JP3848830B2 - Induction heating cooker - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an induction heating cooker that detects the state of a load and controls its heating operation.
[0002]
[Prior art]
An induction heating cooker generates eddy currents in a load such as an iron or stainless steel pan 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]
At this time, if the load is unloaded or small items such as knives, spoons, forks, knives, or aluminum pans or copper pans, an excessive current or high voltage is generated in the circuit through which high-frequency current flows. Circuit elements may be damaged or difficult to heat.
[0004]
Therefore, when such a load is used, it must be detected quickly and the heating operation must be stopped.
[0005]
Therefore, as one conventional method, there is a method for determining the suitability of a load by comparing a signal obtained by detecting and amplifying an input current with a signal changed with a predetermined time constant from the start of operation.
[0006]
As a second conventional method, the input power is adjusted to a certain level at a predetermined timing, and after correcting the input power according to the input voltage at this time, the input power obtained from the input current and the input voltage There is a method of detecting small items by comparing with a certain level. (See JP-A 64-30190, JP-A-5-31068, etc.).
[0007]
However, with these methods, it is possible to energize when the input voltage is close to the rated value, that is, the load that is judged to be suitable is the surrounding circumstances such as the length of the power supply line and the presence or absence of other equipment connected to the power supply and operating. When the input voltage fluctuates and deviates from the vicinity of the rated value, it is determined that energization is impossible, that is, inappropriate.
[0008]
[Problems to be solved by the invention]
As described above, in the conventional induction heating cooker, the load that is determined to be energized, that is, appropriate when the input voltage is close to the rated value, the input voltage fluctuates due to the surrounding circumstances, etc. Cooking may not be possible.
[0009]
The present invention solves this problem, expands the heatable range, and improves the user-friendliness.
[0010]
At the same time, it detects when there is no load, small objects such as knives, spoons, forks, knives, the center of the load and the center of the heating coil are shifted, or aluminum pans or copper pans. The purpose is to stop the heating operation.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention converts input alternating current into direct current by a rectifier circuit and a smoothing circuit, supplies a high frequency current converted from the direct current by a switching element to the heating coil, and supplies the heating coil to the heating coil. In an induction heating cooker that heats a load such as a pan by generating a high-frequency magnetic field, an input voltage detection circuit that detects an input AC input voltage and a primary that detects an input AC input current A current detection circuit; a coil current detection circuit that detects a coil current flowing through the heating coil; a drive circuit that drives the switching element; and a control circuit that includes a microcomputer. The drive circuit is controlled so that gradually increasing power is supplied to the heating coil, and the primary current detection circuit and the The load current is detected based on the output of the current detection circuit. When it is determined that the load is not suitable for heating at each stage, the heating is stopped and at least the power to the heating coil after the second stage is determined. At the time of supply, when the output of the primary voltage detection circuit is less than a predetermined value for the primary current and the output of the input voltage detection circuit is higher than a predetermined value for the input voltage, the output of the input voltage detection circuit is When lower than a predetermined value, power lower than power supplied to the heating coil is supplied to the heating coil, and when the power is supplied to the heating coil in the next stage, the primary current detection circuit and the When it is determined that the load is appropriate from the output of the coil current detection circuit, if the output of the primary current detection circuit is less than a predetermined value for the primary current, the load is determined to be inappropriate. It is obtained so as to stop the heat.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, when detecting the load of the induction heating cooker, the control circuit controls the drive circuit so that gradually increasing power is supplied to the heating coil by the control circuit at the start of heating. Whether to heat the load is determined from the current detection circuit and the output of the coil current detection circuit. If it is determined that the heating of the load is inappropriate at each stage, the heating is stopped, and at least the heating after the second stage is performed. The output of the input voltage detection circuit when the output of the primary current detection circuit is less than a predetermined value with respect to the primary current and the output of the input voltage detection circuit is higher than the predetermined value with respect to the input voltage when power is supplied to the power coil. Is lower than a predetermined value with respect to the input voltage, power lower than the power supplied to the heating coil is supplied to the heating coil, and the heating coil in the next stage is supplied. When power is supplied, if the load is determined to be appropriate from the outputs of the primary current detection circuit and the coil current detection circuit, the load is inappropriate if the output of the primary current detection circuit is less than a predetermined value relative to the primary current. Is determined .
