JP4894191B2 - Induction heating device - Google Patents

Description

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

Conventionally, an induction heating device generates a high-frequency magnetic field from an induction heating coil by a high-frequency current supplied from a high-frequency inverter, and a heated object such as a cooking pan on a top plate is heated by an eddy current due to electromagnetic induction. Further, the temperature of the heated object is detected by temperature detection means such as a thermistor via the top plate, and the output of the high frequency inverter is controlled so that the temperature of the heated object becomes around 200 ° C., for example, during frying cooking. Alternatively, a protection operation is performed in which heating is stopped when the cooking pan, which is the object to be heated, is in an empty state where there is no content such as food (see, for example, Patent Document 1).
JP 2004-247237 A

  However, in the conventional configuration, since the temperature detecting means detects the temperature of the object to be heated through the top plate, there is a problem that the thermal response is slow and appropriate control is difficult. In order to solve such a problem, an expensive infrared sensor is required.

  On the other hand, in the method of detecting the temperature of the object to be heated by changing the control parameters of the high-frequency inverter, when the parameter changes due to improper use such as emptying, and when the food is added after preheating the object to be heated Because the change in the parameters of the two is similar, they cannot be identified, and cannot be detected even though the heated object is in an excessively high temperature state, or even if preheated food is added. There was a problem that the thermal power was limited.

  The present invention solves the above-mentioned conventional problems, and detects that the heated object is in an excessively high temperature state without using a new temperature detection means such as an infrared sensor, and is a safe and user-friendly guidance. The object is to realize a heating device.

  In order to solve the above-mentioned conventional problems, in the induction heating apparatus of the present invention, the detection means 7 detects that the impedance of the resonance circuit has changed due to the characteristic change of the heated object due to heating, and the impedance change continues. In this case, the control means is an induction heating device that controls to stop the heating output of the high-frequency inverter.

  As a result, when the impedance of the resonant circuit changes and there is a change in the parameter, it is determined whether the change in the parameter is transient or continuously changing. It is possible to determine whether it is in a state or a change due to the addition of ingredients, and since heating is stopped only when the heated object becomes excessively hot without erroneous detection, It can be safe and easy to use. Further, appropriate control can be performed without using new temperature detection means such as an infrared sensor.

  The induction heating device of the present invention can be made safe and easy to use by reliably detecting the high temperature state of the object to be heated and stopping the heating output of the high frequency inverter.

A first invention is a high-frequency inverter, a power source for supplying power to the high-frequency inverter, the switching elements connected to the high-frequency inverter, the induction heating coil, and a resonant capacitor, a heated object heated by the induction heating coil the detecting means for detecting that the impedance of the resonance circuit including the induction heating coil and the heated object is changed, the said as input current of the high-frequency inverter is the input current in response to the user's setting the switching element and control means for controlling the conduction time or conduction period of said detection means, the impedance of the resonant circuit detects that it has changed by detecting a change in characteristic exhibiting magnetism of the object to be heated by the heating said control means when a characteristic indicative for magnetic exceeds elevated predetermined value after the decrease of the high-frequency inverter With the induction heating device to stop or suppress the thermal output, when the impedance of the resonance circuit is a change in the changed parameters, the change of the parameter is changed continuously or not transient It is possible to determine whether it is excessively hot due to emptying, etc., or whether it is a change due to the introduction of foodstuffs, and the heated object is excessively hot without false detection Since heating is stopped only when it becomes, it can be made safe and easy to use. Further, appropriate control can be performed without using new temperature detection means such as an infrared sensor.

According to a second aspect of the invention, in particular, in the first aspect of the invention, the detection means detects a change in impedance by a change in the conduction time of the switching elements constituting the high-frequency inverter, so that a voltage detection means or the like is not newly provided. Since detection is possible only by the change in the conduction period of the switching element necessary for the control of the high-frequency inverter, it can be realized at a low cost with a simple configuration.

According to a third aspect of the invention, in particular, in the first aspect of the invention, the detection means detects a change in impedance by a change in the conduction cycle of the switching elements constituting the high-frequency inverter, so that a voltage detection means or the like is not newly provided. Since detection is possible only by the change in the conduction cycle of the switching element necessary for the control of the high-frequency inverter, it can be realized at a low cost with a simple configuration.

