JPH08273827A - Electric current controlling device for arc furnace - Google Patents

Abstract

PURPOSE: To control electric current with proper responds independently of arc resistance which fluctuates based on the arc generating situation by providing a specified function regarding an electric current controlling device for arc furnace having a prescribed system to melt scraps by generating arc discharge. CONSTITUTION: An electric current controlling device for an arc furnace is one composed of an arc furnace 1, a d.c. reactor 3, an electric power transformer 4, an ignition angle controlling apparatus 5 to control the ignition angle of the electric power transformer 4, a current detector 6, and a current adjusting apparatus 7 to give a set instruction to the ignition angle controlling apparatus 5 based on an electric current signal from the current detector 6 as a feedback signal and the current controlling device is to melt scraps 11 by generating arc discharge. In the device, a voltage detector 8 and a computer 9 to carry out multiplication and division are installed, the current adjusting apparatus 7 is provided with an integration time changeable means for integration operation, and thus the current controlling device is provided with a function to compute a resistance value by the computer 9 based on the electric signals from the voltage detector 8 and the electric signals from the current detector 6 and to variably set the integration time by the integration time changeable means based on the value inversely proportional to the resistance value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current control device when a load resistance of a DC arc furnace or the like changes, and more particularly to an optimum current control device for an arc furnace regardless of variations in arc length.

[0002]

2. Description of the Related Art FIG. 3 shows a block circuit diagram of a conventional current control device for an arc furnace. The arc furnace is furnace 1,
And an electrode 2. The current control device of the arc furnace includes a DC reactor 3, a power converter 4, a firing angle controller 5 for controlling the firing angle of the power converter 4, a current detector 6, and this current detection. Scrap material to be charged into the furnace 1 and a current controller 7 which uses the current signal 62 of the reactor 6 as a feedback signal and gives a setting command to the ignition angle controller 5.
An arc discharge 21 is continuously generated between the electrode 11 and the electrode 2 to melt the scrap material 11.

In such a configuration, the detected current of the current detector 6 is rectified by the rectifying means 61 to become the current signal 62, which is negatively fed back as the feedback signal of the current regulator 7. That is, the current regulator 7 (ACR) performs the proportional plus integral operation so that the current signal 62 matches the current command value 63. The output signal 73 of the current regulator 7 is added to the input signal of the firing angle regulator 5 (FAR) to control the firing phase angle of the firing angle regulator 5 (FAR). Then, this firing phase angle output controls the conduction angle of a semiconductor control element of the power converter 4, for example, a thyristor, and controls the output voltage of the power converter 4. The output voltage of this power converter 4 controls the arc current of the arc discharge 21 between the electrode 2 and the furnace 1. The DC reactor 3 is used to suppress overcurrent when the electrode 2 and the furnace 1 are short-circuited.
Further, the average value of the arc voltage can be controlled by controlling the distance between the electrode 2 and the furnace 1.

There are various settling methods for the proportional gain Kp and the integral time Ti of the controller, and many people have various settling methods. Here, the Betlerk method, which is relatively widely applied in the field of arc furnace control, is described here. Describe. Reference: “Optimization of feedback control system (optimum adjustment method by Transdyne control theory)” Fuji Electric Co., Ltd., Catalog No. CP035.

FIG. 4 is an explanatory view for explaining a control settling method based on the Betlerk method. In (A) of FIG. 4, the transfer function GR of the controller having proportional + integral operation (hereinafter, referred to as PI controller) has a proportional gain Vp and an integration time Ti.
It is expressed by equation (1).

[0006]

[Equation 1]

The main delay of the controlled object is a first-order delay, and this transfer function GS has a gain of the controlled object as Vs, a first-order delay time as T1, and a detector including a higher-order delay of the controlled object. If several small delay elements such as are taken as the sum of this small delay time and approximated as there is a first-order delay term of this time constant σ, the transfer function GS of the controlled object including these several small delay elements is It is approximated by Eq. (2) as a secondary delay system.

[0008]

[Equation 2]

Since the main first-order lag term of the controlled object is the main cause of the slow control operation, the PI that compensates for this lag element
A regulator is suitable, and the integration time Ti of the regulator and the main first-order delay time T1 to be controlled are selected to be equal. The open-loop transfer function G0 of the control system in this state is expressed by equation (3).

[0010]

(Equation 3)

The ideal control achieves its control purpose when C = R, but in reality, the closed loop transfer function Gc acts and C = Gc · R. Therefore, the settling method based on the Betlarke method is that the gain 1 can be secured over the range of the frequency ω where the closed-loop transfer function Gc is as wide as possible, as shown in FIG. 4 (B). Ensure such conditions
The proportional gain Vp and the integration time Ti of the PI controller are expressed by equations (4) and (5). Further, the response characteristic of the control amount C to the stepwise change of the target value R at this time is shown in FIG.

[0012]

[Equation 4]

[0013]

(Equation 5)

In the current regulator 7 of the arc furnace, the main primary delay time T1 to be controlled and the gain VS to be controlled are the inductance L of the DC reactor 3 and the DC resistance R (resistance of the DC reactor 3) of this current circuit. RL, arc resistance Ra,
Determined by wiring and furnace resistance Re). That is, the power converter 4
Is the output of, and the current i flowing through the DC reactor 3 is
It is expressed by equation (6).

