JP4945409B2 - Induction heating cooker - Google Patents

Description

  This invention is a technique regarding the induction heating cooking appliance.

  The induction heating cooker can be efficiently heated by generating an eddy current in a metal load (pan) arranged in the vicinity of a heating coil for passing a high-frequency current, and the load itself self-heats by the Joule heat. In recent years, instead of cooking utensils such as gas stoves, replacement with induction heating cookers has progressed because of excellent safety and temperature controllability.

  In addition, induction heating cookers have also been put to practical use that can heat low-resistance nonmagnetic metals such as aluminum and copper that could not be heated. However, in an aluminum pan, if you try to apply a large amount of heating power when the weight including food is light, the repulsive force generated between the pan and the heating coil will increase, causing the pan to float or move. appear.

  Several solutions have been proposed for such problems.

  The first method is a method of reducing the heating power when detecting the rising of the pan (see Patent Document 1), and the second method is arranging a nonmagnetic metal plate between the pan and the heating coil. And it is a method (refer patent document 2) which reduces the repulsive force which generate | occur | produces between a pan and a heating coil while heating a nonmagnetic metal plate.

In the third method, the phase of the current applied to the plurality of heating coils is reversed in phase depending on the material of the load such as a pan, and the mutual inductance between the heating coils is used as the same phase. A method (see Patent Document 3) that enables heating to the same extent is also known.
JP 2004-165127 A JP 2004-273301 A JP 2007-12482 A

  However, the following problems exist in the above solution.

  In the first method, there is a possibility that the heating power necessary for cooking cannot be obtained.

  For example, a lightweight pan or frying pan may easily float against the repulsive force, and when the contents are unevenly distributed, the balance may be lost and move on the top plate. In order to prevent this, ascending is detected and the thermal power is reduced, there are cases where sufficient thermal power for cooking cannot be obtained or cooking cannot be performed.

  In the second method, although the repulsive force generated in the load such as the pan is reduced, the non-magnetic metal plate is heated to heat the glass surface, thereby causing boiled-out baking or after cooking is finished. There is a risk of burns due to the high temperature of the glass surface.

  In the third method, in the case of a magnetic metal load, the phase of the current applied to the heating coil is set to an opposite phase so that the current flows easily to the heating coil. In the case of a non-magnetic metal load, the current flowing to the heating coil is suppressed as the same phase. Thus, since the current values flowing in the heating coils are made to be the same regardless of the difference in load, it does not contribute to suppressing the repulsive force generated between the load and the coil.

In order to solve the above problems, the present invention provides an induction heating cooker comprising a DC power source means, a heating coil section, a high-frequency output control means, etc., wherein the heating coil section has U-shaped ferrite below each. The arranged N (N ≧ 2) heating coils are arranged concentrically on substantially the same plane, and a reference current is applied using one of the N heating coils as a reference coil, and the remaining The high-frequency output control means controls the current applied to the coil so that the phase difference is nπ / N (n is an integer from 1 to N−1) at the same frequency with respect to the reference current. Features .

  The repulsive force generated due to the high-frequency current flowing through the plurality of heating coils has an effect that the maximum value of the repulsive force can be suppressed lower than when the current flows in the same phase.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 and 10 are a schematic configuration diagram of an induction heating cooker according to the present invention and a circuit configuration schematic diagram thereof.

  In FIG. 1, a metal load 1 is a cooking pan made of a nonmagnetic metal such as aluminum and is installed on a glass plate 2. Below the glass plate 2, a disc-shaped first heating coil 10 and a second heating coil 20 are arranged on substantially the same plane, and each of the heating coils 10, 20 is a high-frequency output control means 12, A high frequency current is applied to the terminal 22. Each of the heating coils 10 and 20 is provided with magnetic materials 11 and 21 having a high magnetic permeability to prevent mutual influence between induced currents generated by the magnetic flux based on the current flowing through the heating coils 10 and 20. The magnetic flux is efficiently linked to the load 1.

