JPS6320514A - Control method for reactive power compensating device - Google Patents

Abstract

PURPOSE:To completely compensate reactive power even when a circuit voltage varies and to set a powder factor 1 by controlling a reactive power compensating device in consideration of the variation in the circuit voltage. CONSTITUTION:An effective value detecting circuit 21 outputs the effective value V[Pu] of the circuit voltage and a squaring device 22 finds its square V<2>[Pu]. A driver 23 divides the reactive power QF of a load 4 detected by a reactive power detecting circuit 11 by V<2> to find QF/V<2>. A thyristor 3 is turned on in the phase where said result becomes equal to the output QT of a function generator 12 to control the reactive power consumption of a reactor 2. Therefore, QT=QC-QL=QF/V<2> holds, so reactive power Qs supplied from a power source becomes zero. Thus the reactive power QS supplied from the power source becomes zero regardless of the circuit voltage, so the variation in the reactive power of the load is compensated completely and the power factor becomes 1.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Field of Application) The present invention provides phase control of a variable load in a power system by a thyristor connected in parallel with the variable load, or a combination of an accelerator and a phase advance capacitor. The present invention relates to a method of controlling a reactive power compensator that compensates for reactive power.

(Prior art) In general, when the fluctuations in reactive power are irregular and large as in an arc furnace, in order to effectively compensate for such fluctuations in reactive power, it is necessary to promptly detect the reactive power of the load. ,
It is necessary to determine the firing phase of the thyristor of the reactive power compensator according to the detected reactive power to make the response of the reactive power compensator as fast as possible to reactive power fluctuations.

FIG. 3 shows a schematic block diagram of a conventional reactive power compensator and its control circuit.

In FIG. 3, 1 is a phase advancing capacitor, and its reactive power is Qc. 2 is a reactor, and the current flowing through the reactor 2 is controlled by an anti-parallel thyristor 3 connected in series to the reactor 2.

The delayed phase reactive power QL taken by the reactor 2 from the power supply by the anti-parallel thyristor 3 can be changed arbitrarily between 0 and 100% by controlling the firing angle α as shown in FIG. Phase advancing reactive power Q of phase advancing capacitor
By combining with c, the lagging reactive power OF of load 4
It can be used as a reactive power compensator that compensates for.

For example, in Fig. 3, if the leading reactive power Qc taken by the leading capacitor 1 and the lagging reactive power taken by the reactor 2 are QL, the leading reactive power QT taken from the power supply is QT=QC-O
・・・・・・・・・・・・・・・■. As is clear from equation (2), by controlling the firing angle α of the anti-parallel thyristor 3, it becomes possible to control the phase-advanced reactive power QT taken from the power supply.

Therefore, if the reactive power compensator detects the lagging reactive power QF of the load 4 and takes the leading reactive power QT equal to that value from the power supply, the overall reactive power taken from the power supply becomes O, and the lagging reactive power of the load The reactive power QF will be supplied from the reactive power compensator.

It is generally known that when the reactive power of a load connected to a power system fluctuates, the receiving end voltage fluctuates depending on the impedance of the power system. An example of a load with large reactive power fluctuations is an arc furnace.When an arc furnace is used as a load, slow-phase reactive power with irregular fluctuations and a large fluctuation range flows through the power system, so the power in the system changes rapidly. , causing voltage flicker.

A reactive power compensator shown in FIG. 3 is used as a means for effectively suppressing this type of reactive power fluctuation.

Voltage detection converter 5 for detecting circuit voltage and load current i
The reactive power detection circuit 11 detects the reactive power Qy= of the load 4 from the current transformer 6 that detects F. On the other hand, function generator 1
2 is a circuit that generates the QT of the equation (2) as a function of the firing angle α, and the function is as shown in FIG. 5, which illustrates the equation (2). Therefore, when the signal from the reactive power detection circuit 11 that detects the QF of the load matches the signal from the function generator 12, the comparator 1
3, and the signal is detected by the thyristor 3 via the pulse amplification circuit 14.
If a gate signal is sent to , the QT will be controlled to compensate for the QF of the load 4 . FIG. 6 shows this situation in the form of a time chart.

