JPS61236327A - 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 putting a frequency converter or a converter in a DC power transmission facility C into a bypass pair mode.

[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 C is connected and converts alternating current to direct current or direct current to alternating current by controlling the firing phase of each thyristor. 4
A, 4B are smoothing reactors, 5 is DC power transmission equipment, 6A,
6B is the instrument transformer (P, T) 7A.

7B indicates an instrument current transformer (C, T).

The control devices in such a main circuit configuration include constant current control circuits (ACR) 8A, 8B and constant margin angle control circuit (CI).
J) Consists of 9A, 9B, etc.

In addition to the constant current control circuits 8A, 8B and the constant margin angle control circuits 9A, 9B, a constant voltage control circuit (AVR) or the like may be added for controlling the DC voltage at a constant level.

Constant current control circuit 8A, 8B, jli margin angle control circuit 9
The value calculated by A and 9BC is input as a control voltage (Ec) to the minimum value selection circuit (LVG) IOA and IOB, and this minimum value selection circuit 10B advances the control angle the most among various controls. The control system is automatically selected, and the control voltage selected here is limited by the control voltage limiter circuit 11, IIB (ECL), and input to the phase control circuits 12A and 12B. The phase control circuits 12A and 12B determine the firing phase corresponding to the control voltage and output a firing pulse to the thyristor.In the AC/DC converter configured in this way,
As is well known, the current margin (Δwork) is switched (one is operated by constant current control as a forward conversion device, and the other is operated by constant margin angle control (two).

FIG. 4 is a block diagram of the converters 3A and 3B in FIG. 3,
A typical 6-phase bridge configuration is shown. Arm U, Z
, V, X, W, and Y are usually composed of a plurality of thyristor elements.

Now, each arm in such a bridge configuration ζ2 is
In the steady state, the power is applied for 12 CP periods and is stopped for 240° periods. Therefore, the design of the cooling device for this converter is designed to allow the rated current to flow under these conditions.

Therefore, for example, if arm U does not have a 240° period of rest and the rated current continues to flow, the thyristor elements that make up arm U will normally be destroyed in one or two cycles due to an increase in junction temperature. Ru.

Now, bypass pair (hereinafter abbreviated as BPP for convenience of explanation) mode is the same phase (X% phase, S phase, T
This operation simultaneously energizes the arms connected to the phase (phase), so during the BPP mode, arms U and X, arms V and Y
, either arm W or 2C double flow continues to flow. Therefore, as mentioned above, if the rated current continues to flow for 1 to 2 f cycles during the BPP mode, the BPP
The arm connected to the selected phase will be destroyed.

Naturally, BPP control has been used in the same wave number conversion device and DC power transmission, but until now it has been used during startup or during a protective operation to stop.

When starting or stopping the converter, the disturbance caused by the operation or stopping of the converter has been started or stopped at the minimum current value in order to minimize the disturbance caused by the operation or stopping of the converter. B.P.
There were no problems even when P control was used. Further, during the protection operation, C2 immediately stops the conversion device.

That is, in order to make the current zero, there was no problem even if BPP control was used as a result.

However, in recent years, when an accident such as a lightning strike occurs in an AC system to which an AC/DC converter is connected, operation is continued in BPP mode, and as soon as the accident is recovered, the AC/DC converter is switched from BPP mode to normal operation. A method of transferring the data is being considered.

In a three-phase ground fault caused by lightning strikes, etc., the reclosing time is 300 to 4
00m5, if BPP operation is performed at the rated current during this period, the converter will be destroyed.

[Purpose of the invention]

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks, without changing the design concept of conventional converters, and therefore without causing an increase in cost, and meeting new social needs C: 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 BPP operation command signal.

[Structure of the invention]

FIG. 1 is a circuit diagram of an embodiment showing only the essential parts of the present invention, and the same elements as in FIG. 3 are indicated by the same symbols. Now, if you perform BPP operation for some reason, the BP
The switch f14 is opened and the swing f15 is closed in response to a command signal for the P operation, and the set value set by the setting device 16 is provided as the current set value to the constant current control circuits 8A and 8B.

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 6-phase bridge configuration, as described above, the current in each arm is normally energized for 1200 periods and then stopped for 2400 periods. Therefore, basically, if the current is less than 1% of the rated current, there is no problem even if the current is applied continuously to each arm.

Therefore, first, the setting value of the setting device 16 is set to, for example, 33% of the rated current. When an AC system fault is detected by an AC undervoltage relay and BPP operation is performed, the signal is used to open switch 14 in Figure 1, close switch 15, release BPP operation, and turn off the converter. Normal operation (: When transitioning to normal operation, the BPP operation command signal mentioned above disappears, so switch 14 is automatically closed and switch 15 is opened to return to the previous current setting value. Therefore, during the BPP mode period, the current Since the set value is %, there is no problem even if BPP operation is performed for a long period of time.

As is clear from the above description, according to the present invention C2, new needs can be met by adding only a small number of circuits.

FIG. 2 shows another embodiment. In FIG. 2, the switch Y-17 is normally open, so the output signal of the minimum value selection circuit 18 is Idp, which is normal (: the set current setting value is input to the constant current control circuits 8A and 8B. .

If a converter PPP operation command signal is generated, C;
The signal closes the switch 17. Therefore, if the pre-set current value (Idp in Figure 2 (;)) is 5 or more, % will be automatically selected, and if the pre-set current value is below %, the value will remain unchanged during the BPP period. Therefore, this embodiment provides more fine-grained control than the embodiment shown in FIG.

〔Effect of the invention〕

As explained above, according to the present invention, when the converter is operated in BPP for some reason, the current setting value of the constant current control circuit is set to the continuous current permissible current value of the arm or less by the command signal for the BPP operation. This has the remarkable effect of being able to meet the new needs of activating the group converter after a long period of BPPP operation without incurring an increase in the cost of the converter.

[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. 8A, 8B... constant current control circuit 9A, 9B constant current control circuit 10A, IOB, 18-minimum value selection circuit 14.15.1
7--Swin f 13.13B-Adder 16-・
・Setting device. (7317) Agent Patent Attorney Noriyuki Chika (and others)
Figure 2 Idp Figure 3

Claims (1)

[Claims] In an AC/DC converter equipped with at least a constant current control system and a constant margin angle control system, when the converter is put into bypass pair mode, the current setting value of the constant current control system must be set to a predetermined value or less. Characteristic control method of AC/DC converter.