Induction heating device

Abstract

To enable the fire power of each object to be heated to be adjusted to desired magnitude even while eliminating noise to be generated in the case of simultaneously heating a plurality of objects to be heated.SOLUTION: An induction heating device includes at least two heating coils 1 for inductively heating an object to be heated, an inverter device 2 provided corresponding to the respective heating coils 1 to supply power to the corresponding heating coils, and control equipment 3 for controlling the inverter device 2. The control equipment 3 compares drive frequencies being frequencies of power to be supplied to at least two heating coils 1, changes the drive frequency of a higher frequency side coil 1 having a high drive frequency into a drive frequency of a lower frequency side coil 1 having a low drive frequency, controls the inverter device 2 corresponding to the lower frequency side coil 1 with a prescribed first control mode, and controls the inverter device 2 corresponding to the higher frequency side coil 1 with a second control mode different from the first control mode.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an induction heating device that inductively heats an object to be heated. [Background technology]

[0002] As shown in Patent Document 1, this type of induction heating device is used in, for example, an induction cooker that heats objects to be heated, such as cooking pots, and some devices are equipped with multiple heating coils so that multiple objects to be heated can be induction heated simultaneously.

[0003] When multiple heating coils are used simultaneously, the resonance curves of the objects to be heated are different, as shown in Figure 10. Therefore, if the driving frequencies of the heating coils become different by adjusting the heating power of each object to be heated (for example, around 10 kHz), noise will be generated due to the frequency difference.

[0004] When such noise occurs, it is possible to eliminate the noise by adjusting the heating power to change the frequency difference, but in this case, the problem arises that the desired heating power cannot be obtained. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-103674 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, the present invention has been made to solve all of the above problems at once, and its main objective is to eliminate the noise that occurs when heating multiple heated objects simultaneously, while making it possible to adjust the heating power of each heated object to the desired level. [Means for solving the problem]

[0007] That is, the induction heating device of the present invention comprises at least two heating coils for induction heating an object to be heated, inverter devices provided corresponding to each of the heating coils and supplying power to the corresponding heating coil, and a control device for controlling the inverter devices, wherein the control device compares the drive frequencies, which are the frequencies of the power supplied to the at least two heating coils, and changes the drive frequency of the heating coil having the higher drive frequency (hereinafter also referred to as the high-frequency side coil) to the drive frequency of the heating coil having the lower drive frequency (hereinafter also referred to as the low-frequency side coil), and controls the inverter device corresponding to the low-frequency side coil in a predetermined first control mode, and controls the inverter device corresponding to the high-frequency side coil in a second control mode different from the first control mode.

[0008] With an induction heating device configured in this manner, the drive frequency of the high-frequency side coil is matched to the drive frequency of the low-frequency side coil, thereby preventing noise from occurring due to frequency differences.Furthermore, since the control mode of the inverter device corresponding to the high-frequency side coil is different from the control mode of the inverter device corresponding to the low-frequency side coil, it is possible to adjust the heating power of each of the two heating coils to the desired level.

[0009] A specific embodiment may be one in which the first control mode is a control for turning on and off switching elements constituting the inverter device at a fixed duty ratio, and the second control mode is a control for turning on and off switching elements constituting the inverter device at a variable duty ratio. In this case, the second control mode turns the switching element on and off with a variable duty ratio, and by changing this duty ratio, the heating power of the high frequency side coil can be adjusted to a desired level.

[0010] It is preferable that the control device is configured to switch the control of the inverter device corresponding to the high-frequency side coil from the second control mode to a third control mode when the output of the high-frequency side coil does not reach the target output in the second control mode, and that the third control mode is a control that switches the drive frequency of the high-frequency side coil between a first drive frequency, which is the drive frequency of the low-frequency side coil, and a second drive frequency obtained by adding a predetermined frequency to the first drive frequency. In this case, even if the heating power of the high-frequency coil cannot be adjusted to the desired level by changing the duty ratio in the second control mode, the desired heating power can be obtained by switching from the second control mode to the third control mode.

[0011] In the above-described third control mode, when the drive frequency of the high-frequency side coil is switched from the first drive frequency to the second drive frequency, a frequency difference occurs with respect to the low-frequency side coil. Therefore, it is preferable that the predetermined frequency is 15 kHz or higher. In this way, as described above, it is possible to switch from the second control mode to the third control mode to adjust the heating power to a desired level, while making it difficult for the frequency difference to be recognized as noise.

