JPH10134953A - High frequency thawing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably perform thawing independently of material and mass of a material to be thawed by matching a load impedance of a material to be thawed to an output impedance of a high frequency amplifier circuit with an impedance converting coil transformer. SOLUTION: An impedance converting coil transformer 6 is connected to output of a high frequency oscillator 5 through an input matching detecting circuit 15, and a matching coil 7 and a variable capacitor 8 are connected in series through a tap switching unit 6a so as to supply the high frequency power to an upper and a lower electrodes 2, 3, and a material 4 to be thawed as a load is heated by induction heating. In this high frequency thawing device, the switching unit 6a operates plural switching devices corresponding to each tap of the coil through a control device so as to match the output impedance of the high frequency amplifier circuit to the impedance of the material 4 to be thawed. Furthermore, matching of the impedance of each tap and the load impedance to each other is adjusted through the coil 7 and the variable capacitor 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to matching between the output impedance of a high-frequency amplifier circuit and the load impedance of a non-thawed product in a high-frequency thawing apparatus for thawing frozen food or the like by dielectric heating.

[0002]

2. Description of the Related Art FIG. 6 is a schematic diagram showing a high-frequency thawing apparatus using dielectric heating. An upper electrode plate 2 and a lower electrode plate 3 are installed in an apparatus housing 1, and an object to be thawed 4 is placed between the two electrode plates. Then, high-frequency power is supplied from the high-frequency oscillator 5 between the two electrode plates. In this device, if the output impedance of the high-frequency oscillator 5 does not match the load impedance of the object 4 to be defrosted, the high-frequency oscillator 5 must consume the power of the reflected wave, and the high-frequency oscillator 5 may be damaged. There is. Therefore, it is necessary to match the output impedance of the amplifier circuit with the load impedance.

[0003] In an industrial high-frequency defroster using dielectric heating, the load impedance to be defrosted is constant because the material of the load to be defrosted is constant, and it is not necessary to adjust the impedance by the load.

[0004]

However, if the frozen food to be thawed is not constant, it is very difficult to match the load impedance of the frozen food because the output impedance of the amplifier circuit cannot be varied. Also,
It is even more difficult to adjust the quantity and material of the frozen food to match the output impedance of the amplifier circuit. Further, as the frozen food is thawed, the material and the like become non-uniform and the load impedance fluctuates, so that it is necessary to adjust the impedance matching.

Accordingly, the present invention provides a high-frequency decompression device capable of performing a decompression process irrespective of the material and amount of the decompression object by matching the load impedance of the decompression object with the output impedance of the high-frequency amplification circuit by using an impedance conversion transformer. The purpose is to provide.

[0006]

According to a first aspect of the present invention, there is provided a high-frequency thawing apparatus for thawing a frozen product by dielectric heating. And an impedance conversion coil transformer having a tap switching unit for matching the load impedance of the object to be defrosted, and an impedance of each tap for matching the impedance in the tap switching unit of the impedance conversion coil transformer with the load impedance. A switching control unit that switches the tap switching unit based on the value,
A coil and a variable capacitor for adjusting the matching between the impedance at each tap of the impedance transformer and the load impedance are provided.

According to a second aspect of the present invention, there is provided a high frequency decompression device according to the first aspect of the present invention, wherein the capacitance of the variable capacitor at all taps of the impedance conversion coil transformer is added. And storage means for storing matching data in the case of changing the data, and matching detecting means for detecting an optimum matching position by referring to the matching data.

According to a third aspect of the present invention, there is provided a high-frequency decompression device according to the first aspect of the present invention, wherein the high-frequency decompression device according to the first aspect further includes means for calculating the average value of the impedance of the previous tap and the current tap. , A variable capacitance control unit that changes the capacitance of the variable capacitance capacitor to match the impedance up to the average value of the impedance of the next tap and the impedance of the current tap.

According to a fourth aspect of the present invention, in addition to the high frequency decompression device according to the first aspect, the high frequency amplifying circuit is used when a tap of an impedance conversion coil transformer is switched. And a high-frequency adjusting means for narrowing the output.

According to a fifth aspect of the present invention, there is provided a high-frequency decompression device according to the first aspect of the present invention, wherein a load impedance is provided between an output side of the impedance conversion coil transformer and the load. A load matching monitoring means for monitoring a matching state with the load.

According to a sixth aspect of the present invention, there is provided a high-frequency decompression device according to the first aspect of the present invention, wherein an imaginary component is minimized in response to a change in load impedance. A variable capacitance capacitor adjusting means for changing the capacitance in a direction opposite to the capacitance change at the time of adjusting the variable capacitance capacitor.

