JP4444062B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker used in general homes, offices, restaurants and the like.

  Conventionally, in an induction heating cooker, a high frequency magnetic field is generated from an induction heating coil, and an object to be heated such as a pan is heated by an eddy current due to electromagnetic induction (see, for example, Patent Document 1).

  As shown in FIG. 9, the configuration includes an inverter 1, an induction heating coil 2 connected to the inverter 1, an object to be heated (cooking pan) 3 heated by the induction heating coil 2, and an object to be heated 3. A top plate 4, temperature detecting means 5 for detecting the temperature of the object to be heated 3, and a housing 6. Specifically, the temperature detection means 5 makes a thermistor adhere to the top plate 4 and detects it by heat conduction.

  In this configuration, a high-frequency magnetic field is generated from the induction heating coil 2 by the high-frequency current supplied from the inverter 1, and the article to be heated 3 is heated by the eddy current due to electromagnetic induction. In order to change and stabilize the input power, the power supply current of the inverter 1 is detected by a current transformer (not shown), and the output of the inverter 1 is controlled by changing the drive frequency of the inverter 1 or the conduction ratio of a switching element (not shown). is doing. The temperature of the object to be heated 3 is detected by the temperature detection means 5, and the output of the inverter 1 is controlled so that the temperature of the object to be heated 3 becomes 200 ° C., for example, when cooking fried food.

  In the said structure, since the temperature detection means 5 has detected the temperature of the to-be-heated material 3 via the top plate 4, a thermal response was slow and appropriate control was difficult. A specific example will be described. The solid line in FIG. 10 is the temperature of the object 3 to be heated, and the broken line is the output of the temperature detection means 5. Thus, since the output of the temperature detection means 5 has a time delay with respect to the temperature change of the article 3 to be heated, for example, it is difficult to detect an abnormal temperature rise of the empty pan. From such a background, the magnetic coupling between the induction heating coil 2 and the object to be heated 3 is detected, and the temperature of the object to be heated 3 is detected using the characteristic that the magnetic coupling changes as the temperature of the object to be heated 3 rises. The method to be taken is taken.

An equivalent circuit of the induction heating coil 2 and the article to be heated 3 can be expressed by an equivalent series resistance Ri and an equivalent series inductance Li, and iron, magnetic SUS, nonmagnetic SUS, aluminum, and a plurality of these materials are stacked. When the temperature rises in the article to be heated, particularly when the article to be heated is iron, the equivalent series resistance Ri (dashed line in FIG. 11) and the equivalent series inductance Li (solid line in FIG. 11) increase as shown in FIG. When the control is performed so that the input current is constant (that is, the input power is constant) (for example, when the drive frequency of the inverter 1 is changed), a solid line A in FIG. 12 (input power-frequency correlation at low temperature) ) To the broken line B (high-power input power-frequency correlation), the drive frequency decreases as the temperature rises. Re by stopping the heating if it is possible to prevent abnormal temperature rise, such as when empty pan of the object to be heated 3.
JP-A-53-69938

  However, in the configuration of temperature detection using the conventional magnetic coupling change, the heated object 3 is subjected to some factor during heating (for example, when the heated object is a frying pan and the user's elbow is unconsciously hit) ), The magnetic coupling changes in the same way as when the temperature of the object to be heated 3 is changed, so that false detection is made. In fact, although the temperature increase of the object to be heated 3 is low, it is determined that the temperature increase is large. There was a problem that the heating output was suppressed or stopped. When the object to be heated 3 moves from the vicinity of the center to the outer peripheral direction with respect to the induction heating coil 3, the magnetic coupling change similar to the change from the low temperature to the high temperature is exhibited, and thus the possibility of such a false detection is high. is there.

  The present invention solves the above-described conventional problems, and realizes an easy-to-use induction heating cooker that can detect a temperature change of a heated object at high speed without erroneous detection even when the heated object moves during heating. It is intended to do.

In order to solve the above-described conventional problems, the induction heating cooker according to the present invention is configured such that the time taken for the change in the control amount of the inverter based on the movement of the object to be heated changes the control amount of the inverter based on the temperature rise of the object to be heated Paying attention to the fact that it is sufficiently short compared with the time required for heating, an induction heating coil that generates a high-frequency magnetic field to heat the object to be heated, an inverter that supplies a high-frequency current to the induction heating coil, and an input current of the inverter is constant Control means for controlling the inverter as much as possible, and the control means, when a change in the control amount equal to or greater than a predetermined Δf1 is within the first predetermined time, to the high temperature side of the object to be heated An induction heating cooker that determines that the temperature change is large and suppresses or stops the output of the inverter, wherein the control means changes the control amount by a predetermined Δf3 within the first predetermined time. Serial to the first case was shorter in the second predetermined time than a predetermined time, a configuration to continue heating at least the temperature change larger output than the output value of suppressing the inverter is determined that the large It is what.

