JPS58225593A - Controller for billet heater - 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 The present invention relates to a billet heater control device for inductively heating a metal piece such as a billet.

The billet heater has an air-core coil 6 as shown in Figure 1.
[71I] By sequentially passing through the billet 100', which is a heat product, and passing a high f@e current to the air-core coil 6,
100 induction 7JII heat is applied to the inside of the coil 6).

In conventional billet heaters, when one billet is charged into the core coil, the billet is sent through the coil at a speed of one foot, so magnetic flux concentrates on this billet and comes out of the coil. , the temperature of the billet becomes too high and proper heating is not performed. Therefore, this first 1
There was a problem in that the wood billet was wasted.

The present invention has been made in view of the above-mentioned problems in the prior art.
Its purpose is to detect the input current that changes depending on the amount of billet in the coil of the billet heater, and to determine the output voltage of the inverter that supplies high-frequency voltage to the coil, which is the first point at the start of induction heating. To provide an entire control device for a billet heater capable of controlling the heating of the billet to a value that makes it suitable, and obtaining proper dielectric heating even for the billet with the first grain.

An embodiment of the present invention will be described below based on aspect (8).

As shown in FIG. 2, the input terminal of a three-phase full-wave controllable rectifier 3 is connected to a three-phase AC power supply l via a transformer 2, and the output terminal of this rectifier 3 is connected to a DC reactor 4'fr: and is connected to the input terminal of the inverter 50. The induction heating coil 6 of the billet heater is connected to the output terminal of this innovator 5.
and a power factor correction capacitor 7 are connected in parallel.

8 is a control device that controls induction heating, and the input terminals of this control device 8 are 1. Engineering 2. The output terminal of a current transformer 9 that detects the input current of the rectifier 3 is connected to the terminal 3, and
Input terminals R, s of the control device 8.

T is connected to the power supply, l, via a transformer lo. Furthermore, the output terminal of the inverter 5 is connected to the input terminals U and V of the control device 8 via a transformer 811, and the output terminal R1 of the control device 8 is connected to the gates of the six thyristors that make up the rectifier 3. The output terminal Ii of the control device 8 is connected to the gates of the four thyristors constituting the inverter 5, and the input terminals A, C, and B of the control device 8 are connected to a setting device for setting the output t[ff'(r) of the inverter 5. 12 are connected.

In the above circuit, AC power supplied from a three-phase power supply 1 is transformed to a predetermined voltage value by a transformer 2 and inputted to a rectifier 3, where it is converted to DC power and the firing angle of the tail lifter is changed. Control is performed so that the output voltage of the inverter 5 is constant. The output td of the rectifier gg3 is smoothed by the DC reactor 4 and input to the inverter 5. In the inverter 5, this DC power is converted into high-frequency AC power synchronized with the load voltage at the resonant frequency of the coil 6 and the capacitor 7, which are load circuits.

Constant voltage control is generally performed in induction heating, and for the purpose of overload protection of the thyristors that form the forward conversion section and the inverse conversion section, thyristor inverter type induction heating power supplies use constant voltage control with current limitation. Pressure control is performed. Therefore, in the control device 8, the transformer 1
The phase of the ignition pulse of the input/register 5 is completely determined by the detected value of the output voltage of the input/register 5 inputted through the input/register 1vi-1, and the phase set by the setting device 12 for the rectifier 3 is determined. The set value of the output voltage and the detected value of the output voltage are compared, and the firing angle control l of the thyristor forming the rectifier 3 is performed so that the output voltage of the inverter 5 becomes the set value.

In addition, the input current of the rectifier 3 is detected by the current transformer 9, this detected value is compared with a current limit value set by approximately η, and the output of the rectifier 3 is The voltage is controlled.

In the above-mentioned control device 8, the output voltage of the inverter 5 is set to the rated value in order to prevent the input power from becoming excessive for the first grain billet loaded into the coil at the start of induction heating. To ensure proper induction heating of the billet with the smaller first grain, we modified the firing angle control of the rectifier 3 to achieve the set value.
The control of the output voltage is performed on the 5th day.

As shown in FIG. 3, the above-mentioned control device 8 has a terminal 11 connected to a current transformer 9 (FIG. 2) that detects the input terminal of the rectifier. I2. An input terminal of a rectifier 130 composed of a diode glitch is connected to I3, one output terminal of this rectifier 13 is connected to one input terminal of an arithmetic amplifier 114, and an output terminal of the rectifier 13 is Grounded. Also,
The tenth input terminal of the operational amplifier 14 is grounded. The output terminal of this operational amplifier 14 is connected to one input terminal of an operational amplifier 15, and the tenth input terminal of this operational amplifier 15 is grounded.
The output terminal of the operational amplifier 15 is connected to one input terminal of the operational amplifier 16, the input terminal of the operational amplifier 16 is grounded, and the output terminal of the operational amplifier t@16 is connected to the input terminal of the rectifier phase control circuit 17. Connected.

