JP2010267636A - Induction heating cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To input rated electric power to all load pans to be heated and achieve low-loss operation of an inverter circuit. <P>SOLUTION: Adjustment of a resonance frequency is made by a resonance frequency adjustment means 10, and the resonance frequency is detected by the resonance frequency detecting means 14 according to an output of a load distinction means 9, and a drive frequency of an inverter circuit 3 is varied according to the detected resonance frequency. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an induction heating cooker, and more particularly to an induction heating cooker capable of induction heating all load pans (a magnetic pan and a non-magnetic pan).

  In conventional induction heating cookers, the drive frequency of the inverter circuit is always kept constant regardless of the type of load pan, and the capacity of the resonant capacitor and the gap (interval) between the heating coil and the load pan according to the type of load pan Etc., that is, the resonant frequency of the resonant circuit is adjusted to vary the input power (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-154575 (2nd page, FIG. 1)

  In the conventional induction heating cooker, the resonance frequency is adjusted according to the type of the load pan, but since the drive frequency of the inverter circuit is always constant, the resonance frequency is larger than the drive frequency depending on the type of the load pan. In the case of phase advance operation, the phase advance current flows through the switching element of the inverter circuit, so that the rated power cannot be input and the thermal power becomes insufficient, and the inverter circuit loss increases. There was a problem that it was.

  The present invention has been made to solve the above-described problems, and is capable of supplying rated power to all load pans (magnetic pans and non-magnetic pans) to be heated. Further, the inverter circuit has low loss. An induction heating cooker capable of realizing the operation is obtained.

  An induction heating cooker according to the present invention is an induction heating cooker including a resonance circuit composed of a heating coil and a resonance capacitor, and an inverter circuit that supplies a high-frequency current to the resonance circuit, and is arranged on the upper surface side of the heating coil. A load pan placed on the top plate and heated by supplying a high frequency current to the heating coil, load discriminating means for discriminating the material of the load pan, and adjusting the resonance frequency formed by the resonance circuit It has a resonance frequency adjusting means and a resonance frequency detecting means for detecting the resonance frequency. The resonance frequency adjusting means adjusts the resonance frequency according to the output of the load discriminating means and detects the resonance frequency by the resonance frequency detecting means. The drive frequency of the inverter circuit is changed according to the detected resonance frequency.

  The induction heating cooker according to the present invention adjusts the resonance frequency by the resonance frequency adjustment means according to the output of the load determination means, detects the resonance frequency by the resonance frequency detection means, and inverts the inverter circuit according to the detected resonance frequency. Therefore, the rated power can be input regardless of the type of the load pan, and the increase in the inverter circuit loss due to the phase advance operation can be suppressed.

It is a circuit block diagram of the induction heating cooking appliance which shows Embodiment 1 of this invention. It is a related figure of the resonant frequency and drive frequency of the induction heating cooking appliance which shows Embodiment 1 of this invention. It is a figure which shows an example of the inverter electric current waveform at the time of mounting a magnetic pan in the induction heating cooking appliance which shows Embodiment 1 of this invention. It is a figure which shows an example of the inverter electric current waveform at the time of mounting a nonmagnetic pan in the induction heating cooking appliance which shows Embodiment 1 of this invention. It is a figure which shows an example of the characteristic of an inverter total loss and a thermal power at the time of mounting a magnetic pan in the induction heating cooking appliance which shows Embodiment 1 of this invention. It is a figure which shows an example of the characteristic of an inverter total loss and a thermal power at the time of mounting a nonmagnetic pan in the induction heating cooking appliance which shows Embodiment 1 of this invention. It is a circuit block diagram of the induction heating cooking appliance which shows Embodiment 2 of this invention. It is sectional drawing in a housing | casing of the induction heating cooking appliance which shows Embodiment 3 of this invention. It is a circuit block diagram of the induction heating cooking appliance which shows Embodiment 3 of this invention. It is a circuit block diagram of the induction heating cooking appliance which shows Embodiment 4 of this invention. It is a circuit block diagram of the induction heating cooking appliance which shows Embodiment 5 of this invention. It is a figure which shows an example of the characteristic of an inverter total loss at the time of changing a snubber capacitor capacity | capacitance when a kind of magnetic pan is mounted in the induction heating cooking appliance which shows Embodiment 5 of this invention, and a thermal power. It is a figure which shows an example of the characteristic of an inverter total loss and a thermal power at the time of changing a snubber capacitor capacity | capacitance when a kind of nonmagnetic pan is mounted in the induction heating cooking appliance which shows Embodiment 5 of this invention.

