JP2004362798A - Induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that a relay tends to be out of order due to a contact melting or the like, caused by the frequent change of the capacitances of a resonance capacitors in accordance with the difference of the load of a pan, like the difference between an aluminum pan and an iron pan or the like. <P>SOLUTION: The device is provided with a pan-kind judging means 17 judging the kind of pans by a voltage detecting means 16 detecting voltage of a resonance capacitor 10, a pan-kind memory means 20 memorizing the kind of pans, and a switching means 18 switching the capacitances of the resonance capacitors. Since the resonance capacitors is not switched in accordance with the kind of the pan previously heated even if an inverter 4 ceases to operate, the induction heating device having a switching relay with improved durability, quick in start-up, easy to use, can be provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an induction heating device used in general homes, offices, restaurants, factories, and the like, and more particularly, to an object to be heated made of a material having low magnetic permeability and high electrical conductivity such as aluminum and copper by electromagnetic induction. The present invention relates to an induction heating device such as a cooker or a heating device that heats using a principle.
[0002]
[Prior art]
Hereinafter, as an example of a conventional induction heating device, an induction heating device that generates a high-frequency magnetic field from an induction heating coil and heats an object to be heated such as an aluminum or a pan by eddy current due to electromagnetic induction will be described.
[0003]
In FIG. 6, a power supply 101 is a 200 V commercial power supply that is a low-frequency AC power supply, and is connected to an input terminal of a rectifier circuit 102 that is a bridge diode. A first smoothing capacitor 103 is connected between output terminals of the rectifier circuit 102. A series connection of the choke coil 105 and the second switching element 107 is further connected between the output terminals of the rectifier circuit 102. The heating coil 112 is disposed so as to face an aluminum pot 113 as an object to be heated.
[0004]
Reference numeral 104 denotes an inverter. The low potential side terminal of the second smoothing capacitor 111 is connected to the negative terminal of the rectifier circuit 102, and the high potential side terminal of the second smoothing capacitor 111 is connected to the first switching element (IGBT) 106. The first switching element (IGBT) 106 is connected to the high potential side terminal (collector), and the low potential side terminal is connected to the choke coil 105 and the high potential side terminal (collector) of the second switching element (IGBT) 107. Connected to a point. A series connection of the heating coil 112 and the first resonance capacitor 110a is connected in parallel to the second switching element 107. 100b is a second resonance capacitor which is connected in parallel to the first resonance capacitor 110a by a switching means (relay) 118.
[0005]
The first diode 108 (first reverse conducting element) is connected in anti-parallel to the first switching element 106 (connecting the cathode of the first diode 108 and the collector of the first switching element 106), and Is connected in antiparallel to the second switching element 107.
[0006]
Reference numeral 114 denotes current detection means for detecting an input current flowing from the power supply 101. Output control means 115 outputs a signal to the gates of the first switching element 106 and the second switching element 107 in accordance with the output of the current detection means 114. Is output.
[0007]
116 is a voltage detecting means for detecting the voltage of the resonance capacitor 110a, and the pan type determining means 117 determines the iron load and the aluminum load based on the output of the current detecting means 114 and the output of the voltage detecting means 116. Do.
[0008]
Reference numeral 119 denotes a setting unit for setting the start or stop operation of the inverter 104 and the output power, and includes a plurality of key switches.
[0009]
In the induction heating device configured as described above, the frequency of the resonance current is set to be twice or more the driving frequency of the first switching element 106 and the second switching element 107, so that the first switching is performed. Since the second smoothing capacitor is boosted by the choke coil 105 without increasing the loss of the element 106 and the second switching element 107, a load of low resistance and low magnetic permeability such as aluminum can be output with high output. Induction heating is possible.
[0010]
When the pan type determining means 117 determines that the load is an iron-based load, the second resonance capacitor 110b is connected to the first resonance capacitor 110a, the capacitance of the resonance capacitor is switched, and the first switching element 106, By setting the drive frequency of the second switching element 107 to about 23 KHz and controlling the drive time ratio, the iron-based pan can be induction heated.
[0011]
FIG. 7 shows conditions for starting the inverter 104 and performing the pan type determination. The horizontal axis is the output of the current detecting means 114, the vertical axis is the output of the voltage detecting means 116, and the shaded area is the area for determining the aluminum pan.
