JP3073606B2 - DC arc furnace controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC arc furnace control device, and more particularly to a DC arc furnace control device capable of suppressing fluctuations in arc furnace current and reactive power.

[0002]

2. Description of the Related Art In a DC arc furnace, an arc current is controlled by a thyristor firing angle control by a constant current circuit, and an arc voltage is controlled by an electrode position control. The arc voltage is determined by the product of the arc current and the arc resistance, and the arc resistance is almost equal to the arc resistance.
Since the arc length is determined by the arc length, the arc voltage control is a control of raising and lowering the electrode using the arc voltage as a feedback signal, and is a slower control than the arc current control by the thyristor firing angle control. It is said that the stability of the DC arc furnace is much better than that of the AC arc furnace, which relies solely on the electrode position control, because the thyristor adds constant current control.

[0003]

The constant current circuit reduces the thyristor firing angle when the arc current decreases, and increases the thyristor firing angle when the arc current increases. The minimum angle at which the thyristor can be fired is called the α limit, and when it reaches the α limit, the arc current decreases, and the thyristor firing angle can no longer be reduced and constant current control can no longer be performed. -Unstable current cannot be obtained. On the other hand, the arc voltage by the electrode position control is such that when the firing angle of the thyristor reaches the α limit, the arc current is unstable, the arc voltage is not stable, and the electrode position control with a slow response speed. It is difficult to reach the optimum electrode position. Therefore, in such a state, while the thyristor firing angle has reached the α limit, the state in which the arc current is unstable and the reactive power fluctuation is large continues, and the advantages of the DC arc furnace are impaired. I will. Accordingly, an object of the present invention is to provide a DC arc furnace control device in which an unstable state of the arc current is not continued and an optimum arc voltage and arc current can be obtained.

[0004]

In order to achieve the above object, the present invention has an AC power source 2 as shown in FIG.
A thyristor converter 1, an arc current detector 4, and a constant current control circuit 6 for comparing the output signal of the arc current detector 4 with a set current value Iref to perform constant current control.
And a thyristor gate pulse determined by the output reference signal of the constant current control circuit 6 to generate the thyristor converter 1
A gate pulse generating circuit 7, an arc voltage detector 5, an output signal of the arc voltage detector 5, and a set voltage value V
A constant voltage control circuit 8 that performs a comparison operation with ref to perform constant voltage control
And a DC arc furnace control device comprising an electrode lifting / lowering device 9 for raising / lowering the electrode based on the constant voltage control circuit 68 signal.
When the output signal of the constant current control circuit 6 is out of the specified value, a comparator 11 for generating an electrode lowering signal and an electrode lowering signal generated by the comparator 11 are sent to the electrode lifting / lowering device 9 with priority given to the electrode lowering signal. It is characterized by having an interrupt circuit 12.

[0005]

With the above arrangement, when the output signal of the current control circuit 6 is at the level which has reached the α limit, the comparator 11 passes through the interrupt circuit 12 and the electrode lowering signal is sent to the electrode lifting / lowering device 9. Sent. The electrode lifting device 9 keeps lowering the electrode 10 at a speed corresponding to the response speed. As the arc resistance decreases, the arc current increases, the state exits the α limit state, and stabilizes at the set current and the set voltage.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a correlation chart between active power and reactive power for explaining the operation of FIG.

In FIG. 1, reference numeral 1 denotes a thyristor converter,
The AC power supplied from the AC power source 2 is converted into DC power, and this DC power is supplied to the DC arc furnace 3. A current detector 4 is provided for detecting a current of the DC arc furnace, and a voltage detector 5 is provided for detecting a voltage. The constant current control circuit 6 controls the thyristor converter 1 based on the arc current set value Iref and the feedback signal of the arc current detector 4 to perform constant current control. That is, the gate pulse generation circuit controls the firing phase of the thyristor converter according to the output Ec of the constant current control circuit 6.

The constant voltage control circuit 8 has an arc voltage set value Vre
The electrode lifting device 9 is controlled by f and the feedback signal from the arc voltage detector 5 to control the elevation of the electrode 10 of the DC arc furnace to control the arc voltage.

