High-frequency dielectric heating device
The high-frequency dielectric heating apparatus addresses uneven heating and localized overheating in food by dynamically controlling power distribution based on power reflectance, enhancing thawing efficiency and quality.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- HITACHI GLOBAL LIFE SOLUTIONS INC
- Filing Date
- 2025-01-08
- Publication Date
- 2026-07-21
AI Technical Summary
High-frequency dielectric heating devices in the MHz band face challenges in maintaining efficient thawing while preventing localized overheating and uneven heating of food, particularly at the ends, corners, or parts with specific compositions, leading to deteriorated thawing quality.
A high-frequency dielectric heating apparatus with a control unit that monitors power reflectance and adjusts output power based on the rate of change, employing impedance matching and intermittent or continuous power supply to manage energy distribution, thereby suppressing localized overheating and extending the thawing time.
The apparatus effectively suppresses localized overheating and extends the thawing time while improving the overall thawing quality by ensuring uniform heating and efficient energy utilization.
Smart Images
Figure 2026119807000001_ABST
Abstract
Description
[Technical Field]
[0001] This invention relates to a high-frequency dielectric heating device. [Background technology]
[0002] Food processing plants and similar facilities sometimes process frozen ingredients after thawing them. One type of food thawing machine used in these types of plants is a high-frequency thawing device that applies a high-frequency electric field in the MHz band to frozen food placed between opposing electrodes, thereby thawing the frozen food by dielectric heating (for example, Patent Document 1).
[0003] In this context, high-frequency dielectric heating is a technique in which a high-frequency electric field is applied to a dielectric material (food) to be heated, and the material is heated from the inside by self-heating (dielectric loss) caused by the vibration of polar molecules (such as water molecules) that make up the material.
[0004] Conventional household microwave ovens utilize microwaves (electric fields in the GHz band), but dielectric heating by microwaves has a problem in that, due to the large difference in heat generation between ice and water, when thawing frozen food in a household microwave oven, the thawed portion on the surface of the food heats up excessively, resulting in significant uneven heating.
[0005] On the other hand, high-frequency dielectric heating devices, which use high-frequency electric fields in a lower frequency band (MHz band) than microwaves, have the advantage that the high-frequency energy penetrates the food deeper than in a typical microwave oven, and the difference in heat output between ice and water is also smaller, resulting in less uneven heating.
[0006] For example, Patent Document 1 describes a high-frequency thawing device comprising: a heating chamber; an upper electrode and a lower electrode arranged parallel to each other within the heating chamber, with the object to be thawed inserted between them; a high-frequency power supply and matching circuit for applying a high-frequency voltage between the upper electrode and the lower electrode; a power detection circuit for detecting the reflected power of the applied high-frequency voltage; and a control device that estimates the progress of the object to be thawed based on the change in the detection signal of the power detection circuit from the start of thawing, determines when thawing is complete, and controls the high-frequency power supply based on the determination.
[0007] During the thawing of food, the impedance of the load side, including the food and electrodes, changes significantly due to the changes in the electrical properties of the food as thawing progresses. If there is a discrepancy between the impedance of the high-frequency power supply (output side) and the impedance of the load side, the power returned to the output side (reflected power) increases, which reduces the heating efficiency of the food. Therefore, a technology has been proposed that improves the heating efficiency of food by reducing reflected power by incorporating a matching circuit consisting of a variable capacitor or variable coil between the high-frequency power supply and the electrodes, thereby matching the impedance of the output side and the load side.
[0008] In this regard, paragraph 0020 of Patent Document 1 states, "The control device 7 controls the output of the high-frequency power supply 4 so that the power obtained by subtracting the reflected power from the input electrode remains constant, and increases the incident power in accordance with the increase in reflected power." (It appears that "input electrode" is a typographical error for "incident power.") Furthermore, paragraph 0021 of the same document states, "When the ratio of reflected power (RW) to incident power (FW), RW / FW, exceeds a threshold X, the control device 7 adjusts the variable capacitors 6a, 6b, variable coil 6c, etc., in the matching circuit 6 to set the reflected power to 0W. Such impedance adjustment is repeated each time the ratio exceeds the threshold X." [Prior art documents] [Patent Documents]
[0009] [Patent Document 1] Japanese Patent Publication No. 2020-145114 [Overview of the Initiative]
Problems to be Solved by the Invention
[0010] When thawing food by applying a high-frequency electric field in the MHz band as in Patent Document 1, if impedance matching between the output side and the load side is maintained and almost all of the output power from the high-frequency power supply is continuously input to the food by eliminating the reflected power, the heating efficiency is improved and the thawing time is shortened. However, there is a risk that the electric field will gradually concentrate on the ends, corners, protrusions of the food, or parts with a specific composition. In this case, uneven thawing temperature also occurs in high-frequency dielectric heating in the MHz band, which leads to a problem of deterioration in thawing quality.
