JP2017017003A - High frequency dielectric heating device - Google Patents

Abstract

An object of the present invention is to provide a high-frequency dielectric heating apparatus that achieves fine adjustment of impedance with high precision and ease while reducing the apparatus cost and simplifying the apparatus structure. A high-frequency power source (20), a pair of electrodes (30) arranged facing each other, and a reflected power detection means connected between the electrodes (30) and the high-frequency power source (20) for detecting reflected power generated by heating of an object to be heated. , an impedance matching device 40 for adjusting the reflected power, the matching device 40 comprising a capacitor C1 connected in parallel with the high frequency power supply 20 and at least reactance adjustment connected in series with the electrode 30. A high-frequency dielectric heating device 10 comprising at least one of a possible capacitor C2 or a coil L, and a high-frequency power source 20 configured to be variable in frequency. [Selection drawing] Fig. 1

Description

  The present invention relates to a high-frequency dielectric heating device that heats an object to be heated disposed between opposing electrodes by high-frequency dielectric heating, and more particularly to a high-frequency dielectric heating device that defrosts frozen food by high-frequency dielectric heating.

  Conventionally, as a high-frequency dielectric heating apparatus that heats an object to be heated by high-frequency dielectric heating, a high-frequency dielectric heating apparatus that heats an object to be heated disposed between opposing electrodes by high-frequency dielectric heating is known (for example, a patent) Reference 1). High-frequency dielectric heating is caused by applying high-frequency voltage to the object to be heated (dielectric material), changing the polarity of each molecule constituting the object to be heated at high frequency, and accompanying rotation, collision, vibration, friction, etc. of the molecule. It is a heating method for heating an object to be heated by internal heat generation.

The electrode impedance of the object to be heated varies greatly depending on the shape, type, heating or thawing temperature of the object to be heated. At this time, when there is a difference between the output impedance of the high-frequency power supply and the electrode impedance of the object to be heated, that is, the impedance is not matched, reflected power is generated, the heating or thawing efficiency is lowered, and the circuit element is destroyed or deteriorated. May lead to.
In order to prevent this, a matching device is inserted between the power amplifier circuit and the electrode, and impedance matching is maintained by providing, for example, a capacitor or a coil as its constituent elements.

  Generally, when heating or thawing an object to be heated such as food by high frequency dielectric heating, a vacuum tube type high frequency power source having a simple structure, a high temperature resistance of circuit elements, and excellent resistance to reflected power is used. . However, the vacuum tube type high-frequency power source is large in terms of power amplification characteristics, and there is a problem that the resonance frequency arbitrarily changes depending on the electrode impedance on which the object to be heated is arranged. In particular, since the power frequency affects the uniformity (power half depth) when heating or thawing foods having various shapes, it is not preferable that the resonance frequency changes arbitrarily in each situation. Further, in order to comply with the frequency regulations in the Radio Law, it is preferable to keep within a predetermined frequency fluctuation range.

On the other hand, a semiconductor high-frequency power source that performs power amplification by controlling high-speed switching of a semiconductor is characterized by its small size and high efficiency as a system when combined with a high-resolution automatic matching unit, and has been used for applications such as plasma discharge. Has been.
The impedance matching state is maintained by sequentially changing the values of the variable capacitors and variable coils, which are the components of the matching unit, but the load is large like food, and its shape, type, and temperature When the electrode impedance changes greatly due to the above, it is necessary to provide the capacitor or coil with a large impedance adjustment width in order to maintain the matching state. As a result, there arises a problem that the matching unit is large and the cost is high.

  As a high-frequency dielectric heating device that avoids the problem of an increase in the size of the matching device, a high-frequency dielectric heating device is known in which the matching circuit has a variable coil and a capacitor, and the capacity of the capacitor can be increased by switching means ( For example, see Patent Document 2).

  In the high frequency dielectric heating device described in Patent Document 2, the power reflected by the high frequency power source is detected by the reflected power detection means, and the values of the variable coil and the capacitor are appropriately combined based on the detection signal of the reflected power detection means, and the impedance To maintain the reflected power to a minimum.