Embodiment 1 FIG.
FIG. 1 is a circuit configuration diagram of an induction heating cooker showing Embodiment 1 of the present invention, FIG. 2 is a diagram showing a relationship between a resonance frequency and a drive frequency of the induction heating cooker, and FIG. FIG. 4 is a diagram showing an example of an inverter current waveform when a magnetic pan is placed, FIG. 4 is a diagram showing an example of an inverter current waveform when a non-magnetic pan is placed on this induction heating cooker, and FIG. 5 is this induction heating Fig. 6 shows an example of inverter total loss and thermal power characteristics when a magnetic pan is placed in a cooker. Fig. 6 shows the inverter total loss and thermal power characteristics when a non-magnetic pan is placed in this induction heating cooker. It is a figure which shows an example.

  In FIG. 1, a smoothing capacitor 4 and an inverter circuit 3 are connected to the output side of a rectifier circuit 2 that rectifies an AC power supply 1. The inverter circuit 3 includes a plurality of switching elements 3a, 3b, 3c, and 3d, and a resonance circuit formed by the heating coil 5 and the resonance capacitor 7 is connected to the output side thereof. Snubber capacitors 8a and 8b are connected in parallel with switching elements 3b and 3d, respectively.

  The switching elements 3 a, 3 b, 3 c, 3 d of the inverter circuit 3 perform switching in response to the output signal of the inverter circuit driver 11 b provided in the control means 11 and are arranged on the top surface side of the heating coil 5. 15 (see FIG. 9 to be described later) induction heating the load pan 6 placed. Here, the drive signal control circuit 11a in the control means 11 determines a switching signal (drive frequency, duty, etc.) based on outputs from the set power generation means 12 and the load determination means 9 for determining the material of the load pan 6. And output to the inverter circuit driver 11b. The resonance frequency adjusting means 10 adjusts the resonance frequency of the resonance circuit based on the output from the load determining means 9 (details regarding the adjustment of the resonance frequency will be described later).

Next, the operation will be described with reference to FIGS.
The resonance frequency f ₀ of the resonance circuit is determined based on the inductance value (hereinafter referred to as L value) of the heating coil 5 generated by placing the load pan 6 on the top plate 15 and the 7 capacitance value (hereinafter referred to as L value) of the resonance capacitor. (Referred to as C value).
f0 = 1 / 2π√LC Equation (1)
Here, if the C value, the heating coil specification (the type of wire, the number of twists, the number of turns), and the gap (distance between the heating coil 5 and the load pan 6, see FIG. 8) are unchanged, the resonance frequency f _{0 of the} resonance circuit. Is different depending on the material of the load pan 6. For example, when a magnetic pan such as an iron pan is placed on the top plate 15, the L value increases (for example, the L value is about 100 μH for an iron pan having a diameter of 200 mm), and a non-magnetic pan such as a SUS304 pan is mounted. When placed, the L value becomes small (for example, the L value becomes about 60 μH in a SUS304 pan having a diameter of 200 mm). From this, it can be seen that the resonance frequency f ₀ of the resonance circuit has a low value (f _{0 (A) in} FIG. 2) in the magnetic pan and a high value (f _{0 (B) in} FIG. 2) in the non-magnetic pan. .

