Induction heating cooker

Abstract

To provide an induction heating cooker capable of suppressing generation of interference sound from components of a filter circuit while mitigating reduction of input power, in a case that a pre-stage circuit is commonalized for a plurality of inverter circuits.SOLUTION: An induction heating cooker includes: a rectifying circuit for rectifying output of AC power supply; a pre-stage circuit having a filter circuit for smoothing the output of the rectifying circuit; a first inverter circuit and a second inverter circuit connected in parallel with a subsequent stage of the pre-stage circuit, and supplying high frequency current to a heating coil which performs induction heating for a target heating object; and a control device for controlling driving of the first inverter circuit and the second inverter circuit. The control device performs jitter control which adds random variations on a driving frequency of a driving signal to be sent to the first inverter circuit when the driving signal is simultaneously sent to the first inverter circuit and the second inverter circuit.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an induction heating cooker including a plurality of inverter circuits. [Background technology]

[0002] Conventionally, there is known an induction heating cooker in which two heating coils each inductively heat an object to be heated, and in which a front-stage circuit (rectifier circuit and filter circuit) common to two inverter circuits that supply high-frequency current to the two heating coils is provided. Patent Document 1 discloses such an induction heating cooker in which each inverter circuit is driven in a time-division manner (exclusive drive). In the time-division drive, while one inverter circuit is heating an object to be heated, the heating of the other inverter circuit is stopped, and the inverter circuit that performs heating and the inverter circuit that stops heating are switched on the order of milliseconds or seconds. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 084386 Summary of the Invention [Problem to be solved by the invention]

[0004] The time-sharing drive disclosed in Patent Document 1 involves thinning-out drive of the heated object placed on the heating port, so that even when a user has instructed heating, periods when heating is stopped may occur and the desired integrated power may not be input.

[0005] On the other hand, if the two inverter circuits are not driven in a time-division manner but driven simultaneously, a non-periodic (asynchronous) high-frequency current flows into the filter circuit, and frequency components that are non-periodic waveform components are generated in the audible range, which can cause interference noise from the components of the filter circuit. The frequency components in the audible range are the difference frequency components between the two drive frequencies, and are generated when the drive frequencies (carrier frequencies) of the two inverter circuits are different.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an induction heating cooker that reduces the loss of power input and suppresses the generation of interference noise from filter circuit components when a front-stage circuit is shared among multiple inverter circuits. [Means for solving the problem]

[0007] The induction heating cooker according to the present disclosure comprises a front-stage circuit having a rectifier circuit that rectifies the output of an AC power source and a filter circuit that smoothes the output of the rectifier circuit, a first inverter circuit and a second inverter circuit that are connected in parallel to the rear stage of the front-stage circuit and supply high-frequency current to a heating coil that inductively heats an object to be heated, and a control device that controls the driving of the first inverter circuit and the second inverter circuit, and when simultaneously transmitting a drive signal to the first inverter circuit and the second inverter circuit, the control device performs jittering control that adds random displacement to the drive frequency of the drive signal transmitted to the first inverter circuit. Effect of the Invention

[0008] According to the present disclosure, in the case where the first inverter circuit and the second inverter circuit share the front-stage circuit, the first inverter circuit and the second inverter circuit are driven simultaneously. Therefore, compared with the case where a plurality of inverters are driven in a time-division manner, it is possible to reduce the loss of power input to the object to be heated placed on the heating port corresponding to the inverter. In addition, jittering control is performed on the drive signals of the first inverter circuit and the second inverter circuit. This makes it possible to control the current waveform flowing into the components of the filter circuit and suppress the generation of frequency components in the audible range. Therefore, it is possible to suppress the generation of interference sounds from the components of the filter circuit. This also makes it possible to improve the product reliability of the induction heating cooker. [Brief description of the drawings]

[0009] [Figure 1] 1 is a perspective view showing a configuration example of an induction heating cooker according to a first embodiment. [Diagram 2] 1 is a diagram showing a configuration example of an electric circuit of an induction heating cooker according to a first embodiment. [Diagram 3] 11 is a diagram showing an analysis result of a current flowing into a smoothing capacitor when jittering control is not performed. FIG. [Figure 4] 11A and 11B are diagrams illustrating analysis results of a current flowing into a smoothing capacitor when jittering control is performed. [Diagram 5] FIG. 11 is a circuit diagram showing a schematic configuration of an induction heating cooker according to a second embodiment. [Figure 6] 3A and 3B are diagrams illustrating drive signal waveforms of a first inverter circuit and a second inverter circuit, and a current waveform flowing through a smoothing capacitor. [Figure 7] 11A and 11B are diagrams showing the waveform of a current flowing through a heating coil, the waveform of a current flowing through a smoothing capacitor, and the duty ratio when duty variation control is not performed. [Figure 8] 13 is a diagram showing the generation timing of the difference frequency component superimposed on the waveform of the current flowing through the heating coil when duty variation control is not performed. FIG. [Figure 9]11A and 11B are diagrams illustrating the waveform of a current flowing through a heating coil, the waveform of a current flowing through a smoothing capacitor, and the duty ratio when duty variation control is performed. [Figure 10] 13 is a diagram showing the generation timing of a difference frequency component superimposed on the waveform of a current flowing through a heating coil when duty variation control is performed. FIG. [Figure 11] 4A to 4C are diagrams illustrating drive signals for a first inverter circuit and a second inverter circuit, and a waveform of a current flowing into a smoothing capacitor. [Figure 12] FIG. 11 is a diagram showing a first heating coil and a second heating coil in a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Embodiment 1 The configuration of the induction heating cooker 100 of the first embodiment will be described. FIG. 1 is a perspective view showing one configuration example of the induction heating cooker 100 according to the first embodiment. The induction heating cooker 100 is an IH (Induction Heating) cooking heater that uses a heating coil to inductively heat an object to be heated placed on a plurality of heating ports. The object to be heated is, for example, a cooking pot such as a frying pan. The induction heating cooker 100 has a top plate 60 on which the cooking pot is placed, a housing 50 provided under the top plate 60, an operation unit 51, and a display unit 55.

[0011] The top plate 60 has a first heating port 70a on the left side, a second heating port 70b on the right side, and a third heating port 70c on the back side. The first heating port 70a, the second heating port 70b, and the third heating port 70c are the locations on the top plate 60 where a cooking pot such as a frying pan is placed. The first heating port 70a, the second heating port 70b, and the third heating port 70c are, for example, circular. The top plate 60 is printed with the positions of the first heating port 70a, the second heating port 70b, and the third heating port 70c.

[0012] The heating means in the first heating port 70a, the second heating port 70b, and the third heating port 70c are heating coils that perform induction heating. The number of heating ports in the induction heating cooker 100 may be two or four or more. As long as the heating means in at least two heating ports are heating coils, the form of the heating means in the other heating ports is not particularly limited. For example, the heating means in the third heating port 70c may be an electric heater.

[0013] The operation unit 51 has a main power button 52, a heating button 53, and a heat setting unit 54. The main power button 52 is a button for turning on or off the main power of the induction heating cooker 100. The heating button 53 is a button for inputting instructions to start and stop heating in the first heating port 70a. Although not shown in FIG. 1, the operation unit 51 is also provided with heating buttons 53 for the second heating port 70b and the third heating port 70c. The heat setting unit 54 is a dial for setting the heat during heating in the first heating port 70a to the third heating port 70c.