[0012] In the third control mode described above, as a result of trying to bring the output of the high-frequency coil closer to the target output, the drive time at the second drive frequency may become too long. In this case, the frequency difference between the drive frequency of the low-frequency coil and the drive frequency of the high-frequency coil should be large, and even if the two heating coils are driven at different drive frequencies, it should be difficult to recognize it as noise. Therefore, in the third control mode, when the ratio of the drive time at the second drive frequency to the drive time at the first drive frequency exceeds a threshold value, it is preferable that the control device switches from the third control mode to a control mode in which the at least two heating coils are driven at different drive frequencies. In this way, it is possible to adjust the heating power of both the low-frequency coil and the high-frequency coil to a desired level, while eliminating noise caused by the frequency difference between them.

[0013] When the drive frequency of the heating coil other than the low-frequency side coil becomes lower than the drive frequency of the low-frequency side coil, it is preferable that the control device changes the drive frequency of the low-frequency side coil to the drive frequency of the other heating coil, switches the control mode of the inverter device corresponding to the low-frequency side coil to the second control mode, and switches the inverter device corresponding to the other heating coil to the first control mode. In this way, even if the heating power of multiple heating coils is adjusted and the magnitude relationship of the driving frequencies of those heating coils is reversed, the effect of the control operation described above can be ensured, namely, the effect of being able to adjust the heating power of each heating coil to the desired level while eliminating the noise that occurs when multiple heated objects are heated simultaneously.

[0014] If the adjustable ranges of the drive frequencies of multiple heating coils are different, as shown in Figure 11, when the drive frequency of each heating coil is set to the lowest frequency, the drive frequency of some heating coils will be lower than the frequency at the peak of the resonance curve of the heated object (the frequency marked with an asterisk in Figure 11), which raises concerns about damage to the switching elements due to hard switching. Therefore, it is preferable that the adjustable range of the drive frequency of each of the at least two heating coils is higher than the peak frequency of the resonance curve of the object to be heated by each heating coil. This can prevent the damage caused by the hard switching described above. [Effects of the Invention]

[0015] According to the present invention configured in this manner, it is possible to adjust the heating power of each of the objects to a desired level while eliminating the noise that occurs when multiple objects to be heated are heated simultaneously. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing the overall configuration of an induction heating device according to an embodiment of the present invention; [Figure 2] 4 is a flowchart showing the operation of the control device in the embodiment. [Figure 3] FIG. 4 is a reference diagram for explaining a first control mode in the embodiment. [Figure 4] 6 is a graph showing a range in which the driving frequency of the heating coil can be changed in the embodiment; [Figure 5] FIG. 10 is a reference diagram for explaining a second control mode in the embodiment. [Figure 6] FIG. 10 is a reference diagram for explaining a third control mode in the embodiment. [Figure 7] 6 is a graph showing changes over time in the control content of the control device in the embodiment. [Figure 8] 6 is a graph showing changes over time in on-duty ratio and frequency in the embodiment; [Figure 9] 10 is a flowchart showing the operation of a control device in another embodiment. [Figure 10] FIG. 10 is a reference diagram for explaining the relationship between the resonance curve and noise. [Figure 11] 10 is a reference diagram showing the adjustable range of the driving frequency of the heating coil. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of an induction heating device according to the present invention will be described with reference to the drawings.

[0018] The induction heating device 100 according to this embodiment is used in, for example, an IH cooker, and is used to inductively heat an object to be heated, such as a cooking pot.

[0019] Specifically, as shown in FIG. 1, the induction heating device 100 includes a heating coil 1 that induction heats an object to be heated, an inverter device 2 that supplies power to the heating coil 1, and a control device 3 that controls the inverter device 2.

[0020] Furthermore, as shown in FIG. 1, the induction heating device 100 includes an LC parallel resonant circuit 4 consisting of a resonant capacitor connected in series to the heating coil 1 and a resonant coil element connected in parallel to the resonant capacitor, a current detection unit I that detects the current supplied to the inverter device 2, and a voltage detection unit V that detects the voltage supplied from the commercial power source to the inverter device 2.

