JP3854752B2 - Induction heating cooker - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an induction heating cooker .
[0002]
[Prior art]
An induction heating cooker generates eddy current in a load such as iron or stainless steel close to a heating coil through which a high-frequency current flows, and heats it by the heat generating action of the load itself.
[0003]
Further, when there is no load, aluminum, copper pans, and some stainless steel pans may generate excessive current and high voltage in a high-frequency current generation circuit, so-called inverter circuit. Or it may be difficult to heat.
[0004]
Therefore, when such a load is brought close to the heating state, it must be promptly detected and the heating operation must be stopped.
[0005]
Conventionally, a low energization rate, which is an initial stage of energization, is set, input power is obtained from the input voltage and input current, and if it is equal to or less than a reference value, it is determined as a heating load.
[0006]
Alternatively, from the relationship between the input current and the coil current, a case where the coil current is relatively large with respect to the input current is often determined as a load unsuitable for heating.
[0007]
(For example, see Japanese Patent Application Laid-Open No. 64-30190 and Japanese Patent Application Laid-Open No. 5-129068)
[0008]
[Problems to be solved by the invention]
As a feature of induction heating, the resonance state is used in the inverter circuit system, so the equivalent impedance, that is, the equivalent resistance and equivalent inductance seen from the end of the heating coil changes depending on the material and shape of the load and the distance from the heating coil. However, depending on the combination, an excessive coil current flows or the reverse phenomenon appears, and the inverter switching element, the resonant capacitor, etc. may be overheated or the load itself cannot be heated.
[0009]
Or, although it is not as much as so-called small loads such as spoons and knives, there are cases where the input power is lower than a standard load.
[0010]
In order to protect circuit elements from the occurrence of overcurrent and overvoltage, energization when detecting a load must be performed in a short time with low power. In particular, in an aluminum pan, a copper pan, some stainless steel pans, etc., an excessive current flows inside the inverter, and it is necessary to stop the heating operation promptly.
[0011]
However, in the case of a load whose input power is low as described above, when the load detection power is set low, there is almost no difference between the small load and the input current and the coil current, which may make the determination difficult. In order to solve this, a highly sensitive current detection element is required, which causes an increase in cost.
[0012]
Moreover, since it becomes a load (pan) which cannot be used for a user, the problem that the selection range of a load becomes narrow also arises.
[0013]
Some pans can be used if the power is limited by some deformation.
[0014]
[Means for Solving the Problems]
The present invention is to solve the above problems, switching and rectifying circuitry to convert alternating current into direct current, before SL and smoothing circuits for smoothing the converted DC by the rectifier circuit, the output of the smoothing circuits was converted into a high-frequency current to the element, the heating coil is supplied to the resonance circuit composed of the resonance capacitor, and an inverter circuit for heating a load arranged in the vicinity of the heating coil, and a control circuit for controlling this inverter circuit, the control circuit Setting means for setting the energization power, an input current detection circuit for detecting the input current of the commercial power supply, an input voltage detection circuit for detecting the input voltage of the commercial power supply, and a heating coil current detection for detecting the current of the heating coil In the induction heating cooker provided with a circuit, the control circuit is energized at a low power setting at the beginning of energization, and the output of the input current detection circuit and the heating coil current detection circuit If the heating suitability is determined from the force, and it is determined that it is suitable for heating, energization is performed at a high power setting, and the heating suitability determination based on the output of the input current detection circuit and the output of the heating coil current detection circuit; The current supply is stopped when it is determined that the heating is unsuitable in any of the determinations of the suitability for heating based on the output of the input voltage detection circuit and the output of the input current detection circuit, and otherwise the power supply is continued. The control was performed .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a rectifier circuit that converts alternating current into direct current, a smoothing circuit that smoothes the direct current converted by the rectifier circuit, and an output of the smoothing circuit is converted into a high-frequency current by a switching element. An inverter circuit for heating a load arranged near the heating coil, a control circuit for controlling the inverter circuit, a setting means for setting energization power to the control circuit, and an input of the input alternating current In an induction heating cooker comprising: an input current detection circuit that detects current; an input voltage detection circuit that detects an input AC input voltage; and a heating coil current detection circuit that detects a current of the heating coil. The control circuit is energized at a low power setting at the beginning of energization, and the heating suitability is determined from the output of the input current detection circuit and the output of the heating coil current detection circuit. When it is determined that it is suitable for heating, energization is performed at a high power setting, and determination of suitability for heating based on the output of the input current detection circuit and the output of the heating coil current detection circuit, and the input voltage detection circuit If it is determined that the heating is unsuitable based on the determination of whether heating is appropriate or not based on the output of the input current detection circuit and the output of the input current detection circuit, control is performed so that the energization is stopped and otherwise the energization is continued .
