JPS6152113A - 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 provides a method for connecting an AC power system to one end of the AC power system (= accident The present invention relates to a method of controlling an AC/DC converter when this occurs.

[Technical background of the invention and its problems]

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

In the converter of the DC power transmission system, the DC sides of the converters IA and IB are connected by a DC power transmission line 3 through DC reactors 2 and 2B, respectively, and each converter worker is connected to the converter.

The AC side of IB is connected to converter transformer 4λe4B11. 6 people and 5B of each AC system via disconnectors 5A and 5B.
is configured to be connected to.

Conventional converter: 1 person, IB: constant current control circuit 11A,
IIB is equipped with constant current control circuits 1, 9A, and 13B. Constant current control circuit 11 and 11B are margin angle setter 18A that sets the minimum margin angle of the converter.

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 as a conversion device, are added to the adder 17.
Converter 1 adds the margin angle reference value added in A and 17B.
It operates to follow the margin angle of the person and IB. Further, the current reference value at the output of the constant power control circuit 44 and the DC current detection value detected by the DC current detector 21 and 21B and converted into a value that is easy to handle as a control circuit are added to the addition circuit 23. 28B, and the difference between them is input to the constant current control circuits 13A and 1.9B, thereby controlling the DC power transmission line 8.
The direct current flowing through the current is controlled to follow the current reference value. Of the switches 24 and 24B, only the one corresponding to the converter operating as an inverse converter is closed, and the current margin produced by the output of the current 7-jin setting devices 25A and 25B is manually input to the adder circuits 28A and 28B. Ru. This current margin function, the constant voltage control circuit 11, 11B, the constant current control circuit 18A,
13B, the control advance angle priority circuits 28A and 28B select the output that advances the control advance angle of the converter as the output. Assuming that the driver is open, the control advance angle priority circuits 28A and 28E are supplied with the output of the constant current control circuit 18A, and the control advance angle priority circuit 28B is supplied with the output of the margin angle control circuit 11B.
The output of is given. (For convenience of explanation, the following explanation will be made assuming that the switch 24 is open and the switch 24B is closed.) The outputs of the control advance angle priority circuits 28A and 28B are input to the phase control circuits 29 and 29B, respectively. One converter is converted into a pulse signal that determines the ignition timing of IB, and is provided as a negated pulse signal via pulse amplification circuits BOA and 80B.

Constructing the converter control circuit as described above is based on publicly available technology.

Now, an accident has occurred in the AC system 6A, and the voltage of the AC system 6N has dropped significantly. At this time, one converter cannot be commutated because it is a separately excited converter. Therefore, the fault in the AC system 6A is detected by, for example, an AC undervoltage relay, etc., and the valve connected to the same arm of the converter IA is energized, and after the fault of the AC system 6 is removed, for example, the AC undervoltage relay is used. Since the voltage relay has been restored, normal operation can be resumed.

The operation of energizing a valve connected to the same arm is usually called a bypass bare operation, and is hereinafter referred to as BP.
It is abbreviated as P.

Now, this BPP operation is an operation that consumes only reactive power because the DC voltage of the converter is zero and only DC 47Af is il and i. Therefore, if the AC system GB is strong and healthy without any accidents, in other words, if the ratio of the short-circuit capacity of the AC system 6B to the capacity of the converter, that is, the short-circuit capacity ratio is large, there will be a serious problem in the operation of the converter. does not occur.

However, if the short-circuit capacity ratio is small, there is an inherent problem of causing wide voltage fluctuations in the AC system 6B, and eventually causing system collapse of the AC system 6B. An example of a circuit configured for this purpose is shown in FIG. 3. In FIG. 3, the same elements as those in FIG. 2 are designated by the same reference numerals and their explanations will be omitted.

In FIG. 2, the output of the constant power control amount N44 was directly applied to the adder circuits 2aA and 23B, but
In the figure, in the event of an AC system accident (switch 50 opens twice)
The signal is input to the adder circuit 23 and 23B via the adder circuit 23 and 23B.

- 51A and 51B are AC voltage detectors for detecting the voltage of the AC system, respectively, and their output signals are sent to the voltage setters 52A and 52rl as well as the adder circuits 5aA and 51B.
538, and its deviation is given to each of the seven constant voltage control circuits 54, 54B. The amplified output signal is sent to the adder circuit 23 via switches 55A and 55B.

23B (=13 added constant current control circuits, configured to have a current reference value of 13B).

