JP3835296B2 - Power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply device, and more particularly to a power supply device suitable for supplying power to a device such as a direct current arc furnace or a plasma arc furnace in which an instantaneous stop of a power system is a serious problem.
[0002]
[Prior art]
Instantaneous stoppage of the power system due to an accident such as a lightning strike is a problem in various fields that use power. For example, in a DC arc furnace or a plasma arc furnace used for melting in the steel industry, when the apparatus stops due to an accident in the power system, there is a risk that the steel ingot or electrode being melted will be defective and cause great damage.
[0003]
Conventionally, as a power supply device for a DC arc furnace or a plasma arc furnace, a separately excited conversion type power supply device using a thyristor element has been adopted. FIG. 3 is a diagram showing a schematic configuration of a conventional arc furnace power supply device. The three-phase AC system voltage 1 is converted to a DC output voltage Vdc by the thyristor rectifier 3 and applied between the electrode 6a and the furnace 6b of the arc furnace 6 as the arc furnace voltage Varc. The phase of the system voltage 1 is used for the rectification control of the thyristor rectifier 3. Reference numeral 5 denotes a circuit resistance. In the case of such a separately-excited conversion type power supply device, when the system voltage 1 decreases, the output voltage Vdc of the power supply device decreases following the decrease of the system voltage 1.
[0004]
[Problems to be solved by the invention]
FIG. 4 is a diagram showing the arc current characteristics of the arc furnace, where the straight line D is the output characteristic of the power supply device and the curve A is the arc current characteristic of the arc furnace. When the output voltage Vdc of the power supply device decreases from Vdc1 to Vdc2 due to a decrease in the system voltage 1, the arc current Id of the arc furnace 6 decreases from Id1 to Id2. When the arc current Id decreases and enters the unstable region, the arc of the arc furnace 6 becomes unstable and extinguishes. When the arc of the arc furnace 6 is extinguished, an operation for re-igniting the arc is required, which causes a reduction in the operation efficiency of the arc furnace 6.
[0005]
For this reason, when the arc current Id of the arc furnace 6 decreases during normal operation, the arc voltage Idc is increased by increasing the output voltage Vdc of the power supply device, and the arc of the arc furnace 6 is maintained. However, when an instantaneous stop of the system voltage 1 occurs, the output voltage Vdc of the power supply device cannot be increased.
[0006]
FIG. 5 is a diagram for explaining the change over time of the arc current when the system voltage is lowered by the conventional arc furnace power supply device. In the conventional arc furnace power supply device shown in FIG. 3, as shown in FIG. 5, when the system voltage 1 decreases, the arc current Id of the arc furnace 6 decreases rapidly.
[0007]
3, the AC system voltage 1 is rectified to DC by the thyristor rectifier 3, but the phase of the system voltage 1 is also used for rectification control of the thyristor rectifier 3. It has been. Therefore, when an instantaneous stop of the system voltage 1 occurs, the thyristor rectifier 3 cannot perform a normal rectifying operation, and the apparatus must be stopped.
[0008]
As a technique for facilitating the re-ignition of the arc when the power supply is restored, for example, there is a technique described in JP-A-7-263139. This is to maintain the supply of the control signal to the gate of the control rectifying element within a predetermined period after the arc is stopped by the electric power stored in the storage battery or the like, but it is not possible to prevent the arc from being extinguished.
[0009]
Japanese Patent Application Laid-Open No. 6-168788 discloses a technique for maintaining the lighting of a discharge lamp such as a mercury lamp during a short power failure. This is to use a rectifying and smoothing circuit and a chopper circuit, increase the capacity of the smoothing capacitor in the rectifying and smoothing circuit, detect that the input voltage has become no voltage, and control the chopper circuit to a low power supply state. is there. However, in the configuration disclosed in Japanese Patent Laid-Open No. 6-168788, when the voltage of the smoothing capacitor decreases, the conduction rate of the switching transistor of the chopper circuit increases, and when the conduction rate increases, the voltage from the smoothing capacitor increases. The discharge also increases, and the period during which the discharge lamp can be kept on is shortened.
[0010]
Further, when the technique described in Japanese Patent Laid-Open No. 6-168788 is applied to an arc furnace power supply device, the arc furnace power supply device requires a smoothing capacitor having a large capacity. Must be bigger. In the case of an arc furnace, as shown in FIG. 3, when the arc current decreases and enters an unstable region, the arc becomes unstable and extinguishes. There is a risk of extinguishing rather than maintaining the arc.
[0011]
An object of the present invention is to provide a power supply device that can sustain a certain amount of output current for a long time when an instantaneous stop of an input voltage occurs.
[0012]
Another object of the present invention is to prevent a rapid decrease in the arc current of the arc furnace when the instantaneous stop of the input voltage occurs and to lengthen the arc duration.