Thus, based on the difference in the value of the resonance frequency f ₀ depending on the material of the load pan 6, the load discriminating means 9 discriminates the type of load pan such as a magnetic pan or a non-magnetic pan, and the control means 11. Sets the drive frequency f ₁ of the inverter circuit according to the determination result. Here, the drive signal control circuit 11a is set to be higher than necessarily the resonance frequency f ₀ of the driving frequency f _1. That is, as shown in FIG. 2, the drive frequency f _{1 (A)} when the magnetic pan is placed is set to f _{0 (A)} <f _{1 (A)} with respect to the resonance frequency f _{0 (A)} . The drive frequency f _{1 (B)} when the nonmagnetic pan is placed is set to f _{0 (B)} <f _{1 (B)} with respect to the resonance frequency f _{0 (B)} . Further, since the relationship between the drive frequencies f _{1 (A)} and f _{1 (B)} is the above-mentioned general f _{0 (A)} <f _{0 (B)} , inevitably f _{1 (A)} <f _{1 (B )} .

By the way, the resonance frequency f ₀ value is designed as follows. When the resonance frequency f ₀ is designed on the basis of a magnetic pot having a large L value (that is, the heating coil specification, C value constant, etc. are determined), the driving frequency f ₁ determined according to the output of the load determination means 9 _{(A) The} resonance frequency f _{0 (A)} is set so that the rated power can be input at ₍ around 20 kHz, which is the lower limit of the Radio Law ₎ . Further, when the resonance frequency f ₀ is designed with reference to a nonmagnetic pan having a small L value, the switching loss of the switching elements 3a, 3b, 3c, and 3d determined according to the output of the load determination means 9 does not increase. The resonance frequency is f _{0 (B)} that does not lead to a phase advance operation with respect to the drive frequency f _{1 (B)} (about 27 kHz to 30 kHz ₎ .

According to the above, when the resonance frequency is designed to be f _{0 (A) based} on the magnetic pan (that is, the heating coil specification, C value constant, etc. are determined), the non-magnetic pan is placed on the top plate 15. In response to the output of the load discriminating means 9, the drive frequency is set to f _{1 (B)} , and the load current shown in FIG. 4 flows through the current observation point in FIG. Next, upon receiving the output (or set drive frequency) of the load discriminating means 9 and performing an arbitrary adjustment by the resonance frequency adjusting means 10 to lower the resonance frequency (f _{0 (B) small} ), FIG. ) Phase advance operation can be avoided as shown in FIG. The total inverter loss corresponding to the current waveform of FIG. 4 is shown in FIG. 6. By adjusting the resonance frequency f _{0 (B)} to be low (f _{0 (B) small} ), low loss operation can be performed. I understand.

On the other hand, when the resonance frequency is designed to be f _{0 (B) based} on the nonmagnetic pan (that is, the heating coil specification, C value constant, etc. are determined), when the magnetic pan is placed on the top plate 15, In response to the output of the load discriminating means 9, the drive frequency is set to f _{1 (A)} , and the load current shown in FIG. 3 flows through the current observation point in FIG. Next, upon receiving an output (or a set drive frequency) of the load discriminating means 9 and performing an arbitrary adjustment to increase the resonance frequency (f _{0 (A) large} ) by the resonance frequency adjusting means 10, FIG. The operation is as shown in FIG. The total inverter loss corresponding to the current waveform of FIG. 3 is shown in FIG. 5, but the rated power operation (2.5 kW input in FIG. 5) can be achieved by adjusting the resonance frequency to be high (f _{0 (A) large} ). It becomes possible.

  As described above, the drive frequency of the inverter circuit is changed according to the output of the load determination means 9 at the start of operation, and the resonance frequency formed by the resonance circuit is adjusted by the resonance frequency adjustment means 10 with an arbitrary value. Therefore, the rated power can be input regardless of the type of the load pan, and the increase in the inverter circuit loss due to the phase advance operation can be suppressed.

Embodiment 2. FIG.
In the first embodiment, the drive frequency of the inverter circuit is changed according to the output of the load determination means 9 at the start of operation, and the resonance frequency adjustment means is determined according to the drive frequency (according to the output of the load determination means 9). In the second embodiment, the resonance frequency is detected by the resonance frequency detecting means after the resonance frequency adjusting means is provided, and the resonance frequency is adjusted by the resonance frequency adjusting means. The thing which changes the drive frequency of an inverter circuit according to is shown.