[0012]
FIG. 8 is an operation flowchart of the inverter when heating the iron pot. In step 131, the inverter 104 is started. In step 132, when the pot type is determined by the pot type determining unit 117, the inverter 104 is stopped in step 133. Further, the process waits for 2.0 seconds in step 134 until the voltage of the resonance capacitor decreases and stabilizes, and in step 135, the switching unit 118 turns on the switching relay and switches by adding the resonance capacitor 110b. After waiting for 0.5 seconds in step 136, the inverter 104 is started in step 137. In steps 137 and 138, the driving frequency of the first switching element 106 and the second switching element 107 is about 23 KHz, and the driving time ratio is gradually increased until a predetermined power is obtained. In step 139, the inverter 104 stops heating according to the input from the setting unit 119, and in step 140, waits for 2.0 seconds. In step 141, the resonance capacitor is switched to a state in which the aluminum-based load is heated.
[0013]
[Patent Document 1]
JP-A-2002-75620
[Problems to be solved by the invention]
In a conventional induction heating cooker, when starting an inverter, a low-resistance and low-magnetic-permeability load such as aluminum is heated, and the resonance capacitor is switched to a capacity for heating an aluminum load pan. However, when the user often uses an iron-based load pan rather than an aluminum-based load pan, the number of times the relay for switching the capacity of the resonant capacitor is turned on and off extremely increases. Failure may occur. In addition, when switching the relay, the frequency of stopping the inverter is increased to lower and stabilize the voltage of the resonance capacitor, the time until the predetermined power is reached is slow, and the usability is deteriorated during cooking. There were challenges.
[0015]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides an induction heating device that generates a high-frequency magnetic field from a heating coil by an inverter having a first switching element and a second switching element and induction heats a load. A heating means capable of heating a load of a material having low resistance and low magnetic permeability such as aluminum and a load of a material having a low magnetic permeability, wherein the heating means heats an iron-based load, and heats an aluminum-based load. Switching means for switching the capacity of the pan, pot type determining means for determining iron-based load and aluminum-based load, and the capacity of the resonance capacitor by the switching means according to the pot type determined by the pan type determining means. Output control means for controlling the output by changing the drive frequency and the drive time ratio of the first switching element and the second switching element, and starting and stopping heating. And setting means for inputting the power to be heated, and having a pot type storage means for storing the pan type determined by the pan type determination means, when heating is stopped during heating the iron-based load pan, The switching means does not switch the capacitance of the resonance capacitor.
[0016]
Thereby, failures such as contact welding of the relay are reduced and durability is improved. In addition, even when heating an iron-based load, it is possible to provide an induction heating device that can shorten the time required to reach the set electric power and is easy to use during cooking.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Since the objects of the present invention can be achieved by implementing the configurations described in the claims as embodiments, the significance of the embodiments will be described below by adding actions to the features characterized in the claims. Will be explained in an easy-to-understand manner.
[0018]
According to the first aspect of the present invention, a high-frequency magnetic field is generated from a heating coil by an inverter including a first switching element and a second switching element, and an iron-based load made of iron or stainless steel and a low load of aluminum or the like are used. A heating means for induction heating by switching the capacity of the resonance capacitor between an aluminum load of a material having a low magnetic permeability and a resistance; and a case where the heating means heats an iron load and a case where the aluminum load is heated. Switching means for switching the capacity of the resonance capacitor of the inverter, a pot type determining means for determining the iron-based load and the aluminum-based load, and the resonance capacitor of the resonance capacitor according to the pot type determined by the pot type determining means Output control means for switching the capacity, changing the drive frequency and drive time ratio of the first switching element and the second switching element to control the output of the heating means, Setting means for inputting electric power to start and stop and heating, and a pan type storage means for storing the pan type determined by the pan type determination means, wherein the control means stops heating of the heating means. Since the switching means keeps the selected state of the resonance capacitor and does not perform the switching when the switching operation is performed, even when the iron-based load pan is frequently used, the failure such as the contact welding of the relay is reduced and the durability is improved. . In addition, even when heating an iron-based load, it is possible to provide an induction heating device that can shorten the time required to reach the set electric power and is easy to use during cooking.
[0019]
The invention according to claim 2 is that, in particular, the pan type storage means is stored in a non-volatile memory that retains data even when the power is turned off, so that even after the power is turned on, the pan type storage means is used in accordance with the type of the pan heated last. Therefore, even when the iron-based load pan is used for the first time after the power is turned on, the time until the set power is reached is shortened, and the usability is further improved.
[0020]
The invention according to claim 3 has a counting means for counting the number of times the capacitance of the resonance capacitor is switched by the switching means, and when the number of switching times exceeds a predetermined value, the heating is stopped. The inverter is stopped even if it cannot be correctly determined, such as when the aluminum pan is being heated and the aluminum pan is being determined due to variations in the components that make up the inverter. Since the means switches the capacitance of the resonance capacitor, the durability is improved without repeatedly driving the relay.