[0011] Patent Document 1 does not mention a technique for suppressing such overheating of food, and it is difficult to achieve both suppression of the extension of the thawing time and suppression of overheating.
[0012] An object of the present invention is to provide a high-frequency dielectric heating device that can suppress the extension of the thawing time, suppress local overheating of food, and improve the thawing quality when thawing frozen food or the like using a high-frequency electric field in the MHz band.
Means for Solving the Problems
[0013] To achieve the above objective, the present invention provides a high-frequency dielectric heating apparatus comprising: a high-frequency power supply that outputs high-frequency power in the MHz band; a pair of electrodes that apply a high-frequency electric field to frozen food using the high-frequency power supply; a matching unit connected between the high-frequency power supply and the pair of electrodes and performing impedance matching between the high-frequency power supply and the load side including the frozen food; a power detection unit that measures the output power from the high-frequency power supply to the pair of electrodes and the reflected power from the pair of electrodes to the high-frequency power supply; and a control unit that calculates the power reflectance, which is the ratio of the output power to the reflected power, wherein the control unit determines a first state in which the absolute value of the rate of change of the power reflectance is greater than or equal to a first threshold, and a second state in which the thawing of the frozen food is progressing and the absolute value of the rate of change of the power reflectance is less than the first threshold, and when the second state is determined to be the case, controls the high-frequency power supply so that the average value of the output power is smaller than the average value of the output power in the first state. [Effects of the Invention]
[0014] According to the present invention, when thawing frozen foods and the like using a high-frequency electric field in the MHz band, it is possible to provide a high-frequency dielectric heating device that suppresses localized overheating of food ingredients while suppressing the extension of thawing time and improving thawing quality. [Brief explanation of the drawing]
[0015] [Figure 1] This is a schematic diagram of the high-frequency dielectric heating apparatus 1 according to Embodiment 1 of the present invention. [Figure 2] This figure shows an example of the time evolution of the output power, power reflectance, and the absolute value of the rate of change of power reflectance during the heating of food ingredient 4 in the high-frequency dielectric heating apparatus 1 according to Embodiment 1 of the present invention. [Figure 3] This flowchart shows an example of the heating process of food ingredients 4 using the high-frequency dielectric heating apparatus 1 according to Embodiment 1 of the present invention. [Figure 4] This figure shows an example of the time evolution of the output power, power reflectance, and the absolute value of the rate of change of power reflectance during the heating of food ingredient 4 in the high-frequency dielectric heating apparatus 1 according to Embodiment 2 of the present invention. [Figure 5] This flowchart shows an example of the heating process of food ingredient 4 using the high-frequency dielectric heating device 1 according to Embodiment 2 of the present invention. [Figure 6] This figure shows an example of the time evolution of the output power, power reflectance, and the absolute value of the rate of change of power reflectance during the heating of food ingredients 4 in the high-frequency dielectric heating apparatus 1 according to Embodiment 3 of the present invention. [Figure 7] This flowchart shows an example of the heating process of food ingredient 4 using the high-frequency dielectric heating device 1 according to Embodiment 3 of the present invention. [Figure 8] This figure shows an example of the time evolution of the output power, power reflectance, and the absolute value of the rate of change of power reflectance during the heating of food ingredient 4 in the high-frequency dielectric heating apparatus 1 according to Embodiment 4 of the present invention. [Figure 9] This flowchart shows an example of the heating process of food ingredient 4 using the high-frequency dielectric heating apparatus 1 according to Embodiment 4 of the present invention. [Modes for carrying out the invention]
[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Although each figure is marked with coordinate axes indicating up, down, left, and right, these directions are set for convenience in explanation, and all embodiments described below are not limited to these axial directions. [Examples]
[0017] Figure 1 is a schematic diagram of a high-frequency dielectric heating apparatus 1 according to Embodiment 1 of the present invention. The high-frequency dielectric heating apparatus 1 includes a heating chamber 2, a high-frequency power supply 11, an amplification unit 12, a power detection unit 13, a matching unit 14, a control unit 15, an operation unit (not shown), and a display unit. The details of each part will be described in order below.