[0020]
【Example】
Hereinafter, the present invention will be described with reference to the drawings.
[0021]
FIG. 1 is a block diagram of a main part of an induction heating cooker showing an embodiment of the present invention, which is an example of an inverter circuit for induction heating of a current resonance type.
[0022]
The commercial power source 1 is converted into a DC power source by the rectifier circuit 2, smoothed by the smoothing circuit 3 of the smoothing capacitor, and stabilized. The DC power supply is connected with a series connection of resonance circuits 4 and 5 of a resonance capacitor. A connection point between the resonance circuits 4 and 5 of the resonance capacitor and one end of the heating coil 6 are connected.
[0023]
A damper diode 8 and a snubber circuit 9 connected in reverse parallel to the upper arm switching element 7 are connected to the high voltage side of the DC power source and connected in reverse parallel to the lower arm switching element 10 at the other end of the heating coil 6. The damper diode 11 and the snubber circuit 12 are connected to the low voltage side of the DC power supply.
[0024]
The control circuit 20 performs starting, stopping, heating power setting and the like of the heating operation by setting means 21 operated by the user, and further controls input power correction and the like.
[0025]
The pulse division circuit 14 divides the output of the pulse conversion circuit 13 that converts the thermal power level setting output output by the control circuit 20 into a basic pulse train into alternating drive pulses for the upper and lower arms.
[0026]
Further, the output signal of the pulse division circuit 14 is converted to a signal level suitable for the drive circuit 15 and the drive circuit 16 to drive the switching elements 7 and 10 of the upper and lower arms.
[0027]
The input current detection circuit 18 converts the output level of the current detection element 17 that detects the current viewed from the commercial power source 1 into a signal suitable for the input level of the control circuit 20.
[0028]
The input voltage detection circuit 19 detects the voltage of the commercial power supply 1 and converts it to a signal suitable for the input level of the control circuit 20.
[0029]
The heating coil current detection circuit 23 converts the output signal level of the current detection element 22 that detects the current of the heating coil 6 into a signal suitable for the input level of the control circuit 20.
[0030]
A load 24 is heated by the heating coil 6.
[0031]
FIG. 2 is an equivalent impedance characteristic example (series circuit of equivalent inductance and equivalent resistance) of the load 24 (a heating coil and a magnetically coupled load) viewed from the inverter circuit.
[0032]
The horizontal axis represents the equivalent inductance of the load 24, and the vertical axis represents the equivalent resistance of the load 24.
[0033]
Depending on the presence or absence of the load 24 and the material, combinations of equivalent inductance and equivalent resistance can be broadly divided into blocks A, B, and C in the figure.
[0034]
Block A is a magnetic material load such as iron or enamel.
[0035]
Block B is when there is no load or an accessory load is placed.
[0036]
Block C is for a load made of aluminum, copper or some stainless steel.
[0037]
However, these are divided into blocks for typical loads 24, and there are factors that vary depending on differences in the shape of the load 24, the metal thickness of the bottom surface, the distance from the heating coil 6, and the like.
