JPS5828813B2 - Chiyokuryuutatanshikei Tonoki Dohoushiki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for starting a multi-terminal DC power transmission system, and more particularly to connecting another activated converter to an operating DC power transmission system.

There are several DC power transmission systems that have been put into practical use to date, but all of these systems are DC two-terminal systems in which one converter performs forward conversion operation and the other performs reverse conversion operation.

The starting force formula for this two-terminal DC system is as shown in Fig.
NL, thereafter the α angle of the forward converter and the β angle of the inverse converter are gradually reduced to establish the rated DC voltage, and the DC current is also increased exponentially.

This method has the advantage that overvoltage does not occur because the DC voltage can be started from around zero.

On the other hand, as a starting force formula for a multi-terminal DC power transmission system, it is conceivable to start all the converters simultaneously as forward converters or inverse converters, as in the case of a two-terminal system.

However, this batch start/stop method has many restrictions and inconveniences for the operation of the DC transmission system, so if possible,
It is desirable to be able to operate as both a two-terminal and multi-terminal operation.

In other words, it is desirable to use a starting force type that, for example, when operating as a two-terminal converter, starts up another converter, connects it to the DC power transmission system, and then operates as a three-terminal converter.

However, when trying to additionally start some of the converters in this way, it was found that the starting force formula shown in FIG. 1 could not be adopted.

This will be explained with reference to FIG.

In this figure, 2 is a converter, which is connected to each other via a DC line via a DC disconnector 1.

However, rl r r2 + r3t r4 is a resistance, 4 is a transformer, and 5 is an AC breaker.

In this figure, A, B, C, and D are symbols representing conversion stations.

Now, it is assumed that IA, IB, IC, 5A, 5B, '5C are closed and converters 2A, 2B, 2C are in so-called three-terminal operation, and here II), 5T) are closed and converted. It is assumed that the device 3D is additionally activated.

At the time of this additional start-up, the DC transmission system already has 2A and 2B.
.

2C, and as is well known, the DC current of each converter is determined by the difference voltage between the forward converter terminal voltage and the inverse converter terminal voltage and the resistance of the power transmission system.

On the other hand, the DC voltage of the converter fired at an electrical angle of 85° is approximately zero.

For this reason, when the voltages of various parts of the DC power transmission system are determined to bring the DC current to a desired value, it is equivalent to suddenly grounding a part of the system, causing fluctuations in the DC voltage and current.

This is a disturbance in the DC power, and this influence also spreads to the AC system.

It goes without saying that the occurrence of such power fluctuations is undesirable.

Note that when this additionally started converter is in reverse conversion operation, an overcurrent flows transiently, and when it is in forward conversion operation, no current flows transiently, so that in any case, smooth startup is not possible. Can not.

In this way, in a multi-terminal DC transmission system, when connecting some of the converters to the operating system, if the startup method known for conventional two-terminal DC transmission systems is applied, the DC or AC power system will It was found that this caused power fluctuations.

In view of the above, an object of the present invention is to provide a startup method for a multi-terminal DC power transmission system that does not cause power fluctuations even when additional startup is performed.

In the present invention, since the cause of the power fluctuation is that the voltage distribution of the DC transmission system fluctuates due to the difference between the DC voltage at the connection point and the DC voltage of the activated converter, It is started by making the DC voltage and the DC voltage of the converter almost equal.

Next, the concept for making the DC voltages almost the same will be explained.

Assume that one forward converter 2A and one inverse converter 2B are in operation in the DC four-terminal system shown in FIG.

In this state, one forward converter 2C is activated as follows.

First, turn on the AC breaker 5C, then turn on the DC breaker 1C.
Insert.

At this time, if the DC side voltage of the converter is Edl, the forward converter 2C generated when the gate pulse is turned on
If the no-load DC voltage Edr satisfies Edr>Edl---(1), a current flows through the forward converter 2C.

However, if Edr is too large than Ed7, a large current will flow, so it will be slightly larger, that is, Edr=Edl+1Edl!・－－・・
(2) is desirable.

Now, if the DC winding voltage of main transformer 4C is Eac, then (
2) E d r shown in the formula is Edr = KI Eac
-CO3α.

・・・・・・・・・It is expressed as (3), becomes.

Here, 1 is a constant determined by the rectification method, and in the case of 6-phase Graetz connection, 1=1.35.

Therefore, the starting phase control angle α. If it is determined by equation (4) and the gate pulse is turned on, the current will flow smoothly.

The size of J Edl can be arbitrarily selected according to the idea described later.

Activation of one inverse converter 2D can be performed in exactly the same way as the activation of the forward converter.

If the no-load current voltage of the inverter 2D is Edi, Edi=-Edl+AEdl...
- In (5), the inverter current flows smoothly.

Therefore, similar to equation (4), The starting phase control angle can be determined from .

Note that A Ed7 is selected as, for example, sections 5 to 10 of Edl.

When selecting this AEdl, it is important not to intermittent the current flowing through the additionally activated converter, and this converter current is determined in proportion to AEdl.

With the above-mentioned thinking, it is possible to almost match the DC voltage of the converter and the DC voltage of the connection point, and as a result, additional activation does not disturb the voltage distribution of the DC transmission system and does not cause power fluctuations. .

However, the control angle α obtained from equations (4) and (6). If left as is, the DC current of the additionally activated converter will be very small.

