JPH02135511A - Reactive power compensating device - Google Patents

Abstract

PURPOSE:To improve reactive power compensating accuracy without affecting a reactive power detecting function with a higher harmonic generated by a rectifier by using the DC current, the control angle and the control voltage signal of the rectifier, detecting a basic wave reactive power only consumed by the rectifier and compensating the power. CONSTITUTION:A thyristor rectifier 22 is phase-controlled so that a DC current Id can be kept constant with a control circuit 30. A reactive power arithmetic circuit 15 operates the basic wave reactive power consumed with a fluctuating load 21 by the DC current Id, the control angle of a rectifier and an alternating power source system voltage. Consequently, the thyristor of a reactive power compensating device is phase-controlled by a function generator 12, a comparator 13 and a pulse amplifying circuit 14. In such a way, without being influenced by the higher harmonic generated by the rectifier, the highly accurate reactive power compensation can be attained.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention provides a system for supplying power from a power supply system to a load with severe reactive power fluctuations, in which the power supply system is The present invention relates to a reactive power compensator for suppressing voltage fluctuations.

(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. ,
The firing phase of the thyristor of the reactive power compensator is determined according to the detected reactive power to compensate for the reactive power.

FIG. 5 shows a schematic block diagram of a conventional reactive power compensator and its control circuit.

In FIG. 5, 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 lagging reactive power QL taken by the reactor 2 from the power supply by the anti-parallel thyristor 3 is 0.
-100% can be changed arbitrarily by controlling the phase of the firing angle α as shown in FIG.
Phase advancing reactive power Q of phase advancing capacitor. By combining with the above, it is possible to obtain a reactive power compensator that compensates for the lagging reactive power QF of the variable load 4.

For example, in FIG. 5, if the leading reactive power Qc taken by the leading capacitor 1 and the lagging reactive power taken by the reactor 2 are Qt, the leading reactive power QT taken from the power supply is Qr = Q.
c Qt,...
・・・・・・ ■. As is clear from Equation 0, 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 variable load 4 and takes the leading phase reactive power QT equal to that value from the power source, the overall reactive power taken from the power source will be O,
The lagging reactive power QF of the load will be supplied from the reactive power compensator.

Now, it is generally known that when the reactive power of a load connected to a power grid fluctuates, the receiving end voltage fluctuates depending on the impedance 7 of the grid.

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 voltage of the system changes drastically. This causes voltage flicker.

A reactive power compensator shown in FIG. 5 is used as a means for effectively suppressing this type of reactive power fluctuation.

Voltage detection transformer 5 for detecting circuit voltage and load current i
The reactive power detection circuit 11 detects the fundamental wave reactive power QF of the variable load 4 from the current transformer 6 which detects F. On the other hand, the function generator 12 is a circuit that generates the QT of the 0 equation as a function of the firing angle α, and the function is as shown in FIG. 7, which illustrates the 0 equation. Therefore, the comparator 13 detects the point in time 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, and sends a gate signal to the thyristor 3 via the pulse width circuit 14. For example, the QT is controlled to compensate for the QF of the variable load 4.

FIG. 8 is a time chart showing this aspect.

(Problem to be Solved by the Invention) Direct current arc furnaces have been introduced as a type of arc furnace for steelmaking, but generally, these DC arc furnaces supply DC power through a semiconductor rectifier connected to an AC power supply system. has been done. Therefore, like conventional AC arc furnaces, DC arc furnaces also cause reactive power fluctuations, ie voltage fluctuations in the AC power system. In order to suppress this reactive power fluctuation, a conventional reactive power compensator is required, but since the alternating current of the rectifier contains many harmonics, the QF output of the reactive power detection circuit 11 shown in FIG. (Load fundamental wave reactive power)
This appears as a detection error. Therefore, the reactive power compensation performance of the reactive power compensator is reduced.