Japanese Patent Application Laid-Open No. 08-255682 JP 2005-56781 A

  The high-frequency dielectric heating device described in Patent Document 2 is configured to adjust the impedance by changing the capacitance of the capacitor or the coil. Therefore, it is necessary to increase the impedance adjustment width by the coil or the capacitor, and the matching unit cannot be reduced in size.

  Therefore, the present invention solves these problems, and by performing sequential impedance matching according to changes in electrode impedance such as the shape, type of food, heating or thawing temperature, the oscillation efficiency of the high frequency power supply is improved. Improve and reduce the size of the power supply. Furthermore, by making the power supply frequency variable within a predetermined range, an impedance adjustment function is provided, and the matching unit is simplified and miniaturized. Thus, it is an object of the present invention to provide a high-frequency dielectric heating apparatus that is small and inexpensive and capable of high-quality heating or thawing with respect to various foods.

  The present invention relates to a high-frequency power source, a pair of electrodes arranged opposite to each other, a reflected power detecting means connected between the electrode and the high-frequency power source to detect a reflected power generated by heating of an object to be heated, and a reflected power A high-frequency dielectric heating device comprising an impedance matching device for adjusting a capacitor, the matching device comprising: a capacitor connected in parallel with the high-frequency power source; and a capacitor or a coil capable of at least reactance adjustment connected in series to the electrode. At least one is provided, and the high-frequency power source is configured to have a variable frequency, thereby solving the problem.

  According to the first aspect of the present invention, the reflected power generated by heating or thawing of the object to be heated is detected by the reflected power detection means, and the impedance matching is performed successively, thereby improving the oscillation efficiency of the high frequency power supply and reducing the size of the power supply. Can be achieved. The impedance matching unit includes at least one of a capacitor connected in parallel with the high-frequency power source and at least one of a capacitor or a coil connected in series with the electrode and capable of adjusting the reactance, and the high-frequency power source is configured to have a variable frequency. Thus, by changing the frequency of the power supply, it is possible to adjust the reactance of at least one of the capacitor or the coil connected in series with the electrode with high resolution, while simplifying and downsizing the matching unit. Impedance adjustment can be achieved with high accuracy and ease.

According to the invention of claim 2, by using a semiconductor high-frequency power supply as a high-frequency power supply, impedance matching with excellent responsiveness can be achieved while enjoying the effects of high efficiency, small size and light weight, and low cost. Damage to the power supply can be quickly and satisfactorily suppressed.
According to the third aspect of the present invention, the matching device includes variable means for switching or continuously changing the capacity of at least one of a capacitor connected in parallel with the high-frequency power source or a capacitor connected in series with the electrode. Thus, it is possible to set the reactance adjustment width by changing the frequency of the power supply in the vicinity of the electrode impedance, and it is possible to suppress the reflected power by impedance matching in a shorter time. In addition, since the frequency variable width of the high frequency power supply can be set small, the heating and thawing quality of the food can always be kept good while simplifying and downsizing the matching unit.
According to the fourth aspect of the present invention, since the matching device includes the capacitor connected in parallel with the electrode, it is possible to reduce the rate of change of the electrode impedance accompanying heating or thawing. As a result, since the frequency variable width of the high frequency power supply can be set small, the heating and thawing quality of the food can always be kept good while simplifying and downsizing the matching unit.
This is particularly effective when the rate of change in electrode impedance associated with thawing is large, such as when the electrode is brought into contact with or in accordance with the shape of a food or food package for the purpose of high-efficiency thawing.
According to the invention of claim 5, it is possible to easily obtain accurate information on the food impedance from the impedance information output unit of the matching unit, and set parameters of the matching unit narrowed down to the object to be heated. Or the matching unit can be simplified based on the result.

The circuit diagram which shows the high frequency dielectric heating apparatus which concerns on one Embodiment of this invention. The table | surface which shows the variation | change_quantity of the 2nd capacitor when not providing a 3rd capacitor and when providing. The graph which shows the measurement result of the frequency and reflectance in an experiment example.

  Below, the high frequency dielectric heating apparatus 10 which concerns on one Embodiment of this invention is demonstrated based on drawing.

