JPH0368620B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a frequency conversion device or an inverse conversion device for DC power transmission equipment, which is used for switching the lower limit value of the control delay angle in accordance with various types of accidents. Regarding control method.

[Technical background of the invention]

FIG. 1 shows a schematic diagram of a DC power transmission facility, in which AC buses 1, 1' are connected via converting transformers 2, 2' to converters 3, 3' consisting of, for example, a large number of thyristors connected in series and parallel. The thyristor converts alternating current into direct current or direct current into alternating current by controlling the firing phase of each thyristor. 4, 4' are smooth reactors, 5
is the DC transmission line, and 6 and 6' are the voltage transformers (P/
T), 7, 7' indicate instrument current transformers (C/T).
The control device in such a main circuit configuration includes constant current control circuits (ACR) 8, 8', constant voltage control circuits (AVR) 9, 9', and the like. The constant current control circuit and constant voltage control circuit each have a reference value Idp,
The deviation between Edp and the detected values Id and Ed is converted into a control voltage Ec, and this control voltage Ec is used by the control voltage selection circuit 10,
10'. the control voltage selection circuit 10;
10' is for automatically selecting the control system that advances the control angle the most among various controls, and the control voltage Ec selected here is controlled by the control voltage limiter 11,
At 11', the signal is input to ignition phase control circuits 12 and 12' which are subjected to upper and lower limiters. The ignition phase control circuits 12, 12' determine an ignition phase proportional to the control voltage Ec and output an ignition command to the thyristor. As is well known, in the AC/DC converter configured in this way, by switching the current margin (ΔI), one is operated as a forward converter under constant current control, and the other is operated as an inverse converter under constant voltage control. .

Now, in this configuration, converter 3
Assuming that is a forward converter and converter 3' is an inverse converter, during normal operation, the forward converter 3 is operated by the constant current control circuit (hereinafter abbreviated as ACR) 8, The inverter 3' is operated by the constant voltage control circuit (hereinafter abbreviated as AVR) 9'.

In conventional inverter-side control devices, the control delay angle (hereinafter abbreviated as α) is limited to a range of 90° and 160° in electrical angle. That is, the control voltage limiter 11' limits the angle to 90°≦α≦160°. Incidentally, on the forward converter side, the control voltage limiter 11 limits the angle to 10°≦α≦120°.
The reason for limiting α≧90° on the inverse converter side is to prevent the inverse converter 3' from operating as a forward converter due to a circuit failure such as ACR or AVR.

[Problems with background technology]

Now, if a ground fault occurs in the DC transmission line 5 in this state, the DC voltage on the forward converter 3 and inverse converter 3' side becomes almost zero, but regarding the DC current, the forward converter 3 side A current corresponding to the current setting value flows through the inverter 3', but the current on the inverter 3' side becomes almost zero.
Therefore, in such a state, (1) the current of the inverter 3' may be intermittent, leading to deterioration of the thyristor element.

(2) An amount equivalent to the current setting value, such as the rated current, flows through the ground fault point, so arcing during a ground fault is difficult to extinguish.

There are other problems. This is because the control voltage limiter 11' satisfies α≧90°. That is,
When a ground fault occurs, the ACR
8' is selected and a DC current corresponding to the value obtained by subtracting the current margin ΔI from the current setting value is attempted to flow, but the control voltage limiter 11' prevents α from becoming less than 90°. This is because there is a limit placed on it.

Although the above explanation is for the case where a ground fault occurs on the DC power transmission line, a similar problem occurs also when a ground fault or the like occurs on the AC bus 1 of the forward converter 3.

Therefore, an easily conceivable way to solve the above problem is to eliminate the lower limit value of the control voltage limiter, but if this is done, as mentioned above, due to circuit failure etc. It starts operating and a large current flows. Also, considering the case where a ground fault or the like occurs on the AC bus 1 of the forward converter 3, in recent years, in order to restart at high speed, when a ground fault occurs on the AC bus 1, an AC undervoltage relay, etc. A method is being considered in which the accident is detected, the forward converter 3 is placed in a bypass pair, and the accident is cleared and the system is restarted at high speed. When the reactive power required by the inverse converter 3' on the healthy end increases during the bypass spare period (strictly speaking, during the bypass pair period before the restart), and the AC system on the healthy side is weak. may cause voltage stability problems. The reason why the reactive power required by the inverse converter 3' at the healthy end is large is that while the fault is continuing, that is, while the forward converter 3 is in the bypass pair period, the DC current is calculated by subtracting the current margin from the current setting value. This is because the value is close to the rated current.