[0015]

(Equation 6)

Now, the DC rated voltage is Edo and the DC rated current is
Let Idn be the output v of the power converter 4 and the current i of the DC reactor 3 expressed as v (%) and i (%) in percentage,
Equation (6) can be converted to equation (7).

[0017]

(Equation 7)

That is, the gain Vs to be controlled is given by equation (8).

[0019]

(Equation 8)

Therefore, in the current regulator 7 of the arc furnace, the proportional gain Vp and the integral time Ti of the PI regulator satisfying the setting conditions of the Betlerk method are obtained by substituting the equation (8) into the equation (4).
It can be expressed by equations (9) and (10).

[0021]

[Equation 9] Kp = L · Idn / (2 · σ · Edo) …… (9)

[0022]

[Equation 10] Ti = L / R, R = RL + Re + (Ra) (10) where, L: DC reactor inductance RL; DC reactor resistance Re; Wiring and furnace resistance (Ra); Arc resistance Idn; DC rated current Edo; DC rated voltage σ; Total value of delay time of each part excluding delay component of DC reactor That is, in the current regulator 7 of the arc furnace, proportional gain
Vp is not affected by the arc resistance Ra, but the integration time Ti is affected by the arc resistance Ra.

[0023]

The conventional current control device for the electric arc furnace has the following problems. That is,
In the prior art, the resistance component R of the circuit of the DC reactor during arc generation is expressed by the equation (11) including the arc resistance.

[0024]

[Equation 11] R = RL + Re + Ra (11) In the conventional technique, the settling of the integration time Ti of the current regulator 7 is
State where electrode 2 and furnace 1 are short-circuited (resistance value Ro = RL + R
e) and during arcing (resistance value R = RL + Re + Ra)
Since it has to be settled so as to cover both of the above conditions, the settling must be performed with the electrode 2 short-circuited with the furnace 1 having a slow response, that is, the integration time is long.

While the arc is occurring, the time constant becomes short because the resistance value increases, but the response time of the current regulator 7 is slow because the integration time of the current regulator 7 is fixed and does not change. The present invention has been made in view of the above points, and an object thereof is to solve the above-mentioned problems and perform current control having an optimum response regardless of the arc resistance that varies depending on the arc generation situation such as the length of the arc. It is to provide a current control device for an arc furnace.

[0026]

In order to achieve the above object, in the present invention, an arc furnace comprising a furnace and electrodes, a DC reactor, a power converter, and an ignition angle of the power converter are set. Scrap to be put into the furnace, which consists of a firing angle controller to be controlled, a current detector, and a current regulator which uses the current signal of this current detector as a feedback signal to give a setting command to the firing angle controller. In a current control device for an arc furnace that generates an arc discharge between a material and an electrode to melt scrap material, a voltage detector and a computing unit for performing a multiplication / division operation are provided, and the current regulator has at least an integral operation. Of the voltage signal from the voltage detector and the current signal from the current detector, the resistance value is calculated by a calculator, and the integration time variable means has a value that is inversely proportional to the calculated resistance value. Variable setting of integration time And things.

Further, the arithmetic unit is provided with a limiting means for limiting the output value of the multiplication / division operation output.

[0028]

With the above structure, the integration time (Ti0 = L / Ro) of the calculator and the current regulator is adjusted in the state of the resistance value (Ro = RL + Re) in which the electrodes are short-circuited to the furnace in advance. Next, in the operating state, the calculation of equation (12) is performed from the current signal i (%) and the voltage signal v (%), and the calculation result is the integration time
Used as Ti.

[0029]

[Equation 12] Ti = Ti0 ・ Ro ・ i (%) / v (%) (12) As a result, the voltage and current of the i (%) / v (%) term are controlled stably. In the steady state, the circuit resistance R of the DC reactor 3 including the arc discharge resistance of the arc furnace is shown, and optimal current control can be performed without being influenced by the arc generation status such as the length of the arc.

When the output voltage fluctuation of the power converter 4 changes significantly, the current component is the DC reactor 3
Does not change rapidly. Therefore, in such a case, (1
The fluctuation of the integration time Ti calculated by equation (2) is too severe, and conversely,
It gives an unstable phenomenon to current control. This problem can be solved by limiting the calculation output of the integration time Ti calculated by the expression (12) and limiting the variable range of the optimum integration time Ti.

[0031]

1 is a block circuit diagram of a current control device for an arc furnace according to an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of a circuit in which an arc current flows through a DC reactor, and the same function corresponding to FIG. The members have the same reference numerals. In FIG. 1, the arc furnace comprises a furnace 1 and an electrode 2. The current control device of the arc furnace includes a DC reactor 3, a power converter 4, a firing angle controller 5 (FAR) for controlling the firing angle of the power converter 4, a current detector 6, The scrap material 11 and the electrode to be put into the furnace 1 are composed of a current controller 7 which gives a setting command to the ignition angle controller 5 by using the current signal 62 i (%) of the current detector 6 as a feedback signal. The arc discharge 21 is continuously generated between the two and the scrap material 11 is melted.