[0038]
Generally, only the block A among these blocks is a load 24 suitable for induction heating, and serves as a reference for the distance (gap) between the heating coil 6 and the load 24 and the drive timing of the switching elements 7 and 10. is there.
[0039]
Block B has a large equivalent inductance and a small equivalent resistance.
[0040]
Block C has a small equivalent inductance and a small equivalent resistance.
[0041]
FIG. 3 is a diagram showing a change in equivalent impedance when the distance between the heating coil 6 and the load 24 is changed.
[0042]
In general, the equivalent circuit of the heating coil 6 and the load 24, the heating coil of resistance R ₁ and inductance L _1, the load resistance value R ₂ and the inductance L ₂ is, it may represent a circuit coupled with mutual inductance M .
[0043]
The mutual inductance M varies depending on the distance, material, shape, etc. between the heating coil 6 and the load 24.
[0044]
When this equivalent circuit is further modified, the equivalent impedances L and R as loads of the inverter power supply can be expressed by the following equations.
[0045]
(formula)
L = L ₁ − (ω ² L ₂ M ² ) / (R ₂ ² + ω ² L ₂ ² )
R = R ₁ + (ω ² R ₂ M ² ) / (R ₂ ² + ω ² L ₂ ² )
Therefore, it can be seen that the equivalent inductance and equivalent resistance as viewed from the inverter power supply vary greatly depending on the change of the mutual inductance M, that is, the distance between the heating coil 6 and the load 24 and the material and shape of the load 24. (If the degree of coupling decreases, the equivalent inductance and equivalent resistance approach the value of the heating coil itself.) Since the combination of the equivalent inductance and equivalent resistance varies depending on the load 24, the load can be heated, difficult to load, impossible to load, etc. Can be divided.
[0046]
In addition, since the equivalent inductance and equivalent resistance change depending on the current flowing through the load 24, when it is determined that heating is possible / impossible only by the initial load detection current, the load that is difficult to heat but cannot be heated is actually not heated. Will be misjudged.
[0047]
When the inverter unit is operated at a certain energization rate, the input current and coil current of the load 24 belonging to the block B and the load 24 belonging to the block C have the following tendencies with respect to the load 24 belonging to the block A in FIG.
[0048]
――――――――――――――――――――――――
Input current for block A Coil current ――――――――――――――――――――――――
Block B is small Small block C is small Large ――――――――――――――――――――――――
FIG. 4 shows an allowable region for the load 24 that can be heated by the inverter circuit. In this figure, the allowable range of the coil current with respect to the input current is below the boundary line A.
[0049]
The control circuit 20 may determine that the load 24 of the block C is a load 24 that cannot be heated because the input current and the coil current are distributed above the boundary line A in a certain energization power setting.
[0050]
Further, the load 24 of the block B has a distribution of the input current and the coil current on the lower side with respect to the boundary line of FIG. 4, but is inappropriate as the load 24 to be heated.
[0051]
This is equivalent to low power consumption as viewed from the commercial power source 1 when the inverter is operated at the same energization rate with respect to the load 24 of the block A.
[0052]
FIG. 5 shows an allowable range of the power supply voltage and the input current when the inverter is operated at a certain energization rate. Even if the same load 24 is to be heated, since the degree of coupling decreases as the distance between the load 24 and the heating coil 6 increases, the equivalent inductance increases and the equivalent resistance decreases as shown in FIG. Even if they are made of the same material, the smaller the shape, the lower the degree of coupling between the heating coil 6 and the load 24, so that the equivalent inductance tends to increase and the equivalent resistance tends to decrease.
[0053]
Since the power consumed by the load 24 (heat generation) is due to equivalent resistance, when the energization rate is set to the same value, it is only necessary to determine whether heating is appropriate or not based on the input power obtained from the input voltage and the input current.
[0054]
Therefore, the load 24 existing below the boundary line B in FIG. 5 may be determined as the load 24 not suitable for heating.
