JP2004031247A - Inverter for electromagnetic induction heating, and electromagnetic cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic induction heating inverter and an electromagnetic cooker that have no interference noise in simultaneously heating different kinds of pots out of a magnetic pot, a non-magnetic stainless pot, and a magnetic pot. <P>SOLUTION: This electromagnetic cooker has a plurality of heating circuits for heating one of a magnetic pot, a non-magnetic stainless pot, and a non-magnetic pot 101, 102 mounted on a top plate 103 by electromagnetic induction including inverters 105, 106 and heating coils 104, 104. An inverter control means 109 is provided which sets operating frequencies of a plurality of heating circuits by separating at least 10 kHz or higher in accordance with the equivalent impedance of the heated pots 101, 102, when the plurality of heating circuits heat different kinds of pots 101, 102. Thereby, a noise filter or the like for reducing interference noise is not required and the efficiency of the circuit is improved, and thus it is effective for energy saving, small-sizing and cost reduction of the device. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electromagnetic induction heating inverter including a power switching element and an electromagnetic cooker, and more particularly to suppression of interference noise in an electromagnetic cooker having a plurality of heating units.
[0002]
[Prior art]
An electromagnetic cooker that heats the pot itself by electromagnetic induction has been widely used. The electromagnetic cooker is safe because it does not use fire, and has high efficiency, which is effective for energy saving. In recent years, the induction cooker has been rapidly introduced into ordinary households.
[0003]
FIG. 1 is a block diagram showing a general configuration of a conventional electromagnetic cooker. In the electromagnetic cooker of FIG. 1, a magnetic pan 101 and a non-magnetic stainless steel pan 102 are placed on a top plate (tempered glass) 103. Below the top plate 103, for example, two heating coils 104, 104, a first inverter 105 including an IGBT, a second inverter 106 including an IGBT, current detection circuits 107, 107, and current transformers 108, 108 And an inverter control means 109 including a microcomputer and the like.
[0004]
There are roughly three types of pots that can be heated by an electromagnetic cooker. The first is a magnetic pan typified by an iron pan and a magnetic stainless pan, the second is a non-magnetic stainless pan having characteristics intermediate between the magnetic pan and the non-magnetic pan, and the third is an aluminum pan and copper pan. Non-magnetic pots such as pots.
[0005]
Since the operating frequency of the non-magnetic pan is higher than that of the magnetic pan by at least 10 kHz or more compared to that of the non-magnetic stainless steel pan, even if it is combined with another type of pan, the interference sound does not matter.
[0006]
Therefore, here, the relationship between the operating frequency of the circuit and the input power will be described only for the combination of the magnetic pan and the non-magnetic stainless steel pan where interference is a problem.
[0007]
FIG. 2 is a diagram illustrating a relationship between an operating frequency and input power in a conventional electromagnetic cooker. Since the non-magnetic stainless steel pan has a small self-inductance, the operating frequency is higher by about 5 kHz than that of the magnetic pan. When heating the non-magnetic stainless steel pan, it is driven at an operating frequency higher than the magnetic pan by about 5 kHz to adjust the input power.
[0008]
[Problems to be solved by the invention]
However, in an electromagnetic cooker equipped with at least two current resonance circuits, when different types of pots are used, since the operating frequencies are different, the two types of operating frequencies are combined and an interference sound is generated.
[0009]
Many electromagnetic cookers generally have a plurality of heating units. When different types of pots are used in the respective heating units, since the operating frequencies of the respective inverters are different, a composite wave of the inverter 1 and the inverter 2 is generated. If this synthesized wave is within the human audible frequency (generally 20 to 16 kHz), it will be heard as an interference sound that is unpleasant to humans.
[0010]
In order to suppress the interference sound, there is a method in which the resonance capacitor and / or the heating coil are made variable and driven at the same operating frequency so that the resonance peaks in FIG. 2 overlap.
[0011]
However, in this method, the number of components of the resonance capacitor and the heating coil increases, the number of elements required for switching the resonance capacitor and the heating coil increases, and the cost increases. descend. In addition, the electromagnetic cooker becomes large.
[0012]
For example, as described in JP-A-09-185986 and JP-A-2002-008840, a control signal in which only a delay amount is changed according to a heating output at the same frequency as a control signal for turning on / off a switching element. Is supplied to the switching elements of the individual current paths to perform on / off driving.
[0013]
However, this method complicates the circuit configuration and control procedure.