An output terminal of a rated current setting device 18 for setting a current limit value is connected to a connection point between one output terminal of the rectifier 13 and one input terminal of the operational amplifier zg14. Further, the output terminal of the output voltage setting device 12 (FIG. 2) is connected to the connection point between the output terminal of the operational amplifier 14 and one input terminal of the operational amplifier 15.
Terminal U to which secondary I#111@ of 1 (Fig. 2) is connected
, V are connected to the input terminals of a rectifier 8819 composed of a diode bridge, and one output terminal of this rectifier 19 is connected to the operational amplifier 14 via a resistor 20 for voltage level adjustment.
The output terminal of the operational amplifier 15 is connected to the connection point between the output terminal of the operational amplifier 15 and the single power terminal of the operational amplifier 15. However, the + side output terminal of the rectifier 19 is grounded.

One output terminal of the rectifier 19 described above is connected to an input terminal of an inverter phase control circuit 21, and the output terminal of this inverter phase control circuit 21 is connected to the gate of the thyristor constituting the inverter (5) (Fig. 2). Connected terminal Ii
connected to. Furthermore, terminals R and S are connected to the primary side of the transformer 2' (FIG. 2) via the transformer 10 (FIG. 2).
, 1'' is connected to the input terminal of the synchronizing signal pulse shaping circuit 22, and the output terminal of this synchronizing signal pulse shaping circuit 22 is connected to the input terminal of the rectifier phase control circuit 17. Terminal R to which the output terminal of is connected to the gate of the thyristor constituting the three rectifiers.

connected to.

23 is the current value for detecting the induction heating of the billet with the first grain (this value is the same as the current when there is one piece of steel with the same coil when the rated voltage is applied to the heating coil, and there are two pieces) Is it possible to set the 1st grain heating current to 1 [selected as a value], which is smaller than the current at the time, and the output terminal of this setting device 23 is an operational amplifier? Connected to the 1R24 single power terminal.

Further, one output terminal of the rectifier 13 described above is connected to the connection point between the setting device 23 and the single-power terminal of the operational amplifier 24, and the input terminal of the operational amplifier 24 is grounded. The output terminal of the operational amplifier 24 is connected to the connection point between the output terminal of the operational amplifier 15 and the single power terminal of the operational amplifier 16 described above.

Next, the operation of the above circuit will be explained.

A signal representing the deviation between the output voltage of the rectifier 13 corresponding to the input current of the rectifier 3 and the output voltage of the rated current setting device 18 is input to the output of the operational amplifier 14 . When the input current of the rectifier 3 is equal to or smaller than the rated current setting &@18, the output of the operational amplifier 14 is OV, and the operational amplifier 15 has the output voltage setter 1
A signal corresponding to the deviation between the output of the inverter 2, the output voltage of the inverter 5, and the level-converted signal of the output voltage of the rectifier 8g19 corresponding to the output voltage of the inverter 5 is input. The control signal output from 1@16) is input to the rectifier B'tr phase control circuit 17,
The firing angle of the rectifier 3 is controlled so that the output voltage of the invanitor 5 becomes the set value of the setting device 12. A pulse signal synchronized with the power supply voltage is inputted to the rectifier phase control circuit 17 from the synchronization signal pulse shaping circuit, and the firing angle control of the rectifier 15It unit 3 by the rectifier phase control circuit 17 is performed in synchronization with the power supply voltage. On the other hand, when the input current of the rectifier 3 becomes V larger than the set value of the rated current constant R@18, the operational amplifier 1
For example, the output of 4 is +10V, and this signal is added to the voltage setting signal and the detection signal of the output voltage of the inverter 5 and inputted to the operational amplifier 15. A signal for controlling the input current of the rectifier 3 to a set rated value by lowering the output voltage is input to the rectifier phase control circuit 17.