[0018] The heating chamber 2 is a box-like structure for storing frozen food (hereinafter referred to as food ingredient 4) to be heated and for thawing the food ingredient 4 by dielectric heating. It has a door (not shown) that opens and closes when the food ingredient 4 is inserted or removed, a platform 5 on which the food ingredient 4 is placed, and electrodes 3 that are electrically connected to a high-frequency power supply 11.
[0019] The electrodes 3 are a pair of metal plates positioned opposite each other so as to sandwich the food ingredients 4 stored in the heating chamber 2 from above and below, and are electrically connected to the matching section 14. The electrodes 3 consist of, for example, an upper electrode 3a positioned at the top of the heating chamber 2 and a lower electrode 3b positioned at the bottom of the heating chamber 2. In this embodiment, the upper electrode 3a and the lower electrode 3b constitute a pair of electrodes.
[0020] In Figure 1, the connection is such that a voltage can be applied to either the upper electrode 3a or the lower electrode 3b. However, a configuration in which the lower electrode 3b is grounded is also possible.
[0021] The upper electrode 3a and lower electrode 3b may be fixed in place, or they may be movable vertically by a lifting device (not shown). To shorten the thawing time, it is desirable to raise and lower the upper electrode 3a to bring it as close as possible to the food 4. In the case of a configuration using a lifting device, the heating efficiency can be improved and the thawing time shortened by bringing the upper electrode 3a closer to the food 4 according to the thickness and shape of the food 4.
[0022] The placement platform 5 is a platform for placing the food ingredients 4, and specifically, it is a container, plate, or board made of ceramic or heat-resistant resin that is not heated by dielectric heating.
[0023] The high-frequency power supply 11 is a power supply that outputs high-frequency power in the MHz band.
[0024] The amplification unit 12 is an amplifier circuit that amplifies the high-frequency power output by the high-frequency power supply 11 at an amplification factor specified by the control unit 15. Details of the amplification factor control by the control unit 15 will be described later.
[0025] The power detection unit 13 measures the output power transmitted from the high-frequency power supply 11 to the electrode 3 and the reflected power reflected from the electrode 3 back to the high-frequency power supply 11, and transmits the output power and reflected power information to the control unit 15.
[0026] The matching unit 14 is a circuit that matches the output impedance of the high-frequency power supply 11 with the impedance of the load side, including the food ingredients 4 and electrodes 3. As the thawing of the food ingredients 4 progresses, the dielectric loss of the food ingredients 4 changes significantly, and therefore the impedance of the load side also changes significantly during the thawing of the food ingredients 4. By appropriately adjusting the variable coil and variable capacitor built into the matching unit 14, the output impedance of the high-frequency power supply 11 and the impedance of the load side can be made approximately the same, and the reflected power (reflected wave) returning from the matching unit 14 to the high-frequency power supply 11 can be reduced, thereby improving the heating efficiency of the food ingredients 4.
[0027] Furthermore, the matching unit 14 may be configured by combining, for example, a relay switch, a fixed coil, and a fixed capacitor.
[0028] The control unit 15 calculates the ratio of output power to reflected power (reflected power / output power: hereinafter referred to as power reflectance) based on information from the power detection unit 13, and adjusts the output of the amplification unit 12 and the matching unit 14. Details of the output adjustment and matching adjustment will be described later. Specifically, the control unit 15 is a computer equipped with hardware such as a CPU (Central Processing Unit), a memory device such as semiconductor memory, and a communication device. The arithmetic unit then executes a predetermined program to realize the functions described later, but in the following explanation, such well-known technologies will be omitted as appropriate.