[0014]
Japanese Unexamined Patent Application Publication No. 2002-095562 determines whether the difference between the operating frequencies is 1 kHz or less. If the difference exceeds 1 kHz, the operation is performed by lowering the higher operating frequency so that the difference becomes 1 kHz or less. The method is shown.
[0015]
However, if the difference is 1 kHz or less, the interference sound has an audible frequency. Therefore, according to the confirmation test of the present inventors, it was insufficient as a measure against the interference sound.
[0016]
An object of the present invention is to provide a high-efficiency and low-cost electromagnetic induction heating inverter without interference noise and an electromagnetic cooker employing the electromagnetic induction heating inverter.
[0017]
[Means for Solving the Problems]
The present invention provides an electromagnetic induction heating inverter having a plurality of heating circuits including an inverter and a heating coil and heating a metal load by electromagnetic induction, in order to achieve the above object. An inverter for electromagnetic induction heating comprising inverter control means for setting the operating frequencies of the plurality of heating circuits at least 10 kHz or more apart according to the equivalent impedance of the metal load to be heated when heating is proposed.
[0018]
According to the present invention, when the inverter is driven at different operating frequencies according to the load, by adding a difference of 10 kHz or more, the synthesized wave becomes equal to or higher than the human audible frequency, and interference noise can be eliminated.
[0019]
The present invention also provides an electromagnetic induction heating inverter including a plurality of heating circuits that heat a metal load by electromagnetic induction including an inverter and a heating coil, wherein a current detection circuit that detects a current flowing through the heating coil, When the heating circuit heats different metal loads, an inverter for electromagnetic induction heating comprising inverter control means for setting the operating frequencies of the plurality of heating circuits at least 10 kHz apart according to the detected current is proposed.
[0020]
As described above, the type of the metal load may be determined by detecting the current flowing through the heating coil.
[0021]
The current detection circuit may be a circuit that includes a sense IGBT built in the IGBT of the inverter and a sense resistor and detects a voltage generated by the current.
[0022]
In the present invention, since the sense IGBT and the sense resistor can be produced in the manufacturing process of the IGBT main body, they do not cause a cost increase.
[0023]
The current detection circuit may include a wiring inductance in the inverter, and an integrator that integrates a voltage generated in the wiring inductance and converts the voltage into a current.
[0024]
According to the present invention, a circuit can be configured without using a current transformer or a current detection circuit, and an inexpensive and highly reliable inverter for electromagnetic induction heating can be realized.
[0025]
In order to achieve the above object, the present invention has a plurality of heating circuits including an inverter and a heating coil for heating any one of a magnetic pan, a non-magnetic stainless steel pan, and a non-magnetic pan placed on a top plate by electromagnetic induction. In the electromagnetic cooker, when the plurality of heating circuits heat different types of pots, an inverter control that sets the operating frequencies of the plurality of heating circuits at least 10 kHz or more apart according to the equivalent impedance of the pot to be heated. An electromagnetic cooker with means is proposed.
[0026]
According to the present invention, when the inverter is driven at different operating frequencies according to the load, by adding a difference of 10 kHz or more, the synthesized wave becomes equal to or higher than the human audible frequency, and interference noise can be eliminated.
[0027]
The present invention further provides an electromagnetic cooker having a plurality of heating circuits for heating any one of a magnetic pan, a non-magnetic stainless steel pan, and a non-magnetic pan placed on a top plate by electromagnetic induction, including an inverter and a heating coil. A current detection circuit for detecting a current flowing through a heating coil, and when the plurality of heating circuits heat different types of pots, the operating frequencies of the plurality of heating circuits are set at least 10 kHz apart in accordance with the detected current. The present invention proposes an electromagnetic cooker provided with an inverter control means.
[0028]
As described above, it is possible to determine which of the magnetic pan, the non-magnetic stainless steel pan, and the non-magnetic pan is to be detected by detecting the current flowing through the heating coil.
[0029]
The current detection circuit may include a sense IGBT built in the IGBT of the inverter and a sense resistor, and may be a circuit for detecting a voltage generated by the current.
[0030]
In the present invention, since the sense IGBT and the sense resistor can be produced in the manufacturing process of the IGBT main body, they do not cause a cost increase.
[0031]
The current detection circuit may include a wiring inductance in the inverter, and an integrator that integrates a voltage generated in the wiring inductance and converts the voltage into a current.