The purpose of the present invention is to solve the problems of conventional reactive power compensators caused by harmonics generated by rectifiers as described above. The object of the present invention is to realize a power compensation device.

[Structure of the invention]

(Means for Solving Problem 11) The present invention utilizes the property that the fundamental wave reactive power consumed by a rectifier is uniquely determined by the rectifier's DC current and control angle or its control voltage value.

FIG. 1 is a schematic block diagram of a system including a single-phase rectifier and a reactive power compensator of the present invention, and its control circuit. Fifth
Components with the same functions as those in the figures are given the same reference numerals, and explanations thereof will be omitted.

21 in FIG. 1 is a variable load, 22 is a thyristor rectifier for supplying DC power, 23 is a rectifier transformer, and 24 is a smoothing reactor for stabilizing the DC current. 3
0 is the control angle αR of the machine panel flow switch that maintains the DC current Id detected by the flow divider 25 at a preset current value.
This is a rectifier control circuit for determining F.

Reference numeral 15 in the control circuit 10 of the reactive power compensator is a reactive power calculation circuit for calculating the reactive power consumed by the variable load 21.

(Function) The phase of the thyristor rectifier 22 shown in FIG. 1 is controlled by the control circuit 30 so that its direct current Id is constant. The reactive power calculation circuit 15 calculates the fundamental wave reactive power QF consumed by the variable load 21 based on the DC current Id, the control angle of the rectifier, and the AC power supply system voltage. 12.13.
14 performs phase control of the thyristor to compensate for QF, similar to the conventional reactive power compensator.

(Example) An example of the present invention is shown in FIG. Here, the rectifier is assumed to be a single-phase thyristor bridge circuit, but the same applies to other wiring systems. Further, for convenience, the turns ratio of the rectifier transformer is assumed to be 1:1.

Components in FIG. 2 that have the same functions as those in FIG. Reference numeral 10 denotes a control circuit for the reactive power compensator, which is composed of the following elements. Function generator 16. Sample hold 17. The coefficient unit 189 and the multiplier 19 are equivalent to the reactive power calculation circuit in FIG. Function generator 12. Comparator 13. The pulse amplification circuit 14 is for controlling the phase of the thyristor. 30 is a control circuit for a rectifier, which includes a setter 31, a subtracter 32. Constant current control circuit 33. Function generator 34° comparator 35. Pulse amplification circuit 3
Consisting of 6.

FIG. 3 is a conceptual diagram showing the operating principle of this embodiment. Figure (a) shows the AC system a voltage and the AC current ia of the rectifier. Here, the overlap angle of commutation is ignored.

The smoothing reactor 24 is assumed to have a sufficiently large inductance. Further, the rectifier 22 is subjected to constant current control by its control circuit 30 so that its direct current Ll is constant. That is, the constant current control circuit 33 determines the control voltage Ec so that the deviation between the current setting value d' set by the setting device 31 and the DC current Id becomes zero, and the comparator 35 determines the output d of the function generator 34 and the E. The control angle αR with which
Apply a firing pulse to the thyristor at F. Here, the output Vd of the function generator 34 is 0≦ωt in synchronization with the AC system voltage.
It is a function shown in the following equation in the range of π or π≦ωt<2π.

Here, Vda is a DC voltage when α=O°. The above vd, EC, and ignition pulse are shown in FIGS. 3(b) and 3(c).

The purpose of the reactive power compensator is to compensate for the fundamental wave reactive power of the load.6 In the case of the rectifier shown in Figure 2, it is
), since the current ia contains harmonics, it is necessary to detect only the reactive power caused by the fundamental wave component with high precision.