[0029] In the above configuration, high-frequency power in the MHz band is output from the high-frequency power supply 11 and the amplification unit 12, and supplied to the electrode 3 via the matching unit 14. As a result, a high-frequency electric field is applied from the electrode 3 to the food item 4, allowing the food item 4 to be thawed by dielectric heating.
[0030] As mentioned above, high-frequency electric fields in the MHz band have the characteristic of being able to penetrate deeper into the food 4 compared to microwaves (GHz band) used in microwave ovens. Therefore, by using the high-frequency dielectric heating device 1 of this embodiment, the uniform thawing of the food 4 can be promoted.
[0031] Figure 2 shows an example of the time evolution of the output power, power reflectance, and absolute value of the rate of change of power reflectance during the heating of food ingredient 4 in the high-frequency dielectric heating apparatus 1 according to Embodiment 1 of the present invention. Figure 3 is a flowchart showing an example of the heating process of food ingredient 4 in the high-frequency dielectric heating apparatus 1 according to Embodiment 1 of the present invention. Hereinafter, the control of the high-frequency dielectric heating apparatus 1 of this embodiment will be described in detail using Figures 1 to 3. In Figure 2, the waveform of the output power that is actually measured fluctuates up and down, but in Embodiment 1, the waveform of the output power is shown linearly as an average value. The same applies to the other embodiments.
[0032] When food ingredients 4 are placed in the heating chamber 2 and the heating process is started, first the high-frequency power supply 11 is turned ON, and the control unit 15 adjusts the output of the amplification unit 12 so that the output power becomes P1 (step S1).
[0033] Next, the power detection unit 13 measures the transmitted power and reflected power, and the control unit 15 calculates and monitors the power reflectance (step S2).
[0034] Next, the matching unit 14 performs impedance matching between the power supply side and the load side. Specifically, it makes the output impedance of the high-frequency power supply 11 and the impedance of the load side approximately the same, thereby reducing the reflected power returning from the matching unit 14 to the high-frequency power supply 11 (step S3). Although not shown in Figures 2 and 3, in order to prevent failure of the power supply side due to a momentary increase in reflected power, the amplifier 12 may be controlled so that the output power is less than P1 and P2 (described later) while the impedance matching is being performed by the matching unit 14.
[0035] Next, the control unit 15 determines that the power reflectance is a predetermined threshold R thDetermine whether it is as follows (step S4). If the power reflectance is less than the threshold value R th In the case (Yes in step S4), the control unit 15 executes step S5. If the power reflectance is greater than the threshold value R th In the case where it is larger (No in step S4), the control unit 15 returns to the process of step S3 and re-executes the impedance matching by the matching unit 14.
[0036] In step S5, the control unit 15 evaluates the absolute value V abs of the change rate of the power reflectance. Here, the change rate of the power reflectance is the amount of change in the power reflectance per unit time. The unit time may be appropriately set from, for example, 0.5 seconds, 1 second, 2 seconds, 5 seconds, 10 seconds, etc. <00********>
[0037] In step S5, when the absolute value V abs of the change rate of the power reflectance is greater than or equal to the threshold value V1 (first threshold value) (V1 ≤ V abs ), the control unit 15 adjusts the output of the amplifier unit 12 so that the output power becomes P1 (step S6).
[0038] In step S5, when the absolute value V abs of the change rate of the power reflectance is less than the threshold value V1 (V abs < V1), the control unit 15 adjusts the output of the amplifier unit 12 so that the output power becomes P2, and sets it so that the relationship P1 > P2 holds between P1 and P2 (step S7).
[0039] Next, the control unit 15 determines whether the heating end condition is satisfied (step S8). For example, the temperature of the food 4 may be measured by a temperature sensor (not shown) installed in the heating chamber 2 to determine whether a predetermined temperature has been reached. Also, it may be determined whether a standard heating time has elapsed. The standard heating time may be, for example, a time arbitrarily set by the user with an operation unit not shown, or may be, for example, a time automatically calculated from the food mass measured by a food mass sensor (not shown) installed in the heating chamber ⒉. Further, as will be described later, it may be determined whether the absolute value of the change rate of the power reflectance has become smaller than the threshold value V2 (second threshold value).