[0013]
As a result, a load that can be energized, that is, determined to be appropriate even if the input voltage deviates not only in the vicinity of the rated value but also out of the vicinity of the rated value, is not determined to be unenergized, that is, inappropriate.
[0014]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 is a structural diagram of an induction heating cooker according to the present invention, FIG. 2 is a control circuit block diagram according to the present invention, FIG. 3 is a diagram showing a judgment boundary line at the time of load suitability judgment according to the present invention, and FIG. FIG. 5 is a flowchart of aptitude determination processing, and FIG. 5 is a diagram showing an output method of the present invention.
[0016]
In FIG. 1, reference numeral 1 denotes a top plate on which a load 5 such as a pan is placed. 2 is a heating coil underneath.
[0017]
Reference numeral 3 denotes an operation unit for operating the energization of the heating coil 2 and includes a key input and an operation display unit.
[0018]
Reference numeral 4 denotes a control circuit unit including a microcomputer for controlling all of the above.
[0019]
In FIG. 2, 6 is an AC power source, and a rectifier circuit 7 and a smoothing circuit 8 are sequentially connected to both ends to form a DC power source. A resonance circuit 9 is connected to the DC power source, and a first terminal of the heating coil 2 is connected to a central connection point in the resonance circuit 9.
[0020]
Reference numeral 10 denotes a capacitor, two of which are connected in series, one end of which is connected to the high-voltage side of the DC power supply (the + terminal portion of the rectifier circuit 7; the same applies hereinafter), and the other end is connected to the low-voltage side of the DC power supply ( The negative terminal of the rectifier circuit 7 is connected to the negative terminal of the rectifier circuit 7. The two series connection points are connected to the second terminal of the heating coil 2.
[0021]
A damper diode 11 is connected in series, one end is connected to the high-voltage side of the DC power supply, the other end is connected to the low-voltage side of the DC power supply, and two series connection points are used for heating. The second terminal of the coil 2 is connected.
[0022]
A switching element IGBT 12 is connected in series, one end is connected to the high voltage side of the DC power supply, the other end is connected to the low voltage side of the DC power supply, and the two series connection points are used for heating. The second terminal of the coil 2 is connected.
[0023]
The output part of the IGBT drive circuit 13 is connected to the gate parts of the two IGBTs 12.
[0024]
An input voltage detection circuit 14 has its input connected to both ends of the power source 6, that is, both ends of the input of the control circuit, and its output connected to the first analog / digital conversion input of the microcomputer 15.
[0025]
Reference numeral 16 denotes a primary current detection circuit, whose input section is connected to a primary current detection sensor 17 installed to detect a current flowing between the power source 6 and the rectifier circuit 7, and whose output section is the second of the microcomputer 15. It is connected to the analog / digital conversion input section.
[0026]
A coil current detection circuit 18 has an input connected to a coil current detection sensor 19 installed to detect a current flowing in the heating coil 2, and an output connected to the third analog / digital conversion of the microcomputer 15. Connected to the input section.
[0027]
The microcomputer 15 is connected to the input voltage detection circuit 14, the primary current detection circuit 16, and the coil current detection circuit 18, and the digital / analog conversion output unit is connected to the IGBT drive circuit 13. It is connected also to the operation part 3 and the display part of the top plate 1 which are not displayed in FIG.
[0028]
In FIG. 3, Iin on the horizontal axis is the value of the input current obtained from the primary current detection circuit 16, IL on the vertical axis is the value of the coil current obtained from the coil current detection circuit 18, and the determination boundary line is The boundary for determining the suitability of the load 5 is shown.
[0029]
In this figure, when the relationship between the input current Iin and the coil current IL is in the region b above the determination boundary line, the suitability of the load 5 is determined to be inappropriate, and in the case of the region a below the determination boundary line. Is to determine the suitability of the load 5 as appropriate in combination with other conditions described later.
[0030]
Iin1 is a value that represents the lower limit of the input current Iin that can be determined when determining the suitability of the load 5.
[0031]
The details of the operation of the main circuit portion of the control circuit, the operations of the three detection circuits, and the overall operation will be described below with reference to FIG.
[0032]
When the AC power supply 6 is turned on, it is converted to DC by the rectifier circuit 7, smoothed by the smoothing circuit 8 to form a DC power supply, and the DC is supplied to other elements and circuits.