  The high-frequency output control means 12 and 22 are supplied with electric power obtained by rectifying the alternating-current power supply 101 with the direct-current power supply means 100 and converting the electric power to the heating coils 10 and 20 with a predetermined phase difference. Apply.

Next, the phase difference performed by the high frequency output control means will be described.

図１における第１、第２の加熱コイル１０，２０の巻き数を同一のｎとしたとき、各加熱コイル１０、２０に印加される電流Ｉによってそれぞれの加熱コイル１０、２０に発生する電力Ｐ_１、Ｐ_２と反発力Ｆ_１、Ｆ_２は各々以下の式３、４、５、６となる。

このとき、各加熱コイル１０，２０と負荷１の間に発生する反発力Ｆ_１、Ｆ_２は加熱コイル１０、２０に印加される電流波形に依存する。つまり、各加熱コイル１０、２０に周波数ｆの正弦波電流が流れており、それぞれの電流位相をθ₁、θ₂とおけば、加熱コイル１０、２０と負荷１の間に発生する瞬時的な反発力は、以下の式７、８で表され、ここでω＝２πｆである。

反発力は負荷１に発生する誘導電流自体と加熱コイル１０、２０の電流の間に発生するため、その力は電流の向きにかかわらず常に正となるので、Ｆ_１、Ｆ_２は正の値をとる。 In induction heating, the power P for heating the load 1 and the repulsive force F generated between the load 1 and the heating coil are expressed as follows: n is the number of turns of the heating coil and I is the current flowing through the heating coil. Since it is proportional to the square of the product of the number of turns and the flowing alternating current, and the repulsive force is proportional to the change in the generated magnetic flux, it is proportional to the product of the number of turns of the heating coil and the alternating current. Can be represented.

When the number of turns of the first and second heating coils 10 and 20 in FIG. 1 is the same n, the electric power P generated in each heating coil 10 and 20 by the current I applied to each heating coil 10 and 20. ₁ , P ₂ and repulsive forces F ₁ , F ₂ are represented by the following expressions 3, 4, 5, 6 respectively.

At this time, the repulsive forces F ₁ and F ₂ generated between the heating coils 10 and 20 and the load 1 depend on the current waveform applied to the heating coils 10 and 20. That is, a sinusoidal current having a frequency f flows through the heating coils 10 and 20, and if the current phases are θ ₁ and θ ₂ , instantaneous moments generated between the heating coils 10 and 20 and the load 1 are generated. The repulsive force is expressed by the following equations 7 and 8, where ω = 2πf.

Since the repulsive force is generated between the induced current itself generated in the load 1 and the current of the heating coils 10 and 20, the force is always positive regardless of the direction of the current, and therefore F ₁ and F ₂ are positive values. Take.

  However, since the electric power represented by Equations 3 and 4 is an effective value, it is not affected by the above phase.

同様に、θ_１とθ_２の差があるとき、その差分をθとすれば、発生する反発力Ｆｂは以下の式１０となる。

したがって、負荷１に発生する反発力は、瞬時的な力が大きいほど負荷１を浮上(ないしは移動)させるものとなるから、使用者にとってはその極大値が大きければ大きいほど負荷１が浮いた感覚を受ける。よって、当該浮上感覚を減少させるためには、前記式１０におけるＦbの最大値が最も小さくなるθを設定すればよいこととなる。 Here, when θ ₁ and θ ₂ are θ ₁ = θ _2, that is, when the phase difference is zero, the repulsive force Fa generated is the repulsive force of the heating coils 10 and 20 against the load 1. Since it is an instantaneous value, the following equation 9 is obtained.

Similarly, when there is a difference between θ ₁ and θ ₂ , if the difference is θ, the repulsive force Fb that is generated is given by Equation 10 below.

Therefore, since the repulsive force generated in the load 1 increases (or moves) the load 1 as the instantaneous force increases, the user feels that the load 1 floats as the maximum value increases. Receive. Therefore, in order to reduce the floating feeling, it is only necessary to set θ that minimizes the maximum value of Fb in the equation (10).