  Thereby, even if movement of the object to be heated occurs during heating, it is possible to make it easy to use so that a temperature change of the object to be heated can be detected at high speed without erroneous detection.

  The induction cooking device of the present invention can detect the temperature change of the heated object at high speed without erroneous detection even if the heated object moves during heating.

A first invention is an induction heating coil that generates a high-frequency magnetic field to heat an object to be heated, an inverter that supplies a high-frequency current to the induction heating coil, and the inverter is controlled so that an input current of the inverter is constant. Control means, and the control means determines that the temperature change to the high temperature side of the object to be heated is large when the change in the control amount equal to or greater than the predetermined Δf1 is within the first predetermined time. An induction heating cooker that suppresses or stops the output of the inverter,
Wherein, Oite within the first predetermined time, when the change of the control amount of the predetermined △ f3 is Tsu shorter second der within a predetermined time than the first within the predetermined time, at least By using an induction heating cooker in which heating is continued at an output larger than the output value of the inverter which is judged to be large when the temperature change is suppressed, the object to be heated is moved during the heating. Even if the control amount changes greatly, heating is not suppressed or stopped, so that the temperature change of the object to be heated can be detected at high speed without erroneous detection.

In a second aspect of the invention, an induction heating coil that generates a high frequency magnetic field to heat an object to be heated, an inverter that supplies a high frequency current to the induction heating coil, and the inverter is controlled so that an input current of the inverter is constant. Control means, and the control means determines that the temperature change to the high temperature side of the object to be heated is large when the change in the control amount equal to or greater than the predetermined Δf1 is within the first predetermined time. An induction heating cooker that suppresses or stops the output of the inverter,
In the first predetermined time, when the change in the control amount of the predetermined Δf3 occurs within the second predetermined time shorter than the first predetermined time, the control means starts heating. Induction heating cooker in which heating is continued at an output larger than the output value of the inverter at least when the change in control amount is equal to or greater than the predetermined Δf1 and the temperature change is judged to be large. Therefore, even if movement of the object to be heated occurs during heating and the controlled variable of the inverter changes greatly, heating is not suppressed or stopped, so the temperature of the object to be heated can be changed without erroneous detection. It can be easy to use and can be detected at high speed.

  In the third invention, in particular, in the first or second invention, the second predetermined time is set to approximately 5 seconds or less, so that the user can move the object to be heated intentionally or mistakenly during heating. Does not suppress or stop heating.

  In the fourth invention, in particular, in the first to third inventions, by setting the first predetermined time to about 20 seconds or more, it is possible to accurately suppress an abnormal temperature rise such as emptying of an object to be heated. Become.

According to a fifth aspect of the invention, in the first to fourth aspects of the invention, in the first predetermined time, the change in the control amount of the predetermined Δf3 is shorter than that in the first predetermined time. If the control amount changes over time and the control amount change from the start of heating becomes a control amount change greater than or equal to a predetermined Δf1 + Δf3 , the output of the inverter is suppressed or stopped so that the object to be heated is heated during heating. It becomes possible to accurately suppress an abnormal temperature rise such as emptying of the heated object after the movement.

  In a sixth aspect of the invention, in particular, in the first to fifth aspects of the invention, the control means uses a microcomputer, and the change in the controlled variable is the change in the drive frequency of the inverter or the conduction time of the switching element that generates a high-frequency current inside the inverter Therefore, the temperature change of the object to be heated can be detected with higher accuracy.

  The seventh invention has an informing means in the first to sixth inventions in particular, and when the output of the inverter is suppressed or stopped, by notifying the outside, the abnormal high temperature of the object to be heated is notified to the user. Notification becomes possible, and usability is further improved.

  In an eighth aspect of the invention, in particular, in the first to seventh aspects of the present invention, the pan type determination means further includes a pot type determination means, and the predetermined value of the control amount change is changed according to the determination result of the pot type determination means. It becomes possible to detect the temperature rise of the object to be heated with high accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment)
FIG. 1 shows an induction heating cooker according to an embodiment of the present invention.