[0021]
The invention according to claim 4 is a pot that has an abnormality notification unit, and when the number of times of switching exceeds a predetermined value by the counting unit, stops heating and notifies the abnormality, thereby making the pot unusable. I can let you know.
[0022]
In the invention according to claim 5, in particular, the pot type storage means stores the condition for determining the type of the pot, and the type of pot determination means compares the condition with the previous type of pot determination, and when the condition is within a predetermined range, Since the heating is stopped, the switching unit can detect that the load pan has been replaced even if the load pan is replaced by performing the switching operation of the resonance capacitor, so that the unusable load pan can be properly determined. .
[0023]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0024]
(Example 1)
FIG. 1 is a diagram showing a circuit configuration of the induction heating device of the present embodiment. The power supply 1 is a 200 V commercial power supply that is a low-frequency AC power supply, and is connected to an input terminal of a rectifier circuit 2 that is a bridge diode. A first smoothing capacitor 3 is connected between output terminals of the rectifier circuit 2. A series connection of the choke coil 5 and the second switching element 7 is further connected between the output terminals of the rectifier circuit 2. The heating coil 12 is arranged so as to face the aluminum pot 12 to be heated.
[0025]
Reference numeral 4 denotes an inverter. The low potential side terminal (emitter) of the second smoothing capacitor 11 is connected to the negative terminal of the rectifier circuit 2, and the high potential side terminal of the second smoothing capacitor 11 is connected to the first switching element (IGBT). ) 6 is connected to the high potential side terminal (collector), and the low potential side terminal of the first switching element (IGBT) 6 is connected to the high potential side terminal (collector) of the choke coil 5 and the second switching element (IGBT) 7. Is connected to the connection point. A series connection of the heating coil 12 and the first resonance capacitor 10a is connected to the second switching element 7 in parallel. A second resonance capacitor 10b is connected in parallel to the first resonance capacitor 10a by a switching means (relay) 18.
[0026]
The first diode 8 (first reverse conducting element) is connected in antiparallel to the first switching element 6 (connecting the cathode of the first diode 8 and the collector of the first switching element 6), and (Second reverse conducting element) is connected to the second switching element 7 in anti-parallel.
[0027]
Reference numeral 14 denotes current detection means for detecting an input current flowing from the power supply 1. Output control means 15 outputs a signal to the gates of the first switching element 6 and the second switching element 7 in accordance with the output of the current detection means 14. Is output.
[0028]
Reference numeral 16 denotes voltage detecting means for detecting the voltage of the first resonance capacitor 10a, and the pot type determining means 17 detects an iron-based load and an aluminum-based load based on the output of the current detecting means 14 and the output of the voltage detecting means 16. Is determined.
[0029]
Reference numeral 19 denotes setting means for setting the starting or stopping operation of the inverter 4 and the output power, and is constituted by a plurality of key switches.
[0030]
The operation of the induction heating device configured as described above will be described below. The power supply 1 is full-wave rectified by a rectifier circuit 2 and supplied to a first smoothing capacitor 3 connected to an output terminal of the rectifier circuit 2. The first smoothing capacitor 3 functions as a supply source for supplying a high-frequency current to the inverter.
[0031]
While the second switching element 7 is being driven, resonance occurs in a closed circuit formed by the second switching element 7, the second diode 8, the heating coil 12, and the resonance capacitor 10, and the first switching element 7 Are driven, a resonance occurs in a closed circuit formed by the first switching element 7, the first diode 8, the heating coil 12, and the resonance capacitor 10. When the second switching element 7 is turned off, the voltage of the second smoothing capacitor is boosted by the choke coil 5, so that a load of low resistance and low magnetic permeability such as aluminum can be induction-heated with high output.
[0032]
In the present embodiment, the driving time of the heating coil 12, the resonance capacitor 10, and the first switching element 6 and the driving time of the second switching element 7 are set such that the resonance period becomes 2/3 of the driving time. Therefore, if the driving frequency is about 20 kHz, the frequency of the resonance current is about 60 kHz.
[0033]
When heating an iron-based load, the switching means 18 connects the second resonance capacitor 10b in parallel with the first resonance capacitor 10a, makes the drive frequency constant (23 KHz), and changes the drive time ratio. Supplies a predetermined power.
[0034]
In the present embodiment, the drive frequency of the first switching element 6 and the second switching element 7 is determined by using a PWM function built in the microcomputer, and the drive frequency is set by setting the drive cycle in the microcomputer. Has been realized. The output of the current detecting means 14 and the output of the voltage detecting means 16 are input to the microcomputer by using an A / D conversion function built in the microcomputer.
