JPH0213531B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an operation control method for a DC multi-terminal power transmission system, and particularly to an operation control method for a DC multi-terminal power transmission system suitable for stable operation in the event of an accident.

[Prior art]

In order to stably operate a parallel DC multi-terminal power transmission system in which three or more converters are connected in parallel to a DC transmission line (the length of the transmission line may be 0), one converter station of the multi-terminal power transmission system ( It is best to have the DC system voltage determined by the DC system, and the rest determined by the current. A specific method for this purpose is an operation control method that provides a current margin between the sum of the current settings of the forward converter and the sum of the current settings of the inverse converter, based on the same idea as in the case of two-terminal power transmission. However, the drawback is that a high-speed communication device is required to always satisfy this relationship. As a countermeasure to this problem, an operation control method has been considered in which the converter is provided with a margin in advance, and this margin is used up in the event of an abnormality to ensure stable operation at all times. However, even with this operation control method, stable operation cannot be achieved unless the voltage setting value of the DC multi-terminal power transmission system is carefully selected and the voltage of the system is determined.

For example, as shown in Figure 1, there are two forward converters (REC1, REC2) and two inverse converters (Inv1, Inv
2) Considering a 4-terminal power transmission system that is connected in parallel to the line DL via a DC reactor DCL,
Assuming that the actual current value i of each converter is Rec1
i ₁ = 100 (A), i ₂ of Rec2 = 50 (A), i ₃ of Inv1 =
50 (A), and i ₄ of Inv2 = 100 (A). The operation during steady operation at this time is the "O" point on the voltage (V _d )-current (I _d ) characteristic of each converter shown in FIG. 2a.

In the figure, I ₁ I ₂ I ₃ I ₄ is the current setting value of each converter, and there is a relationship of (I ₁ + I ₂ )−(I ₃ +I ₄ )=ΔI _d . However, ΔI _d : current margin. Further, there is a relationship between the currents flowing through each converter: i ₁ +i ₂ =i ₃ +i ₄ i ₁ :i ₂ :i ₄ :i ₃ =100:50:50:100. Further, the voltage setting values of each converter have the following relationship: E ₁ =E ₄ >E ₂ >E ₃ .

In Figure 1, T _r is a transformer, AC is an alternating current system, CONO is a central control device, CON1 to CON4 are terminal control devices, and CON0 and CON1 to CON
4 are connected by communication devices COM0 to COM4. If Inv1 suddenly stops due to a failure in this situation, if the communication system COM is normal,
When Inv1 is stopped, the current of Rec1 or Rec2 is reduced and the current setting value is adjusted so that stable operation can be achieved. However, when the communication system is abnormal (for example, fading when using microwaves), the current setting value cannot be adjusted.
No current flows in Rec2, and the current of Rec1
Since the current setting values of Inv2 are equal, the above-mentioned current margin is lost, and stable operation cannot be performed. This is shown in FIG. 2b.

[Purpose of the invention]

The purpose of the present invention is to eliminate the above-mentioned disadvantages.
The object of the present invention is to provide a control method that allows stable operation even in abnormal situations by appropriately selecting voltage determination for a multi-terminal power transmission system.

[Summary of the invention]

The above-mentioned disadvantages occur at each converter station (device) in a multi-terminal system.
It has become clear that this problem occurs because the voltage setting value of I decided to make a decision.

[Embodiments of the invention]

First, the operating state when the voltage of a multi-terminal system is determined at each terminal will be explained.

Figure 3 shows the healthy state when the voltage setting value E ₁ of Rec1 is set lower than the setting value E ₂ of Rec2.
Figure a) and when Inv1 suddenly stops (Figure b)
In either case, a stable operating point "O ¹ " or "O" can be obtained.