[0021] The heating coil 1 is provided below a top plate (not shown) on which a cooking pot or the like is placed, and induction heats the cooking pot via the top plate. In this embodiment, two heating coils 1 are provided. However, the number of heating coils 1 is not limited to this, and it is sufficient that at least two heating coils are provided.

[0022] The inverter devices 2 are provided corresponding to the respective heating coils 1, and specifically, are configured with an inverter circuit 21 that supplies high-frequency current to the heating coils 1, and a drive circuit 22 that drives the inverter circuit 21.

[0023] The inverter circuit 21 converts the voltage supplied from a commercial power source into high-frequency current and supplies high-frequency current to the heating coil 1, and here is of a half-bridge type using a switching element SW. However, the specific configuration of the inverter circuit 21 may be changed as appropriate, for example, to a full-bridge type.

[0024] The drive circuit 22 operates the switching element SW that constitutes the inverter circuit 21, and switches the switching element SW on and off based on a control signal from the control device 3, which will be described later.

[0025] The control device 3 controls the inverter device 2 so that the object to be heated is heated with a desired heating power, and controls the drive frequency, which is the frequency of the power supplied from the inverter device 2 to the heating coil 1.

[0026] As shown in FIG. 1, the control device 3 of this embodiment has a function as an individual control unit 31 that controls each inverter device 2, and a function as a main control unit 32 that controls these individual control units 31 in an integrated manner.

[0027] The individual control unit 31 functions as a power calculation unit 311 that calculates the actual power (i.e., the actual output) based on the detected current and voltage detected by the current detection unit I and voltage detection unit V described above, and an inverter control unit 312 that controls the inverter device 2 so that this actual voltage approaches the target voltage (i.e., the target output).

[0028] The main control unit 32 is a controller operated by the user, and functions as a power command unit 321 that outputs the power (i.e., output) corresponding to the heating power of the heating coil set by the user to the inverter control unit as the target power, and a control mode command unit 322 that switches the control mode by the inverter control unit 312.

[0029] A specific control operation of the control device 3 will be described below with reference to FIG. For ease of explanation, one of the two heating coils 1 will be referred to as the first heating coil 1A and the other as the second heating coil 1B, the inverter device 2 that supplies power to the first heating coil 1A will be referred to as the first inverter device 2A, and the inverter device 2 that supplies power to the second heating coil 1B will be referred to as the second inverter device 2B. When distinguishing between the individual control units 31, the individual control unit 31 that controls the first inverter device 2A will be referred to as the first control unit 3A, and the individual control unit 31 that controls the second inverter device 2B will be referred to as the second control unit 3B.

[0030] Here, a case will be described in which the first burner corresponding to the first heating coil 1A is started, and then the second burner corresponding to the second heating coil 1B is started.

[0031] First, the power command unit 321 of the main control unit 32 instructs the first control unit 3A and the second control unit 3B on the target power (for example, wattage) that is the target output corresponding to the thermal power of each burner.

[0032] Based on instructions from this main control unit 32, as shown in FIG. 2, the first control unit 3A adjusts the driving frequency of the power supplied from the first inverter device 2A to the first heating coil 1A (S1), and the second control unit 3B adjusts the driving frequency of the power supplied from the second inverter device 2B to the second heating coil 1B based on instructions from the main control unit 32 (S2).

[0033] More specifically, in each of the first control unit 3A and the second control unit 3B, the inverter control unit 312 controls the drive frequency of each inverter device 2 so that the actual power calculated by the power calculation unit 311 becomes the target power.

[0034] At this point, the first control unit 3A and the second control unit 3B control the respective inverter devices 2 in a predetermined first control mode, and the driving frequencies of the respective heating coils 1A and 1B are different from each other. For convenience of explanation, the driving frequency of the first heating coil 1A is designated as Fleq A, and the driving frequency of the second heating coil 1B is designated as Fleq B, as shown in FIG.

[0035] 3, this first control mode is a control that turns on / off the switching element SW that constitutes the inverter device 2 at a fixed duty ratio, and in this case is PFM (pulse frequency modulation) control with an on-duty ratio fixed at 50%. However, the fixed duty ratio is not limited to 50% and may be changed as appropriate as long as the high side and low side have a complementary relationship, for example, 60% for the high side and 40% for the low side, and the specific control mode is not limited to PFM control and may be PWM (pulse width modulation) control or the like.

