JPH0353872B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for starting an AC/DC converter that is capable of stably starting an AC/DC converter that is directly connected to a generator.

(Prior Art) Conventionally, there are various methods for starting an AC/DC converter, but one of them is to set the control delay angle (hereinafter referred to as α) at the time of starting to around 90 degrees electrical angle. A method is adopted in which the conversion device is deblocked at the above α, and after deblocking, the transition is controlled so that a predetermined α is achieved. This method has the advantage that systematic disturbances can be relatively suppressed.

FIG. 1 shows a schematic configuration of an AC/DC converter that employs this type of method. In the figure,
The AC buses 1, 1' are connected via converting transformers 2, 2' to converters 3, 3' consisting of, for example, a number of thyristors connected in series and parallel, and the firing phase of each thyristor is controlled. Converts alternating current to direct current or direct current to alternating current. 4, 4' are smooth reactors,
5 is a DC power transmission line, 6 and 6' are potential transformers (P/T), and 7 and 7' are potential current transformers (C/T). The control device in such a main circuit configuration includes constant current control circuits (ACR) 8, 8', constant voltage control circuits (AVR) 9, 9', and the like.
Constant current control circuit 8, 8', constant voltage control circuit 9,
9' converts the deviation between the reference values I _dp , E _dp and the detected values I _d , E _d, respectively, into a control voltage E _c , and this control voltage E _c is input to the control voltage selection circuits 10, 10'. . The control voltage selection circuits 10 and 10' automatically select the control system that advances the control angle most among various types of control, and the control voltage selection circuit 10, 10' automatically selects the control system that advances the control angle most, and the control voltage E _c selected here is
is the upper limit at the control voltage limiter circuits 11 and 11',
Ignition phase control circuit 1 with lower limit limiter applied
2, 12'. The ignition phase control circuits 12, 12' determine an ignition phase proportional to the control voltage E _c and output an ignition command to the thyristor. As is well known, in AC/DC converters configured in this manner, one is operated as a forward converter under constant current control and the other is operated as an inverse converter under constant voltage control by switching the current margin (ΔI). .

Now, in equipment with such a configuration,
FIG. 2 shows a load start-up pattern when the above-mentioned start-up method is adopted. In FIG. 2, it is assumed that the current reference value I _dp at startup is 10% of the rated value.
Naturally, the smaller the current reference value I _dp , the smaller the systematic disturbance caused by converter startup. _dp cannot be lower than 10%. That is, if it is less than 10%, there is a risk that the current will be interrupted, and as a result, the thyristor element may be destroyed. Therefore, in conventional equipment, the minimum current reference value is 10%. Further, in FIG. 2, the time until the transmitted power rises to 10%, ie, _T1 , is about 200 ms to 300 ms.

(Problems to be Solved by the Invention) Now, in FIG. 1, consider a case where the AC bus 1 is directly connected to a generator via a step-up transformer or the like. For example, there is a case where nuclear power is transmitted to a consumption area via an AC/DC converter. The same applies not only to nuclear power but also to thermal power. In nuclear power generation, when the rated load is increased from a no-load state, it is done slowly over a long period of time, and an example is shown in Figure 3. That is, at the beginning of startup, the generator output G ₁ is a few percent of the rated value, the time of T ₁ is several tens of seconds, the time from T ₁ to T ₂ is about 10 minutes, and the generator output G ₁ to generator output G ₂ (Usually 10% of the rating)
The time from T ₂ to T ₃ is about 1 day, and the time from T ₄ to T ₅ , that is, the time to start up the generator output from G ₂ to the rated output, is about 1 hour. In the case of thermal power, although it is not as fast as nuclear power, it is started up at a speed that is incomparable to the load start-up speed of an AC/DC converter. Therefore, in an AC/DC converter directly connected to a generator, the above-mentioned conventional starting method cannot be adopted, and there is a strong demand for a new starting method.

An object of the present invention is to provide a method for starting an AC/DC converter that is capable of stably starting an AC/DC converter that is directly connected to a generator.