In FIG. 2, it is assumed that, for example, an accident occurs on an 8-phase ground road involving six people in an AC system. At this time, as described above, this AC system fault is detected by an undervoltage relay or the like, and the output signal is used to close the switch 55B and open the switch 50. Then, the output signal of the constant voltage control circuit 54B changes to maintain the voltage of the healthy end AC system 6B constant (two changes), and the output signal becomes the current reference value of the constant current control circuit 13I3, so that the healthy end AC The DC current is controlled according to the voltage fluctuation of the system 6B. Therefore, the reactive power of the AC system is controlled by one converter. In other words, if the surplus AC system 6B becomes overvoltage, the The voltage control circuit 54B suppresses the overvoltage by increasing the direct current, that is, increasing the consumption of reactive power by the conversion device,
Conversely, if the voltage of the healthy line AC system 6B decreases, the voltage drop is suppressed by reducing the DC current, that is, by reducing the consumption of reactive power by the converter.

This is because the change in AC voltage is approximately equal to the product of the change in reactive power and the actance of the AC system, so the AC voltage can be controlled by controlling the reactive power.

In addition, if an accident occurs in the AC system 6B in Fig. 2, the switch 55 will be closed and the switch 50 will be open, and in this case, the voltage control for the healthy AC system 6 people will be activated, and the following will occur. Same as in the case of the accident involving 6 people in the AC system (= the conversion device works.

However, in these cases (if we focus on the operation of the constant current control circuit on the side of the two inverters), the current reference value input to the constant current control circuit is connected via an adder. The value is smaller than the output value of the constant voltage control circuit by the amount of the current margin signal added to the adder mentioned above.This means that if the output signal value of the constant voltage control circuit and the current margin setting value are If the values are the same, the output of the adder will be "zero" and the input signal of the constant current control circuit will also be the same, so the constant current control circuit will not be able to do so.

In such a state, the DC current flowing through the DC transmission line 3 becomes non-existent or intermittent, and the intended purpose of stabilizing the AC system by controlling the converter cannot be achieved, and the converter This may lead to inconveniences such as destruction of the thyristor elements constituting the thyristor element.

[Purpose of the invention]

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks, and to minimize the influence on the healthy AC system and the AC system on the side of the accident, and maintain stable operation of the AC/DC converter. The present invention provides a control method for an AC/DC converter.

[Summary of the invention]

In order to achieve the above object, the present invention uses a BPP operation signal of a converter acting as a forward converter to generate a current reference signal as an input signal of a constant current control circuit of a converter acting as an inverse converter. Remove the current margin added to the current margin. Furthermore, when switching the current reference output from the constant power control circuit to the current reference output from the constant voltage control circuit of the undamaged AC system by BPP operation, the reactive power can be reduced by delaying the switching time by an arbitrary amount of time. This is intended to prevent the occurrence of AC system overvoltage caused by sudden changes in V').

[Embodiments of the invention]

FIG. 1 is a block diagram showing one embodiment of the present invention.

The circuit configuration in FIG. 1 will be explained below.

Similarly, in FIG. 1, the same elements as in FIGS. 2 and 3 are denoted by the same reference numerals, and explanations thereof will be omitted.

The circuit 60 is an accident detection circuit for AC undervoltage H electric appliances and the like. Human ND circuit 62. Timer circuit 63.65, inverter circuit 64. Switch 56. 59 people, 59B, 'Upper pressure setting device 58. Adder 57. It is composed of a BPP command circuit 66.

Next, the operation of this circuit will be explained.

For example, one converter operates as a forward converter with the output signal of the constant power control circuit 44 as a reference value and the output signal of the constant current control circuit 13A being given priority, while the converter IB operates as a forward converter. , an inverse converter operation in which the output signal of the constant reactive power control circuit 48 and the output of the margin angle setter 18B are added by the adder 17B as the margin angle reference value, and the output of the constant margin angle control circuit 11B is prioritized. Suppose that it is a state. Here, the AND circuit 620 input signal B is a signal indicating that one converter is a forward converter, and when one converter is a forward converter (
Second, it is a signal with "positive" logic.

In the operating state described above, suppose that the AC system 6A
B.
The PI' operation circuit 65 instantaneously operates one converter connected to the system on the second accident end side from normal converter operation to the BPP state. In this case, one converter operated by BPP is
Since the direct current cannot be controlled, the converter IB changes from the control by the constant margin angle control circuit 11B to the zero power control by the constant current control circuit 13B with the output of the constant voltage control circuit 54B as the current reference value. Transition to rate operation state.

