JPS61114320A - Power supply device for dc arc furnace - Google Patents

Abstract

PURPOSE:To reduce the cost of the titled power supply device by connecting in cascade the DC sides of the self-excited and separately excited rectifiers capable of phase control connected to an AC power supply to output to an arc furnace, and securing the offset between the reactive power components of both rectifiers based on an error between the applied power and its set power value. CONSTITUTION:A self-excited rectifier 2-1 and a separately excited rectifier 2-2 are connected a DELTA winding and a Y winding at the secondary side of a phase shift transformer 11 for rectifier. The output terminals at the DC sides of both rectifiers are cascaded and also connected to an arc furnace electrode 4-1 and a furnace body 4-2. Then a DC voltage transformer 5-1 and a current transformer 5-2 provided to rectifiers 2-1 and 2-2 are connected to an applied power operator 6-1 of a controller 6. Then a control error detector 6-3 compares the applied power with the set applied power, and the limitation is supplied when the error is equal to values excepting a prescribed level for acquisition of a control angle. The ignition control is given to a thyristor of the rectifier 2-1 by a phase controller 6-7. Based on this control angle, the control angle of the rectifier 2-2 is obtained. Then the thyristor is controlled by a phase controller 7-2.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a DC type arc furnace tube II device that can effectively supply DC power to a large-capacity arc furnace for steel manufacturing. [Technical background of the invention and its problems] [Points] Conventionally, in large-capacity arc furnaces for steelmaking and the like, AC arc furnace power supplies have been the mainstay, with a furnace transformer equipped with an on-load voltage regulator as the power supply equipment.

By the way, recent advances in semiconductor technology have made it possible to increase the capacity of power semiconductor elements, and with this, the arc furnace N2m
Equipment is also transitioning from AC arc furnace tube 8I equipment to DC arc furnace power supply equipment.

FIG. 3 shows a schematic circuit configuration of such a DC type electric arc furnace I apparatus. In FIG. 3, 1 is a rectifier transformer whose primary side is connected to an AC N source, and 2 is a phase-controllable separately excited rectifier whose AC input terminal is connected to the secondary side of the rectifier transformer 1. One of the DC side output ends of this separately excited rectifier 2 is connected to the arc furnace electrode 4-1 of the arc furnace 4 via the smoothing reactor 3, and the other DC side output end is connected to the furnace body 4 of the arc furnace 4. -2, forming a DC power supply path. On the other hand, 6 is 1il of separately excited rectifier 2.
This device 2 converts the DC voltage input from the DC voltage transformer 5-1 connected between the DC output terminals of the separately excited rectifier 2 and the DC current transformer provided in the DC power supply path into the DC voltage transformer 5-1. an input power calculation unit 6-1 that calculates input power based on the DC current input from the unit 5-2;
Input power setting device 6-2 for setting input power, input power output from input power calculation unit 6-1 and input power setting device 6
A control error detector 6-3 that calculates the error Δ by comparing the set value outputted from -2, and this ilIw error detector 6-3.
a limiter circuit 6-4 which applies a limiter when the value of Δ outputted from is below or above l[; an error integrator that integrates the output of this limiter circuit 6-4 to obtain an error amount;
The control angle is calculated based on the error amount output from the error integrator 6-5.
A phase controller 6-7 is provided which generates a phase control signal from the control angle determined by the II11111 angle control device 6-6.

Therefore, if a feedback control system is configured to control the thyristor of the separately excited rectifier 2 using the phase control signal output from the phase controller 6-7 of the 1lJllIl device 6, the control from the separately excited rectifier 2 to the arc furnace 4 can be configured. This means that the desired DC power can be supplied. However, if the setting of the DC power supplied to the arc furnace 4 is low, it is not possible to simply control the separately excited rectifier 2 using the antibacterial device 6. Interchange 1 because it is narrowed down to nearby! The power factor seen from the source side will be bad. Therefore, in preparation for such a case, a reactive power compensator 100 for compensating for reactive power is separately installed as shown in the figure to improve the power factor. This reactive power compensator 100 is connected to an AC power source and has a shunt reactor 100-1 that supplies delayed reactive power.
and a variable AC power converter 100 connected in series thereto.
-2 and a filter/phase advance capacitor 1 that supplies a phase advance valve
It consists of 00-3. The AC power converter 100-2 of this reactive power compensator 100 is controlled by the control 1 device 106 of the reactive power compensator 100. In other words, this III 11111 106 is based on the AC voltage input from the AC voltage transformer 1o5-1 connected to the AC power supply and the AC current input from the AC current transformer 105-2 provided in the AC power supply path. A control amount calculator 106 that calculates the reactive power control amount taken by the device
-1, control angle calculator 106- which calculates the control angle from the reactive power control amount output from this control amount calculator 106-1;
2 and a phase controller 106-3 that generates a phase control signal based on the control angle determined by the control angle calculator 106-2.
It is equipped with Therefore, the phase IIIWJ signal output from the phase controller 106-3 of this control device 106 causes the AC power converter 100- of the reactive power compensator 100 to
The power factor can be improved by compensating for the delayed reactive power using the shunt reactor 100-1 using the thyristor No. 2 with phase III 1OL.

However, in this way, the rectifier transformer 1, the separately excited rectifier 2, the shunt reactor 100-1, the AC power converter 100-2, and the filter/phase advance capacitor provided in the reactive power compensator 100 are used as arc furnace power supply equipment. 100-3 has the disadvantage that if the power input to the arc furnace is pmax, the capacity of these must also be Pmax, and therefore the total installed capacity of the power supply equipment needs to be five times Pmax, making the equipment cost relatively high. There is.

[Purpose of the invention]

The present invention eliminates the above-mentioned drawbacks, maintains a high power factor as seen from the AC power source even when the DC power supplied to the arc furnace is set at a low level, and reduces the total installed capacity of power equipment. It is an object of the present invention to provide a DC type arc furnace power supply device that can reduce the equipment cost by keeping the costs low.

[Summary of the invention]

In order to achieve the above object, the present invention provides a DC arc furnace which supplies DC power to the arc furnace from an AC power source through a separately excited rectifier that can be phased. ! In the device, the AC side input ends of the phase controllable self-excited rectifier and the phase controllable separately excited rectifier are connected to an AC ATM via a rectifier phase shifting transformer, and the DC side output ends of both of these current differencers are are connected in cascade, and a DC power supply path is configured to supply the DC output to the arc furnace. A phase control device that determines a phase angle such that a lagging reactive power component taken by the excited rectifier and a leading reactive power component taken by the self-excited rectifier cancel each other out, and controls the phase so that a desired DC power is obtained. It is characterized by that it is provided.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the circuit configuration of a DC type arc furnace power supply device according to the present invention, and the same parts as in FIG. 3 will be described with the same symbols. In Fig. 1, reference numeral 11 denotes a rectifier phase shift transformer having six windings on the primary side and two windings Δ and Y on the secondary side. Connected to power. 2-1 and 2-2 are a separately excited rectifier and a self-help rectifier, respectively, which can control the phase, and the AC side input terminal of the separately excited rectifier 2-1 is connected to the 6th winding on the secondary side of the rectifier phase shift transformer 11. The input end of the self-help rectifier 2-2 on the AC side is connected to the secondary Y winding of the rectifier phase shift transformer 11, and the DC input terminal of the self-help rectifier 2-2 is connected to the secondary Y winding of the rectifier phase shift transformer 11. The side output ends are connected in cascade. The negative end of the separately excited rectifier 2-1 is connected to the arc furnace electrode 4-1 of the arc furnace 4 via the smoothing reactor 3, and the positive end of the self-excited rectifier 2-2 is connected to the furnace body 4-2 of the arc furnace 4. are connected to each other to form a DC power supply path.

On the other hand, 6 is a separately excited rectifier 2-
This control device 6 is a separately excited rectifier 2.
DC voltage transformer 5- connected between the DC output terminals of -1
an input power calculator 6-1 that calculates input power based on the DC voltage input from 1 and the DC current input from the DC current transformer 5-2 provided in the DC power supply path; Input power setter 6-2 to set, input power output from input power calculator 6-1 and input power setting device 6-2
A control error detector 6-3 calculates the error Δ by comparing the set value output from the control 1w4 difference detector 6-3, and when the value of Δ output from the control 1w4 difference detector 6-3 becomes below or above a certain value, a limiter is applied. Limiter circuit 6-4, this limiter circuit 6-
4, an error integrator 6-6 that calculates the control angle based on the error amount output from the error integrator 6-5, and a control angle calculator 6-6 that calculates the control angle based on the error amount output from the error integrator 6-5. -6
A phase controller 6-7 is provided which generates a phase control signal from the control angle determined by and controls the ignition of the thyristor of the separately excited rectifier 2-1. In addition, 7-1 is a control angle calculator 6-
Based on the control angle determined by 6, the self-help rectifier 2
-2, a control angle calculator 7-2 generates a phase control signal from the control angle calculated by the control angle calculator 7-1 to turn on the thyristor of the self-help rectifier 2-1. It is a phase controller that performs arc control, and these control angle calculator 7-1 and phase controller 7-2 control m+ of the separately excited rectifier 2-1.
The phase control device 7 of the automatic rectifier 2-2 includes the device 6.

Next, the operation of the DC arc furnace power supply device configured as described above will be described. Now, if we consider a model in which the self-commutated rectifier 2-2 shown in FIG. It can be expressed as shown in a). However, parts that are the same as those in FIG. 1 are designated by the same reference numerals. In addition, O is AC power supply, 4-3
represents the equivalent arc resistance.

In such a model, now AC power l! It is assumed that AC power P+jQ is input to the self-excited rectifier 2-2 from o and that the thyristor of the self-excited rectifier 2-2 is controlled by the phase control device 7 at a phase control angle α.

Here, the maximum voltage on the DC side is EdO1, the current on the DC side is Id,
Assuming that the arc resistance is R, there is the following relationship between them.

p -E do fist 1dcO3α Q-Edo-1d sin a ld -judo-cos (Z/R From these relational expressions, the AC side power at any arc resistance RA sRA can be calculated as shown in Fig. 2 using the phase IIIll angle α as a parameter. In FIG. 2(b), 200 is an active power line segment, 210 is a reactive power line segment, and 201 is a separately excited rectifier 2-
1 power locus P+ -N, 202 is the power locus P+ -p, 200-1 + of self-excited rectifier 2-2, and input power 11
1 constant f[Po, 200-2c1/RA1. : The power trajectory at , 200-3 is the power trajectory at 1/RA, 20
2-1 is the 1llNH1 angle αr of the separately excited rectifier 2-1, 2
02-2 is the control angle α2 of the self-excited rectifier 2-2.

Therefore, as is clear from Fig. 2(b), it is a separately excited type! If the single-current converter 2-1 and the self-excited rectifier 2-2 are operated at the same time, with the control phase angle set to α-α1-α2, and each is operated as a phase subdivision, and the desired input power Po is obtained, the other It can be understood that it is possible to cancel out the reactive power component taken by the excited rectifier 2-1 and the active power component taken by the self-help rectifier 2-2. Therefore, in calculating the phase angle α, it is necessary to input 1/2 of the desired input power PG using the control angle control device 6-6 in the m control device 6 of the separately excited rectifier 2-1 shown in FIG. The control angle calculator 7-1 determines the phase angle α1 and also controls the self-help rectifiers 2 to 2 in the control m+ device 7.
In order to input 1/2 of the desired input power PG, the phase angle α2 is
By determining ``-1α11 and controlling the separately excited rectifier 2-1 and the self-help m flow device 2-2, the reactive power can be canceled out.