[0032]
According to the present invention, a circuit can be configured without using a current transformer or a current detection circuit, and an inexpensive and highly reliable inverter for electromagnetic induction heating can be realized.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 3 is a block diagram showing the overall configuration of the electromagnetic cooker according to the present invention having two heating units. In the electromagnetic cooker according to the present invention shown in FIG. 3, a magnetic pan 101 and a non-magnetic stainless steel pan 102 are placed on a top plate (tempered glass) 103. Below the top plate 103, two heating coils 104, 104, a first inverter 105 including an IGBT, a second inverter 106 including an IGBT, and inverter control means 109 including a microcomputer are arranged. ing.
[0034]
In the present embodiment, there are no current detection circuits 107, 107 and current transformers 108, 108 provided in the conventional electromagnetic cooker shown in FIG.
[0035]
A feature of the present embodiment is that the magnetic pan and the non-magnetic stainless steel pan are operated at an operating frequency of 10 kHz or more. As described above, the operating frequency of the non-magnetic pan is at least 10 kHz higher than that of the magnetic pan and of the non-magnetic stainless steel pan. No special measures are required because sound is not a problem.
[0036]
Embodiment 1
FIG. 4 is a circuit diagram showing a configuration of the first embodiment of the electromagnetic induction heating inverter according to the present invention.
[0037]
The current resonance type electromagnetic induction heating inverter illustrated in FIG. 4 includes an AC power supply 201, a rectifier circuit 202 including a rectifier circuit such as a diode bridge, a smoothing reactor 203, a smoothing capacitor 204, an upper arm IGBT 205, The lower arm IGBT 206, the upper arm diode 207, the lower arm diode 208, the snubber capacitors 209 and 210, the resonance capacitors 211 and 212, the heating coil 213, the resistors 214 and 215, and the gate drive circuits 216 and 217 Be composed.
[0038]
When compared with the entire configuration of the electromagnetic cooker in FIG. 3, the current resonance type electromagnetic induction heating inverter of the first embodiment corresponds to the first inverter 105 or the second inverter 106, and the heating coil 213 corresponds to the heating coil 104. Equivalent to.
[0039]
The operation of this current resonance type electromagnetic induction heating inverter will be described. First, consider the state where the upper arm IGBT 205 and the lower arm IGBT 206 are off. In this state, since no signal is output from the gate drive circuit 216 and the gate drive circuit 217, the gates of the IGBT 205 and the IGBT 206 are at 0 V, and no current flows through the heating coil 213. The output voltage of the rectifier circuit 202 is applied between the collector of the IGBT 205 and the emitter of the IGBT 206.
[0040]
Next, the ON state will be described. When an ON signal is input from the gate drive circuit 216 to the gate of the IGBT 205, the IGBT 205 is turned on, and current starts to flow through the IGBT 205, the heating coil 213, the resonance capacitor 212, the resonance capacitor 211, and the snubber capacitor 209.
[0041]
When the IGBT 205 is turned off at a predetermined timing, the current flowing through the IGBT 205 is cut off. By the energy stored in the heating coil 213, current flows through the loop of the resonance capacitor 212, the snubber capacitor 210, and the heating coil 213, and the loop of the resonance capacitor 211, the snubber capacitor 209, and the heating coil 213.
[0042]
Next, when the snubber capacitor 209 is charged and the snubber capacitor 210 is discharged, a loop of the resonance capacitor 211, the smoothing capacitor 204, the diode 208, and the heating coil 213 and a loop of the resonance capacitor 212, the diode 208, and the heating coil 213 are formed. Then, a current flows.
[0043]
When the energy stored in the heating coil 213 is exhausted, a current starts to flow in the opposite direction due to the energy charged in the resonance capacitor 211 and the resonance capacitor 212.
[0044]
Before the current flows in the reverse direction, an on signal is input from the gate drive circuit 217 to the lower arm IGBT 206 and the IGBT 206 is turned on, so that the current flows from the resonance capacitors 211 and 212 to the IGBT 206 through the heating coil 213. .
[0045]
When the IGBT 206 is turned off at a predetermined timing, the current flowing through the IGBT 206 is cut off. Due to the energy stored in the heating coil 213, current flows through the loop of the resonance capacitor 212, the heating coil 213, and the snubber capacitor 210, and the loop of the heating coil 213, the resonance capacitor 211, and the snubber capacitor 209.
[0046]
Next, when the snubber capacitor 209 is discharged and the snubber capacitor 210 is charged, the diode 207 is turned on, and the loop of the resonance capacitor 211 and the heating coil 213, and the resonance capacitor 212, the heating coil 213, the diode 207, and the smoothing capacitor 204 Current flows through the loop.
