JPS6343530A - Electric source - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a power supply device for an alternating current load whose impedance fluctuates drastically, such as in an electric arc furnace for steel making.

[Prior Art] FIG. 3 is a configuration diagram showing a conventional power supply device for an arc furnace disclosed in, for example, Japanese Unexamined Patent Publication No. 55-150737.
In the figure, 1 is a steelmaking arc as an AC load with large impedance fluctuations, 2A is a load tap switching type furnace transformer connected to the secondary side of the arc furnace 1, and 3 is a furnace transformer 2A. 4 is a filter capacitor, 5 is a reactor, and 6 is an instrument current transformer (CT) connected to the primary side of the furnace transformer 2A.
, 7 is a potential transformer (PT) connected to the power supply system 3,
8 is a reactive power compensation thyristor connected to the power supply system 3; 9 is a control device for controlling the phase of the thyristor 8; 10
is a shunt reactor whose current is regulated by a thyristor 8.

And thyristor 8. The control device 9 and the shunt reactor 10 constitute a reactive power compensator.

Next, the operation will be explained. During the initial operation of the arc furnace 1, the load impedance value is small and the fluctuation range is large, so the furnace transformer 2A is operated at a low tap position, and the electric power is transferred from the power supply system 3 to the arc furnace 1 via the furnace transformer 2A. Predetermined power is supplied.

When scrap etc. are melted in the arc furnace 1, the load impedance value increases accordingly.
This load fluctuation is dealt with by raising the tap positions of the two furnace transformers.

Next, the reactive power generated on the primary side of the furnace transformer 2A is detected by the instrument current transformer 6 and the instrument transformer 7, and the control device 9 determines the firing phase of the thyristor 8. performs phase control.

By controlling the current flowing through the shunt reactor 10 in this way, the function of the phase advancing capacity by the capacitor 4 is also combined, and voltage flicker disturbances due to fluctuations in reactive current in the power supply system 3 are suppressed.

[Problems to be Solved by the Invention] By the way, to explain the output voltage waveform and output current waveform of the conventional power supply device for the arc furnace 1, FIG. 4 is a graph showing an example of the output voltage waveform and output current waveform. As shown in Fig. 4, when a sinusoidal voltage is applied to the arc furnace 1, only a small current flows between the electrodes of the arc furnace 1 near zero voltage due to the spark discharge voltage-current characteristics of the air. When the voltage does not flow and the voltage rises and passes the glow discharge region, an arc discharge occurs and a large current flows. Therefore, the current waveform has an isometrically delayed phase, and the reactive power increases accordingly. Furthermore, even in the arc discharge region, the load impedance fluctuates violently, causing distortion in the current waveform, which is a factor in the occurrence of flicker failures.

Therefore, in conventional electric power supplies for arc furnaces, a reactive power compensator as described above must be installed in parallel in order to suppress the above-mentioned flicker failure, but even with this reactive power compensator, the control response is Due to limitations, etc., as shown in FIG. 4, there are problems such as the delay in current relative to voltage cannot be sufficiently corrected and it is difficult to maintain a flicker compensation rate above a certain value.

This invention was made to solve the above-mentioned problems, and makes it possible to reliably suppress flicker disturbances in the power supply system without installing a reactive power compensator in parallel.
The purpose is to obtain a power supply device.

[Means for Solving the Problems] A power supply device according to the present invention is provided with an inverter that controls AC output to the AC load by performing pulse width modulation according to impedance fluctuations of the AC load. .

[Function] In the power supply device according to the present invention, the AC output to the AC load is controlled by the inverter through pulse width modulation according to the impedance fluctuation of the AC load, so that the AC output to the AC load is controlled with a constant sine wave shape. current is supplied.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1st
The figure is a configuration diagram showing a power supply device according to an embodiment of the present invention.
A furnace transformer is connected to the next side, 3 is a power supply system that supplies current to the arc furnace 1 via the furnace transformer 2, 4 is a filter capacitor, and 5 is a reactor.

In addition, 11 is a thyristor rectifier, 12 is an electrolytic capacitor that stores voltage energy, and 13 is a pulse width modulation (PWM) using gate turn-off, etc.
This inverter 13 controls the AC output to the arc furnace 1 by performing pulse width modulation according to impedance fluctuations of the arc furnace 1.

In this embodiment, 14 is a current transformer (CT), and 15 is a transformer for the thyristor rectifier 11.

The thyristor rectifier 11 is connected to the power supply system 3 via the transformer 15, while the pulse width modulation inverter 13
is connected to the primary side of the furnace transformer 2 via a line to which an instrument current transformer 14 is attached. and thyristor rectifier 11. The pulse width modulation inverter 13 and the electrolytic capacitor 12 are arranged in parallel, and the arc furnace 1 is connected to the above-mentioned transformer 15. Thyristor rectifier 11. '! solution capacitor 12. It is connected to a power supply system 3 via a pulse width modulation inverter 13 and a furnace transformer 2, and receives power from this power supply system 3.

Furthermore, 16 is a control device, and the same control device! 16 receives the current detection signal from the instrument current transformer 14 and controls the thyristor rectifier 11 and constant current control of the pulse width modulation inverter 13.

FIG. 2 shows a pulse width modulation inverter 13 in this invention.
FIG. 2 is a graph showing the output voltage waveform and output current waveform of FIG. 2, and the operation of the power supply device of this embodiment will be explained with reference to FIG. The output voltage from the pulse width modulation inverter 13 is pulse width modulated at a high frequency by the pulse width modulation inverter 13 and the control device 16 based on the current detection signal from the instrument current transformer 14. ) A high voltage is output near the zero point to apply forcing.

This makes the glow discharge period between the electrodes in the arc furnace 1 as short as possible.

Next, when the arc discharge region is reached, the output voltage basic component is set to a value lower than the sine wave value (see FIG. 4) according to the spark discharge voltage-current characteristics of the arc furnace 1.

The output voltage is subjected to pulse width modulation by a pulse width modulation inverter 13 so that the current waveform has a sine wave shape.

In this way, by pulse width modulating the output voltage to the arc furnace 1 using the pulse width modulation inverter 13 and appropriately distorting it, the current waveform can maintain a sine wave shape even if the load impedance changes in the arc discharge region. controlled as
The occurrence of flicker failure in the power supply system 3 is reliably prevented.

Furthermore, since the current waveform and frequency of the AC output to the arc furnace 1 can be arbitrarily controlled by the pulse width modulation inverter 13, there is also the advantage that the operation rate of the arc furnace 1 is improved.

In the above embodiments, the arc furnace is used as an AC load, but other variable loads such as welding machines and nonlinear impedance loads may be used as AC loads, and the same effects as in the above embodiments can be obtained.

[Effects of the Invention] As described above, according to the present invention, an inverter is provided to control the AC output to the AC load by performing pulse width modulation according to the impedance fluctuation of the AC load, so it is possible to This has the effect of reliably suppressing flicker disturbances without providing a reactive power compensation device such as the one described above.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a power supply device according to an embodiment of the present invention, FIG. 2 is a graph showing an AC output waveform from an inverter in the present invention, and FIG. 3 is a block diagram showing a conventional power supply device. FIG. 4 is a graph showing the AC output waveform of the conventional device. In the figure, 1--A steelmaking arc furnace serves as an AC load, and 13...A pulse width modulation inverter serves as an inverter. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A power supply device for an AC load with large impedance fluctuations, characterized in that the power supply is provided with an inverter that controls AC output to the AC load by performing pulse width modulation according to impedance fluctuations of the AC load. Device.