JPS6093536A - Control method of reactive power compensating device - Google Patents

Abstract

PURPOSE:To simplify a circuit and to improve control precision by detecting reactive power on the basis of the value obtained by subtracting the current which flows to a reactive power compensating device from the current at the composite initial power receiving point of a load and the reactive power compensating device. CONSTITUTION:A current transformer 14 detects load currents i3-1-i3-n and the composite current IT of the current iC of the compensating capacitor 8-2 of the reactive power compensating device and the current iL of the compensating reactor 8-1. Namely, iT=iS-1+-+iS-n+iL-iCo. The current transformer 8-5 detects the composite current iS of the current iC of the capacitor 802 and the current i1 of the reactor 8-1. Namely, iS=iL-iCo. Those outputs of the current transformer are inputted to a subtracting circuit 6-1 to perform arithmetic according to iT-iS=i3-1+-+iL-iC-(iL-iC)= i3-1+-+iS-no. Consequent ly, this circuit constitution simplifies the arithmetic. Further, the current signal inputted to a control circuit 7 does not contains the currents of the capacitor 8-2 and reactor 8-1.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention utilizes a combination of a compensation reactor and a compensation capacitor that are connected in parallel with a variable load in a power system and whose phase is controlled by a thyristor to open-loop the reactive power of the variable load. The present invention relates to a control method for a reactive power compensator that compensates for

[Technical background of the invention and its problems]

In a power system to which a load that generates reactive power that fluctuates irregularly and rapidly, such as an arc furnace, is connected, voltage fluctuations occur due to fluctuations in reactive power, and flicker occurs. A reactive power compensator is installed to suppress this. This will be explained using FIG.

FIG. 1 is a block diagram and load of a conventional reactive power compensator for a thyristor-controlled compensation reactor.

In the figure, 1 is the generator, 2 is the line impedance, and 3-
1 to 3-n are loads, 4-1 to 4-n are current transformers, 5 is a voltage transformer, 6 is an addition circuit, 7 is a control circuit for a reactive power compensator, 8 is a reactive power compensator, 8- 1 is a compensation reactor,
8-2 is a compensation capacitor, and 8-3 and 8-4 are cyrisks.

An actual example of the plurality of loads 3-1 to 3-n is an arc furnace or an electric motor. These load currents are detected by current transformers 4-1 to 4-n, and an adder circuit 6 synthesizes a load current signal. The addition circuit will be explained later. The load current signal synthesized here is input to the control circuit 7 of the reactive power compensator. Moreover, the system voltage is detected using the voltage transformer 5, and the voltage signal is input to the control circuit 7 of the reactive power compensator. This control circuit 7 calculates the reactive power of the load based on the voltage signal and the current signal, and further, the reactive power compensator 8 calculates the reactive power to be supplied to the load, and adjusts the firing phase of the thyristors 8-3 and 8-4. decide. Furthermore, the ignition pulse corresponding to the ignition phase is set to the thyristor 8-
Send it to 3 and 8-4. The compensation 1-noctor 8-1 supplies delayed phase reactive power to the power system using current controlled by the thyristors 8-3 and 8-41. Also, compensation capacitor 8-
2 supplies phase-advanced reactive power. That is, in the thyristor-controlled compensation reactor, the equivalent reactance can be continuously changed by the value of the control delay angle α, and the compensation capacitor 8
-2, it is possible to freely supply leading and lagging reactive power to the grid and control it. As a result, the voltage drop due to line impedance 2 of the power transmission line is compensated for,
It is possible to keep the voltage constant and stabilize the power system.

Next, the disadvantages of the conventional system will be explained using FIG. 1, FIG. 2, and FIG. 3. As shown in Figure 1, load 3-
When a plurality of feeders 1 to 3-n are connected to a system, it is necessary to detect the current for each load of each feeder in order to perform open loop control. These currents are detected by current transformers 4-1 to 4-
n current transformers are required. Furthermore, circuits such as those shown in FIGS. 2 and 3 are used to combine these currents. FIG. 2 is called a composite current transformer, in which the currents of each winding flowing to the negative side are combined and output to the secondary side. When the current transformation ratios of the current transformers 4-1 to 4-n are different, each winding on the primary side is configured to have a turn ratio corresponding to the respective current transformation ratio. Next, the configuration of FIG. 3 will be explained.