[0040] In step S8, when the heating end condition is not satisfied (No in step S8), the control unit 15 returns to step S4 and continues the heat treatment while constantly monitoring the power reflectance and the absolute value V of the change rate of the power reflectance. abs
[0041] In step S8, when the heating end condition is satisfied (Yes in step S8), the control unit 15 proceeds to step S9, turns off the high-frequency power supply, and ends the heat treatment.
[0042] In the section from time 0 to t3 (the first state) in FIG. 2, since V1≤V is satisfied in the determination of the absolute value of the change rate of the power reflectance in step S5, the output power is controlled to P1. Also, at times t1 and t2, since the power reflectance exceeds the threshold value R abs impedance matching is performed in step S3, and as a result, the power reflectance is reduced. In FIG. 2, due to impedance matching, the power reflectance instantaneously decreases at times t1, t2, and t3. Therefore, originally, the absolute value V of the change rate of the power reflectance in FIG. 2 th would increase, but since the power reflectance is an instantaneous change, in FIG. 2, the absolute value V of the change rate of the power reflectance corresponding to the instantaneous change abs is omitted from the illustration. Also, in the control of the output power, an instantaneous change in the absolute value is ignored. The same applies to other embodiments described separately. abs
[0043] In the section from time t3 to t5 in FIG. 2, since V abs <V1 is satisfied in the determination of the absolute value of the change rate of the power reflectance in step S5, the output power is controlled to P2 in the section from time t3' to t5 (the second state). Also, at time t4, since the power reflectance exceeds the threshold value R th impedance matching is performed in step S3, and as a result, the power reflectance is reduced. Also, at time t5, it is determined that the heating end condition is satisfied, and the heat treatment is ended.
[0044] The output power is the absolute value V of the change rate of the power reflectance abs at time t3 when V abs satisfies <V1, and then decreases from P1 to P2 from time t3 to time t3'.
[0045] Next, the effects of this embodiment will be described.
[0046] For example, when heat-treating food 4 frozen to about -20°C, immediately after starting the heating, thermal energy is applied to substantially the entire area of food 4, and solid-state water (ice) begins to change to liquid-state water. Along with this change, the electrical properties (dielectric constant, dielectric loss, etc.) of food 4 as a whole change greatly, so the impedance on the load side fluctuates greatly. Along with this, the power reflectance fluctuates greatly. This process corresponds to the section from time 0 to t3 in FIG. 2 in this embodiment.
[0047] In the process of heat treatment, when an electric field gradually concentrates on the ends, corners, protrusions, or parts with a specific composition (hereinafter referred to as specific parts) of food 4, the electrical energy absorbed by the specific parts increases, and there is a risk of local overheating progressing and generating uneven heating. This process corresponds to the section from time t3 to t5 in FIG. 2 in this embodiment. In this section, in addition to the overall temperature and state change in food 4 (change from solid-state water (ice) to liquid-state water), electrical energy absorption by specific parts occurs, so the fluctuation of the power reflectance becomes smaller than in the section from time 0 to t3. Conversely, it can be said that by monitoring the change rate of the power reflectance in the heat treatment process, it is possible to determine the presence or absence of local overheating in food 4.
[0048] The present invention is based on this mechanism, and since the output power P2 in the time interval from t3 to t5 is set to be smaller than the output power P1 in the time interval from 0 to t3, it is possible to cause a global temperature and state change without applying excessive energy to a specific part of the food 4. On the other hand, instead of setting a small output throughout the entire section, a relatively large output power is set in the time interval from 0 to t3, so that an increase in the required time for the entire heat treatment can be suppressed.
[0049] As described above, according to the high-frequency dielectric heating device 1 of the present embodiment, when thawing frozen foods or the like using a high-frequency electric field in the MHz band, it is possible to suppress an increase in the thawing time, suppress local overheating of the food, and improve the thawing quality.
Embodiment
[0050] Next, Example 2 of the present invention will be described with reference to FIGS. 4 and 5. FIG. 4 is a diagram showing an example of the time transition of the output power, power reflectance, and absolute value of the change rate of the power reflectance during the heat treatment of the food 4 in the high-frequency dielectric heating device 1 according to Example 2 of the present invention. FIG. 5 is a flowchart showing an example of the flow of the heat treatment of the foodstuff 4 of the high-frequency dielectric heating device 1 according to Example 2 of the present invention.
[0051] Hereinafter, the description will focus on the differences from Example 1. In Example 2, the processing after step S5 is different from that in Example 1.