[0013]
[Means for Solving the Problems]
A power supply apparatus according to the present invention includes an input voltage detecting means for detecting an input voltage, an intermediate circuit for charging the input voltage, a chopper circuit for switching and outputting the voltage of the intermediate circuit by a self-excited element, and a load current Load current detection means for detecting the load current, control means for controlling the self-excited element of the chopper circuit so that there is no deviation between the load current command value and the detection value of the load current detection means, and a current command for generating a current command value Value generating means, and when the detection result of the input voltage detecting means is higher than a predetermined value , the control means uses the current command value of the current command value generating means as the load current command value, and the input voltage detecting means. When the detection result is equal to or less than a predetermined value, the detection value of the load current detection means is used as the load current command value.
[0014]
The chopper circuit is a voltage regulator that adjusts an output voltage by switching and cutting a voltage charged in an intermediate circuit such as a capacitor. For this reason, the normal output voltage of the chopper circuit is smaller than the maximum output voltage when not cut by switching. On the other hand, a separately-excited conversion type power supply device using a conventional thyristor rectifier does not have a function of storing electric power, and the normal output voltage is substantially equal to the maximum output voltage. In the present invention, by using the chopper circuit, when an instantaneous stop of the input voltage occurs, the output current can be maintained to some extent by the amount of the maximum output voltage. Then, the control means limits the conduction rate of the self-excited element of the chopper circuit by using the detected value of the load current detecting means as the load current command value, and continues the operation of the chopper circuit. Since the voltage of the intermediate circuit does not decrease during the reflux period, the output current maintenance period becomes longer.
[0015]
When the input voltage is alternating current, a direct current voltage can be supplied to the chopper circuit by providing a rectifying means that rectifies the alternating current input voltage and converts it into a direct current voltage.
[0016]
When the output voltage of the power supply device of the present invention is supplied to the arc furnace, when an instantaneous stop of the input voltage occurs, it is possible to prevent a rapid decrease in the arc current of the arc furnace and lengthen the arc duration.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a configuration diagram of a power supply device according to an embodiment of the present invention. The present embodiment shows an example in which a three-phase AC voltage is used as an input voltage of a power supply device and an arc furnace is connected as a load. The power supply device includes a diode rectifier 2, a DC reactor 4, a chopper circuit 10, and a control circuit unit 100. The control circuit unit 100 includes a comparator 20, a voltage setting circuit 30, a pulse generation circuit 40, a current control circuit 50, a current command circuit 60, a current detection circuit 70, and a switch SW.
[0018]
The diode rectifier 2 rectifies the three-phase AC system voltage 1 to convert it into a DC voltage and supplies it to the chopper circuit 10. The chopper circuit 10 includes a capacitor 11, a self-excited element 12, and a freewheeling diode 13, and has a function of adjusting a DC voltage. The capacitor 11 that is an intermediate circuit charges the DC voltage supplied from the diode rectifier 2. The self-excited element 12 is switched by a pulse from the pulse generation circuit 40 and adjusts a period during which the intermediate circuit flows from the intermediate circuit to the arc furnace 6 as a load. When the conduction ratio of the self-excited element 12 is α, the output voltage Vdc, the intermediate circuit voltage Edc, the arc current Id of the arc furnace 6 and the resistance value R of the circuit resistance 5 are
Vdc = Edc × α
Id = Vdc / R
The relationship holds. Here, the voltage drop when the self-excited element 12 is on is ignored.
[0019]
During the period when the self-excited element 12 is off, the return current flows through the return diode 13 due to the back electromotive force of the DC reactor 4. For this reason, the intermediate circuit voltage Edc does not decrease during the reflux period.
[0020]
The comparator 20 detects the system voltage 1 and compares the detection result with the set value from the voltage setting circuit 30. The comparator 20 connects the contact of the switch SW to the current command circuit 60 side when the system voltage 1 is higher than the set voltage, and switches the contact of the switch SW to the current detection circuit 70 side when the voltage is equal to or lower than the set voltage.
[0021]
The current command circuit 60 generates a command value for the arc current Id of the arc furnace 6. The current detection circuit 70 detects the arc current Id of the arc furnace 6. During normal operation, the contact of the switch SW is connected to the current command circuit 60 side, and the current control circuit 50 receives a deviation between the command value of the current command circuit 60 and the detected value of the current detection circuit 70. The current control circuit 50 controls the self-excited element 12 of the chopper circuit 10 via the pulse generation circuit 40 so that there is no input deviation.
