JPH0326020B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method for starting a converter in a DC power transmission system.

Technical Background of the Invention Fig. 1 is a parallel four-terminal DC power transmission system diagram to which the present invention can be applied, in which 1 to 4 are AC/DC converters, 5 to 8 are DC reactors, 9 to 12 are DC lines, 13 to 2
0 is a switch such as a DC disconnector or a DC disconnector.

In such a configuration, when converters 1 and 2 are already in operation as forward converters and converter 3 is already in operation as an inverse converter, converter 4 is started as an inverse converter. For example, the switch 19, After inserting 20,
When the voltage on the DC line side of the converter is E _dl , the inverse converter output voltage E _di changes from E _dl to the predetermined bias voltage ΔE _d
A method has been proposed in which the control angle is calculated so as to be the value obtained by subtracting the value, and the gate pulse is turned on to perform additional activation.

Problems with the background technology This is because the output voltage is higher than the voltage E _dl on the grid side.
When the inverter is started at a control angle that produces E _di ,
Immediately after startup, the current is cut off, which puts stress on the converter, and this seems to be to prevent this. However, recent converters do not cause any problems even if the current is interrupted for a certain period of time, and there is a demand for a startup method that is suitable for such situations and causes less disturbance to the system.

Purpose of the Invention Therefore, the purpose of the present invention has been made to satisfy such a need, and is to minimize the disturbance caused to the system when adding a converter as an inverter to a DC system that is already in operation. The purpose is to provide a startup method with fewer problems.

Examples of the invention Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention, and the same elements as in FIG. 1 are indicated by the same symbols.
In FIG. 2, reference numeral 21 indicates a start/stop device, 22 indicates a constant current control device, which controls the current to a constant value using the current setting value I _dp and the current detection value I _d detected by the instrument current transformer 23 as input, and 24 25 is a constant margin angle control device that uses the current detection value I _d and the AC system voltage value E _AC connected to the inverter 4 as input to control the margin angle to a constant value; 25 is a constant current control device 22 and a constant margin angle control device; a control voltage selection device 26 for selecting the output of the angle control device 24 that lowers the DC voltage of the converter;
Reference numeral 27 indicates a control voltage limiter device that limits the control voltage, 27 a phase control device that determines the ignition pulse, and 28 a gate pulse generator that sends a gate pulse to the converter.

FIG. 3 shows an embodiment of the constant current control device 22 in FIG. 2 according to the present invention, where 29 is a switch that is closed by a start command of the start/stop device 21 in _{FIG. , _ _}

Next, we will discuss the effect.

The operation of the present invention when the converter is additionally activated in such a configuration will be explained.

The switches 19 and 20 in FIG. 2 are closed,
When an operation command is given to the inverter 4, the start/stop device 21 sets the initial value of _X2 of the constant current control device 22 in FIG. Close the constant current control device 22
At the same time, a gate pulse is given to the inverter 4.

On the other hand, if the minimum margin angle is 17°, the output of the constant margin angle control device 24 will change from 180° to 17° since no current is flowing through the additional converter 4 and the overlap angle is 0°. It outputs a control voltage that corresponds to a control angle of 163° after subtracting . Therefore, the control voltage selection device 25 selects the output of the constant current control device 22. In a multi-terminal DC transmission system, the most stable operation is when one converter determines the DC voltage and the other converters determine the current using constant current control.
Since there is a converter that already determines the voltage in the DC system, the AC side voltage is selected so that the converter that is additionally activated is controlled with constant current.
The control voltage selection device 25 continues, not only immediately after startup.
selects the output of the constant current control device 22. When the control angle limiter device is first started from a state where the DC system is completely stopped, the control angle limiter gradually starts from the starting phase around the control angle of 90°, as shown by the broken line in Figure 4, which is common in two-terminal systems. However, in the case of additional activation, the limiter is set from the beginning to the minimum control angle (usually 90° for an inverter) and the maximum control angle (usually 160° for an inverter), as shown by the solid line. Leave open to control voltage.

As described above, the inverse converter 4 is connected to the phase control device 2.
7. The gate is deblocked via the gate pulse generator 28 at a starting phase of about 160° of the constant current controller 22, and thereafter the control angle is determined according to the output of the constant current controller 22.

Generally, the control angle in the steady state of the additionally activated inverter 4 is 140° to 155°, and the DC average voltage E _di at which the control angle of 160° occurs is the voltage E of the DC system already in operation. Much higher than _dl . Therefore,
Even when a gate pulse is applied to the converter 4, the DC current does not suddenly flow, and the constant current control device 22 tries to cause the current to flow, thereby reducing the control angle and lowering the DC output voltage E _di . The current begins to flow smoothly from the moment E _di becomes equal to E _dl . This is equivalent to automatically deblocking at a control angle such that the DC output voltage E _di and the DC line voltage E _dl are equal. This means that there will be fewer startups.