According to the above configuration, the high-frequency decompression device according to the first aspect of the present invention matches the load impedance with the output impedance of the high-frequency oscillation circuit by switching the tap switching unit of the impedance conversion coil transformer. High frequency power can be efficiently applied to the object to be thawed.

The high-frequency decompression device according to the second aspect of the present invention can reliably detect a matching position by referring to matching data corresponding to a change in the capacitance of the variable capacitor at all taps.

In the high frequency decompression apparatus according to the third aspect of the present invention, the capacitance of the variable capacitor to be used can be set to the minimum value by clearly determining the impedance range in which the matching adjustment is performed.

In the high-frequency decompression apparatus according to the fourth aspect of the present invention, the reflection of the high-frequency power from the load-side circuit is eliminated by reducing the output of the high-frequency amplifier circuit at the time of tap switching, and the high-frequency oscillation circuit is damaged. To prevent

The high-frequency decompression apparatus according to the fifth aspect of the present invention can eliminate the imaginary component of the impedance of the object to be decompressed by monitoring the matching state with the load impedance, and efficiently consumes high-frequency power. be able to.

The high-frequency decompression device according to the sixth aspect of the present invention prevents the loss of control when the capacitive coupling is lost by changing the capacity of the variable capacitor in the direction opposite to that at the time of adjustment.

[0018]

FIG. 1 is a schematic circuit diagram of a high-frequency decompression device according to a first embodiment of the present invention. The output of the high-frequency oscillator 5 is connected to the coil transformer 6 for impedance conversion via the input matching detection circuit 15. The matching coil 7 and the variable capacitor (varicon) 8 are connected in series via the tap switching section 6a, and high frequency power is supplied to the upper and lower electrode plates 2 and 3.

Here, the purpose of impedance matching is to maximize the effective power applied to the load between the electrode plates of the high-frequency decompression device. FIG. 2 shows an equivalent circuit of the object to be defrosted as a load. In this case, the power W applied to the object to be decompressed includes a reactance component Zi composed of the L component and the C component, a resistance component Zr due to the R component, and
From the voltage V applied to the object to be thawed,

(Equation 1) Becomes Here, if Zi disappears, the electric power consumed by the object to be thawed becomes maximum.

In the circuit of FIG. 1, when the L component and the C component cancel each other, the C component in the frozen food must also be canceled by considering the frozen food in an equivalent circuit of the R component and the C component. For this reason, the matching coil 7 and the variable condenser 8 are controlled so that the imaginary component of the impedance of the entire circuit becomes zero.
Adjust the components and the C component. As a result, in the entire circuit, the resistance component exists only in the object to be defrosted. Therefore, all the input voltage is applied to the resistance component of the object to be defrosted, so that the object to be defrosted can be efficiently defrosted.

The load impedance becomes Zr when matching is performed so that the imaginary component becomes zero. Since this value is determined by the size and material of the frozen food, the fixed value is not determined unless the object to be thawed such as the frozen food is constant. Therefore, the impedance conversion transformer coil 6
Is switched to convert the load impedance according to the object to be thawed such as frozen food.

Next, FIG. 3 shows details of the tap switching section 6a. In order to search for the optimum matching point, the tap 11 drawn from the impedance conversion coil transformer 6 is provided with a plurality of switching devices 9 that can be switched by a signal from the control device 10. The switching device 9 is configured by a relay or the like, and the control device 10 is configured by a microcomputer or the like.

FIG. 4 shows a control mechanism of the variable condenser 8, in which a drive unit 13 controlled by a signal from the control unit 10 changes the capacity of the variable condenser 8 connected through the insulating shaft 12. The driving device 13 is configured by a stepping motor or the like. The control device 10 changes the capacity of the variable condenser 8 in a range from the minimum capacity to the maximum capacity at all the taps taken out from the coil transformer 6 for impedance conversion. The degree of matching with the load impedance is stored in a memory in advance. Then, by comparing with the contents of this memory, the most optimal tap position and the variable capacitor capacity are searched.

When the matching degree with the load impedance of the object to be defrosted is actually searched for all the regions, the reflected wave is detected by the SWR (standing wave ratio) meter even at the tap near the original optimum tap. If the impedance matching is performed so that is smaller, the matching degree is improved. Here, the impedance Z on the load side is represented by the following equation (2).

(Equation 2)

Therefore, if the output impedance of the impedance converting coil transformer 6 and the impedance Z on the load side have the same value, there is no reflected wave.
The value is 1. However, since the power consumed by the load is smaller than the maximum value unless the imaginary component is 0, it differs from the matching position to be obtained. Therefore, the input matching detection circuit 15 monitors the input power, stores a plurality of matching positions of the variable capacitor 8,
After the search in all areas, the optimum position is detected, and the matching position is searched.