(Problems to be Solved by the Invention) Although voltage fluctuations are ignored in the above description, in reality, voltage fluctuations occur due to other fluctuating loads connected to the same system. Isometrically, the reactor 2 is regarded as a variable reactance controlled by the phase control of the thyristor 3, so its current and reactive power consumption depend on the circuit voltage. Furthermore, since the capacitor 1 has a constant susceptance, the reactive power generated by the capacitor 1 also depends on the circuit voltage. Now, if we review the formula with the circuit voltage as V (Pu), the power is 2 of the voltage.
Since it is proportional to the power, QT' = V” (QCQL) ・・・・・・・・・
・・・・・・・・・■. However, here, Qc and QL are the reactive powers of the capacitor 1 and the reactor 2 when V=IPu. Therefore, the reactive power Qs supplied from the power source is the compensated reactive power QT' of the reactive power compensator.
and the reactive power consumption QF of load 4, that is, O3 "QT' Qt= = V" (QCQL) -QF ......
・・・・・・・・・・It is expressed as ■. In the conventional control method, QL is controlled as much as possible so that QCQL = QF according to equation (2), so that reactive power equal to (%) is supplied from the power supply. Therefore, when the circuit voltage fluctuates, there is a problem that Qs is not constant and reactive power is not completely compensated. Further, even if the circuit voltage does not vary, the reactive power Q8 supplied from the power supply does not become zero when the power source is not IPu, so there is a problem that the power factor of the circuit does not become 1.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for controlling a reactive power compensator that can completely compensate for fluctuations in the reactive power of a load and maintain a power factor of 1 even when the circuit voltage fluctuates.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides a reactor and a capacitor in parallel between a power supply system and a load, detects reactive power of the load, and current flows through the reactor. In a reactive power compensator in which the load voltage is controlled by a thyristor, a reactive power conversion means is added to the conventional device to detect the effective value of the load voltage and convert the unloaded reactive power of the load to the reactive power in the rated type.

(Function) The reactive power of the load is converted to the reactive power at the rated voltage using the reactive power conversion means, this converted value is compared with the output of the function generator, and when they match, the thyristor is fired and the reactor current is control.

(Embodiment) The embodiment of the present invention is shown in FIG. 1, and the same functions as those in FIG. 3, which shows a schematic block diagram of a conventional reactive power compensator and its control circuit, are given the same reference numerals and explanations are omitted. do.

The circuit voltage detected by the voltage detection converter 5 is input to an effective value detector 21, and its output is input to a squarer 22. The output of the reactive power detection circuit 11 and the output of the squarer 22 are input to a divider 23. The process of inputting the output of the divider 23 and the function generator 12 to the comparator 13 and generating an ignition pulse when the two values match is the same as in the conventional method.

Next, the operation of this embodiment will be explained. The effective value detection circuit 21 outputs the effective value V (Pu) of the circuit voltage, and the squarer 22 calculates the square of the value V'' (Pu).
divides the reactive power QF of the load 4 detected by the reactive power detection circuit 11 by 2 to obtain QF/V''.This result and the output of the function generator 12, QT given by the equation The reactive power consumption of the reactor 2 is controlled by firing the thyristor 3 at a phase where the Substitute the above relational expression into the formula
5)■ becomes.

In this way, according to the embodiment of the present invention, the reactive power Q3 supplied from the power supply is zero regardless of the circuit voltage, so the fluctuations in the reactive power of the load are completely compensated for, and the power factor also becomes 1. Effects can be obtained.

Next, another embodiment is shown in FIG. 2. The circuit voltage and load current detected by the voltage detection converter 5 and current transformer 6 are input to a current reactive component detection circuit 24. This circuit detects the reactive component IFq of the current, and although the value does not take into account the effective voltage value, there is a relationship such as IFQ=QF/V. The effective value detection circuit 21 and the divider 23 are the same as in the previous embodiment.Since the output of the 1-divider 23 is QF/V'', from then on, as in the previous embodiment, the power supply is connected to the power source regardless of the circuit voltage. The supplied reactive power Qs becomes zero, and the reactive power is completely compensated.

〔Effect of the invention〕

As is clear from the above description, the present invention controls the reactive power compensator by taking circuit voltage fluctuations into account, so even when the circuit voltage fluctuates, complete reactive power compensation is possible. This has the effect of making the power factor 1.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a reactive power compensator and its control circuit according to an embodiment of the present invention, FIG. 2 is a schematic block diagram of another embodiment, and FIG.
The figure shows a schematic block diagram of a conventional reactive power compensator and its control circuit, Figure 4 shows the relationship between the reactive power flowing through the beam accelerator and the firing angle, and Figure 5 shows the reactive power of the reactive power compensator and the point. FIG. 6, which is a diagram showing the relationship between arc angles, is a time chart for explaining the operation of the conventional device. 1... Phase advance capacitor, 2... Reactor, 3
...Thyristor, 4...Load, 5...Voltage detection transformer, 6...Current transformer, 11...Reactive power detection circuit, 12...Function generator, 13... comparator,
14... Pulse amplification circuit, 21... Effective value detection circuit, 22... Squarer. 23... Divider, 24... Current reactive component detection circuit. Agent Patent Attorney Noriyuki Chika Yudo Hirofumi MitsumataFigure 3Figure 5

Claims (1)

[Claims] In a reactive power compensator, a reactor and a capacitor are installed in parallel between a power supply system and a load, and the reactive power of the load is detected and the current flowing through the reactor is controlled by a thyristor. A method for controlling a reactive power compensator, comprising converting reactive power into reactive power at a rated voltage, and using the converted value to control a current flowing through the reactor.