JPS6215794A - Power source unit for channel type induction furnace - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application This invention relates to a power supply device for a trench type induction furnace using a self-limiting inverter.

B6 Summary of the Invention This invention relates to an inductor (heating chamber) for a conductor furnace.
A power supply device in which the output of a self-limiting inverter is connected to the next winding via a matching capacitor, and the inverter supplies AC power at the resonance frequency of a tank circuit consisting of the inductor and the matching capacitor, the output frequency of the inverter a frequency limiting means for advancing the firing phase of the inverter to suppress a frequency drop when the inverter becomes less than a set value;
A matching capacitor control means is provided to reduce the capacity of the matching capacitor when the output current of the inverter exceeds a set value.Thus, even if the inductance on the load side increases rapidly due to the disappearance of molten steel in the groove, The output frequency of the inverter was prevented from falling below a set value, and the output current was prevented from exceeding a set value.

C0 Conventional technology A power supply device for a trench induction furnace using a self-limiting inverter connects the output of the self-limiting inverter to the primary winding of the inductor of the trench induction furnace via a matching capacitor, and connects the output of the self-limiting inverter to the primary winding of the inductor of the trench induction furnace. The inverter supplies alternating current power at the resonant frequency of the tank circuit consisting of the following.

□ D1 Problem to be solved by the invention The above-mentioned inductor has a molten metal groove formed from a stamp material to form one turn of a secondary short-circuited winding in an iron core having a primary winding.

When the molten steel in the molten metal groove disappears, this is equivalent to opening the secondary winding, and the inductance of this inductor as seen from the power supply side increases rapidly. Then, the resonant frequency of the tank circuit rapidly decreases, and the output frequency of the self-limiting inverter accordingly decreases accordingly.

In conventional power supplies, when the molten steel runs out, the output frequency of the inverter drops to a very low value as described above. Therefore, in consideration of such a low frequency range, the inductor mentioned above must have a wide range of frequency characteristics, and the variable amount of the matching capacitor must also be made large. The price was high.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to make it possible even if the frequency characteristics of the inductor are relatively narrow (small and inexpensive), and even if the variable amount of the matching capacitor is relatively small. It is an object of the present invention to provide a power supply device for a trench type induction furnace (which is small and inexpensive) and which does not cause any trouble.

Means for Solving Problem E1 Therefore, the present invention includes a frequency limiting means for advancing the firing phase of the inverter to suppress the frequency drop when the output frequency of the inverter becomes equal to or less than a set value, and a frequency limiting means for suppressing the frequency drop by advancing the firing phase of the inverter when the output frequency of the inverter becomes equal to or lower than a set value. A matching capacitor control means is provided which reduces the capacitance of the matching capacitor when the capacitance exceeds the value.

7. When the molten steel in the working groove runs out, the inductance of the inductor increases dramatically, and the output frequency of the inverter tends to drop rapidly. Then, the frequency limiting means functions to advance the firing phase of the inverter to prevent the output frequency from falling below the set value.

As the firing phase advances, the output current of the inverter increases. When the current exceeds a set value, the matching capacitor functions, the capacitance of the matching capacitor decreases, and the resonant frequency of the tank circuit increases, suppressing the advance of the ignition phase to a certain extent and preventing an increase in the output current.

G. Embodiment The figure shows an embodiment of the invention. 1o is an inductor of a groove-type induction furnace, which is composed of a primary winding 12, an iron core 14, and a molten metal groove 16.

18 is an inverter controlled by the ignition control circuit 20; 22 is a matching capacitor unit connected between the output of the inverter 18 and the primary winding 12; 24 is an inverter connected to the output of the inverter 18 via a transformer 26; A voltage zero point detection circuit that detects the voltage zero point, and a VCO (@pressure controlled variable frequency oscillator) 30 that provides the gate timing signal GP, which is the basis of the gate signal to the inverter 18, to the ignition control circuit 20. 32 is a frequency setter and amplifier that provides a control voltage for the VCO 28; 34 is the negative input voltage V of the amplifier 321;
s1, a monostable multivibrator (hereinafter referred to as mono-multi), 36 supplies a positive input voltage v'o1 to the amplifier 32.
38 is a curve generator that provides a negative input voltage Δ■ to amplifier 32; 40 is a frequency detection circuit that detects the excavation frequency of VCO 28 (same as the output frequency of inverter 18); 46 is a frequency lower limit setter that sets the limit value (lower limit) of the output frequency, a current upper limit setter that sets the limit value (upper limit) of the output current of the inverter 18, and 46 is a current transformer that detects the output current of the inverter 18. , 48 are the output of the current transformer 46 and il! The matching capacitor section 22 is compared with the setting value of the current upper limit setting device.
This is a current comparator that controls the zero control relay 50.