[0033]
When the IGBT drive circuit 13 receives a heating signal from the digital / analog conversion output section of the microcomputer 15, the IGBT drive circuit 13 drives the IGBT 12, and based on this drive, the resonance circuit 9 and the heating coil 2 resonate to perform heating. A high-frequency current flows through the coil 2, an eddy current is generated in the load 5 by the electromagnetic induction action of this high-frequency current, and heating is performed by the heat generation action of the load itself.
[0034]
The input voltage detection circuit 14 detects the voltage of the power supply 6, that is, the input voltage of the control circuit, converts the voltage into a signal suitable for the input level, and inputs it to the first analog / digital conversion input section of the microcomputer 15.
[0035]
The primary current detection circuit 16 detects a primary current flowing between the power supply 6 and the rectifier circuit 7 by a primary current detection sensor 17, and the detected signal is a second analog / digital conversion input section of the microcomputer 15. The signal is converted into a signal suitable for the input level and input.
[0036]
The coil current detection circuit 18 detects the coil current flowing through the heating coil 2 by the coil current detection sensor 19 and inputs the detected signal to the third analog / digital conversion input section of the microcomputer 15. The signal is converted into a signal suitable for the input.
[0037]
When the user sets power from the operation unit 3 and inputs setting start, the signal is transmitted to the microcomputer 15, and the microcomputer 15 controls the display unit of the operation unit 3 and the display unit of the top plate 1. A signal is output to control display, and a signal for controlling the IGBT drive circuit 13 is output from the digital / analog conversion output unit. The IGBT drive circuit 13 drives two IGBTs 12, and the two IGBTs 12 control the heating of the load 5 by driving the heating coil 2.
[0038]
When heating is started, load suitability determination processing is first performed in parallel with this based on the signal of the input voltage detection circuit 14, the signal of the primary current detection circuit 16, and the signal of the coil current detection circuit 18. If the suitability is appropriate, heating is performed with the power set by the user and cooking is performed. If the suitability is inappropriate, the power supply is stopped and the process is terminated.
[0039]
Next, the details of the operation for determining the suitability of the load 5 will be described with reference to FIGS. 3 and 5 centering on the flowchart of FIG.
[0040]
When heating is started, an output value (hereinafter referred to as a D / A output value) of the digital / analog conversion output section of the microcomputer 15 is output at level A. This is the first stage indicated by (1) in FIG. 5, and the input current Iin and the coil current IL at this stage are taken in and determined.
[0041]
Then, it is examined whether the relationship between the input current Iin and the coil current IL is in the region a or the region b divided by the determination boundary line in FIG.
[0042]
When the result is the region b, the load 5 is aluminum, copper, or the like, and the suitability is unsuitable, the suitability determination process for the load 5 is terminated, and the energization is stopped.
[0043]
If the result is in region a, the D / A output value is output at level B greater than level A.
[0044]
This is the second stage indicated by (2) in FIG. 5, and the input current Iin and the coil current IL at this stage are captured and determined.
[0045]
Then, it is examined whether the relationship between the input current Iin and the coil current IL is in the region a or the region b divided by the determination boundary line in FIG.
[0046]
When the result is the region b, the load 5 is aluminum, copper, or the like, and the suitability is unsuitable, so the process for determining the suitability of the load 5 is terminated and the energization is stopped.
[0047]
When the result is in the region a, Iin in the second step (2) is compared with the fixed value Iin1, and when Iin is equal to or greater than Iin1, the suitability of the load 5 is appropriate. Then, the process of determining the suitability of the load 5 is terminated, and the D / A output value is gradually increased to a level E that is the set power for heating the load 5 by soft start, and the load 5 is shifted to the heating state.
[0048]
When Iin is less than Iin1, the input voltage is less than a predetermined value (in the case of a low voltage), the center of the load 5 and the center of the heating coil 2 are shifted, or the diameter of the bottom surface of the load is small. It is estimated that it is inappropriate (when load is inappropriate).
[0049]
Therefore, in order to determine whether the voltage is low or unsuitable for the load, the input voltage Vin in the second stage {circle around (2)} is captured and determined.
