JPS593773B2 - Reactive power fluctuation compensator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reactive power fluctuation compensator capable of quickly compensating for reactive power fluctuations of an inductive load.

5. Fluctuations in load impedance due to, for example, changes in arc resistance in an arc furnace cause reactive power fluctuations, which cause rapid changes in power supply voltage, a phenomenon called voltage flicker.

As a measure against this voltage flicker, a device as shown in FIG. 1 has already been proposed by the present inventors. In FIG. 1, 1 and 2 are human power terminals connected to an AC power supply 3, 4 and 5 are output terminals for taking out an output voltage, and a variable load 12 is connected between these output terminals 4 and 5. 6
is a series reactor, and 75T is a switch device with an igniter connected between the input terminals 1 and 2 via the series reactor 6, and is composed of switch elements 71 and 72 that can control the ignition phase, such as a thyristor. ing.

8 is a transformer, a primary winding 81 is connected between the terminals of the switch device T, and a secondary winding 82 has one end connected to an impedance, for example, a reactor 10, which will be described later, and the other end connected to a detection control, which will be described later. It is connected to the device 11.

9 is a current transformer, a primary winding 91 is connected between input and output terminals 1 and 4, and a secondary winding 92 is connected to a reactor 10/5.

The detection control device 11 detects a voltage difference between the terminal voltage VT of the switching device T and a voltage proportional to the terminal voltage of the reactor 10 that occurs when the load current IL flows through the reactor 10, and detects this difference voltage. In order to keep the average value of V constant 30, when the integral value becomes a constant value every half cycle, it is compared with the reference voltage Es and the switch device 7 is turned on. Note that the transformer 8
, and the current transformer 9 are shown in the figure as having a winding ratio of 1:1, but this is to simplify the explanation of their operation, and in reality, the transformer 8 is 1:
The current transformer 9 is wound at a turns ratio of 1 n'. In the device shown in FIG.
If XB, E and XB can be regarded as constant in equation (4), so the average value of the differential voltage V, that is, the integral value, is compared with the reference voltage Es every half cycle, and the detection control device detects it when they match. When an ignition pulse is issued from 11 to ignite and conduct the switch device 7, the terminal voltage VT is controlled so that the average value, that is, the integral value of the differential voltage v every half cycle is constant, and from equation (4), IT+IL is the average value. It is controlled so that the value remains constant.

However, in the above configuration, the no-load condition, that is, XIL-XB
Since V=VT when IT=O, the control circuit 81
→8→82→11→7→81 is V with Es as the reference voltage
A constant voltage control system for T is configured, and its buffer reactance is via the series reactor 6, which has a relatively larger reactance than the reactance on the power supply side.
Since the switch device 7 cannot respond to a sudden change in the load current 1L, especially a sudden change with a frequency that is twice or more faster than the power supply frequency, the positive feedback may be involved in the above-mentioned control closed loop and hunting may occur.

Accordingly, in order to suppress this, according to general control theory, it is sufficient to provide the control circuit with an anti-hunting circuit consisting mainly of a filter circuit with a delay element, but by adding this circuit, reactive power fluctuations The compensation device will lose its quick response, which can be called its life. Furthermore, this hunting phenomenon is amplified by the harmonic components contained in the load current 1L, resulting in a disadvantage. In view of the above-mentioned matters, this invention was proposed for the purpose of obtaining a reactive power fluctuation compensator that reduces control errors due to harmonics contained in load current without losing quick response. One embodiment of this will be explained based on FIGS. 2 to 5.

In FIG. 2, the same reference numerals as in FIG. 1 indicate substantially the same components. However, the transformer 8 is connected not from the VT at both ends of the switch device 7 with igniter, but from the input terminals 1 and 2.
Alternatively, a power supply voltage difference across the output terminals 4 and 5 is applied to the primary winding 81 thereof. Further, the detection control device 11 includes a time division integrator 111 that starts integration after resetting the detection signal voltage V at a certain point in every half cycle, and a time division integrator 111 that starts integration after resetting the detection signal voltage V at a certain point in time every half cycle, and a time division integrator 111 that sets the detection signal voltage V at a certain point in time in every half cycle. a level comparator 112 that emits a pulse when the level is reached, and this level comparator 112
and a pulse amplifier 113 that amplifies the pulses from the igniter and ignites the igniter-equipped switch device 7. In addition,
The transformer 8 and the current transformer 9 are shown with a turns ratio of 1:1, but this is different from the first one.
Similar to the one shown in the figure, this is to simplify the explanation of the operation, and in reality, the transformer 8 is 1:n and the current transformer 9 is 1:n'.
It is wound to a winding ratio of . Next, to explain the operation of the present invention by illustrating only the reactive power component of an inductive variable load, the voltage of the AC power supply 3 is E, the reactance of the series reactor 6 is XBl, the current flowing through the series reactor 6 is IT, The load current is IL, and the terminal voltage of the switch device 7 is V.
Let X be the reactance of the Tl reactor 10.

(1) First, when there is no load (when IL=0), the detection control device 11 starts integrating the voltage V, that is, the power supply voltage, from an angle of 1β, and the integral value FtVCOSOdθ is
An ignition pulse is emitted at an angle θ (i.e. +β) at the moment when ECldθ is reached, and the switch element 7 of the switch device 7, for example,
2 (that is, the area of the diagonal line in FIG. 3 is the comparison level ErtC for generating the ignition pulse).
(is equal to OSOdθ).