Next, as the object to be thawed, such as frozen food, is thawed, the load impedance changes due to the change of ice into water, a change in the temperature of the material, and the like. Therefore, the matching between the output impedance of the impedance conversion coil transformer 6 and the load impedance deteriorates, and the effective power to the load decreases. For this reason, it is necessary to perform load follow-up and control so as to always be in a matching state.

On the input side and output side of the coil transformer for impedance conversion, the input power is E, the output impedance of the current Nth tap of the coil transformer for impedance conversion is Z _N, and the load impedance of the object to be decompressed is Z _L. Then the power on the load is

(Equation 3) Becomes For this reason, the control device 10, when exceeding the impedance value that is the matching control range in each tap,
That is, the effective power to the load is increased by switching the tap when the power becomes P _N <P _{N + 1} .

Now, the power value is as shown in equation (3). Therefore, the range of the impedance adjustment by the variable condenser 8 is sufficient if it is between the impedance value of the previous tap and the impedance value of the next tap, but P _N <P _{N + 1}
If the impedance is adjusted under the condition of switching the tap at the time of, the required variable capacitor capacity can be reduced. If the tap output impedance is Z _N , the output impedance at the next tap is Z _{N + 1} , and the load impedance is Z _L ,

(Equation 4) And the load impedance Z _L is

(Equation 5) Becomes

Therefore, the control range of the variable condenser falls within the range of the following equation (6).

(Equation 6) For this reason, if there is a variable condenser capacity capable of controlling between taps at which the difference between Z _N−1 and Z _{N + 1} is the largest, control can be performed in all ranges.

When the tap output impedance of the impedance converting coil transformer 6 does not match the load impedance, the reflected power increases when the tap is switched. If the reflected power becomes large, the power consumption of the reflected wave must be consumed in the high-frequency oscillation circuit, so that the high-frequency oscillation circuit may be damaged. Therefore, the control device 10 controls the power control unit (not shown) when switching the taps, narrows the high-frequency output power, and gradually applies the high-frequency power to prevent the high-frequency oscillation circuit from being damaged.

FIG. 5 is a schematic circuit diagram of a high-frequency decompression device according to a second embodiment of the present invention. As described in the first embodiment, even if the output impedance of the impedance conversion coil transformer 6 is adjusted to be equal to the impedance on the load side, the maximum power cannot be applied to the object to be defrosted as the load. Power cannot be used effectively. Therefore, the impedance transformation coil transformer 6
The load matching monitoring circuit 14 is provided between the variable condenser 8 connected to the output side coil and the load as shown in FIG. In response to the matching degree monitoring signal from the load matching monitoring circuit 14, the control device 10 adjusts the variable condenser 8 to eliminate the imaginary component of the load impedance of the object to be defrosted, and to reduce the load impedance to only the real component. Thereby, high-frequency power can be efficiently input to the load.

Next, as another embodiment, a method for eliminating the imaginary component of the impedance of the object to be thawed without providing the load matching monitoring circuit 14 will be described below. Now select the output impedance Z _N of the coil transformer 6 so as to be smaller than the actual load impedance Z _L of the thawed.
Then, the following relational expression (7) holds.

(Equation 7)

The control device 1 satisfies the expression (7).
By 0 controls the variable capacitor 8, when the difference of the load impedance Z _L and the output impedance Z _N of the coil transformer 6 of the thawed becomes smallest, high-frequency power is applied to the object to be thawed. For this reason, the imaginary term of the impedance is minimized. Thus, the optimum matching position can be detected with the same circuit configuration as in the first embodiment without providing the load matching monitoring circuit 14. In this case, the matching time increases due to an increase in the number of control processes. However, compared to the case where the load matching monitoring circuit 14 is provided, the imaginary component of the impedance of the object to be thawed can be eliminated at lower cost,
High frequency power can be efficiently consumed.

In the high-frequency decompression device, due to its structure, coupling capacitance and other stray capacitance are generated between the electrode plate to which high-frequency power is applied and the case grounded. Among them, those that can be treated as constant terms for control, such as stray capacitance, need not consider variation factors. However, when a variable that needs to be treated as a variation term such as a coupling capacitance occurs, the magnitude of the input high-frequency power greatly differs depending on the matching between during coupling and when coupling is separated. Therefore, when the coupling is separated, unless the capacitance is largely changed in the direction opposite to the direction adjusted by the variable condenser 8, the reflected wave may damage the high-frequency oscillation circuit. The control device 10
Quickly changes the capacitance of the variable condenser 8 based on the detection signal from the input matching detection circuit 15. That is, when the matching is largely deviated due to the separation of the capacitive coupling, the variable capacitor 8
By making a large change in the direction opposite to the change in capacitance at the time of adjustment, readjustment of the matching can be performed quickly.