[0036] Next, the control mode command unit 322 of the main control unit 32 acquires the drive frequency Fleq A of the first heating coil 1A and the drive frequency Fleq B of the second heating coil 1B, and compares them (S3).

[0037] Hereinafter, of the first heating coil 1A and the second heating coil 1B, the one with the higher driving frequency will be referred to as the high-frequency coil, and the one with the lower driving frequency will be referred to as the low-frequency coil.

[0038] Then, the control mode command unit 322 commands the inverter control unit 312 that controls the high frequency side coil to change the drive frequency of the high frequency side coil to the drive frequency of the low frequency side coil (S4, S5).

[0039] As a result, the drive frequencies of the first heating coil 1A and the second heating coil 1B become equal (hereinafter, this drive frequency will be referred to as the first drive frequency).

[0040] Here, as shown on the left side of Figure 4, if the adjustable ranges of the drive frequencies of the first heating coil 1A and the second heating coil 1B are different, when the drive frequency of the high-frequency side coil is matched to the frequency of the low-frequency side coil, the drive frequency of the high-frequency side coil may become lower than the frequency at the peak of the resonance curve (the frequency indicated by the star in Figure 4), which raises concerns about damage to the switching element SW due to hard switching.

[0041] Therefore, in this embodiment, as shown on the right side of Figure 4, the number of turns and resonance capacitor of each heating coil 1 are adjusted so that the adjustable range of the drive frequency of the first heating coil 1A is higher than the frequency at the peak of the resonance curve of the object to be heated by the second heating coil 1B, and the adjustable range of the drive frequency of the second heating coil 1B is higher than the frequency at the peak of the resonance curve of the object to be heated by the first heating coil 1A.

[0042] In this way, when the drive frequencies of the first heating coil 1A and the second heating coil 1B are made equal, the drive frequency of the high-frequency coil is reduced from the initial drive frequency (the frequency of S1 or S2) to the first drive frequency. As a result, the heating power of the high frequency side coil becomes greater than the desired heating power, and therefore control to reduce the heating power becomes necessary.

[0043] Therefore, the control device 3 of this embodiment is configured to maintain the control of the inverter device 2 corresponding to the low-frequency side coil in a first control mode, while switching the control of the inverter device 2 corresponding to the high-frequency side coil to a second control mode different from the first control mode (S4, S5).

[0044] As shown in FIG. 5, this second control mode is a control in which the switching elements SW constituting the inverter device 2 are turned on and off with a variable duty ratio, and is an asymmetric control in which the on-duty ratio of the high-side switching element SW is made different from the on-duty ratio of the low-side switching element SW.

[0045] Specifically, in this second control mode, the inverter control unit 312 compares the actual power, which is the actual power supplied to the high-frequency side coil, with the target power corresponding to the target thermal power, and reduces the on-duty ratio of the high-side switching element SW so that the actual power matches the target power, in other words, so that the output of the high-frequency side coil matches the target output.

[0046] However, in this control, if the on-duty ratio of the high-side switching element SW falls below 30%, for example, in this embodiment, this may lead to a failure of the switching element SW. Note that the lower limit of the on-duty ratio that may cause a failure of the switching element SW is not limited to 30%, but varies depending on the device configuration.

[0047] Therefore, in this embodiment, the on-duty ratio of the high-side switching element SW can be changed to between 30% and 50%, so that the on-duty ratio of the low-side switching element SW is 100% minus the on-duty ratio of the high-side switching element SW.

[0048] In this way, when the on-duty ratio of the high-side switching element SW is reduced and the actual power of the high-frequency side coil matches the target power, the output of the high-frequency side coil matches the target output, thereby adjusting the heating power of the burners corresponding to the first heating coil 1A and the second heating coil 1B to the desired level.

[0049] On the other hand, if the actual power of the high-frequency side coil does not reach the target power, i.e., the output of the high-frequency side coil does not reach the target output, even though the on-duty ratio of the high-side switching element SW is lowered to the lower limit of the changeable range (here, 30%), it means that the heat power of the burner corresponding to the high-frequency side coil has not been adjusted to the desired level.

