JPS61264416A - Control system for reactive power compensating device - Google Patents

Abstract

PURPOSE:To increase the average power factor after compensation by changing the gain of compensation of a reactive power compensating device in response to the shift bias value equal to the quantity of load electricity. CONSTITUTION:A reactive power compensating device consisting of a capacitor, a thyristor, etc. is provided to an AC power supply connected to an arc furnace having large fluctuation of load. A reactive power detecting circuit of said compensating device is provided with a thyristor firing angle control circuit 14, a multiplier 15 serving as a variable gain circuit, a primary delay circuit 16 serving as a shift bias arithmetic circuit, a subtraction circuit 17, a gain setting circuit 18 and an addition circuit 19. When the reactive power QA is generated, the shift bias QM is calculated by the circuit 16 and multiplied by the power QA via the circuits 17-19. As a result, the output of the reactive power compensating device shows the large value in an area having small power QA and compensates completely the value smaller than the compensation capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control method for a reactive power compensator.

[Conventional technology]

FIG. 4 is a circuit diagram showing the control method of a conventional static type non-dynamic power compensator shown in the magazine 1'-OHMJ (published in January 1975). In FIG. 4, 1 is an AC power supply , 2 is the system impedance connected to AC power supply 1, 3
is a furnace transformer whose primary side is connected to grid impedance 2, 4 is an arc furnace connected to the secondary side of furnace transformer 3, and 5 is between the connection path between grid impedance 2 and furnace transformer 3 and the arc. It is a capacitor connected to 6 is a reactor, and 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 in parallel with the capacitor 5 to form a reactive power compensator 11. 8 is a current transformer, 9 is a voltage transformer, 10
is the control circuit.

FIG. 5 shows a block diagram of an example of the configuration of the control circuit 10, in which a reactive power detection circuit 12, a compensation gain setting circuit 13, and a thyristor firing angle control circuit 14 are sequentially connected as electrical quantity calculation circuits. It consists of

Next, the operation will be explained. When the slow phase reactive power QA (hereinafter abbreviated as QA) flowing into the arc furnace load 4 fluctuates, a voltage fluctuation 37 occurs at point A in FIG. 4 according to the formula below.

ΔVA = X-QA where X is the reactance (p, u) of power system impedance 2, and QA is the reactive power flowing into the arc furnace load.

To reduce this voltage fluctuation, K, capacitor 5,
A reactive power compensator 11 consisting of a reactor 6 and a thyristor device 7 is connected between point A and boo 18 of the connection path connecting the system impedance 2 and the primary side of the furnace transformer 30 at point A, and the power flowing into the arc furnace 4 Compensated reactive power -Qo proportional to reactive power is controlled.

In this case, the reactive power Qs flowing to the power supply side is Qs=QA
The voltage fluctuation ΔVA at point A caused by the reactive power Qs is expressed as ΔVA=X−Qs=X·(QAQO), and the reactive power compensator 11 can reduce the voltage fluctuation ΔVA.

Therefore, the voltage ■ and 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. 9 reactive power flows into the area are detected.

This detected value QA is input to the next stage compensation gain setting circuit 13, multiplied by a constant gain, and input to the thyristor firing angle control circuit 14. This thyristor firing angle control circuit 1
In step 4, the thyristor firing phase angle α for outputting reactive power corresponding to -QAK to the input signal is determined, and a gate firing command is given to the thyristor at the phase of the firing angle α. As a result, the reactive power compensator 11 outputs a reactive power of -QA.

[Problem that the invention seeks to solve]

Since the conventional reactive power compensator 110 control circuit is configured as described above, the output Qo of the reactive power compensator 11
will be controlled by Qo = -QA. For example, if the reactive power of 9 people with arc furnace load 4 changes as shown in the solid line in Fig. 6 (al),
The output Qo will be controlled as shown by the dotted line in FIG. 6 (al).