[Purpose of the invention]

Therefore, an object of the present invention has been made to eliminate such drawbacks, and is to suppress the current flowing to the ground fault point and prevent current interruption in the inverter when an accident occurs on the DC transmission line. However, in the event of an AC transmission line fault, control of the converter will reduce the DC current to suppress disturbances to the AC system during restart, and will also control the conversion equipment to prevent as much as possible an increase in DC current due to circuit failure, etc. The goal is to provide a method.

[Summary of the invention]

In order to achieve this object, the present invention is characterized in that the control delay angle lower limiter is switched in response to a DC power transmission line fault, an AC power transmission line fault, or the like.

[Embodiments of the invention]

FIG. 2 shows a control voltage limiter circuit showing an embodiment of the present invention, 13, 14, and 15 are upper and lower limiter circuits, and the upper limiter values are all the same value, but the lower limiter value is, for example, 13. 14 is a value equivalent to a control delay angle α of 85°, and 15 is a value equivalent to a control delay angle α of 70°. Also, 1
6, 17, and 18 are switches; for example, 16 is a switch that is turned on during normal operation and turned off in the event of a DC or AC transmission line accident; 17 is a switch that is turned on only in the event of an AC transmission line accident; and 18 is a switch that is turned on when an AC transmission line accident occurs. It is a switch that is turned on only when the power is turned on.

Now, in the present invention, the following control is performed by providing the control voltage limiter circuit having such a configuration in the control device on the inverter side. That is,
In FIG. 2, since the switch 16 is on during normal operation, the control voltage is limited by the upper and lower limiter circuit 13. That is, even if the constant voltage control circuit or the like malfunctions and the control voltage becomes equivalent to α=0°, for example, the upper/lower limit limiter circuit 13 becomes the control voltage equivalent to α=90°, so no large current will flow. If an accident occurs in the AC system on the forward converter side, switch 17 is activated by the accident detection signal.
is turned on, so the control voltage is equivalent to α=85°.
Therefore, since the inverter is operated with a minimum load current, the reactive power required by the inverter is minimized, and disturbances to the AC system can be suppressed. Further, when a DC transmission line failure occurs, the switch 18 is turned on by the fault detection signal, so that the control voltage becomes equivalent to α=70°, and a DC current close to the rated DC current value can flow.

In the above explanation, the upper and lower limiter circuits 14, 1
The lower limit value of 5 is equivalent to α=85°, respectively.
Although a value corresponding to α=70° was used, it goes without saying that this value is determined by taking into account the resistance value of the DC transmission line, the minimum load current, the intermittent limit current value, etc. or,
In reality, it is preferable that the switches 17 and 18 not be linked to the accident detection signal, but that when the switches 17 and 18 are turned off, they are turned back on with some time delay after the accident has been recovered.

〔Effect of the invention〕

As explained above, according to the present invention, the lower limit value of the control delay angle limiter of the converter operated in reverse is set to 90° or more during normal operation, and the lower limit value is set to 90° or more in the event of a DC circuit fault or AC circuit fault. By changing the lower limiter value to a value less than °, it is possible to prevent further accidents due to circuit failures, etc.

It is possible to suppress the current flowing through the ground fault point when a DC transmission line ground fault occurs.

In the event of an AC system accident, disturbances to the AC system can be suppressed and a high-speed restart can be achieved.

It has a remarkable effect.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a DC power transmission facility to which the present invention can be applied, and FIG. 2 is a block diagram showing only the essential parts of the present invention. 1, 1'... AC bus, 2, 2'... Conversion transformer, 3, 3'... Converter, 4, 4'... Smoothing reactor, 5... DC transmission line, 6, 6'... ...Instrument transformer, 7,7'...Instrument current transformer, 8,8'...
constant current control circuit, 9,9'... constant voltage control circuit,
10, 10'... Control voltage selection circuit, 11, 1
1'... Control voltage limiter circuit, 12, 12'...
Ignition phase control circuit, 13, 14, 15... Upper and lower limit limiter circuit, 16, 17, 18... Switch.

Claims (1)

[Scope of Claims] 1. In a DC power transmission equipment equipped with an AC/DC converter that converts AC to DC and DC to AC, the lower limit value of the control delay angle limiter of the converter operated in reverse is set to 90 during normal operation. A control method for a converter device, characterized in that the lower limit value is set to a preset lower limit value of less than 90 degrees in the event of a DC circuit failure or an AC circuit failure.