  As shown in FIG. 1, the high-frequency dielectric heating device 10 includes a high-frequency power source 20, a pair of electrodes 30, a matching unit 40 connected between the electrode 30 and the high-frequency power source 20 and impedance matching with the high-frequency power source 20, A reflected power detector (not shown) that detects power reflected to the high-frequency power source 20 and a controller (not shown) that controls each part, and a frozen food disposed between a pair of opposed electrodes 30 are provided. Thawing by high frequency dielectric heating.

  The high frequency power source 20 is configured as a variable frequency semiconductor high frequency power source having a variable frequency. The high frequency power supply 20 is configured to suppress or stop the high frequency output by a protection function when the reflectance detected by the reflected power detection unit exceeds a predetermined threshold.

  As shown in FIG. 1, the matching unit 40 includes a reactance circuit 50 connected in series to the electrode 30, a first capacitor C <b> 1 connected in parallel with the electrode 30 between the reactance circuit 50 and the high-frequency power source 20, and A third capacitor C <b> 3 connected in parallel with the electrode 30 is included between the electrode 30 and the reactance circuit 50.

  The reactance circuit 50 includes at least one reactance element connected in series to the electrode 30. In the present embodiment, as shown in FIG. 1, the second capacitor C2 connected in series to the high-frequency power source 20 and A coil L is provided.

FIG. 2 shows that the frequency of the high frequency power supply is 13.56 MHz, the capacitance of the first capacitor C1 is 1500 pF, the inductance of the coil L is 1.8 μH, various foods are thawed, and the reflected power by the reflected power detection unit is always minimized. Thus, the value (capacity%) when the capacity of the second capacitor C2 is adjusted is shown.
As can be seen from FIG. 2, in the case where the third capacitor C3 is not disposed, the capacity% of the second capacitor C2 at the start of thawing differs depending on the type and number of ingredients, and further, the second capacitor C2 at the end of thawing. The capacity% is greatly decreasing.
When the third capacitor C3 is disposed, the change in the capacitance% of the second capacitor C2 due to the type and number of ingredients at the start and end of thawing is small. From this result, by disposing the third capacitor C3, it is possible to reduce the rate of change of the electrode impedance accompanying the thawing of the ingredients, and the frequency variable width of the high frequency power source 20 can be set small.

The matching unit 40 includes variable means (not shown) including a contact means such as a relay, a variable condenser, or the like that switches or continuously changes the capacity of the first capacitor C1 connected in parallel with the high-frequency power source 20.
The specific mode of the variable means is not limited to the above, and any means may be used as long as the capacity of the first capacitor C1 is switched or continuously changed in multiple stages, and the variable means is connected in series with the electrode 30. The capacitance of the connected capacitor may be switched in multiple stages or continuously changed.

  Based on the reflectance detected by the reflected power detection unit, the control unit switches the capacity of the first capacitor C1 in a decreasing direction according to the thawing state of the object to be heated, and adjusts the frequency of the high-frequency power source 20, Designed for impedance matching.

  Hereinafter, experimental examples of the present invention will be described.

  In this experimental example, the capacitance of the second capacitor C2 of the reactance circuit 50 is 93 pF, the inductance of the coil L is 1.8 μH, and the impedance of the reactance circuit 50 is adjusted by adjusting the frequency of the high-frequency power supply 20. The capacitance of the third capacitor C3 is 400 pF. The high frequency power supply 20 is configured such that the high frequency output is stopped by the protection function when the reflectance detected by the reflected power detection unit exceeds 40%. In addition, as the objects to be thawed (objects to be heated) disposed between the pair of electrodes 30, four freezers were used.

  FIG. 3 shows the results of measuring the frequency and reflectance every minute after the start of thawing.

  In the case where the matching adjustment is not performed in accordance with the decompression, when the capacitance of the first capacitor C1 is set to 1500 pF and the frequency of the high frequency power supply 20 is fixed to 13.56 MHz, the reflectivity reaches the threshold value in about 3 minutes. 40%), high-frequency oscillation of the high-frequency power source 20 was stopped, and thawing was interrupted.