[0052] In step S5, when the absolute value V abs of the change rate of the power reflectance is less than the threshold value V1 (V abs < V1), the control unit 15 causes the high-frequency power supply to continuously output with the output power remaining at P1 (step S10).
[0053] Also, in step S5, when the absolute value V abs of the change rate of the power reflectance is greater than or equal to the threshold value V1 (V1 ≤ V abs), the control unit 15 intermittently outputs the high-frequency power supply while keeping the output power at P1 (step S11). The duty cycle of the intermittent output can be set arbitrarily; for example, the ON time of the high-frequency power supply can be set to 10%, 20%, 33%, 50%, 80%, etc.
[0054] This control also makes it possible to make the average output power in the time interval t3 to t5 smaller than the average output power in the time interval 0 to t3. In other words, it is possible to allow the overall temperature and state changes to proceed without supplying excessive energy to specific parts of food ingredient 4. In Example 2 as well, the output power is the absolute value V of the rate of change of power reflectance. abs V1 ≤ V at time t3 abs After satisfying the conditions, the high-frequency power supply is intermittently output from time t3', which is slightly delayed from time t3.
[0055] As described above, the high-frequency dielectric heating device 1 of this embodiment also uses a high-frequency electric field in the MHz band to thaw frozen foods, thereby suppressing localized overheating of the food while suppressing the extension of the thawing time and improving the thawing quality. [Examples]
[0056] Next, Embodiment 3 of the present invention will be described with reference to Figures 6 and 7. Figure 6 is a diagram showing an example of the time evolution of the output power, power reflectance, and the absolute value of the rate of change of power reflectance during the heating of food ingredient 4 in the high-frequency dielectric heating apparatus 1 according to Embodiment 3 of the present invention. Figure 7 is a flowchart showing an example of the flow of the heating of food ingredient 4 in the high-frequency dielectric heating apparatus 1 according to Embodiment 3 of the present invention.
[0057] The following explanation will focus on the differences from Example 1. In Example 3, the processing from step S5 onward differs from that of Example 1.
[0058] Example 3 assumes a case where, at time t5 in Example 1, it is not determined that the heating end condition is satisfied, and the heat treatment is continued until time t6. As described above, according to the high-frequency dielectric heating device 1 of Example 1, overall temperature and state changes can be advanced without applying excessive energy to a specific part of the food material 4. Therefore, at time t5, it is considered that the food material 4 is thawed over almost the entire region and has a temperature near 0°C. After the solid-state water (ice) has almost completely changed to liquid-state water, the electrical properties of the entire food material 4 become stable, so the impedance change on the load side becomes small, and thus the change rate of the power reflectance also becomes small. Conversely, by determining whether the absolute value V abs of the change rate of the power reflectance is less than V2, which is even smaller than V1, it is possible to know whether almost the entire region of the food material 4 has been thawed near 0°C. In the description of Example 1, when determining whether the heating end condition is satisfied (step S8), stating that it may be determined whether the absolute value V abs of the change rate of the power reflectance is less than the threshold value V2 reflects this principle.
[0059] Here, as a requirement of the user of the high-frequency dielectric heating device 1, it is conceivable that the food material 4 is desired to be heated to a temperature of 0°C or higher. In this case, in the section where V abs ]< V2 is satisfied, that is, in the section after time t5 in Example 3 (for example, the section from time t5 to t6: the third state), the output voltage may be set as P3 so that the relationship P3 > P2 holds between P3 and P2.
[0060] The following describes the process. In step S5', when the absolute value V abs of the change rate of the power reflectance is greater than or equal to the threshold value V1 (V1 ≤ V abs ), the control unit 15 adjusts the output of the amplification unit 12 so that the output power becomes P1 (step S6).
[0061] Also, in step S5', when the absolute value V abs of the change rate of the power reflectance is less than the threshold value V1 and greater than or equal to V2 (V2 ≤ V abs<V1), the control unit 15 adjusts the output of the amplification unit 12 so that the output power becomes P2, and sets it so that the relationship P1 > P2 holds between P1 and P2 (step S7).
