WO2013061493A1

WO2013061493A1 - Induction heating cookware

Info

Publication number: WO2013061493A1
Application number: PCT/JP2012/004433
Authority: WO
Inventors: 澤田　大輔; 藤井　裕二; 富永　博
Original assignee: パナソニック株式会社
Priority date: 2011-10-28
Filing date: 2012-07-09
Publication date: 2013-05-02
Also published as: JPWO2013061493A1; JP5979386B2

Abstract

A first inverter circuit (4a) and a second inverter circuit (4b) are controlled such that each inverter supplies electricity in a high-power mode and in a low-power mode alternately and exclusively in a repeated manner at a predetermined control cycle. When the peak vale of an input current input from an alternating-current power supply (1) to a rectification smoothing circuit (13) has become equal to or lower than a threshold value Ith, the heating operation of either the first inverter circuit (4a) or the second inverter circuit (4b), whichever is supplying electricity in the high-power mode, is stopped, and the other inverter circuit alone is controlled to perform the heating operation by means of continuous control.

Description

Induction heating cooker

The present invention relates to an induction heating cooker that includes two inverter circuits and drives each inverter circuit by switching individually.

FIG. 5 is a block diagram showing the configuration of an induction heating cooker according to the prior art described in Patent Document 1, for example. In FIG. 5, a rectifier circuit 52 rectifies AC power from an AC power supply 51, and DC output power from the rectifier circuit 52 is smoothed by a smoothing circuit including a choke coil 53 and a smoothing capacitor 54, and an inverter circuit 60a and To 60b. Here, the inverter circuit 60a includes a heating coil 55a, a resonance capacitor 56a, a switching transistor 58a, and a damper diode 57a. The inverter circuit 60b includes a heating coil 55b, a resonance capacitor 56b, A switching transistor 58b and a damper diode 57b are provided. The two

inverter circuits

60 a and 60 b share the rectifier circuit 52, the choke coil 53, and the smoothing capacitor 54. The

switching elements

58a and 58b perform an on / off operation in accordance with a drive signal from the drive circuit 62.

In FIG. 5, the zero volt detection circuit 61 detects the zero point of the voltage between the terminals of the AC power supply 51 and outputs a zero point detection signal to the drive circuit 62. In addition, the drive circuit 62 drives the two

inverter circuits

60a and 60b alternately instead of simultaneously, and adjusts the heating power according to the drive time ratio. Further, when switching to the other inverter circuit during the operation of one of the

inverter circuits

60a and 60b, the drive circuit 62 stops one of the inverter circuits near the zero point of the voltage between the terminals of the AC power supply 51. The other inverter circuit is driven after passing through the zero point. Thereby, it is possible to prevent an inrush current from occurring in the

heating coil

55a or 55b every time heating is started, and to eliminate the “knack and knack” sound generated in the pan when the inrush current is generated.

JP-A-2-270293

According to the above-described prior art, the same load such as a single iron plate or pan is placed on two heating coils, and only one heating coil is used for, for example, stewed cooking that requires a strong heating power. However, in the case of an induction heating cooker that can change the heating area according to the cooking content, such as using two heating coils for teppanyaki cooking that requires a wide heating area, etc. Occurrence can be eliminated. However, for example, in an induction heating cooker provided with two cooking heaters each having one heating coil, different loads are arranged directly above the two heating coils, and 2 similarly to the induction heating cooker according to the prior art. When one inverter circuit is controlled, when a load is removed from just above one heating coil, a pot knack noise may be generated from a pan placed just above the other heating coil.

The reason why the above phenomenon occurs will be described below. There is already known a method for detecting that the load has been removed from the heating coil and stopping the heating operation based on the input current from the AC power source and the resonance current flowing in the heating coil or the resonance voltage generated in the resonance capacitor. It has been. Here, in particular, when the load is removed quickly, there may be a slight time delay from when the heating coil is overloaded until the heating operation is stopped. In an induction heating cooker having two heating coils, during the period from when the load is removed from one heating coil until the operation of the one heating coil is stopped, the one heating coil is unloaded. Therefore, for example, the electric charge discharged from the smoothing capacitor 54 in FIG. 5 is extremely small, and the smoothing capacitor 54 is substantially charged (smooth state). In addition, since the two heating coils operate alternately, an inrush current flows to the other heating coil with the load being placed each time heating is started, and a pot knack noise is generated from the load on the other heating coil. .

An object of the present invention is to solve the above problems and to provide an induction heating cooker that can eliminate unpleasant sounds such as a pot knack caused by an inrush current when the pot is removed.

In order to solve the conventional problem, an induction heating cooker according to the present invention converts a direct current input from an alternating current power source through a rectifying and smoothing circuit into a predetermined first high frequency current, and a first load. A first inverter circuit that supplies a first heating coil for induction heating, converts the direct current into a predetermined second high-frequency current, and supplies the second load to a second heating coil for induction heating Induction heating cooking comprising a second inverter circuit, input current detection means for detecting an input current input from the AC power source to the rectifying and smoothing circuit, and control means for controlling the first and second inverter circuits In the apparatus, the control means has the first input power so that the input power of the first inverter circuit becomes a predetermined first input power larger than a predetermined first target input power in a predetermined first period. Inva And controlling the second inverter circuit so that the input power of the second inverter circuit becomes a predetermined second input power smaller than a predetermined second target input power. The first inverter circuit is set so that the input power of the first inverter circuit becomes a predetermined third input power smaller than the first target input power in a predetermined second period following the first period. And controlling the second inverter circuit so that the input power of the second inverter circuit becomes a predetermined fourth input power larger than the second target input power, and the first period; By repeating the second period at a predetermined control cycle, the average input power of the first inverter circuit becomes the first target input power, and the average input power of the second inverter circuit The first and second inverter circuits are controlled so as to be the second target input power, and when it is detected that the input current is not more than a predetermined threshold value, the first and second inverter circuits are The inverter circuit is controlled to stop the heating operation of one inverter circuit that has been controlled so that the input power becomes the first or fourth input power at the detected timing.

According to the induction heating cooker according to the present invention, when the first and second inverter circuits are driven alternately, the pan is removed from the first and second inverter circuits, and no load is applied. Thus, the heating operation of the one inverter circuit can be quickly stopped as compared with the prior art. Therefore, the other inverter circuit can be controlled so as not to start the heating operation from the state in which the smoothing capacitor is substantially charged (smooth state), and the occurrence of inrush current to the heating coil is prevented to eliminate the pot knack noise. be able to.

It is a block diagram which shows the structure of the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a timing chart which shows operation | movement of the induction heating cooking appliance of FIG. 4 is a timing chart showing temporal changes in input power of the first inverter circuit 4a and the second inverter circuit 4b when switching from time division control to continuous control in the second inverter circuit 4b of FIG. 1; 3B is a timing chart showing a time change of input power equivalent to a time change of input power of the second inverter circuit 4b of FIG. 3A. It is a timing chart which shows the operation | movement which concerns on Embodiment 2 of this invention of the induction heating cooking appliance of FIG. It is a block diagram which shows the structure of the induction heating cooking appliance which concerns on a prior art.

The induction heating cooker which concerns on a 1st aspect converts the direct current input from an alternating current power supply via a rectification smoothing circuit into the predetermined 1st high frequency current, and the 1st heating which carries out induction heating of the 1st load A first inverter circuit to be supplied to the coil, a second inverter circuit to convert the DC current into a predetermined second high-frequency current and to supply a second heating coil for induction heating the second load, and AC In an induction heating cooker comprising input current detection means for detecting an input current input from a power source to the rectifying and smoothing circuit, and control means for controlling the first and second inverter circuits, the control means comprises: Controlling the first inverter circuit so that the input power of the first inverter circuit becomes a predetermined first input power larger than a predetermined first target input power in a predetermined first period; The second inverter circuit is controlled so that the input power of the second inverter circuit becomes a predetermined second input power smaller than a predetermined second target input power, and a predetermined value following the first period is determined. In the second period, the first inverter circuit is controlled so that the input power of the first inverter circuit becomes a predetermined third input power smaller than the first target input power, and the second The second inverter circuit is controlled so that the input power of the inverter circuit becomes a predetermined fourth input power larger than the second target input power, and the first period and the second period are By repeating at a predetermined control cycle, the average input power of the first inverter circuit becomes the first target input power, and the average input power of the second inverter circuit becomes the second target input power. As described above, when the first and second inverter circuits are controlled and it is detected that the input current is equal to or lower than a predetermined threshold value, the detected timing of the first and second inverter circuits. The control is performed to stop the heating operation of one inverter circuit that has been controlled so that the input power becomes the first or fourth input power.

Therefore, when the first and second inverter circuits are driven alternately, the heating operation of one of the first and second inverter circuits that has been removed from the pan and has no load. Can be quickly stopped as compared with the prior art. Therefore, the other inverter circuit can be controlled so as not to start the heating operation from the state in which the smoothing capacitor is substantially charged (smooth state), and the occurrence of inrush current to the heating coil is prevented to eliminate the pot knack noise. be able to.

The induction heating cooker according to the second aspect is the induction heating cooker according to the first aspect, wherein when the control means detects that the input current is equal to or less than the threshold value, Of the second inverter circuits, the other inverter circuit is controlled so that the input power of the other inverter circuit becomes a predetermined third target input power.

Therefore, the heating operation of one inverter circuit, which has become unloaded after the pan is removed, is quickly stopped as compared with the prior art, and the control method for the other inverter circuit is continuously performed independently. Can be changed to control. For this reason, the other inverter circuit can be controlled so as not to start the heating operation from the state in which the smoothing capacitor is substantially charged (smooth state), and the occurrence of inrush current to the heating coil can be prevented and Can be eliminated.

The induction heating cooker according to a third aspect is the induction heating cooker according to the second aspect, wherein the third target input power is the other inverter of the first and second target input powers. It is set to be the same as the target input power of the circuit.

Therefore, at the timing when it is detected that the input current is less than the threshold value, the input power is arranged directly above the heating coil connected to the other inverter circuit that has been controlled to become the second or third input power. Stable power supply can be performed regardless of whether the control method of the other inverter circuit is changed with respect to the load to be performed.

An induction heating cooker according to a fourth aspect is the induction heating cooker according to any one of the first to third aspects, wherein the second and third input powers are each set to zero. It is characterized by that.

Therefore, since the first and second inverter circuits are not driven at the same time, it is possible to eliminate interference sound (buzzing sound).

An induction heating cooker according to a fifth aspect is the induction heating cooker according to any one of the first to third aspects, wherein the frequency of the drive signal of the second inverter circuit in the first period is Is set to a frequency twice the frequency of the drive signal of the first inverter circuit in the first period, and the frequency of the drive signal of the first inverter circuit in the second period is the second frequency The frequency is set to twice the frequency of the drive signal of the second inverter circuit in the period.

Therefore, since there is no frequency difference between the frequency of the second harmonic of the drive signal of one inverter circuit and the frequency of the drive signal of the other inverter circuit, it is possible to eliminate interference sound (buzzing sound).

An induction heating cooker according to a sixth aspect is the induction heating cooker according to any one of the first to fifth aspects, and notifies the state of the heating operation of the first and second inverter circuits. In addition, the control means controls the notifying means so as to notify that the one inverter circuit stops the heating operation after stopping the heating operation of the one inverter circuit. It is characterized by that.

Accordingly, the user can easily recognize, for example, visually or audibly that the heating operation is automatically stopped by removing the load immediately above the heating coil.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a block diagram showing the configuration of the induction heating cooker according to Embodiment 1 of the present invention. 1, the induction heating cooker according to the present embodiment includes an AC power source 1, a rectifying / smoothing circuit 13 including a rectifying circuit 2 and a smoothing capacitor 3, and a first heating coil for induction heating a first load. 5a, the second heating coil 5b for induction heating the second load, the first inverter circuit 4a, the second inverter circuit 4b, the first drive circuit 8a, and the second drive circuit 8b The control means 9, the current detection means 10, the notification means 11 provided with the first notification means 11a and the second notification means 11b, and the zero volt detection circuit 12 are configured. For example, a first load such as a pan is placed immediately above the first heating coil 5a, and a second load such as a pan is placed directly above the second heating coil 5b. The first inverter circuit 4a includes a first resonant capacitor 6a and two

first semiconductor switches

7a and 7b, and the first inverter circuit 4b includes a second resonant capacitor 6b and Two second semiconductor switches 7c and 7d are provided.

Here, the rectifier circuit 2 rectifies and outputs an alternating current from the alternating current power source 1. Further, the output current from the rectifier circuit 2 is smoothed by the smoothing capacitor 3. The direct current from the smoothing capacitor 3 is output to the first inverter circuit 4a and the second inverter circuit 4b. Further, the current detection means 10 detects an input current input from the AC power source 1 to the rectifying / smoothing circuit 13 using, for example, a current transformer, detects a peak value of the detected input current, and detects the detected peak value. Is output to the control means 9. Further, the zero volt detection circuit 12 detects the zero point of the voltage between the terminals of the AC power supply 1, generates a zero point detection signal that is a pulse signal indicating the timing at which the zero point is detected, and outputs the zero point detection signal to the control means 9.

The control means 9 comprises a microcomputer, and based on the current detection signal from the current detection means 10 and the zero volt detection signal from the zero volt detection circuit 12, the

first semiconductor switches

7a and 7b and the second semiconductor switch A control signal for controlling the switches 7c and 7d is generated and output to the first drive circuit 8a and the second drive circuit 8b. The first drive circuit 8a generates a drive signal for driving the

first semiconductor switches

7a and 7b based on the control signal from the control means 9, and outputs the drive signal to the

first semiconductor switches

7a and 7b. The second drive circuit 8b generates a drive signal for driving the second semiconductor switches 7c and 7d based on the control signal from the control means 9, and outputs the drive signal to the second semiconductor switches 7c and 7d. To do. The control means 9 controls the first inverter circuit 4a and the second inverter so that the peak value of the input current detected by the current detection means 10 is substantially equal to a predetermined set value held in the microcomputer. The

first semiconductor switch

7a, 7b and the second semiconductor switch 7c, 7d in the circuit 4b are controlled to control the power of the first inverter circuit 4a and the second inverter circuit 4b. Furthermore, the control means 9 outputs to the notification means 11 a signal indicating whether or not the first inverter circuit 4a is performing a heating operation and whether or not the second inverter circuit 4b is performing a heating operation. A specific method for controlling the first inverter circuit 4a and the second inverter circuit 4b by the control means 9 will be described later.

The first notification means 11a is a light-emitting diode, which is turned on when the first inverter circuit 4a is performing the heating operation, and is turned off when the first inverter circuit 4a is not performing the heating operation. The state of the heating operation of the first inverter circuit 4a is notified. The second notification means 11b is a light emitting diode, and lights up when the second inverter circuit 4b is performing a heating operation, while it is turned on when the second inverter circuit 4b is halting a heating operation. The light is turned off and the state of the heating operation of the second inverter circuit 4b is notified.

The first inverter circuit 4a is a half bridge circuit. Here, the series connection circuit of the

first semiconductor switches

7 a and 7 b is connected in parallel to the smoothing capacitor 3. Further, the series connection circuit of the first heating coil 5a and the first resonance capacitor 6a includes the midpoint of the series connection circuit of the

first semiconductor switches

7a and 7b and the reference potential (ground potential) side of the smoothing capacitor 3. Between the two electrodes. The first inverter circuit 4a converts a direct current input from the alternating current power supply 1 through the rectifying and smoothing circuit 13 into a predetermined first high-frequency current, and a first heating coil 5a that induction-heats the first load. To supply.

Similarly to the first inverter circuit 4a, the second inverter circuit 4b is a half-bridge circuit. Here, the series connection circuit of the second semiconductor switches 7 c and 7 d is connected in parallel to the smoothing capacitor 3. Further, the series connection circuit of the second heating coil 5b and the second resonance capacitor 6b includes the midpoint of the series connection circuit of the second semiconductor switches 7c and 7d and the reference potential (ground potential) side of the smoothing capacitor 3. Between the two electrodes. The second inverter circuit 4b converts a direct current input from the alternating current power source 1 through the rectifying and smoothing circuit 13 into a predetermined second high frequency current, and a second heating coil 5b for induction heating the second load. To supply. The first inverter circuit 4 a and the second inverter circuit 4 b share the rectifier circuit 2, the smoothing capacitor 3, and the current detection means 10.

Although the first and

second inverter circuits

4a and 4b of the present embodiment are each configured by a half bridge circuit, the same effects as those of the present embodiment can be obtained even when configured by a full bridge circuit.

Next, the operation of the control means 9 will be described in detail. As described above, the control means 9 controls the heating operation of the first inverter circuit 4a and the second inverter circuit 4b by outputting control signals to the first drive circuit 8a and the second drive circuit 8b. To do. Specifically, when the control means 9 heats only the first inverter circuit 4a, the control means 9 sets the first inverter circuit 4a so that the input power continuously becomes the predetermined first target input power P1. 1 inverter circuit 4a is controlled. Further, when the control means 9 heats only the second inverter circuit 4b, the second inverter circuit 4b continuously controls the second inverter circuit 4b so that the input power becomes the predetermined second target input power P2. The circuit 4b is controlled. Hereinafter, the operation of heating only one of the first inverter circuit 4a and the second inverter circuit 4b as described above is referred to as “the inverter circuit is heated by continuous control”.

The control means 9 controls the first inverter circuit 4a and the second inverter circuit 4b as follows when both the first inverter circuit 4a and the second inverter circuit 4b are heated. The control means 9 performs a predetermined control on the energization period in the high power mode and the energization period in the low power mode so that the average input power of the first inverter circuit 4a becomes the predetermined first target input power P1. The first inverter circuit 4a is controlled so as to repeat at a cycle. Here, during the energization period in the high power mode, the input power of the first inverter circuit 4a is controlled to be a predetermined input power P1a larger than the first target input power P1, while in the low power mode. During the energization period, the input power of the first inverter circuit 4a is controlled to be a predetermined input power P1b that is smaller than the first target input power P1. In the present embodiment, the input power P1b in the low power mode is set to 0 W, and the first inverter circuit 4a stops operating. Further, the control means 9 determines the energization period in the high power mode and the energization period in the low power mode so that the average input power of the second inverter circuit 4b becomes the predetermined second target input power P2. The second inverter circuit 4b is controlled so as to be repeated at the control cycle. Here, during the energization period in the high power mode, the input power of the second inverter circuit 4b is controlled to be a predetermined input power P2a larger than the second target input power P2, while in the low power mode. During the energization period, the input power of the second inverter circuit 4b is controlled to be a predetermined input power P2b that is smaller than the second target input power P2. In the present embodiment, the input power P2b in the low power mode is set to 0 W, and the second inverter circuit 4b stops operating. Further, the first target input power P1 and the second target input power P2 are set to arbitrary input powers by the user, for example.

Further, the control means 9 repeats the first inverter circuit 4a and the second inverter circuit 4b alternately and exclusively in the high power mode and in the low power mode at the above-described control cycle. To control. In the present embodiment, since the input powers P1b and P2b in the low power mode are set to 0 W, the first inverter circuit 4a and the second inverter circuit 4b are driven alternately without being driven simultaneously. The control means 9 controls the power of the first heating coil 5a according to the ratio of the operation period of the first inverter circuit 4a in the high power mode, and the operation period of the second inverter circuit 4b in the high power mode. The power of the second heating coil 5b is controlled according to the ratio.

Further, similarly to the induction heating according to the prior art, the control means 9 switches from energization in the high power mode to energization in the low power mode in each

inverter circuit

4a, 4b in accordance with the zero volt detection signal from the zero volt detection circuit 12. Or, switching from energization in the low power mode to energization in the high power mode. Thus, when switching between energization in the high power mode and energization in the low power mode, the residual voltage of the smoothing capacitor 3 is suppressed to a relatively low voltage, and the first heating coil 5a or the second at the time of starting is suppressed. The inrush current of the heating coil 5b can be suppressed. Accordingly, it is possible to reduce the pot knack sound generated each time switching between energization in the high power mode and energization in the low power mode to a level that is not problematic for the user. Hereinafter, the heating operation of both the first inverter circuit 4a and the second inverter circuit 4b as described above is "the heating operation of the first inverter circuit 4a and the second inverter circuit 4b is performed by time-sharing control". That's it.

Further, the control means 9 has a predetermined peak value of the input current detected by the current detection means 10 when the first inverter circuit 4a and the second inverter circuit 4b are heated by time division control. When it is detected that the threshold value is less than or equal to the threshold value Ith, one of the first inverter circuit 4a and the second inverter circuit 4b was energized in the high power mode at the detected timing (that is, operated) The heating operation of the inverter circuit was stopped, and the other inverter circuit that was energized in the low power mode at the detected timing (that is, in the present embodiment, the energization was stopped) was heated by continuous control. Make it work. At this time, the target input power of the other inverter circuit described above is set to be the same as the target input power of the other inverter circuit just before the timing when the peak value of the input current becomes equal to or lower than the predetermined threshold value Ith. .

The operation and action of the induction heating cooker configured as described above will be described.

FIG. 2 is a timing chart showing the operation of the induction heating cooker of FIG. In FIG. 2, first, two cooking heaters corresponding to the first inverter circuit 4a and the second inverter circuit 4b are used at the same time. As such a cooking mode, for example, a cooking mode in which a stewed cooking such as curry or stew and a water heater are performed simultaneously is conceivable. In this case, different first and second loads (pans) are disposed immediately above the first heating coil 5a and the second heating coil 5b. And the control means 9 heat-operates the 1st inverter circuit 4a and the 2nd inverter circuit 4b by time division control. Further, the first notification means 11a turns on the light emitting diode to visually notify the user that the first inverter circuit 4a is performing the heating operation, and the second notification means 11b turns on the light emitting diode. By doing so, the user is visually informed that the second inverter circuit 4b is performing the heating operation.

In FIG. 2, during the period when the first inverter circuit 4a and the second inverter circuit 4b are controlled by time-sharing control, at the rising timings t1, t3, and t5 of the zero point detection signal from the zero volt detection circuit 12, The first inverter circuit 4a is switched from the energized state in the low power mode to the energized state in the high power mode, while the second inverter circuit 4b is switched from the energized state in the high power mode to the energized state in the low power mode. It is done. In addition, at the rising timing t4 and t4 of the zero point detection signal from the zero volt detection circuit 12, the first inverter circuit 4a is switched from the energized state in the high power mode to the energized state in the low power mode, The inverter circuit 4b is switched from the energized state in the low power mode to the energized state in the high power mode.

Next, when the first load is removed from one cooking heater corresponding to the first heating coil 5a during the simultaneous use of the two cooking heaters at a predetermined timing after the timing t5, the first inverter Since the circuit 4a operates in a no-load state, the input current from the AC power source 1 is extremely reduced. For this reason, as shown in FIG. 2, the peak value of the input current becomes equal to or less than the threshold value Ith at timing t51 after timing t5.

When the control means 9 detects that the peak value of the input current is equal to or less than the threshold value Ith at timing t51, the control means 9 performs the heating operation of the first inverter circuit 4a that has been energized in the high power mode at timing t51. The first inverter circuit 4a is stopped at the next timing t6 when the energization state of the inverter circuit 4a is switched from energization in the high power mode to energization in the low power mode. Further, the control means 9 causes the second inverter circuit 4b to perform a heating operation independently by continuous control at timing t6.

After the timing t6, the second inverter circuit 4b does not perform time-division control that repeats the heating operation and the stop at a predetermined control cycle, but performs continuous control so that the input power continuously becomes the second target input power P2. Heating operation. Furthermore, the control means 9 outputs to the notification means 11 a signal indicating that the first inverter circuit 4a has stopped the heating operation at timing t6. In response to this, the light emitting diode of the notification means 11a is turned off, and the user is visually notified that the pan has been removed from the first heating coil 5a.

FIG. 3A is a timing chart showing temporal changes in input power of the first inverter circuit 4a and the second inverter circuit 4b when switching from time-division control to continuous control in the second inverter circuit 4b of FIG. FIG. 3B is a timing chart showing the time change of the input power equivalent to the time change of the input power of the second inverter circuit 4b of FIG. 3A.

3A, the second target input power P2 of the second inverter circuit 4b is set to 1500 W, and the control period of the time division control is set to 20 milliseconds. At this time, the average input power of the second inverter circuit 4b during the time-sharing control is the input power P2a × (operation period length / control cycle) in the high power mode, so the operation period length is set to 10 milliseconds. Is done. That is, the second inverter circuit 4b is heated with an average input power of 3000 W × (10 milliseconds / 20 milliseconds) = 1500 W. Furthermore, after the control method of the second inverter circuit 4b is changed from the time division control to the continuous control, the second inverter circuit 4 performs the continuous heating operation so that the input power is continuously 1500 W. The generated power (input power) from the second inverter circuit 4b does not change before and after the change of the control method (see FIG. 3B).

As described above, the induction heating cooker according to the first embodiment is
(A) A first DC current input from the AC power supply 1 via the rectifying and smoothing circuit 13 is converted into a predetermined first high-frequency current and supplied to the first heating coil 5a for induction heating the first load. Inverter circuit 4a of
(B) a second inverter circuit 4b that converts the direct current into a predetermined second high-frequency current and supplies the second load to a second heating coil 5b that induction-heats the second load;
(C) input current detection means 10 for detecting an input current input from the AC power supply 1 to the rectifying and smoothing circuit 13;
(D) A control means 9 for controlling the first and

second inverter circuits

4a and 4b is provided.

Here, the control means 9 is such that the input power of the first inverter circuit 4a is greater than the predetermined first target input power P1 in a predetermined first period (for example, the period from the timing t1 to t2 in FIG. 2). The first inverter circuit 4a is controlled so as to have a large predetermined first input power P1a, and the second input power of the second inverter circuit 4b is smaller than the second predetermined target input power P2. The second inverter circuit 4b is controlled so as to be the input power P2b. Further, the control means 9 determines that the input power of the first inverter circuit 4a is the first target input in a predetermined second period (for example, the period from timing t2 to t3 in FIG. 2) following the first period. The first inverter circuit 4a is controlled so as to have a predetermined third input power P1b smaller than the power P1, and the input power of the second inverter circuit 4b is larger than the second target input power P2. The second inverter circuit 4b is controlled so that the input power P2a becomes the same. Then, the control means 9 repeats the first period and the second period at a predetermined control cycle, whereby the average input power of the first inverter circuit 4a becomes the first target input power P1, and the second The first and

second inverter circuits

4a and 4b are controlled so that the average input power of the inverter circuit 4b is equal to the second target input power P2.

When the control means 9 detects that the peak value of the input current is less than or equal to a predetermined threshold value Ith, the detected timing (for example, in FIG. 2) of the first and

second inverter circuits

4a and 4b. Control is performed so as to stop the heating operation of one inverter circuit that has been controlled so that the input power becomes the first input power P1a or the fourth input power P2a at the timing t51).

Further, when the control means 9 detects that the peak value of the input current is equal to or less than the threshold value Ith, the control means 9 switches the other inverter circuit out of the first and

second inverter circuits

4a and 4b to the other inverter. Control is performed so that the input power of the circuit becomes a predetermined third target input power. Here, the third target input power is set to be the same as the target input power of the other inverter circuit among the first and second target input powers P1 and P2.

Therefore, of the first inverter circuit 4a and the second inverter circuit 4b, the heating operation of one of the inverter circuits that has been removed from the pan and has become unloaded is quickly stopped as compared with the prior art, and the other The operation mode of the inverter circuit can be changed to an operation mode in which the heating operation is performed by continuous control independently. For this reason, the heating operation is not started from the state in which the smoothing capacitor 3 is substantially charged (smooth state), and the occurrence of inrush current to the first heating coil 5a and the second heating coil 5b is prevented. You can eliminate the sound of hot pot.

Further, in the first embodiment, the input power P1b and P2b in the low power mode during the time division control is set to 0 W, so that the inverter circuit does not operate during the energization period in the low power mode. Therefore, the first and

second inverter circuits

4a and 4b are not driven simultaneously. Therefore, it is possible to eliminate an interference sound (buzzing sound) generated by a resonance phenomenon due to a frequency difference between the high-frequency currents flowing in the two heating coils arranged close to each other.

In the first embodiment, the control means 9 is energized in the low power mode at the timing when the input current is detected to be equal to or lower than the threshold value Ith (that is, in the case of the present embodiment, The other inverter circuit that has been de-energized is heated by continuous control. At this time, the target input power of the other inverter circuit described above is set to the target input power immediately before the timing when the peak value of the input current becomes equal to or lower than the predetermined threshold value Ith. Therefore, the inverter circuit is controlled by time-sharing control with respect to the load arranged immediately above the heating coil connected to the inverter circuit that has been de-energized at the timing when the input current is detected to be equal to or less than the threshold value Ith. Thus, stable power supply can be performed regardless of whether the control is performed by continuous control (that is, regardless of the operation mode).

Moreover, the induction heating cooker according to the first embodiment includes notification means 11 that notifies the state of the heating operation of the first inverter circuit 4a and the second inverter circuit 4b. Further, when the control means 9 stops the heating operation of one of the first inverter circuit 4a and the second inverter circuit 4b based on the input current, the heating of the one inverter circuit is stopped. The notification means 11 notifies that the operation is stopped. Therefore, the user can easily recognize visually that the load is removed from directly above the heating coil and the heating operation is automatically stopped. In the present embodiment, the first notification means 11a and the second notification means 11b are light emitting diodes, but the present invention is not limited to this, and may be other notification means such as a buzzer. When the 1st alerting | reporting means 11a and the 2nd alerting | reporting means 11b are buzzers, the user can recognize audibly that the inverter circuit stopped.

In the first embodiment, the control means 9 performs power control using an input current from an AC power supply, but the present invention is not limited to this. The control means 9 may perform power control using a resonance current or voltage generated in the first heating coil 5a and the second heating coil 5b, the first resonance capacitor 6a, and the second resonance capacitor 6b.

In the first embodiment, as shown in FIG. 3A, the control cycle of the first inverter circuit 4a and the second inverter circuit 4b at the time-sharing control is set to 20 milliseconds, and in the high power mode. The energization period length (that is, the operation period length) and the energization period length in the low power mode (that is, the stop period length) were set to 10 milliseconds, respectively, and the operation was performed alternately, but the present invention is not limited to this, Even if the control period, the operation period length, and the stop period length are different from these values, the same effect as the present embodiment can be obtained.

In the first embodiment, the control means 9 switches the input power of the second inverter circuit 4b between 3000 W and 0 W during the time-sharing control so that the average input power is 1500 W, and the input power during the continuous control. However, the present invention is not limited to this, and even if the target input power is other than 1500 W, the same effect as this embodiment can be obtained. can get.

(Embodiment 2)
A second embodiment of the present invention will be described with reference to the drawings. The difference from the first embodiment is only the operation method in the low power mode in the time division control, and the description of the other similar contents is omitted.

FIG. 4 is a timing chart showing the operation of the induction heating cooker of FIG. 1 according to Embodiment 2 of the present invention. In the first embodiment, during the energization period of the first inverter circuit 4a in the low power mode, the input power P1b of the first inverter circuit 4a is set to 0 W, and the second inverter circuit 4b in the low power mode During the energization period, the input power P2b of the second inverter circuit 4b was set to 0W. In contrast, in the present embodiment, during the energization period of the first inverter circuit 4a in the low power mode, the input power P1b of the first inverter circuit 4a is other than 0W, which is smaller than the first target input power P1. Control is performed to achieve a predetermined input power. Further, during the energization period of the second inverter circuit 4b in the low power mode, the input power P2b of the second inverter circuit 4b is controlled to be a predetermined input power other than 0 W, which is smaller than the second target input power P2. Is done.

As in the first embodiment, the control means 9 outputs control signals to the first drive circuit 8a and the second drive circuit 8b to perform the heating operation of the first inverter circuit 4a and the second inverter circuit 4b. Control. At this time, the first inverter circuit 4a and the second inverter circuit 4b are controlled so that energization in the high power mode and energization in the low power mode are alternately and exclusively repeated at a predetermined control cycle. Further, the control means 9 controls the power of the first heating coil 5a by the average input power for each control cycle of the first inverter circuit 4a, and changes the first by the average input power for each control cycle of the second inverter circuit 4b. The power control of the second heating coil 5b is performed.

In FIG. 4, the high power mode of the first inverter circuit 4a is described as A, the low power mode of the first inverter circuit 4a is described as B, and the high power mode of the second inverter circuit 4b is described as C. The low power mode of the second inverter circuit 4b is denoted as D. As shown in FIG. 4, when the first inverter circuit 4a is operating in the high power mode A, the second inverter circuit 4b is operated in the low power mode D, and the first inverter circuit 4a is operated in the low power mode D. During the operation in B, the second inverter circuit 4b is operated in the high power mode C.

Furthermore, in the present embodiment, the frequency of the drive signal (hereinafter referred to as drive frequency) of the

semiconductor switch elements

7a, 7b, 7c and 7d in each mode A, B, C and D is set as follows.
(1) The drive frequency of the

semiconductor switch elements

7a and 7b in the high power mode A of the first inverter circuit 4a is set to 25 kHz.
(2) The drive frequency of the

semiconductor switch elements

7a and 7b in the low power mode B of the first inverter circuit 4a is set to 46 kHz.
(3) The drive frequency of the semiconductor switch elements 7c and 7d in the high power mode C of the second inverter circuit 4b is set to 23 kHz.
(4) The drive frequency of the semiconductor switch elements 7c and 7d in the low power mode D of the second inverter circuit 4b is set to 50 kHz.

That is, the drive frequency (46 kHz) of the low power mode B of the first inverter circuit 4a is set to a frequency twice the drive frequency (23 kHz) of the high power mode C of the second inverter circuit 4b. The drive frequency (50 kHz) of the low power mode D of the inverter circuit 4b is set to a frequency twice the drive frequency (25 kHz) of the high power mode A of the first inverter circuit 4a. As described above, in the present embodiment, as in the first embodiment, the first inverter circuit 4a and the second inverter circuit 4b are heated by time-sharing control, and energization and low power in the high power mode are performed. Control is performed so that energization in the mode is alternately and exclusively repeated at a predetermined control cycle. Furthermore, the drive frequency of one inverter circuit energized in the low power mode is set to a frequency twice that of the other inverter circuit energized in the high power mode. Therefore, there is no frequency difference between the frequency of the second harmonic of the drive signal of one inverter circuit and the frequency of the drive signal of the other inverter circuit.

As described above, in the second embodiment, the driving frequency of the semiconductor switch in either the first or second inverter circuit that is operating in the low power mode is the same as that in the high power mode. The frequency of the second harmonic of the drive signal of one inverter circuit and the frequency of the drive signal of the other inverter circuit are set to a frequency twice the drive frequency of the semiconductor switch in the other inverter circuit. Since no frequency difference occurs between the two, the interference sound (buzzing sound) can be eliminated.

In the second embodiment, in the time division control, the driving frequencies in the high power modes A and C of the first inverter circuit 4a and the second inverter circuit 4b are set to 25 kHz and 23 kHz, respectively. The present invention is not limited to this, and the same effect as in the present embodiment can be obtained even at a driving frequency different from the above-described driving frequency.

In each of the above embodiments, the input current detecting means 10 detects the peak value of the input current input from the AC power supply 1 to the rectifying and smoothing circuit 13, and the control means 9 has a predetermined threshold value of the input current. Although it is detected that the value is equal to or less than the value Ith, the present invention is not limited to this. The input current detection means 10 may detect the input current input from the AC power supply 1 to the rectifying / smoothing circuit 13. Further, the control means 9 has a predetermined threshold value calculated based on the input current between the zero points of the voltage between the terminals of the AC power supply 1 (half period of the AC voltage from the AC power supply 1). What is necessary is just to detect that it is below a value. Specifically, the control means 9 calculates the integrated value of the input current by detecting and summing the input current a plurality of times during the half cycle of the AC voltage from the AC power supply 1, and calculates the calculated integral. You may detect that a value is below a predetermined threshold value. Further, the control means 9 smoothes the input current waveform to such an extent that detection delay does not become a problem in the half cycle period of the AC voltage from the AC power supply 1, and after smoothing at a predetermined timing in the latter half of the half cycle period. It may be detected that the input current is less than or equal to a predetermined threshold value.

As described above, the induction heating cooker according to the present invention generates a pot knack sound from a pan placed just above the other heating coil even when the load is removed from just above one heating coil. Since it can prevent, it is effective in the induction heating cooking appliances which energize two heating coils alternately and exclusively without being limited by the mounting state of the load immediately above the heating coil.

DESCRIPTION OF SYMBOLS 1, 51 AC power supply 2, 52

Rectifier circuit

3, 54 Smoothing capacitor 4a 1st inverter circuit 4b 2nd inverter circuit 5a 1st heating coil 5b 2nd heating coil 6a 1st resonance capacitor 6b

2nd resonance Capacitors

7a, 7b First semiconductor switch 7c, 7d Second semiconductor switch 8a First drive circuit 8b Second drive circuit 9 Control means 10 Current detection means 11 Notification means 11a First notification means 11b Second notification Means 12, 61 Zero Volt Detection Circuit 13 Rectification Smoothing Circuit

Claims

A first inverter circuit for converting a direct current input from an alternating current power source through a rectifying and smoothing circuit into a predetermined first high-frequency current and supplying the first load to a first heating coil for induction heating;
A second inverter circuit for converting the direct current into a predetermined second high-frequency current and supplying the second load to a second heating coil for induction heating;
An input current detection means for detecting an input current input to the rectifying / smoothing circuit from an AC power supply;
In an induction heating cooker comprising control means for controlling the first and second inverter circuits,
The control means includes
Controlling the first inverter circuit so that the input power of the first inverter circuit becomes a predetermined first input power larger than a predetermined first target input power in a predetermined first period; Controlling the second inverter circuit so that the input power of the second inverter circuit becomes a predetermined second input power smaller than a predetermined second target input power;
The first inverter so that the input power of the first inverter circuit becomes a predetermined third input power smaller than the first target input power in a predetermined second period following the first period. Controlling the circuit and controlling the second inverter circuit so that the input power of the second inverter circuit becomes a predetermined fourth input power larger than the second target input power,
By repeating the first period and the second period at a predetermined control cycle, the average input power of the first inverter circuit becomes the first target input power, and the second inverter circuit Controlling the first and second inverter circuits so that the average input power becomes the second target input power;
When it is detected that the input current is less than or equal to a predetermined threshold value, the input power becomes the first or fourth input power at the detected timing in the first and second inverter circuits. An induction heating cooker that controls to stop the heating operation of one of the inverter circuits that has been controlled.
When the control means detects that the input current is less than or equal to the threshold value, the control circuit controls the other inverter circuit of the first and second inverter circuits so that the input power of the other inverter circuit is predetermined. The induction heating cooker according to claim 1, wherein control is performed so that the third target input power is obtained.
3. The third target input power is set to be the same as the target input power of the other inverter circuit among the first and second target input powers. Induction heating cooker.
The induction heating cooker according to any one of claims 1 to 3, wherein the second and third input powers are each set to zero.
The frequency of the drive signal of the second inverter circuit in the first period is set to a frequency twice the frequency of the drive signal of the first inverter circuit in the first period,
The frequency of the drive signal of the first inverter circuit in the second period is set to twice the frequency of the drive signal of the second inverter circuit in the second period. The induction heating cooker according to any one of claims 1 to 3.
A notification means for notifying the state of the heating operation of the first and second inverter circuits;
The control means controls the notifying means so as to notify that the one inverter circuit stops the heating operation after stopping the heating operation of the one inverter circuit. Item 6. The induction heating cooker according to any one of Items 1 to 5.