  FIG. 7 is a circuit configuration diagram of an induction heating cooker showing Embodiment 2 of the present invention. In the figure, the same reference numerals are given to the same or corresponding parts as those in the first embodiment, and the description will be omitted. Resonance frequency detection means 14 for detecting the resonance frequency is provided on the resonance circuit formed by the heating coil 5 and the resonance capacitor 7, and the output of the resonance frequency detection means 14 is connected (input) to the drive signal control circuit 11a. In the second embodiment, the difference from the first embodiment is that the output of the load determination means 9 is not connected (inputted) to the drive signal control circuit 11a.

Next, the operation will be described.
When the load pan 6 is placed on the top plate 15 and the type (material) of the load pan 6 such as a magnetic pan or a non-magnetic pan is discriminated by the load discriminating means 9, the resonance frequency adjusting means 10 is selected according to the type. Thus, the resonance frequency of the resonance circuit is uniquely adjusted.
Here, when the load pan 6 is made of a material such as a magnetic pan, the rated power operation can be performed by adjusting the resonance frequency f _{0 (A) to} be high as in the first embodiment. . For this reason, the resonance frequency adjusting means 10 uniquely adjusts the resonance frequency to be higher (for example, to increase f _{0 (A)} to f _{0 (A))} when the material is determined to be a material such as a magnetic pot. Do.
Further, when the load pan 6 is made of a material such as a non-magnetic pan, it is possible to perform a low loss operation by adjusting the resonance frequency f _{0 (B) to} be low as in the first embodiment. Become. For this reason, the resonance frequency adjusting means 10 uniquely adjusts the resonance frequency to be lower (for example, to reduce f _{0 (B)} to f _{0 (B))} when it is determined that the material is a non-magnetic pan or the like. To do.

After the resonance frequency is uniquely adjusted by the resonance frequency adjusting means 10 as described above, the resonance frequency formed by the resonance circuit is detected by the resonance frequency detecting means 14. Here, the resonance frequency detecting means 14 has a configuration for detecting the resonance frequency by detecting a load current (resonance current) flowing in the resonance circuit. As a specific detection method, for example, a detection load current is supplied to the inverter circuit 3 by a command of the control means 11 at the start of operation of the induction heating cooker, that is, an inverter circuit configured by the switching elements 3a to 3d. In this case, first, the switching elements 3a and 3d or the switching elements 3c and 3b are supplied by being turned on by a command of the control means 11, and then the switching elements 3a and 3c are turned off and the switching elements 3b and 3d are turned on. Since the resonance current continues to flow through the resonance circuit, the resonance frequency is detected by detecting the zero cross point of the resonance current.
As another method of detecting the resonance frequency, a load current for detection is supplied to the inverter circuit 3 by the command of the control means 11 at the start of the operation of the induction heating cooker, and then the switching elements 3a and 3d and the switching elements 3c and 3b It is also possible to detect the frequency at which the load current value (peak value, effective value, etc.) flowing through the resonance circuit becomes maximum when the frequency for turning on and off is swept in combination.

When the resonance frequency f ₀ is detected by the other method described above, the drive signal control circuit 11a determines the drive frequency to the inverter circuit 3 according to the detected resonance frequency, and the inverter circuit 3 is connected to the inverter circuit 3 via the inverter circuit driver 11b. Supply a switching signal. Here, the drive frequency f ₁ is determined by the relationship of f ₁ > f ₀ regardless of the type of load pan as shown in FIG.

  As described above, the resonance frequency adjustment unit first uniquely adjusts the resonance frequency in accordance with the load determination unit output at the start of operation, and the control unit 11 drives the inverter circuit 3 in accordance with the adjusted resonance frequency. Therefore, the operation point is determined not on the resonance frequency side but on the drive frequency side, and the adjustment value of the resonance frequency can be uniquely determined as compared with the first embodiment, and the control is performed. The method becomes easy.