[0022]
When the system voltage 1 decreases, the contact of the switch SW is connected to the current command circuit 60 side until the system voltage 1 reaches the set value of the voltage setting circuit 30. The intermediate circuit voltage Edc decreases as the system voltage 1 decreases. The current control circuit 50 increases the conduction ratio α of the self-excited element 12 of the chopper circuit 10 to keep the arc current Id constant. Since the conduction ratio α increases, the intermediate circuit voltage Edc decreases.
[0023]
When the system voltage 1 decreases and reaches the set value of the voltage setting circuit 30, the comparator 20 switches the contact point of the switch SW from the current command circuit 60 side to the current detection circuit 70 side. As a result, the current control circuit 50 uses the detection value of the current detection circuit 70 as a command value of the arc current Id, and since there is no input deviation, the current flow rate α of the self-excited element 12 of the chopper circuit 10 is kept constant. The conduction ratio α is a ratio of the intermediate circuit voltage Edc and the output voltage Vdc at this time (α = Vdc / Edc).
[0024]
After the system voltage 1 decreases and reaches the set value of the voltage setting circuit 30, the chopper circuit 10 maintains the ratio between the intermediate circuit voltage Edc and the output voltage Vdc and continues operation. Since the intermediate circuit voltage Edc does not decrease during the recirculation period, the period for maintaining the arc current Id becomes longer.
[0025]
FIG. 2 is a diagram for explaining the change over time of the arc current of the arc furnace when the system voltage is lowered by the power supply device of the present invention. In the conventional arc furnace power supply apparatus, when the system voltage 1 decreases as shown in FIG. 5, the arc current Id decreases rapidly, whereas in the present invention, the system voltage 1 decreases as shown in FIG. Even so, the arc current Id gradually decreases, and a certain amount of arc current can be maintained for a long time.
[0026]
According to the embodiment described above, the system voltage 1 is rectified using the diode rectifier 2, and the chopper circuit 10 performs switching using the self-excited element 12, whereby the system voltage 1 is used for rectification and switching control. There is no need to use the phase of. Therefore, when an instantaneous stop occurs in the system voltage 1, the operation of the apparatus does not stop as in the prior art. The rectifying means of the present invention is not limited to the diode rectifier 2 and may be any means that can convert an AC voltage into a DC voltage. Further, when a DC voltage is directly input, no rectifying means is necessary.
[0027]
The power supply device of the present invention is not limited to an arc furnace, and can be used when supplying power to various devices in which an instantaneous stop of the power supply is a serious problem.
[0028]
【The invention's effect】
According to the power supply device of the present invention, when a chopper circuit is used and the input voltage decreases, the control means uses the detected value of the load current as the load current command value, thereby maintaining a certain amount of output current for a long time. Can do.
[0029]
When a current is supplied to the arc furnace by the power supply device of the present invention, when an instantaneous stop of the input voltage occurs, a rapid decrease in the arc current of the arc furnace can be prevented, and the arc duration can be lengthened. Therefore, the occurrence frequency of arc stop accidents in the arc furnace can be suppressed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a power supply device according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining a temporal change in arc current of an arc furnace when a system voltage is lowered by the power supply device of the present invention.
FIG. 3 is a diagram showing a schematic configuration of a conventional power source device for an arc furnace.
FIG. 4 is a diagram showing arc current characteristics of an arc furnace.
FIG. 5 is a diagram for explaining a temporal change in arc current when a system voltage is lowered by a conventional arc furnace power supply device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... System voltage, 2 ... Diode rectifier, 4 ... DC reactor, 5 ... Circuit resistance, 6 ... Arc furnace, 10 ... Chopper circuit, 11 ... Capacitor, 12 ... Self-excited element, 13 ... Free-wheeling diode, 20 ... Comparator, DESCRIPTION OF SYMBOLS 30 ... Voltage setting circuit, 40 ... Pulse generation circuit, 50 ... Current control circuit, 60 ... Current command circuit, 70 ... Current detection circuit, 100 ... Control circuit part

Claims (3)

An input voltage detecting means for detecting an input voltage;
A chopper circuit that has an intermediate circuit for charging an input voltage, and switches and outputs the voltage of the intermediate circuit by a self-excited element;
Load current detecting means for detecting the load current;
Control means for controlling the self-excited element of the chopper circuit so that there is no deviation between the load current command value and the detection value of the load current detection means ;
Current command value generating means for generating a current command value ,
When the detection result of the input voltage detection means is higher than a predetermined value , the control means sets the current command value of the current command value generation means as a load current command value, and
When the detection result of the input voltage detection means is less than or equal to a predetermined value, the detection value of the load current detection means is used as a load current command value. The power supply apparatus according to claim 1, further comprising a rectifying unit that rectifies an AC input voltage and converts the AC input voltage into a DC voltage. The power supply apparatus according to claim 1, wherein an output voltage of the chopper circuit is supplied to an arc furnace.

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