JPS6334697B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a power system, and more particularly to a control device for supporting power from a DC system to a weak AC system.

The AC system has its own power self-recovery ability; for example, when there is a sudden increase in load, it detects the resulting drop in grid frequency and uses the governor action at each power plant to stop generating electricity until the specified frequency is reached. It acts to increase power and maintain a balance between power supply and demand.
However, in the case of only an AC system, there is a long time delay until stabilization, and this tendency is particularly strong as the system becomes weaker, and the self-recovery ability is lower.

This problem can be solved by connecting an AC system and a DC system (generally, an AC system is provided behind it). In other words, when the frequency decreases due to a sudden increase in load, it is possible to quickly recover from the frequency decrease by increasing the amount of power supplied to the AC system rather than the DC system. As is well known, emergency power support using a DC system can be performed with almost no delay.

Power support using a DC system has conventionally been achieved by detecting the frequency of the AC system and controlling an AC/DC converter so that the amount of support power is proportional to the frequency of the AC system. Therefore, according to this proportional control, the period of power support was a period of frequency drop. In the case of an AC system with a high self-recovery ability, this proportional control is very effective, and by the time the frequency is restored by support power, the power generated by the AC system itself has increased, and therefore the increased load can be compensated for. This can be covered by the generated electricity. On the other hand, in the case of a weak system with low self-recovery ability, when the frequency is recovered by support from the DC system, the generated power of the AC system itself hardly increases, but proportional control of the frequency is applied. The added support power is the same as the amount of power before the sudden load increase. For this reason, the frequency will drop again and the support power will be increased, but as long as the power generated in the AC system does not increase, this will not be an essential solution, and the frequency and power fluctuations will repeat oscillatorily. It goes without saying that the above-mentioned fluctuations in a weak AC system are unfavorable in terms of stability.

In light of the above, an object of the present invention is to provide a control device for power support in the event of a sudden increase in load in a power system that links a weak AC system and a DC system, taking into consideration the stability of the weak AC system. shall be.

In the present invention, the frequency is detected and the amount of supporting power is determined according to the integrated value.

In the present invention, first, it is necessary to increase the support power, but this can be done by increasing the DC power, and there are two methods for this: increasing the DC current and increasing the DC voltage. However, since a general DC power transmission device uses constant current control on the forward converter side and constant voltage control on the inverse converter side, considering the problem of commutation failure, it is better to use DC current control.

Secondly, in order to continue control even after recovery according to the frequency, there is a method of configuring an integral closed loop system. FIG. 1 shows an example in which a frequency closed loop is constructed and its output is applied to a constant current control system.

In the figure, CON is an AC/DC converter, whose AC terminal is connected to the power grid G via a transformer Tr, and whose DC terminal is connected to the opposite end converter CON via a line L having a DC reactor DCL. Ru. CC is a converter control device, which converts the DC current I _d by the DC current transformer DCCT to the DC voltage transformer
DC voltage V _d through DCPT, also setting device SC
Obtain the current setting value I _dp , current margin ΔI _dp , voltage setting value V _{dp, etc.} from
Via PT, control the firing angle of the converter CON.
In addition, since the setting device SC is placed at one of the A and B end electrical stations (in the example shown in the figure, it is installed at the A end electrical station),
The output of the SC is sent to the B-end electrical station via the transmission device TRC. In this figure, it is assumed that the A-end AC system is a weak system and is supplied with power from the B-end electric station.

FIG. 2 is a diagram showing an outline of the setting device SC,
1 is a current setting value I _dp determining means, and 2 is a voltage setting value determining means. Reference numeral 5 denotes a power flow direction determining means consisting of a current margin ΔI _d determining means 3 and a ΔI _d switching means 4, in which the current margin ΔI _d , which is the output of 3, is applied to one terminal determined by the switch 8, and the other One end is O(V). Note that the signal applied to the A end is ΔI _d1 and the signal applied to the B end is ΔI _d2 . When the A end is selected, the switching means 4 sets the output P to "1" and closes the switch 8 to the A end side.
When the B end is selected, the output P is set to "0" and the switch 8 is closed to the B end side. Current margin ΔI _d
The terminal to which is applied becomes inverse conversion operation as will be described later. Here, since the A-terminal converter is an inverse converter as described above, the switch 8 is closed to the A-side, and the current margin ΔI _d is applied to the A-terminal.
Here, the current setting value determining means 1 is, for example, a power control circuit, and the current setting value determining means 1 is, for example, a power control circuit, which is configured to determine the DC power transmission power P _d and the setting power P _dp1.
The current setting value I _dp is determined by inputting the deviation from the current value I dp.
The present invention is characterized in that the auxiliary power setting value ΔP _dp is determined corresponding to the frequency deviation Δf on the weak power system side, and the integral signal of Δf is set as ΔP _dp . In this diagram, AD ₁
is an adder and calculates P _dp +ΔP _dp −P _d . 8
is a switch, and switches to the side of the terminal that is connected to the inverter. 6 is an integrator, 7 is a proportional circuit,
AD ₂ is an adder circuit for obtaining the A-end side frequency deviation f _AP -f _A , and AD ₃ is an adder circuit for obtaining the B-end side frequency deviation f _BA -f _B. 9
is a dead band circuit. Therefore, when feeding power to end A, which is a weak system, ΔP _dp = ∫Δf _Adt , and when feeding power to end B, which is a strong system, ΔP _dp = KΔf _B
It is said that