In Fig. 4, the output Qo is the sum of the reactive power Qc of the fixed phase advance capacitor 5 and the lagging reactive power -QR of the reactor controlled by the thyristor.
), the reactor's reactive power QR (hereinafter abbreviated as QR) is controlled in the direction of the arrow in Figure 6 (bl), and QR is controlled in the direction of the arrow in Figure 6 (di). As a result, reactive power Qs (hereinafter abbreviated as Qs) flows out to the power supply system.
is as shown in FIG. 6(c), and reactive power fluctuations can be suppressed.

However, even though QA is less than the maximum compensation capacity Qc (hereinafter abbreviated as Qc) in the small QA region It is necessary to do so. Therefore, a large current is passed through the reactor 6 and the thyristor device 7, and there is a problem that the electrical loss of the reactor 6 and the thyristor device 7 is large in a small area of nine people.

Furthermore, as shown in FIG. 6(a), in region (2) and region (2), although QA<Qc, Qs becomes slow in phase and the power factor decreases.

This invention was made in order to solve the above-mentioned problems, and it is a reactive power compensator that can reduce the loss of the thyristor device and reactor in the light load region of the arc furnace and improve the power factor after compensation. The purpose is to obtain a control method.

[Means for solving problems]

The control method of the reactive power compensator according to the present invention increases the compensation gain of the control circuit when the arc furnace load is light, and returns the compensation gain to the original value when the load becomes large.

[Effect]

The control method of the reactive power compensator in this invention calculates the moving bias value of the reactive power of the detected arc furnace load, and adds the compensation gain to change according to the magnitude of the moving bias value. Increase the compensation gain and restore the compensation gain during heavy loads to the original value.

[1st Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1, in which the same parts as in FIG. 4 are given the same reference numerals.

In FIG. 1, 15 is a multiplier as a variable gain circuit for changing the magnitude of the control gain, and 16 is a first-order delay as a moving noise calculation circuit for creating a moving bias of the detected reactive power value Q. circuit, 17 is a subtraction circuit, 18
1 is a gain setting circuit, and 19 is an addition circuit.

Next, the operation will be explained. Figures 2 and 3 show the above-mentioned 7
It is a diagram showing the same reactive power operation for nine people as shown in the figure.

Now, if the same reactive power QA of arc furnace load 4 as shown in FIG. 6(a) occurs as shown by the dotted line in FIG. 3(a), the moving bias of the nine people will be QM shown in FIG. QM is calculated by the first-order lag circuit 16 in FIG. Note that the time constant T in the -order delay circuit 16 is selected to be a relatively large value so as to be a time constant in a frequency domain that does not cause a problem as flicker.

The subtraction circuit 17 calculates the difference between the constant value Qz and the moving bias value QM (hereinafter abbreviated as QM) output from the first-order lag circuit 16, and outputs (QI QM). Here, the value of QR is selected to be approximately the maximum value of QM, as shown by the dashed line in FIG. 3(a). Therefore, (Qz
QM) has the waveform shown by the two-dot chain line in FIG. 3(a). (QI QM) is input to the next stage gain setting circuit 18, multiplied by a certain gain K1, and output as 57jKt (QI QM) as shown in FIG. 3(b).

In the adder circuit 19, the constant value is 2 and the above-mentioned value is 1.(
QRQM) is calculated, and 2+ Kt (Qz Q M ) is output as shown in FIG. 3 (blK).

(Kg +Kt (Qz M)) is the multiplier circuit 1
5, it is multiplied by the output QA of the reactive power detection circuit 12 and becomes (Kg +Kt (Qz M )) ・Q h
is the output salel. Here, (K2 + 1 (Qz M
)) acts as a variable gain, and as shown in Figure 3 (bl), it is almost close to 2 in the area ■ where QA is large, and it is significantly larger than 2 in areas ■ and ■ where QA is small. Become.

In the thyristor firing angle control circuit 14 of FIG.
KI (QRQM)) QA Vc equivalent, ri”)-
b') Since the star firing angle α is selected and a firing signal is given to the thyristor device 7, the reactive power output Qo of the reactive power compensator 11 is Qo=(Kz+Kl(Qz QM)'t ・9 Become a person.