[0050] Therefore, in this case, the control mode command unit 322 of this embodiment issues a command to the inverter control unit 312 to switch the control of the inverter device 2 corresponding to the high frequency side coil from the second control mode to a third control mode.

[0051] As shown in Figure 6, this third control mode is a control in which the drive frequency of the high-frequency side coil is switched between the above-mentioned first drive frequency and a second drive frequency obtained by adding a predetermined frequency to the first drive frequency at a predetermined cycle.

[0052] In this third control mode, when the drive frequency of the high-frequency side coil switches from the first drive frequency to the second drive frequency, the drive frequency of the low-frequency side coil remains at the first drive frequency, resulting in a frequency difference between the drive frequencies of the two coils.

[0053] If this frequency difference were, for example, about 10 kHz, there would be a concern that noise would be generated due to this frequency difference, so in this embodiment, the above-mentioned predetermined frequency is set to 15 kHz or higher.

[0054] In this third control mode, the inverter control unit 312 is configured to change the ratio between the drive time of the first drive frequency and the drive time of the second drive frequency included in one cycle, and specifically, the drive time of the second drive frequency is extended so that the actual power of the high-frequency side coil matches the target power, in other words, so that the output of the high-frequency side coil matches the target output.

[0055] In this way, when the drive time of the second drive frequency is extended and the actual power of the high-frequency side coil matches the target power, the output of the high-frequency side coil matches the target output, thereby adjusting the heating power of the burners corresponding to the first heating coil 1A and the second heating coil 1B to the desired level.

[0056] On the other hand, in this third control mode, as a result of trying to bring the actual power of the high-frequency coil closer to the target power, the drive time at the second drive frequency may become too long. In this case, the frequency difference between the drive frequency of the low-frequency coil and the drive frequency of the high-frequency coil should be large, and even if the two heating coils 1 are driven at different drive frequencies, it should be difficult to recognize it as noise.

[0057] Therefore, when the ratio of the drive time at the second drive frequency to the drive time at the first drive frequency exceeds a threshold value, the control mode command unit 322 issues a command to the inverter control unit 312 to switch from the third control mode to a control mode in which the first heating coil 1A and the second heating coil 1B are driven at different drive frequencies.

[0058] In this embodiment, the control mode after this switching is the first control mode, and the switching element SW constituting the first inverter device 2A and the switching element SW constituting the second inverter device 2B are each PFM controlled at the same fixed duty ratio.

[0059] By the above control, as shown in FIG. 7, the drive frequency of either the first heating coil 1A or the second heating coil 1B is controlled by the first control mode, and the drive frequency of the other is controlled by the first to third control modes.

[0060] As a result, as shown in FIG. 8, while the on-duty ratio of the switching element SW fluctuates, the drive frequency of the first heating coil 1A and the drive frequency of the second heating coil 1B are synchronized, and the heat power of the burners corresponding to the first heating coil 1A and the second heating coil 1B is adjusted to the desired magnitude.

[0061] According to the induction heating device 100 configured in this manner, the drive frequency of the high-frequency side coil is matched to the drive frequency of the low-frequency side coil, so that it is possible to prevent noise from occurring due to frequency differences. Furthermore, the control mode of the inverter device 2 corresponding to the high-frequency side coil is switched to a second control mode or a third control mode which is different from the first control mode of the inverter device 2 corresponding to the low-frequency side coil, so that it is possible to adjust the heating power of each of the two heating coils 1 to the desired magnitude.

[0062] The present invention is not limited to the above-described embodiment.

[0063] For example, a change in the heating power of a plurality of burners may reverse the magnitude relationship between the drive frequencies of a plurality of heating coils 1. Even in such a case, the control device 3 may operate as shown in the flowchart of FIG. 9 so as to be able to adjust the heating power of each heating coil 1 to a desired level while eliminating noise.

[0064] In other words, when the drive frequency of a heating coil 1 other than the low-frequency side coil becomes lower than the drive frequency of the low-frequency side coil, the control device 3 is configured to change the drive frequency of the low-frequency side coil to the drive frequency of the other heating coil 1, switch the control mode of the inverter device 2 corresponding to the low-frequency side coil to the second control mode, and switch the inverter device 2 corresponding to the other heating coil 1 to the first control mode. The other heating coil 1 may be the high-frequency side coil, or may be a heating coil 1 different from the high-frequency side coil.

[0065] To explain the control operation of this control device 3 in more detail, as shown in FIG. 9, the operation (S1 to S5) of matching the drive frequency of the high-frequency side coil to the drive frequency of the low-frequency side coil is the same as in the above embodiment.

[0066] Then, a case where the inverter device 2 corresponding to the high frequency side coil is controlled in the second control mode will be described.

[0067] In this case, when the heat output of the burner of the low frequency side coil is reduced, the drive frequency of the low frequency side coil increases, and accordingly, the on-duty ratio of the switching element SW corresponding to the high frequency side coil increases (S6, S7).

[0068] Then, when the drive frequency of the low frequency side coil reaches the frequency that the high frequency side coil was originally outputting, the on-duty ratio of the drive frequency of the high frequency side coil reaches 50%.

[0069] Therefore, as shown in FIG. 9, the control device 3 determines whether the on-duty ratio of the switching element SW corresponding to the high-frequency side coil has reached 50% (S8, S9), and if so, reverses the definition of the high-frequency side coil and the low-frequency side coil.

[0070] That is, when the on-duty ratio of the switching element SW corresponding to the high-frequency side coil reaches 50%, the control device 3 switches the control of the heating coil 1, which had been controlled as the high-frequency side coil, to the low-frequency side coil, and also switches the control of the heating coil 1, which had been controlled as the low-frequency side coil, to the high-frequency side coil (S4, S5).

[0071] With this configuration, even if the magnitude relationship of the drive frequencies that realize the target heating power is reversed, the heating power of each burner can be adjusted to the desired magnitude while eliminating noise.

[0072] Furthermore, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0073] 100...Induction heating device 1. Heating coil 2. Inverter device 21 Inverter circuit SW: Switching element 22 Drive circuit 3. Control equipment 31 Individual control unit 311 Power calculation unit 312 Inverter control unit 32 Main control section 321...Electric power control department 322 Control mode command unit

Claims

1. At least two heating coils for induction heating an object to be heated; an inverter device provided corresponding to each of the heating coils and supplying power to the corresponding heating coil; a control device for controlling the inverter device, The control device comparing drive frequencies, which are frequencies of power supplied to the at least two heating coils; The driving frequency of the heating coil having a higher driving frequency (hereinafter also referred to as the high-frequency side coil) is changed to the driving frequency of the heating coil having a lower driving frequency (hereinafter also referred to as the low-frequency side coil), controlling the inverter device corresponding to the low frequency side coil in a predetermined first control mode, and controlling the inverter device corresponding to the high frequency side coil in a second control mode different from the first control mode; When the output of the high frequency side coil does not reach a target output in the second control mode, control of the inverter device corresponding to the high frequency side coil is switched from the second control mode to a third control mode, an induction heating device in which the third control mode is control for switching the drive frequency of the high-frequency side coil between a first drive frequency that is the drive frequency of the low-frequency side coil and a second drive frequency that is the first drive frequency plus a predetermined frequency.

2. the first control mode is a control for turning on and off a switching element constituting the inverter device at a fixed duty ratio, 2. The induction heating device according to claim 1, wherein the second control mode is a control for turning on and off a switching element constituting the inverter device with a variable duty ratio.

3. 3. The induction heating device according to claim 1, wherein the predetermined frequency is 15 kHz or higher.

4. In the third control mode, when a ratio of a drive time at the second drive frequency to a drive time at the first drive frequency exceeds a threshold value, The induction heating device according to any one of claims 1 to 3, wherein the control device switches from the third control mode to a control mode in which the at least two heating coils are driven at different drive frequencies.

5. When the driving frequency of the heating coil other than the low frequency side coil becomes lower than the driving frequency of the low frequency side coil, The control device changing the drive frequency of the low-frequency side coil to the drive frequency of the other heating coil, and switching the control mode of the inverter device corresponding to the low-frequency side coil to the second control mode; The induction heating device according to claim 1 , wherein the inverter device corresponding to the other heating coil is switched to the first control mode.

6. 6. The induction heating device according to claim 1, wherein the adjustable range of the drive frequency of each of the at least two heating coils is higher than the frequency of the peak of a resonance curve of the object to be heated by each heating coil.

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