JPH0326021B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Description of the 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 4-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, the converter 2 is already in operation as a forward converter, and the converters 3 and 4 are already in operation as inverse converters,
As a method for starting the converter 1 as a forward converter, for example, after turning on the switches 13 and 14,
Calculate the control angle such that the time-sequential converter output voltage Edr is greater than Edl by adding a predetermined bias voltage ΔEd, assuming that the DC line side voltage of converter 1 is Edl, and turn on the gate pulse for additional activation. A method is proposed.

Background technology and problems This is an output voltage lower than the voltage Edl on the grid side.
This seems to be to prevent the forward converter from starting up at a control angle that produces Edr, since no current flows immediately after startup, which puts stress on the converter. but,
Recent converters do not have 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 meet such demands, and is to minimize disturbance to the system when additionally starting a converter as a forward converter to a DC system that is already in operation. The purpose is to provide a simple startup method.

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

FIG. 2 is a block diagram showing one 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 that controls the current to a constant value by inputting the current setting value Idp and the current detection value Id detected by the instrument current transformer 23, and 24 is the voltage setting value Edp and the voltage detection value detected by the potential transformer 25
A constant voltage control device that controls the voltage to be constant using Edl as input; 26 is a control voltage selection that selects the output of the constant current control device 22 and the constant voltage control device 24 that lowers the DC voltage of the converter. device, 27
Reference numeral 28 indicates a control voltage limiter device that limits the control voltage, 28 a phase control device that determines the ignition pulse, and 29 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 30 is a switch that is closed by a start command of the start/stop device 21 in FIG. 2, and 31 is a switch for inputting _X1. , X ₂ as output and keeps the DC current Id at the current setting value Idp.

4 shows an embodiment of the constant voltage control device 24 according to the present invention in FIG.
The switch 33, which is closed by the activation command of the activation/stopping device 21 in the figure, is a device that uses X ₃ as an input and X ₄ as an output, and controls the DC voltage Edl to be maintained at the voltage setting value Edp.

Next, we will discuss the effect.

The operation of the present invention when the converter 1 is additionally activated in such a configuration will be explained. Although it has become common to include the constant voltage control device 24 in FIG. 2, it is not always necessary, and to simplify the explanation, a case without the constant voltage control device 24 will be described first.

The switches 13 and 14 in FIG. 2 are closed,
When an operation command is given to the forward converter 1, 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 applied to converter 1. At this time, since the constant voltage control device 24 is not present, the control voltage selection device 26 selects the output of the constant current control device 22 as is. When the control angle limiter is first started from a complete stop of the DC system, it gradually opens the control angle from the starting phase of around 90°, as shown by the broken line in Figure 5, which is common in two-terminal systems. However, in the case of additional activation, the limiter is set from the beginning as shown by the solid line, which is normally (10°) with the minimum control angle forward converter.
and the control voltage corresponding to the maximum control angle (usually 120° for forward converters). Therefore, the forward converter 1 includes a phase controller 28 and a gate pulse generator 2.
9, the control angle is deblocked at a control angle of approximately 90°, which is the starting phase of the constant current control device 22. Thereafter, the control angle is determined according to the output of the constant current control device 22.

The average DC voltage at a control angle of 90° is 0 under no load, which is much smaller than the system DC voltage Edl, and no current flows through the forward converter 1 immediately after deblocking. Therefore, in order to cause current to flow, the constant current control device 22 reduces the control angle and lowers the DC output voltage.
Raise Edr. Current begins to flow from the moment Edr becomes equal to Edl. This is equivalent to automatically deblocking at a control angle such that the DC output voltage Edr and the DC line voltage Edl are equal, and this is similar to synchronous joining in an AC system, resulting in the least disturbance. This is how it starts.

The time required from deblocking to when current actually starts flowing is approximately 10 ms when using constant current control constants like those normally used in Japan, and this degree of delay is not a problem in practice. The far greater advantage is that no matter what the grid voltage is, it can be added to the grid that is already in operation with as little disturbance as possible.

Next, a case where the constant voltage control device 24 is provided will be explained. The time constant of the constant voltage control device 24 is generally larger than the time constant of the constant current control device 22, and when the output of the constant voltage control device 24 is set to output a voltage lower than the DC voltage Edl of the system at startup, , it takes a considerable amount of time for the current to start flowing, which causes inconvenience. In addition, in the DC system that is already in operation, there is a converter that determines the DC voltage of the system by constant voltage control or constant margin angle control, and it is desirable from the viewpoint of cooperation that the converter 1 to be additionally activated performs constant voltage control. constant current control operation should be performed. Therefore, at the time of additional activation, the constant voltage control of the converter to be additionally activated may be disabled.

