A branch line closing control system in a DC multi-terminal power transmission system according to claim 1, wherein the AC/DC converter is switched to an inverse converter when the line is turned on.