但し、０≦ωt＜π
半角公式、加法定理にて「式１１」を変形すると以下の「式１２」となる

Here, even if “Equation 10” is transformed into the following “Equation 11”, ωt and θ that take the extreme values do not change, so that “Equation 11” will be examined.

However, 0 ≦ ωt <π
Transforming “Equation 11” with the half-width formula and the addition theorem yields the following “Equation 12”

When total differentiation is performed in order to obtain the extreme value in the formula “Formula 12”, the following “Formula 13” is obtained.

Solving the binary linear simultaneous equations shown in the above “Formula 13”, as shown in the following “Formula 14” and “Formula 15”, the phase difference becomes an extreme value at θ = 0, π / 2, and the phase difference θ = 0 is the maximum value, and phase difference θ = π / 2 is the minimum value.

  Further, FIG. 3 shows that the phase difference is changed from 0 to π by numerical analysis, and the added value of the repulsive force of the first heating coil and the second heating coil and the repulsive force at each phase is set for each ωt (for each angle). FIG. 2A is a chart obtained for one period, and the maximum values for each phase difference are plotted based on the chart, which is in agreement with the above examination results.

Here, when the phase is changed, the phase difference θ = π / 2 at which the maximum value in the phase is the lowest, and the maximum value ωt is obtained based on “Expression 10”. As shown in Equation 16, ωt = π / 4 and 3π / 4.

また、位相差ゼロ、すなわち、第１、第２加熱コイルを同位相で電流を流した場合はそれぞれの電流に起因する反発力は１つの加熱コイル電流に起因する反発力の２倍に相当し、極大値(sinωt=１または−１)のタイミングも一致するので、その値は以下の「式１８」となる。

したがって、その比は、以下の「式１９」に示されるように√２倍となる。

つまり、加熱コイルが２個の場合、同じ電力を負荷に投入しつつ、反発力の瞬時最大値を1／√２に下げることができる。 When the value of ωt = π / 4 is calculated based on “Expression 10”, the following “Expression 17” is obtained.

In addition, when there is no phase difference, that is, when current flows through the first and second heating coils in the same phase, the repulsive force caused by each current is equivalent to twice the repulsive force caused by one heating coil current. Since the timing of the local maximum value (sinωt = 1 or −1) also coincides, the value is expressed by the following “Equation 18”.

Therefore, the ratio becomes √2 times as shown in the following “Equation 19”.

That is, when there are two heating coils, the instantaneous maximum value of the repulsive force can be reduced to 1 / √2 while supplying the same power to the load.

  Further, this point will be described with reference to FIG.

  FIG. 4 is a diagram schematically showing the relationship between the repulsive force and the coil current in the two heating coils.

  In the figure, when a coil current flows without providing a phase difference in the group A, a repulsive force when a coil current flows with a phase difference of 1/4 period, that is, π / 2, is applied to the group B. It is shown in time series when the period is T. In addition, since it becomes left-right symmetry, only a half surface is shown.

  At time 0, no current flows through any coil in group A. In group B, the peak current Ip flows only in the coil 2. At this time, the repulsive force generated in the group A becomes zero, and in the group B, the repulsive force caused only by the coil 2 is generated, and the magnitude thereof is proportional to | Ip |.

  At time T / 8, a current of √2Ip / 2 flows through group A, and the repulsive force caused by the current is proportional to √2 | Ip |. In group B, current starts to flow through coil 1 to become √2Ip / 2, coil 2 decreases and current of √2Ip / 2 flows, and the repulsive force resulting from these currents is proportional to √2 | Ip |.

  At time T / 4, a current of Ip flows through each group A, and the repulsive force resulting from the current is proportional to 2 | Ip |. In group B, the current in coil 1 is Ip, the current in coil 2 is zero, and the repulsive force resulting from that current is proportional to | Ip |.

