JPS619126A - 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 method for controlling an AC/DC converter in a system in which a rotary capacitor is connected to one terminal of the AC/DC converter such as a frequency converter or DC power transmission equipment. .

[Technical background of the invention and its problems]

In a conventional DC interconnection system, 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. It was possible to sufficiently supplement electricity. 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 a rotary capacitor (hereinafter abbreviated as RoC) for supplying reactive power. However, in a DC interconnection system that is connected to a weak AC system to which R and C are connected, there is no known control method for the AC/DC converter in the event that R or C is stopped due to maintenance or an accident. do not have.

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

The converter of the DC power transmission equipment requires one converter, and the DC side of the IB has two DC reactors, each connected by a DC transmission line 3 via 2B, and one converter for each.

The AC side of IB is connected to 1 converter transformer, and the AC side of slB is connected to 6 AC systems, 6B, respectively, via 4 converter transformers, 4B, L, and disconnectors 5A, 5B. It is composed of

Conventional converters IA and IB have 11 constant margin angle control circuits,
11B, constant current control circuits 13A and 13B, and a constant margin angle control circuit 11A and 111B sets the minimum margin angle of the converter. This margin angle setting device 18A.

The maximum φ margin angle reference value, which is the output of 18B, and the output of the constant reactive power control circuit, which is necessary when the converter performs reactive power control of an AC system, are added by adder 17 and 17B, and the margin angle is It operates so that one converter follows the reference value with a margin angle of 1B. In addition, the current reference value that is the output of the constant power control circuit 44 and the DC current detected by the DC current detectors 21A and 21B are converted to the current/IE pressure conversion circuit 22A and 22.
The DC current detection value converted by B into a value that is easy to handle as a control circuit is input to the adder circuit 23A123B, and the difference is input to the constant current control circuit 13A.

By inputting 13B lζ, the DC current flowing through the DC power transmission line 3 is controlled to follow the current reference value 1.

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

The current margin which is the output of 25B is the current margin of the adder circuit 23A.
, 23B.

This current margin function and the constant margin angle control circuit 11
A, IIB, the function of the control lead angle priority circuit 28, 28B which selects as its output only the output with the most advanced control lead angle of the converter among the outputs of the constant current control circuits 13A and 13B; Now, if switch 24B is closed and switch 24 is open, then the control advance angle priority circuit 28A.

1, □, □＃[m*13 eh. 6ka, 8□ゎ1. This is the margin angle control circuit 11B.
(For convenience of future explanation, switch 24B
is open and switch 24B is closed).

The outputs of the control advance angle priority circuits 28 and 28B are input to the phase control circuits 29A and 29B, where they are converted into pulse signals that determine the firing timing of the converter and IB, and the outputs of the control advance angle priority circuits 28 and 28B are input to the pulse amplification circuit 30. , 30B to converters 1+IB as their gate pulse signals.

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 Figure 3, (a), (b), and H are the operations of converter IA in forward converter operation (assuming that 24 switches are open, converter IA is in forward converter operation). With a curve (
Parts (a) and (b) are regulation parts determined by the commutation impedance including the four converter transformers, and parts (b) and (c) are parts of constant current characteristics due to the movement of the constant current control circuit 13A. On the other hand, (→(e) and (f) are the operating curves of converter IB in inverse converter operation (assuming switch 24B is closed, converter IB is in inverse converter operation)) (E) is a constant current characteristic part due to the movement of the constant current control circuit 13B, and (E) and (F) are the constant margin angle control circuit 11.
This is a part of the constant margin angle characteristic of the converter IB due to the function of B. Here, the difference in DC current between points (C) and (→) of the operating characteristic curve in FIG. 3 corresponds to the current margin.

The converter of the DC transmission system is operated at the intersection of the operating curves of converter IA and converter IB in Fig. A constant power control circuit 44 is provided in the converter of the DC transmission system in order to control the transmitted power.It is determined by the power setting device 41!The output of the power detector 43 that detects the power reference value and the transmitted power is determined by the power setting device 41. The power detection value is inputted to the adder 42# with different polarities, and the output (difference) thereof is error amplified by the constant power control circuit 4, and the signal is used as the current reference value. The control circuit is configured so that the transmitted power follows the value.

In other words, as is clear from the characteristic curve in Figure 3, 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 respective AC system, regardless of whether it is in forward conversion operation or inverse conversion operation, and its power factor is the control delay of the converter. It is well known that the angle or lead angle is approximately proportional to 1. Therefore, in order to control the 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 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 with the minimum margin angle reference value using adders 17A and 17B. Ru.

Although not shown here, when controlling the reactive power of the AC system 6A, it is necessary to detect the AC system 6 people, and when controlling the reactive power of the AC system 6B, it is possible to detect the reactive power of the AC system 6B. Of course, even if one converter is operating as a forward converter and controlling the reactive power of six people in an AC system, the output of the reactive power control circuit will control the converter. If the margin angle of 1B is controlled, the control angle of one converter changes accordingly, so naturally the reactive power of the six AC system members will be controlled.

