JP2799315B2 - High frequency induction heating device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter-type high-frequency induction heating apparatus using a high-frequency oscillation unit with a plurality of switching elements that turn on and off at a high speed, and particularly to heating of an output end. The present invention relates to a high-frequency induction heating device provided with protection means when a coil is blown.

b. Conventional technology In the past, vacuum tubes were used for high-frequency induction heating devices with a frequency of 10 kHz or more, but electrostatic induction transistors with short turn-on and turn-off times, power MOS transistors (MOS FETs), and bipolar types MOS FET or IGBT
With the advent of power semiconductor switching elements capable of high-speed switching, such as (insulated gate bipolar transistors), inverter-type high-frequency induction heating devices using these elements in a high-frequency oscillation unit have become widespread.

FIG. 3 shows a circuit configuration of a conventional high-frequency induction heating device. In the figure, 1 is a DC power supply unit, 2 is a high-frequency oscillation unit using the switching elements 2a and 2a, and is constituted by a voltage-type or current-type (voltage-type) single-phase bridge, and 3 is a series resonance circuit. 3a, and a matching unit having an output transformer 3b for sending a low voltage and a large current to the output side.
Is a heating coil for generating a high-frequency magnetic flux, and heats the object to be heated 5 which is a load. 6 is a control circuit unit for controlling the high frequency oscillator 2, the control circuit section 6, both ends of the high-frequency voltage of the capacitor C ₃ of among resonant circuit 3a of the matching portion 3, it is fed back via a feedback transformer 7 ing.

This high-frequency induction heating device uses a direct-current
Then, a high-frequency alternating current is generated, and its output is generated in a matching unit 3 by using a series or parallel (series in FIG. 3) resonance circuit 3a to generate a high-frequency high voltage or large current, which is output to an output transformer.
It is supplied to the heating coil 4 via 3b. A large current of high frequency and low voltage flows through the heating coil 4 to generate a high frequency magnetic flux,
The heated object 5 of the load is heated by eddy current loss and hysteresis loss.

The control circuit unit 6 of this device is a self-extinguishing type switching element that switches to the high-frequency oscillation unit 2 at high speed.
Since 2a and 2a are used, the PLL (phas) is internally provided so that the phase of the output voltage and the output current of the high-frequency oscillation unit 2 are always the same, that is, the power factor of the high-frequency output is 1.0.
The system is controlled by an automatic frequency tracking circuit using an e-locked loop) circuit to operate the device with maximum efficiency.

c. Problems to be Solved by the Invention However, since a high-frequency current of several thousand amperes or more flows through the heating coil 4 of this type of high-frequency induction heating device, the heating coil 4 is frequently blown. In this case, due to the fusing of the heating coil 4, the load state seen from the high-frequency oscillating unit 2 changes abruptly, and the operation of the automatic frequency tracking circuit in the control circuit unit 6 cannot be completely followed. There was a problem of becoming.

Also, for this reason, depending on the switching timing of the switching elements 2a, 2a constituting the high-frequency oscillator 2,
There is a problem that a surge voltage or an overcurrent exceeding the maximum rated value is applied to the switching elements 2a, 2a, and often damages the elements 2a, 2a or the drive circuit sections 2b, 2b of the elements.

The present invention has been made in view of such a point, and an object of the present invention is to solve the above-mentioned problems, and to protect a switching element and the like in a device when a heating coil is blown, and to protect the same device by operating the device. An object of the present invention is to provide a high-frequency induction heating device provided with a protection means for stopping.

d. Means for Solving the Problems According to a configuration of the present invention for achieving the above object, an inverter configured to use a plurality of switching elements that turn on and off at a high speed in a high-frequency oscillating unit and control these by a control unit is provided. (1) A protection coil having a sufficiently large inductance compared to the heating coil is provided in parallel with the heating coil, and the device is protected when the heating coil is blown. And

(2) A protection coil having an inductance sufficiently larger than the heating coil is provided in parallel with the heating coil, and the control means is provided with a frequency detection means for detecting an output frequency of the device, and the heating coil is blown. An output frequency at the time is detected, and the operation of the device is stopped based on the detection signal.

e. Operation FIG. 1 is a circuit diagram showing a configuration of a main part of the high-frequency induction heating device according to the present invention. In the figure, a protection coil 10 having a sufficiently large inductance compared to the heating coil 4 is attached in parallel with the heating coil 4 connected to the secondary side of the output transformer 3b of the matching section 3. Thereby, even when the heating coil 4 is blown, the protection coil 10 plays the role of the heating coil 4 instantaneously. That is, the automatic frequency tracking circuit in the control circuit section 6 of the device also performs a tracking operation, and keeps controlling the device, thereby preventing the control from being disabled.

