JP4821791B2 - Induction heating cooker - Google Patents

Description

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

  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.

  Hereinafter, an example of a conventional induction heating cooker will be described with reference to FIG. In the figure, 1 is an inverter, 2 is an induction heating coil connected to the inverter 1, and 3 is an object to be heated, which is a cooking pot in this embodiment. Reference numeral 4 denotes a top plate on which the object to be heated 3 is placed. Reference numeral 5 denotes temperature detecting means for detecting the temperature of the object to be heated 3. Specifically, a thermistor is brought into close contact with the top plate 4 and is detected by heat conduction.

  As shown 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 object 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). ing. 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 conventional configuration described above, the temperature detecting means 5 detects the temperature of the object to be heated 3 via the top plate 4, so that there is a problem that the thermal response is slow and appropriate control is difficult. A specific example will be described with reference to FIG. The solid line in FIG. 13 is the temperature of the article 3 to be heated, and the broken line is the output of the temperature detecting means 5. As shown in the figure, the output of the temperature detecting means 5 is delayed with respect to the temperature change of the article 3 to be heated. As a result, for example, it is difficult to detect boiling or abnormal temperature rise of an empty pan. This is a problem.

From such a background, what detects the temperature of the to-be-heated material 3 using an infrared sensor is disclosed recently (for example, refer patent document 1).
JP 2002-299029 A

  However, such a method has a problem that an expensive infrared sensor is required.

  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 an object to be heated 3 at high speed without using a new temperature detecting means such as an infrared sensor. It is intended.

In order to solve the conventional problems, an induction heating cooker according to the present invention includes a top plate on which an object to be heated is placed , and induction heating that generates a high-frequency magnetic field and heats the object to be heated on the top plate. A coil, an inverter for supplying a high-frequency current to the induction heating coil, a control means for controlling the inverter so that an input current of the inverter is constant, and a temperature of an object to be heated provided in close contact with the back surface of the top plate detecting a and a thermistor, the control means, there is a change in a predetermined or more control amount within a predetermined time, and the inverter when the temperature detection information from the thermistor is at a temperature change of more than a predetermined The output is suppressed or stopped.

  Since the temperature change of the object to be heated is detected by adding information from the temperature detecting means used conventionally, for example, even when the bottom surface of the object to be heated is deformed during heating, the abnormal temperature rise of the object to be heated is accurately detected. Is possible.

  The induction heating cooker of the present invention can accurately detect an abnormal temperature rise of a heated object even when the bottom surface of the heated object is deformed during heating.

The invention described in claim 1 includes a top plate on which an object to be heated is placed, an induction heating coil that generates a high-frequency magnetic field and heats the object to be heated on the top plate, and a high-frequency current in the induction heating coil. A control means for controlling the inverter so that the input current of the inverter is constant, and a thermistor that is provided in close contact with the back surface of the top plate and detects the temperature of the object to be heated, The control means is an induction heating cooker that suppresses or stops the output of the inverter when there is a change in the control amount more than a predetermined value within a predetermined time and the temperature detection information from the thermistor is a temperature change more than a predetermined value. Therefore, the temperature change of the object to be heated is also detected by adding information from the temperature detecting means that has been used conventionally. For example, the bottom surface of the object to be heated is added. It becomes possible abnormal temperature rise detection of precisely the object to be heated in the case of deformation in the.

  Embodiments of the present invention will be described below with reference to the drawings.

( Reference Example 1)
The first reference example will be described below with reference to the drawings. FIG. 1 is a schematic circuit diagram of the induction heating cooker of this reference example . In FIG. 1, 9 is an object to be heated by induction heating, and 11 is a commercial power source. The commercial power supply 11 is input to the rectifying / smoothing unit 13. The rectifying / smoothing unit 13 is connected to a full-wave rectifier composed of a bridge diode and a low-pass filter composed of a choke coil and a smoothing capacitor between its DC output terminals.

  The inverter circuit 7 is connected to the output of the rectifying and smoothing unit 13, and the induction heating coil 8 is connected to the inverter circuit 7. The inverter circuit 7 and the induction heating coil 8 constitute a high frequency inverter. The inverter circuit 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 both switching elements of the series connection body and the negative terminal of the rectifying and smoothing unit 13.