[0047]
FIG. 5 is a diagram showing an example of a waveform of a synthetic wave in the electromagnetic induction heating inverter according to the first embodiment of the present invention. The operating frequency of the inverter 1 of this example is 20 kHz, and the operating frequency of the inverter 2 is 30 kHz. At this time, the synthesized wave becomes 16 kHz, which is close to the upper limit of the human audible frequency, so that the interference sound cannot be heard.
[0048]
FIG. 6 is a diagram illustrating the relationship between the difference between the operating frequency of INV1 and the operating frequency of INV2 in the electromagnetic induction heating inverter according to the first embodiment of the present invention and the frequency of the composite wave.
[0049]
The operating frequency of the inverter 1 at this time is fixed at 20 kHz. When the operating frequency of the INV2 is lower than 30 kHz, the frequency of the synthesized wave becomes equal to or lower than the upper limit of the audible frequency of 16 kHz, so that an interference sound can be heard.
[0050]
On the other hand, when the operating frequency of INV2 is higher than 30 kHz and the difference from the operating frequency of INV1 becomes 10 kHz or more, the operating frequency of INV2 approaches 20 kHz.
[0051]
Therefore, when the operating frequency of the non-magnetic stainless steel pan is higher than the operating frequency of the magnetic pan by 10 kHz or more, the synthesized wave becomes higher than the audible frequency, and the interference sound disappears.
[0052]
According to the first embodiment, when the pots of the two inverters are different from each other, they are driven at operating frequencies separated by 10 kHz or more, and the frequency of the synthesized wave is set to the audible frequency of humans or higher, thereby eliminating interference noise.
[0053]
Embodiment 2
FIG. 7 is a circuit diagram showing a configuration of an electromagnetic induction heating inverter according to a second embodiment of the present invention. The second embodiment employs an upper arm IGBT 601 having a built-in sense IGBT and a lower arm IGBT 602 having a built-in sense IGBT with respect to the first embodiment shown in FIG. This is a circuit to which a sense resistor 604 is added.
[0054]
In the second embodiment, a sense IGBT is built in the IGBTs of the upper and lower arms to detect a current flowing through a load. Since the sense IGBT and the sense resistor can be produced in the manufacturing process of the IGBT main body, they do not cause a cost increase.
[0055]
FIG. 8 is a diagram showing an example of an operation waveform in Embodiment 2 of the electromagnetic induction heating inverter according to the present invention. Compared to the IGBT main body, the sense IGBT has a conduction area of about 1/1000. Therefore, about 1/1000 of the current flowing through the IGBT main body flows in the sense IGBT in proportion to the conduction area.
[0056]
Since a voltage is generated in the sense resistor by the current flowing through the sense IGBT, a current value is detected from the voltage. The inverter control means 109 determines the load based on the detected current value, and drives the IGBT at an operating frequency according to the load.
[0057]
According to the second embodiment, a circuit can be configured without using a current transformer or a current detection circuit, and an inexpensive and highly reliable electromagnetic induction heating inverter can be realized.
[0058]
Embodiment 3
FIG. 9 is a circuit diagram showing a configuration of an electromagnetic induction heating inverter according to a third embodiment of the present invention. The third embodiment is a circuit in which wiring inductances 801 and 802 and integrators 803 and 804 are added to the first embodiment of FIG. Since the wiring inductances 801 and 802 always exist with the circuit pattern, it is only necessary to add the integrators 803 and 804.
[0059]
In the third embodiment, a voltage generated in the wiring inductance is converted into a current value by the integrators 803 and 804 using the wiring inductances 801 and 802.
[0060]
Also in the second embodiment, since a circuit can be configured without using a current transformer or a current detection circuit, an inexpensive and highly reliable electromagnetic induction heating inverter can be realized.
[0061]
Here, the emitter side wiring of the IGBT is used, but the same effect can be obtained by using another wiring.
[0062]
【The invention's effect】
According to the present invention, when the inverter is driven at different operating frequencies according to the load, by adding a difference of 10 kHz or more, the synthesized wave becomes equal to or higher than the human audible frequency, and interference noise can be eliminated.
[0063]
In addition, a noise filter or the like for reducing interference noise is not required, circuit efficiency is improved, energy is saved, and the size and cost of the device are reduced.
[0064]
Further, with the increase in the efficiency of the circuit, there is no need to take measures to dissipate heat. This is also effective in reducing the size and cost of the device.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a general configuration of a conventional electromagnetic cooker.
FIG. 2 is a diagram illustrating the relationship between frequency and input power in a conventional electromagnetic cooker.
FIG. 3 is a block diagram showing an overall configuration of an electromagnetic cooker according to the present invention having two heating units.