On the other hand, while converter IA is being operated in BPP,
Since the output condition of the AND circuit 62 is satisfied, this output signal is used to control the constant current control circuit 13B of the converter IB operating as an inverse converter. 25B output signal to the switch 59
B is removed by opening the circuit.

Through these series of operations, even if the output of the constant voltage control circuit 54B reaches the minimum value at which the converter can operate stably due to a drop in the system voltage, for example, the output signal of the constant current control circuit 18B remains unchanged. , the shadow of the current margin # (assuming that the output value of the constant voltage control circuit described above is n(p, u),
When the current margin setting value is also n(pu) and the current margin is applied, the output of the adder 23B is n n
= 0 (p+ u)), and as a result, it is possible to prevent problems such as the intermittent occurrence of DC current.

Further, after the time set by the timer circuit 63, an operation is performed to shift the control from the constant power control circuit 44:2 to the control by the constant voltage circuit 54B.

According to this operation, since the control transition is performed after the constant voltage control circuit 54B responds, fluctuations in the current reference value that occur during the transition can be minimized, and the fluctuation in the current reference value that occurs during the transition can be minimized. Since fluctuations in the reactive power generated in the AC system can also be minimized, voltage fluctuations that can damage the AC system 6B can also be prevented.

On the other hand, in the accident recovery of six people in the AC system, the timer circuit 6G operates and the arbitrary value set by the voltage setting device 58 is used as the current reference value to switch the switch 5G for a period set by the circuit. Since it is configured so that it is added to the adder 57 through The occurrence of overvoltage due to reclosing can be prevented by increasing the reactive power consumption of the converter.

In the example shown in FIG. 1, only the two converter control circuits at one end where the converter is installed have been described, but it goes without saying that similar control can be performed in the event of an AC system accident on either side.

In addition, although this example has been explained as an example in which the current margin is separated, conversely, it is also possible to add a signal with a polarity opposite to that of the current margin, or to invert the polarity of the current margin. Furthermore, when the current margin is set to -α(pu), the lower limiter of the output of the constant voltage control circuit is set to -α(o, , ) under the BPP operating conditions of the forward converter. (
However, the same effect can be expected by setting k>α].

Furthermore, in the embodiments of the present invention, explanations have been given taking as an example the case where an AC system accident occurs, but not only the AC system but also the case where one converter becomes inoperable for some reason, such as continuous commutation failure, etc. (It goes without saying that the present invention is also applicable to the second case.

〔Effect of the invention〕

As explained above, according to the present invention, when an accident occurs in the AC system, the DC current of the converter does not become zero, and
By controlling the converter, it is possible to stabilize the AC system charging pressure.

[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 an AC/DC converter used in a DC transmission system, and Fig. be. IA, IB...Converter 2A, 2[3・
...DC reactor; j...DC transmission line 4 people, 4n...Converter transformer 5A, 5B...breaker 15 people, 5B...AC system 118, 11B...
- Constant voltage control circuit 18A, 13B...constant current control circuit 17A,
17B, 23A, 28B, 42.46...
-Addition circuit IgA, 18B...minimum margin angle setter 24A, 24B...S/F edge 25A, 25B...current margin setter 21 people,
21B...22 DC' current detectors, 22B...
28 current-voltage conversion circuits, 28B...control advance angle priority circuit 29A, 29B...phase control circuit 3QA,
30B...Belsueso[1] circuit 41...Power setting device 13...Psychic force detector 45...Invalid 4
Power setting device = +7... Swallow effect force detector 44... Constant power control circuit (18... Constant: net effect, 1 force control circuit 5
0.55 people, 55B...Switch 5], A, 51B...AC voltage detection circuit 52A,
52B... Voltage setting device 54A, 54B... Constant voltage control circuit 53 people, 53
B... Addition circuit 60... Accident detection circuit 62... AND circuit 68, 66... Timer circuit 64... Inverter circuit 65... BPP operation circuit 56, 59A, 59B... Switch 58 ...Voltage setting circuit 57... Addition circuit ('7817) Agent: Patent attorney Noriyuki Chika (and 1 other person) Fig. 1 Fig. 2 Fig. 3

Claims (1)

[Claims] In an AC/DC converter that has at least a constant current control system and a constant margin angle control system, if a fault occurs in the AC system on the forward converter side, the AC system fault is detected and the constant current control system on the reverse converter side is detected. A method for controlling an AC/DC converter, characterized by operating a current margin signal applied to a current control system.