[0062] Furthermore, in step S5’, when the absolute value V of the change rate of the power reflectance abs is less than the threshold value V2 (V abs < V2), the control unit 15 adjusts the output of the amplification unit 12 so that the output power becomes P3, and sets it so that the relationship P1 > P3 > P2 holds among P1, P2, and P3 (step S12). That is, when the absolute value V of the change rate of the power reflectance abs is less than the threshold value V2, the control unit 15 adjusts the output of the amplification unit 12 and controls the high-frequency power supply so that the average value of the output power becomes P3, which is greater than P2. In FIG. 6, a case of P1 > P3 > P2 is shown as an example, but it may be set so that P3 > P1 > P2.
[0063] As described so far, at time t5, local overheating of the specific part is suppressed, and since the food material 4 is thawed over almost the entire region and has reached a temperature near 0°C, even with a relatively large output voltage, it is possible to suppress the occurrence of heating unevenness and efficiently heat the entire food material 4.
[0064] Note that the output power is such that the absolute value V of the change rate of the power reflectance abs satisfies V abs < V1 at time t3, then decreases from P1 to P2 from time t3 to time t3’, and the absolute value V of the change rate of the power reflectance abs satisfies V abs < V2 at time t5, and then increases from P2 to P3 from time t5 to time t5’.
[0065] As described above, according to the high-frequency dielectric heating device 1 of the present embodiment, when thawing frozen food or the like using a high-frequency electric field in the MHz band, for example, even when it is desired to heat the food material 4 to a temperature of 0°C or higher, it is possible to suppress an extension of the thawing time, suppress local overheating of the food material, and improve the thawing quality.
Example
[0066] FIG. 8 is a diagram showing an example of the time transition of the output power, power reflectance, and absolute value of the change rate of the power reflectance during the heating process of the foodstuff 4 in the high-frequency dielectric heating apparatus 1 according to Example 4 of the present invention. FIG. 9 is a flowchart showing an example of the flow of the heating process of the foodstuff 4 in the high-frequency dielectric heating apparatus 1 according to Example 4 of the present invention.
[0067] Hereinafter, the description will focus on the differences from Example 2. In Example 4, the processing after step S5 is different from that in Example 2.
[0068] Example 4 assumes a case where the heating end condition is not determined to be satisfied at time t5 in Example 2, and the heating process is continued until time t6. As described above, according to the high-frequency dielectric heating apparatus 1 of Example 2, it is possible to advance the overall temperature and state changes without applying excessive energy to a specific part of the foodstuff 4. Therefore, at time t5, it is considered that the foodstuff 4 is thawed over almost the entire region and has a temperature near 0°C. After the solid-state water (ice) has almost completely changed to liquid-state water, the electrical physical properties of the entire foodstuff 4 become stable, so the impedance change on the load side becomes small, and thus the change rate of the power reflectance also becomes small. That is, in Example 4, similar to Example 3, by determining whether the absolute value V abs of the change rate of the power reflectance is less than V2, which is even smaller than V1, it is possible to know whether almost the entire region of the foodstuff 4 has been thawed near 0°C.
[0069] Hereinafter, the processing will be described. In step S5', when the absolute value V abs of the change rate of the power reflectance is less than the threshold value V1 (V abs < V1), the control unit 15 continuously outputs the high-frequency power supply with the output power remaining at P1 (step S10).
[0070] Also, in step S5', when the absolute value V absWhen it is equal to or greater than the threshold value V1 (V1 ≤ V abs ), the control unit 15 causes the high-frequency power supply to output intermittently with the output power remaining at P1 (step S11). The duty ratio of the intermittent output may be set arbitrarily. For example, the ON time of the high-frequency power supply may be set to 10%, 20%, 33%, 50%, 80%, etc.
[0071] Furthermore, in step S5’, when the absolute value V abs of the change rate of the power reflectance is less than the threshold value V2 (V abs < V2), the control unit 15 sets the output power to P1 and causes the high-frequency power supply to output continuously (step S13). That is, when the absolute value V abs of the change rate of the power reflectance is less than the threshold value V2, the control unit 15 adjusts the output of the amplification unit 12 and controls the high-frequency power supply 11 so that the average value of the output power becomes P1, which is greater than the intermittent output.
