JPH06140136A - High frequency processing device - Google Patents

Abstract

PURPOSE:To provide a high frequency processing device capable of precise power control. CONSTITUTION:A high frequency output generated from an inverter 12 is supplied to a high frequency heating coil 13 connected in series to a resonance capacitor 15 and a current transformer(CT) 16. The inverter 12 is formed of a main circuit part 17 for switching current and a gate signal generating circuit 18 for generating gate signals Vg1, Vg2 and transmitting them to the main circuit. The Vg1 and Vg2 are supplied to the bases of TR1, TR4 and the bases of TR2, TR3, respectively. The output of a high frequency current detecting circuit for detecting current intensity on the basis of the high frequency momentary current signal from the CT 16 is transmitted to an error detecting circuit 20 and compared with a standard voltage from a standard voltage source 21, and the obtained difference signal is transmitted to a voltage-frequency converting circuit 22 and converted into a frequency signal. On the basis of the timing signal obtained by shaping this frequency signal and the high frequency momentary current signal by a shaping circuit 23, Vg1 and Vg2 are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency processing apparatus for supplying high frequency power from a high frequency oscillator to a high frequency heating coil for processing.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a conventional high frequency processing apparatus. In FIG. 1, reference numeral 1 is a rectifier circuit that receives electric power from a three-phase commercial power supply, and for example, the output voltage can be adjusted by controlling the distribution angle by a thyristor. The DC voltage from the rectifier circuit 1 is supplied to a high frequency oscillator circuit 2 using a vacuum tube, a transistor, a thyristor and the like. Oscillation circuit 2
The high-frequency output generated from is supplied to the high-frequency heating coil 3 in which the object to be heated 4 is arranged. Reference numeral 5 denotes a voltage detection circuit for detecting the DC voltage from the rectifier circuit 1. The detection output is sent to the error detection circuit 6 and the difference from the reference voltage from the reference voltage source 7 is obtained. The obtained difference signal is sent to the control circuit 8 which controls the distribution angle by the thyristor and adjusts the output voltage of the rectifier circuit 1. By feedback control with such a difference signal, the voltage supplied to the high-frequency oscillator circuit is stabilized, and by changing the reference voltage,
The power supplied to the coil can be adjusted.

[0003]

As described above, in the prior art, the DC voltage is controlled based on the detection output obtained by detecting the DC voltage supplied to the high-frequency oscillation circuit to control the power supplied to the object to be heated. However, depending on the object to be heated, the DC voltage supplied to the high frequency oscillation circuit and the high frequency power applied to the object to be heated may not correspond one-to-one. For this reason, even if the reference voltage is kept constant, the heating power may differ depending on the nature of the object to be heated, and it has not been possible to accurately control the input power to the load.

The present invention has been made in view of the above points, and an object of the present invention is to provide a high-frequency processing device capable of accurately controlling the electric power supplied to a load.

[0005]

The present invention provides a high frequency processing apparatus for supplying high frequency power from a high frequency oscillator, which oscillates based on power from a DC power source, to a high frequency heating coil for processing. A detection circuit for generating an output corresponding to a high frequency current value, a circuit for obtaining a difference between a detection signal from the detection circuit and a predetermined value, and an oscillation frequency of the high frequency oscillator based on an output of the difference circuit. And a control circuit for controlling the operation.

[0006]

According to the present invention, the detection circuit for generating an output corresponding to the high frequency current value supplied to the high frequency heating coil, the circuit for obtaining the difference between the detection signal from the detection circuit and the predetermined value, and the difference circuit By providing a control circuit that controls the oscillation frequency of the high-frequency oscillator based on the output, it is possible to accurately control the electric power supplied to the load. Less than,
The present invention will be described in detail with reference to the drawings.

[0007]

FIG. 2 shows an embodiment of the present invention.
In the figure, 11 is a rectifier circuit that receives power from a three-phase commercial power supply. The DC voltage from the rectifier circuit 11 is supplied to the transistor inverter 12. The high frequency output generated from the inverter 12 is supplied to the high frequency heating coil 13 in which the article to be heated 14 is arranged. 15 and 16
Are a resonance capacitor and a current transformer connected in series to the coil 13.

The inverter 12 includes a main circuit section 17 for switching the current supplied to the coil 13, and a gate signal generating circuit 18 for generating a gate signal and sending it to the main circuit section.
Composed of. The main circuit section 17 has a configuration in which two sets of transistors TR1, TR2 and TR3, TR4 connected in series are connected in parallel between the output terminals of the rectifier circuit. A protection diode D is connected in antiparallel between the collector and the emitter of each transistor. The gate signal generating circuit 18 generates the gate signals Vg1 and Vg2, and the gate signal Vg1 is transferred to the bases of TR1 and TR4.
2 is supplied to the bases of TR2 and TR3, respectively.

Reference numeral 19 is a high frequency current detection circuit for generating a detection output corresponding to the current intensity such as an effective value or a peak-peak value based on the high frequency instantaneous current signal obtained from the current transformer 16, and the detection output is , Is sent to the error detection circuit 20 and the difference from the reference voltage from the reference voltage source 21 is obtained. The obtained difference signal is sent to the voltage-frequency conversion circuit 22 and converted into a frequency signal. This frequency signal and the high-frequency instantaneous current signal are shaped by the shaping circuit 2
Based on the timing signal obtained by waveform shaping in 3, the gate signal generation circuit 17 causes the gate signals Vg1 and Vg2
To create.

FIGS. 3A and 3B show gate signals Vg1,
Vg2 is shown respectively, and TR1 and TR are shown by Vg1.
During the period when 4 is ON, the current I1 is TR1-capacitor 15
-Coil 13-Current flowing through TR4 and Vg2 is ON during the time when TR2 and TR3 are ON.
-Capacitor 15-flows with TR2. FIG. 3C shows the waveform of the current (I1 + I2) flowing through the coil 13 as a result, which is basically a sine waveform.

By the way, in the transistor inverter,
The loss of the transistor can be roughly classified into ON voltage loss and switching loss. ON voltage loss is ON in ON state
It is a loss caused by the product of voltage and flowing current, which can be measured statically and is not related to frequency. Switching loss has a finite rise / fall characteristic when the current path is switched from TR1, TR4 to TR2, TR3 (or vice versa), so that the current is transiently much higher than the ON voltage. It depends on the time period that can flow. This switching loss increases in proportion to the repetition frequency, and in the frequency range above 100 KHz,
Will account for most of the loss.

In order to minimize this switching loss,
The gate signal generation circuit 17 turns on the gate signals Vg1 and Vg2 so that the current paths are switched based on the current waveform at the timing when the current flowing through the coil is zero, that is, at points A and B in FIG. 3 (c). The timing (on-delay) is decided. On the other hand, turn the transistor from ON to OF
Since the off delay of the transistor is large, the timing of turning on F is turned off earlier than the turning on of the transistors of the branches opposite to each other by that much, and TR1 and TR2
, It prevents short circuit current from flowing between TR3 and TR4. Therefore, an OFF period is included in both of the switching between the two sets of transistors.

In this way, turning on the transistor at the point where the current flowing through the coil crosses zero is controlled so that the operating frequency is shifted to the higher side and the gate signal is delayed if the zero point of the current is ahead of the gate signal. On the contrary, if the zero point of the current is delayed, the operating frequency is shifted to the lower side and the gate signal is controlled to advance. Therefore,
By utilizing the resonance characteristics of the load, the voltage-current phase relationship is adjusted by changing the frequency, and the operating point that minimizes the switching loss is selected.

Load impedance in the case of series resonance,
The frequency characteristic of the change in the phase angle of the load current with respect to the load current and voltage is as shown in FIG. 4, and the on-delay described above is set so that the phase angle comes to a point slightly higher than the resonance point of the frequency f0 (point P). As a result, it can be turned on near the zero point of the current.

The value of the load current can be changed by changing the output voltage of the reference voltage source 21. For example, if the operating frequency is shifted to the higher side by decreasing the voltage, the operation is performed in a region where the load impedance is large according to the load current characteristic of FIG. 4, so that the current decreases and the phase of the current increases at the same time. There will be a delay and the effective output current will decrease. This means that the current waveform C in FIG. 5 shifts to D. The shaded area in FIG. 5 represents the current component flowing through the diode connected in antiparallel to the transistor. Even if the frequency changes in this way, the transistor is turned on in the vicinity of the zero point of the current, so that the switching loss of the transistor does not increase.

As described above, the load current setting control is performed by changing the frequency by utilizing the load resonance frequency characteristic, so that the resonance frequency of the load can be changed along with the current control and the frequency fluctuation can be changed depending on the temperature of the load. It also serves as the automatic frequency control (AFC) that follows. That is, in FIG. 4, when the resonance frequency of the load becomes low, the current waveform signal becomes the same as that when the current becomes low, and control is performed so as to lower the operating frequency. On the contrary, when the load resonance frequency becomes high, the current waveform signal becomes the same as that when the current becomes large, and control is performed so that the operating frequency rises.
Since this operating frequency is sufficiently higher than the frequency of the commercial power source such as 100 kHz, the response characteristic of the loop is sufficiently fast.

[0017]

As described above in detail, according to the present invention, a detection circuit for generating an output corresponding to the high frequency current value supplied to the high frequency heating coil, a detection signal from the detection circuit and a predetermined value are provided. Since the circuit for obtaining the difference and the control circuit for controlling the oscillation frequency of the high-frequency oscillator based on the output of the difference circuit are provided, it is always constant even when the resonance characteristic of the heating target changes with temperature. It is possible to realize a high-frequency processing device that can supply electric power to a load, has a small switching loss, and has excellent responsiveness to a load failure or abnormality.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional example.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a waveform diagram for explaining the operation of the embodiment of FIG.

FIG. 4 is a diagram showing frequency characteristics of a phase angle of a load current with respect to a load impedance, a load current, and a voltage.

5 is a waveform diagram for explaining the operation of the embodiment of FIG.

[Explanation of symbols]

 11: Rectifier circuit 12: Transistor inverter 13: High frequency heating coil 15: Resonance capacitor 16: Current transformer 17: Main circuit part 18: Gate signal generation circuit 19: High frequency current detection circuit 20: Error detection circuit 21: Reference voltage source 22: Voltage-frequency conversion circuit 23: shaping circuit

Claims (1)

[Claims] 1. A high-frequency processing apparatus for supplying high-frequency power from a high-frequency oscillator, which oscillates based on power from a DC power supply, to a high-frequency heating coil for processing, corresponding to a high-frequency current value supplied to the high-frequency heating coil. A detection circuit that generates an output, a circuit that obtains a difference between a detection signal from the detection circuit and a predetermined value, and a control circuit that controls the oscillation frequency of the high-frequency oscillator based on the output of the difference circuit are provided. A self-excited oscillation type high frequency processor.