[0055]
Further, in FIGS. 4 and 5, the hatched portion is a portion that is at a level lower than the current value that can be normally detected by the current detection element 17 and the current detection element 22. In this region, problems such as insensitive parts due to non-linear elements (semiconductors and the like) used for the input current detection circuit 18 and the heating coil current detection circuit 23 and weakness to noise contamination due to circuit operation occur.
[0056]
Therefore, when both detection outputs are in the shaded area, it is possible to avoid using high-sensitivity parts and increasing the cost by setting a power supply rate that can obtain a higher detection level. .
[0057]
However, when an attempt is made to heat the load 24 that is not suitable for heating, the generation of an abnormally high current or high voltage must be suppressed in the inverter circuit.
[0058]
Therefore, the initial setting is made so that the suitability of the load 24 can be detected at a low current rate, and the suitability of the load 24 is judged again at a current rate higher than the initial low current rate, unless the result is inappropriate. do it.
[0059]
In general, rather than starting energization with the load 24 of the block B, overcurrent generated when attempting to energize the load 24 of the block C such as an aluminum pan or some stainless steel pans is more likely to cause stress on the inverter circuit. However, since these loads 24 generate a high coil current even at a low energization rate, they must be determined at an early stage.
[0060]
For these reasons, the load 24 of the block C may be detected first at a low energization rate, and then the load 24 of the block B may be detected at a higher energization rate.
[0061]
FIG. 6 shows an energization rate setting pattern for detecting the load 24 in consideration of the above points.
[0062]
The horizontal axis represents time, and the vertical axis represents the energization rate set by the control circuit 20.
[0063]
The current is not energized before time T0. It is assumed that energization is started from time T0 by the user's operation.
[0064]
At time T0, energization is started with the first energization rate setting S1.
[0065]
The first load determination is performed at time T1. The determination at this time uses the determination region shown in FIG. As a result, when it is determined that heating is not possible, the energization operation is stopped.
[0066]
If it is determined that the load 24 can be heated, the energization is continued with the second energization rate setting S2. Here, the relationship between the energization rate settings S1 and S2 is:
S1 <S2 (S2 has larger energization power than S1)
And
[0067]
A second load determination is performed at time T2. The determination at this time uses both determination areas shown in FIGS.
[0068]
As a result, energization is continued only when it is determined that both can be heated at the same time, and energization is stopped as a load 24 that cannot be heated otherwise.
[0069]
The intervals from time T0 to T1 and from T1 to T2 are set to a time sufficient for stable power supply voltage detection, input current detection, and heating coil current detection. (Normally within 1 second)
FIGS. 7, 8, and 9 are operation examples when load detection is performed on the representative loads 24 of the blocks A to C with the above-described energization pattern. The first load determination is T1 determination, and the second load. The determination is T2.
[0070]
FIG. 7 is a timing diagram of the detection waveform, and FIGS. 8 and 9 show the relationship between the detection value at the time of load determination and the determination region. The determination based on the comparison of power is referred to as determination B. (However, when the input voltage is constant)
8 and 9, A (T1) represents a current or a current detection result at time T1 with respect to the load 24 of the block A.
[0071]
The detection results of the blocks A to C are summarized as follows.
[0072]
―――――――――――――――――――――――――――――――
Load \ Judgment T1 Judgment T2 Judgment ――――――――――――――――――――――――――――――――
Block A OK OK
Block B OK judgment A / OK judgment B / NG
Block C Judgment A / NG (Not executed)
―――――――――――――――――――――――――――――――
In the load C of block C, in the T1 determination, B (T1) in FIG. 8 is in an unstable output portion, but the coil current shows a high value and is in a normal output range. The load 24 can be determined.
[0073]
Further, depending on the load 24, in the determination at time T2, there may be a case where determination A is NG and determination B is OK. In the case of such a load 24, the coil current tends to increase as the energization rate is further increased. Therefore, a state in which an abnormal current or voltage is generated for the inverter circuit can be prevented in advance.