10-1 to 10-n are current-voltage converters, 11-1 to 11
-n is an input resistor, 12 is a feedback resistor, and 13 is an operational amplifier. Current-voltage converters 610-1 to 10-n are current transformers 4-
It has a function of converting 1 to 4-n current signals into voltage signals. The output is input to input resistors 11-1 to 11-n,
Combined by an operational amplifier. Each gain is determined by the feedback resistor 12 and input resistors 11-1 to 11-n.

As can be seen from the above results, the conventional method requires many current transformers and current combining circuits, which makes it complicated, and the detection accuracy deteriorates.

[Object of the Invention] In view of the above points, an object of the present invention is to provide a control method for a reactive power compensator that can simplify the detection circuit while keeping the control loop open.

[Summary of the invention]

In order to achieve this object, the present invention detects reactive power by subtracting the current flowing through the reactive power compensator from the combined current at the receiving point of the load and the reactive power compensator. In this way, control can be performed in an open loop.

[Embodiments of the invention]

Hereinafter, a configuration example of the present invention will be explained with reference to FIG. 4. In FIG. 4, the same numbers as in FIG. 1 indicate the same items. 6-1 is a subtraction circuit, and 8-5 and 14 are current transformers.

The load current i3-□-...curve r13- by the current transformer 14
A composite current i7 of n, the current 4o of the compensation capacitor 8-2 of the reactive power compensator, and the current iL of the compensation reactor is detected.

That is, it can be expressed as follows. (The lagging current is plus and the leading current is minus.) Ite=is-+ +・・・・・・・・・+13-1 +
iL-i(,......(11) Also, the current i(1
A composite current 18 of the compensation reactor current iL and the current iL of the compensation reactor is detected.

18= iL-i(, ・・・・・・・・・・・・・・・
(2) The outputs of these current transformers are input to the subtraction circuit 6-1, and the following calculations are performed.

it-js=Ig-1+----+13-7l+1L-i
o-(L, to)"'m-1+...+1s-n
・・・・・・・・・・・・・・・・・・・・・・・・
(3) Therefore, calculations using such a circuit configuration will be simpler. Furthermore, as can be seen from equation (3), the current signal input to the control circuit 7 does not include the currents of the compensation capacitor 8-2 and the compensation reactor 8-1. In other words, it becomes open loop control.

〔Effect of the invention〕

According to the present invention, even if there is a large load, the number of current transformers can be reduced, resulting in a simple circuit configuration and improved control accuracy.

Furthermore, since it is an open-loop control, control with a quick response to rapid changes in load is possible. Therefore, the greater the number of feeders in the load, the greater the effects of the present invention.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional reactive power compensator for a thyristor-controlled compensation reactor, Figure 2 is a circuit diagram of a composite current transformer used in Figure 1, and Figure 3 is an adder circuit used in Figure 1. FIG. 4 is a configuration diagram showing an embodiment of the present invention. l... Generator 2... Line impedance 3-1.
~, 3-n...Load 4-1. ~, 4-n...Current transformer 5...Voltage transformer 6...Addition circuit 7...Control circuit of reactive power compensator 8...Reactive power compensator 8-1...Compensation Reactor 8-2...Compensation capacitors 8-3 and 8-4...Sirisk 8-5...Current transformer 10-1. ~+1On...Current voltage converter 11-1.
~, 11-11-=input resistance 12...feedback resistance 13
-, operational amplifier 14...Current transformer (7317) Agent Patent Attorney - Kensuke Chika (and 1 other person) District 1, No. 2 Figure @ Figure 3

Claims (1)

[Claims] In a reactive power compensator, a compensating reactor and a compensating capacitor are provided in parallel between an electric power system and a plurality of loads in order to compensate for reactive power generated by a load, and the phase of a subcurrent flowing to the compensating reactor is controlled by cyrisk, A method for controlling a reactive power compensator, comprising subtracting a current flowing through the reactive power compensator from a current flowing in the power system to detect the plurality of load currents, and controlling the reactive power compensator using this value.