[Structure of the invention]

(Means and effects for solving the problem) In order to achieve the above object, the present invention provides a generator that converts alternating current into direct current or direct current into alternating current by controlling a converter with a control device. In a method for starting a directly connected AC/DC converter, if the frequency of the generator drops below a predetermined value when starting the AC/DC converter, the AC/DC converter is activated by an amount corresponding to the frequency deviation from the predetermined value. By correcting the DC voltage reference value to a small value and controlling the DC voltage of the AC/DC converter in accordance with the corrected DC voltage reference value, it is possible to suppress significant frequency fluctuations, thereby reducing the generator's low output. It is possible to perform interconnected operation with a DC power transmission device from the area, and to prevent current interruption in the AC/DC converter.

(Example) Hereinafter, an example of the present invention shown in the drawings will be described.

FIG. 4 is a block diagram showing an example of the configuration of the main parts of the AC/DC converter according to the present invention. In FIG. 4, 51 is a control circuit which is a combination of proportional, integral, differential elements, etc. and has a control function F(s).
A predetermined value of the frequency of the AC bus 1 (or 1') directly connected to the turbine generator (usually 50Hz or
The output signal from a frequency deviation detector (not shown) that detects the deviation Δ from the frequency deviation Δ from 60 Hz) is input, and is converted into a voltage signal proportional to the frequency deviation Δ and output. Reference numeral 52 denotes a limiter circuit which receives the output signal of the control circuit 51, and applies its output to the constant voltage control circuit 9 (or 9') together with the reference value E _dp and the detected value E _d .

Here, the limiter circuit 52 limits the positive output from the control circuit 51 and does not send that output, and outputs an output proportional to the magnitude of the negative output to the reference value E. The configuration is such that the reference value E _dp is apparently reduced by being given as a correction signal for _dp .

Note that in the above, the output signal from the control circuit 51 is obtained as a signal that ultimately reduces the frequency deviation Δ.

Furthermore, the output of the limiter circuit 52 is actually configured to be applied to each of the constant voltage control circuits 9 and 9' in FIG.
In its original meaning, the output of the constant voltage control circuit should be given as the control voltage E _c to the selected constant voltage control circuit 9 or 9' with priority. In addition, here, one converter 3
Assuming that the converter 3' is operated as a forward converter under constant current control and the other converter 3' is operated as an inverse converter under constant voltage control, the output of the limiter circuit 52 is applied to the constant voltage control circuit 9'. Let's talk about the case.

Next, a method of starting up the AC/DC converter of this embodiment based on this configuration will be described.

When steam enters the turbine generator, which is currently operating under no load at the rated frequency, the turbine torque corresponding to the generator output G ₁ increases, causing the frequency to rise.
If the AC/DC converter is deblocked at this time, the DC power P _d will rapidly decrease to the minimum power (for example, 10%).
try to become Furthermore, as explained in Fig. 3, the rise of the turbine torque is slower than the rise of the DC power _Pd , so the so-called decrease in the generator speed due to the electrical output of the generator becoming larger than the input mechanical torque can be avoided. and the frequency decreases.

As a result, the frequency of the turbine generator decreases below a predetermined value, so that the frequency deviation Δ from the frequency deviation detector input to the control circuit 51 becomes negative. When this frequency deviation Δ becomes negative, the output signal of the control circuit 51 also becomes negative and is input to the limiter circuit 52. As a result, the limiter circuit 52 provides a negative output proportional to the magnitude of the output of the control circuit 51 to the constant voltage control circuit 9' together with the reference value E _dp and the detected value E _d . In this case, since the output of the limiter circuit 52 is negative, the output acts to apparently reduce the reference value E _dp ,
A smaller deviation output than originally is given to the constant voltage control circuit 9'. Therefore, the input to the constant voltage control circuit 9' decreases, and the DC voltage resulting from the control decreases.
E _d decreases. Further, since the DC current I _d is controlled to be constant at, for example, 10%, the DC power P _d decreases as the DC voltage _Ed decreases. Then, when this DC power P _d decreases and becomes smaller than the turbine generator torque G ₁ , the frequency of the generator increases.

FIG. 5 shows the output and frequency response when this startup method is applied. In the figure,
P _G is the torque of the turbine generator, P _d is the DC power,
Δ is the frequency deviation. As you can see from the figure,
Due to the deblocking of the AC/DC converter, the DC power P _d tends to increase rapidly, but Δ decreases, so by the control of the present invention described above, the DC power P _d decreases and the frequency deviation Δ recovers to zero. .