[0014] The display unit 55 displays the heating power settings for the first heating port 70a, the second heating port 70b, and the third heating port 70c, setting information, and information to alert the user, etc. The display unit 55 is composed of a lamp or a liquid crystal display.

[0015] Next, the configuration of the electric circuit of the induction heating cooker 100 will be described. FIG. 2 is a diagram showing an example of the configuration of the electric circuit of the induction heating cooker 100 according to the first embodiment. As shown in FIG. 2, the induction heating cooker 100 is supplied with power from an AC power source 200. The induction heating cooker 100 has a front-stage circuit 5, a first inverter circuit 10a and a second inverter circuit 10b, a first resonant circuit 20a and a second resonant circuit 20b, current detection devices 80, 81a and 81b, and a control device 30. The control device 30 is connected to the first inverter circuit 10a and the second inverter circuit 10b, an operation unit 51, and a display unit 55. Although not shown, the control device 30 is connected to the current detection devices 80, 81a, and 81b by wire or wirelessly so as to receive the detection results of these devices. In FIG. 2, the current detection devices 80, 81a, and 81b are conceptually shown for the sake of illustration.

[0016] In the first embodiment, the object to be heated placed on the first heating port 70a is heated by the first heating coil 21a of the first resonant circuit 20a, and the object to be heated placed on the second heating port 70b is heated by the second heating coil 21b of the second resonant circuit 20b. However, the first heating coil 21a and the second heating coil 21b may heat the object to be heated at other heating ports, for example, the second heating port 70b and the third heating port 70c, instead of the first heating port 70a and the second heating port 70b.

[0017] The front-stage circuit 5 is a power conversion circuit connected to an AC power supply 200, which is a commercial power supply, and rectifies and smoothes the output of the AC power supply 200. The front-stage circuit 5 converts an AC current supplied from the AC power supply 200 into a DC current, and supplies the DC current to a first inverter circuit 10a and a second inverter circuit 10b. The front-stage circuit 5 has a rectifier circuit 6 and a filter circuit 7.

[0018] The front-stage circuit 5 is provided in front of the first inverter circuit 10a and the second inverter circuit 10b, and is a circuit common to the first inverter circuit 10a and the second inverter circuit 10b. One filter circuit 7 is connected to the output side of one rectifier circuit 6, and the first inverter circuit 10a and the second inverter circuit 10b are connected in parallel to the output side of the filter circuit 7. In other words, the front-stage circuit 5 including the filter circuit 7 is shared by the first inverter circuit 10a and the second inverter circuit 10b. This reduces the number of circuit components and reduces the size and weight of the circuit compared to a configuration in which a front-stage circuit is provided for each of the first inverter circuit 10a and the second inverter circuit 10b.

[0019] In addition, in a configuration in which the front-stage circuit 5 is common to the first inverter circuit 10a and the second inverter circuit 10b, the output stage of the front-stage circuit 5, i.e., the output stage of the filter circuit 7, is referred to as a bus. In the circuit configuration shown in Fig. 1, the buses of the first inverter circuit 10a and the second inverter circuit 10b are commonly connected, and therefore such a circuit configuration is referred to as a common bus system.

[0020] The rectifier circuit 6 rectifies the output of the AC power supply 200, that is, the AC current supplied from the AC power supply 200. The rectifier circuit 6 is composed of, for example, a plurality of diodes 6a in a bridge configuration.

[0021] The filter circuit 7 smoothes the output of the rectifier circuit 6. The filter circuit 7 is an LC passive filter having a choke coil 8 and a smoothing capacitor 9. The choke coil 8 reduces noise current in the power line. The smoothing capacitor 9 is, for example, a film capacitor, and reduces common mode noise.

[0022] In this configuration, when the first inverter circuit 10a and the second inverter circuit 10b are driven simultaneously, interference noise is generated from the components of the filter circuit 7. Specifically, when the differential frequency Δf between the drive frequency f1 of the first inverter circuit 10a and the drive frequency f2 of the second inverter circuit 10b flows into the filter circuit 7, the printed circuit board on which the filter circuit 7 is provided and the components mounted thereon vibrate, generating interference noise. In addition, the differential frequency Δf becomes interference noise mediated by air, and is generated as an audible sound from the first heating port 70a and the second heating port 70b of the induction heating cooker 100. The drive frequency will be described later.

[0023] The first inverter circuit 10a is, for example, a half-bridge inverter circuit. A first resonant circuit 20a is connected to the output side of the first inverter circuit 10a. The first inverter circuit 10a supplies a high-frequency current to the first resonant circuit 20a. The first inverter circuit 10a has switching elements 11a and 12a connected in series. The switching elements 11a and 12a are, for example, IGBTs (Insulated Gate Bipolar Transistors). The switching elements 11a and 12a are alternately switched between an on state and an off state according to a drive signal input from the control device 30, and generate a high-frequency current.

[0024] The second inverter circuit 10b is, for example, a half-bridge inverter circuit. A second resonant circuit 20b is connected to the output side of the second inverter circuit 10b. The second inverter circuit 10b supplies a high-frequency current to the second resonant circuit 20b. The second inverter circuit 10b has switching elements 11b and 12b connected in series. The switching elements 11b and 12b are, for example, IGBTs. The switching elements 11b and 12b are alternately switched between an on state and an off state according to a drive signal input from the control device 30, and generate a high-frequency current.

[0025] 2 shows a case where the inverter circuit system in the first inverter circuit 10a and the second inverter circuit 10b is a half-bridge circuit system combining two switching elements, but is not limited to this case. For example, other circuit systems such as a single-transistor voltage resonant circuit system or a full-bridge circuit system may be used.

[0026] The first resonant circuit 20a has a first heating coil 21a and a resonant capacitor 22a. The first resonant circuit 20a is, for example, a current resonant system in which the first heating coil 21a and the resonant capacitor 22a are connected in series from the output point of the first inverter circuit 10a. The first heating coil 21a is disposed directly below the first heating port 70a, and is supplied with high-frequency current from the first inverter circuit 10a to inductively heat an object to be heated placed on the first heating port 70a.

[0027] The second resonant circuit 20b has a second heating coil 21b and a resonant capacitor 22b. The second resonant circuit 20b is, for example, a current resonant system in which the second heating coil 21b and the resonant capacitor 22b are connected in series from the output point of the second inverter circuit 10b. The second heating coil 21b is disposed directly below the second heating port 70b, and is supplied with high-frequency current from the second inverter circuit 10b to inductively heat an object to be heated placed on the second heating port 70b.

[0028] In the following description, when the first heating port 70a and the second heating port 70b are not distinguished from each other, the suffixes "a" and "b" are omitted, as in the case of heating port 70. The same applies when the first inverter circuit 10a and the second inverter circuit 10b, the first resonant circuit 20a and the second resonant circuit 20b, and the first heating coil 21a and the second heating coil 21b are not distinguished from each other.

[0029] The current detection device 80 detects the current flowing through the rectifier circuit 6, i.e., the input current. The current detection device 80 transmits the detection result to the control device 30. The current detection device 81a detects the current flowing through the first heating coil 21a, i.e., the coil current. The current detection device 81a transmits the detection result to the control device 30. The current detection device 81b detects the current flowing through the second heating coil 21b, i.e., the coil current. The current detection device 81b transmits the detection result to the control device 30.