Further, when the impedance of the reactance circuit 50 is adjusted by switching the capacity of the first capacitor C1 and adjusting the frequency of the high frequency power supply 20, the capacity of the first capacitor C1 is set to 1500 pF and defrosting is started. , It takes 7 minutes for the reflectivity to reach the threshold (40%) because the frequency changes with decompression (13.53 MHz → 13.48 MHz), and the time it takes for the reflection to reach the threshold compared to when the frequency is not adjusted. It was possible to lengthen.
When the reflectivity reaches the threshold value, the capacitance of the first capacitor C1 is switched to 1270 pF, so that the reflectivity is reduced to about 15%, and at the same time, the frequency changes (13.48 MHz → 13.55 MHz). The frequency almost recovered to 13.53 MHz. Similarly, by switching the capacitance of the first capacitor C1 to 1030 pF, 970 pF, and 880 pF as appropriate according to the reflectance, high-frequency application was possible while maintaining the reflectance below the threshold, and thawing was completed.

  From the above, it is confirmed that the high-frequency dielectric heating device 10 can achieve impedance matching at low cost by adjusting the impedance of the reactance circuit 50 by variably adjusting the frequency of the high-frequency power source 20 and switching the matching unit 40 with multiple stages such as relays. It was done. Furthermore, by using a variable capacitor for adjusting the capacitor capacity in the matching unit 40, it is possible to easily achieve more accurate impedance adjustment. Further, when the frequency of the high frequency power supply 20 is variably adjusted, the frequency variable width can be reduced by using the capacitor capacity adjustment in the matching unit 40 together.

  As mentioned above, although embodiment of this invention was explained in full detail, this invention is not limited to the said embodiment, A various design change can be performed without deviating from this invention described in the claim. Is possible.

  For example, in the above-described embodiment, the high-frequency dielectric heating device has been described as thawing frozen food by high-frequency dielectric heating, but the high-frequency dielectric heating device may be used for heating an object to be heated, It is not limited to thawing ingredients.

  In addition to the above-described embodiment, an impedance information output unit that outputs impedance information (for example, the state of the first capacitor) of the matching unit to a monitoring monitor or the like may be provided. In this case, it is possible to easily obtain accurate information on food impedance from the impedance information output unit of the matcher, and set the matcher parameters narrowed down to the object to be heated and match based on the result. The device can be simplified.

  The semiconductor type high frequency dielectric heating device of the present invention is not only suitable for rapid thawing of frozen foods etc., but can also be widely applied as an industrial dielectric heating device. Industrial applicability is high, for example, it can be incorporated into a microwave oven or refrigerator.

DESCRIPTION OF SYMBOLS 10 ... High frequency dielectric heating apparatus 20 ... High frequency power supply 30 ... Electrode 40 ... Matching device 50 ... Reactance circuit C1 ... First capacitor C2 ... Second capacitor C3 ... First 3 capacitors L ... Coil

Claims (5)

A high-frequency power source, a pair of electrodes arranged opposite to each other, a reflected power detecting means connected between the electrode and the high-frequency power source for detecting reflected power generated by heating the object to be heated, and an impedance for adjusting the reflected power A high-frequency dielectric heating device comprising a matching unit,
The matching unit includes at least one of a capacitor connected in parallel to the high-frequency power source and a capacitor or a coil capable of adjusting at least reactance connected in series to the electrode, and the high-frequency power source is configured to have a variable frequency. A high-frequency dielectric heating device characterized by comprising:   The high frequency dielectric heating apparatus according to claim 1, wherein the high frequency power supply is a semiconductor high frequency power supply.   The matching unit includes variable means for switching or continuously changing at least one of the capacitance of a capacitor connected in parallel with the high-frequency power source or a capacitor connected in series with the electrode. The high frequency dielectric heating apparatus according to claim 2.   The high-frequency dielectric heating device according to any one of claims 1 to 3, wherein the matching unit includes a capacitor connected in parallel with the electrode.   The high frequency dielectric heating apparatus according to any one of claims 1 to 4, further comprising an impedance information output unit that outputs impedance information of a matching unit to the high frequency dielectric heating apparatus.

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