A fourth invention is, in particular, in the first invention, further comprising a first voltage detection means for detecting the voltage of the resonance capacitor, the sensing means, impedance than the change in voltage the first voltage detection unit detects By detecting this change, it is possible to detect with the voltage of the resonance capacitor that constitutes the resonance circuit, so that it can be realized with a simple configuration at low cost.

In particular, the fifth invention further includes boosting means for boosting the voltage supplied from the power source and supplying the boosted voltage to the high-frequency inverter in the first invention. By detecting the change in impedance based on the change in voltage, when the output of the high-frequency inverter is controlled by the boosting means, it can be detected only by the change in the boosting ratio that is the control parameter of the boosting means. It can be realized at low cost.

According to a sixth aspect of the invention, in particular, in the first aspect of the invention, the voltage supplied from the power source is boosted, the boosting means for supplying the boosted voltage to the high-frequency inverter, and the voltage boosted by the boosting means is detected. a voltage detecting means and the further detecting means, by the second voltage detecting means for detecting a change in impedance than the change in the voltage detected, when controlling the output of the high-frequency inverter by boosting means Can be detected only by a change in the boosted voltage, which is the control result of the boosting means, and can be realized at a low cost with a simple configuration.

  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 1)
FIG. 1 shows an induction heating apparatus according to Embodiment 1 of the present invention.

  As shown in the figure, the induction heating apparatus in the present embodiment includes a high-frequency inverter 1, a power source 2 that supplies power to the high-frequency inverter 1, a switching element 3 that is connected to the high-frequency inverter 1, an induction heating coil 4, And a resonant capacitor 5 connected in series with the induction heating coil 4, a heated body 6 such as a cooking pot heated by the induction heating coil 4, the heated body 6, the induction heating coil 4, and the resonant capacitor 5. Detection means 7 for detecting that the impedance of the resonance circuit has changed, control means 8 for controlling the high-frequency inverter 1, and a detection result of the detection means 7 and a control result of the control means 8, to the induction heating apparatus user. And informing means 9 for reporting the abnormality.

  Further, the first voltage detecting means 10 for detecting the voltage of the resonance capacitor 5, the voltage supplied from the power supply 2 is boosted, and the boosted voltage is boosted by the boosting means 11 and the boosting means 11 that supply the boosted voltage to the high frequency inverter 1. The second voltage detecting means 12 for detecting the detected voltage and the top plate 13 made of glass or the like on which the heated body 6 is placed are also provided.

  The high-frequency inverter 1 includes a switching element 3, an induction heating coil 4, and a resonance capacitor 5, and supplies a high-frequency current to the induction heating coil 4 by switching the current path of the power supplied from the power source 2 by the switching element 3. To do. A high frequency magnetic field is generated from the induction heating coil 4, an eddy current due to electromagnetic induction flows in the heated body 6, and the heated body 6 is heated by the Joule heat. As the control of the high-frequency inverter 1, the control means 8 performs feedback control so as to detect the input current of the high-frequency inverter 1 and use the power set by the user of the induction heating apparatus.

  The power source 2 includes a boosting unit 11 and supplies a DC power source obtained by converting a commercial single-phase 100V or 200V AC power source into a DC by a diode bridge to the high frequency inverter 1.

  The detecting means 7 detects that the impedance of the resonance circuit has changed due to the characteristic change of the heated body 6 due to heating, and the control means 8 stops the heating output of the high-frequency inverter 1 when the impedance change continues. So as to control. That is, the detection means 7 is connected to the control means 8 that controls the heating output of the heated body 6 by changing the conduction time and conduction period of the switching element 3 constituting the high-frequency inverter 1. It detects that the impedance of the resonant circuit has changed due to changes in time or conduction period. The detection means 7 and the control means 8 may be the same and realized by a microcomputer or a DSP, but may be a custom IC.