  The current transformer 14 detects a power supply current input from the commercial power supply 11 of the inverter circuit 7 and outputs a detection signal to the power supply current detection circuit 15. 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 control means 18 drives the first switching element 7c and the second switching element 7d in the inverter circuit 7. The control means 18 is connected to the notification means 19 and the input means 20. In the case of this reference example, the notification means 19 is configured to notify the outside by sound waves from a piezoelectric speaker. The input means 20 is configured to allow the user to input by key input, and specifically includes a key switch for the boiled food 1 and boiled food 2 shown in FIG.

  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 the waveform of each part in this reference example . 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-2) shows a waveform of a current flowing through the second switching element 7d and the diode 7f. A waveform (A-1) indicates a waveform of a current flowing through the first switching element 7c and the diode 7e. 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 the closed circuit of the first switching element 7c (or the second diode), 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 circuit 18 receives an output signal proportional to the magnitude of the power supply current from the power supply current detection circuit 15, the input power (the output value of the high frequency inverter) is input to the first switching element 7c and the second switching element 7d. Control is performed by varying the drive frequency so as to control to a predetermined value.

FIG. 3 is a diagram showing the correlation between the drive frequency and the input power, where the solid line indicates when the temperature of the object to be heated is low and the broken line indicates when the temperature of the object to be heated is high. The correlation changes depending on the temperature of the object to be heated. The resistivity of the object to be heated changes as the temperature rises (generally, the resistivity increases as the temperature rises). As a result, the induction heating coil 8 and the object to be heated are changed. This is because the magnetic coupling of 9 changes. As shown in the figure, for example, when it is attempted to stably supply 2000 W of power, the drive frequency gradually decreases as the temperature of the object to be heated increases. Therefore, the drive frequency when a constant power is supplied is as shown in FIG. In FIG. 4A, the solid line is the temperature of the article 3 to be heated, (b) is the drive frequency, and (c) is the input power. As the temperature of the article to be heated 3 rises, the driving frequency decreases. When the temperature of the article to be heated 3 becomes constant, the driving frequency becomes constant. From the above relationship, the temperature change of the object to be heated 3 can be understood by the time change of the drive frequency. FIG. 5 shows the control in the present reference example when the temperature of the object to be heated 3 such as heating of an empty pan rises abnormally. When the control means 18 has a predetermined control amount change (Δf1) or more during the predetermined time A shown in FIG. The drive frequency is lowered to reduce it. Therefore, the input power is reduced, and as a result, it is possible to avoid an abnormal temperature rise of the article 3 to be heated. 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 3 to be heated.

FIG. 6 shows the control of this reference example when the temperature of the object 3 to be heated, such as a water heater, becomes constant. The control means 18 determines that the boiling is completed when the change in control amount (Δf2) is less than or equal to the predetermined control amount change (Δf2) during the predetermined time B shown in FIG. Therefore, it is possible to avoid spillage. Further, since the notification means 19 notifies the outside at this time, the user can know that the kettle is completed.

As shown in FIG. 7, in the case of this reference example , the heating power after the boiling detection can be set in advance. That is, in the case of boiled food 1, the heating power after boiling detection is about half of the rated power, and in the case of boiled food 2, the same power is about 1/4 of the rated power. The user can control in accordance with the cooking menu by inputting in advance with the keys shown in FIG. Although not particularly shown in the case of this reference example , for example, an input means such as a water heater key may be provided, and the water heater detection may be performed only when this key is pressed.

In this reference example , a two-stone type SEPP inverter configuration is used. However, any configuration or input may be used as long as the input current changes due to a magnetic coupling change with a load (an object to be heated) such as a one-stone type voltage resonance inverter. A control type inverter may be used. Furthermore, although the power variable is performed using the frequency, this is not limited, and it goes without saying that, for example, a method of changing the conduction ratio of two stone switching elements at a constant frequency may be used.