In Figure 4, the constant voltage control setting Edp of the converter that is additionally activated is set higher than the constant voltage control setting value of the converter that is already operating under constant voltage control, _and After the initial value of is set to a value corresponding to a small control angle, such as the minimum control angle or a control angle that generates a DC voltage at a constant voltage control setting, switch 32 in FIG. 4 is closed simultaneously with the deblocking of the converter. Therefore, immediately after deblocking, the output of the constant voltage control is a control voltage corresponding to a control angle of about 10 degrees, and the control voltage selection device 26 in FIG. 2 selects the output of the constant current control device 22.
Smooth startup can be performed in the same way as described when the constant voltage control device 24 is not provided.

The simulation results obtained by additionally activating the forward converter 1 in FIG. 1 in this way are shown in FIGS. 6 and 7.
As shown in the figure. In the figure, the forward converter 2 in FIG.
Inverse converter 3 and inverse converter 4 are completely stopped in the same way as normal 2-terminal power transmission, and the control angle limiter is set to 5th.
As shown in the figure, after gradually opening and starting, the forward converter 1 is additionally started. Figure 6 shows the forward converter 1,
The current waveforms of forward converter 2, inverse converter 3, and inverse converter 4 are shown, and FIG. 7 shows the DC line side voltage of forward converter 1, forward converter 2, inverse converter 3, and inverse converter 4 from the top. It shows.

Approximately 10ms after deblocking the forward converter 1, the current of the forward converter 1 quickly rises,
It causes almost no disturbance to the grid voltage. on the other hand,
When additionally starting a forward converter as in the past, if the output voltage of the forward converter is higher than the DC system voltage, the DC current will flow out, so the DC current on the inverter side during operation will increase. , a problem occurs in that the current oscillation continues until it is stabilized by the constant current control of the additionally activated forward converter. In contrast, in the present invention, as described above, the output voltage of the forward converter that is additionally activated is made 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 90°.

Another embodiment of the present invention will be described.

Regarding the constant voltage control device, in addition to the configuration shown in FIG. 4, a configuration as shown in FIG. 8 is also conceivable.
In FIG. 8, the same elements as in FIG. 4 are indicated by the same symbols. When the start/stop device 21 in FIG. 2 receives a start command, the switch 32 closes first.
Further, the switch 34 closes after a certain period of time. Since the constant voltage control set value Edp is set higher than the grid voltage Edl, by the time the switch 34 is closed after a certain period of time, the output of the control circuit 33 will be saturated and the control voltage corresponding to a control angle of 10° will be reduced. Output.
Therefore, similarly to the constant voltage control device having the configuration shown in FIG. 4, immediately after startup, the output of the constant current control device is selected instead of the output of the constant voltage control device.

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 90°, but the voltage generated is lower than the lowest voltage value at which the DC system is normally operated. It is sufficient if the control voltage is such that If it is smaller than 90°, the current intermittent time at startup will be shortened accordingly. Furthermore, although it is somewhat complicated, a control voltage that produces a DC output voltage Edr lower than the voltage Edl on the DC line side may be calculated and determined, and the initial value may be set to that value.

The control voltage limiter device was left open from the beginning, but if you are willing to sacrifice some start-up time, the control angle can be changed even during additional start-ups as shown in Figure 5.
It is also possible to gradually open the opening from around 90°.
In this case, there is an advantage that an overvoltage will not be generated in the converter equipment even if the switches 13 and 14 are opened by mistake and are additionally activated.

The above explanation was given for a parallel 4-terminal multi-terminal DC transmission system, but a 2-terminal power transmission system can also be used.
The starting method according to the present invention can be applied to a system in which a plurality of converters are connected in parallel to one terminal as shown in the figure.

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 forward converter to be additionally started is set to a voltage lower 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 drawings]

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 Figs. 3 and 4 explain a part of Fig. 2. FIG. 5 is a diagram for explaining the present invention, FIGS. 6 and 7 are characteristic diagrams for explaining the effects of the present invention, and FIG. 8 is another implementation of FIG. 4. FIG. 9, a block diagram showing an example, is another system configuration diagram to which the present invention can be applied. 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 converter, 24... Constant voltage control device, 25... Instrument transformer, 26... Control voltage selection device, 27... Control voltage limiter device,
28... Phase control device, 29... Gate pulse generator, 30, 32, 34... Switch, 31,
33...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 a forward converter and joined to the DC system. , the converter is gated deblocked at a control delay angle that generates a voltage lower than the operating DC line voltage set as the starting phase of the constant current controller included in the converter, and then the 1. A method for starting a converter in a DC power transmission system, characterized in that the phase of the converter is controlled by the output of a current control device.