[0035]
FIG. 2 is an operation flowchart of the inverter when heating the iron pan. In step 31, the inverter 4 is started. In step 32, when the pot type is determined by the pot type determining means 17, the inverter 4 is stopped in step 33. Further, the process waits for 2.0 seconds in step 4 until the voltage of the resonance capacitor decreases and stabilizes, and in step 35, the switching means 18 turns on the switching relay, thereby switching by connecting the resonance capacitor 10b. After waiting for 0.5 seconds in step 36, the inverter 54 is started in step 37. In steps 37 and 38, the driving frequency of the first switching element 56 and the second switching element 57 is about 23 KHz, and the driving time ratio is gradually increased until a predetermined power is obtained. In step 39, the input of the setting means 19 causes the inverter 4 to stop heating. At this time, since the output of the switching relay is not switched by the switching means 18 according to the pan type stored in the pan type storage means 20, when the inverter 4 is started by the input of the setting means 19, the iron-based load is The inverter 4 is started from a state in which is heated.
[0036]
As described above, according to the present embodiment, in an inverter that heats a load having low resistance and low magnetic permeability such as aluminum and a load such as iron and stainless steel, a user often uses an iron-based load pan. In this case, the number of times of switching the resonance capacitor is reduced, so that the relay is less likely to fail due to contact welding or the like, and the down time of the inverter due to the switching of the relay is reduced, so that a convenient induction heating device can be provided. Things.
[0037]
(Example 2)
The second embodiment of the present invention has the same configuration as that of the first embodiment. In FIG. 1, a non-volatile storage element that retains data even when the power is turned off is used as the pot type storage unit 20 in FIG. It is a difference.
[0038]
FIG. 3 is an operation flowchart of the inverter after the power is turned on. After the power is turned on in step 41, the result of the pot type determining means 17 at the time of the previous use is read from the non-volatile memory which is the pot type storing means 20, and if an iron-based load is used, the resonance capacitor is switched in step 43. And waits for 0.5 seconds in step 44, and waits for the setting means 19 to start the inverter 4 in a state where the iron-based load can be heated immediately. If the load pan used last time in step 42 is an aluminum pan, the setting unit 19 waits for the inverter 4 to be activated while the aluminum load can be heated immediately.
[0039]
The external storage means may be any storage element that retains data even when the power is turned off.
[0040]
As described above, according to the present embodiment, even after the power is turned on, the heater can be immediately heated in advance in accordance with the previously used load pan, so that the inverter is started quickly and the usability is improved.
[0041]
(Example 3)
In the third embodiment of the present invention, a counting means 21 is added to the first embodiment.
[0042]
In FIG. 1, reference numeral 21 denotes a counting means for counting the number of times the switching means 18 drives the relay for switching the resonance capacitor by the output control means 15.
[0043]
FIG. 4 is a flowchart in a case where the resonance capacitor is continuously switched by the switching unit 18 according to the determination result of the pan type determining unit 17. After starting heating from the state of heating the aluminum load pan, in step 51, the counter means 21 initializes (sets to 0) the counter. In Step 52, the inverter 4 is started. In Step 53, when the pot type is determined by the pot type determining means 17, in Step 54, the resonance capacitor switching operation is performed. (In the resonance capacitor switching operation, after stopping the inverter 4 and waiting for 2.0 seconds, the resonance capacitor is switched, and further, the standby operation is performed for 0.5 seconds.) In step 55, the counting means 21 sets the count value to 1 If the count value is equal to or greater than 5 in step 56, the heating is stopped. If the count value is less than 5 in step 56, the inverter 4 is started in step 57. If the pan type determining means 17 determines in step 53 that the pan is an aluminum pan, in step 59, a resonance capacitor switching operation is performed. In step 60, the counting means 21 increases the count value by one, and if the count value is 5 or more in step 61, the heating is stopped. If the count value is less than 5 in step 56, the inverter 4 is started in step 62 and the process proceeds to step 53.
[0044]
As described above, according to the present embodiment, heating is stopped when it is determined that the load pan is not of an aluminum type or an iron type due to the variation of each part constituting the inverter 4, so that the relay as the switching means is switched. Continuous driving is not performed, and an induction heating device with less trouble can be realized.
[0045]
(Example 4)
The fourth embodiment of the present invention is obtained by adding an abnormality notifying unit 22 to the third embodiment of the present invention.
[0046]
FIG. 5 is a display example of the abnormality notifying means 22 when heating is stopped because the count value has reached a predetermined number by the counting means 21. By displaying "H43" in the time display area of the LCD, Inform the user of the cause of the heating stop.
[0047]
In this embodiment, the information is displayed on the LCD, but may be displayed by an LED element, or more preferably, by a buzzer.