  The notification unit 9 is connected to the control unit 8 and transmits an abnormality to the user of the induction heating apparatus based on the detection result of the detection unit 7 and the control result of the control unit 8. The notification means 9 may be a notification by sound from a buzzer or a speaker, a visual recognition such as an LED or a display, or a recognition recognized by vibration or the like when the user of the induction heating device touches it. It does not matter.

  Next, operation | movement of the induction heating apparatus in the said structure is demonstrated.

  When the cooking pan which is the object to be heated 6 is a magnetic body such as iron, there is a Curie temperature, and the magnetic property gradually decreases as the temperature increases. Some cooking pans as the heated body 6 have a multilayer structure in which a plurality of different metals are laminated. Alternatively, some are processed so that induction heating can be performed by pasting a metal other than the metal that forms the pan at the bottom of the cooking pan, and depending on the combination of those metals, it is compared with a single metal The Curie temperature may be low. Therefore, when cooking in the air, the temperature of the cooking pan rises in a relatively short time, so that the characteristic showing magnetism may gradually weaken and become red-hot. That is, when such a heated body 6 is heated, the impedance of the resonance circuit including the induction heating coil 4 gradually changes. The change in impedance can be read from the voltage of each component connected to the high frequency inverter 1, the change in the control parameter of the high frequency inverter 1, and the like. These changes are detected by the detection means 7.

  However, the change in the voltage of each component connected to the high frequency inverter 1 or the control parameter of the high frequency inverter 1 is due to the change in impedance due to the rise in the temperature of the heated body 6, or the cooking pan and the induction heating coil. When the relative position of 4 is changed, or when some load is applied to the heated body 6, specifically, the cooking pan as the heated body 6 is cooked such as water or food. It is not possible to determine whether this is a change caused by the insertion of

  Therefore, in the present embodiment, when a change in impedance of the resonance circuit is detected, whether the change continues or whether the temperature of the heated body 6 has increased or the heated body 6 has moved. Or when the load is applied to the heated body 6, it is determined that the temperature of the heated body 6 is rising only when the change continues, and the heated body 6 can be detected without erroneous detection. By controlling to stop heating at high temperatures, the heated body 6 is controlled so as not to reach a dangerous temperature, and a safe and easy-to-use induction heating apparatus can be realized.

  Alternatively, instead of stopping heating, control is performed so that the heating output of the high-frequency inverter 1 is suppressed, so that the heated body 6 is controlled so as not to become a dangerous temperature, and an induction heating device that is safe and easy to use is provided. It can be realized.

  The impedance change due to the temperature rise of the heated body 6 and a method for determining whether a load is applied to the heated body 6 will be described in more detail.

  FIG. 2 shows changes in parameters when the impedance changes due to the temperature rise of the heated body 6.

  Assuming that the parameter for detecting the change in impedance is P, after the heating output of the high-frequency inverter 1 is stabilized, the parameter P decreases as the temperature of the heated body 6 increases. This is because the resistance value of the heated body 6 gradually increases as the temperature rises. Meanwhile, the minimum value of the parameter P is obtained, and the minimum value of P is set to P (T2).

  When the temperature of the heated body 6 rises and approaches the Curie temperature, and the magnetic properties gradually weaken, the parameter P starts to rise, so that the impedance changes when P increases by α from P (T2). In the case of the specification for determining that there has been an impedance, it is detected that the impedance has changed at T3 in FIG. If the heating is continued thereafter, the parameter P further increases.

  FIG. 3 shows changes in parameters when a load is applied to the heated body 6.

  The change in the parameter P after the heating output becomes constant decreases with the change in the impedance. However, when a load such as water or food is put into the cooking pan as the heated body 6, the parameter P is empty. As a result, the temperature rises more rapidly than the temperature rises due to the heated body 6 becoming hot, and is detected as a change in impedance when α rises (T3). For this reason, when control is performed to stop the heating output when there is a change in impedance, an erroneous detection that heating stops when a load is applied to the heated object 6 occurs.

  When the heating output is continued after the change in impedance is detected, the parameter P further increases as shown in FIG. 2 when flying, whereas when the load is turned on, the parameter is set when the load is turned on. P rises but remains constant thereafter. Therefore, as in this embodiment, it is possible to determine whether the load is applied or empty by determining whether or not the change in impedance continues.

