JPS6110917A - Method of controlling 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 system in which a rotary capacitor is connected to one terminal of an AC/DC converter such as a frequency converter d or a DC power transmission equipment. Regarding control method.

[Technical background of the invention and its problems]

In conventional DC interconnection systems, the capacity of the AC system to which the AC/DC converter is connected is sufficiently large compared to the capacity of the AC/DC converter, that is, it is a strong AC system, so the reactive power consumed by the AC/DC converter is It was possible to sufficiently compensate for this.

However, in recent years, so-called inverse conversion has been introduced, where the capacity of the AC system to which the AC/DC converter is connected is significantly smaller than the capacity of the converter, or where power is supplied via DC transmission to isolated islands with no AC power supply. DC interconnection equipment is often constructed in locations where there is no power source such as a synchronous generator on the AC side of the equipment. In such a system, it is preferable to install rotary capacitors (hereinafter abbreviated as R and C) for supplying reactive magnetic force. However, in a DC interconnection system connected to a weak AC system to which R and C are connected, a control method for an AC/DC converter in the event that the RoC is stopped due to maintenance inspection, an accident, etc. has not been published to date.

FIG. 2 shows a schematic block diagram of a control device for a conventional converter for DC power transmission equipment.

In the converter of the DC power transmission equipment, the DC sides of converters IA and IB are connected by a DC transmission line 3 via DC reactors 2A and 2B, respectively, and the AC sides of each converter IA and IB are connected to converter transformers 4A and 4B. , L and disconnector 5A, 5B
It is configured to be connected to the respective AC systems 6A and 6B via the AC lines 6A and 6B.

Conventional converters IA, IB have a constant margin angle control circuit 11A.
.

One circuit 13A, 13B is provided for the 11B1 constant current system, and the constant margin angle control circuits 11A, IIB set the minimum margin angle of the converter. This margin angle setting device 18A,
Adders 17A and 17B add the minimum margin angle reference value, which is the output of 18B, and the output of the constant reactive power control circuit 48, which is necessary when the converter performs reactive power control of an AC system, to obtain the margin angle reference value. It operates to follow the margin angle of converters IA and IB. In addition, the current reference value, which is the output of the constant power control circuit material, and the DC current detected by the DC current detector 2 21B are converted into current/voltage conversion circuits 22A, 2.
The DC current detection value converted by 2B into a value that is easy to handle as a control circuit is input to adder circuits 28A and 28B, and the difference is input to constant current control circuits 18A and 18B, so that the DC current flowing through DC transmission line 3 is It will be controlled to follow the current reference value.

The switches 24A and 24B are closed only on the converter side that performs reverse conversion operation of the converter, and the current margin setting device 25A.

The current margin which is the output of 25B is the current margin of the adder circuit 28A.
, 28B.

This current margin function and the constant margin angle control circuit 11
A, IIB, and the function of the control lead angle priority circuits 28A, 28B which selects only the output with the most advanced control lead angle of the converter as its output among the outputs of the constant current control circuits 18A, 18B. Now, if the switch 24B is closed and the switches 24 are open, the output of the 13 constant current control circuits is output to the 28 control lead angle priority circuits, and the output of the 13 constant current control circuits is output to the control lead angle priority circuits 28. The output of the margin angle control circuit 11B is output to 28B (for the sake of convenience, the following explanation will be based on the assumption that the switch 24 is open and the switch 24B is closed).

The outputs of the control advance angle priority circuits 28A and 213B are input to phase control circuits 29A and 29B, where they are converted into pulse signals that determine the firing timing of converters IA and IB, and pulse amplification circuits 80A and BO.
B to one converter, IB, as their gate pulse signal.

Configuring a converter control circuit in this way is a known technique, and the operating curve of such DC interconnection equipment is shown in Figure 3, with DC current Id on the horizontal axis and DC voltage Bd on the vertical axis. It is also a well-known fact that

In Fig. 8, (a), (b), and (c) are converter IA in forward converter operation (assuming that switch 24A is open, converter IA is in forward converter operation). In the operating curve, parts (a) and (b) are the regulation part determined by commutation impedance, etc., including the four converter transformers, and (b) is the constant current characteristic part due to the movement of the 18 constant current control circuits. On the other hand, )(e)(f) is the operating curve of converter IB which is in inverse converter operation (assuming switch 24B is closed, converter IB is in inverse converter operation))( E) is a constant current characteristic portion due to the operation of the constant current control circuit 18B, and (E) and (F) are portions of the constant margin angle characteristic of the converter IB due to the action of the constant margin angle control circuit 11B. Here, the difference in direct current between points (c) and (c) of the operating characteristic curve in FIG. 3 corresponds to the current margin.

The DC power transmission system converter is operated at point (A), which is the intersection of the operating curves of converter IA and converter IB in FIG.
Generally, DC transmission systems have 6 people on AC systems.

A constant power control circuit 44 is provided in the converter of the DC power transmission system in order to control the transmitted power that is interchanged six times.

The power reference value determined by the power setting device 41 and the power detection value which is the output of the power detector 43 that detects the transmitted power are input to the adder 42 with different polarities, and the output (difference) is input to the constant power control circuit material. The control circuit is configured such that the transmitted power follows the power reference value by configuring the error amplified signal as the current reference value.

In other words, as is clear from the characteristic curve in Figure 8, the converter in reverse converter operation determines the DC voltage, and the converter in forward converter operation controls the DC current to determine the transmitted power. come to control.