The time required from deblocking to when current actually starts flowing is 2 to 3 ms when using the constant current control constant normally used in Japan.
This degree of delay poses no practical problem, and the far greater advantage is that no matter what the DC voltage of the system is, it can be added to the system that is already in operation with as little disturbance as possible.

The simulation results obtained by additionally activating the inverse converter 4 in FIG. 1 in this manner are shown in FIGS. 5 and 6. In the figure, the forward converter 1, forward converter 2, and inverse converter 3 in Figure 1 are completely stopped, as in normal two-terminal power transmission, and the control angle limiter is gradually adjusted as shown by the broken line in Figure 4. After opening and starting, the inverse converter 4 is additionally started, and FIG.
Figure 6 shows the current waveforms of converter 1,
The DC line side voltages of forward converter 2, inverse converter 3, and inverse converter 4 are shown.

2-3 after gate deblocking inverter 4
After ms, the current of the inverter 4 quickly rises, causing almost no disturbance to the grid voltage.
On the other hand, when starting up an additional inverter as in the past,
If the output voltage of this inverse converter is lower than the DC starting voltage, the direct current will flow in, so disturbances such as an increase in the DC current of the forward converter during operation and a decrease in DC current on the inverter side will occur. is likely to occur.
Furthermore, in a system with a small short-circuit capacity of the AC system connected to the inverter to be additionally started, if the inflow current at startup is large, the reactive power consumption will increase, leading to a drop in the AC system voltage, and furthermore, the DC starting voltage will decrease. There is also the possibility that problems such as a drop in the current flowing through the forward converter during operation may occur. In contrast, in the present invention, as described above, the output voltage of the additionally activated inverter is set higher than the DC line voltage, so these problems can be effectively prevented.

The above explanation is based on the case where the DC line voltage is positive in Figure 1, but the direction of the converter is
Even when the DC line voltage is negative (contrary to the diagram), smooth startup can be achieved by deblocking the startup phase by setting the startup phase to about 160°.

Other embodiments of the present invention will be described.

In the explanation so far, the initial value of the output control voltage of the constant current control device has been set to a value corresponding to a control angle of approximately 160°, but the voltage generated is higher than the highest voltage value at which the DC system is normally operated. It is clear that any control voltage that does this will suffice. 160°
If it is smaller than , the current intermittent time at startup is shortened by that amount. Although it is more complicated, a control voltage that produces a DC output voltage E _di higher than the voltage E _dl on the DC line side may be calculated and set as the initial value.

The above explanation was made for a multi-terminal DC transmission system with four terminals in parallel, but as shown in Figure 7,
The starting method according to the present invention can also be applied to a terminal power transmission system, if the system has a plurality of converters connected in parallel to one terminal.

Effects of the Invention As explained above, according to the present invention, in a DC system in which three or more converters are connected in parallel, the inverter to be additionally started is set to a voltage higher than the DC voltage of the system already in operation. By gate deblocking at the control delay angle that generates voltage and joining the system by taking advantage of constant current control, it has the remarkable effect of allowing additional activation without disturbing the system that is already in operation.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a DC multi-terminal system to which the present invention can be applied, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a block diagram for explaining a part of Fig. 2. Figure 4 is a diagram for explaining the present invention, Figures 5 and 6 are characteristic diagrams for explaining the effects of the present invention, and Figure 7 is another system configuration diagram to which the present invention can be applied. It is. 1-4... AC/DC converter, 5-8... DC reactor, 9-12... DC line, 13, 20... Switch, 21... Start/stop device, 22... Constant current control device, 23... ...Instrument current transformer, 24...Constant margin angle control device, 25...Control voltage selection device, 26...
...Control voltage limiter device, 27...Phase control device, 28...Gate pulse generator, 29...Switch, 30...Control circuit.

Claims (1)

[Claims] 1 In a DC system where at least three or more converters are connected in parallel, when multiple converters are already in operation, a stopped converter is additionally started as an inverse converter and joined to the DC system. , the inverter is gated deblocked at a control delay angle that generates a voltage higher than the operating DC line voltage set as the starting phase of the constant current controller included in the converter; 1. A method for starting a converter in a DC power transmission system, characterized in that the phase of the inverse converter is controlled by the output of a constant current control device.