Similarly, FIG. 4a shows the operating point "O" of each converter in the steady state when Rec2 is used to determine the voltage. Even if Inv1 is brought to an emergency stop due to an accident in this state, a stable operating point cannot be obtained as shown in FIG. 4b, and operation cannot be performed. However, as shown in Figure 4c, if Rec1 determines the voltage without Rec2 determining the voltage, a stable operating point "O" can be obtained even if Inv1 stops, and operation can be performed. become. Furthermore, Fig. 5a shows the operating state when Inv2 is made to determine the voltage, but if Inv2 makes an emergency stop from this state, stable operation cannot be performed as shown in Fig. 5b, and in this case, the Diagram a
Alternatively, a countermeasure is to set the operating state as explained in FIG. 4c. In other words, at the time of an emergency stop of the inverter, it is best to lower the voltage setting value of the converter with a large power transmission power in the forward converter. Since the voltages are selected in order from the lowest voltage setting value, it is preferable to ensure a sufficiently large current margin. Also, when having one of the inverters determine the voltage, it is a good idea to have the one with the smaller power receiving power determine the voltage, in order to ensure a current margin in the event of an emergency stop of the inverter. . For this reason, the current of the converter is constantly monitored, and priority is given to the forward converter with the largest power transmission power or the inverse converter with the smallest power reception power to determine the system voltage. In addition, the voltage setting value of the converter should be set lower for converters with large power transmission power than those with low power, and on the other hand, those with low power reception power are set lower than those with high power, so that they are more likely to be automatically selected as the voltage determining converter station in the event of an abnormality. I did it like that.

An embodiment of the present invention is shown in FIGS. 6 to 8. FIG. 6 shows processing software for selecting a converter for determining the voltage of a multi-terminal system, which is one of the processing contents of the central control unit CON0 shown in FIG. first,
When determining the system voltage using the forward converter Rec
If YES or inverter is used, determine NO branch. This is given arbitrarily by the operator. Next, among the current setting values of the forward converter or inverse converter, select the converter with the larger current setting value if it is a forward converter, or the converter with the smaller current setting value if it is an inverse converter, and then select the converter with the smaller current setting value if it is a forward converter. A voltage margin application command is issued to the device via the communication device. This process completes the process of commanding the system's voltage determining converter. In addition, the central controller creates commands for converted power, commands for forward/reverse conversion operation, commands for starting/stopping the system, etc. for each terminal, and sends the commands to each terminal control device via the communication device. Therefore, the current setting value of each converter station mentioned above is known in the central control unit, and the above-mentioned processing can be carried out without any problems. Note that in the above, the converted power setting value may be used instead of the current setting value to select the converter with the maximum value or the minimum value. In this case, the current setting value is the converted power value divided by the DC voltage,
Since the DC voltage is equal at each terminal if the loss of the power transmission line is ignored, it can be considered as the current setting value conversion power setting value.

Figure 7 shows the voltage (V _d ) - current (I _d ) characteristics of the converter, where I _i is the current setting value (given by the central controller) and E _i ′ is the voltage setting value, which was previously set. The set value, ΔI _d , is the current margin, and ΔE _i is the voltage margin, both of which are preset values.Whether or not to add to the current or voltage set value is commanded by the central controller, and the voltage margin If the ΔE _i application command is present, the voltage setting value of the applied converter station will be the lowest voltage setting value among the converters in the multi-terminal system, and will determine the voltage of the system.

FIG. 8 shows a concrete block diagram of the control circuit of each terminal control device CON _i . COM _i is a terminal communication device, SW1 and SW2 are switches that are turned on and off according to commands from the central control unit, SUM1 and SUM2
is an adder that performs addition with the polarity shown in the figure, where I _i is the current setting value, ΔI _d is the current margin, i _i is the current flowing through the converter, E _i ′ is the voltage setting value, and e _i is the DC current of the converter. Line voltage and ΔE _i are voltage margins, and the relationship between each set value is shown in FIG. Further, I _i is a command value sent from the central control device, and ΔI _i , ΔE _i , and E _i ′ are known quantities set in advance. AMP1, AMP
2 is an amplifier that amplifies the current deviation and voltage deviation, respectively, LV is a voltage selection circuit that selects the smaller output value from the output of amplifier AMP1 or AMP2, and AP is an automatic pulse phase shifter when the input voltage is small. An automatic pulse phase shifter that outputs a pulse with the characteristic that the control delay angle α is advanced and delayed in the opposite direction when it is large.GA is a gate amplifier circuit, and this control circuit and the converter (consisting of a three-phase thyristor bridge) By combining these, a converter having the voltage-current characteristics shown in FIG. 7 can be obtained. The voltage-current characteristic of the converter when no voltage margin or current margin is added is as shown by the solid line in Figure 7, and the operating point during steady operation is when the converter is in forward operation.
O ₁ point, O ₂ points when inverter operation. When the converter determines the voltage, a voltage margin is added to this voltage setting value, and the characteristics become as shown by the dashed line. At this time, when the forward converter is operating, the current setting value is
It is set to I _i +ΔI _d , and I _i −ΔI _d when the inverter is operating. The operating point is O ₁ as in the case without voltage determination,
O ₂ points.