  FIG. 4 shows changes in parameters when the impedance is changed due to the temperature rise of the heated object 6 in the case of detection by the method of the present embodiment.

  Let P (T2) be the minimum value of the parameter P after the heating output of the high-frequency inverter 1 is stabilized. A time point when α increases from P (T2) is defined as T3, and a time point after a predetermined time has elapsed from T3 as T4. Whether the load is applied or not can be determined by detecting the change in impedance at the time when β further rises from P (T4), which is P at T4.

  FIG. 5 shows changes in parameters when a load is applied to the heated body 6 in the case of detection by the method of the present embodiment.

  Let P (T2) be the minimum value of the parameter P after the heating output of the high-frequency inverter 1 is stabilized. A time point when α increases from P (T2) is defined as T3, and a time point after a predetermined time has elapsed from T3 as T4. Impedance change is detected when the parameter P rises from P (T4), which is P at T4, to P (T4) + β, which is further increased by β. However, since the parameter P does not increase after T4 when the load is applied, It does not correspond to the change detection, and heating is continued.

  In this way, it is possible to discriminate between a change in impedance due to the temperature of the heated body 6 rising to near the Curie temperature and a change in impedance due to the load being applied to the heated body 6. .

  In the example shown in FIGS. 2 to 5, the parameter for detecting a change in impedance is described as P. In this example, it has been explained that the parameter P decreases with heating and starts increasing when the temperature approaches the Curie temperature. However, other parameters that detect a change in impedance increase with heating and decrease when the temperature approaches the Curie temperature. Although there are parameters, the decrease and increase are only reversed, and the description thereof is omitted.

  In this embodiment, after detecting a change in impedance, the heating is stopped to completely stop the temperature increase of the heated body 6 and to ensure safety, but the heating output is suppressed. It may be as described above. Further, by notifying the user by the notification means 9, it is notified that the heated body 6 is in a dangerous state at high temperature, and the heating output is suppressed or a load such as water or food is applied to the heated body 6. It can be urged to be put in, is safe and secure and easy to use.

(Embodiment 2)
Next, the induction heating apparatus in Embodiment 2 of this invention is demonstrated. Since the basic configuration is the same as that of the first embodiment, the description thereof will be omitted, and only differences will be described.

  In the present embodiment, as a method in which the detection means 7 detects a change in impedance of the heated body 6, a change in impedance is detected from a change in conduction time of the switching element 3 constituting the high-frequency inverter 1.

  The change in the conduction time of the switching element 3 moves in the opposite direction to the parameter P described with reference to FIGS. 2 to 5 in the first embodiment.

  This detection method is used when the voltage supplied to the high frequency inverter 1 and the conduction cycle of the switching element 3 are constant and the heating output of the high frequency inverter 1 is controlled by the conduction time of the switching element 3.

(Embodiment 3)
Next, the induction heating apparatus in Embodiment 3 of this invention is demonstrated. Since the basic configuration is the same as that of the first embodiment, the description thereof will be omitted, and only differences will be described.

  In the present embodiment, as a method in which the detection means 7 detects a change in impedance of the heated body 6, a change in impedance is detected from a change in the conduction period of the switching element 3 constituting the high-frequency inverter 1.

  The change in the conduction cycle of the switching element 3 is the same as the movement of the parameter P described with reference to FIGS. 2 to 5 in the first embodiment.

  This detection method is used when the voltage supplied to the high-frequency inverter 1 and the conduction time of the switching element 3 are constant and the heating output of the high-frequency inverter 1 is controlled by the conduction cycle of the switching element 3.

(Embodiment 4)
Next, the induction heating apparatus in Embodiment 4 of this invention is demonstrated. Since the basic configuration is the same as that of the first embodiment, the description thereof will be omitted, and only differences will be described.

  In the present embodiment, the detection unit 7 detects a change in impedance of the body 6 to be heated by detecting a change in voltage detected by the first voltage detection unit 10.

  The change in the voltage detected by the first voltage detection means 10 is the same as the movement of the parameter P described with reference to FIGS. 2 to 5 in the first embodiment.

  When this detection method is used, it does not depend on the control method of the high-frequency inverter 1.

(Embodiment 5)
Next, an induction heating apparatus according to Embodiment 5 of the present invention will be described. Since the basic configuration is the same as that of the first embodiment, the description thereof will be omitted, and only differences will be described.

  In the present embodiment, as a method in which the detection unit 7 detects a change in impedance of the heated body 6, a change in the boost ratio of the boost unit 11 is detected.

  The change in the step-up ratio of the step-up means 11 is the reverse of the parameter P described with reference to FIGS. 2 to 5 in the first embodiment.

  In order to use this detection method, the conduction cycle and conduction time of the switching element 3 of the high-frequency inverter 1 are constant, and the heating output of the high-frequency inverter 1 is controlled by the boost ratio of the booster 11.

  The boosting means 11 boosts the voltage of a DC power source obtained by converting a commercial single-phase 100V or 200V AC power source into a DC by a diode bridge, and supplies the boosted voltage to the high-frequency inverter 1. The power source 2 including the booster 11 is used.

  Since the voltage of the power supply 2 is boosted by the boosting means 11, the current can be reduced when the same power is supplied to the high frequency inverter 1, so that the component rating of each component constituting the high frequency inverter 1 is lowered. Therefore, it is possible to reduce the size and cost of the components, and to make the product cheaper and smaller, which can bring benefits to the user. Therefore, it is desirable that the voltage of the power supply 2 is higher.

(Embodiment 6)
Next, the induction heating apparatus in Embodiment 6 of this invention is demonstrated. Since the basic configuration is the same as that of the first embodiment, the description thereof will be omitted, and only differences will be described.

  In the present embodiment, as a method for detecting a change in the impedance of the heated body 6 by the detecting means 7, the control voltage of the boosting means 11, that is, the voltage supplied to the high-frequency inverter 1 is the second voltage detecting means 12. It is assumed to detect by voltage change.

  The voltage change of the second voltage detection means 12 moves in the opposite direction to the parameter P described with reference to FIGS. 2 to 5 in the first embodiment.

  To use this detection method, the conduction cycle and conduction time of the switching element 3 of the high-frequency inverter 1 are constant, and the heating output of the high-frequency inverter 1 is controlled by the boosted voltage of the boosting means 11.

(Embodiment 7)
Next, the induction heating apparatus in Embodiment 7 of this invention is demonstrated. Since the basic configuration is the same as that of the first embodiment, the description thereof will be omitted, and only differences will be described.

  In the present embodiment, a predetermined time is provided until it is determined whether or not the impedance change continues.

  In the first embodiment, as described with reference to FIG. 2, the parameter P continues to increase after turning from decreasing to increasing in the case of airing, whereas when the load is applied to the heated object 6. As described with reference to FIG. 3, the parameter P changes from decreasing to increasing, and thereafter becomes a substantially constant value.

  Therefore, in order to determine whether or not the change in impedance continues, it can be determined by looking at the value of the parameter after a lapse of a predetermined time after shifting from decrease to increase.

That is, with reference to FIG. 4, it is detected that there is a change in impedance at the point of time T3 when T2 changes from decrease to increase and becomes P (T2) + α. Whether or not the impedance change continues can be confirmed by continuing to follow the parameter value, but after a predetermined time has elapsed from T3, T4 is taken and the magnitude relationship between P (T3) and P (T4) is observed. It shall be determined by When the impedance continues to change, P (T3) <P (T4). However, when the load is turned on, the impedance does not continue to change, so P (T3) = P (T4) or P (T T3)> P (T4).

  Therefore, as in the present embodiment, the detection means 7 detects that the impedance of the resonance circuit including the induction heating coil 4 has changed, and a predetermined time is required until it is determined whether or not the change in impedance continues. Since it is not affected by the transient change of impedance when food is thrown into the cooking pan that is the heated body 6, it becomes possible to discriminate between empty cooking and loading, In the case of airing, an induction heating device that is safe and easy to use can be realized by stopping or suppressing the heating output or notifying the user.

(Embodiment 8)
Next, an induction heating apparatus in Embodiment 8 of the present invention will be described. Since the basic configuration is the same as that of the first embodiment, the description thereof will be omitted, and only differences will be described.