This operation causes a current IT to flow through the reactor 6. In the next half cycle as well, the polarity is reversed, but an ignition pulse is applied to the switch element 71 under exactly the same control, and a current of T flows through the reactor 6. (2) Now assuming that the maximum lagging current 1Lmax with a power factor of 0 flows as the variable load 12, a terminal voltage of JILmaxx is generated at the terminal of the reactor 10 of the secondary circuit of the current transformer 9, as shown in FIG. It is integrated as shown in .

Since the input voltage is (E - JILmOx), the integration starts from the angle - β and becomes yβ (? - JILmaxX) d
It is clear that an ignition pulse is generated when the integral value θ reaches the comparison level EK3cOsOdθ.

Now, if the value of the reactance X of the reactor 10 is selected as follows, the ignition pulse generation angle β will be equal to the maximum value 1Lmax of the load current at the delayed zero power factor.

That is, the thyristor current is brought to zero under the influence of the load current 1L. i.e.)? β (ILmax ) to β
(L-JiLX) The integral of dθ is fired before θ reaches one, and as mentioned above, as IL changes from zero to the maximum, current IT changes from the current corresponding to IL-0 to zero. Continuously? You can roll.

(3) Next, if we consider the case where the power factor of the load current is 100%, as shown in Figure 5, integration starts from the 1β point (EjXIL), but clearly the integral value of -j x 1L is As can be seen in the area indicated by the vertical line in Figure 5, it becomes zero from 1β to +β, and in the end, dθ1L? dθ, i.e. (
At the same phase angle β as in the no-load state described in 1), the above-mentioned integral value reaches the comparison level, causing the switch device 7 to conduct a current of T.

In other words, this shows that the current control of the switch device 7 is not sensitive to a load with a power factor of 100% that does not include reactive power, regardless of the magnitude of the load current.

(4) For a load with an arbitrary lagging power factor, this load current is 1
It is well known that the current vectors can be separated into two current vectors, 00% power factor and 0% power factor lag. As explained in (2) above, only for the power component load current, the switch device 7 reduces the current of the reactor 6 as the reactive power load increases.

That is, the reactive power consumed by the reactor 6 is reduced. As is clear from the above explanation, by setting the integration start at the point 1β for the firing angle β of the switch device under no load, and comparing the level of the integral output of V from 1β to 1, the load can be adjusted. It is possible to perform time-division reactive power adjustment that inversely responds to increases and decreases in reactive power every half cycle, and it is possible to flatten the influence of reactive power fluctuations on the power supply.

In other words, the system is open-loop, the composite voltage is integrated every half cycle of the power supply frequency, and this integrated value is compared with a set level and then integrated in a time-division manner, so that the reactive power fluctuation compensation device It can be seen that control errors due to harmonics contained in the load current can be reduced without impairing the quick response of the load current. Note that the selection of the angle β has the following advantages: (1) When the IL waveform has a lot of distortion - the JXIL waveform will also be distorted, but the larger β is, the wider the integration period will be, so the effect on the error will be smaller; In addition, (2) the smaller β is, the smaller the waveform distortion factor of IT corresponding to the amount of reactive power that can be controlled by IT is advantageous. Generally speaking, in cases where the IL waveform distortion is large, such as an arc furnace, β-300 is appropriate.For cases where the IL waveform distortion is relatively small, such as a rectifier load, β-10 is appropriate. .

As described above, according to the present invention, it is possible to reduce control errors due to harmonic components contained in load current without losing quick response, and to reduce the constantly consumed reactive power to the necessary minimum, resulting in an economical It is possible to prevent reactive power fluctuations. Further, there is an effect that no hunting phenomenon occurs and there is no fear that the hunting phenomenon will be amplified by harmonic components contained in the load current. The igniter-equipped switch device of the present invention may be replaced by an ignitron or the like in place of the thyristor used in the above-mentioned embodiments.In short, any switch element that can adjust the ignition phase may be used. good.

Further, in the above-mentioned embodiments, the case where the present invention is applied to a single-phase circuit has been described, but it goes without saying that the same effect can be achieved even when the present invention is applied to a three-phase circuit.

[Brief explanation of the drawing]

FIG. 1 is a wiring diagram showing a conventional example, FIG. 2 is a wiring diagram showing an embodiment of the present invention, and FIGS. 3 to 5 are waveform diagrams for explaining the present invention. 3...AC power supply, 6...Series reactor, 7. ...Switch device with igniter, 8...
...Transformer, 9...Current transformer, 10...
Impedance, 11...Detection control device, 11
1... Time division integrator, 112... Level comparator, 113... Pulse amplifier, 12...
...Fluctuating load.

Claims (1)

[Claims] 1. A switching device with an igniter that can control the ignition phase and a series reactor are connected in series in parallel to an inductive variable load connected to a power source, and the ignition phase angle of the switching device with an igniter is controlled. In a reactive power fluctuation compensator that operates the series reactor as a fast-moving variable inductance, the voltage of the power supply and the voltage proportional to the current of the fluctuating load are combined, and this combined voltage is synchronized with the power supply zero point and Integration is started from a point in time when the phase is delayed by π/2)-β, the value is compared with the set level, and time-division integration is performed so as to reset the integral value by π, so that the integral value reaches the set level. The ignition phase angle of the igniter-equipped switch device is controlled by the pulse emitted when the igniter is reached, thereby performing time-division integral reactive power control that inversely corresponds to the increase or decrease of the reactive power of the fluctuating load every half cycle. A reactive power fluctuation compensator characterized by: