JPH07104740B2 - Controller for reactive power compensator - Google Patents

Description

The present invention relates to a control device for a reactive power compensator.

[Conventional technology]

FIG. 4 is a circuit diagram showing a control device of a conventional static var compensator shown in, for example, the magazine “OHM” (issued in January 1975). In FIG. System impedance connected to AC power supply 1, 3 is a furnace transformer whose primary side is connected to system impedance 2, 4 is an arc furnace connected to the secondary side of furnace transformer 3, and 5 is system impedance 2 and furnace It is a capacitor connected between the connection path of the transformer 3 and the arc. 6 is a reactor, 7 is a thyristor device for controlling the reactive power of the reactor. These reactor 6 and thyristor device 7 are connected in series, and the capacitor 5
And a var compensator 11 which is connected in parallel with.
Reference numeral 8 is a current transformer, 9 is a voltage transformer, and 10 is a control circuit.

FIG. 5 shows a block diagram of the configuration of the control circuit 10. The reactive power detection circuit 12, the compensation gain setting circuit 13, the thyristor firing angle control circuit 14 which are sequentially connected as the electric quantity calculation circuit are connected. It is composed of.

Next, the operation will be described. When the lagging reactive power Q _A (hereinafter abbreviated as Q _A ) flowing into the arc furnace load 4 changes,
At point A in FIG. 4, a voltage fluctuation ΔV _A occurs according to the following equation.

ΔV _A = x · Q _A where x is the reactance component (p, u) of the power system impedance 2 and Q _A is the reactive power flowing into the arc furnace load.

In order to reduce this voltage fluctuation ΔV _A , the reactive power compensator 11 composed of the capacitor 5, the reactor 6 and the thyristor device 7 is connected to the point A of the connection path connecting the system impedance 2 and the primary side of the reactor transformer 3. Connect between earth E, arc furnace 4
The compensation reactive power −Q _O proportional to the reactive power flowing in

In this case, the reactive power Q _S flowing on the power supply side is Q _S = Q _A −Q _O , and the voltage fluctuation ΔV _{A at} point A caused by the reactive power Q _S is ΔV _A = x · Q _S = x · (Q _A− Q _O ), and the voltage fluctuation ΔV _A can be reduced by the reactive power compensator 11.

Therefore, the voltage V and the current I of the arc furnace load 4 detected by the voltage transformer 9 and the current transformer 8 are input to the reactive power detection circuit 12 of the control circuit 10 shown in FIG. Reactive power Q _A flowing into is detected.

This detected value Q _A is input to the compensation gain setting circuit 13 in the next stage, multiplied by a constant gain K times, and then the thyristor firing angle control circuit.
Entered in 14. In the thyristor firing angle control circuit 14, the thyristor firing phase angle α for outputting the reactive power corresponding to the input signal K · Q _A is determined, and the gate firing command is issued at the phase of the firing angle α. Give to. As a result,
The reactive power compensator 11 outputs the reactive power of K · Q _A.

[Problems to be solved by the invention]

Since the control circuit of the conventional reactive power compensator 11 is configured as described above, the output Q _O of the reactive power compensator 11 is controlled by Q _O = K · Q _A. When the reactive power Q _A of No. 4 changes as shown by the solid line in FIG. 6 (a), the output Q _O is controlled as shown by the dotted line in FIG. 6 (a).

In FIG. 4, the output Q _O is the sum of the reactive power Q _C of the fixed phase advance capacitor 5 and the lagging reactive power −Q _R of the reactor by the thyristor control, so that the output Q _O of FIG. when controlled as shown by the dotted line, reactor reactive power Q _R (hereinafter, referred to as Q _R) will be controlled in the direction of the arrow in Figure 6 (b), Q _R is FIG. 6 (d ) Will be followed. As a result, the reactive power Q _S (hereinafter abbreviated as Q _S ) flowing out to the power system side becomes as shown in FIG. 6 (c), and the fluctuation of the reactive power can be suppressed.