As shown in the figure, an induction heating coil 8 that generates a high-frequency magnetic field to heat an object to be heated, an inverter 7 that supplies a high-frequency current to the induction heating coil 8, a commercial power source 11, and a commercial power source 11 are input. Rectifying and smoothing unit 13, a current transformer 14 that detects a power supply current input from the commercial power supply 11 of the inverter 7, a power supply current detection circuit 15 that inputs a detection signal of the current transformer 14, and a high-frequency current flowing through the induction heating coil 8. A current transformer 16 for detecting the current, a coil current detection circuit 17 for inputting a detection signal of the current transformer 16, a control means 18 for controlling the inverter 7 so that an input current of the inverter 7 is constant, and a connection to the control means 18. Detecting means 19 and the current flowing through the induction heating coil 8 and the power source current are detected, and the resonance frequency due to the difference in the pot material The difference (e.g., the resonance frequency of the non-magnetic SUS is higher than the resonant frequency of the iron) and a pot-type determination unit 20 determines the pan species utilized.

  The inverter 7 is provided with a series connection body of a first switching element 7c (IGBT in the present embodiment) and a second switching element 7d (IGBT in the present embodiment). The first diode 7e is connected in antiparallel to the first switching element 7c, and the second diode 7f is connected in antiparallel to the second switching element 7d. A series connection body of the induction heating coil 8 and the resonance capacitor 7g is connected between the connection point of the switching elements 7c and 7d of the series connection body and the negative terminal of the rectifying and smoothing unit 13.

  The rectifying / smoothing unit 13 is connected to a full-wave rectifier formed of a bridge diode and a low-pass filter formed of a choke coil and a smoothing capacitor between its DC output terminals.

The power supply current detection circuit 15 outputs a detection signal proportional to the magnitude of the power supply current to the control means 18. The coil current detection circuit 17 outputs a detection signal proportional to the magnitude of the induction heating coil current to the pot type determination means 20. The pot type determination means 20 determines the pot type and transmits it to the control means 18.

  Then, the control means 18 determines that the temperature change to the high temperature side of the article 9 to be heated is large when there is a change in the control amount more than a predetermined value within the first predetermined time, and the inverter 7 Is suppressed or stopped, and within the first predetermined time, there is a change in the control amount that is greater than or equal to the predetermined amount within a second predetermined time based on the movement of the heated object 9, or the heated object 9 When the sum of the change in the control amount before the movement of and the change in the control amount within the second predetermined time becomes the change in the control amount equal to or greater than the predetermined amount, at least the temperature change is judged to be large and suppressed. Control is performed so as to continue heating at an output larger than the output value of the inverter 7.

  Specifically, the control means 18 and the pan type determination means 20 are constituted by a microcomputer, the clock thereof is 16 MHz, and the minimum control width of the ON time of both the switching elements 7c and 7d is 0.125 μs. Since the time change accompanying the temperature rise is several μs or more, it is possible to read the change sufficiently within the control range of the microcomputer. In this embodiment, the minimum change amount of the control amount change of the microcomputer is set to about 0.1 μs or less.

  In this embodiment, the notification means 19 is configured to notify the outside by sound waves from a piezoelectric speaker, but may be notification by characters, voice, light, or a combination thereof.

The operation of the induction cooking device configured as described above will be described. The commercial power supply 11 is rectified by the rectifying / smoothing unit 13 and supplies power to the high-frequency inverter having the inverter 7 and the induction heating coil 8.

  FIG. 2 shows each part waveform in the present embodiment. A waveform (a) shows a drive signal of the second switching element 7d, which is ON in the HIGH state and OFF in the LOW state. A waveform (A-1) indicates a waveform of a current flowing through the first switching element 7c and the diode 7e. A waveform (A-2) indicates a waveform of a current flowing through the second switching element 7d and the diode 7f. A waveform (c) shows a voltage generated between the collector and the emitter of the second switching element 7d.

  When the first switching element 7c is on, a resonance current is generated in a closed circuit of the first switching element 7c (or the second diode 7f), the induction heating coil 8, and the resonance capacitor 7g. When the first switching element 7c is turned off, a current flows through the second diode 7f.

  After the first switching element 7c is turned off, the second switching element 7d is turned on. Therefore, after the current flows through the second diode 7f, the second switching element 7d (or the first diode 7e) is turned on. Then, a resonance current flows through a closed circuit including the induction heating coil 8 and the resonance capacitor 7g.

  The driving frequency of the first switching element 7c and the second switching element 7d is varied in the vicinity of about 20 kHz, and the driving time ratio is varied in the vicinity of about ½ as shown in FIG.

  Since the control means 18 receives an output signal proportional to the magnitude of the power supply current from the power supply current detection circuit 15, the first switching element 7c and the second switching element 7d are connected to the input power (the output value of the high frequency inverter). ) Is controlled by varying the drive frequency so as to be controlled to a predetermined value.