It is clear that according to the embodiments shown in FIGS. 6 to 8, the voltage determination described above can be performed by the converter with the largest transmitting power or the converter with the smallest receiving power; As shown in Figures 4 and 4, stable operation can be achieved in the event of an abnormality.

In the above example, we explained how to give the voltage setting value of the voltage determining converter station in the grid, but it is also possible to change the voltage setting value of the converter that specifies the current other than the voltage determining terminal depending on the converted power. Even if the voltage determining converter erroneously comes to an emergency stop, the next converter with larger converted power will be selected as the voltage determining terminal, which is preferable. At this time, it is best to give priority to the forward converter over the inverse converter in order to ensure a voltage margin in the event of an abnormality. Processing software for determining the voltage determination order of the central control unit for this purpose is shown in FIG. First, the converters are ranked in descending order of the converted power among the forward converters, and then the converters are ranked in the descending order of the converted power among the inverse converters. In this case, it is preferable that the voltage setting values for each terminal be given from the central controller. This is because if the voltage setting value is set in advance for each terminal and the voltage margin value is sent to each terminal via the communication device, it is easier to send the voltage setting value if the same analog amount is sent. This is because the number of terminals is small and each terminal control device is simple. The block diagram of the control circuit for each terminal at this time is shown in Figure 1.
As shown in Figure 0 and described above, the voltage setting value E _i ′, like the current setting value I _i , is sent from the central controller, and the voltage margin concept as described in the previous example is applied. is unnecessary in this case. The other blocks are the same as those in FIG. 8, and their explanation will be omitted.

With this operation control method, the voltage determining terminal is selected according to the converted power, and the voltage setting values of other converters are determined accordingly. In this case, the next voltage determining terminal is automatically selected, allowing stable operation.

[Brief explanation of drawings]

Fig. 1 is a diagram of a multi-terminal power transmission system targeted by the present invention, Figs. 2 to 5 are voltage-current characteristic diagrams of the converter of Fig. 1, and Fig. 6 is a voltage-current characteristic diagram of the converter of the present invention. 7 is a voltage-current characteristic diagram of the converter, FIG. 8 is a block diagram of the control circuit of each terminal control device, and FIG. 9 is a central control device according to another embodiment of the present invention. FIG. 10 is a block diagram of the control circuit of each terminal control device. AC1 to AC4...AC system, Tr...transformer,
Rec1~Rec2...Forward conversion station (vessel), Inv1~Inv
2...Reverse conversion station (device), DCL...DC reactor, DL...DC transmission line, CON0...Central control device, CON1 to CON4...Each terminal control device, CON
0~COM4...Communication device, SUW1~SUW2...
...Adder, AMP1~AMP2...Amplifier, LV...
...voltage selection circuit, AP...automatic pulse phase shifter,
GA...Gate amplifier, SW1~SW2...Switch.

Claims (1)

[Claims] 1. Three or more converters are connected in parallel to a DC power transmission line, and among the converters, either a forward converter with the largest transmitted power or an inverse converter with the smallest received power In an operation control method for a multi-terminal power transmission system that determines the voltage of a multi-terminal system, (1) among multiple forward converters, the DC voltage setting value of the one with the largest transmitted power is set higher than that of the other forward converters; (2) of the plurality of inverters, the set value of the DC voltage of the inverter receiving the least power is lower than that of the other inverters; A method for controlling the operation of a multi-terminal power transmission system, characterized in that control is performed by at least one of the steps (2) and (2).