JPH05227652A - Direct current transmission facility - Google Patents

Abstract

(57) [Abstract] [Purpose] In DC power transmission equipment, when the inverse converter is under constant current control, do not cause intermittent DC current even if the operating current falls below the minimum operating current range. To do. [Configuration] In DC power transmission equipment, the control of the inverse converter is constant current control, and means for detecting that the DC current is less than or equal to the minimum operating current; and by this means, control of the inverse converter is constant current control, Further, when it is detected that the direct current is below the minimum operating current, a means for keeping the direct current above the minimum operating current is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a DC power transmission facility,
In particular, the present invention relates to a DC power transmission facility that prevents DC current from being interrupted when the inverse converter is under constant current control.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a schematic configuration of a DC power transmission facility. The AC busbars 1,1 'are connected via converter transformers 2,2' to converters 3,3 ', which are, for example, series-parallel connections of a plurality of thyristors, and control the firing phase angle of each thyristor. As a result, AC is converted into DC and DC is converted into AC. 4 is a DC transmission line, and 5 is a metal return line.
In FIG. 5, one of the converters 3 and 3'is a forward converter,
The other operates as an inverse converter. FIG. 6 is an example of a block of a control circuit that determines the firing phase angle of a thyristor in such a DC power transmission facility. The control circuit has a control circuit 21 for determining the control angle of the forward converter and a control circuit 21 'for determining the control angle of the inverse converter. Each control circuit is a constant current control circuit (ACR: Automatic Current Regu) that matches the detected value Id of the direct current with the command value Idp of the direct current.
22) and a constant voltage control circuit (AVR: Automatic Voltage Regulator) 23, 2 for keeping the DC voltage constant.
3'and a constant margin angle control circuit (A
γR: Automatic γ Regulator) 24, 24 ', and the output of each control circuit is a signal selection circuit 25, 25' for selecting a minimum value or the like.
Finally selects the control angles for the forward and inverse converters. Normally, a constant current control is selected for the control of the forward converter, and a constant voltage control is selected for the control of the inverse converter, so that the current command value Idp of the inverse converter is biased by a current margin −ΔIdp.

As shown in FIG. 7, the operating point of the DC power transmission equipment resulting from such control is represented on the DC current / voltage characteristic. The straight lines 31 and 32 represent the control characteristics of the forward converter, the straight line 32 represents the constant current control characteristics of the forward converter, and the straight line 31 represents the characteristics of a constant control angle. The characteristic that the control angle is constant means that the forward converter cannot operate at a smaller control angle, and is normally controlled by the limiter of the control device. The straight lines 33, 34 and 35 are the control characteristics of the inverse converter, the straight line 33 is the constant current control characteristic of the reverse converter, the straight line 34 is the constant voltage control characteristic of the reverse converter, and the straight line 35 is the constant margin of the reverse converter. Represents angular characteristics. P, which is the intersection of the characteristics of the forward converter and the inverse converter
The points represent the operating points of the converter.

[0004]

In the above-mentioned prior art, when the AC voltage on the forward converter side is lowered, the operation of the DC power transmission equipment becomes the point P'shown in FIG. In FIG. 8, the forward converter causes a decrease in DC voltage even if the control angle is kept at a minimum,
Since the DC voltage to be maintained by the constant voltage control of the inverse converter is lower than that of the DC voltage, the forward converter has a constant minimum control angle characteristic and the inverse converter has constant current control. The operating point P'at this time is a DC voltage determined by the AC voltage and control angle on the forward converter side and a DC current determined by the constant current control of the inverse converter, that is, a current smaller than the DC command value by a current margin. Normal,
For the DC current command value, the minimum operating current is calculated so that the ripple current superimposed on the DC current will not interrupt the current, and a limit is set at this value. This value is, for example, 10 of the rated current.
The value is%. However, when the current command value is small in the above state, the DC current becomes smaller than the intended minimum operating current by the current margin as shown in FIG. 9, and the DC current is interrupted. If the DC current is intermittent, normal operation cannot be maintained, and in some cases it is necessary to detect the intermittent current and stop the converter. The present invention has been made in view of the above circumstances, and even if the operating current is in the range of the minimum operating current or less when the inverse converter is in the constant current control, the direct current is not interrupted. It is intended to provide power transmission equipment.

[0005]

In order to achieve the above object, in a direct current power transmission facility, the control of an inverse converter is constant current control, and means for detecting that the direct current is below a minimum operating current, A means is provided for keeping the direct current above the minimum operating current when it is detected by the means that the control of the inverse converter is constant current control and the direct current is below the minimum operating current.

[Operation] When the AC voltage on the forward converter side drops and the DC current operating point of the DC power transmission equipment falls below the minimum operating current due to the constant current control of the inverse converter, the DC current exceeds the minimum operating current. Therefore, the intermittent current can be prevented.

[0006]

Embodiments will be described below with reference to the drawings. Figure 1
FIG. 1 is a configuration diagram of an embodiment of a DC power transmission facility according to the present invention. In the present embodiment, the conventional control block shown in FIG. 6 has a coincidence detection circuit 11, a comparison circuit 12, a logical product circuit 13, a switch 15 closed when the output of the logical product circuit 13 is "1", and a current command value. And a bias amount setting circuit 14 for giving a bias amount ΔIdp ′. Other configurations are the same as those in FIG. In the present embodiment, the inverse converter operates in constant current control,
Moreover, the following means are used as means for detecting that the operating current is less than or equal to the minimum operating current. Match detection circuit 11
The output of the constant current control circuit 22 'of the inverse converter and the output of the signal selection circuit 25' are compared with each other, and if they match, the condition "the inverse converter is operating at constant current" is determined, and it holds. In this case, the output is set to "1". The comparison circuit 12 determines whether or not the current command value Idp will be equal to or less than the minimum operating current when the current margin ΔIdp is reduced, and outputs a logic “1” when the result is “less than or equal to the minimum operating current”. AND circuit
At 13, the logic "1" is output from the output of the coincidence detection circuit 11 and the output of the comparison circuit 12 when "the inverse converter is operating under constant current control and the operating current is less than the minimum operating current". ..

Further, the following means are used as means for keeping the operating current above the minimum operating current. AND circuit 13
When the inverter is operating under constant current control and the operating current is less than the minimum operating current, the switch 15 that closes when the output of is 1 is the bias amount of the predetermined current command value. This is realized by adding ΔIdp ′ to the current command. As described above, according to the present embodiment, it is possible to prevent the reverse converter from performing constant current control and prevent the current operating point from becoming equal to or less than the minimum operating current, and to provide a DC power transmission facility that does not interrupt the current. FIG. 2 shows a case where the AC voltage on the side of the forward converter decreases when added in the present invention, and the DC current becomes equal to or less than the minimum operating current unless added in the present invention.

FIG. 3 is a block diagram of another embodiment. In the present embodiment, as a means for detecting that the inverse converter is in constant current control operation and the operating current is less than or equal to the minimum operating current, the determination circuit 16 is used as a condition that "the inverse converter is in constant current control operation".
Is performed by determining the condition "the control angle of the forward converter is at the minimum value limit", and by determining the logical product of this and the output of the comparison circuit 12 used in the above embodiment. FIG. 4 is a block diagram of another embodiment.
In the present embodiment, the inverse converter is in constant current control operation, and the discrimination circuit 17 is provided as a means for detecting that the operating current is less than or equal to the minimum operating current, whereby the main circuit current is less than or equal to the minimum operating current. It is detected and used. Further, in FIG. 3, a means for keeping the operating current at or above the minimum operation is realized by negatively biasing the detected value of the current. In any of the examples, the effect is similar to that of the embodiment shown in FIG.

[0009]

As described above, according to the present invention, the inverse converter is under constant current control to prevent the current operating point from falling below the minimum operating current, and to prevent direct current interruption. Power transmission equipment can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating an embodiment of the present invention.

FIG. 2 is a control characteristic diagram in the case where the AC voltage on the forward converter side is reduced when the present invention is added, and the DC current is equal to or less than the minimum operating current unless the present invention is added.

FIG. 3 is a configuration diagram of another embodiment of the present invention.

FIG. 4 is a configuration diagram of still another embodiment.

FIG. 5 is a schematic configuration diagram of DC power transmission equipment.

FIG. 6 is a schematic block diagram of control of DC power transmission equipment.

FIG. 7 is a control characteristic diagram of DC power transmission equipment in normal operation.

FIG. 8 is a control characteristic diagram when the forward converter side AC voltage is reduced.

FIG. 9 is a control characteristic diagram in the case where the AC voltage on the forward converter side is reduced and the operating point of the DC current is less than or equal to the minimum operating current.

[Explanation of symbols]

 11 Match detection circuit 12 Comparison circuit 13 AND circuit 14 Current command value bias setting circuit 15 Switch 16, 17 Discrimination circuit 1, 1'AC bus 2, 2 'Transformer for transformer 3, 3' Converter 4 DC transmission line 5 Metal return route 21, 21 'Control circuit 22, 22' Constant current control circuit 23, 23 'Constant voltage control circuit 24, 24' Constant margin angle control circuit 25, 25 'Signal selection circuit

Claims (1)

[Claims] 1. In a DC power transmission facility having a forward converter and an inverse converter, means for detecting that the control of the inverse converter is constant current control and that the DC current is not more than a minimum operating current, and the means. According to the above, the DC power transmission equipment is characterized in that the control of the inverse converter is constant current control, and when it is detected that the DC current is less than or equal to the minimum operating current, the DC current is maintained at or above the minimum operating current.