[0030] The control device 30 is configured with hardware such as a circuit device that realizes its functions, or a memory and a CPU (Central Processing Unit) that executes programs stored in the memory.

[0031] The control device 30 receives the detection results of the current detection device 80, the detection results of the current detection devices 81a and 81b, and instructions from the user via the operation unit 51. The control device 30 controls the operation of the induction heating cooker 100 in response to the inputs. The control device 30 executes a load judgment sequence and a heating sequence.

[0032] The control device 30 performs a load judgment sequence before heating the object. In the load judgment sequence, the control device 30 judges the load state based on the detection results of the current detection devices 81a and 81b. The control device 30 judges the presence or absence of the object to be heated above the first heating coil 21a and the second heating coil 21b and the material of the object to be heated as the load state. Specifically, when the object to be judged is the object to be heated corresponding to the first heating coil 21a, the first inverter circuit 10a is driven at a driving frequency for load judgment. At this time, the load state of the first heating coil 21a is judged based on the ratio between the input current measured by the current detection device 80 and the coil current of the first heating coil 21a measured by the current detection device 81a. The same applies when the object to be judged is the object to be heated corresponding to the second heating coil 21b. In addition, when it is required to detect the load simultaneously on the first inverter circuit 10a side and the second inverter circuit 10b side, the load judgment operation of one of the inverter circuits having a higher priority (e.g., the first inverter circuit 10a) may be performed first, and after this is completed, the load judgment operation may be moved to the other inverter circuit having a lower priority (the second inverter circuit 10b).

[0033] The control device 30 determines the driving frequency of the driving signal, which is a PWM signal for oscillation of the first heating coil 21a and the second heating coil 21b, based on the result of the load judgment. When the object to be heated is made of a non-magnetic material such as aluminum or copper, its electrical resistance is very small. Therefore, when the object to be heated is made of a non-magnetic material, it is necessary to increase the driving frequency to generate the required heat, compared to when the object to be heated is made of a magnetic material.

[0034] Following the load determination sequence, a heating sequence is performed. In the heating sequence, the control device 30 drives the first inverter circuit 10a and the second inverter circuit 10b by transmitting drive signals at the drive frequencies determined in the load determination sequence to the first inverter circuit 10a and the second inverter circuit 10b.

[0035] The first inverter circuit 10a and the second inverter circuit 10b receive a drive signal, which is a PWM signal, and perform high-frequency driving to supply high-frequency current to the first heating coil 21a and the second heating coil 21b. That is, the switching elements 11a and 12a of the first inverter circuit 10a receive a drive signal from the control device 30 and perform switching. As a result, a high-frequency current is supplied to the first heating coil 21a, and an object to be heated arranged above the first heating coil 21a is inductively heated. In addition, the switching elements 11b and 12b of the second inverter circuit 10b receive a drive signal from the control device 30 and perform switching. As a result, a high-frequency current is supplied to the second heating coil 21b, and an object to be heated arranged above the second heating coil 21b is inductively heated. Note that the high-frequency driving here refers to driving at a frequency of, for example, 20 kHz to 100 kHz.

[0036] The drive signal in the first embodiment will be described in detail. First, the control device 30 fixes the drive frequency (oscillation frequency) and changes the duty ratio of the drive signals issued to the first inverter circuit 10a and the second inverter circuit 10b. When the user changes the heat setting (set power) of each heating port 70, the control device 30 changes the heat by changing the duty ratio while keeping the drive frequency fixed.

[0037] Here, the duty ratio is the on-time ratio of the high-side switching element in the half-bridge system. When the duty ratio is, for example, 30%, the on-time ratio of the low-side switching element is 70%.

[0038] Specifically, when a user increases the heating power setting of the first inverter circuit 10a, the control device 30 increases the duty ratio of the drive signal to the first inverter circuit 10a (for example, from 30% to 45%). The same applies to the second inverter circuit 10b. Also, when a user decreases the heating power setting of the second inverter circuit 10b, the control device 30 decreases the duty ratio of the drive signal to the second inverter circuit 10b (for example, from 40% to 20%). The same applies to the first inverter circuit 10a.

[0039] When the user sets both the first heating port 70a and the second heating port 70b to perform heating, the control device 30 performs different controls depending on the material of the objects placed on the first heating port 70a and the second heating port 70b. The material of the objects placed on the first heating port 70a and the second heating port 70b is determined by the load determination sequence described above.

[0040] First, when the object to be heated placed on the first heating port 70a and the object to be heated placed on the second heating port 70b are both made of magnetic materials, the control device 30 operates the first inverter circuit 10a and the second inverter circuit 10b at the same drive frequency. The drive frequency at this time is, for example, 22 kHz. This is because, in a current resonance circuit configuration, the drive frequency needs to be set to a value higher than the resonant frequency of the resonant circuit to realize the operation of the inverter, but when the object to be heated is a magnetic material, the resonant frequency f0 is designed to be about 17 kHz. In other words, the control device 30 outputs a signal with a drive frequency f1=22 kHz and a variable duty ratio to the first inverter circuit 10a. Also, the control device 30 outputs a signal with a drive frequency f2=22 kHz and a variable duty ratio to the second inverter circuit 10b.

[0041] Secondly, even when both the object to be heated placed on the first heating port 70a and the object to be heated placed on the second heating port 70b are made of non-magnetic materials, the control device 30 operates the first inverter circuit 10a and the second inverter circuit 10b at the same driving frequency. The driving frequency at this time is higher than when the object to be heated is made of magnetic material, for example, 31 kHz. This is because when the object to be heated placed on the heating port 70 is made of non-magnetic material, the inductance L value specific to the object to be heated is smaller than when the object to be heated is made of magnetic material, and the resonance frequency f0 is larger than when the object to be heated is made of magnetic material. In the case of a current resonance circuit configuration, in order to realize inverter operation in the delay phase region in the resonance characteristics, it is necessary to increase the driving frequency f1 of the first inverter circuit 10a and the driving frequency f2 of the second inverter circuit 10b as the resonance frequency f0 increases.

[0042] In this way, when the object to be heated placed on the first heating port 70a and the object to be heated placed on the second heating port 70b are made of the same material, the duty width [%] of the first inverter circuit 10a and the second inverter circuit 10b takes different values ​​depending on the heat power setting of the user. However, the drive frequency is common to the first inverter circuit 10a and the second inverter circuit 10b. In other words, the drive frequencies of the first inverter circuit 10a and the second inverter circuit 10b are synchronized and operated. By synchronizing the drive frequency of the first inverter circuit 10a and the drive frequency of the second inverter circuit 10b, a current of only the drive frequency component flows into the filter circuit 7, which is a common component. In other words, in the above example, when a magnetic material is placed on the first heating port 70a and the second heating port 70b, a current of 22 kHz component flows in. Furthermore, when a non-magnetic material is placed on the first heating port 70a and the second heating port 70b, a current with a 31 kHz component flows in.

[0043] Thirdly, when the object to be heated placed on the first heating port 70a is made of a magnetic material and the object to be heated placed on the second heating port 70b is made of a non-magnetic material, the control device 30 operates the first inverter circuit 10a and the second inverter circuit 10b at different drive frequencies. For example, the drive frequency of the first inverter circuit 10a is 22 kHz, and the drive frequency of the second inverter circuit 10b is 31 kHz. For the above reasons, the second inverter circuit 10b for heating the non-magnetic material operates at a drive frequency higher than that of the first inverter circuit 10a for heating the magnetic material.

[0044] At this time, in the circuit configuration of Fig. 2, a difference frequency component is formed in addition to the frequency component of the drive signal, and is superimposed on the inflow current of the smoothing capacitor 9 of the filter circuit 7. When the first inverter circuit 10a is operated at a drive frequency of 22 kHz and the second inverter circuit 10b is operated at a drive frequency of 31 kHz, a difference frequency of Δf = 31 kHz - 22 kHz = 9 kHz is formed. The difference frequency component of 9 kHz flows into the filter circuit 7. The difference frequency is a frequency in the audible range, and may be heard by the user as interference sound.

[0045] The differential frequency occurs only when objects to be heated made of different materials (magnetic and non-magnetic materials) are placed on the first heating port 70a and the second heating port 70b, and does not occur when objects to be heated made of the same material (magnetic materials or non-magnetic materials) are placed on the first heating port 70a and the second heating port 70b. This is because, as described above, when objects to be heated made of the same material are placed on the first heating port 70a and the second heating port 70b, induction heating is performed by the same driving frequency in the first inverter circuit 10a and the second inverter circuit 10b, and no differential frequency occurs.

[0046] Here, in the first embodiment, jittering control is performed on either or both of the drive signal of the first inverter circuit 10a and the drive signal of the second inverter circuit 10b. Jittering control is a control that adds a small random displacement (temporal displacement, fluctuation) to the drive frequency of the drive signal. The width of the displacement (jittering width) superimposed on the inverter circuit carrier frequency is, for example, about ± several kHz.

[0047] As an example, a minute variation of ±1.5 kHz is applied to the 23 kHz of the first inverter circuit 10a. In this case, the drive frequency of the first inverter circuit 10a varies within the range of 23 kHz±1.5 kHz=21.5 kHz to 24.5 kHz. Similarly, a minute variation of ±1.5 kHz is applied to the 34.5 kHz of the second inverter circuit 10b. In this case, the drive frequency of the second inverter circuit 10b varies within the range of 34.5 kHz±1.5 kHz=33 kHz to 36 kHz.

[0048] The dispersion of the difference frequency peak by the jittering control will be explained. FIG. 3 is a diagram showing an analysis result of the current flowing into the smoothing capacitor 9 when the jittering control is not performed. FIG. 4 is a diagram showing an analysis result of the current flowing into the smoothing capacitor 9 when the jittering control is performed. FIG. 3 and FIG. 4 show the result of FFT (Fast Fourier Transform) analysis of the current flowing into the smoothing capacitor 9 when the circuit shown in FIG. 2 is simulated. As an example, the FFT analysis result is shown when the first inverter circuit 10a is operated at a drive frequency of 23 kHz corresponding to the object to be heated of a magnetic material, and the second inverter circuit 10b is operated at a drive frequency of 34.5 kHz corresponding to the object to be heated of a non-magnetic material. As shown in FIG. 3 and FIG. 4, a Δ11.5 kHz component of the difference frequency is generated, and this current component flows into the smoothing capacitor 9.

[0049] In FIG. 3, where jittering control is not performed, the frequency peak in the FFT analysis of the differential frequency Δ11.5 kHz component is 123.4 dBμA. On the other hand, in FIG. 4, where jittering control is performed, the frequency peak in the FFT analysis of the differential frequency Δ11.5 kHz component is 114.2 dBμA. In FIG. 4, the jittering width is set to the drive frequency ±1.65 kHz as an example, and other conditions of the electric circuit are the same in FIG. 3 and FIG. 4. By performing jittering control, the frequency peak of 23 kHz, which is the drive frequency of the first inverter circuit 10a, and the frequency peak of 34.5 kHz, which is the drive frequency of the second inverter circuit 10b, are each dispersed. When the frequency peak of 23 kHz, which is the drive frequency of the first inverter circuit 10a, and the frequency peak of 34.5 kHz, which is the drive frequency of the second inverter circuit 10b, are each dispersed, the differential frequency peak formed by the drive frequencies of the two inverter circuits is also dispersed. In this way, by performing jittering control, the peak of the difference frequency, which is in the audible range, is dispersed and attenuated.

[0050] As described above, according to the first embodiment, in the case where the first inverter circuit 10a and the second inverter circuit 10b share the front-stage circuit, the first inverter circuit 10a and the second inverter circuit 10b are driven simultaneously. Therefore, compared with the case where a plurality of inverters are driven in a time-division manner, it is possible to reduce the loss of power input to the object to be heated placed on the heating port corresponding to the inverter. In addition, jittering control is performed on the drive signals of the first inverter circuit 10a and the second inverter circuit 10b. This makes it possible to control the current waveform flowing into the components of the filter circuit 7 and suppress the generation of frequency components in the audible range. Therefore, it is possible to suppress the generation of interference sounds from the components of the filter circuit. In addition, this makes it possible to improve the product reliability of the induction heating cooker 100.

[0051] In the above description, the case where the jittering control is performed on the drive signals of both the first inverter circuit 10a and the second inverter circuit 10b has been exemplified. However, the jittering control may be performed on only one of the first inverter circuit 10a or the second inverter circuit 10b. Even in this case, the peak of the difference frequency Δf is dispersed, and the generation of interference noise can be suppressed.

[0052] In addition, when the jittering width in the first embodiment is increased, the dispersion width of the FFT components also increases, so the effect of suppressing the interference noise is enhanced, but the input power changes according to the driving frequency, so the fluctuation of the input power increases. Therefore, it is desirable to make the jittering width as large as possible while taking into account the fluctuation of the input power.

[0053] Embodiment 2 The induction heating cooker 100 of the first embodiment applies jittering control to the drive frequency of the drive signal to suppress the sound pressure peak of the difference frequency occurring in the audible range. However, the induction heating cooker 100A of the second embodiment performs duty variation control to apply duty correction to the drive signal in synchronization with the generation timing of the difference frequency component. The following describes the second embodiment, focusing on the differences from the first embodiment. Note that the same reference numerals are used for components having the same functions and actions as those of the first embodiment, and their description will be omitted.

[0054] Fig. 5 is a circuit diagram showing a schematic configuration of an induction heating cooker 100A according to embodiment 2. As shown in Fig. 5, the induction heating cooker 100A has a current peak detection device 90. Note that in Fig. 5, for the sake of illustration, the current peak detection device 90 is conceptually shown. The current peak detection device 90 detects the timing (peak timing) at which the maximum current flows through the filter circuit 7. The operation of the current peak detection device 90 will be described in detail later.

[0055] Also in Embodiment 2, similar to Embodiment 1, when the material of the object to be heated is the same material, the control device 30 operates the first inverter circuit 10a and the second inverter circuit 10b at the same and fixed drive frequency according to the material. Further, when the materials of the objects to be induction-heated are different materials, the first inverter circuit 10a and the second inverter circuit 10b are operated at different drive frequencies.

[0056] In Embodiment 2, regarding the drive frequency f1 of the first inverter circuit 10a and the drive frequency f2 of the second inverter circuit 10b, it is set so that f2 = 1.5 × f1 is satisfied. This is to synchronize the differential frequency with the drive frequency f1 of the first inverter circuit 10a or the drive frequency f2 of the second inverter circuit 10b and generate the differential frequency component periodically. This will be specifically described below.

[0057] When set to f2 = 1.5 × f1, the relationship between the differential frequency Δf (= f2 - f1) and the drive frequency f1 is as shown in the following equation (1). Also, the relationship between the differential frequency Δf (= f2 - f1) and the drive frequency f2 is as shown in the following equation (2).

[0058] Δf = f2 - f1 = 1.5 × f1 - f1 = 1 / 2 × f1 ··· Equation (1)

[0059] Δf = f2 - f1 = f2 - 2 / 3 × f2 = 1 / 3 × f2 ··· Equation (2)

[0060] As shown in Equation (1), the differential frequency component is generated with a period twice that of the drive frequency f1. Also, as shown in Equation (2), the differential frequency component is generated with a period three times that of the drive frequency f2. For this reason, in the smoothing capacitor 9 of the filter circuit 7, a current waveform in which the differential frequency component is superimposed on the drive frequency appears with a constant amplitude and period.

[0061] The duty variation control will be described. As described above, the duty variation control is a control that applies a duty correction to the drive signal in synchronization with the generation timing of the difference frequency component. In the duty variation control, the duty ratio described in the first embodiment is changed in accordance with the generation timing of the difference frequency component.

[0062] First, a method for detecting the occurrence timing of the difference frequency component will be described. Based on the detection result of the current peak detection device 90, the control device 30 recognizes the peak timing of the current amplitude, that is, the timing when the difference frequency component occurs.

[0063] FIG. 6 is a diagram showing the drive signal waveforms of the first inverter circuit 10a and the second inverter circuit 10b, and the current waveform flowing through the smoothing capacitor 9. Here, the first inverter circuit 10a is driven at 23 kHz, and the second inverter circuit 10b is driven at 34.5 kHz. These values ​​satisfy the above-mentioned f2=1.5×f1. Since the inflow current due to the 23 kHz component and the inflow current due to the 34.5 kHz component flow into the filter circuit 7 at the same time, a current component of Δf=34.5 kHz-23 kHz=11.5 kHz is generated as shown in FIG. 6. When the difference frequency component is superimposed on the drive frequency, the current amplitude becomes a peak and is detected by the current peak detection device 90. In the example of FIG. 6, the peak of the actual current waveform at the timing when the difference frequency component occurs is 100 A, and does not reach 100 A at the timing when the difference frequency Δf does not occur.

[0064] Here, the current peak detection device 90 has a current threshold set inside the device. When performing current detection, the current peak detection device 90 detects the maximum peak current in the process of shifting the current threshold downward from a state where it is set to a high value. Specifically, the current peak detection device 90 sets the current threshold to, for example, 200A in the initial state and starts detection of the maximum current. In the waveform example of FIG. 6, since no current is detected at the threshold of the initial value of 200A, the detection is continued while gradually shifting the threshold downward. When the current threshold shifts downward to 100A, the current peak detection device 90 detects that a current reaching the threshold flows through the smoothing capacitor 9. At this time, the current peak detection device 90 detects that a current of 11.5kHz component flows through the smoothing capacitor 9 and the occurrence timing. This is because the peak of the actual current waveform at the timing when the difference frequency component occurs is 100A. Note that the peak at the timing when the difference frequency component does not occur does not reach 100A. For this reason, the current peak detection device 90 cannot grasp the current components of 23kHz and 34.5kHz and the occurrence timing.

[0065] In this way, the control device 30 can recognize the occurrence timing of the difference frequency component by the current peak detection device 90 detecting the current of the 11.5 kHz component.

[0066] Next, the duty correction applied to the drive signal will be described. The control device 30 applies the duty correction to the drive signal in accordance with the generation timing of the detected difference frequency component. Specifically, the control device 30 minutely varies the duty ratio at the generation timing of the difference frequency component. By increasing the duty ratio, it is possible to increase the component current of the difference frequency component (the current flowing through the heating coil 21 and the current flowing through the smoothing capacitor 9), and by decreasing the duty ratio, it is possible to decrease the component current of the difference frequency component. As in the example of FIG. 6, when the current value of the difference frequency component increases, the component current of the difference frequency component can be decreased by decreasing the duty ratio, thereby suppressing the generation of the difference frequency component.

[0067] Moreover, the drive frequency f1 of the first inverter circuit 10a and the drive frequency f2 of the second inverter circuit 10b are determined based on an instruction from the control device 30. Furthermore, the control device 30 obtains the differential frequency Δf by subtracting the drive frequency f1 of the first inverter circuit 10a and the drive frequency f2 of the second inverter circuit 10b, that is, Δf=|f2-f1|. Therefore, the control device 30 can recognize the drive frequency f1 of the first inverter circuit 10a, the drive frequency f2 of the second inverter circuit 10b, and the differential frequency Δf.

[0068] Since the differential frequency Δf=1 / 2×f1 and the differential frequency Δf=1 / 3×f2, the differential frequency Δf can be synchronized with the drive frequency f1 or f2. Therefore, by causing the current peak detection device 90 to perform a detection operation at a cycle three times the drive frequency f2, triggered by the PWM rising timing of the drive frequency f2, the detection of the differential frequency component can be performed with high efficiency and high accuracy. Also, by causing the current peak detection device 90 to perform a detection operation at a cycle twice the drive frequency f1, triggered by the PWM rising timing of the drive frequency f1, the detection of the differential frequency component can be performed with high efficiency and high accuracy.

[0069] Here, the effect of the duty variation control of the present application will be described in comparison with the case where the duty variation control is not performed. First, the problem that occurs when the duty variation control is not performed will be described. FIG. 7 is a diagram showing the waveform of the current flowing through the heating coil 21, the waveform of the current flowing through the smoothing capacitor 9, and the duty ratio when the duty variation control is not performed. FIG. 7 shows an example in which the first inverter circuit 10a is simultaneously driven at a drive frequency of 23 kHz and the second inverter circuit 10b is simultaneously driven at a drive frequency of 34.5 kHz in the circuit configuration shown in FIG. 5.

[0070] The current flowing through the first heating coil 21a is a superposition of the 23 kHz component of the drive frequency f1 of the first inverter circuit 10a and the 34.5 kHz component of the drive frequency f2 of the second inverter circuit 10b. The current flowing through the second heating coil 21b is a superposition of the 23 kHz component of the drive frequency f1 of the first inverter circuit 10a and the 34.5 kHz component of the drive frequency f2 of the second inverter circuit 10b. That is, the current flowing through the heating coil 21 is a mixed current of the 23 kHz component and the 34.5 kHz component. Furthermore, in the example of FIG. 7, the inflow current due to the 23 kHz component and the inflow current due to the 34.5 kHz component flow simultaneously into the smoothing capacitor 9 of the filter circuit 7, and the component of the difference frequency Δf=34.5 kHz-23 kHz=11.5 kHz is also superimposed. That is, the current waveform in FIG. 7 shows the result of superimposing currents of 23 kHz components, 34.5 kHz components, and 11.5 kHz components having different amplitudes.

[0071] Here, the duty ratio of the drive signal transmitting the drive frequency of 23 kHz for the first inverter circuit 10a and 34.5 kHz for the second inverter circuit 10b is a constant value, for example, 30%. The "duty ratio" in Fig. 7 means that the duty ratio is an output that does not change from 30%, that is, no duty variation control is performed.

[0072] FIG. 8 is a diagram showing the waveform of the current flowing through the heating coil 21 superimposed with the generation timing of the differential frequency component when duty variation control is not performed. In FIG. 8, the generation timing of the differential frequency is indicated by an arrow marked td. As described above, the duty ratio is fixed at the generation timing of the differential frequency. In other words, duty variation control is not performed. Since the current amplitude of the Δf=11.5 kHz component is different from the current amplitude of the 23 kHz component and the 34.5 kHz component of the drive frequency (the current values ​​dBμA are different), as shown in FIG. 8, a current waveform with a small amplitude in which the differential frequency component is superimposed on the drive frequency component is formed. Thus, from FIG. 8, it can be seen that when duty variation control is not performed, a small amplitude 11.5 kHz component is generated by superimposing the 23 kHz component and the 34.5 kHz component of the drive frequency. Then, the generation of the differential frequency component within the audible range causes interference noise.

[0073] Next, the effect of duty variation control will be described. Fig. 9 is a diagram showing the waveform of the current flowing through the heating coil 21, the waveform of the current flowing through the smoothing capacitor 9, and the duty ratio when duty variation control is performed. Fig. 9 shows an example in which the first inverter circuit 10a is simultaneously driven at a drive frequency of 23 kHz and the second inverter circuit 10b is simultaneously driven at a drive frequency of 34.5 kHz in the circuit configuration shown in Fig. 5.

[0074] The "duty ratio" in Fig. 9 shows that duty variation control is performed to reduce the duty ratio at the timing when the difference frequency component occurs. Fig. 9 shows an example in which the duty ratio temporarily drops from 30% to 25% at the timing when the difference frequency component occurs.

[0075] Fig. 10 is a diagram showing the timing of occurrence of the differential frequency component superimposed on the waveform of the current flowing through the heating coil 21 when duty variation control is performed. In Fig. 10, the timing of occurrence of the differential frequency component is indicated by an arrow marked "td". As shown in Fig. 10, by performing duty variation control that reduces the duty ratio at the timing of occurrence of the differential frequency component, the occurrence of frequency components with different amplitudes is suppressed.

[0076] As described above, by performing duty variation control synchronized with the differential frequency Δf component, it is possible to remove the current waveform of the differential frequency Δf component as shown in Fig. 9. Even after the current waveform of the differential frequency Δf component is removed, by continuing the duty variation control at the previously detected timing, it is possible to continue removing the current of the differential frequency Δf component in the component current.

[0077] As described above, in the second embodiment, duty variation control is performed to apply duty correction to the drive signal in synchronization with the difference frequency. Therefore, it is possible to remove the difference frequency component in the audible range caused by the simultaneous operation of the first inverter circuit 10a and the second inverter circuit 10b. This makes it possible to suppress interference noise generated from components due to the current of the difference frequency. This also makes it possible to improve the product reliability of the induction heating cooker 100A.

[0078] Moreover, by setting the relationship between the drive frequencies of the two inverter circuits to f2=1.5×f1, the relationship is such that the differential frequency Δf=1 / 2×f1 and the differential frequency Δf=1 / 3×f2 as shown in formulas (1) and (2). Since the differential frequency Δf is an integer multiple of the drive frequency f1 or the drive frequency f2, it is possible to synchronize the generation of the differential frequency component detected by the current peak detection device 90 with the drive frequency f1 or f2 of the drive signal output from the control device 30. Therefore, the control device 30 can perform duty fluctuation control efficiently and with high accuracy by having the current peak detection device 90 perform a detection operation in synchronization with the drive frequency, and therefore it is possible to more reliably achieve suppression of interference noise.

[0079] Here, a case will be described in which the relationship between the drive frequency of the first inverter circuit 10a and the drive frequency of the second inverter circuit 10b is different from that described in the second embodiment. For example, the drive frequency f2 is set to an integer multiple of the drive frequency f1, such as f2=2×f1. In this case, the relationship between the difference frequency Δf and the drive frequency f1 is as shown in the following formula (3). Moreover, the relationship between the difference frequency Δf and the drive frequency f2 is as shown in the following formula (4).

[0080] Δf=f2-f1=2×f1-f1=f1...Equation (3)

[0081] Δf=f2-f1=f2-1 / 2×f2=1 / 2×f2...Equation (4)

[0082] As shown in formulas (3) and (4), the differential frequency Δf is an integer multiple of the drive frequency f1 or the drive frequency f2. Therefore, similarly to the case where f2=1.5×f1, the generation of the differential frequency component can be synchronized with the drive frequency of the drive signal output from the control device 30 by utilizing the drive frequency of the drive signal.

[0083] Here, by increasing the drive frequency f2 of the second inverter circuit 10b, it is possible to deal with the fact that the resonant frequency becomes high (= the inductance L value of the heated object becomes low) when the heated object placed on the second heating port 70b is a non-magnetic material. However, if the drive frequency f2 is increased to f2=2×f1 (for example, if f1=23kHz, then f2=46kHz), it may not be possible to input power up to the maximum set heating power desired by the user to the heated object made of a non-magnetic material. Therefore, although interference noise can be suppressed accurately even if f2=2×f1, it is preferable to set f2=1.5×f1.

[0084] Furthermore, a case will be described where the relationship between the drive frequency of the first inverter circuit 10a and the drive frequency of the second inverter circuit 10b does not satisfy f2=1.5×f1 and f2=2×f1 (or other integer multiples). For example, when the drive frequency is fixed so that f2 / f1 is an indivisible value, such as drive frequency f1=23.12kHz and drive frequency f2=25.53kHz, and control is performed to change the duty ratio, f2=(25.53 / 23.12)×f1. Therefore, the relationship between the difference frequency Δf and the drive frequency f1 is as shown in the following formula (5). Moreover, the relationship between the difference frequency Δf and the drive frequency f2 is as shown in the following formula (6).

[0085] Δf=f2-f1=(25.53 / 23.12)×f1-f1≒0.10424×f1...Equation (5)

[0086] Δf=f2-f1=f2-(23.12 / 25.53)×f2≒0.09440×f2...Equation (6)

[0087] As shown in formulas (5) and (6), the difference frequency Δf is not an integer multiple of the drive frequency f1 or the drive frequency f2. Therefore, in the case of such a drive frequency setting, it becomes difficult to detect the occurrence of the difference frequency component and perform duty variation control using the drive signal from the control device 30 to the first inverter circuit 10a or the second inverter circuit 10b as a trigger.

[0088] Fig. 11 is a diagram showing the drive signals of the first inverter circuit 10a and the second inverter circuit 10b, and the waveform of the current flowing into the smoothing capacitor 9. As described above, Fig. 11 shows the drive signals to the inverter circuits and the waveform of the current flowing into the smoothing capacitor 9 when the drive frequency f1 is 23.12 kHz and the drive frequency f2 is 25.53 kHz. As shown in Fig. 11, the waveform of the current flowing into the smoothing capacitor 9 becomes a non-periodic waveform due to the relationship between 23.12 kHz and 25.53 kHz, making it difficult to synchronize the generation of the difference frequency component with the drive frequency f1 or the drive frequency f2.

[0089] Furthermore, another example will be described in which the relationship between the drive frequency of the first inverter circuit 10a and the drive frequency of the second inverter circuit 10b does not satisfy f2=1.5×f1 and f2=2×f1 (or other integer multiples). Here, a case where f2 / f1 is divisible will be described. For example, when the drive frequency f1 is fixed at 24 kHz assuming induction heating of a magnetic material, and the drive frequency f2 is fixed at 31.2 kHz assuming induction heating of a non-magnetic material, and control is performed to change the duty ratio, f2=1.3×f1. Therefore, the relationship between the difference frequency Δf and the drive frequency f1 is as shown in the following formula (7). Moreover, the relationship between the difference frequency Δf and the drive frequency f2 is as shown in the following formula (8).

[0090] Δf=f2-f1=1.3×f1-f1=0.3×f1(≠1 / 3×f1)...Equation (7)

[0091] Δf=f2-f1=f2-(1 / 1.3)×f2≒0.23077×f2...Equation (8)

[0092] As shown in formulas (7) and (8), the difference frequency Δf is not an integer multiple of the drive frequency f1 or the drive frequency f2. Therefore, even if f2 / f1 is divisible, it is difficult to detect the occurrence of the difference frequency component and perform duty variation control using the drive signal from the control device 30 to the first inverter circuit 10a or the second inverter circuit 10b as a trigger.

[0093] In this way, when f2 ≠ 1.5 × f1 and f2 ≠ N × f1 (N is an integer of 2 or more), it is difficult to remove the differential frequency component by duty variation control. Therefore, when performing duty variation control, it is desirable to set the relationship between the driving frequency f1 and the driving frequency f2 so that the differential frequency Δf is an integer multiple of the driving frequency f1 or the driving frequency f2, such as f2 = 1.5 × f1 or f2 = 2 × f1. In particular, it is particularly desirable to set f2 = 1.5 × f1 in order to realize maximum power input to the non-magnetic heated object.

[0094] Embodiment 3 In the first and second embodiments, the first inverter circuit 10a is an inverter circuit for the first heating port 70a on the left side of the induction heating cooker 100 and 100A, and the second inverter circuit 10b is an inverter circuit for the second heating port 70b on the right side of the induction heating cooker 100 and 100A. In the third embodiment, the first inverter circuit 10a and the second inverter circuit 10b may be made to correspond to each of the two heating coils 21 that inductively heat the object to be heated placed on one heating port 70. FIG. 12 is a diagram showing the first heating coil 21a and the second heating coil 21b in the third embodiment. FIG. 12 shows an example in which the object to be heated placed on the first heating port 70a is heated by the first heating coil 21a arranged on the inside and the second heating coil 21b arranged on the outside.

[0095] The first heating coil 21a and the second heating coil 21b are formed electrically independent. A high-frequency current is input from the first inverter circuit 10a to the first heating coil 21a, and a high-frequency current is input from the second inverter circuit 10b to the second heating coil 21b. By driving the first inverter circuit 10a at a driving frequency f1, the part of the object to be heated that is directly above the first heating coil 21a on the inside is inductively heated at the driving frequency f1. By driving the second inverter circuit 10b at a driving frequency f2, the part of the object to be heated that is directly above the second heating coil 21b on the outside is inductively heated at the driving frequency f2. The other circuit configurations are the same as those in the first embodiment, so a description thereof will be omitted.

[0096] When the bottom surface of the object to be heated is made of a single material, the control device 30 performs induction heating with the driving frequency f1 and the driving frequency f2 set to the same frequency, and changes the duty ratios of the first inverter circuit 10a and the second inverter circuit 10b. This allows the input power of the first inner heating coil 21a and the input power of the second outer heating coil 21b to be set separately. At this time, since the driving frequency f1 and the driving frequency f2 are the same frequency, no difference frequency Δf is generated. Therefore, no interference noise is generated.

[0097] When the bottom surface of the object to be heated is not made of a single material, the control device 30 sets the drive frequency so that the drive frequency f1 of the first inverter circuit 10a is smaller than the drive frequency f2 of the second inverter circuit 10b. For example, the magnetic material part on the inside of the object to be heated is induction heated at drive frequency f1=22kHz, and the non-magnetic material part on the outside of the object to be heated is induction heated at drive frequency f2=36kHz. The control device 30 also controls the input power by performing duty ratio variable control on each of the first inverter circuit 10a and the second inverter circuit 10b. The case where the bottom surface of the object to be heated is not made of a single material is, for example, a case where the inside of the bottom surface is made of a magnetic material and the outside of the bottom surface is made of a non-magnetic material such as aluminum.

[0098] In this way, when the bottom surface of the heated object is not formed of a single material, the drive frequency f1 ≠ drive frequency f2 generates a differential frequency Δf component. Therefore, interference noise is generated from the filter circuit 7. However, even in the third embodiment, the jittering control described in the first embodiment or the duty variation control described in the second embodiment is performed. As a result, even when two heating coils 21 are associated with one heating port 70 to perform induction heating, interference noise from the filter circuit 7 can be suppressed regardless of the material of the heated object. In addition, the convenience and reliability of the induction heating cooker 100 can be improved.

[0099] Other heating operations when jittering control and duty variation control are not performed will be described. The induction heating cooker 100 of the third embodiment may drive only the first inverter circuit 10a corresponding to the inner first heating coil 21a at the driving frequency f1. In this case, a small-diameter object to be heated can be efficiently heated. The induction heating cooker 100 may drive only the second inverter circuit 10b corresponding to the outer second heating coil 21b at the driving frequency f2. In this case, the outside of a large-diameter object to be heated (for example, the surface of a frying pan) can be intensively heated.

[0100] When heating the outside of a large-diameter object, it is preferable to control as follows. That is, the first inner heating coil 21a is also fixed to a driving frequency f1, and power control with a variable duty ratio is performed continuously or intermittently, while the second outer heating coil 21b is fixed to a driving frequency f2, and power control with a variable duty ratio is performed. This allows independent power control of the first inner heating coil 21a and the second outer heating coil 21b, and fine control of the heating distribution including the inside of the bottom of the pan.

[0101] Also, the first inner heating coil 21a and the second outer heating coil 21b may be energized simultaneously, while varying the energizing power and time for each heating coil 21. Specifically, continuous energization and intermittent energization may be interwoven in each heating coil 21, or the intermittent time may be varied when energizing the heating coil 21 intermittently. In this case, too, it is possible to promote convection in the object to be heated (such as water in a cooking vessel). However, when the first inner heating coil 21a and the second outer heating coil 21b are driven in a time-division manner (exclusive operation control), it is not necessary to perform the jittering control described in the first embodiment or the duty variation control described in the second embodiment. This is because no difference frequency component is generated when the time-division drive is performed.

[0102] As described above, in the third embodiment, the jittering control described in the first embodiment or the duty variation control described in the second embodiment is also performed. Therefore, even when two heating coils 21 corresponding to one heating port 70 perform induction heating simultaneously, it is possible to suppress the generation of differential frequency components and interference noise. Furthermore, since it is possible to simultaneously drive two heating coils 21 corresponding to one heating port 70 while suppressing the generation of interference noise, it is possible to finely control the heating distribution on the bottom surface of the pan to promote convection in the heated object and improve the finish of the food.

[0103] Although the case where the heating coils 21 are arranged inside and outside the first heating port 70a has been described, there is no limitation on the arrangement of the multiple heating coils 21. Instead of or in addition to the first heating port 70a, the second heating port 70b or the third heating port 70c may also be provided with two heating coils to perform the jittering control described in the first embodiment or the duty variation control described in the second embodiment.

[0104] The above is a description of the embodiments of the present disclosure, but the present disclosure is not limited to the configurations of the above embodiments, and various modifications are possible within the scope of the technical concept thereof.

[0105] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) a front-stage circuit including a rectifier circuit for rectifying an output of an AC power supply and a filter circuit for smoothing the output of the rectifier circuit; A first inverter circuit and a second inverter circuit are connected in parallel to the rear stage of the front stage circuit and supply a high-frequency current to a heating coil that inductively heats an object to be heated; A control device that controls driving of the first inverter circuit and the second inverter circuit, The control device includes: When a drive signal is simultaneously transmitted to the first inverter circuit and the second inverter circuit, jittering control is performed to add a random deviation to the drive frequency of the drive signal transmitted to the first inverter circuit. Induction heating cooker. (Appendix 2) a front-stage circuit including a rectifier circuit for rectifying an output of an AC power supply and a filter circuit for smoothing the output of the rectifier circuit; A first inverter circuit and a second inverter circuit are connected in parallel to the rear stage of the front stage circuit and supply a high-frequency current to a heating coil that inductively heats an object to be heated; a current peak detection device for detecting a peak of a current flowing into the preceding circuit; A control device that controls driving of the first inverter circuit and the second inverter circuit, The control device includes: When a drive signal is simultaneously transmitted to the first inverter circuit and the second inverter circuit, the current peak detection device is used to detect a generation timing of a current component of a difference frequency between a drive frequency of the drive signal of the first inverter circuit and a drive frequency of the drive signal of the second inverter circuit, and a duty variation control is performed to vary a duty ratio, which is an on-time ratio of a switching element of the first inverter circuit, of the drive signal in synchronization with the generation timing. Induction heating cooker. (Appendix 3) The control device includes: The first inverter circuit and the second inverter circuit are operated at different drive frequencies, and the drive frequency of the first inverter circuit is set to 1.5 times the drive frequency of the second inverter circuit. 5. An induction heating cooker as described in appended claim 2. (Appendix 4) The control device includes: The first inverter circuit and the second inverter circuit are operated at different drive frequencies, and the drive frequency of the first inverter circuit is set to twice the drive frequency of the second inverter circuit. 5. An induction heating cooker as described in appended claim 2. (Appendix 5) The current peak detection device detects a peak of a current flowing into the previous stage circuit in the process of downwardly shifting a current threshold value that is initially set to a high value. 5. An induction heating cooker as described in appendix 2. (Appendix 6) The control device includes: The first inverter circuit and the second inverter circuit are operated at different drive frequencies. 6. An induction heating cooker according to any one of claims 1, 2, or 5. (Appendix 7) The control device includes: The power supplied to the object to be heated is changed by changing a duty ratio, which is an on-time ratio of switching elements of the first inverter circuit and the second inverter circuit. 7. An induction heating cooker according to any one of claims 1 to 6. (Appendix 8) A first heating port; A second heating port; The heating coil may include a first heating coil connected to the first inverter circuit; A second heating coil connected to the second inverter circuit, The first heating coil is provided in the first heating port, The second heating coil is provided in the second heating port. An induction heating cooker according to any one of appendixes 1 to 7. (Appendix 9) A heating port and The heating coil may include a first heating coil connected to the first inverter circuit; A second heating coil connected to the second inverter circuit, The first heating coil and the second heating coil are provided in the heating port. An induction heating cooker according to any one of appendixes 1 to 7. [Explanation of symbols]

[0106] 5 Pre-stage circuit, 6 Rectifier circuit, 6a Diode, 7 Filter circuit, 8 Choke coil, 9 Smoothing capacitor, 10a First inverter circuit, 10b Second inverter circuit, 11a, 11b, 12a, 12b Switching element, 20a First resonant circuit, 20b Second resonant circuit, 21 Heating coil, 21a First heating coil, 21b Second heating coil, 22a, 22b Resonant capacitor, 30 Control device, 50 Housing, 51 Operation unit, 52 Main power button, 53 Heating button, 54 Heating power setting unit, 55 Display unit, 60 Top plate, 70 Heating port, 70a First heating port, 70b Second heating port, 70c Third heating port, 80 Current detection device, 81a Current detection device, 81b Current detection device, 90 Current peak detection device, 100, 100A Induction cooker, 200 AC power supply.

Claims

1. a front-stage circuit including a rectifier circuit for rectifying an output of an AC power supply and a filter circuit for smoothing the output of the rectifier circuit; A first inverter circuit and a second inverter circuit are connected in parallel to the rear stage of the front stage circuit and supply a high-frequency current to a heating coil that inductively heats an object to be heated; a control device that controls driving of the first inverter circuit and the second inverter circuit, The control device includes: When a drive signal is simultaneously transmitted to the first inverter circuit and the second inverter circuit, jittering control is performed to add a random deviation to the drive frequency of the drive signal transmitted to the first inverter circuit. Induction heating cooker.

2. a front-stage circuit including a rectifier circuit for rectifying an output of an AC power supply and a filter circuit for smoothing the output of the rectifier circuit; A first inverter circuit and a second inverter circuit are connected in parallel to the rear stage of the front stage circuit and supply a high-frequency current to a heating coil that inductively heats an object to be heated; a current peak detection device for detecting a peak of a current flowing into the preceding circuit; a control device that controls driving of the first inverter circuit and the second inverter circuit, The control device includes: When a drive signal is simultaneously transmitted to the first inverter circuit and the second inverter circuit, the current peak detection device is used to detect a generation timing of a current component of a difference frequency between a drive frequency of the drive signal of the first inverter circuit and a drive frequency of the drive signal of the second inverter circuit, and a duty variation control is performed to vary a duty ratio, which is an on-time ratio of a switching element of the first inverter circuit, of the drive signal in synchronization with the generation timing. Induction heating cooker.

3. The control device includes: The first inverter circuit and the second inverter circuit are operated at different drive frequencies, and the drive frequency of the first inverter circuit is set to 1.5 times the drive frequency of the second inverter circuit.

3. The induction heating cooker according to claim 2.

4. The control device includes: The first inverter circuit and the second inverter circuit are operated at different drive frequencies, and the drive frequency of the first inverter circuit is set to twice the drive frequency of the second inverter circuit.

3. The induction heating cooker according to claim 2.

5. The current peak detection device detects a peak of a current flowing into the previous stage circuit in the process of downwardly shifting a current threshold value that is initially set to a high value.

3. The induction heating cooker according to claim 2.

6. The control device includes: The first inverter circuit and the second inverter circuit are operated at different drive frequencies.

6. An induction heating cooker according to claim 1, 2 or 5.

7. The control device includes: The power supplied to the object to be heated is changed by changing a duty ratio, which is an on-time ratio of switching elements of the first inverter circuit and the second inverter circuit. The induction heating cooker according to any one of claims 1 to 5.

8. A first heating port; A second heating port; The heating coil may include a first heating coil connected to the first inverter circuit; A second heating coil connected to the second inverter circuit, The first heating coil is provided in the first heating port, The second heating coil is provided in the second heating port. The induction heating cooker according to any one of claims 1 to 5.

9. A heating port and The heating coil may include a first heating coil connected to the first inverter circuit; A second heating coil connected to the second inverter circuit, The first heating coil and the second heating coil are provided in the heating port. The induction heating cooker according to any one of claims 1 to 5.

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