However, Q _A is a small region and the region of Q _A maximum compensation capacitor Q _C (hereinafter, abbreviated as Q _C) despite less, because it is controlled to the magnitude of Q _O = K · Q _A , Q _R needs to be increased. Therefore, a large current flows through the reactor 6 and the thyristor device 7, and there is a problem that the electric loss of the reactor 6 and the thyristor device 7 is large in a region where Q _A is small.

Further, as shown in FIG. 6 (a), although Q _A <Q _C in the area and the area, Q _S has a delay and the power factor decreases.

The present invention has been made to solve the above problems, and a reactive power compensator capable of improving the power factor after compensation while reducing the loss of the thyristor device and the reactor in the light load region of the arc furnace load. The purpose is to obtain a control device.

[Means for solving problems]

The control device of the reactive power compensator according to the present invention increases the control gain of the control circuit when the fluctuation of the arc furnace load is small, and restores the control gain when the fluctuation becomes large.

[Action]

The control device of the reactive power compensating device according to the present invention calculates the amount of fluctuation of the detected reactive power of the arc furnace and changes the control gain according to the magnitude of the amount of fluctuation, thereby reducing the reactive power fluctuation region. Then, the control gain is increased, and the control gain is returned to the original value in the region where the reactive power fluctuation is large.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1 in which the same parts as those in FIG. In FIG. 1, reference numeral 15 is a reset filter as an electric quantity change detection circuit for detecting a change ΔQ _A (hereinafter, abbreviated as ΔQ _A ) in the reactive power detection value Q _A , and 16 is an absolute value of ΔQ _A | ΔQ _A | (hereinafter, ｜
Absolute value circuit for obtaining ΔQ _A |
_A first-order delay circuit for obtaining the average value ΔQ _M of ΔQ _A |, 18 is a subtraction circuit that inputs the average value ΔQ _M and a constant value Q _M , 19 is a gain setting circuit, 20 is the output of the gain setting circuit 19, and is constant gain
An addition circuit for inputting K _O , 21 is a multiplication circuit as a variable gain circuit for inputting the output of the reactive power detection circuit 12 and the output of the addition circuit 20, and the output of this multiplication circuit 21. Is input to the thyristor firing angle control circuit 14.

Next, the operation will be described. 2 and 3 are the same as in FIG.
FIG. 9 is a diagram showing an operation for the same reactive power Q _A as shown in the figure.

Now, consider a case where the same reactive power Q _A of the arc furnace load 4 as shown in FIG. 6 (a) occurs as shown by the solid line in FIG. 3 (a). The reactive power Q _A of the arc furnace load 4 is the reactive power detection circuit 12
Is calculated and output. Q _A is the reset filter circuit 15
Is input, the change in Delta] Q _A of Q _A is calculated. As shown in FIG. 3B, ΔQ _A has a waveform in which only the variation of Q _A is extracted. ΔQ _A is input to the absolute value circuit 16 in the next stage, and | ΔQ _A | is calculated as shown in FIG. This | ΔQ _A | is input to the first-order delay circuit 17, and the average value ΔQ _M of | ΔQ _A | is obtained as shown in FIG.

Then in the subtracting circuit 18 is determined difference between the average value Delta] Q _M constant value Q _K, in Figure 3 (e), as shown by the solid line (Q _K -
ΔQ _M ) is calculated. Here, the constant value Q _K is chosen to be approximately equal to the maximum value of ΔQ _A.

As shown in Fig. 3 (e), when the change in Q _A is large,
(Q _K −ΔQ _M ) becomes a value close to 0, and when the change in Q _A is small, (Q _K −ΔQ _M ) becomes a value close to Q _K. This (Q _K −Q _M ) is further multiplied by a constant gain K ₁ in the gain setting circuit 19 in the next stage, and then input to the adder circuit 20. In the adding circuit 20, the sum of the constant gain K ₀ and the output ΔK = K ₁ (Q _K −ΔQ _M ) of the gain setting circuit 19 is calculated, and {K ₀ + K ₁ is obtained as shown in FIG. 3 (f). (Q _K −ΔQ _M )} That is,
(K ₀ + ΔK) is output. Here, K ₀ is selected as the control gain in the conventional control method shown in FIG.

The output {K ₀ + K ₁ (Q _K −ΔQ _M )} of the adder circuit 20 is multiplied by Q _A output from the reactive power detection circuit 12 in a multiplication circuit 21, and {K ₀ + K ₁ (Q _K −ΔQ M _M )} ・ Q _A is output. here,
The value of _{{K 0 + K 1 (Q} K -ΔQ M)} acts as a variable gain, the area change is large Q _A, as shown in FIG. 3 (b) located substantially in the vicinity of the constant gain K ₀ Q _{In a} region where the change in _A is small, the value is larger than the constant gain K ₀ .

In the thyristor firing angle control circuit 14 of FIG. 1, {K ₀ + K
₁ (Q _K −ΔQ _M )} · Q _{A The} thyristor firing angle α corresponding to Q _A is selected and acts to give a firing signal to the thyristor device 7, so the reactive power Q _O of the reactive power compensator 11 is Q _O = {K ₀ + K ₁ (Q _K −Q _M )} · Q _A.

As a result, the output Q _O of the reactive power compensator 11 is shown in FIG. 2 (b).
The waveform becomes as shown by the solid line in Figure 5, and compared with the conventional control method shown by the dotted line in the figure, Q _O shows a large value in the region where the change in Q _A is small, and Q _O smaller than the maximum reactive power compensation capacity. _A can be almost completely compensated.

Therefore, as shown by the solid line in FIG. 2 (c), the reactive power Q _S on the power source side in the control method of the present invention is shown by the dotted line in the figure in the region where the fluctuation of Q _A is small. It can be made smaller than in the case of the conventional control method, the reactive power fluctuation can be reduced, and the average power factor can be improved.

Further, as shown by the solid line of FIG. 2 (d), the reactive power Q _R of the reactor in the case of the control apparatus of the present invention, be reduced compared to Q _R in the case of the conventional controller shown in a dotted line Therefore, the operating loss of the reactor (6) and the thyristor device 7 in the reactive power compensator 11 shown in FIG. 4 can be reduced.

In the above embodiment, the control gain is changed according to the amount of change in the reactive power detection value.However, the amount of change in the amount of electricity such as the current value of the load and active power is changed. The control gain may be changed accordingly, and the same effect as that of the above-described embodiment is obtained.

〔The invention's effect〕

As described above, according to the present invention, the control gain of the reactive power compensator is changed according to the magnitude of the variation of the electric quantity of the load, so that the average power factor after compensation can be improved. At the same time, there is an effect that the operation loss of the thyristor device and the reactor, which are the components of the reactive power compensator, can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a controller of a reactive power compensator according to an embodiment of the present invention, FIGS. 2 and 3 are diagrams for explaining the operation of the controller of the present invention, and FIG. 4 is a reactive power. FIG. 5 is a system diagram to which a compensator is applied, FIG. 5 is a circuit diagram showing a controller of a conventional reactive power compensator, and FIG. 6 is a diagram for explaining the operation of the conventional controller. 8 is a current detection means (current transformer), 9 is voltage detection means (voltage transformer), 10 is a control circuit, 11 is a reactive power compensator, 12 is an electric quantity calculation circuit (reactive power detection circuit), 15 is electricity Quantity change amount detection circuit (reset filter circuit), 21 is a variable gain circuit (multiplication circuit). In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A reactive power detection circuit for detecting reactive power from a voltage and a current supplied to a fluctuating load, a reactive power change amount detection circuit for detecting a change amount of the reactive power, and an absolute value of the change amount. An absolute value circuit for obtaining, a first-order delay circuit for obtaining the average value of the absolute values, a gain setting circuit for multiplying a subtraction value obtained by subtracting a constant value from the average value by a constant gain, and a constant gain at the output of the gain setting circuit. Reactive power compensation including a variable gain circuit that inputs the added value and the reactive power, increases the control gain in a region in which the variation of the reactive power is small, and restores the control gain in the region in which the variation in the reactive power is large. The control device of the device.