[0048]
As described above, the user can know the cause of the stop of the heating and can determine the pot that cannot be used, thereby improving the usability.
[0049]
(Example 5)
The fifth embodiment of the present invention has the same configuration as that of the third embodiment of the present invention, and the pan type storage unit 20 stores the current detection unit 14 and the voltage detection at the time when the pan type determination unit 17 detects the pan type. The difference is that the output value of the means 16 is stored.
[0050]
In FIG. 4, the output values of the current detecting means 14 and the voltage detecting means 16 at the time when the pan type determining means 17 detects the pan type in steps 53 and 58 are stored. Next, in Steps 53 and 58, the output values of the current detecting means 14 and the voltage detecting means 16 at the time when the pan type determining means 17 detects the pan type and the output values of the previously stored current detecting means 14 and the voltage detecting means 16 If the differences are both at a predetermined value (in this embodiment, ± 5 or more in the 8-bit AD conversion value of the microcomputer), it is determined that the pan has changed from the previous time, and the counting means 21 counts. Initialize the value.
[0051]
As described above, even when the load pan is changed when the inverter is stopped during the resonance capacitor switching operation, the counting unit 21 initializes the counter, so that it is possible to more accurately determine that the pan cannot be heated.
[0052]
【The invention's effect】
As is clear from the above description, according to the present invention, when heating is stopped, the switching means does not switch the capacity of the resonance capacitor, so that failures such as contact welding of the relay serving as the switching means are reduced and the durability is reduced. The performance is improved. In addition, even when heating an iron-based load, it is possible to provide an induction heating device that can shorten the time required to reach the set electric power and is easy to use during cooking.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram illustrating a configuration of an induction heating device according to a first embodiment of the present invention. FIG. 2 is a flowchart illustrating a capacitance switching operation of a resonance capacitor of the induction heating device according to the first embodiment. FIG. 4 is a flowchart showing a capacity switching operation of the resonance capacitor when the power supply of the induction heating device according to the second embodiment of the present invention is turned on. FIG. FIG. 5 is a schematic diagram of an abnormality display example of an induction heating device according to a fourth embodiment of the present invention. FIG. 6 is a circuit block diagram showing a configuration of a conventional induction heating cooker. FIG. FIG. 8 is a diagram showing a pot type determination threshold value of the heating device. FIG. 8 is a flowchart showing a capacitance switching operation of a resonance capacitor of the conventional induction heating device
4 Inverter 6 First switching element 7 Second switching element 10 Resonant capacitor 12 Heating means 14 Current detection means 15 Output control means 16 Voltage detection means 17 Pot type determination means 18 Switching means 19 Setting means 20 Pot type storage means 21 Count Means 22 abnormality notification means

Claims (5)

A high frequency magnetic field is generated from a heating coil by an inverter having a first switching element and a second switching element, and an iron-based load made of iron or stainless steel and aluminum of low resistance and low magnetic permeability such as aluminum are used. Heating means for induction heating by switching the capacity of the resonance capacitor between the load of the system and the capacity of the resonance capacitor of the inverter when the heating means heats an iron-based load and when the heating means heats an aluminum-based load. Switching means for switching, pan type determining means for determining an iron-based load and an aluminum-based load, and switching the capacitance of the resonance capacitor according to the pan type determined by the pan type determining means; An output control means for controlling the output of the heating means by varying the drive frequency and the drive time ratio of the element and the second switching element; Setting means for inputting electric power, and pan type storage means for storing the type of pan determined by the type of pan determination means, wherein the control means is configured such that when the heating of the heating means is stopped, the switching means An induction heating device that keeps the selected state of the resonance capacitor and does not switch. The pan type storage means stores the data of the pan type in a non-volatile memory even when the power is turned off, and when the power is turned on next time, the resonance is performed according to the last heated pan type until the power is turned off. The induction heating device according to claim 1, wherein the capacitor is selected and switched. 3. The method according to claim 1, further comprising: counting means for counting the number of times the capacitance of the resonance capacitor has been switched by the switching means, wherein the control means stops heating of the heating means when the count number of the counting means exceeds a predetermined value. An induction heating device as described. 4. The induction heating according to claim 3, further comprising an abnormality notification unit, wherein the control unit stops heating the heating unit when the count number of the counting unit exceeds a predetermined value, and notifies the abnormality by the abnormality notification unit. apparatus. The pot type storage means stores a condition for determining the type of the pot, and the control means stops heating of the heating means when the type of the pot is within a predetermined range as compared with the previous condition for determining the type of the pot. Item 5. The induction heating device according to any one of Items 1 to 4.

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