JPH04236131A - Controller for converter - Google Patents

Abstract

PURPOSE:To stably operate an AC system and converter by detecting the hunting of a control system and automatically changing the gain of the control system. CONSTITUTION:The variation of the hunting of a control system is detected by means of a primary delay circuit 17 and adder circuit 18. When it is discriminated that the hunting becomes larger than a set value by means of level detection circuits 19 and 20, monostable multivibrators 21 and 22 are actuated. In case the hunting continues and the set time of a timer circuit 24 has elapsed during the time of the circuits 21 and 22, a signal is inputted to a reactive power decision circuit 14 and the gain of the control system is lowered. Therefore, even when the hunting occurs due to a decrease in the ground capacity caused by the accident of an AC system or a change in the status of a load, stable operation can be maintained by lowering the gain of the control system.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

[Industrial Application Field] The present invention relates to a control device for a converter connected to an AC system, such as a reactive power converter or an AC/DC converter, and in particular a converter capable of suppressing hunting that occurs due to a decrease in short-circuit capacity. The present invention relates to a control device for a device.

0002

2. Description of the Related Art A conventional technique in which a reactive power compensator is used as a converter will be described with reference to FIG.

[0003] In the figure, an AC power supply 1 and a power supply impedance
The main circuit 3 of the reactive power compensator connected to the power system equivalently represented by the dance 2 has a capacitor 4 and a reactor 5 connected in parallel, and the reactor 5 is connected to a thyristor 6,
It is constructed by connecting 7 anti-parallel circuits in series.

On the other hand, in the control circuit 10, a voltage detection circuit 11 detects the voltage of the power system, and a deviation detection circuit 13 detects the deviation between this detected value V and a reference value Vref set in a reference voltage setting circuit 12. ing. On the other hand, the current from the power system is detected by the output current detection circuit 21, and this detected value I is also input to the deviation detection circuit 13. The deviation detection circuit 13 provides a deviation output obtained according to the difference between the two voltage input signals V and Vref and the current input signal I to a reactive power determining circuit 14 comprising an amplifier circuit, a phase compensation circuit, and the like. The reactive power determining circuit 14 supplies a reactive power signal to be compensated determined according to the voltage deviation to the thyristor firing angle control circuit 15, and sets the firing pulses of the thyristors 6 and 7 of the main circuit 3 according to the reactive power signal. Generate in phase. This ignition pulse is applied via a pulse amplifier 16 to the gates of the thyristors 6,7.

In this configuration, when the voltage of the power system decreases, the voltage detection circuit 11 detects the system voltage V, and the deviation between this voltage V and the reference value Vref is detected by the deviation detection circuit 13.
Detected in This deviation is the output I of the output current detector 21.
In some cases, it may be corrected. The output signal of the deviation detection circuit 13 is further amplified by the reactive power determining circuit 14 to become a reactive power signal, and the firing angle control circuit outputs a firing pulse with a phase corresponding to this signal. This firing pulse output is amplified by a pulse amplifier 16 to fire the thyristors 6 and 7. As a result, the lagging current flowing through the reactor 5 decreases, and the sum total with the leading phase current flowing through the capacitor 4 changes, thereby suppressing a drop in the system voltage.

On the other hand, when the grid voltage increases, feedback control is performed to control the firing pulse phases of the thyristors 6 and 7 to increase the current flowing to the reactor 5 and suppress the rise in the grid voltage. Implemented.

[0007]

SUMMARY OF THE INVENTION In a reactive power compensator and an AC/DC converter, the minimum short-circuit capacity for operation is determined. However, if an accident occurs in the AC system, the converter, etc., or if the short-circuit capacity of the system changes significantly due to load conditions, it is necessary to change the gain of the converter. If the short-circuit capacity of the grid decreases while the gain of the converter remains high, hunting will occur and the grid voltage will fluctuate, not only making stable operation impossible but also causing overvoltage or alternating current adversely affect the system. Furthermore, in AC/DC converters installed for the purpose of DC power transmission and frequency conversion, there is a problem that commutation failure on the inverter side is induced, making stable operation impossible.

The present invention detects hunting in a control system from a control voltage signal (hereinafter referred to as Ec) ΔV of a control device, and automatically changes the gain. If the AC/DC converter is not stable even if the gain is lowered, and if multiple converters are connected in parallel, the AC system and converter can be stabilized by automatically changing the gain according to the operating conditions. The purpose of the present invention is to provide a method for operating a conversion device that allows stable operation. [Structure of the invention]

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a reactive power compensator connected to an AC system,
In a control device for a converter such as an AC/DC converter, means for detecting hunting that occurs due to a reduction in short-circuit capacity due to an accident in the AC system or a change in load conditions; The present invention is characterized in that it includes means for lowering the gain of a control system that controls.