For this reason, it is necessary to adjust the individual control angles using a control device (not shown) for each converter shown in FIG. 2, so that the direct current in each part becomes desired.

The transition to this new operating state is performed at an appropriate time thereafter.

FIG. 3 shows a schematic configuration of a control device to which a starting device according to the present invention is added.

Among these, the one consisting of 11.13 is a conventionally known control device. For example, the phase control circuit 13 provides a voltage signal according to the deviation between the DC current setting value Idp and the actual current, and generates a gate pulse. The generating circuit 11 supplies the converter 2 with a gate pulse having an ignition phase corresponding to this voltage signal.

Although a circuit for constant current control is shown here, this part may be a constant DC voltage control circuit or a margin angle control circuit, as is already well known.

A control circuit other than these is a starting circuit according to the present invention,
When the DC disconnector 1 and the AC breaker 5 are closed, the DC voltage detector 7 detects the DC voltage Edl at the converter end, and the AC voltage detector 6 detects the DC winding voltage Eac, and divides them. A circuit 8 calculates Edl/Eac.

If the output is multiplied by 1/1 by the coefficient unit 9, it becomes cosα.

is obtained, and the starting phase control angle α is further calculated by the inverse cosine function generating circuit 10.

Obtain a voltage signal corresponding to . cosα.

From α. It goes without saying that in order to obtain , an approximation circuit may be used instead of an inverse cosine function generating circuit.

And this α.

If α0 is sent to the startup phase setting circuit 12 and a gate pulse is turned on based on this α0, a DC voltage shown in equation (2) will be generated.

Note that A F,dl is determined, for example, by 2·Idp.

K2 is appropriately determined based on commutation noactance and line resistance.

Assuming that the DC voltage detector 7 outputs a positive output during forward converter operation and a negative output during reverse converter operation, (2),
(5) Both equations can be satisfied.

The starting phase setting circuit 12 is an upper and lower limit limiter circuit, and each limiter value is α.

Since it is set to , the control angle is α.

However, the limiter is set by the gate pulse generation circuit.
is released after a certain time constant.

Therefore, after that, the output is freely controlled at a control angle determined by the output of the control system (constant current control system in FIG. 3).

In other words, in a DC multi-terminal system consisting of four converter stations as shown in Figure 2, for example, one converter station determines the DC line voltage, and the remaining three converter stations control the DC current. Now, suppose that three of the four converter stations in Figure 2 are in operation, and the remaining one converter station is additionally activated and the gate is turned on to match the DC voltages, then the DC current of each converter is For example, it is adjusted as follows.

However, the current setting value of the additionally activated converter is set to '1ctp, and the limiter of the activation phase setting circuit 12 is gradually released, and the following adjustment is performed.

(1) When additionally starting as a forward converter (when transmitting power) Increase the current setting value of the inverse converter whose received power during O operation is desired to be increased by Idp.

Alternatively, reduce the current setting value of the forward converter whose transmitted power during O operation is desired to be reduced by Idp.

(2) When additionally starting as an inverter (when receiving electric power) Reduce the current setting value of the inverter whose received power during O operation is desired to be reduced by Idp.

Alternatively, the current setting value of the forward converter whose transmitted power during zero operation is desired to be increased is increased by Idp.

Through these operations, the current balance of the entire DC system is maintained after the additional start-up is completed.

As described in detail above, in the present invention, since the firing angle is determined so that the DC terminal voltage of the converter matches the connection point voltage, the DC voltage distribution of the DC power transmission system immediately after connection is not changed, and therefore, Does not cause power fluctuations.

Moreover, even when the output of the converter that is activated afterward increases, power fluctuation does not occur.

According to the present invention, it is possible to smoothly start up a DC multi-terminal system without causing any disturbance to the system, and this invention is effective in improving the reliability of DC multi-terminal power transmission technology.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the starting method of a DC 2-terminal system, Fig. 2 is a diagram showing a DC 4-terminal system, and Fig. 3 is an example of the starting force type of a DC multi-terminal system of the present invention. FIG. 1...DC disconnector, 2...Forward converter,
3... Inverse converter, 4... Main converter, 5
...AC breaker, 6...AC voltage detector, 7...DC voltage detector, 8...
Division circuit, 9...Coefficient unit, 10...Inverse cosine function generation circuit, 11...Gate pulse generation circuit, 12...Start phase setting generation circuit, 13.
・Question phases. control circuit.

Claims (1)

[Claims] 1. In the starting force formula for a DC multi-terminal system in which at least two or more AC/DC converters are connected to a DC line and a new AC/DC converter is activated during DC power transmission operation to participate in the DC power transmission operation, In addition to connecting the DC and AC terminals of the AC/DC converter to be additionally started to the DC line and AC system, respectively, the DC voltage generated at the AC/DC terminals of the AC/DC converter when the ignition signal is applied will be activated as a forward converter in this order. The DC current of the converter should be slightly higher than the DC line voltage so that it is not intermittent, and when it is activated as an inverter, the DC current of this inverter should be slightly higher than the DC line voltage so that the DC current is not intermittent. A starting method for a DC multi-terminal system, characterized in that the control angle of an initial firing signal given to an AC/DC converter is determined according to the ratio of DC line voltage to AC terminal voltage so as to be low.