Reference numeral 11 denotes a comparator which generates an electrode lowering signal when the output signal of the constant current control circuit 6 is out of a prescribed value. Reference numeral 12 gives priority to the electrode lowering signal generated by the comparator 11 to the electrode lifting / lowering device 9. An interrupt circuit is shown.

The constant current control circuit 6 has an arc current set value Ire
Constant current control is performed by f and a feedback signal of the arc current detector 4. On the other hand, the constant voltage control circuit 8 performs constant voltage control based on the arc voltage set value Vref and the feedback signal of the arc voltage detector 5. When the output signal Ec of the constant current control circuit 6 reaches the α limit, an electrode lowering signal is sent from the comparator 11 through the interrupt circuit 12 to the electrode lifting / lowering device 9 to lower the electrode 10.

The relationship between the arc current, the arc voltage, and the α limit will be described with reference to FIG. In a DC arc furnace in which constant current control is performed by controlling the firing angle of the thyristor and constant voltage is controlled by controlling the position of the electrodes, the correlation between the reactive power on the AC side and the active power is a fan shape as shown in FIG. Becomes The radius of the fan is the apparent power determined by the set value of the AC current (the value obtained by converting the set value of the arc current into AC) and the rated AC voltage. The thyristor firing angle substantially corresponds to the power factor angle. At a thyristor firing angle of 90 degrees, active power = 0, reactive power = point D of apparent power, and conversely, point C at the α limit. The constant current control can be performed on the circumference from point C to point D. On the straight line from the point C to 0, the thyristor firing angle is at the α limit, and the arc current changes along with the arc resistance.

The arc furnace input set power P0 is given by an arc voltage set value Vref and an arc current set value Iref. As shown in FIG. 2, points at which the set power P0 is satisfied are point A and point B. Near the point A, constant current control is performed.
The thyristor firing angle is controlled in accordance with the change in the arc resistance, and the electrode position becomes the optimum position in a state where both the arc current and the reactive power are stable. At the point B, the α limit is set and the control is unstable, the arc current changes with the change of the arc resistance, the arc current intermittently occurs, and the reactive power starts from around the point B. It changes through point C to point D. In this state, although the electrode position is an inappropriate position, the arc voltage greatly changes. Therefore, in an electrode position control with a slow response, a control jam occurs, and it becomes difficult to adjust the electrode to the optimum point A.
As in the present invention, when the α limit is detected and the electrode is lowered, B
From the point to the point C, the state escapes from the α limit state and the arc current becomes stable, and the point A is reached.

[0013]

As described above, according to the present invention,
Since the thyristor firing angle α limit is detected and the electrode is lowered, the arc current can be shifted from an unstable state to a stable state, and the DC arc furnace can be controlled in a stable state.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a DC arc furnace control device showing an embodiment of the present invention.

FIG. 2 is a correlation diagram between active power and reactive power for explaining the relationship between the arc voltage arc current and the α limit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Thyristor converter, 2 ... AC power supply, 3 ... DC arc furnace, 4 ... Current detector, 5 ... Arc voltage detector, 6 ... Constant current control circuit, 7 ... Gate pulse generation circuit, 8 ... constant voltage control circuit, 9 ... electrode elevating device, 10 ... electrode, 11 ... comparator, 12 ... interrupt circuit,

Claims (1)

(57) [Claims] A constant current control circuit for controlling an output current of a thyristor converter to which an arc current set value and a feedback signal from an arc current detector are applied, an arc voltage set value and an arc voltage. In a DC arc furnace control apparatus provided with a constant voltage control circuit for controlling a position of an electrode of a DC arc furnace to which a feedback signal from a voltage detector is applied, an output of the constant current control circuit is an output of the thyristor converter. A comparator for generating an output signal when a limit in a direction to increase the output is reached; and an interrupt circuit for generating a signal for forcibly lowering the electrode when the comparator generates an output. DC arc furnace controller.