  Thereafter, it is periodically repeated as shown in the figure. However, even if the direction of the current is reversed, the repulsive force is the same direction.

  FIG. 5 is a graph showing the state of FIG.

  The relative comparison when the maximum value of the repulsive force when the present invention is not applied is set to 1 is shown.

  In FIG. 5, waveform 1 is the repulsive force ratio when current is flowing at zero phase, waveform 2 is the repulsive force ratio when current of phase difference T / 4, that is, π / 2 is flowing, and waveform 3 is The combined repulsive force ratio of group A, waveform 4 is the combined repulsive force ratio of group B.

  Group A shows a maximum at T / 4 or π / 2 and 3T / 4 or 3π / 2.

  In the group B, the maximum is obtained at the time T / 8, that is, π / 4 has elapsed, and the minimum is obtained at T / 4, T / 2, 3T / 4, that is, π / 2, π, 3π / 2.

  As a result, the repulsive force ratio of group B to group A is 1 / √2.

  If the configuration of the present invention is not employed, the instantaneous maximum value of the repulsive force is determined by the oscillation frequency of the inverter per unit time, so that the load is continuously receiving a large force. Become. However, if the configuration of the present invention is adopted, the instantaneous maximum value of the repulsive force that is generated is reduced, so that the force that increases the load that receives this force is reduced.

  In addition, since the momentary maximum value becomes lower than the limit value (maximum value of the static frictional force) at which the load is unbalanced by the repulsive force and starts moving, the present invention is applied to the electric power input to the load. Application also suppresses movement. Furthermore, even when the movement starts, the moving distance is shortened because the instantaneous maximum value of the repulsive force is reduced.

  From these points, when power equivalent to that in the past is applied to the load, the induction heating cooker that is convenient for the user can be provided because the floating and movement of the load are suppressed. Moreover, when allowing the load to float and move at the same level as in the past, higher power than in the conventional case can be applied to the load, and cooking that requires a large heating power can be handled.

  Next, the number of turns n of each coil related to the repulsive force and the current I applied to the coil will be described.

    The repulsive force of each heating coil is generated for each heating coil in proportion to the product of the number of turns n of the heating coil and the current I flowing through the heating coil, that is, the amount of change in the generated magnetic flux.

  Using two heating coils as described above, if the ratio of the number of turns n of the coil and the current I applied to the coil, the ratio of n × I is 5: 5, the maximum value of the repulsive force is both However, if the ratio is, for example, 2: 8, the contribution of the latter repulsive force is the main factor. Therefore, the maximum value reduction degree in the latter case is less effective than the former. Decrease.

  Furthermore, the arrangement of the heating coil is not concentric as shown in FIG. 8, but has the same effect even in the case of the circumferential division type in which the circumference is divided as shown in FIG. 9 described later.

  In any case, assuming that the number of turns of the heating coil is M1, M2,... And the flowing current is I1, I2,..., The values of M1 × I1, M2 × I2,. If it is made, good effects can be expected.

  2 (a) and 2 (c) correspond respectively to FIG. 2 (a) relating to the two-divided heating coil in the case of three-division and four-division obtained in the same manner as the division of the heating coil. 6 and 7 respectively correspond to FIG. 5 relating to the two-divided heating coil obtained in the same manner, and the phase difference in this case is the same as that of the three-divided coil of FIG. Each π / 3 is π / 4 in the quadrant coil of FIG.

  As described above, when a current is passed through a plurality of heating coils, the phase setting method for reducing the instantaneous maximum repulsive force most is as described above. If the appearing timings are arranged at equal intervals, the effect of the present invention can be enhanced.

  Generalizing the above conditions, if the current flowing through one of the N heating coils is used as a reference, the current flowing through the other n-th coil is about nπ / N relative to the reference current. It is set so as to have a phase difference (where n is 1 to N-1). This is π / 2 with respect to the reference coil current if the number of coils is 2, π / 3 and 2π / 3 with respect to the reference coil current if the number of coils is 3, and the reference coil if the number of coils is 4. The current is passed so as to provide a phase difference of π / 4, π / 2, and 3π / 4 with respect to the current.