Embodiment 3 FIG.
In contrast to the first and second embodiments described above, an embodiment in which a specific method of the resonance frequency adjusting means is presented will be described next. FIG. 8 shows a cross-sectional view inside the casing of the induction heating cooker in such a case. FIG. 9 shows a circuit configuration diagram of the induction heating cooker in such a case.
In FIG. 8, the load pan 6 is heated by being placed on a top plate 15 disposed on the upper surface side of the heating coil 5, and a gap (referred to as a gap) is provided between the heating coil 5 and the top plate 15. ) And is used for cooling the heating coil 5 or the like. Gap varying means 16 for varying the gap length is provided at the lower stage of the heating coil 5 and is fixed by a housing sheet metal 17.

Next, the operation will be described.
If the load pan type and heating coil specifications (wire, number of twists, number of turns) are unchanged, the L value takes different values depending on the gap. When the gap is increased, the L value is increased, and when the gap is decreased, the L value is decreased. Therefore, when the load determining means 9 determines that the load pan 6 is made of a material such as a magnetic pot, the gap variable means 16 performs the gap. To reduce the L value and adjust the resonance frequency higher. When it is determined that the load pan 6 is made of a material such as a non-magnetic pan, the gap variable means 16 increases the gap to increase the L value, and the resonance frequency is adjusted to be low.
Specifically, the gap varying means 16 can be configured using an actuator (motor, air cylinder, hydraulic cylinder, piezo element, etc.).
Note that the gap variable means 16 has either the control sequence of the first embodiment or the second embodiment (the drive frequency setting of the inverter circuit according to the load pan type after the load determination by the load determination means 9, and Note that the present invention is also applicable to a sequence until the resonance frequency is adjusted.

  In addition to changing the gap by the gap changing means 16 having the structure shown in FIG. 8, the entire top plate 15 is driven up and down with respect to the housing sheet metal 17 to change the gap (not shown) or the load pan of the top plate 15. Only the mounting portion is driven up and down to adjust the resonance frequency by changing the drive frequency by a method such as variable gap (not shown), and further by changing the capacitance of the resonance capacitor (not shown), along with the drive frequency setting. It should be mentioned that there is a method of adjusting the resonance frequency.

  As described above, since the gap variable means using an actuator or the like is used for the resonance frequency adjustment, it is possible to obtain an induction heating cooker having a simple structure design and a small-scale resonance frequency adjustment means. .

Embodiment 4 FIG.
In contrast to the above-described embodiment, an embodiment in which phase detection means for detecting the phase state of the load current that next flows to the inverter circuit is provided in the induction heating cooker will be described.
FIG. 10 shows a circuit configuration diagram of the induction heating cooker in such a case.
In the figure, a phase detector 14 is provided at the output of the rectifier circuit 2 and detects the phase state of the load current flowing through the switching elements (3a to 3d) of the inverter circuit 3. The output of the phase detection means 19 is connected to the resonance frequency adjustment means 10 and / or the drive signal control circuit 11a to adjust the resonance frequency according to the phase detection result and / or change the drive frequency. I will let you.
Other configurations are the same as those of the first embodiment, and the description thereof is omitted.

Next, the operation will be described.
First, the drive frequency of the inverter circuit 3 is changed according to the output of the load discriminating means 9 at the start of operation, and the resonance frequency formed by the resonance circuit is adjusted by the resonance frequency adjusting means 10. The control sequence here may be either the first embodiment or the second embodiment, that is, the order in which the resonance frequency adjustment and the drive frequency setting are performed does not matter. Here, when the load pan is made of a material such as a non-magnetic pan, the resonance frequency adjustment means 10 and the load discrimination means 9 adjust the resonance frequency and set the drive frequency of the inverter circuit 3, although FIG. ) May lead to the switching element. This is because the resonance frequency f ₀ after adjustment of the resonance frequency by the resonance frequency adjusting means 10 is too high, or the drive frequency f ₁ setting by the load determining means 9 is too low.
When the phase detection means 19 detects a phase advance current as shown in FIG. 4A, the phase detection means 14 sends a command to the resonance frequency adjustment means 10 so that the resonance frequency f _{0 at} which the phase advance current does not flow. ₀ lower, and (or) leading current does not flow the driving frequency f ₁ and so as to drive signal control circuit may flow inverter circuit 3 binary phase current by increasing the feed f ₁ directly command to 11a To avoid.