0010

[Operation] In this invention, even if an accident or the like occurs in the AC system and the converter, and the short-circuit capacity of the AC system changes and the control system becomes unstable, the control system can be controlled before a trip occurs due to a serious failure of the converter. Stable operation can be maintained by lowering the gain.

[0011]

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, the first-order delay circuit 17 is a circuit that creates a standard for detecting hunting in the control voltage signal Ec, and calculates the average value of Ec so that the actual Ec and the hunting variation can be detected by the addition circuit 18. It is configured. Furthermore, when the hunting becomes larger than the value set by the level detection circuits 19 and 20, the output of the level detection circuits 19 and 20 becomes "1", and the monomulti circuits 21 and 22 operate. Since this mono multi circuit is configured with a retrigger mono multi circuit, if hunting continues within the time of the mono multi circuit, the output of the mono multi circuit becomes "1" continuously and the timer circuit 24
After the time has elapsed, a signal is input to the reactive power determining circuit 14 to reduce the gain of the control system.

Referring to FIG. 3, a case where hunting occurs due to a system accident will be explained. Assume that an accident occurs at the timing in (f) and the short circuit capacity becomes small. In the waveform shown in (a), it is assumed that hunting occurs at Ec. The waveform shown in (b) is the output of the first-order lag circuit and has a large time constant, so the average value of Ec is detected and becomes a flat value. The two solid lines shown in (c) are the set values of the level detection circuit, and the dotted line in the middle is the output of the first-order lag circuit 17. In the waveform shown in (d), the signal shown by the solid line represents the output of the level detection circuit 19, and the output shown by the dotted line is the output of the retrigger mono-multi circuit 21. Although only an example in which only the positive amplitude is detected is explained here, the negative side detection circuit L
The same applies to D20 and the mono multi-circuit 22. When continuous hunting continues and exceeds the set value of the timer circuit 24, a signal is detected as shown in (e), and in the SVC device, the signal is input to the reactive power determining circuit 14 and the hunting is converged. It works to reduce the gain up to. Further, FIG. 2 shows an example of a frequency converter and DC power transmission equipment. The stability of the control system in a separately excited converter depends on the short-circuit capacity of the system and the converter capacity, so by reducing the current reference of the current reference circuit 26 by hunting the control voltage Ec, Even if the short-circuit capacity of the system is significantly reduced, it is possible to maintain operation by preventing trip accidents due to serious converter failure, although the transmission power is reduced. Furthermore, in a reactive power compensator, when multiple converters are connected in parallel, the detection circuit 30 detects the gain when multiple converters are operated and when one converter is operated using an operating signal or converter current, etc.
By detecting and automatically switching the gain, it is possible to maintain more stable operation in combination with a gain reduction circuit based on hunting, even in a reactive power compensator that requires high-speed control.

[0013] Although an example of detecting hunting in the control system using Ec has been described, hunting can also be detected by similarly detecting ΔV, ΔI, ΔQ, ΔP, etc.

[0014]

As explained above, according to the present invention, if hunting occurs due to a decrease in short-circuit capacity due to an accident in the AC system or a change in load conditions, the hunting is detected by the detection means and converted. Stable operation can be maintained by lowering the gain of the control system that controls the device.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention when a reactive power compensator is used as a converter.

FIG. 2 is a configuration diagram showing an embodiment of the present invention when an AC/DC converter is used as the converter.

FIG. 3 is a waveform diagram for explaining the operation of the present invention.

FIG. 4 is a configuration diagram of a conventional device using a reactive power compensator as a converter.

[Explanation of symbols]

1...AC system, 2...AC impedance, 3...main circuit,
4... Capacitor, 5... Reactor, 6, 7,... Thyristor, 9... Current detection circuit, 10... Control circuit, 11... Voltage detection circuit, 12... Reference voltage setting circuit, 13... Deviation detection circuit, 14... Reactive power determination Circuit, 15... Firing angle control circuit, 1
6... Pulse amplifier, 17... First order delay circuit 18... Adding circuit, 19, 20... Level detection circuit, 21, 22... Mono multi circuit, 23... OR circuit, 24... Time delay circuit,
30...Driving status detection circuit.

Claims (1)

[Claims] Claim 1: In a control device for a converter such as a reactive power compensator or an AC/DC converter connected to an AC system, hunting occurs due to a decrease in short-circuit capacity due to an accident in the AC system or a change in load conditions. What is claimed is: 1. A control device for a converter, comprising: means for detecting the change in the converter; and means for reducing the gain of a control system for controlling the converter in response to the detecting means.