[0050]
Then, the process proceeds to the third stage (3). Vin is compared with a predetermined fixed value Vin1 lower than the rated input voltage. If Vin is Vin1 or more, the D / A output value is output at level C. When Vin is less than Vin1, the D / A output value is output at level D.
[0051]
At this time, level D is larger than level C.
[0052]
In the third stage (3), the input current Iin and the coil current IL are captured and determined.
[0053]
Then, it is examined whether the relationship between the input current Iin and the coil current IL is in the region a or the region b divided by the determination boundary line in FIG.
[0054]
When the result is the region b, the load 5 is aluminum, copper, or the like, and the suitability is unsuitable, the suitability determination process for the load 5 is terminated, and the energization is stopped.
[0055]
When the result is in the region a, Iin at the stage (3) is compared with the fixed value Iin1, and when Iin is less than Iin1, the center of the load 5 and the heating coil 2 are compared. Or the load 5 is small, such as a knife, spoon, fork, knife, etc., and the suitability is unsuitable, and the process for determining the suitability of the load 5 is terminated, and the energization is stopped.
[0056]
If Iin is greater than or equal to Iin1, the suitability of load 5 is appropriate, the suitability determination process for load 5 is terminated, and the D / A output value is softened to level E, which is the set power for heating load 5 The output is gradually increased at the start, and the load 5 is heated.
[0057]
The relationship between the magnitudes of the aforementioned D / A output value levels is A <B <C <D <E. The output power is a value proportional to the D / A output value.
[0058]
Note that, as an example, the stage of outputting the electric power changed according to the input voltage is the third stage, but it can be considered to be the second stage or the third stage or later.
[0059]
【The invention's effect】
According to the induction heating cooker of the present invention as described above, that the load input voltage which is determined energizable i.e. applicable in the vicinity rated value is determined to energization Call i.e. unsuitable by variations in the input voltage In addition to being able to prevent, the heating operation can be stopped by quickly detecting when the load is unloaded or inappropriate.
[0060]
Therefore, cooking is possible even when the input voltage fluctuates due to surrounding circumstances and the like, and the user's convenience is improved.
[0061]
At the same time, it detects when there is no load, small objects such as knives, spoons, forks, knives, the center of the load and the center of the heating coil are shifted, or aluminum pans or copper pans. The heating operation can be stopped.
[Brief description of the drawings]
FIG. 1 is a structural diagram of an induction heating cooker according to the present invention.
FIG. 2 is a block diagram of a control circuit of the present invention.
FIG. 3 is a diagram showing a determination boundary line at the time of load suitability determination according to the present invention.
FIG. 4 is a flowchart of load suitability determination processing according to the present invention.
FIG. 5 is a diagram showing an output method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Top plate 2 Heating coil 3 Operation part 4 Control circuit part 5 Load 6 Power supply 14 Input voltage detection circuit 15 Microcomputer 16 Primary current detection circuit 18 Coil current detection circuit

Claims (1)

  The input alternating current is converted into direct current by a rectifier circuit and a smoothing circuit, a high-frequency current converted from the direct current by a switching element is supplied to the heating coil, and a high-frequency magnetic field is generated in the heating coil, thereby loading a load such as a pan. In an induction heating cooker configured to heat, an input voltage detection circuit for detecting an input AC input voltage, a primary current detection circuit for detecting an input AC input current, and a coil flowing in the heating coil A coil current detection circuit for detecting current, a drive circuit for driving the switching element, and a control circuit including a microcomputer are provided, and at the start of heating, the control circuit supplies a plurality of stages of gradually increasing power to the heating coil. The drive circuit is controlled so that load is applied from the outputs of the primary current detection circuit and the coil current detection circuit at each stage. When determining that the heating of the load is inappropriate at each stage, the heating is stopped, and at the time of supplying power to the heating coil at the second stage and thereafter, the output of the primary current detection circuit When the output of the input voltage detection circuit is higher than a predetermined value for the input voltage when the output of the input voltage detection circuit is lower than a predetermined value for the input voltage. When a power lower than the power supplied to the heating coil is supplied to the heating coil and power is supplied to the heating coil in the next stage, a load is generated from the outputs of the primary current detection circuit and the coil current detection circuit. When it is determined to be appropriate, if the output of the primary current detection circuit is less than a predetermined value for the primary current, it is determined that the load is inappropriate and control is performed to stop heating. Induction heating cooker to be.

Images