JPH05290958A - Inductive heating device - Google Patents

Abstract

PURPOSE:To efficiently undertake heating treatment by providing a circuit for detecting reactive power or a signal proportional thereto from current and voltage across a heating coil, and controlling a PWM control signal on the basis of the detected signal. CONSTITUTION:An article as a treatment object in a vessel 1 is heated due to the high frequency of an induction coil 2. As the power factor of current flowing through the coil 2 changes, depending upon the quality, shape and size of the article, energy fed from an inverter cannot be efficiently consumed in the coil 2 and reactive power increases. For this reason, the reactive power is detected with a detector 10 in the form of a signal for current and voltage across the coil 2. Then, the detected signal is compared with a reference value by a comparator 11 and outputted therefrom. In other words, comparison by and output from the comparator 11 is so controlled that output voltage increases upon an increase in the reactive power, and decreases according to the drop thereof. This output voltage is applied to a comparator 7 and compared with an output pulse from an oscillator 8. In addition, the comparator output is applied to a switch 4 for the switching control of a transformer 3, thereby controlling the increase and decrease of inverter output.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an induction heating device.

[0002]

2. Description of the Related Art An induction heating apparatus is an induction heating coil wound around a container and heated by an induction current generated by passing an alternating current around the container to heat the raw material supplied into the container for casting, sintering, heat treatment, etc. It is something to do. Conventionally, there is a high-frequency power source that uses an inverter, but the μ value changes depending on the material to be treated in the container, the size and shape of chips, pellets, powder, temperature rise, melting state, etc. There was a drawback that it changed and could not always supply a constant power.

[0003]

SUMMARY OF THE INVENTION In view of this conventional drawback, the present invention has improved a power source so that a required power can always be efficiently supplied to an object to be processed in a container which is heat-treated by induction heating. The purpose is to do.

[0004]

In an induction heating apparatus having an HF inverter for transforming a high frequency generated by high frequency switching of a semiconductor switch into a high frequency transformer and outputting the transformed high frequency to an induction heating coil, a control pulse is applied to the semiconductor switch. And a circuit for detecting a reactive power or a signal proportional to the reactive power from the current and voltage flowing through the heating coil, and the PWM control circuit is controlled by the signal of the detection circuit. Is characterized by.

[0005]

According to the present invention, since the PWM control circuit is provided for controlling the semiconductor switch of the HF inverter as described above, the generation of high frequency, the pulse width, the duty and the frequency control are extremely easy, and the duty cycle is 1% to 99%. % Can be changed in a wide range, and a pulse having an arbitrary pulse width can be generated.
In addition to providing such a control circuit, a circuit for detecting the reactive power from the current and voltage flowing through the heating coil is provided, and the PWM control circuit is controlled by the signal of this detection circuit to control the output voltage of the HF inverter to the reactive power. Since it is changed according to the above, the required power can always be efficiently supplied.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment of the drawings. In FIG. 1, 1 is a heating container, 2 is an induction heating coil wound around the container, 3 is a high frequency transformer for supplying an HF inverter output, and the output DC of a rectifier 5 for rectifying commercial AC is a MOS type FET semiconductor switch. The high frequency that is switched on and off by 4 is transformed and supplied to the coil 2. 6 is a capacitor circuit for discharging the electromagnetic energy of the primary coil of the transformer, 7 is a comparator for outputting a PWM control pulse, and detects the output pulse of the high frequency oscillator 8 of 50 k to 1 MHz and the voltage across the induction coil 2. The PWM control pulse is output by comparing the generated signal voltage. Reference numeral 10 is a detection circuit for detecting the reactive power by detecting the currents I and V flowing in the induction coil 2, 11 is a comparator for comparing the detection signal with a reference value, and this output is applied to the comparator 7 through the amplifier 9. In addition, 12, 13, and 14 are photocouplers inserted in the voltage and current detection circuits.

The oscillator 8 oscillates at the set oscillation frequency,
The sawtooth wave A shown in FIG. 2 is output. This output is applied to the comparator 7, while the detection voltage B of the amplifier 9 is input to the other side of the comparator 7, and the comparator 7 generates the comparison output pulse C of B> A to control the switch 4. As described above, the output of the comparator 7 outputs the pulse width modulation pulse C whose pulse width changes according to the change of the detection voltage B, and controls the switching speed of the switch 4. The HF inverter converts the DC output of the rectifier 5 into a high frequency HF by turning on and off the semiconductor switch 4, and the transformer 3
A high-frequency alternating current is supplied to the induction coil 2 through. Since the switch 4 controls the supply voltage by the PWM control pulse, the terminal voltage of the induction coil 2 is always controlled to be constant.

