JPH01683A - High frequency heating device - 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 The present invention relates to an improvement in a high-frequency heating device in which power is supplied from an oscillating vacuum tube to a high-frequency heating coil or electrode plate.

b. Prior Art There are two types of high-frequency heating: induction heating and dielectric heating, and a vacuum tube is usually used as an oscillation tube that supplies high-frequency power to a coil or electrode plate for high-frequency heating.

FIG. 4 shows this type of conventional vacuum tube type high frequency induction heating device. In the figure, 1 is a three-phase commercial power supply terminal, 2 is a tie transformer, 3a and 3b are power on switches, and 4 is a A transformer, 5, is inserted between the power supply switch 3b and the primary side of the transformer 4 in order to change the conduction angle of the commercial power supply, and 6 is a DC voltage for the secondary side output of the transformer 4. 7 is a vacuum tube (oscillator tube) that converts the DC voltage from the rectifier 6 (anode DC voltage) into a high frequency voltage, 8 is a self-biasing grid resistor that determines the operating point of the vacuum tube 7, 9 is the vacuum tube 7 A high frequency induction heating coil to which higher frequency power is supplied; 10 is an object to be heated;
11 is a control circuit that outputs a predetermined gate pulse to the thyrisk stack 5 in order to keep the anode DC voltage supplied from the rectifier 6 to the anode of the vacuum tube 7 constant;
12 is a potentiometer.

In this device, a thyristor SCR constituting a thyristor stack 5 is inserted into the primary side of a transformer 4 which is an anode voltage supply source for a vacuum tube 7, and a control circuit 11 controls the gate signal of the thyristor SCR. The phase angle was changed, thereby changing the anode DC voltage E of the vacuum tube 7.

That is, in this case, when the gate pulse phase angle of the thyristor SCR constituting the above-mentioned thyristor stack 5 is α, and the maximum anode DC voltage is Eo, the anode DC voltage E is expressed by the following equation.

B, = E, cos a (Q≦α≦−)Eb
=t! o (1+cos(cr +-)) On the other hand, the power factor Pf of the commercial power source is expressed by the following equation.

By doing so, the output power of the vacuum tube 7 can be changed from the maximum value to zero. Specifically, is controlled to be high, and when □≧α>0, the anode voltage is controlled to be low as shown in FIG.

Further, depending on the type of signal fed back to the control circuit 11, constant voltage, constant current, and constant temperature control are possible.

Problems to be Solved by the C0 Invention However, in the conventional device as described above, when the commercial three-phase power supply voltage becomes 3.3 kV or 6.6 kV, the commercial It was necessary to provide a tie transformer 2 to lower the three-phase power supply voltage to 440v. Therefore, a space is required for installing the tie transformer 2, which increases the size of the device. In addition, since the SIRISK stack 5 is inserted on the primary side of the transformer 4, the required current capacity is large at 100A to 500A.
Therefore, as the power increases, the cost increases. Moreover, since the amount of heat generated was large, it was necessary to take measures for heat dissipation.

Moreover, the power factor p deteriorated from 0.955 to around zero, posing a problem with the power factor.

The present invention was made in view of these circumstances, and its purpose is to eliminate the need for a tie transformer even when using a three-phase commercial power supply voltage of 3.3 kV or 6.6 kV.
To provide a vacuum tube type high-frequency heating device that requires small current capacity (and generates a small amount of heat), does not require special heat radiation measures, and does not cause deterioration of power factor.

d1 Means for Solving Problems In order to solve the above-mentioned problems, the present invention provides a high-frequency heating device in which power is supplied from an oscillation vacuum tube to a high-frequency heating coil or electrode plate. A control means is provided for applying a cut-off bias to the grid of the vacuum tube at arbitrary intervals, and the control means changes the ratio between the oscillation time and the oscillation stop time of the vacuum tube, thereby controlling the high-frequency heating coil or The power supplied to the electrode plate is controlled.

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 shows the circuit configuration of a high-frequency induction heating device to which the present invention is applied. The power is supplied directly to a transformer 22 via a power-on switch 21, and the output of the transformer 22 is further supplied via a rectifier 23 to the anode (plate) of a vacuum tube 24 for oscillation. In addition, the transformer 22 and the rectifier 2
3 and between the rectifier 23 and the anode of the vacuum tube 24, protection circuits 25 and 26 for preventing abnormal voltage generation are provided, respectively.

The anode of the vacuum tube 24 described above is connected via a blocking capacitor CI to a parallel resonant circuit 27 consisting of a series circuit of a coupling coil L1 and a high-frequency induction heating coil L8, and a capacitor C. On the other hand, the grid of the vacuum tube 24 has a coupling coil L2. A resistor R and a transistor module 28 are connected in series, and a capacitor C1 is connected between the coil and the midpoint of the resistor R and the cathode of the vacuum tube 24. Then, the above-mentioned coupling coil L1. Ls are electromagnetically coupled to each other to form an anode-tuned oscillation circuit.

In addition, blocking capacitor CI and parallel resonant circuit 27
A high frequency voltage multiplier 29 is connected between the multiplier 29 and the voltage signal Vt (divided voltage signal) obtained from the multiplier 29 is supplied to the electronic control circuit 30.

Then, from this electronic control circuit 30, the voltage signal V
I and the voltage signal v obtained from the potentiometer 31
2, a predetermined control signal is applied to the field effect transistors TR+, T which constitute the transistor module 28.
The signals are supplied to the gates of Rz, respectively.

Further, a predetermined negative voltage is supplied from a bias power supply circuit 32 to an intermediate point between the resistor R and the transistor module 28.

Next, the operation of the high-frequency induction heating device configured as described above will be described.

First, when the power supply switch 21 is turned on, 220V, 400V,
3.3kV, 6.6kV (three-phase, 50/60H
z) is stepped up by a transformer 22 and supplied to a rectifier 23. The rectifier 23 outputs a DC voltage of, for example, about 10 kV to 15 kV as an anode voltage of the vacuum tube 24, and a predetermined DC voltage is supplied to the anode of the vacuum tube 24.

When high-frequency induction heating is not performed, the field effect transistors TR1 and TR of the transistor module 28 are placed in an OFF state. Therefore, a negative output voltage (for example, -2kV to -3kV) is generated from the bias power supply circuit 32.
) is applied as a cut-off bias to the grid of the vacuum tube 24, and accordingly, the vacuum tube 24 as an oscillation element enters a cut-off state and does not oscillate. Therefore, no high-frequency current flows through the high-frequency induction heating coil L2, and the heated object 33
is not high frequency induction heated.

On the other hand, during high-frequency induction heating, first both transistors "R+" and "TRz" of the transistor module 28 are turned off.
It is switched to the N state, and thereafter ON-OFF switching control is performed periodically based on the output signal from the electronic control circuit 30. That is, when the field effect transistors TR, TR, become conductive in response to a heating start command, the bias power supply circuit 32
Since the output terminal of the vacuum tube 24 is grounded, the vacuum tube 24 starts oscillating, and accordingly, a large high-frequency current flows through the high-frequency induction heating coil tz, and the object to be heated 33 is heated by high-frequency induction. At this time, a constant value output voltage Vl is supplied from the high frequency voltage multiplier 29 to the electronic control circuit 30, and this signal V.

and the voltage signal V preset by the potentiometer 31.
A signal of a predetermined frequency is output from the voltage controlled oscillator in the electronic control circuit 30 based on the signal g. Specifically, the voltage of the potentiometer V! When V is increased, a higher frequency signal is output from the voltage controlled oscillator, and when this voltage V is decreased, a lower frequency signal is output from the voltage controlled oscillator. Then, the frequency signal from this voltage controlled oscillator is supplied to a one-sit multivibrator in the electronic control circuit 30, and every time the frequency signal is input to this one-sit multivibrator, a predetermined width T+ (second Only one pulse signal (see FIGS. 3(A) and 3(A)) is output and supplied to the gates of the field effect transistors TR, TR, of the transistor module 28. Along with this, the transistors TR+ and TRg are switched to the ON state during the pulse period T, so that the vacuum tube 24 enters an oscillating state.

After this period T, the transistors TR+ and TRg are switched to the OFF state for a period Tx (see FIGS. 2 and 3) until the subsequent one-shit pulse signal is supplied. Since a cutoff bias is applied from the grid bias power supply circuit 32 of the vacuum tube 24, the vacuum tube 24 stops oscillating. Therefore, the vacuum tube 24 repeats an oscillation state and an oscillation stopped state at a predetermined period based on the output signal from the electronic control circuit 30.

Note that in this example, the period T2 can be arbitrarily changed by adjusting the potentiometer 31.

Here, the oscillation time of the vacuum tube 24 is T and the oscillation stop time is ↑
2, the average high frequency output P is? .

(However, P is the output voltage at T!-0).

Incidentally, as shown in Figure 2? + -1ms, Tt-
If it is 10aS, then as shown in Figure 3, T+ -1+*5
When STz -1m5, it becomes.

In this way, the average high frequency output P can be controlled by keeping the oscillation time T of the vacuum tube 24 constant and changing the oscillation stop time rz. Note that the oscillation stop time T2 is not limited to this, and the oscillation time T2 can be changed by changing the pulse width of the one-shot pulse output from the electronic control circuit 30.
, or by changing both of these, the average high-frequency output P can be arbitrarily set by changing the ratio of the oscillation time T1 to the oscillation start period Tm (see Figure 2), that is, the duty factor. is possible.

The present invention has been described above with reference to the case where it is applied to a high frequency induction heating device, but the present invention is not limited to this, but is applicable to a high frequency dielectric heating device in which dielectric material is sandwiched between a pair of electrode plates to perform dielectric heating. Needless to say, it is also applicable.

e0 Effects of the Invention As described above, the present invention provides a control means for applying a cutoff bias to the grid of an oscillating vacuum tube at arbitrary intervals, thereby changing the ratio between the oscillation time and the oscillation stop time of the vacuum tube. As a result, the power supplied to the high-frequency heating coil or electrode plate is controlled, so there is no need to use a conventional method of changing the phase angle of the thyristor gate using a thyristor stack. ,
Therefore, even if the commercial power supply voltage becomes 3.3 kV or 6.6 kV, there is no need to provide a tie transformer, and the operating current of the control means described above is a small current (for example, in the embodiment,
The required current capacity of the transistor Moseal 28 is IA to 5A.
), and since the amount of heat generated is small, there is no need to take special measures for heat dissipation. Therefore, it is possible to reduce the size and cost of the high-frequency heating device.

Furthermore, since the power is adjusted without taking any means to change the phase angle of the thyristor gate signal, the input power factor P will never deteriorate below 0.955. It does not cause an increase in harmonic components.
Therefore, it is possible to provide a high-frequency heating device that is highly practical and has no risk of adversely affecting not only the inside of the factory but also other consumers of commercial power.

[Brief explanation of the drawing]

FIGS. 1 to 3 are for explaining one embodiment of the present invention, and FIG. 1 is a circuit diagram of a high-frequency induction heating device according to the present invention, and FIGS. Figure (^) is a pulse waveform diagram showing the cant-off bias applied to the grid of the vacuum tube, and Figures 2 (B) and 3 (B) show the oscillation time Tt and oscillation stop time T8 of the vacuum tube. The output waveform diagrams and FIGS. 4 to 6 showing the relationships are for explaining the conventional high frequency induction heating device. FIG. 4 is a circuit diagram of the high frequency induction heating device, and FIG. 5 is a thyristor diagram. FIG. 3 is a diagram showing the phase angle α of the gate signal in relation to the voltage. 20... Three-phase commercial power supply terminal, 22... Transformer,
23... Rectifier, 24... Vacuum tube for oscillation, 28-) Runlis module, 29-... High frequency voltage multiplier, 30-... Electronic control circuit, 31... Potentiometer, 32. ... Bias power supply circuit, 33... Heated object, Ls-Ls "" coupling coil, Lz "' high frequency induction heating coil. Fig. 2 (A) Fig. 3 (B) (B)

Claims (1)

[Claims] In a high-frequency heating device configured to supply power from a vacuum tube for oscillation to a coil or electrode plate for high-frequency heating, a control means is provided for applying a cut-off bias to the grid of the vacuum tube at arbitrary intervals, and the control means A high-frequency heating device, characterized in that the electric power supplied to the high-frequency heating coil or electrode plate is controlled by changing the ratio between the oscillation time and the oscillation stop time of the vacuum tube.