In this way, according to the configuration of the above embodiment, the self-excited rectifier 2
-2 is cascaded to separately excited rectifier 2-1, and these rectifiers 2-1, 2-2 are connected in phase 11 based on the principle described above.
By using Jtll, even when the power setting is low, AC 1! It is possible to maintain a high power factor as seen from the source side, and it is also possible to respond and stabilize instantaneously to transient load fluctuations, resulting in greater power factor improvement and flicker suppression effects. Furthermore, since there is no need to separately provide a reactive power compensator as in the prior art, the total installed capacity of the VL power supply equipment can be significantly reduced. In this case, assuming that the input power is Pmax, the installed capacity of the power supply equipment at this time is that the capacity ω of the rectifier phase shift transformer 11 is Pmax, the capacity of the separately excited rectifier 2-1 is 1/2Pmax, and the capacity of the self-excited rectifier 2- 2 capacity is 1/2P
max and the total installed capacity as a whole can be reduced to 2Pmax, which is 40% of the conventional total installed capacity. Moreover, eliminating the need for a reactive power compensator means that there is no need for power factor correction capacitors or filter equipment, making the equipment more compact and eliminating mechanical parts such as L-C, improving reliability. will improve.

〔Effect of the invention〕

As described above, according to the present invention, the AC side input ends of the phase-controllable self-excited rectifier and the phase-controllable separately-excited rectifier are connected to the AC power source via the rectifier phase shift transformer, and both of these rectifiers A DC power supply path is configured in which the DC side output ends of the DC output terminals are connected in cascade and the DC output thereof is supplied to the arc furnace, and for the self-commutated rectifier and the separately excited rectifier, input power and input power set value are connected. A control phase angle is determined from the error amount so that the lagging reactive power component of the separately excited rectifier and the leading reactive power component of the self-commutating rectifier are offset, and the phase is adjusted so that the desired DC power is obtained. F1
Since a phase control device is installed to control the DC power supplied to the arc furnace, the power factor seen from the AC power source side can be maintained high even when the DC power supplied to the arc furnace is set at a low level, and the total equipment capacity of the power supply equipment can be maintained. It is possible to provide a DC arc furnace power supply device that can reduce the equipment cost by suppressing the power consumption to a small capacity.

[Brief explanation of drawings]

FIG. 1 shows a direct current arc furnace 'RII!' according to the present invention. Figures 2 (a) and 2 (b) are circuit configuration diagrams showing one embodiment of the device, and are for explaining the operation of the same embodiment. A diagram showing a model when supplying AC all power, (b) is a diagram expressing AC all force using the phase control angle α as a parameter in the relationship between active power component and reactive power component, and Figure 3 is a diagram showing a conventional DC arc furnace power supply. It is a block diagram showing the device. 11... Phase shifting transformer for rectifier, 2-1...
...Separately excited rectifier, 2-2...Self-excited rectifier,
3... Smooth reactor, 4... Direct current arc furnace, 4-1... Arc furnace, 4-2.
... Furnace body, 5-1 ... DC voltage transformer,
5-2...DC current transformer, 6...Control of separately excited rectifier [I8 position, 6-1...Input power calculator, 6-2... ... input power setting device, 6-3
...Control error detector, 6-4...Limiter circuit, 6-5...Error integrator, 6-6...
... Control angle calculator, 6-7 ... Phase shift controller, 7 ... Self-excited rectifier till device, 7-
1... Control angle calculator, 7-2... Phase shift controller. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 211 (b) Figure 3

Claims (1)

[Claims] In a DC arc furnace power supply device that supplies DC power to an arc furnace from an AC power source through a phase-controllable separately-excited rectifier, a phase-controllable self-excited rectifier and an AC input end side of the phase-controllable separately-excited rectifier are connected to the rectifier. The self-excited rectifier and For the separately-commutated rectifier, the lagging reactive power component taken by the separately-commutated rectifier and the leading reactive power component taken by the self-excited rectifier are canceled out based on the amount of error between the input power and the input power set value. 1. A DC arc furnace power supply device comprising a phase control device that determines each control phase angle and performs phase control to obtain desired DC power.