As described above, the impedance conversion coil transformer 6 is used to match the output impedance of the high-frequency amplifier circuit to the load impedance of the frozen food. That is, impedance conversion is performed by connecting the load circuit to the tap output of the impedance conversion coil transformer 6 at a position where the output impedance of the amplifier circuit matches the load impedance. Further, the capacitance of the variable capacitor is changed so that the imaginary component of the impedance is minimized for matching with the load impedance, and the effective power is kept at the maximum. Further, the change in load impedance accompanying the thawing of the frozen food is adjusted by changing the capacitance of the variable capacitor to keep the effective power at a maximum.

[0036]

As described above, according to the first aspect of the present invention,
The high-frequency decompression device described in 1) can match the load impedance with the output impedance of the high-frequency oscillation circuit by switching the tap switching unit of the impedance conversion coil transformer, and can efficiently apply the high-frequency power to the object to be defrosted. Can be used effectively.

The high-frequency decompression device according to the second aspect can reliably detect a matching position by referring to matching data corresponding to a change in the capacitance of the variable capacitor at all taps.

In the high-frequency decompression apparatus according to the third aspect, by clearly determining the impedance range for performing the matching adjustment, the capacity of the variable capacitor to be used can be set to the minimum value, and the matching time is shortened. can do.

In the high-frequency decompression device according to the fourth aspect, when the tap is switched, the output of the high-frequency amplifier circuit is reduced to eliminate reflection of high-frequency power from the load-side circuit,
Prevents damage to the high-frequency oscillation circuit.

The high-frequency decompression device according to the fifth aspect monitors the matching state with the load impedance,
The imaginary component of the impedance of the object to be thawed can be eliminated, and high-frequency power can be efficiently consumed.

In the high-frequency decompression apparatus according to the sixth aspect, by changing the capacity of the variable capacitor in the opposite direction to that at the time of the adjustment, it is possible to prevent the loss of control when the capacitive coupling is lost and to reduce the adjustment time at the time of readjustment. Can be shortened.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of a high-frequency decompression device according to a first embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of an object to be defrosted.

FIG. 3 is a diagram showing details of a tap switching unit 6a.

FIG. 4 is a view showing a control mechanism of a variable condenser 8;

FIG. 5 is a schematic circuit diagram of a high-frequency decompression device according to a second embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of a high-frequency decompression device using dielectric heating.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Device housing 2 Upper electrode plate 3 Lower electrode plate 4 Thawed object 5 High frequency oscillator 6 Impedance conversion coil transformer 6a Tap switching part 7 Matching coil 8 Variable capacitance capacitor (varicon) 9 Switching device 10 Control device 11 Tap 12 Shaft 13 Drive unit 14 Load matching monitoring circuit 15 Input matching detection circuit

Claims (6)

[Claims] 1. A high-frequency thawing apparatus for thawing a frozen product by dielectric heating, comprising: a coil transformer for impedance conversion having a tap switching unit for matching an output impedance of a high-frequency amplifier circuit with a load impedance of the object to be thawed; A switching control unit that switches the tap switching unit based on the impedance value of each tap to match the impedance at the tap switching unit of the conversion coil transformer with the load impedance; and an impedance at each tap of the impedance conversion coil transformer. A high-frequency decompression device comprising: a coil for adjusting the matching between the load impedance and the load impedance; and a variable capacitor. 2. A storage means for storing matching data when the capacitance of a variable capacitor at all taps of the coil transformer for impedance conversion is changed, and detecting an optimum matching position by referring to the matching data. 2. The high-frequency decompression device according to claim 1, further comprising a matching detection unit that performs the matching. 3. The variable capacitance of the variable capacitor is changed from an average value of the impedance of the previous tap and the current tap to a mean value of the impedance of the next tap and the current tap. 2. The high-frequency decompression device according to claim 1, further comprising a variable capacitance control unit that performs matching. 4. The high-frequency decompression device according to claim 1, further comprising a high-frequency adjusting unit that narrows down the output of the high-frequency amplifier circuit when switching the tap of the coil transformer for impedance conversion. 5. The high-frequency decompression apparatus according to claim 1, further comprising a load matching monitoring means for monitoring a matching state with a load impedance between an output side of the impedance conversion coil transformer and the load. 6. A variable capacitance capacitor adjusting means for changing a capacitance in a direction opposite to a capacitance change at the time of adjusting the variable capacitor so as to minimize an imaginary component in response to a change in load impedance. The high-frequency decompression device according to claim 1, wherein