FIG. 4 is a circuit diagram showing a configuration of an electromagnetic induction heating inverter according to a first embodiment of the present invention.
FIG. 5 is a diagram illustrating an example of a waveform of a synthetic wave in the electromagnetic induction heating inverter according to the first embodiment of the present invention.
FIG. 6 is a diagram showing the relationship between the difference between the operating frequency of INV1 and the operating frequency of INV2 in the first embodiment of the electromagnetic induction heating inverter according to the present invention, and the frequency of the composite wave.
FIG. 7 is a circuit diagram showing a configuration of an electromagnetic induction heating inverter according to a second embodiment of the present invention.
FIG. 8 is a diagram showing an example of an operation waveform in Embodiment 2 of the inverter for electromagnetic induction heating according to the present invention.
FIG. 9 is a circuit diagram showing a configuration of an electromagnetic induction heating inverter according to a third embodiment of the present invention.
[Explanation of symbols]
101 Magnetic pot 102 Non-magnetic stainless pot 103 Top plate (tempered glass)
104 Heating coil 105 (First) Inverter 106 (Second) Inverter 107 Current detection circuit 108 Current transformer 109 Inverter control means 201 AC power supply 202 Rectifier circuit 203 Smoothing reactor 204 Smoothing capacitor 205 Upper arm IGBT
206 Lower arm IGBT
207 Upper arm diode 208 Lower arm diode 209 Snubber capacitor 210 Snubber capacitor 211 Resonant capacitor 212 Resonant capacitor 213 Heating coil (104)
214 Resistance 215 Resistance 216 Gate drive circuit 217 Gate drive circuit 601 Upper arm IGBT incorporating sense IGBT
602 Lower arm IGBT with built-in sense IGBT
603 Upper arm sense resistor 604 Lower arm sense resistor 801 Wiring inductance 802 Wiring inductance 803 Integrator 804 Integrator

Claims (8)

In an electromagnetic induction heating inverter having a plurality of heating circuits including an inverter and a heating coil and heating a metal load by electromagnetic induction,
When the plurality of heating circuits heat different metal loads, inverter control means is provided for setting the operating frequencies of the plurality of heating circuits at least 10 kHz or more apart according to the equivalent impedance of the metal load to be heated. And an inverter for electromagnetic induction heating. In an electromagnetic induction heating inverter having a plurality of heating circuits including an inverter and a heating coil and heating a metal load by electromagnetic induction,
A current detection circuit for detecting a current flowing through the heating coil, and when the plurality of heating circuits heat different metal loads, the operating frequencies of the plurality of heating circuits are set at least 10 kHz apart in accordance with the detected current. An inverter for electromagnetic induction heating, comprising: The electromagnetic induction heating inverter according to claim 2,
An electromagnetic induction heating inverter, wherein the current detection circuit is a circuit that includes a sense IGBT built into the IGBT of the inverter and a sense resistor, and detects a voltage generated by the current. The electromagnetic induction heating inverter according to claim 2,
An inverter for electromagnetic induction heating, wherein the current detection circuit includes a wiring inductance in the inverter, and an integrator for integrating a voltage generated in the wiring inductance and converting the voltage into a current. An electromagnetic cooker having a plurality of heating circuits for heating any one of a magnetic pan, a non-magnetic stainless steel pan, and a non-magnetic pan placed on a top plate by electromagnetic induction including an inverter and a heating coil,
When the plurality of heating circuits heat different types of the pans, inverter control means is provided for setting the operating frequencies of the plurality of heating circuits at least 10 kHz or more apart according to the equivalent impedance of the pan to be heated. An electromagnetic cooker characterized by the following. An electromagnetic cooker having a plurality of heating circuits for heating any one of a magnetic pan, a non-magnetic stainless steel pan, and a non-magnetic pan placed on a top plate by electromagnetic induction including an inverter and a heating coil,
A current detection circuit for detecting a current flowing through the heating coil, and when the plurality of heating circuits heat different types of pots, the operating frequencies of the plurality of heating circuits are separated by at least 10 kHz in accordance with the detected current. An electromagnetic cooker comprising an inverter control means for setting. The electromagnetic cooker according to claim 6,
An electromagnetic cooker, wherein the current detection circuit is a circuit that includes a sense IGBT built in the IGBT of the inverter and a sense resistor, and detects a voltage generated by the current. The electromagnetic cooker according to claim 6,
An electromagnetic cooker, wherein the current detection circuit includes a wiring inductance in the inverter, and an integrator for integrating a voltage generated in the wiring inductance and converting the voltage into a current.

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