[0074]
Furthermore, even when the load 24 having an equivalent impedance corresponding to the boundary of each block is to be heated, it is possible to appropriately determine whether or not the load 24 can be heated from the above two-stage two-type determination results.
[0075]
In this example, the determination of the input current and the heating coil current uses the same determination area for the first energization and the second energization, but separate determination areas may be used.
[0076]
In this example, the current resonance type induction heating cooker has been described. However, even in a voltage resonance type circuit configuration, the equivalent impedance of the heating coil 6 and the load 24 is applicable because the above relationship is established.
[0077]
【The invention's effect】
According to the present invention, it is possible to determine the load of the material or shape, the appropriateness of the inverter load due to variations in the distance from the heating coil at appropriate and accurate.
[0078]
In addition , stress such as overcurrent and overvoltage applied to the inverter circuit of the induction heating cooker can be reduced, and load detection can be performed appropriately for the user, improving usability.
[0079]
In addition, those near the judgment value are not immediately usable, but the upper limit is set and the usable range is set, so that the range of use of the pan is expanded and the usability is improved.
[Brief description of the drawings]
FIG. 1 is a block diagram of an induction heating cooker showing an embodiment of the present invention.
FIG. 2 is an impedance characteristic diagram of a load of an induction heating cooker showing an embodiment of the present invention.
FIG. 3 is a variation diagram of equivalent impedance of the induction cooking device showing an embodiment of the present invention.
FIG. 4 is a permissible region diagram of a coil current with respect to an input current of an induction heating cooker showing an embodiment of the present invention.
FIG. 5 is an allowable area diagram of an input current with respect to an input voltage of an induction heating cooker showing an embodiment of the present invention.
FIG. 6 is a load detection energization rate setting pattern diagram of the induction heating cooker showing one embodiment of the present invention.
FIG. 7 is an operation waveform diagram of load detection of the induction heating cooker showing one embodiment of the present invention.
FIG. 8 is a determination (input current and coil current) of load detection of the induction heating cooker showing one embodiment of the present invention.
FIG. 9 is a diagram (input voltage and input current) of load detection of the induction cooking device showing an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Rectification circuit 3 Smoothing circuit 4 Resonance circuit 5 Resonance circuit 6 Heating coil 7 Switching element 8 Damper diode 9 Snubber circuit 10 Switching element 11 Damper diode 12 Snubber circuit 13 Pulse conversion circuit 14 Pulse division circuit 15 Drive circuit 16 Drive circuit 17 current detection element 18 input current detection circuit 19 input voltage detection circuit 20 control circuit 22 current detection element 23 heating coil current detection circuit 24 load

Claims (1)

A rectifier circuitry to convert alternating current into direct current, a smoothing circuits for smoothing the direct current converted by the pre-Symbol rectifier circuit converts the output of the smoothing circuits and more high-frequency current to the switching element, the heating coil, the resonant An inverter circuit that supplies a resonance circuit composed of a capacitor and heats a load disposed in the vicinity of the heating coil, a control circuit that controls the inverter circuit, setting means that sets energization power to the control circuit, and an input AC In an induction heating cooker comprising: an input current detection circuit that detects an input current of the input current; an input voltage detection circuit that detects an input voltage of an input alternating current; and a heating coil current detection circuit that detects a current of the heating coil. The control circuit is energized at a low power setting at the beginning of energization, determines the heating suitability from the output of the input current detection circuit and the output of the heating coil current detection circuit, and adds When it is determined to be suitable for heating, energization is performed at a high power setting, determination of suitability for heating based on the output of the input current detection circuit and the output of the heating coil current detection circuit, the output of the input voltage detection circuit, and the Induction characterized by controlling to stop energization if it is determined to be unsuitable for heating based on whether the heating is appropriate or not based on the output of the input current detection circuit, and otherwise continue energization Cooking cooker.

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