When the number of billets that cover the entire length of the coil 6 is charged into the coil 6 and induction heating is performed, that is, during rated operation, the magnetic flux is uniformly distributed to each piece of the rectifier 3 ( The input current to (Fig. 2) is also the rated value. In this state, a negative voltage signal, for example, -10V, corresponding to this rated current value is output to the 13th power terminal on one side of the rectifier 13. Since the output of the rated current setting device 18 is a positive voltage signal corresponding to the rated current value, for example +IOV, the single power of the operational amplifier 14 is Ov, and 1ζ Therefore, the operational amplifier 1
The output of 4 is OV. In this case, the operational amplifier 15 has a signal obtained by converting the output voltage t level of the rectifier 19 corresponding to the output voltage of the inverter 5 (Fig. 2) and the output of the voltage setting device 12 (the output of the second (2) A signal representing the deviation from the voltage is input, and during rated operation, a signal of -10V is output from the arithmetic intensifier 15.

1, 1st grain 7JLl The setting value of the thermal current setting device 23 is, for example, 10 to 20% of the rated current value, and the output voltage of this setting device 23 is +1. to +2V'''c'6.Operation amplifier 2
The output of No. 4 becomes OV since the output voltage of the rectifier 13 is higher than the output voltage of the setting device 23 during rated operation. Therefore, in this case, the output voltage of the operational amplifier 15 is input to the operational amplifier 16, and the output +IOV of the operational amplifier 16 at this time is the phase control circuit 1 for rectification gg.
7, and the firing angle of the rectifier 3 is controlled so that the output voltage of the inverter 5 becomes the set value.

On the other hand, at the start of induction heating, the first billet is 1
When only the coil 6 is charged f', the input current to the rectifier 3 is smaller than the rated value, and the 1st grain 7JIJ
It becomes smaller than the setting value of the thermal current setting device 23. the result,
Since the output voltage of the rectifier 13 is smaller than the output voltage of the setting device 23, the output of the operational amplifier g=24 is 10. For example, if the input current is about 20% of the rated current, +8V and 7i-, The operational amplifier 15 is connected to the operational amplifier 16.
The output of Ruruichi 10V and the output of operational amplifier 24 +
12■, which is the addition of 8V, is input. Therefore, the output of the operational amplifier 16 at this time is +2V, and this +2V signal is input to the rectifier phase control circuit 17, which controls the output voltage of the rectifier 3 to be lower than the rated voltage M11. That is, when fewer than the rated number of billets are charged, such as at the start of induction heating, the operational amplification? : The input signal of the arithmetic amplifier 1 partition 16 is forcibly changed by the output signal of @24, the firing angle of the rectifier 3 is controlled, and the output voltage of the inverter 5 is lowered.

Therefore, even if the magnetic flux concentrates on one charged billet, the electric power input to that one billet is reduced, and an excessive rise in billet temperature is prevented. on the other hand,
During rated operation, the output signal of the operational amplifier 24 is set to Ov, and the firing angle of the rectifier 3 is controlled so that the output voltage of the inverter 5 becomes a set value.

As explained above, in the invention, in a billet heater driven by the output of a variable voltage inverter, the amount of billet in the coil is detected by the input current force to the inverter, and the amount of billet in the coil is detected. When the number of billets is less than the rated number, the above in/<-
- Since the output voltage is controlled to be lowered at night, when there is only one billet in the coil (as at the start of induction heating), the magnetic flux will concentrate on this billet. Even when the billet is heated, the temperature of the billet does not become too high, and induction heating can be performed at an appropriate temperature even for the first grain of the billet.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing a billet heating method in a billet heater, Fig. 2 is a circuit diagram showing a billet heater power supply device equipped with an uninvented control device, and Fig. 3 is an implementation of an uninvented control device. FIG. 2 is a circuit diagram showing an example. 3... Rectifier, 5... Inverter, 6...
・Coil, 8...Control device, 9...Tan H island, 1
0.11...Transformer, 13.19...Rectifier,
14.15.16°24... operational amplifier, 17.
... Rectifier phase control circuit, 22 ... Synchronous signal pulse shaping circuit, 23 ... 1 wood grain heating current setting device, 10
0... Billet. Patent applicant: Fuji Electric Manufacturing Co., Ltd. Representative Patent Attorney Aoyama, 2 people

Claims (1)

[Claims] (1) In a control device for a billet heater that is driven by a power supply device having a variable voltage type inverter and is equipped with one or more billet heaters and induction coils that are sequentially inserted into the billet heater, the induction coil of the billet heater is A setting means for setting the total input current to the inverter when the number of billets to be charged is less than the rated number, and comparing the actual value of the input current to the inverter with the setting value of the above setting means. A control device for a billet heater, comprising: voltage control means for reducing the output voltage of the inverter according to the output signal of the comparison means when the actual value of the input current is less than the set value.