  FIG. 3 shows the correlation between the drive frequency and the input power. The solid line indicates when the temperature of the heated object 9 is low, and the broken line indicates when the temperature of the heated object 9 is high. The correlation changes depending on the temperature of the heated object 9 because the resistivity of the heated object 9 changes with increasing temperature (generally, the resistivity increases with increasing temperature), and as a result, the induction heating coil 8 This is because the magnetic coupling of the object 9 to be heated changes. More specifically, since the equivalent series resistance increases and the equivalent inductance also increases, the resonance frequency decreases and Q also decreases. As shown in the figure, for example, when 2000 W of power is to be supplied stably, the drive frequency gradually decreases as the temperature of the article 9 to be heated increases (from point A to point B in the figure). Therefore, the drive frequency when a constant power is supplied is as shown in FIG. 4A shows the temperature of the object 9 to be heated, FIG. 4B shows the driving frequency, and FIG. 4C shows the input power. As the temperature of the article 9 to be heated rises, the drive frequency decreases. When the temperature of the article 9 to be heated becomes constant, the drive frequency becomes constant. From the above relationship, the temperature change of the article 9 to be heated can be understood by the time change of the drive frequency.

  FIG. 5 shows the control in the present embodiment when the temperature of the object 9 to be heated, such as empty pan heating, rises abnormally. The control means 18 determines that the temperature rise of the article 9 to be heated is large when there is a predetermined control amount change Δf1 or more at the first predetermined time shown in FIG. Reduce the driving frequency as much as possible. Therefore, the input power is reduced, and as a result, it is possible to avoid an abnormal temperature rise of the article 9 to be heated. In the case of the present embodiment, the temperature of the article 9 to be heated is set to be approximately 320 ° C. or less. At this time, the notification means 19 notifies the outside by sound waves, so that the user can notice an abnormal temperature rise of the article 9 to be heated. In addition, the change in the control amount uses the change in the driving frequency after stabilization at 2000 W after the start of heating.

  Next, the operation when the article 9 to be heated moves during heating will be described. FIG. 6 shows the frequency and input power correlation when the object 9 is moved (moved from near the center to near the outer periphery with respect to the induction heating coil 8). As shown in the figure, the resonance frequency decreases just as when the temperature of the article 9 to be heated increases. Therefore, when the input power is controlled to 2000 W, the driving frequency is lowered.

  FIG. 7 shows the operation when the user moves the article 9 to be heated for some reason during heating. When the article 9 to be heated moves during the second predetermined time shown in FIG. 5B, the drive frequency decreases by Δf3, and when it is summed with Δf2 changed from the start of heating, it becomes the same as Δf1. However, since Δf3 changes within the second predetermined time, the control means 18 does not decrease the input power. Further, when the temperature rises and Δf 4 changes, Δf 1 = Δf 2 + Δf 4, so the control means 18 reduces the input power and prevents an abnormal temperature rise of the article 9 to be heated.

  That is, the control means 18 determines that the temperature change to the high temperature side of the article 9 to be heated is large when there is a change in the control amount over a predetermined value within the first predetermined time, and the output of the inverter 7 Is suppressed or stopped, and within a first predetermined time, when there is a change in the control amount more than a predetermined amount within a second predetermined time based on the movement of the object 9 to be heated, or before the object 9 is moved When the sum of the change in the control amount and the change in the control amount within the second predetermined time is a change in the control amount that is greater than or equal to the predetermined amount, at least the output value of the inverter 7 that suppresses the temperature change is judged to be large The heating is continued with a large output.

  In the present embodiment, the first predetermined time is 20 seconds or longer, and the second predetermined time is 5 seconds or shorter. Normally, if the user moves the object 9 for some reason, it takes about 1 second, and the time until the object 9 reaches the abnormal temperature is 20 seconds or more. It is possible to distinguish the difference between the movement of the object 9 and the temperature rise. The first predetermined time is 20 seconds and the second predetermined time is 5 seconds or less, which is an optimum value in actual use, but is approximately 20 seconds and 5 seconds. It is not limited to.

  FIG. 8 shows the correlation between the temperature, the equivalent series resistance Ri, and the equivalent series inductance Li when the object 9 to be heated has a nonmagnetic SUS thickness of 1 mm. As shown in the figure, the change with respect to temperature is small as compared with the case where the article 9 to be heated is iron (FIG. 11). Therefore, in the case of the present embodiment, the pot type determination means 20 determines whether it is iron or nonmagnetic SUS immediately after the start of heating, and Δf1 is set according to the pot type. Specifically, in the case of iron, Δf1 is set larger than that of nonmagnetic SUS.