  As described above, the repulsive force caused by the coil current is a force in a direction that always repels regardless of whether the current is positive or negative, and therefore, the phase difference is set in a half-cycle section of the coil current.

  On the other hand, when the timing at which the maximum value of each current appears in the half-cycle section of the coil current is not arranged at equal intervals, a larger peak appears than when the current waveforms at close timing are added to each other when they are arranged at equal intervals As a result, the maximum value of the repulsive force also increases.

  Next, the configuration of the heating coil will be described.

  FIG. 8 is a schematic cross-sectional view in the case where the winding center axes are the same and two heating coils are configured concentrically.

  The U-shaped ferrites 11a, 11b,... Are arranged for the heating coil 10, and the U-shaped ferrites 21a, 21b,. The magnetic fluxes that are generated are made difficult to interfere with each other. Further, interference can be made difficult by increasing the distance between the coils and providing the space 23 larger.

  FIG. 9 is composed of three heating coils in which a winding center axis is arranged on the same circumference.

  The winding start of each heating coil 10, 20, 30 is on substantially the same circumference, the shape is substantially the same, and the arrangement is divided into three. The heating coils 10, 20, and 30 are respectively provided with ferrites 11, 21, and 31 to make it difficult for the magnetic fluxes generated by the heating coils to interfere with each other.

  In addition to the examples shown in FIGS. 8 and 9, the number of coils may be two or more, but in any case, the magnetic separation means composed of a magnetic material such as ferrite is disposed between the coils. Or by preventing the generated magnetic flux from interfering with other coils by securing a distance between the coils.

  Insufficient magnetic separation results in inductive reverse currents generated by each other's coil currents, resulting in reduced efficiency and greater current flow to provide the necessary power to the load. Disappear. As a result, the size of the inverter is increased, and the structure for cooling the generated loss is increased, which increases the cost.

The schematic block diagram of the induction heating cooking appliance as one Example of this invention Comparison of repulsive force by the number of heating coils and current phase difference applied to the coils A chart in which the horizontal axis represents the phase difference and the vertical axis represents the combined repulsive force of the first heating coil and the second heating coil for each ωt (angle) in the number of heating coils. Schematic diagram of repulsive force in the conventional example and the embodiment of the present invention Comparison of repulsive force when the number of heating coils is 2 and the phase difference is zero and π / 2 Comparison of repulsive force when the number of heating coils is 3 and the phase difference is different from zero by π / 3 Comparison of repulsive force when the number of heating coils is 4 and the phase difference is different from zero by π / 4 Configuration example of heating coil in the present invention Other configuration examples of the heating coil in the present invention Circuit configuration schematic diagram as an embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal load 2 Glass plate 10 1st heating coil 11 Magnetic material 12 High frequency output control means 20 2nd heating coil 21 Magnetic material 22 High frequency output control means 100 DC power supply means 101 AC power supply

Claims (3)

In the induction heating cooker composed of DC power supply means, heating coil section, high frequency output control means, etc.
The heating coil section has a configuration in which N (N ≧ 2) heating coils each having a U-shaped ferrite disposed below are arranged concentrically on substantially the same plane. A reference current is applied using one of the reference coils as a reference coil, and a current applied to the remaining coils is set to the same frequency as that of the reference current with a phase difference of nπ / N (n is an integer of 1 to N−1). The induction heating cooker in which the high-frequency output control means controls the current so that   An induction heating cooker in which N is 2 in claim 1. The current applied to the N heating coils according to claim 1 or 2 is when the number of turns of each of the heating coils N1 to NN is M1 to MN, and the high frequency current flowing through each of the heating coils N1 to NN is I1 to IN. , M1 × I1,..., MN × IN induction heating cooker controlled by the high-frequency output control means so as to be substantially equal.

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