The monomulti is triggered by the gate timing signal GPjC and outputs a negative square wave pulse vs1 with a predetermined width and a predetermined voltage.

The flip-flop 36 is set by the gate timing signal GP and reset by the output of the voltage zero point detection circuit 24 (zero point timing signal Go), so that
A square wave pulse vn1 of a predetermined voltage and a width equal to the time difference between the gate timing signal GP and the zero point timing signal GO is output from the flip-flop 36.

The output frequency of the inverter 8 is the setting value FD of the setting device 42.
Higher, the output voltage ΔV of the curve generator 38 is zero. The output frequency of the inverter 18 is the set value F'.

If it becomes lower, a voltage ΔV proportional to the difference is outputted from the curve generator 38.

Under normal conditions, the inductor 10 and matching capacitor section 2
Resonant frequency of tank circuit consisting of 2 and frequency setter 3
The setting value FS of 0 is equal. In this case, the curve generator 38
The output voltage Δ■ is zero, and the output pulse width of the monomulti 34 and the output pulse width of the flip-flop 36 are equal. The vao 28 oscillates at a frequency according to the set value FS, and the output frequency of the inverter 18 is equal to the consonant frequency of the tank circuit. When the resonant frequency of the tank circuit changes,
The output pulse width of flip-flop 36 changes, which changes the oscillation frequency of VCO 28 via amplifier 32, changing the firing phase of inverter 18 to cause the output frequency to track the resonant frequency.

When the molten steel in the molten metal groove 16 runs out, the inductance of the inductor 10 increases rapidly, the resonance frequency of the tank circuit rapidly decreases, and the output frequency of the inverter 18 also tends to decrease rapidly following this. However, when the output frequency becomes less than the set value FD, a negative voltage Δ proportional to the difference from FD
V is output from curve generator 38 and input to amplifier 32. At this time, the voltage Δ■ acts to increase the oscillation frequency of the VCO 28. In other words, inverter 18
advances the ignition phase to prevent the output frequency from dropping below the set value.

As the advance angle of the ignition phase increases, the output current of the inverter 18 increases. When the output current becomes equal to or higher than the set value Va, the current comparator 48 is activated, and the relay 50 is activated to reduce the capacitance of the matching capacitor section 22. The common frequency of the tank circuit then increases, preventing an increase in current and a decrease in frequency.

The matching capacitor section 22 is configured to reduce the capacitance in multiple stages by separating a large number of capacitors one by one using relay contacts. Relay 50 outputs from current comparator 48 (capacitor disconnection command)
Each time, ・Sequentially disconnect the capacitors and gradually reduce the capacitance.

■1 Effects of the Invention As explained in detail above, according to the power supply device for a groove-type induction furnace according to the present invention, even if there is no molten steel in the groove, the output frequency of the inverter does not drop suddenly. There is no need to use an inductor with particularly wide frequency characteristics as the load-side inductor, and a small and inexpensive inductor can be used. In addition, since the ignition phase is advanced to the upper limit of the output current value and the frequency is controlled by the matching capacitor, the frequency fluctuation width is compressed and controlled in response to fluctuations on the load side. It is economical because it can be designed with less.

[Brief explanation of the drawing]

The figure is a block diagram of an apparatus according to an embodiment of the present invention. 10...Inductor, 12...Primary winding, 14...
・Iron core, 16... Molten metal groove, 18... Inverter, 22
... Matching capacitor section, 42 ... Frequency lower limit setter, 44 ... Current upper limit setter, 48 ... Current comparator, 50 ... Capacitor control relay.

Claims (1)

[Claims] (1) Connect the output of a self-limiting inverter to the primary winding of the inductor of the groove-shaped guideway via a matching capacitor, and supply AC power at the resonance frequency of the tank circuit consisting of the inductor and the matching capacitor from the inverter. In the power supply device to be supplied, the frequency limiting means advances the firing phase of the inverter to suppress a frequency drop when the output frequency of the inverter becomes less than a set value, and the matching capacitor controls the matching capacitor when the output current of the inverter becomes more than the set value. A power supply device for a trench type induction furnace, characterized in that it is provided with a matching capacitor control means for reducing the capacity of the channel.