The object to be processed in the container 1 is heated by the high frequency of the induction coil 2 and subjected to heat treatment such as casting and sintering. However, the temperature rises due to the material, shape and size of the object to be processed and by heating. Due to temperature changes such as melting
When the value changes, the power factor (cos) of the electric current flowing through the coil 2
Since φ) changes, the energy supplied from the inverter cannot be effectively consumed in the coil 2, and the reactive component increases. Therefore, the reactive power is detected by the detection circuit 10 as the current I and the voltage V flowing in the induction coil 2, and the detection signal is compared with the reference value by the comparator 10 to output the voltage. That is, the comparison output of the comparator 10 increases the output voltage of the comparator 10 when the detected reactive power increases, and controls the output voltage to decrease as the reactive power decreases. This output is voltage B
As shown in FIG. 2, when the output pulse width C of the comparator 7 is increased and the output pulse width C of the comparator 7 is increased by the increase of the voltage B, the voltage B is decreased. The pulse width of the output C of the comparator 7 decreases. That is, when the reactive power increases, the pulse width of the output C of the comparator 7 increases, and when the reactive power decreases, the output pulse width C decreases. Then, the modulation pulse C is applied to the switch 4 to perform switching control, thereby applying a current proportional to the pulse width of the pulse C to the transformer 3 to increase / decrease the inverter output voltage. Therefore, the inverter output voltage rises when the reactive power increases and decreases when the reactive power decreases, whereby the average power P (= VIcosφ) supplied to the coil 2 is increased.
Is controlled to be constant.

In this way, the required power can always be supplied to the induction coil 2, and thus the heat treatment of the object in the container 1 can be stably and efficiently performed. Further, this control can perform pulse width control in a wide range by pulse width modulation control, duty control can be performed, and a wide range of control can be controlled with a high speed response by a detection signal. Since the voltage and the current capacity can be supplied to the induction coil 2, the processing such as casting and sintering can be performed very stably and satisfactorily.

FIG. 3 shows another embodiment of the PWM control circuit.
6 is an astable multivibrator having a set frequency, 17 is a monostable multivibrator, which drives the monostable multivibrator 17 with a signal from the astable multivibrator 16 and outputs a pulse output from the AND gate 15. The output pulse can output a duty pulse having a pulse width set by the monostable multivibrator 17 at a frequency set by the astable multivibrator 16, and returns the operation time of the monostable multivibrator 17 to change the pulse width and change the duty. You can control. This also makes it possible to control the output pulse width of the PWM control by controlling the oscillation operation time of the monostable multivibrator 17 using the reactive power detected from the induction coil 2 as a signal, thereby controlling the power supplied to the coil 2. It can be carried out.

The reactive power of the current flowing through the induction coil may be detected by detecting the phase difference φ between the voltage and the current. Since this detected phase difference φ is proportional to the reactive power, the PWM is used as a signal. Can be controlled. Further, the power factor corresponding to the reactive power or the active power can be used as the detection signal.

[0012]

As described above, according to the present invention, since the PWM control circuit is provided for controlling the semiconductor switch of the HF inverter, the generation of high frequency, the pulse width, the duty, and the frequency control are extremely easy, and the duty cycle is 1%. ~ 99
% Can be changed in a wide range, and a pulse having an arbitrary pulse width can be generated. A circuit for detecting reactive power or a signal proportional thereto is provided from the current and voltage flowing through the heating coil, and the PWM control circuit is controlled by the signal of this detection circuit so that the output voltage of the HF inverter corresponds to the reactive power. Since the heating coil can always be supplied with the required power, the object to be heat-treated by induction heating of the heating coil can always be heat-treated optimally and efficiently, and can be cast and sintered. There is an effect that treatments such as carburizing and quenching can be stably and favorably performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a partial operation explanatory view of FIG.

FIG. 3 is a partial circuit diagram of another embodiment of the present invention.

[Explanation of symbols]

 1 Container 2 Heating Coil 3 High Frequency Transformer 4 Semiconductor Switch 5 Rectifier 6 Capacitor 7 Comparator 8 Oscillator 9 Amplifier 10 Reactive Power Detection Circuit 11 Comparator 12, 13, 14 Photocoupler

Claims (1)

[Claims] 1. An induction heating apparatus comprising an induction heating coil provided with an HF inverter for transforming a high frequency generated by high frequency switching of a semiconductor switch by a high frequency transformer and outputting the transformed high frequency PWM. A control circuit is provided, a circuit for detecting reactive power or a signal proportional thereto is provided from the current and voltage flowing through the heating coil, and the PWM is generated by the signal of the detection circuit.
An induction heating device characterized in that a control circuit is controlled.