JPS61236328A - Control system for ac-dc converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control method for an AC/DC converter when a commutation failure occurs in an AC/DC converter such as a frequency converter or a DC power transmission facility.

[Technical background of the invention and its problems]

FIG. 3 shows a schematic configuration diagram of a DC power transmission facility, in which AC buses IA and IB are connected to a converter 3A consisting of a series-parallel connection of a plurality of thyristors, for example, through converting transformers 2A and 2B.
3B, and converts alternating current into direct current or vice versa by controlling the firing phase of each thyristor. 4
A, 4B are smoothing reactors, 5 is a DC transmission line, 5A,
5B indicates a potential transformer (P, T), and 7A and 7B indicate a potential current transformer (C, T).

The control device in such a main circuit configuration is a constant current control circuit (ACR) 8A, 8B and a constant voltage control circuit (CER).
Consists of 9A, 9B, etc. In addition, the constant current control circuit g
In addition to the constant margin angle control circuits 9A and 9B, there is a constant voltage control circuit (AVR) for controlling the DC voltage at a constant level.
etc. may be added. Constant current control circuit gA, 3B,
The value calculated by the constant margin angle control circuits 9A and 9B is used as the control voltage (Ec) by the minimum value selection circuit (LVG) IO
A, input to IOH, this minimum value selection circuit 10A
, IOB automatically selects the control system that advances the control angle the most among various controls, and the control voltage selected here is the control voltage limiter circuit 11A, IIB (BCL
), a limiter is applied by the phase control circuit 12A.
, 12B. This phase control circuit 12A, 1
2B determines the firing phase corresponding to the control voltage and outputs a firing pulse to the thyristor.

In the AC/DC converter configured in this manner, one is operated as a layer converter under constant current control and the other is operated under constant margin angle control by switching the current margin (ΔF) as is well known.

FIG. 4 is a block diagram of the converters 3A and 3B in FIG. 3,
A typical 6-phase bridge configuration is shown.

Arms U, Z, V, X, W, and Y are usually composed of a plurality of thyristor elements.

Now, in a steady state, each arm in such a bridge configuration is energized for 1200 periods and is inactive for 2400 periods. Therefore, the design of the cooling device for this converter is designed to allow the rated current to flow under these conditions.

Therefore, if the rated current continues to flow, for example, without a pause during the arm U K 240° period, normally 1
In ~2 cycles, the junction temperature of the thyristor elements forming arm U increases and the thyristor elements are destroyed.

Now, the causes of commutation failure can be broadly classified into two types: one is due to a so-called circuit failure such as loss of the gate pulse to the converter, and the other is due to a circuit failure when the converter is connected. Some of these problems are caused by AC system disturbances (AC system accidents, AC system waveform distortion, etc.). In the conventional method, when a commutation failure occurs for any reason, the commutation failure is detected and the control advance angle (hereinafter abbreviated as β for convenience of explanation) is advanced. If the conversion continued, the conversion device was immediately stopped temporarily and restarted after a predetermined period of time, or permanently stopped. Naturally, if a circuit failure is detected by a monitor circuit or the like, a permanent stop will be immediately performed.

In recent years, systems in which AC/DC converters are connected to weak AC systems have been increasing. Naturally, in a weak AC system, small disturbances in the AC system induce large disturbances. Therefore, in such systems, the likelihood of commutation failures occurring increases.

If the conventional system were to be used and the converter was stopped immediately after commutation failure occurred two or three times in a row, the operating rate would drop significantly. Therefore, it is preferable to use a control system that allows operation to continue even if a commutation failure occurs many times, and to resume normal operation as soon as the cause is removed.

However, if operation continues under such conditions, the converter may be destroyed. This is the case as follows.

In Figure 4, each arm is U −+ Z −+ V→
A commutation operation is performed by the head pressure of X → W → Y → U, but now that arm U and arm 2 are energized, arm U cannot commutate to arm ■, and commutation also occurs to arm W. This is the case where the rated current continues to flow through the arm U. In such a case, as described above, the thyristor element of arm U will be destroyed.