In addition, since the inductance of the protection coil 10 has a value at least several tens of times greater than that of the heating coil 4, the output frequency when the heating coil 4 is melted and the protection coil 10 is operated is , Lower than the frequency when operating with the heating coil 4. For this reason, the output frequency when the operation of the protection coil 10 is started is detected by the frequency detection means, and based on this detection signal, the driving of the high-frequency oscillation unit is stopped and the operation of the device is stopped.

f. Embodiment Hereinafter, a preferred embodiment of the present invention will be illustratively described in detail with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, wherein the frequency is 40 kHz to 6 kHz.
FIG. 2 is a circuit configuration diagram of a high-frequency induction heating device having an output of 200 kW using a static induction type transistor as a switching element of a high-frequency inverter at 0 kHz.

In FIG. 1, a thyristor rectifier 13 controlled by a power supply control circuit 12 is used for a DC power supply unit 11, and a high-frequency oscillation unit 14 is a voltage-type single-phase bridge using a plurality of electrostatic induction transistors 15, 15. The transistors 15 and 15 have respective drive circuit units 16 and
Driven by 16. The output of the high-frequency oscillator 14 is matched to the matching unit 17
Sent to The matching unit 17 is composed of a capacitor circuit 19 that resonates in series at one frequency of 40 kHz to 60 kHz, an output transformer 20, and a feedback transformer 21 for feeding back a high-frequency voltage across the capacitor C in the capacitor circuit 19. Become. The matching section 17 inputs a high-frequency high voltage generated in the series resonance circuit to the primary side of the output transformer 20 and supplies high-frequency power to the load side 23 including the object to be heated 22 via the output transformer 20. The protection coil 10 is connected to the secondary side of the output transformer 20 in parallel with the heating coil 24, and supplies high-frequency power of low voltage and large current to the heating coil 24.

The control circuit unit 25 has an automatic frequency tracking circuit using a PLL circuit for controlling the oscillation of the high-frequency oscillation unit 14,
While driving each of the drive circuit sections 16, 16, the matching section 1
By the feedback from the feedback transformer 21 of 7, the operation is performed such that the phase of the output voltage and the output current of the predetermined frequency are completely matched while detecting the frequency, and
When the detected frequency changes more than a predetermined frequency, the detection signal is used to drive the driving circuits 16 and 16 to shut off the gates of the transistors 15 and 15 and stop driving the high-frequency oscillation unit 14. I do.

 Next, the test results of this example are shown.

In this test, the inductance of the protection coil 10 is
The driving frequency of the high-frequency induction heating device under test is 47 kHz (actual value) in a state where the inductance of the heating coil 24 is set to 6 μH, which is about 300 times, and the object 22 is heated by the heating coil 24.
Met. Next, the circuit of the heating coil 24 is opened, and the frequency in the case of only the protection coil 10 is 41 kHz as an actually measured value,
There was a frequency drop of about 15%. When the frequency reached this frequency, the control circuit unit 25 stopped driving the high-frequency oscillation unit 14 and stopped the operation of the test induction heating apparatus.

Even if the protection coil 10 is connected in parallel with the heating coil 24, the inductance of the protection coil 10
, The efficiency of the induction heating device was hardly reduced.

Further, in the process of actually fusing the heating coil 24, the induction heating device simultaneously melts the heating coil 24,
The operation was stopped while operating only with the protection coil 10. In the meantime, the result is that the automatic frequency tracking circuit in the control circuit unit 25 continues to operate without being disabled.

Note that the technology of the present invention is not limited to the technology in the above-described embodiment, and may be implemented by means of another embodiment that performs the same function. Addition is possible.

g. Effects of the Invention As is apparent from the above description, according to the present invention, a protection coil having a sufficiently large inductance as compared with the heating coil at the output end of the high-frequency induction heating device is provided in parallel with the heating coil. , Even when the heating coil is blown,
The device is normally controlled by the control means, and protects the switching elements used in the device without damaging them.

Further, the control means is provided with a means for detecting the output frequency of the device, the output frequency when the heating coil is blown is detected, and the operation of the device is stopped based on this detection signal. The device can be sufficiently protected.
As a result, the reliability of the protection coordination of the device becomes higher.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a main part of a high-frequency induction heating apparatus according to the present invention, FIG. 2 is a circuit diagram of a high-frequency induction heating apparatus showing one embodiment of the present invention, and FIG. FIG. 2 is a circuit configuration diagram of the device. 4,24 Heating coil, 10 Protection coil, 19 Capacitor circuit, 21 Feedback transformer, 25 Control circuit section.

Claims (2)

(57) [Claims] 1. An inverter-type device in which a plurality of switching elements that turn on and off at a high speed are used in a high-frequency oscillating unit and are controlled by control means. A high-frequency induction heating device comprising a protection coil having a sufficiently large inductance to protect the device when the heating coil is blown. 2. An inverter-type device in which a plurality of switching elements that turn on and off at a high speed are used in a high-frequency oscillation unit and controlled by control means. A protection coil having a sufficiently large inductance is provided, and the control means is provided with frequency detection means for detecting an output frequency of the device, and detects an output frequency when the heating coil is blown, and based on the detection signal, A high-frequency induction heating device, wherein the operation of the device is stopped.