The effective value Iax of the fundamental wave component of ia is obtained from the coefficient when expanded into a Fourier series. Further, the fundamental wave power factor cosφ1 in this case is clearly equal to cosαRF, so the fundamental wave reactive power QRF recorded by the rectifier is as follows. In the control circuit 10 of FIG. 2, the fundamental wave reactive power QRF is calculated using this relational expression. V sin αRF is obtained by sampling and holding the value of the timing at which the thyristor of the device fires (see FIG. 3(e)), and on the other hand, the effective DC radio wave value Iat is obtained by the coefficient multiplier 18. By multiplying the output of the sample holt 17 and the output of the coefficient multiplier 18 by the multiplier 19, the fundamental reactive power QRF shown in equation (A) can be obtained.

Using this QRF as a reference, a function generator 12. The phase of the thyristor of the reactive power compensator is controlled by the comparator 13 and the pulse amplification circuit 14 in the same manner as in the prior art.

As shown in FIG. 5, a conventional reactive power compensator detects reactive power from an AC system voltage and an AC current of a load, and controls the phase of a thyristor to compensate for the reactive power. Third
In the case of the alternating current iB of the rectifier load shown in FIG.
Vs is synchronized with the AC system voltage as shown in Figure 3(d).
A function inωt is generated. This is rectified by the sample hold 17. Comparing this with the fundamental wave effective value 1ax obtained by equation 0, there is a difference of about 10%. Therefore, more accurate reactive power compensation can be performed compared to conventional devices that detect reactive power using effective current values.

Another embodiment is shown in FIG. In this embodiment, the control voltage signal EC is used instead of the control angle αRF of the rectifier in the embodiment of FIG. Type 0 and Figure 3(b)
It is clear from the operating waveform that . Therefore, the reactive power factor calculator 20 calculates . Multiplying the output Iat of the coefficient unit 18 and the output of the reactive power factor calculator 20 by a multiplier 19,
The fundamental wave reactive power given by equation (a) is determined, and the phase of the thyristor of the reactive power compensator is controlled in the same manner as in the embodiment shown in FIG.

〔Effect of the invention〕

The present invention uses the DC current and control angle of the rectifier or its control voltage signal to detect only the fundamental reactive power consumed by the rectifier and compensate for it, so harmonics generated by the rectifier are disabled. It is possible to realize a device with high reactive power compensation accuracy without affecting the power detection function.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a reactive power compensator and its control circuit according to the present invention, FIG. 2 is a detailed block diagram of FIG. 1, and FIG.
2 is a time chart for explaining the operation of FIG. 2, FIG. 4 is a block diagram showing another embodiment of the present invention, and FIG. 5 is a block diagram of a conventional reactive power compensator and its control circuit.
Figure 6 shows the relationship between the reactive power consumed by the reactor and the control angle of the thyristor, Figure 7 shows the relationship between the reactive power of the reactive power compensator and the control angle, and Figure 8 shows the relationship between the reactive power consumed by the reactor and the control angle of the thyristor. 5 is a time chart for explaining the operation of the power compensation device. 1... Phase advance capacitor 2... Reactor 3...
・Anti-parallel thyristor 4...Variable load 5...Voltage detection transformer 6...Current transformer 7...System impedance 10...Control circuit 12...Function generator 14...Pulse amplification Circuit 16... Function generator 18... Coefficient unit 20... Reactive power factor calculator 22... Rectifier 24... Smoothing reactor 30... Rectifier control circuit 32... Subtractor 34... Function generator 36... Pulse amplification circuit 11... Reactive power detection circuit 13... Comparator 15... Reactive power calculation circuit 17... Sample hold 19... Multiplier 21... Variable load 23... Rectifier transformer 25... Shunt switch 31... Setting device 33... Constant current control circuit 35... Comparator

Claims (1)

[Claims] In a reactive power compensator, a reactor device and a phase advance capacity are provided in parallel between a power supply system and a rectifier to control the conducting current by phase control of a thyristor, and reactive power of the rectifier is compensated by the reactor device and the phase advance capacity. , A reactive power compensator characterized in that the energizing current of the reactor device is controlled according to the DC current and control angle of the rectifier or the control voltage signal thereof.