Now, 8 is R and C, and the case where these a, c, and B are connected and the reason why they are connected are as described above.

Now, suppose that this R0C8 is disconnected at the circuit breaker 7 for some reason, for example, due to maintenance inspection or an accident. At this time, as a matter of course, the short-circuit capacity of the AC system 6B decreases due to the stop of R1C8, so the voltage of the AC bus to which the converter IB 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 power transmission power due to a drop in AC voltage, it is necessary to increase the DC current to maintain the power transmission power constant. do. That is, in FIG. 3, the operating point of the AC/DC converter shifts from the "man" point to the "man" point. Then, since the consumption of reactive power by the AC/DC converter increases, the AC voltage further decreases. Therefore, the DC current increases again by constant power control. This pattern repeats, eventually leading to system collapse. There is a problem that a so-called voltage instability phenomenon occurs.

OBJECTS OF THE INVENTION The present invention aims to eliminate the above-mentioned problems and provide a method for controlling an AC/DC converter to operate the AC/DC converter stably.

[Summary of the invention]

The present invention aims to maintain a stable AC/DC converter by correcting the current setting value of the constant margin angle control system based on the AC voltage value at the receiving end when R and C are stopped.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG. 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.

In FIG. 1, the AC voltage of AC system IB is detected by AC voltage detector 49A, and the detected value is sent to current set value correction circuit 50A. This current setting value correction circuit 50A is
As the AC voltage value detected by the AC voltage detector 49A decreases, the output value of the constant current control circuit is decreased via the switch 51A, that is, the current setting value is decreased.

The switch 51A is a switch shown in the figure when R0C8 is stopped, and 52A is an adder circuit.

Now, if we consider the case where the box C in FIG. 2 stops, the AC bus voltage to which the converter IB is connected drops, as described above. Then, the output of the current setting value correction circuit 50 increases in accordance with the amount of decrease, and the output is inputted to the addition circuit 52A via the switch 51A.

That is, the current setting value decreases. Naturally, as the current setting decreases, the DC current also decreases, but a decrease in the DC current isometrically reduces the reactive power consumed by the AC/DC converter, so the AC system IB Voltage drop is improved. When the voltage of the AC system IB is improved, the output of the current setting value correction circuit 50A decreases and the current setting value increases again. However, since the current setting value correction circuit 50A is a feedback control system, It will calm down.

When the present invention is applied to actual equipment, it is not preferable that the current setting value correction circuit 5M operates due to slight alternating current voltage fluctuations. Therefore, in this case, in FIG. 1, the detection value of the AC voltage detector 49A is configured to be input to the current set value correction circuit 50A through a dead zone of, for example, 10%.

In other words, the current setting value correction circuit 50A is not activated by slight alternating current voltage fluctuations, but is activated only when the alternating current voltage becomes 10% or less. In this way, the current setting value correction circuit 50A will not operate unnecessarily, and the operating characteristics will be improved.

〔Effect of the invention〕

As explained above, according to the present invention, the LC
If R1C stops in a DC-interconnected system where a This has the remarkable effect of preventing system collapse.

[Brief explanation of the drawing]

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. 3 is a diagram for explaining the operation of Fig. 2. . IAj IB...Converter 2AI2B...DC reactor 3...DC transmission line 4 people, 4B...
Converter transformer 5 people + 5B + 7... Breaker 6
A + 6 B...AC system 11A, IIB...constant power control circuit 13A, 13B...constant current control circuit 17 people, 17B, 23A, 23B, 42.46...addition circuit 18A71□8B・・Minimum margin angle setting device 24A
124B...25 switches, 25B...Current margin setter 2IAI21
B... DC current detector, 22A, 22B... Current-voltage conversion circuit 28A,
28B... Control advance angle priority circuit 29A, 29B...
Phase control circuit 30A130B-/'#-Xt4[[1B
f41...Power setting device 43...21. Power detector 45..., 1. Reactive power setter 47...0, Reactive power detector 44... Constant power control circuit 48... Constant reactive power control circuit 8... Rotary capacitor 49A. ...AC voltage detector 50A...Current set value correction circuit 51 people...Switch (7317) Representative Patent Attorney Kensuke Noriyuki (and 1 other person) Fig. 1 Fig. 2 Fig. 3

Claims (1)

[Claims] (1) An AC/DC converter having at least a constant current control system and a constant margin angle control system is connected to 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. and the rotary capacitor was connected to the converter station on the AC system B side, and the rotary capacitor stopped while the power from the AC/DC converter was being transmitted from AC system A to AC system B. In this case, a current setting value of the constant current control system is corrected based on an AC voltage value of an AC system B at a power receiving end.