As a result, the output Qo of the reactive power compensator 11 is as shown in FIG.
The waveform becomes as shown by the solid line in b), and compared to the case of the conventional control method shown by the dotted line in Fig. 2 (bl), Qo shows a large value in a small QA region, and is smaller than the maximum reactive power compensation capacity. It becomes possible to almost completely compensate for the value of QA.

Therefore, as shown by the solid line in FIG. 2(C), the reactive power Q8 on the power supply side in the control method of the present invention is lower than that of the conventional control method shown in FIG. QsK can be made smaller than that of the case, and it is possible to reduce the reactive power fluctuation and improve the average power factor.

Furthermore, as shown by the solid line in Fig. 2(d), the reactive power QR of the steering wheel in the case of the control method of the present invention is as shown in Fig. 2(d).
Since the QR can be made smaller than the QR in the case of the conventional control method shown by the dotted line, the operating loss of the reactor 6 and thyristor device 7 in the reactive power compensator 11 shown in FIG. 5 can be reduced. will be possible.

In addition, in the above embodiment, the case where the compensation gain is changed according to the moving bias value of the reactive power detection value is shown, but it is also possible to change the compensation gain according to the moving bias value of the electric quantity such as the current value of the load or the active power. The compensation gain may be changed, and the same effect as in the above embodiment can be obtained.

Also, as the amount of time change in the amount of electricity of the load, 1
Although the moving bias value calculated using the next delay circuit 16 was used, it is also possible to use the moving bias value that is changed stepwise according to the magnitude of the electric quantity using the comparing circuit as shown in FIG. Good, the same effects as in the above embodiment can be achieved. In FIG. 4, 21 is an adder circuit, and in the illustrated example, the moving bias value QM as the output of the adder circuit 21 is 3 depending on the output values of the three stages of the comparator circuits 20a, 20b, and 20c. It is a step-by-step change.

〔Effect of the invention〕

As described above, according to the present invention, since the compensation gain of the reactive power compensator is changed according to the moving bias value of the magnitude of the electrical quantity of the load, it is possible to improve the average power factor after compensation. This has the effect of reducing operating loss of the thyristor device and the accelerator, which are components of the reactive power compensator.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a control method of a reactive power compensator according to an embodiment of the present invention, FIGS. 2 and 3 are diagrams explaining the operation of the control method of the present invention, and FIG. 5 is a circuit diagram of a reactive power compensator, FIG. 6 is a circuit diagram showing a conventional control method, and FIG. 7 is a diagram explaining the operation of the conventional control method. . 8 is a current detection means (current transformer), 9 is a voltage detection means (
voltage transformer), 10 is a control circuit, 11 is a reactive power compensator, 12 is an electrical quantity calculation circuit (reactive power detection circuit), 15
16 is a variable gain circuit (multiplication circuit), 16 is a moving bias calculation circuit (first-order delay circuit), and 20.21 is a moving bias calculation circuit (comparison circuit, addition circuit). Note that the same reference numerals in the figures indicate the same or equivalent parts. Patent applicant: Mitsubishi Electric Corporation (2 others) Fig. 1 12: Reactive power detection circuit (a) (C) (d) Figure 3 (a) (b) Figure 4 Figure 6

Claims (3)

[Claims] (1) In a control method for a reactive power compensator that controls a reactive power compensator based on voltage and current supplied to a fluctuating load, voltage and current detection means for detecting the voltage and current of the fluctuating load; an electrical quantity calculation circuit that calculates an electrical quantity of a load from the detected voltage and current; a moving bias computing circuit that computes a moving bias amount that follows temporal changes in the electrical quantity; and a variable gain circuit that can vary the control gain accordingly, and the variable gain circuit changes the control gain for the output of the electrical quantity calculation circuit in accordance with the amount of movement bias to control the reactive power output. A control method for a reactive power compensator characterized by: (2) A control method for a reactive power compensator according to claim (1), characterized in that the moving bias calculation circuit is constituted by a first-order lag circuit. (3) A control method for a reactive power compensator according to claim (1), wherein the moving bias calculation circuit is constituted by a plurality of comparison circuits and an addition circuit that adds the outputs of the comparison circuits.