  Here, since the phase advance current has a surge shape with a large peak as shown in FIG. 4A, a method of detecting the current by setting, for example, a current threshold (upper limit value) as the phase detection means 19 is conceivable. .

  In the case of the inverter circuit configuration shown in FIG. 10, the phase detection means 19 is provided at the output of the rectifier circuit 2 shown in FIG. 10, or the output line of the switching element 3a (collector line in the case of the switching element shown in FIG. 10), or It should be noted that the same effect can be obtained even if provided on the output line of the switching element 3c (or the collector line in the case of the switching element shown in FIG. 10).

  As described above, since the phase detection means for detecting the phase state of the load current flowing to the inverter circuit is provided, when the load pan is made of a material such as a non-magnetic pan, the operation in which the phase advance current does not flow The point can be set reliably, and it is possible to reliably avoid an operation that significantly increases the loss.

Embodiment 5 FIG.
As means for further reducing the loss of the inverter circuit, an embodiment in the case of changing the snubber capacitor capacity in addition to the first to fifth embodiments will be described.
FIG. 11 shows a circuit configuration diagram of the induction heating cooker in such a case. FIG. 12 shows an example of the inverter total loss-heating power characteristic when the snubber capacitor capacity is changed when a kind of magnetic pot (called pot A) is placed, and FIG. 13 shows a kind of non-magnetic pot (called pot B). 7 shows an example of inverter total loss-thermal power characteristics when the snubber capacitor capacity is changed when is mounted.

In FIG. 11, the outputs of the load discriminating means 9 and the set power generating means 12 are connected to the drive signal control circuit 11a (similar to the previous embodiment), and the snubber capacitor switching driver for driving the snubber capacitor switching means 13 is used. 11c is configured to receive a command from the drive signal control circuit 11a.
Other configurations are the same as those of the first embodiment, and the description thereof is omitted.

Next, the operation will be described with reference to FIGS.
As shown in FIG. 11, snubber capacitors (8a and 8b in FIG. 11) are connected in parallel to the switching elements of the inverter circuit 3 configured by 3a to 3d for the purpose of noise reduction and loss reduction. When the set power is large, the switching element loss is reduced as the snubber capacitor capacity is increased. Conversely, when the set power is small, the switching element loss is reduced as the snubber capacitor capacity is decreased.

FIG. 12 shows an example of inverter total loss-thermal power characteristics when the load pan is made of a material such as a magnetic pan. When the thermal power (= set power) is large, it is better to increase the snubber capacitor capacity (for example, 0.3 μF). It can be seen that the total inverter loss is small. This is because when the set power is large, the voltage rise at the time of switching element 3b turn-off becomes slower and the turn-off loss of switching element 3b is reduced when the snubber capacitor capacity is increased. On the other hand, when the thermal power (= set power) is small, it can be seen that the total loss of the inverter is smaller when the snubber capacitor land is made smaller (for example, 0.064 μF). This is because when the set power is small, the smaller the snubber capacitor capacity, the smaller the current flowing from the output of the rectifier circuit 2 to the switching element 3a when the switching element 3a is turned on, and the conduction loss of the switching element 3a is reduced.
In particular, when the load pan in FIG. 13 is made of a material such as a non-magnetic pan, the difference in inverter total loss due to the difference in snubber capacitor capacity becomes obvious.

  Therefore, the load discriminating means 9 discriminates the type of the load pan (magnetic pan or non-magnetic pan, etc.) and drives based on the information on both the output of the set power generation means 12 (ie, the thermal power set value by the user) and the load pan type. The signal control circuit 11a turns on / off the snubber capacitor switching means 13 via the snubber capacitor switching driver 11c. Specifically, for example, from FIG. 12, when the load discriminating means 9 determines that the load pan is made of a material such as a magnetic pan, the set power is about 1.5 kW or more, the snubber capacitor capacity is large, and the set power is about 1.5 kW or less. Snubber capacitor capacity is small. Further, for example, from FIG. 13, when the load discriminating means 9 determines that the load pan is made of a material such as a non-magnetic pan, the snubber capacitor capacity is large when the set power is about 0.7 kW or more, and the snubber capacitor is set when the set power is about 0.7 kW or less. Small capacity.