  In the present embodiment, the predetermined time until it is determined whether or not the change in impedance described in the seventh embodiment is continued is 2 seconds or more.

  It has been found that the transient change in the parameter change when loading is experimentally subsided in less than about 2 seconds.

  Therefore, as in the present embodiment, if the predetermined time is set to 2 seconds or more, it can be determined whether or not the impedance change continues without being affected by the transient change caused by the load application.

(Embodiment 9)
Next, an induction heating apparatus in Embodiment 9 of the present invention will be described. Since the basic configuration is the same as that of the first embodiment, the description thereof will be omitted, and only differences will be described.

  In the present embodiment, when the impedance change does not continue, the subsequent impedance change is not detected.

  That is, as described in each of the first to eighth embodiments, a change in the parameter due to an excessive temperature rise of the heated body 6 due to emptying and a change in the parameter due to the input of water or food to the heated body 6 are discriminated. Is possible. However, when the load is applied, there is a user on the induction heating device side, so there is no need to change the heating output of the high-frequency inverter 1. On the other hand, if the heating output is changed, the heating power is weak, and it becomes inconvenient such that the intended cooking cannot be performed.

  Therefore, as in the present embodiment, when the impedance change is temporary, it is due to the food being put into the cooking pan, which is the heated body 6, so that the heated body 6 has an excessive temperature. Since it does not rise into a dangerous state, it is possible to continue heating, and it is possible to prevent erroneous detection due to some factor by not performing subsequent detection.

As described above, the induction heating device according to the present invention can be made safe and easy to use by reliably detecting the high temperature state of the object to be heated and stopping the heating output of the high frequency inverter. It can be applied to various induction heating apparatuses as well as cooking devices.

The circuit block diagram of the induction heating apparatus in Embodiment 1-9 of this invention The figure which shows the change of the parameter by the temperature rise of the to-be-heated body in an induction heating apparatus The figure which shows the change of the parameter at the time of applying a load to the heated object The figure which shows the other change of the parameter by the temperature rise of the to-be-heated body The figure which shows the other change of the parameter at the time of applying load to the to-be-heated body

DESCRIPTION OF SYMBOLS 1 High frequency inverter 2 Power supply 3 Switching element 4 Induction heating coil 5 Resonance capacitor 6 Heated object 7 Detection means 8 Control means 9 Notification means 10 1st voltage detection means 11 Boosting means 12 2nd voltage detection means

Claims (6)

And high-frequency inverter, a power source for supplying power to the high-frequency inverter, the switching elements connected to the high-frequency inverter, the induction heating coil, and a resonant capacitor, a heated object heated by the induction heating coil, and the object to be heated detecting means for detecting that the impedance of the resonance circuit including the induction heating coil is changed, the conduction time or conduction period of the switching element such that the input current is an input current in accordance with the setting of a user of the high frequency inverter and control means for controlling said detection means detects that the impedance of the resonant circuit is changed by detecting a change in characteristic exhibiting magnetism of the object to be heated by heating shows the magnetic characteristics the control means stops the heating output of the high frequency inverter when but exceeded elevated predetermined value after reduction Others inhibit induction heating device. The detection means is an induction heating device according to claim 1 for detecting a change in the impedance by changing the conduction time of the switching element. The detection means is an induction heating device according to claim 1 for detecting a change in the impedance by changing the conduction period of the switching element. Further comprising a first voltage detection means for detecting a voltage of the resonant capacitor, the sensing means according to claim 1, wherein the first voltage detecting means detects a change in the impedance than the change in voltage detected Induction heating device. To boost the voltage supplied from said power source, said high frequency inverter further comprising a step-up means for supplying said detection means, according to claim 1 for detecting a change in the impedance than the change of the step-up ratio of the step-up means Induction heating device. To boost the voltage supplied from said power source, wherein the boosting means for supplying a high-frequency inverter, further comprising a second voltage detecting means for detecting the voltage boosted by said boosting means, said detecting means, said The induction heating apparatus according to claim 1 , wherein the change in impedance is detected from a change in voltage detected by the second voltage detection means.