In this way, in this embodiment, when starting up the AC/DC converter that is directly connected to the turbine generator, the current reference value I _dp of the constant current control circuit is set to a value that does not cause intermittent current.
When the frequency of the turbine generator decreases below a predetermined value, the DC voltage reference value E dp of the low voltage control circuit 9 of the AC/DC converter is increased by an amount corresponding to the frequency deviation Δ of the turbine generator frequency from the predetermined value _. This corrected DC voltage reference value E _dp
The DC voltage E _d of the AC/DC converter is controlled according to the following.

Therefore, it is possible to match the DC power P _d with the turbine generator output, suppress large frequency fluctuations, and maintain the frequency at a predetermined value. It is possible to perform interconnected operation with the AC/DC converter, and to prevent current interruptions in the AC/DC converter. As a result, it becomes possible to start up the AC/DC converter directly connected to the turbine generator in an extremely stable manner.

It should be noted that the present invention is not limited to the above embodiments, but can also be implemented as follows.

(a) FIG. 6 shows another embodiment according to the present invention, and the same parts as in FIG. 4 are designated by the same reference numerals. That is, FIG. 6 shows the upper limit value at the output of the limiter circuit 52 in FIG.
A signal to which UP is added is given to the control voltage limiter circuit 11 (or 11'), and this signal is used to control the control voltage limiter circuit 11 (or 1).
1') is configured to set an upper limit value.

In such a configuration, as described above, when the DC power increases at startup and the frequency deviation Δ becomes negative, the output of the limiter circuit 52 becomes negative and the control voltage limiter circuit 11 (or 1
1') is lowered. When the upper limit value of this control voltage limiter circuit 11 (or 11') decreases, the control voltage of the DC voltage determining terminal decreases, reducing the DC voltage, and as a result, the DC voltage
P _d is reduced, and the same effect as in the above embodiment can be obtained.

(b) Naturally, the control circuit 51 can also be realized by a computer program or the like having the same functions.

(c) Furthermore, in the above embodiment, a thyristor is used as the converter, but it is also possible to use a chopper or the like.

In addition, the present invention can be modified and implemented in various ways without changing the gist thereof.

〔Effect of the invention〕

As explained above, according to the present invention, when the frequency of the generator decreases below a predetermined value when the AC/DC converter directly connected to the generator is started, an amount corresponding to the frequency deviation from the predetermined value of the frequency is reduced. Since the DC voltage reference value of the AC/DC converter is corrected to a smaller value and the DC voltage of the AC/DC converter is controlled according to the corrected DC voltage reference value, it is possible to suppress significant frequency fluctuations. This allows for interconnected operation with the DC power transmission equipment from the low output range of the generator, as well as preventing current interruptions in the AC/DC converter, resulting in extremely reliable startup operation. A method for starting an AC/DC converter with high efficiency can be provided.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram showing the AC/DC converter, Figure 2
Fig. 3 shows a starting pattern of a conventional converter, Fig. 3 shows a load starting pattern of a nuclear power generator output, Fig. 4 is a block diagram showing an embodiment of the present invention, and Fig. 5 shows the same. FIG. 6 is a block diagram showing another embodiment of the present invention. 1, 1'... AC bus, 2, 2'... Conversion transformer, 3, 3'... Converter, 4, 4'... Smoothing reactor, 5... DC transmission line, 6, 6'... ...P.T.
7, 7'...C・T, 8, 8'... Constant current control circuit, 9, 9'... Constant voltage control circuit, 10, 10'...
... Control voltage selection circuit, 11, 11'... Control voltage limiter circuit, 12, 12'... Firing phase control circuit, 51... Control circuit, 52... Limiter circuit.

Claims (1)

[Scope of Claims] 1. A method for starting an AC/DC converter directly connected to a generator, which converts alternating current to direct current or direct current to alternating current by controlling a converter by a control device, comprising: When the frequency of the generator falls below a predetermined value at startup, the DC voltage reference value of the AC/DC converter is corrected to be smaller by an amount corresponding to a frequency deviation of the frequency from the predetermined value, and this correction is performed. A method for starting an AC/DC converter, characterized in that the DC voltage of the AC/DC converter is controlled in accordance with a DC voltage reference value determined by the DC/DC converter.