  As described above, since the snubber capacitor capacity switching means is provided and the capacity of the snubber capacitor is switched based on the information of both the load pan type and the set power, in addition to the effects of the first to fourth embodiments, It is possible to further reduce the total inverter loss.

  In addition, the inverter circuit configuration in the above embodiment can reduce the load current and reduce the inverter loss by adopting the full bridge configuration as shown in FIG. 1, FIG. 7, FIG. 9, FIG. However, it should be noted that there is no difference in the contents of the present invention even when the inverter circuit has a configuration other than the full-bridge configuration.

  Examples of utilization of the present invention include an induction heating cooker, a water heater using induction heating, a rice cooker, and the like.

  DESCRIPTION OF SYMBOLS 1 AC power supply, 2 Rectifier circuit, 3 Inverter circuit (switching element), 4 Smoothing capacitor, 5 Heating coil, 6 Load pan, 7 Resonance capacitor, 8 Snubber capacitor, 9 Load discrimination means, 10 Resonance frequency adjustment means, 11 Control means , 11a Drive signal control circuit, 11b Inverter circuit driver, 11c Snubber capacitor switching driver, 12 Set power generation means, 13 Snubber capacitor switching means, 14 Resonance frequency detection means, 15 Top plate, 16 Gap variable means, 17 Housing Sheet metal, 19 phase detection means.

Claims (7)

In an induction heating cooker comprising a resonance circuit composed of a heating coil and a resonance capacitor, and an inverter circuit that supplies a high-frequency current to the resonance circuit,
A load pan placed on a top plate arranged on the upper surface side of the heating coil and heated by supplying a high frequency current to the heating coil,
Load discriminating means for discriminating the material of the load pan;
Resonance frequency adjusting means for adjusting the resonance frequency formed by the resonance circuit;
Resonance frequency detection means for detecting the resonance frequency,
The resonance frequency is adjusted by the resonance frequency adjusting means according to the output of the load determining means, and the resonance frequency is detected by the resonance frequency detecting means, and the drive frequency of the inverter circuit is changed according to the detected resonance frequency. An induction heating cooker characterized by being made.   The induction cooking device according to claim 1, wherein the resonance frequency is adjusted by the resonance frequency adjusting means by changing a distance between the top plate and the heating coil.   The induction heating cooker according to claim 2, wherein the interval is varied using an actuator.   The induction heating cooker according to claim 1, wherein the resonance frequency is adjusted by the resonance frequency adjusting means by changing a capacity of the resonance capacitor.   Phase detection means for detecting the phase state of the load current flowing to the inverter circuit is provided, and when the phase detection means detects the phase advance current of the inverter circuit, resonance is performed by the resonance frequency adjustment means so that no phase advance current flows. The induction heating cooker according to any one of claims 1 to 4, wherein a frequency is adjusted or a drive frequency of the inverter circuit is changed by the phase detection means. A snubber capacitor connected to a switching element on a low potential side among the switching elements connected in series constituting the resonance circuit and the inverter circuit;
Snubber capacitor switching means connected to the snubber capacitor, and further comprising:
The snubber capacitor is
Consists of multiple capacitors connected,
The induction heating cooker according to any one of claims 1 to 5, wherein the snubber capacitor switching means switches the number of capacitors to be connected among the plurality of capacitors to change the capacity. Control means for controlling the snubber capacitor switching means based on the determination of the load determination means;
A set power generation unit that outputs information on the set power set by the user to the control unit;
The control means includes
7. The induction heating cooker according to claim 6, wherein the snubber capacitor switching unit is controlled based on the output of the load determination unit and information on the set power to change the capacity of the snubber capacitor.

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