( Example )
Embodiments of the present invention will be described below with reference to the drawings. The difference in configuration between the present embodiment and the first reference example is the presence or absence of the temperature detecting means described in the conventional example, and the others are the same. That is, the present embodiment has a temperature detecting means using a thermistor conventionally used, and the configuration thereof is the same as that described in the conventional example. The control means 18 performs control in consideration of the output of the temperature detection means indicated by the broken line in FIG. As shown in the figure, only when the temperature change from the temperature detecting means is Δt1 or more and the condition of the reference example 1 is satisfied, the control means 18 determines that the temperature rise of the article 3 to be heated is abnormal and the inverter 7 Since the output is reduced, for example, during normal heating, if the bottom surface of the object to be heated 3 is gradually deformed by heating and the magnetic coupling between the induction heating coil 8 and the object to be heated 9 is changed, the temperature rise is erroneously abnormal. Judgment is lost. FIG. 9 shows the control of this embodiment at the time of boiling water. As in FIG. 8, the broken line in (a) is the output from the temperature detecting means. Even in this case, the control means 18 increases the temperature below Δt2 and reduces the output of the inverter 7 only when the condition described in the reference example 1 is satisfied. For example, the bottom surface of the object to be heated 3 is deformed by heating. However, it is possible to avoid mistakenly determining that the boiling has been completed when the degree of deformation becomes small with time.

(Reference Example 2 )
Hereinafter, a second reference example will be described with reference to the drawings. FIG. 10 shows a cross-sectional view of this reference example. In the case of this reference example, it is the same as the reference example 1 except that the distance measuring means 30 is provided at the center of the induction heating coil 8 as shown in the figure. The distance measuring means 30 is specifically composed of a set of a light emitting diode and a phototransistor, and the induction heating coil depends on the time until the light generated from the light emitting diode is reflected by the article 9 to be heated and returns to the phototransistor. 8 and the object 9 to be heated are measured. With the above configuration, in the case of this reference example, the deformation of the object 9 to be heated can be detected by the distance measuring means 30, so that the erroneous detection due to the deformation of the object 9 to be heated described in the embodiment is avoided. It is something that can be done. Specifically, control is performed such that detection of boiling water is performed only when the distance between the induction heating coil 8 and the object 9 to be heated from the distance measuring means 30 is equal to or less than a predetermined value. Further, when there is a change in distance more than a predetermined distance, an abnormality notification may be given as an inappropriate heating load.

(Reference Example 3 )
Hereinafter, a third reference example will be described with reference to the drawings. FIG. 11 shows a cross-sectional view of this reference example. In the figure, the induction heating coil 8 is divided into two parts 8a and 8b, an outer peripheral part and an inner peripheral part, and each is connected to an independent inverter 7. Accordingly, only the outer peripheral portion 8a, only the inner peripheral portion 8b, and both can be heated. With the above configuration, two pieces of magnetic coupling information between the object to be heated 9 and the induction heating coils 8a and 8b can be obtained.

  In the case of this reference example, temperature detection is performed based on magnetic coupling information of the outer peripheral portion 8a (that is, a change in the driving frequency of the inverter 7 connected to the outer peripheral portion 8a). With this control, the deformation of the bottom surface of the object to be heated 9 is particularly large in the central portion and the outer peripheral portion is small, so that erroneous detection due to the deformation can be avoided.

Schematic circuit diagram of the induction heating cooker in Reference Example 1 The figure which shows the operation waveform of each part of the circuit The figure which shows the frequency and input power correlation at the time of the temperature change of the to-be-heated object The figure which shows the time change of the temperature of a to-be-heated material, a drive frequency, and input electric power similarly The figure which shows the control in case the temperature rise of a to-be-heated object is abnormal The figure which shows control when the temperature rise of a to-be-heated object becomes constant similarly Figure showing the input means The figure which shows the control in case the temperature rise of the to-be-heated material of the induction heating cooking appliance in the Example of this invention is abnormal. The figure which shows control when the temperature rise of a to-be-heated object becomes constant similarly Sectional drawing of the induction heating cooking appliance in the reference example 3 Sectional drawing of the induction heating cooking appliance in the reference example 4 Sectional view of a conventional induction heating cooker The figure which shows the output of a to-be-heated object and a temperature detection means similarly

9 Object to be heated 8 Induction heating coil 7 Inverter 18 Control means 19 Notification means 20 Input means 30 Distance measurement means

Claims (1)

A top plate on which an object to be heated is placed; an induction heating coil that generates a high-frequency magnetic field to heat the object to be heated on the top plate; an inverter that supplies a high-frequency current to the induction heating coil; Control means for controlling the inverter so that the input current is constant, and a thermistor that is provided in close contact with the back surface of the top plate and detects the temperature of the object to be heated. An induction heating cooker that suppresses or stops the output of the inverter when there is a change in the control amount and the temperature detection information from the thermistor is a temperature change greater than or equal to a predetermined value.

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