The current controller of one embodiment according to the present invention comprises a voltage detector 8 and an arithmetic unit 9 for performing multiplication / division operation. Further, the current regulator 7 includes at least integration time varying means 72 for integration operation. Further, in the illustrated example, the arithmetic unit 9 is configured to include a multiplier 91, a divider 92, and a limiting unit 93 that limits the output value of the multiplication / division operation output.

In such a configuration, the voltage signal 81 v (%) from the voltage detector 8 and the current signal 62 i from the current detector 6
(%), The resistance value (R) is calculated by the calculator 9, and the integration time Ti is variably set by the integration time changing means 72 with a value inversely proportional to the calculated resistance value R.
Optimum control of the arc current in the arc furnace. Current regulator 7
In the hardware configured by the analog technology, the voltage controller 8 and the divider are added to the current control device described in the related art.
An arithmetic unit 9 including 92, a multiplier 91 and an output limiter 93 is added. Further, in the hardware in which the current regulator 7 is configured by digital technology, only the voltage detector 8 is added, and the computing means of the computing unit 9 is executed by the program processing of the current regulator 7.

The arithmetic operation performed by the arithmetic unit 9 is the arithmetic operation Ti = Ti0.Ro.i (%) / v (%) expressed by the equation (12), which is the integration time Ti of the current regulator 7. When the electrode 2 and the furnace 1 are short-circuited, Ti0 is used as the integration time of the current regulator,
Use Ti0 / Ro / (Ro + Ra) during arc generation. Here, the arc resistance Ra changes depending on the arc length. Therefore, the arc resistance Ra changes due to the melting of scrap in the furnace 1, but the resistance (Ro + Ra) is equal to the DC voltage v (%).
/ Since the calculation is performed by the DC current i (%), the integration time Ti of the current regulator 7 can always be kept at an optimum adjustment value that is compensated for the arc resistance Ra.

FIG. 2 shows an equivalent circuit diagram of a circuit in which the arc current flows through the DC reactor. FIG. 2A shows the case where the electrode 2 and the furnace 1 are short-circuited, and the arc current flows through the DC reactor. The equivalent circuit of the circuit consists of the DC resistance RL of the DC reactor 3, the wiring and the furnace resistance Re,
(B) shows when arc discharge is occurring between the electrode 2 and the furnace 1, and at this time, arc resistance Ra is further added.

Further, in FIG. 1, the output limiter 93 has an unstable phenomenon (integration time) in the current control when the above-calculated integration time Ti of the current regulator 7 changes transiently and largely.
Ti is too small) or it takes a long time to set the current (integration time
Ti is too large). Therefore, by limiting the calculation output of the calculated integration time Ti and limiting the variable range of the optimum integration time Ti, it is possible to avoid the above-mentioned adverse effect that occurs transiently.

[0037]

According to the present invention, the control parameter of the current regulator can take an optimum value even when the electrode and the furnace are short-circuited or during arc generation, and varies depending on the arc generation condition such as the length of the arc. It is possible to perform the current control having an optimum response regardless of the arc resistance, stabilize the arc current control, and make it difficult for the arc to break.
Further, since arc breakage is less likely to occur, the operating time of the arc furnace can be shortened and the power efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an electric current control device for an arc furnace according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of a circuit in which an arc current flows through a DC reactor.

FIG. 3 is a block circuit diagram of a conventional arc furnace current control device.

FIG. 4 is an explanatory diagram illustrating a control settling method based on the Betlerk method.

[Explanation of symbols]

1 furnace 2 electrode 3 direct current reactor 4 power converter 5 ignition angle adjuster 6 current detector 62, i (%) current signal 63 current command value 7 current regulator 71 proportional operating means 72 integral operating means 8 voltage detector 81 , V (%) Voltage signal 9 Operator 91 Multiplier 92 Divider 93 Limiter L DC inductor inductance Ra Arc resistance Re Wiring and furnace resistance RL DC reactor circuit resistance Idn DC rated current Edo DC rated voltage σ DC reactor Value of total delay time of each part excluding the delay component of Ti, Ti0 integration time

Claims (2)

[Claims] 1. An arc furnace comprising a furnace, an electrode, a DC reactor, a power converter, a firing angle controller for controlling the firing angle of the power converter, a current detector, and a current detector. And a current controller which uses the current signal of the current detector as a feedback signal to give a setting command to the ignition angle controller, and an arc discharge is generated between the scrap material charged into the furnace and the electrode. In a current control device for an arc furnace that melts, a voltage detector and a calculator for performing a multiplication / division operation are provided, and the current regulator is provided with at least an integration time variable means for integration operation. And a current signal from the current detector, the resistance value is calculated by the calculator, and the integration time is variably set by the integration time variable means with a value inversely proportional to the calculated resistance value. Current control of arc furnace Control device. 2. The electric current control device for an electric arc furnace according to claim 1, wherein the arithmetic unit includes a limiting means for limiting an output value of the multiplication / division operation output. .