[Purpose of the invention]

Therefore, it is an object of the present invention to eliminate the above-mentioned drawbacks, without changing the design concept of conventional converters, and therefore without incurring an increase in cost, and meeting new social needs. The aim is to provide a control system for an AC/DC converter that can handle the following situations.

[Summary of the invention]

In order to achieve the above object, the present invention proposes that the current set value of the constant margin angle control system be set to a predetermined value or less using a commutation failure detection signal.

[Embodiments of the invention]

FIG. 1 is a circuit diagram showing an embodiment of only the main parts of the present invention, and the same elements as in FIG. 3 are indicated by the same symbols. If a commutation failure occurs for some reason, the commutation failure detection signal opens the switch 14, closes the switch 15, and the setting value set by the setting device 16 is applied to the constant current control circuit 3A.
, 8B as the current setting value.

In the above example, the converters 3A and 3B have a six-phase bridge configuration, so the present invention will be explained in detail again using that configuration.

In the six-phase Noritsu configuration, as described above, the current in each arm is normally applied for a period of 120° and stopped for a period of 240°. Therefore, basically, if the current is 33% or less of the rated current, there is no problem even if the current is continuously passed through each arm.

Therefore, first, the setting value of the setting device 16 is set to, for example, 1K of the rated current. Commutation failure is detected by a commutation failure detection relay, and the detection signal opens switch 14 in FIG. 1 and closes switch 15. K to ensure normal commutation
If this occurs, the detection signal disappears, and the switch 14 is automatically closed and the switch 15 is opened, returning to the previous current setting value. Therefore, during the commutation failure period, the current setting value will be 33%, even if the There is no problem in continuing to operate the converter even during the period when a flow failure occurs.

As is clear from the above description, according to the present invention, new needs can be met by adding only a small number of circuits.

FIG. 2 shows another embodiment. In FIG. 2, the switch 17 is normally open, so the output signal of the minimum value selection circuit 18 is Idp, and the normally set current value is input to the constant current control circuits 3A and 3B. If a commutation failure is detected, the signal closes the switch 17. Therefore, the pre-set current value (I in Fig. 2)
If dp ) is 33% or more, 33% is automatically selected, and if the pre-set current value is 33% or less, that value will remain selected even during the commutation failure period. Therefore,
This embodiment provides more detailed control than the embodiment shown in FIG.

〔Effect of the invention〕

As explained above, according to the present invention, if the converter fails commutation for some reason, the detection signal can be used to reduce the current setting value of the constant current control circuit to the continuous energization allowable current value of the arm or less. As a result, the converter can continue to operate even during a commutation failure period without increasing the cost of the converter, and pre-current operation can be resumed immediately after commutation failure recovery, improving the operating rate and improving the operation rate, especially when the AC/DC converter is weak. It has a remarkable effect that it can be applied when connected to an AC system.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the main part of the present invention, Fig. 2 is a circuit diagram showing another embodiment of the invention, Fig. 3 is a schematic configuration diagram of DC power transmission, and Fig. 4 is a 6-phase converter. FIG. 3 is a diagram showing a bridge configuration. gA, QB...constant current control circuit, 9A, 9B...
Constant current control circuit, IOA, 10B, 18... Minimum value selection circuit, 14, 15, 17... Switch, 13.1
3B...Adder, 16...Setter. (7317) Agent: Patent Attorney Noriyuki Chika (
1 other person) / 8 al al Figure 2

Claims (1)

[Claims] At least in an AC/DC converter equipped with a constant current control system and a constant margin angle control system, when a commutation failure occurs, the commutation failure is detected and the current setting value of the constant current control system is set to a predetermined value. A control method for an AC/DC converter that is characterized by lowering the voltage below a certain value.