FIG. 3 is a diagram showing details of the control device CC into which various setting values determined as described above are input. First, the control device CC includes a constant current control circuit consisting of an adder _AD4 and an amplifier A1 for calculating I _dp -I _d -ΔI _d , an adder AD5 and an amplifier A2 for calculating V _dp -V _d .
The low value priority circuit LVG selects the lowest value signal among the outputs of these control circuits. As is well known, the amplifier A1 saturates positively at the terminal to which a predetermined value is given as the current margin ΔI _d .
The output of the constant current control circuit is not selected, and a reverse conversion operation is performed by another control system, and the constant current control circuit output is selected at the terminal where ΔI _d =0, and a forward conversion operation is performed.

As is clear from the above explanation, the forward converter is controlled by the frequency control system (AFC), the power control system (APR),
It is a cascade control of the current control system (ACR),
Control on the inverter side is voltage control (AVR).
Further, when power is supplied to the weak system A, integral type frequency control is used, and when power is supplied to the strong system B, proportional type frequency control is used. Figure 4 shows the response when a sudden load occurs. However, figure a is an example of power feeding to a weak system, and figure b is an example of power feeding to a strong system.

In the figure, it is assumed that at time t ₁ the load suddenly increases by _PL and the frequency begins to drop, and at t ₂ an output Δf is obtained from the dead band circuit 9. As a result, it is assumed that the frequency is recovered at time _t3 . In the case of a weak system (a in the same figure), the supporting power ΔP _dp from the DC system continues to increase between t ₂ and _{t 3} due to the action of the integrating circuit 6, and has a certain amount even at t ₃ . And this amount is maintained even after t ₃ . In the case of a powerful system that employs proportional frequency control (Figure b), the support power becomes zero at time _t3 . Incidentally, the amount of power increase due to the self-recovery power of the AC system itself is ΔP _AC , and in a powerful system, enough generated power can be obtained by t ₃ to match the sudden increase in load _PL . Therefore, after _t3 , the sudden increase in load can be covered only by ΔP _AC . On the other hand, in the case of a weak system, the power generated by the AC system is as small as ΔP _AC ,
Although the load P _L cannot be covered by ΔP _AC alone,
P _L can be covered by the sum with the support power ΔP _dp that continues even after t ₃ . According to this control, the integral value is maintained after t ₃ , and the point at which input that causes the integral value to decrease (input due to frequency increase) is given.
Continue until t ₄ .

As described in detail above, power support from the DC system when the load suddenly increases in a weak system continues even after the frequency recovery time _t3 , so the frequency drop phenomenon does not repeat and the stability can be improved. can be achieved. The control shown in Fig. 2 above shows an example in which the support power is controlled by operation on the forward converter side, but in this case, the output of the switch 8 is given to the voltage setting value determining means 2 to make the voltage setting variable. By doing so, the support power can also be controlled by operation on the inverter side. Furthermore, in the example shown in Fig. 2, the setting device SC gives a signal according to the frequency.
This can also be applied to the control devices at each end shown in FIG. 3 to obtain the same effect. in short,
The embodiment shown in Fig. 2 describes the provision of a dead band circuit and an integrating circuit as a specific embodiment for power support even after frequency recovery, and where in the control circuit the signal is applied. is not an essential problem of the present invention.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a power system including a DC line and its control device, and Fig. 2 is an installation device of the present invention shown in Fig. 1.
A detailed explanatory diagram of SC, Figure 3 is the control device CC in Figure 1.
FIG. 4 is a diagram showing the relationship between frequency and support power according to the present invention. AD...Adder, 9...Dead band circuit, 6...Integrator circuit, 7...Proportional circuit.

Claims (1)

[Scope of Claims] 1. A DC line is connected between the respective DC terminals of at least two sets of AC/DC converters, and an optical current line, at least one of which is weak, is connected to each AC terminal side. In a power system in which the transmitted power is controlled by controlling the firing angle of the AC/DC converter, a control device that controls the firing angle of the AC/DC converter derives a frequency deviation of the weak AC system. a first means; a second means for obtaining a target signal of transmitted power from a signal obtained by integrating the output of the means;
1. A control device for a power system, comprising: third means for controlling a firing angle of an AC/DC converter according to an output of the means, and controlling an amount of electric power given to a weak power system. 2. A DC line is connected between the DC terminals of at least two sets of AC/DC converters, and a weak AC line is connected to one side of each AC terminal side, and a relatively powerful AC line is connected to the other side, and the In a power system in which the transmitted power is controlled by controlling the firing angle of the AC/DC converter, the control device that controls the firing angle of the AC/DC converter has a first control device that derives the frequency deviation of the weak AC system. a second means for obtaining a target signal of the transmitted power from a signal obtained by integrating the output of the means; a third means for deriving the frequency deviation of the strong AC system; a fifth means for selecting the signal of the second means when the power supply direction is a weak power system, and selecting the signal of the fourth means when the power supply direction is a strong power system; A power system control device comprising: sixth means for controlling the firing angle of the AC/DC converter according to the output of the means.