[0072] In this embodiment, at time t5, local overheating of the specific part is suppressed, and since the food material 4 is thawed over almost the entire area and has reached a temperature near 0°C, even with a relatively large output voltage, the occurrence of heating unevenness can be suppressed and the entire food material 4 can be efficiently heated.
[0073] Note that the output power is such that when the absolute value V abs of the change rate of the power reflectance satisfies V abs < V1 at time t3, it outputs intermittently from time t3’ which is slightly delayed from time t3, and when the absolute value V abs of the change rate of the power reflectance satisfies V abs < V2 at time t5, it outputs continuously from time t5’ which is slightly delayed from time t5.
[0074] Also, in step S13, the control unit 15 causes the high-frequency power supply to output continuously with the output power remaining at P1. However, for example, the high-frequency power supply may be caused to output continuously with the output power set to P3 as in Embodiment 3.
[0075] As described above, according to the high-frequency dielectric heating device 1 of this embodiment, when thawing frozen foods, etc., using a high-frequency electric field in the MHz band, even when it is desired to heat the food ingredient 4 to a temperature of 0°C or higher, it is possible to suppress the extension of the thawing time, suppress localized overheating of the food ingredient, and improve the thawing quality.
[0076] The present invention is not limited to the embodiments described above, and includes various modifications. For example, the above-described embodiments are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with configurations from other embodiments. [Explanation of Symbols]
[0077] 1...High-frequency dielectric heating device, 2...Heating chamber, 3...Electrode, 3a...Upper electrode, 3b...Lower electrode, 4...Food ingredients, 5...Placement platform, 11...High-frequency power supply, 12...Amplifier, 13...Power detection unit, 14...Matching unit, 15...Control unit
Claims
1. A high-frequency power supply that outputs high-frequency power in the MHz band, Using the aforementioned high-frequency power supply, a pair of electrodes are used to apply a high-frequency electric field to the frozen food, A matching unit is connected between the high-frequency power supply and the pair of electrodes, and performs impedance matching between the high-frequency power supply and the load side including the frozen food. A power detection unit that measures the output power from the high-frequency power supply to the pair of electrodes and the reflected power from the pair of electrodes to the high-frequency power supply, A high-frequency dielectric heating apparatus comprising a control unit for calculating the power reflectance, which is the ratio of the output power to the reflected power, The control unit, A high-frequency dielectric heating apparatus characterized by determining a first state in which the absolute value of the rate of change of the power reflectance is greater than or equal to a first threshold, and a second state in which the thawing of the frozen food has progressed and the absolute value of the rate of change of the power reflectance is less than the first threshold, and when the second state is determined to be present, controlling the high-frequency power supply so that the average value of the output power is less than the average value of the output power in the first state.
2. A high-frequency dielectric heating apparatus according to claim 1, The control unit, A high-frequency dielectric heating device characterized by intermittently outputting power when the second state described above is determined to be present.
3. A high-frequency dielectric heating apparatus according to claim 1 or 2, The control unit, A high-frequency dielectric heating apparatus characterized by determining a third state in which the thawing of frozen food has progressed further and the absolute value of the rate of change of the power reflectance has fallen below a second threshold value which is smaller than the first threshold value, and if the third state is determined to be reached, controlling the high-frequency power supply so that the average value of the output power is greater than the average value of the output power in the second state.
4. A high-frequency dielectric heating apparatus according to claim 3, The control unit, A high-frequency dielectric heating apparatus characterized in that, when the third state is determined to be present, the high-frequency power supply is controlled such that the average value of the output power is greater than the average value of the output power in the second state and less than the average value of the output power in the first state.
5. A high-frequency dielectric heating apparatus according to claim 1 or 2, The control unit, A high-frequency dielectric heating apparatus characterized in that, when the matching unit performs impedance matching and the power reflectance falls below a predetermined threshold, it determines whether the absolute value of the rate of change of the power reflectance is greater than or equal to or less than the first threshold.
6. A high-frequency dielectric heating apparatus according to claim 1 or 2, The high-frequency dielectric heating apparatus is characterized in that the pair of electrodes consists of an upper electrode positioned at the top of the heating chamber and a lower electrode positioned at the bottom of the heating chamber.
7. A high-frequency dielectric heating apparatus according to claim 6, The high-frequency dielectric heating apparatus is characterized in that the upper electrode is movable in the vertical direction.