  In the present embodiment, the input power is suppressed when it is determined that the object 9 to be heated is at a high temperature, but the heating may be stopped. Further, although the power control of the inverter 7 is performed by changing the drive frequency, the power control may be performed by making the drive frequency constant and changing the conduction ratio of the switching elements 7e and 7f. In this case, the same control can be performed by detecting the amount of change in the ON time of the switching element 7e or 7f.

  As described above, the induction heating cooker according to the present invention can detect a temperature change of a heated object at high speed without erroneous detection even if the heated object moves during heating, so that it can be detected at ordinary homes, offices, restaurants It can be applied to induction heating cookers used in

The schematic circuit diagram of the induction heating cooking appliance in embodiment of this invention The figure which shows the operation | movement waveform of each part of a circuit in the induction heating cooking appliance The figure which shows the frequency and input power correlation at the time of the temperature change of the to-be-heated material in the induction heating cooking appliance. The figure which shows the time change of the temperature of a to-be-heated material, a drive frequency, and input electric power in the same induction heating cooking appliance. The figure which shows control when the temperature rise of the to-be-heated object in the induction heating cooking appliance is abnormal The figure which shows the frequency and input power correlation when the to-be-heated material moves in the induction heating cooking appliance The figure which shows control when the temperature rise of a to-be-heated material is abnormal when the to-be-heated material moves in the induction heating cooking appliance The figure which shows the temperature, equivalent series resistance, and equivalent series inductance correlation when the to-be-heated material in the induction heating cooking appliance is nonmagnetic SUS Schematic cross-sectional view of a conventional induction heating cooker The figure which shows the output of the to-be-heated object and temperature detection means in the induction heating cooking appliance The figure which shows the temperature, equivalent series resistance, and equivalent series inductance correlation when the to-be-heated object in the same induction heating cooking appliance is iron The figure which shows the frequency and input power correlation at the time of the temperature change of the to-be-heated material in the induction heating cooking appliance.

7 Inverter 8 Induction Heating Coil 9 Object to be Heated 18 Control Unit 19 Notification Unit 20 Pot Type Determination Unit

Claims (8)

An induction heating coil that generates a high-frequency magnetic field to heat an object to be heated; an inverter that supplies a high-frequency current to the induction heating coil; and a control unit that controls the inverter so that an input current of the inverter is constant. The control means determines that the temperature change to the high temperature side of the object to be heated is large when the change in the control amount equal to or greater than the predetermined Δf1 is within the first predetermined time , and An induction heating cooker that suppresses or stops output,
Wherein, Oite within the first predetermined time, when the change of the control amount of the predetermined △ f3 is Tsu shorter second der within a predetermined time than the first within the predetermined time, at least An induction heating cooker configured to continue heating at an output larger than an output value of an inverter that is determined to suppress the temperature change to be large. An induction heating coil that generates a high-frequency magnetic field to heat an object to be heated; an inverter that supplies a high-frequency current to the induction heating coil; and a control unit that controls the inverter so that an input current of the inverter is constant. The control means determines that the temperature change to the high temperature side of the object to be heated is large when the change in the control amount equal to or greater than the predetermined Δf1 is within the first predetermined time, and An induction heating cooker that suppresses or stops output,
In the first predetermined time, when the change in the control amount of the predetermined Δf3 occurs within the second predetermined time shorter than the first predetermined time, the control means starts heating. Induction heating cooker in which heating is continued at an output larger than the output value of the inverter at least when the change in control amount is equal to or greater than the predetermined Δf1 and the temperature change is judged to be large. . The induction heating cooker according to claim 1 or 2, wherein the second predetermined time is approximately 5 seconds or less. The induction heating cooker according to any one of claims 1 to 3, wherein the first predetermined time is approximately 20 seconds or longer. Within the first predetermined time, the change in the control amount of the predetermined Δf3 occurs in the second predetermined time that is shorter than the first predetermined time, and the change in the control amount from the start of heating is the predetermined Δf1 + Δ. The output of the inverter is suppressed or stopped when the control amount change is greater than or equal to f3.
The induction heating cooker according to any one of the above. The control means uses a microcomputer, and the change in the controlled variable is a change in the drive frequency of the inverter or a change in the conduction time of the switching element that generates a high-frequency current inside the inverter. Induction heating cooker. The induction heating cooker according to any one of claims 1 to 6, wherein the induction heating cooker has notification means and notifies the outside when the output of the inverter is suppressed or stopped. The induction heating cooker according to any one of claims 1 to 7, further comprising a pot type determination unit, wherein the predetermined value of the control amount change is changed according to a determination result of the pot type determination unit.

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