On the other hand, in order to control reactive power, the converter is considered to be a type of lagging load from the perspective of the AC system, regardless of whether the converter is in forward conversion operation or inverse conversion operation, and its power factor is determined by the converter's control lag. It is well known that it is approximately proportional to the angle or advance angle. Therefore, in order to control reactive power, the reactive power reference value determined by the reactive power setter 45 and the reactive power detection value which is the output of the reactive power detector 47 that detects reactive power are input to the adder 46 with different polarities. , the reactive power control circuit is configured to control the margin angle reference value by adding a signal obtained by amplifying the error of the difference in the constant reactive gravity control circuit 48 to the minimum margin angle reference value in adders 17A and 17B. be done.

Although not shown here, when controlling the reactive power of the AC system 6, it is necessary to detect the reactive power of the AC system 6A, and when controlling the reactive power of the AC system 6B, it is necessary to detect the reactive power of the AC system 6B. Of course, even if one converter is operating the forward converter and the reactive power of the AC system 6A is controlled, the output of the reactive power control circuit 48 is used to control the converter IB. If the margin angle is controlled, the control angle of the converter IA will change accordingly, so naturally the reactive power of the six AC system members will be controlled.

Now, 8 is R, C, and the case where R, C8 is connected and the reason why they are connected are as described above.

Suppose now that a, c, and B are disconnected by the circuit breaker 7 for some reason, for example, due to maintenance or an accident. At this time, as a matter of course, the short-circuit capacity of the AC system 6B decreases due to the stoppage of TL, C80), so the converter I
The voltage of the AC bus to which B is connected decreases. on the other hand,
As mentioned above, the AC/DC converter is operated by constant power control, so in order to compensate for the AC voltage drop (2), the DC current is increased to maintain the power transmission power constant. That is, in Fig. 3, the operating point of the AC/DC converter shifts from point A to point A2.Then, the consumption of reactive power by the AC/DC converter increases, so the AC voltage further decreases.Therefore, the power becomes constant again. The DC current increases due to control. This pattern is repeated, eventually leading to system collapse. There is a problem that a so-called voltage instability phenomenon occurs.

[Object of the Invention] The present invention aims to solve the above-mentioned problems and provide a control method for an AC/DC converter for stably operating the AC/DC converter. [Summary of the Invention] The present invention has the following features: , R, and C stop, the current set value of the constant margin angle control system is limited to maintain a stable AC/DC converter. [Embodiment of the Invention] An embodiment of the present invention is Shown in Figure 1. In Figure 1, the second
Components with the same functions as those in the figures are denoted by the same reference numerals, and description thereof will be omitted.

49A is a setting device, 50A is a switch that closes under the condition that R and C8 are stopped, and 51 is a low value selection circuit.

Now, the container in Figure 2. Considering the case where C8 stops, as mentioned above, the AC bus voltage to which converter IB is connected decreases, so the constant power control circuit I in FIG. 3 tries to maintain the power transmission power constant. The output value of constant power control circuit 44 increases. However, since the switch 50A is closed under the condition that R and C8 are stopped, the low value selection circuit 51A does not increase the current set value beyond the set value of the setter 49A.

Or 1. (If the output value of the constant power control circuit 44 is already equal to or higher than the set value of the setting device 49Δ while C8 is in operation, the switch 50A is closed under the condition that R and C8 have stopped. Therefore, when the switch 50A is closed, the first value selection circuit 51 sets u4.
The set value of 9A becomes the current set value.

Therefore, if you use digital simulation or a simulator to find in advance the maximum current setting value that will not cause voltage instability when n and C8 stop, and use that current setting value as the setting value of the setting device 49A, you can prevent voltage instability. Stability phenomena can be prevented.

In the above embodiment, a circuit configuration was adopted to prevent voltage instability by introducing the low value selection circuit 51A.
For example, a similar implementation can be achieved by providing a limiter to the constant power control circuit 44 itself.

〔Effect of the invention〕

As explained above, according to the present invention, R,
In a DC interconnection system where R and C are connected, if the above R and C stop, a simple operation of limiting the current setting value of the constant margin angle control system can eliminate the system caused by the '4 pressure instability phenomenon. It has the remarkable effect of preventing collapse.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a control block diagram of DC power transmission equipment to which the present invention is applied, and FIG. 8 is a diagram for explaining the operation of FIG. 2. . IA, IB...Converter, 2A, 2B...DC reactor, 3...DC transmission line, 4A, 4B・
...Converter transformer, 5A, 5B, ? ...breaker,
, 6fiL, 6B... AC system, 11 people, 11B...
・Constant current ml control circuit, 13A, 18B...constant current m
l control circuit, 17 people, 17B, 28A, 28B
, 42, 46...addition circuit, 11.18B...minimum margin angle setter, 24A, 24B...switch,
25 people, 25B...Current margin setting device, 21A,
21B...DC current detector, 22A, 22B.
...Current/voltage conversion circuit, 28 people, 28B...Control advance angle priority circuit, 29A, 29B...Phase control circuit, 30 people, 80B...Nokurusu amplifier circuit, 41...
Power setting device, 43...Power detector, 45...Reactive power setting device, 47...Reactive power detector, 44...Constant power control circuit, 电...Constant reactive power control circuit, 8 ...Rotary capacitor, 49 people...Setting device, 50A.
...Switch, 51A...Low value selection circuit. (7817) Agent Patent Attorney Noriyuki Chika (and others) Figure 1 Figure 2

Claims (1)

[Claims] An AC/DC converter having at least a constant current control system and a constant margin angle control system has an AC system A having a relatively large short circuit capacity and an AC system B having a small short circuit capacity relative to the AC/DC converter capacity.
A rotary terminal is connected to the converter station on the AC system B side.
If the rotary capacitor stops while the capacitor is connected and the power from the AC/DC converter is being transmitted from AC system A to AC system B, the current setting value of the constant current control system is limited. A method for controlling an AC/DC converter, characterized in that: