JP4948351B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker.

  2. Description of the Related Art Conventionally, regarding an electromagnetic cooker, “a heating coil for an electromagnetic cooker having a safety structure capable of obtaining sufficient heating power and a uniform heating pattern regardless of the size of an object to be heated, such as a pan, is provided. As a technique for the purpose of the above, “the inner coil 1 and the outer coil 2 are arranged concentrically and substantially on the same plane, and the coils 1 and 2 are subjected to high-frequency current in the circumferential direction. In parallel connection so as to be in the same direction, when heating the small pan 5 by supplying a high-frequency current from the power source 3, the heating power is concentrated on the inner coil 1. Is proposed (Patent Document 1).

  In addition, according to the technique described in the above-mentioned Patent Document 1, “for a large object to be heated having a size equal to or larger than the outer diameter, it functions in the same manner as one heating coil as in the past, For small objects to be heated that are smaller than the inner diameter of the heating coil located outside, the high-frequency current of the heating coil that contributes to induction heating increases, so heating power sufficient for cooking regardless of the size of the object to be heated There is an effect that a value is obtained. Furthermore, the heating coil that does not contribute to the induction heating of a small object to be heated has an effect that the high-frequency current is reduced, so that leakage of the electromagnetic field is less than before and safety is improved.

JP-A-8-55678 (Summary, Effects of Invention)

Some pans for induction heating cookers have magnetic metal sprayed or pasted on the bottom of an aluminum pan.
In such a pan, if an aluminum part that is not thermally sprayed with magnetic metal is placed above the heating coil, the current flowing through the outer heating coil increases and the switching element may be overcurrent destroyed. It is necessary to prioritize current suppression over operation, and electric power necessary for heating cannot be obtained, and sufficient heating cannot be performed in some cases.

  The present invention has been made to solve the above-described problems, and induction heating cooking in which a part of the pan bottom can sufficiently heat even a pan made of a low-resistance nonmagnetic material such as aluminum. The purpose is to obtain a vessel.

An induction heating cooker according to the present invention includes a DC power supply circuit that rectifies AC power and converts it into DC power, an inner heating coil and an outer heating coil arranged concentrically, and an AC to the inner heating coil and the outer heating coil. An inverter for supplying current, an inner heating coil current detecting means for detecting a current flowing in the inner heating coil, an outer heating coil current detecting means for detecting a current flowing in the outer heating coil, and a control means for driving and controlling the inverter ; The inverter has a common arm, an inner heating coil arm, and an outer heating coil arm, each arm having two switching elements connected in series between the output DC buses of the DC power supply circuit , It is connected so that the circulation direction of the current flowing out from the common arm is the same in the inner heating coil and the outer heating coil, and the control means is a switch of the common arm. Phase difference between the drive signals to the switching elements of the drive signal and the internal heat arm coil to grayed element alpha, and a drive signal to the switching element driving signal and the arm outer heating coil to the switching elements of the common arm of by adjusting the phase difference beta, together with the input power to the DC power supply circuit is controlled to the set value, if the current flowing through the inner heating coil is greater than the current flowing through the outer heating coil, the phase difference α When the current flowing through the outer heating coil is larger than the current flowing through the inner heating coil, the phase difference α is increased or the phase difference β is reduced to flow through the inner heating coil. Control is performed so that the current and the current flowing through the external heating coil have substantially the same magnitude.

  According to the induction heating cooker according to the present invention, the current flowing through the inner heating coil and the outer heating coil is controlled approximately equally, and the input power is controlled by adjusting the phase difference, so that an overcurrent flows through the switching element. In addition, it is possible to obtain sufficient input power and perform sufficient heating even for a pan having a low resistance non-magnetic material such as aluminum.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram of an induction heating cooker according to Embodiment 1 of the present invention.
In FIG. 1, AC power supplied from a commercial AC power supply 1 is converted into DC power by a DC power supply circuit 10.
The DC power supply circuit 10 includes a rectifier diode bridge 11 that rectifies AC power, a reactor 12, and a smoothing capacitor 13. The input current input to the DC power supply circuit 10 is detected by the input current detection means 2.
The power converted into DC power by the DC power supply circuit 10 is supplied to an inverter circuit 100 composed of arms 20, 30, and 40 described later.

The inverter circuit 100 includes three arms 20, 30 and 40.
Each arm is constituted by two switching elements (for example, an IGBT: Insulated Gate Bipolar Transistor) connected in series between output buses of the DC power supply circuit 10 and diodes connected to the switching elements in antiparallel. Is done.
The three arms 20 to 40 share the arm 30, and the arms 20 and 30 and the arms 30 and 40 each constitute a full bridge circuit.
The full bridge circuit composed of the arms 20 and 30 supplies an alternating current to an inner heating coil 51 described later, and the full bridge circuit composed of the arms 30 and 40 supplies an alternating current to an outer heating coil 52 described later.

Hereinafter, the switching elements on the high potential bus side of each arm 20 to 40 are referred to as upper switches 21, 31, 41, respectively, and the switching elements on the low potential bus side are referred to as lower switches 22, 32, 42, respectively.
Further, as necessary, the arm 30 is called a common arm, the arm 20 is called an inner heating coil arm, and the arm 40 is called an outer heating coil arm.

The common arm 30 is an arm connected to an inner heating coil load circuit and an outer heating coil load circuit described later.
The common arm 30 is composed of an upper switch 31 and a lower switch 32 and diodes connected in antiparallel to each of them, and a connection point between the upper switch 31 and the lower switch 32 is an output point of the common arm 30. .
A snubber capacitor 33 is connected to the lower switch 32 in parallel.

The inner heating coil arm 20 is an arm to which an inner heating coil load circuit described later is connected.
The inner heating coil arm 20 is composed of an upper switch 21 and a lower switch 22 and diodes connected in antiparallel to the upper switch 21 and the lower switch 22, respectively, and the connection point between the upper switch 21 and the lower switch 22 is the inner heating coil arm 20. It is an output point.
A snubber capacitor 23 is connected to the lower switch 22 in parallel.

The external heating coil arm 40 is an arm to which an external heating coil load circuit described later is connected.
The outer heating coil arm 40 is composed of an upper switch 41 and a lower switch 42 and diodes connected in antiparallel to the upper switch 41 and the lower switch 42, respectively. It is an output point.
A snubber capacitor 43 is connected to the lower switch 42 in parallel.

The switching elements included in the arms 20 to 40 are driven on and off based on instructions from the control means 61.
The control means 61 turns each switch alternately so that the lower switch 22 is turned off while the upper switch 21 is turned on, and the lower switch 22 is turned on while the upper switch 21 is turned off. Drive control. The other switching elements are similarly driven and controlled in the same manner.

  The snubber capacitors 23, 33, and 43 delay output voltage fluctuations when the respective switches 21, 22, 31, 32, 41, and 42 of the inner heating coil arm 20, the common arm 30, and the outer heating coil arm 40 are turned off. And is provided to reduce the turn-off loss of each switching element.

The inner heating coil 51 is a small-diameter heating coil wound in a substantially circular shape.
The outer heating coil 52 is a large-diameter heating coil wound in a substantially circular shape.
The outer heating coil 52 is disposed on the outer periphery of the inner heating coil 51 so that the center positions of both the heating coils substantially coincide.
The inner heating coil 51 and the outer heating coil 52 are wound in the same circumferential direction as viewed from the common arm 30, and the circumferential direction of the current flowing out from the common arm 30 is the same in the inner heating coil 51 and the outer heating coil 52. So connected.
Further, the inner heating coil 51 and the outer heating coil 52 have impedance values substantially equal in a state where a large-diameter pan having a uniform pan bottom material is placed (the state shown in FIG. 2A described later). It shall be adjusted.

The inner resonance capacitor 53 is connected in series to the inner heating coil 51 and forms a series resonance circuit (an inner heating coil load circuit) together with the inner heating coil 51.
This inner heating coil load circuit includes an output point of the common arm 30 (a connection point between the upper switch 31 and the lower switch 32), an output point of the inner heating coil arm 20 (a connection point between the upper switch 21 and the lower switch 22), and Connected between.

The external resonance capacitor 54 is connected in series to the external heating coil 54 and forms a serial resonance circuit (external heating coil load circuit) together with the external heating coil 52.
This external heating coil load circuit is connected between the output point of the common arm 30 and the output point of the external heating coil arm 40 (the connection point of the upper switch 41 and the lower switch 42).

The internal heating coil current detection means 55 detects the current flowing through the internal heating coil 51 and outputs a detection value to the control means 61.
The external heating coil current detection unit 56 detects a current flowing through the external heating coil 52 and outputs a detection value to the control unit 61.

  The control means 61 controls the whole induction heating cooker of FIG. 1, and performs drive control of each switching element. Moreover, the control means 61 controls operation | movement, such as a heating output, based on the instruction | indication input from the operation part which is not shown in figure.

Further, the control means 61 controls the phase difference of the drive signal of each switching element so that the power based on the detection value of the input current detection circuit 2 becomes the power set by the input instruction from the operation unit. At the same time, the detection value of the inner heating coil current detection means 55 and the detection value of the outer heating coil current detection means 56 are controlled to be substantially equal.
The drive signal output to each of the arms 20 to 40 is output at a drive frequency higher than the resonance frequency of the inner heating coil load circuit and the outer heating coil load circuit, and the voltage applied to the load circuit by the current flowing through each load circuit It is controlled so as to flow with a delayed phase compared to.

In addition, the phase difference of the drive signal of each switching element described above is the following two (1) and (2). Details will be described later with reference to FIGS.
(1) Phase difference between drive signal to common arm 30 and drive signal to inner heating coil arm 20 (2) Phase difference between drive signal to common arm 30 and drive signal to outer heating coil arm 40

The control means 61 can be configured by hardware such as a circuit device that realizes the function, or can be configured by an arithmetic device such as a microcomputer or a CPU and software that defines the operation thereof.
Further, the control means 61 appropriately includes a drive circuit (for example, a drive IC) necessary for driving each switching element as necessary.

The circuit configuration of the induction heating cooker according to the first embodiment has been described above.
Next, the case where an overcurrent flows through the outer heating coil 52 depending on the material and size of the pan will be described together with the difference in the material and size of the pan.

  FIG. 2 shows the positional relationship between the magnetic flux generated by the current flowing through the heating coil and the bottom of the pan when various pans are placed on the inner heating coil 51 and the outer heating coil 52 via the top plate 71. is there.

FIG. 2A shows a state in which a large-diameter pan 200a larger than the outer diameter of the outer heating coil 52 is placed with the material of the pan bottom being uniform (hereinafter referred to as uniform material) regardless of the position of the diameter. .
FIG. 2B shows a state in which a medium-sized medium-diameter pan 200 b having a material larger than the outer diameter of the inner heating coil 51 and smaller than the outer diameter of the outer heating coil 52 is placed.
FIG. 2C shows a state in which a small-diameter pan 200 c having a uniform material and a diameter equal to or smaller than the outer diameter of the inner heating coil 51 is placed.
FIG. 2 (d) shows a state in which a large-diameter pan (a pan having a different material depending on the position of the diameter) 200d, in which an aluminum alloy is used as a base material, and a magnetic metal is sprayed or pasted on the pan bottom, is placed.
FIG.2 (e) shows the no-load state which has not mounted the pan.

  In FIG. 2, broken line arrows around the inner heating coil 51 and the outer heating coil 52 indicate the high frequency magnetic flux generated by the high frequency current flowing through the inner and outer heating coils. This high frequency magnetic flux is reversed according to the direction of the current.

  When the large-diameter pan 200a having the uniform material shown in FIG. 2A is placed, the magnetic flux generated by the high-frequency current flowing in the inner heating coil 51 and the magnetic flux generated by the high-frequency current flowing in the outer heating coil 52 are the same. The eddy current is induced to the bottom of the pan by interlinking with the bottom of the pan.

  When the uniform medium-diameter pan 200b shown in FIG. 2 (b) is placed, the magnetic flux generated by the high-frequency current flowing through the inner heating coil 51 is linked to the bottom of the medium-diameter pan 200b. Of the magnetic flux generated by the high-frequency current flowing in the coil 52, the magnetic flux not linked to the bottom of the medium-diameter pan 200b increases.

When the small-diameter pan 200c of uniform material shown in FIG. 2C is placed, the magnetic flux generated by the high-frequency current flowing through the inner heating coil 51 is linked to the pan bottom of the small-diameter pan 200c, but the outer heating coil 52 The magnetic flux that is generated by the high-frequency current flowing through and does not link to the bottom of the small-diameter pan 200c greatly increases, the impedance of the external heating coil 52 increases, and the external heating coil current decreases.
Moreover, since the magnetic flux linked to the bottom of the pan is reduced, the power consumed by the induced eddy current flowing in the bottom of the pan is reduced, so the input current is reduced.

When an aluminum alloy large-diameter pan 200d obtained by spraying the magnetic metal of FIG. 2D on the pan bottom is placed, the magnetic flux generated by the high-frequency current flowing in the inner heating coil 51 is applied to the magnetic metal portion sprayed on the pan bottom. Although interlinkage occurs, the magnetic flux generated by the high-frequency current flowing through the outer heating coil 52 also interlinks with the aluminum alloy portion where the magnetic metal is not sprayed.
Therefore, a large induced eddy current flows through the aluminum alloy part, canceling out the magnetic flux, and the impedance of the inner heating coil load circuit is reduced. Therefore, when the same voltage is applied to the inner heating coil load circuit and the outer heating coil load circuit, The outer heating coil current is significantly larger than the inner heating coil current.

  In the no-load state shown in FIG. 2 (e), neither the magnetic flux generated by the high-frequency current flowing in the inner heating coil 51 nor the magnetic flux generated by the high-frequency current flowing in the outer heating coil 52 is linked to the pan bottom. Since no power is consumed, the input current is small.

As described above, the current flowing through the outer heating coil 52 varies greatly depending on the material and size of the pan.
In particular, when an excessive current flows through the external heating coil 52, it is necessary to suppress the current in order to prevent an overcurrent breakdown of the switching element, which results in insufficient input power and insufficient heating output. There is.
In the example of FIG. 2, in the case of FIG. 2D, since the large output necessary for heating the aluminum portion cannot be obtained by suppressing the current of the outer heating coil 52 related to the aluminum portion, Bias may occur.

As described above, the example in which the heating output is insufficient by suppressing the current of the heating coil has been described with reference to FIGS.
Hereinafter, the details of the heating control operation of the induction heating cooker according to the first embodiment will be described. Prior to this, the outline of the phase difference control used in the first embodiment will be described with reference to FIG.

FIG. 3 is an example of a drive signal output to each arm 20-40. Here, an example of a drive signal when high frequency power is output to the inner heating coil load circuit and the outer heating coil load circuit is shown.
The control means 61 outputs a high-frequency drive signal to the upper switch 31 and the lower switch 32 of the common arm 30, and outputs a drive signal whose phase is advanced from the drive signal to the upper switch 21 and the lower switch of the inner heating coil arm 20. It outputs to the switch 22 and the upper switch 41 and the lower switch 42 of the arm 40 for external heating coils.

The inner heating coil phase difference α is a phase difference between driving signals to the upper switch 21 and the lower switch 22 of the inner heating coil arm 20 with respect to the driving signals to the upper switch 31 and the lower switch 32 of the common arm 30.
The external heating coil phase difference β is a phase difference between the driving signals to the upper switch 41 and the lower switch 42 for the outer heating coil arm 40 with respect to the driving signals to the upper switch 31 and the lower switch 32 of the common arm 30.

The output point of each arm (the connection point between the upper switch and the lower switch) has a high potential side bus potential or a low potential side bus potential that is the output of the DC power supply circuit 2 depending on the on / off state of the upper switch and the lower switch. Is switched at high frequency and output.
The potential difference between the output point of the common arm 30 and the output point of the inner heating coil arm 20 is applied as a voltage to the inner heating coil load circuit, and the output point of the common arm 30 and the outer heating coil are applied to the outer heating coil load circuit. The potential difference at the output point of the arm 40 is applied as a voltage.

  Accordingly, the phase difference α between the drive signal to the upper / lower switch of the common arm 30 and the drive signal to the upper / lower switch of the inner heating coil arm 20, and the drive signal to the upper / lower switch of the common arm 30 and the arm 40 for the outer heating coil. The high frequency voltage applied to the inner heating coil load circuit and the outer heating coil load circuit is set to different values by setting the phase difference β with the drive signal to the upper and lower switches to different values (α ≠ β). be able to.

As shown in the drive signal example of FIG. 3, the control means 61 controls the phase difference between the drive signals of the common arm 30 and each arm, thereby varying the voltage applied to each heating coil, so that the heating output and Each heating coil current can be controlled.
That is, the control unit 61 obtains input power based on the input current detected by the input current detection unit 2, controls the applied voltage by adjusting the phase differences α and β in FIG. 3, and is set by the operation unit. The heating operation can be controlled so that a high heating output can be obtained.

  FIG. 3 shows an example in which different applied voltages are output to the internal heating coil load circuit and the external heating coil load circuit, and the applied voltage to the internal heating coil load circuit is larger than the applied voltage to the external heating coil load circuit. (Β <α in the figure).

The outline of the phase difference control used in the first embodiment has been described above with reference to FIG.
Next, the details of the heating control operation of the induction heating cooker according to the first embodiment will be described.

  FIG. 4 is a heating control operation flow of the induction heating cooker according to the first embodiment. Hereinafter, each step will be described. Note that the phase differences α and β in FIG. 4 correspond to the phase differences α and β in FIG.

(S401)
The control means 61 starts the heating control process in response to an input of a heating start instruction from the operation unit.
When a heating start instruction is input, the control unit 61 controls each of the arms 20 to 40 to apply a predetermined identical high-frequency voltage to the inner heating coil load circuit and the outer heating coil load circuit.
At this time, the control means 61 sets the phase differences α and β to the same initial value, and outputs predetermined drive signal outputs to the upper and lower switches of the common arm 30, the inner heating coil arm 20, and the outer heating coil arm 40. Start.

(S402)
The control means 61 acquires the input current, the internal heating coil current, and the external heating coil current from the input current detection circuit 2, the internal heating coil current detection means 55, and the external heating coil current detection means 56.
(S403)
The control means 61 determines whether or not the outer heating coil arm 40 is being driven. If it is driven, the process proceeds to step S408, and if it is stopped, the process proceeds to step S404.

(S404)
The control means 61 determines whether or not the internal heating coil current is an excessive current that damages the switching element of the inverter circuit 100. If it is an overcurrent, the process proceeds to step S405. If not, the process proceeds to step S406.
(S405)
The control means 61 delays the phase of the drive signal to the inner heating coil arm 20 to reduce the phase difference α from the drive signal to the common arm 30 and suppresses the inner heating coil current.

(S406)
The control means 61 compares the input power obtained from the input current detected in step S402 with the power set from the operation unit.
If the input power is larger, the process proceeds to step S405. If the set power is larger, the process proceeds to step S407. If the input power is substantially equal to the set power, the drive signal to the inner heating coil arm 20 is transmitted. The phase is left as it is, and the process proceeds to step S424.
(S407)
The control means 61 advances the phase of the drive signal to the inner heating coil arm 20 to increase the phase difference α with the drive signal to the common arm 30 and increase the inner heating coil current.

(S408)
The control means 61 compares the inner heating coil current detected in step S402 with the outer heating coil current.
If the inner heating coil current is larger, the process proceeds to step S409. If the outer heating coil current is larger than the inner heating coil current, the process proceeds to step S414. If the inner heating coil current and the outer heating coil current are substantially equal, Proceed to step S421.

(S409)
The control means 61 determines whether or not the internal heating coil current is an excessive current. If it is an overcurrent, the process proceeds to step S410. If not, the process proceeds to step S411.
(S410)
The control means 61 delays the phase of the drive signal to the inner heating coil arm 20 to reduce the phase difference α from the drive signal to the common arm 30 and suppresses the inner heating coil current.

(S411)
The control means 61 compares the input power obtained from the input current detected in step S402 with the power set from the operation unit.
If the input power is larger, the process proceeds to step S410. If the input power is substantially equal to the set power, the process proceeds to step S412. If the set power is larger, the process proceeds to step S413.

(S412)
The control means 61 delays the phase of the drive signal to the inner heating coil arm 20 (phase difference α reduction) and advances the phase of the drive signal to the outer heating coil arm 40 (phase difference β enlargement). Thereby, the inner heating coil current is suppressed and the outer overheating coil current is increased.
(S413)
The control means 61 advances the phase of the drive signal to the arm 40 for the external heating coil, expands the phase difference β with the drive signal to the common arm 30, and increases the external overheating coil current.

(S414)
The control means 61 determines whether or not the external heating coil current is an excessive current. If it is an overcurrent, the process proceeds to step S415. If not, the process proceeds to step S418.
(S415)
The control means 61 determines whether or not the phase difference β is larger than a predetermined lower limit value. If the phase difference β is larger than the lower limit value, the process proceeds to step S416, and if it is equal to or smaller than the lower limit value, the process proceeds to step S417.

(S416)
The control means 61 delays the phase of the drive signal to the external heating coil arm 40 to reduce the phase difference β with the drive signal to the common arm 30 and suppresses the external heating coil current.
(S417)
The control means 61 stops outputting the drive signal to the outer heating coil arm 40.

(S418)
The control means 61 compares the input power obtained from the input current detected in step S402 with the power set from the operation unit.
If the input power is larger, the process proceeds to step S415. If the input power is substantially equal to the set power, the process proceeds to step S420. If the set power is larger, the process proceeds to step S419.
(S419)
The control means 61 advances the phase of the drive signal output to the inner heating coil arm 20 to increase the phase difference α from the drive signal to the common arm 30 and increase the inner heating coil current.
(S420)
The control means 61 advances the phase of the drive signal to the inner heating coil arm 20 to increase the phase difference α and increase the inner heating coil current.

(S421)
The control means 61 compares the input power obtained from the input current detected in step S402 with the power set from the operation unit.
If the set power is larger, the process proceeds to step S422. If the input power and the set power are substantially equal, the process proceeds to step S424. If the input power is larger, the process proceeds to step S423.
(S422)
The control means 61 advances the phase of the drive signal output to the inner heating coil arm 20 and the outer heating coil arm 40 and expands the phase differences α and β from the drive signal to the common arm 30. As a result, both the inner heating coil current and the outer heating coil current are increased to bring the input power closer to the set power.
(S423)
The control means 61 delays the phase of the drive signal to the inner heating coil arm 20 to reduce the phase difference α, and suppresses the inner heating coil current.

(S424)
The control means 61 determines whether or not there is an instruction input for stopping the heating from the operation unit. If there is no stop instruction input, the process returns to step S402, and if there is a stop instruction, the process proceeds to step S425.
(S425)
The control means 61 stops the drive signal to each arm and ends the heating output control process.

With the above operation flow, the control means 61 controls the input power to be the set power by adjusting the phase differences α and β, and an overcurrent flows through the inner heating coil 51 and the outer heating coil 52. Can be suppressed.
That is, the control means 61 can achieve the above-described object by the following control operations (1) to (3).

(1) In step S408, the internal heating coil current and the external heating coil current are monitored so as to be substantially the same, so that overcurrent does not flow only in one of the heating coils. Yes. This prevents overcurrent destruction of the switching element.
(2) If the currents of the heating coils are not substantially equal, the overcurrent is secondarily monitored in steps S409 and S414 to reliably prevent overcurrent destruction of the switching element.
(3) Under the premise that the currents of the heating coils are substantially equal or that no overcurrent has occurred, the input power becomes the set power by expanding or reducing the phase differences α and β in each step. adjust.

FIG. 5 shows an example of a drive signal when output of the drive signal to the outer heating coil arm 40 is stopped.
As shown in the figure, a high-frequency drive signal is output to the upper switch 31 and the lower switch 32 of the common arm 30, and the drive signal whose phase is advanced from the drive signal is connected to the upper switch 21 of the inner heating coil arm 20. It outputs to the lower switch 22 and outputs an off signal to the upper switch 41 and the lower switch 42 of the arm 40 for the external heating coil.
As a result, the high potential side bus potential or the low potential side bus potential, which is the output of the DC power supply circuit 10, is switched and output at the high frequency at the output point of the common arm 30 and the output point of the inner heating coil arm 20, respectively. The
The output point of the arm 40 for the outer heating coil is clamped between the low potential side bus potential and the high potential side bus potential of the DC power supply circuit 10, and the output potential is indefinite.
Therefore, the output voltage of the DC power supply circuit 10 is applied to the inner heating coil load circuit by the phase difference as a potential difference between the output point of the common arm 30 and the output point of the inner heating coil arm 20. Since the output point potential of the arm 40 for the external heating coil is indefinite, no high frequency voltage is applied.

As described above, in the first embodiment, in the induction heating cooker in which the inner heating coil 51 and the outer heating coil 52 are energized simultaneously and separately, a portion of the pot bottom is made of a low-resistance nonmagnetic material such as an aluminum alloy. The voltage applied to the inner heating coil load circuit and the outer heating coil load circuit by separately controlling the phases of the driving signal to the inner heating coil arm 20 and the driving signal to the outer heating coil arm 40. And the current flowing in each heating coil is controlled to be substantially equal.
Therefore, it is possible to avoid damaging the switching elements constituting the inverter circuit 100 due to an excessive current flowing through any of the load circuits.

  Further, according to the first embodiment, when the currents of the respective heating coils are not substantially equal, the phase difference of the arm having the larger current is adjusted and the heating coil current is suppressed, so that overcurrent is reliably prevented. can do.

  In addition, according to the first embodiment, the overcurrent is prevented from flowing through the switching element, and the phase differences α and β are adjusted so that the input power becomes the set power. Sufficient heating output can be obtained by causing an induced eddy current to flow in a high part.

Embodiment 2. FIG.
In the induction heating cooker according to the first embodiment, the current flowing through the inner heating coil 51 and the current flowing through the outer heating coil 52 are controlled approximately equally.
The induction heating cooker according to Embodiment 2 of the present invention controls the current flowing in the outer heating coil 52 to be substantially equal to or less than the current flowing in the inner heating coil 51. Thereby, even in the case of FIG. 2D, the external heating coil current is prevented from becoming excessive.
Note that the circuit configuration of the induction heating cooker according to the second embodiment is the same as the circuit configuration shown in FIG. 1 of the first embodiment, and a description thereof will be omitted.

  In the second embodiment, the control means 61 sends the phase difference β between the drive signal to the up / down switch of the common arm 30 and the drive signal to the up / down switch of the arm 40 for the external heating coil to the up / down switch of the common arm 30. And a drive signal to the upper / lower switch of the inner heating coil arm 20 is controlled within a range of a phase difference α or less. Details of the heating control operation will be described below.

  FIG. 6 is a heating control operation flow of the induction heating cooker according to the second embodiment. Hereinafter, each step will be described. Note that the phase differences α and β in FIG. 6 correspond to the phase differences α and β in FIG. 3.

(S601) to (S607)
Since this is the same as steps S401 to S407 described in FIG. 4 of the first embodiment, a description thereof will be omitted.
(S608)
The control means 61 compares the inner heating coil current detected in step S602 with the outer heating coil current.
If the inner heating coil current is larger, the process proceeds to step S609. If the inner heating coil current and the outer heating coil current are substantially equal, the process proceeds to step S624, and the outer heating coil current is greater than the inner heating coil current. If it is larger, the process proceeds to step S621.

(S609)
The control means 61 determines whether or not the internal heating coil current is excessive. If it is an overcurrent, the process proceeds to step S610, and if it is not an overcurrent, the process proceeds to step S615.
(S610)
The control means 61 includes a phase difference α between the drive signal to the common arm 30 and the drive signal to the inner heating coil arm 20, and the drive signal to the common arm 30 and the drive signal to the outer heating coil arm 40. The phase difference β is compared.
When the phase difference α is larger than the phase difference β, the process proceeds to step S614, and when the phase difference α is equal to or smaller than the phase difference β, the process proceeds to step S611.

(S611)
The control means 61 determines whether the phase difference β is larger than the lower limit value. If the phase difference β is larger than the lower limit value, the process proceeds to step S612. If the phase difference β is equal to or smaller than the lower limit value, the process proceeds to step S613.
(S612)
The control means 61 delays the phases of the drive signal to the inner heating coil arm 20 and the drive signal to the outer heating coil arm 40 to reduce the phase difference α and the phase difference β. As a result, the inner heating coil current is suppressed, and the outer heating coil current is suppressed to substantially equal to or less than the inner heating coil current.

(S613)
The control means 61 stops the drive signal to the outer heating coil arm 40 so as not to flow a high frequency current to the outer heating coil 52, and delays the phase of the drive signal to the inner heating coil arm 20 in common. The phase difference α with the drive signal to the arm 30 is reduced, and the inner heating coil current is suppressed.
(S614)
The control means 61 delays the phase of only the driving signal to the inner heating coil arm 20 to reduce the phase difference α, and suppresses the inner heating coil current.

(S615)
The control means 61 compares the input power calculated from the input current detected in step S602 with the power set from the operation unit.
If the input power is larger, the process proceeds to step S610. If the input power is substantially equal to the set power, the process proceeds to step S619. If the set power is larger, the process proceeds to step S616.
(S616)
The control means 61 includes a phase difference α between the drive signal to the common arm 30 and the drive signal to the inner heating coil arm 20, and the drive signal to the common arm 30 and the drive signal to the outer heating coil arm 40. The phase difference β is compared.
When the phase difference α is larger than the phase difference β, the process proceeds to step S617, and when the phase difference α is equal to or smaller than the phase difference β, the process proceeds to step S618.

(S617)
The control means 61 determines that the phase of the drive signal to the inner heating coil 51 is ahead of the phase of the drive signal to the outer heating coil 52 in order to increase the input power, and the driving signal to the arm 40 for the outer heating coil. Only the phase is advanced to increase only the phase difference β, and the external heating coil current is increased.
(S618)
The control means 61 advances the phase of the drive signal to the inner heating coil arm 20 and the phase of the drive signal to the outer heating coil arm 40, and expands both the phase difference α and the phase difference β. Increase current and external heating coil current.

(S619)
The control means 61 compares the phase difference α and the phase difference β. When the phase difference α is larger than the phase difference β, the process proceeds to step S620, and when the phase difference α is equal to or smaller than the phase difference β, the process proceeds to step S627.
(S620)
The control means 61 reduces the phase difference α and enlarges the phase difference β to reduce the difference between the inner heating coil current and the outer heating coil current.

(S621)
The control means 61 determines whether or not the phase difference β between the drive signal to the common arm 30 and the drive signal to the outer heating coil arm 40 is greater than a predetermined lower limit value.
When the phase difference β is larger than the lower limit value, the process proceeds to step S622, and when the phase difference β is equal to or smaller than the lower limit value, the process proceeds to step S623.
(S622)
The control means 61 delays the phase of the drive signal output to the arm 40 for the external heating coil to reduce the phase difference β and suppress the external heating coil current.
(S623)
The control means 61 stops the drive signal output to the arm 40 for the external heating coil so that no high frequency current flows through the external heating coil.

(S624)
The control means 61 compares the input power calculated from the input current detected in step S602 with the power set from the operation unit.
If the set power is larger, the process proceeds to step S625. If the set power is substantially equal to the input power, the process proceeds to step S627. If the input power is greater than the set power, the process proceeds to step S626.
(S625)
The control means 61 advances the phase of the drive signal to the inner heating coil arm 20 and the phase of the drive signal to the outer heating coil arm 40 to expand the phase difference α and the phase difference β with the common arm 30, The input power is increased by increasing the heating coil current and the external heating coil current.
(S626)
The control means 61 delays the phase of the drive signal to the inner heating coil arm 20 to reduce the phase difference α, and suppresses the inner heating coil current.

(S627)
The control means 61 determines whether or not there is an instruction input for stopping the heating from the operation unit. If there is no stop instruction input, the process returns to step S602, and if there is a stop instruction, the process proceeds to step S628.
(S628)
The control means 61 stops the drive signal to each arm and ends the heating output control process.

With the above operation flow, the control means 61 controls the input power to be the set power by adjusting the phase differences α and β, and controls the outer heating coil current to be equal to or less than the inner heating coil current. can do.
That is, the control means 61 can achieve the above-described object by the following control operations (1) to (3).

(1) In step S608, the external heating coil current is monitored so as to be equal to or less than the internal heating coil current, so that overcurrent does not flow through the external heating coil. Thereby, the overcurrent destruction of the switching element corresponding to the external heating coil 52 is prevented.
(2) If the outer heating coil current is equal to or smaller than the inner heating coil current, the overcurrent of the inner heating coil is monitored in step S609 to prevent overcurrent destruction of the switching element corresponding to the inner heating coil 51.
(3) In order to maintain the condition that the phase difference β is equal to or smaller than the phase difference α, in step S612, the phase difference β is reduced as the phase difference α is reduced. In step S613, internal heating is performed as the phase difference α is reduced. The coil arm 40 is stopped.

  In the second embodiment, it has been described that the outer heating coil current is controlled to be equal to or less than the inner heating coil current value. However, depending on the process of the control operation, the state of the object to be heated, etc. The current is allowed to be substantially equal to the inner heating coil current.

  Further, in the second embodiment, it has been described that the phase difference β is controlled so as to be equal to or smaller than the phase difference α. However, the phase difference β is different depending on the process of the control operation, the state of the object to be heated, and the like. It is allowed to be substantially equal to α.

As described above, in the second embodiment, in the induction heating cooker that energizes the inner heating coil 51 and the outer heating coil 52 simultaneously and separately, while controlling the input power to be the set power, the outer heating coil The phase differences α and β are adjusted so that the applied voltage of the load circuit falls within the range below the applied voltage of the internal heating coil load circuit, and the external heating coil current is controlled to be below the internal heating coil current value.
Therefore, when the impedance of the outer heating coil 52 is larger than the impedance of the inner heating coil 51, such as heating a small-diameter pan of uniform material, the input power set in the operation unit can be obtained, The outer heating coil current becomes smaller than the inner heating coil current, the magnetic flux leaking around the heating port is suppressed, and efficient heating can be performed.

In the second embodiment, when heating a non-magnetic material pan such as an aluminum alloy pan sprayed with a magnetic metal, the pan bottom portion (aluminum alloy portion) where the magnetic metal is not sprayed is on the outer heating coil. Even when placed on the outer heating coil current, the outer heating coil current is controlled to be equal to or less than the inner heating coil current.
Therefore, it is possible to avoid damaging the switching elements constituting the inverter circuit 100 without flowing an excessive current through the external heating coil load circuit.

  In the second embodiment, the aluminum alloy pan in which the magnetic metal is sprayed on the bottom of the pan is a small-diameter pan smaller than the outer diameter of the outer heating coil, and the magnetic flux generated by the high-frequency current flowing in the outer heating coil is linked to the pan bottom. Even when the ratio to be performed is low, the outer heating coil current is controlled to be equal to or less than the inner heating coil current, so that the magnetic flux leaking around the heating port can be suppressed and the heating efficiency can be improved.

3 is a circuit diagram of the induction heating cooker according to Embodiment 1. FIG. The positional relationship of the magnetic flux produced by the electric current which flows into a heating coil at the time of mounting various pans on the heating coil, and a pan bottom is shown. It is an example of the drive signal output to each arm 20-40. It is a heating control operation | movement flow of the induction heating cooking appliance which concerns on Embodiment 1. FIG. The drive signal example when the drive signal output to the arm 40 for outer heating coils is stopped is shown. It is a heating control operation | movement flow of the induction heating cooking appliance which concerns on Embodiment 2. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Commercial AC power supply, 2 Input current detection means, 10 DC power supply circuit, 11 Rectifier diode bridge, 12 Reactor, 13 Smoothing capacitor, 20 Arm for heating coil, 21 Upper switch, 22 Lower switch, 30 Common arm, 31 Upper switch , 32 Lower switch, 40 Arm for outer heating coil, 41 Upper switch, 42 Lower switch, 51 inner heating coil, 52 outer heating coil, 53 inner resonance capacitor, 54 outer resonance capacitor, 55 inner heating coil current detection means, 56 outer Heating coil current detection means, 61 control means, 100 inverter circuit.

Claims (3)

A DC power supply circuit that rectifies AC power and converts it into DC power;
An inner heating coil and an outer heating coil arranged concentrically;
An inverter for supplying an alternating current to the inner heating coil and the outer heating coil;
An inner heating coil current detecting means for detecting a current flowing through the inner heating coil;
An external heating coil current detecting means for detecting a current flowing through the external heating coil;
Control means for driving and controlling the inverter;
With
The inverter is
A common arm, the inner heating coil arm, and the outer heating coil arm;
Each said arm
Two switching elements connected in series between the output DC buses of the DC power supply circuit;
The circulation direction of the current flowing out from the common arm is connected so that the inner heating coil and the outer heating coil are in the same direction,
The control means includes
Phase difference between the drive signals to the switching elements of the said heating arm coil and the driving signal to the common arm of the switching element alpha, and the drive signal to the switching elements of the common arm and of the outer heating arm coil By adjusting the phase difference β with the drive signal to the switching element,
While controlling the input power to the DC power supply circuit to be a set value,
If the current flowing through the inner heating coil is greater than the current flowing through the outer heating coil,
Reducing the phase difference α or increasing the phase difference β;
If the current flowing through the outer heating coil is greater than the current flowing through the inner heating coil,
Enlarging the phase difference α, or reducing the phase difference β,
The induction heating cooker characterized by controlling so that the electric current which flows into the said inner heating coil, and the electric current which flows into the said outer heating coil may become a substantially equivalent magnitude | size. A DC power supply circuit that rectifies AC power and converts it into DC power;
An inner heating coil and an outer heating coil arranged concentrically;
An inverter for supplying an alternating current to the inner heating coil and the outer heating coil;
An inner heating coil current detecting means for detecting a current flowing through the inner heating coil;
An external heating coil current detecting means for detecting a current flowing through the external heating coil;
Control means for driving and controlling the inverter;
With
The inverter is
A common arm, the inner heating coil arm, and the outer heating coil arm;
Each said arm
Two switching elements connected in series between the output DC buses of the DC power supply circuit;
The circulation direction of the current flowing out from the common arm is connected so that the inner heating coil and the outer heating coil are in the same direction,
The control means includes
Phase difference between the drive signals to the switching elements of the said heating arm coil and the driving signal to the common arm of the switching element alpha, and the drive signal to the switching elements of the common arm and of the outer heating arm coil By adjusting the phase difference β with the drive signal to the switching element,
While controlling the input power to the DC power supply circuit to be a set value,
If the current flowing through the outer heating coil is greater than the current flowing through the inner heating coil,
Reducing the phase difference β so that the phase difference β is substantially equal to or less than the phase difference α,
When the current flowing through the inner heating coil is greater than the current flowing through the outer heating coil and is equal to or greater than a predetermined overcurrent determination value,
The phase difference α is reduced so that the phase difference β is substantially equal to or less than the phase difference α.
An induction heating cooker, wherein the current flowing through the outer heating coil is controlled to be substantially equal to or less than the current flowing through the inner heating coil. The control means includes
If it said phase difference β is equal to or less than a predetermined value, according to claim 1 or 2, characterized in that energizing only in said heating coil to stop the drive signal to the outer heat arm coil Induction heating cooker.

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