JP2721285B2 - Control device of AC / DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an AC / DC converter constituting a bipolar DC power transmission system sharing a neutral line.

[0002]

2. Description of the Related Art FIG. 4 shows a bipolar 1 for interconnecting two AC systems.
Fig. 3 shows a configuration example of DC power transmission of a line. In FIG. 4, a certain AC system 1 is connected to an AC system 2 and connected to AC / DC converters 5 and 6 via conversion transformers 3 and 4.
Now, when transmitting power from the AC system 1 to the AC system 2,
The AC / DC converters 5 and 6 at one terminal function as forward converters and convert AC power into DC power. This DC power is sent to the AC / DC converters 13 and 14 at the other terminals via the conversion reactors 7, 8, 9, and 10 and the main lines 11 and 12, where the DC power is converted back to AC power, and the AC bus 17 The power is transmitted to another AC system 18 via. For convenience of explanation, AC / DC converters 5 and 13, conversion reactors 7 and 9, main line 11, neutral line
P ₁ pole the configured electrode 19, called the other electrode and P ₂ pole. The P ₁ pole and the P ₂ pole share the neutral wire 19. Conventionally,
When a ground fault occurred in the neutral wire 19, the ground circuit breaker 20 was repeatedly turned on and off so that the potential of the neutral wire became temporarily zero for the purpose of extinguishing the ground fault arc.

[0003]

Since the earthing breaker 20 for recovering the ground fault of the neutral conductor has a limit in the number of operations, if the accident does not recover even after repeating the opening and closing a certain number of times, The operation of both bipolar units had to be temporarily stopped, and the effect on the AC system was immeasurable. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an AC / DC converter that does not have a temporary fluctuation in transmission power as well as a bipolar stop.

[0004]

To achieve the above object, according to an aspect of, the present invention changes in working power of P _1-pole AC-DC converter, so as to cancel each other changes in working power of P ₂ pole, the total power Means are provided for changing the operating power of each pole regularly and periodically without affecting the power.

Since the operating power of each pole is changed regularly and periodically, a zero point is generated in the current flowing through the neutral line, and at this time, the potential of the neutral line becomes zero everywhere.
At the time of neutral current ground fault, when this current becomes zero, the ground fault arc can be extinguished.

[0005]

An embodiment will be described below with reference to the drawings. FIG.
FIG. 2 is an embodiment diagram showing what current command value is applied to each pole by the control device of the AC / DC converter according to the present invention, and FIG. 2 is a circuit configuration example diagram. First, the total operation power command value is equally divided and passed by the current command determination circuit 21 of FIG. In this case, I _d1 = I _d2 , but there is actually a control error or the like, so that I _d1 * I _d2 (* means almost equal), and the current I _dN -I _d1 -I _d2
$ 0 is flowing. Now, upon detection of ground faults in the neutral conductor, each pole current command value determining circuit based on the information, for example, as shown in FIG. 1, the P _1-pole current command value (I _d1 + ΔI _d) When given, the P ₂ pole has (I _d1 −ΔI _d )
Given current command value, on the contrary, the P ₂ poles (I _d2 + ΔI _d)
When giving the current command value, the P ₁ pole (I _d1 - [delta
The current command value of I _d ) is given, and this operation is repeated until the ground fault arc is extinguished, that is, until a neutral fault detecting device provided separately stops detecting a neutral fault. One example of determining the current command value difference ΔI _dp is shown below. P ₁
Since the direction of the current I _d1 flowing through the neutral _{conductor due} to the pole and the direction of the current I _d2 flowing through the neutral _{conductor due} to the P ₂ pole are opposite, the current I _dN flowing through the neutral _conductor is the difference between the two. When the operating powers of the bipolars are balanced, only the current corresponding to the control error flows through the neutral conductor, and is very small, usually several percent of the rated current. This relationship is the same when a ground fault occurs in the neutral wire. That is, regardless of the magnitude of the ground fault point resistance, the fault current is not much different from the current flowing through the normal neutral wire. Therefore, ΔI _dp is a value having a certain margin for the error in the current control between the P ₁ pole and the P ₂ pole.

The current I _dN flowing through the neutral wire is I _dN = I _d1 −
Since I _d2 , if the above control is repeated, I _dN > 0, =
0 and <0 are repeated, and when the current direction of the neutral line changes, a zero point of the current occurs in the neutral line. At this time, the potential of the neutral wire is zero everywhere,
The ground fault arc is extinguished. Even with such control,
Since there is no change in the total operating power, it can be repeated any number of times until the neutral fault recovers. In FIG. 1, the current command value is changed by the equally-spaced square wave. According to the above-described embodiment, without affecting the total transmission power, that is, without causing any fluctuation on the AC system side, and without relying on the ground circuit breaker having limited operational responsibilities, The fault can be eliminated.

FIG. 3 is a diagram showing how to give a power command value for another embodiment. In this embodiment, a function of adjusting the operating power of the other pole as shown in FIG. 3 in accordance with the start and stop of the other pole is provided. FIG. 3 shows a case where the P ₂ pole is started and stopped during the P ₁ pole operation.
According to the stepwise power increase when P ₂ pole is activated,
Since the step reduced the operating power of P ₁ pole,
The total transmission power does not fluctuate and has no effect on the grid.
Conversely, when P ₂ pole stopped in accordance with the power reduction of P ₂ pole P ₁
Increase the pole power, and use P ₁
It responds by increasing the number of poles. Therefore, also in this case, no fluctuation appears in the total transmission power, and no fluctuation is caused in the AC system. According to the above-described embodiment, the step-like power fluctuation accompanying the start and stop of the converter is not given to the AC system.

[0008]

As described in the foregoing, in the bipolar DC power transmission system according to the present invention, the changes in working power of P ₁ pole,
Since the configuration canceled by changes in working power of P ₂ pole, without affecting the total transmitted power can be provided a control device for the driving power of each pole regularly and periodically alterable AC-DC converter.

[Brief description of the drawings]

FIG. 1 is an embodiment diagram showing what current command value is given to each pole by a control device of an AC / DC converter according to the present invention.

FIG. 2 is a circuit diagram for determining a current command value of each pole.

FIG. 3 is a characteristic diagram of another embodiment.

FIG. 4 is a diagram illustrating a conventional technique.

[Explanation of symbols]

21 Current command value determination circuit for each pole 22 P ₁ pole control circuit 23 P ₂ pole control circuit

Claims (2)

(57) [Claims] In a bipolar DC transmission system sharing a neutral line, means for detecting DC voltage and DC current of each pole is provided.
From these, the means for calculating the DC transmission power and the operation for each pole
Means for allocating power and specified operating power for each pole
Means for controlling operation, wherein the increase / decrease of the operating power of one pole is canceled by the increase / decrease of the operating power of the other pole, and the operating power of each pole is converted regularly and periodically. A control device for an AC / DC conversion device, characterized in that: 2. The control device for an AC / DC converter according to claim 1, further comprising means for increasing or decreasing the amount of change in the operating power accompanying the stop and start of the other pole to the own pole power.