JP2011071005A - Induction heating device - Google Patents

Abstract

In a system in which two inverters are operated in a configuration in which a rectifier circuit is shared, interference sound is generated even if a frequency difference between heating coils is provided in an audible range or more.
When two inverters 4 and 5 are operated simultaneously, the other inverter is operated at a frequency twice as high as the heating frequency of one inverter, so that the second harmonic of the heating frequency of one inverter can be obtained. Since the interference sound between the heating frequencies of the other inverter can be prevented, the sound during operation can be quieted.
[Selection] Figure 1

Description

  The present invention relates to an induction heating apparatus that heats an object to be heated using induction heating by a high-frequency magnetic field.

  Conventionally, this type of induction heating apparatus will be described with reference to the drawings. FIG. 8 shows a conventional induction heating apparatus. The induction heating device of this conventional example includes an AC power source 1, first and second heating coils 6 and 7, a rectifier circuit 2 that rectifies a commercial power source, a smoothing capacitor 9 that smoothes the voltage of the rectifier circuit 2, and a smoothing capacitor. The first and second inverters 4 and 5 that convert the output of 9 into high-frequency power and supply high-frequency power to the first and second heating coils 6 and 7 and the input current that detects the input current from the AC power source 1 Control means 8 comprising a detection means 3 and a microcomputer for controlling the operation state of the semiconductor switches in the first and second inverters 4 and 5 so that the value of the input current detection means 3 becomes a set value. It is made up of.

  Next, the operation of this conventional example will be described. The control means 8 detects the input current from the AC power source 1 by the input current detection means 3 constituted by a current transformer or the like, and the first and second inverters so that the input current becomes a preset current value. The required high frequency current is supplied to the first and second heating coils 6, 7 connected to the inverters 4, 5 by controlling the conduction time of the semiconductor switches in 4, 5.

  A high-frequency magnetic field is generated from the first and second heating coils 6 and 7 by the high-frequency current supplied to the first and second heating coils 6 and 7, such as a pan that is magnetically coupled to the heating coil. A high frequency magnetic field is applied to the load. Due to the applied high-frequency magnetic field, an eddy current is generated in a load such as a pan, and the pan itself generates heat due to the eddy current and the skin resistance of the pan itself.

  Here, when the first and second heating coils 6 and 7 operate at different frequencies, the frequency of the difference between the frequency of the current flowing through the first heating coil 6 and the frequency of the current flowing through the second heating coil 7 is When the frequency is in the audible range (approximately 20 kHz or less), the device user can hear a sound (hereinafter referred to as interference sound) due to the difference frequency.

  Therefore, a method of heating with a frequency difference of approximately 20 kHz or more has been proposed.

US Patent Application Publication No. 2007/0135037 Japanese Utility Model Publication No. 57-179296

  However, in such a conventional induction heating apparatus, in one heating coil, when adjusting the kind of pan and the power supplied to the heating coil by changing the drive frequency of the semiconductor switch in the inverter, the width is about 15 kHz. Therefore, in order to avoid the interference sound, the drive frequency of the semiconductor switch in the inverter of the other heating coil becomes about 60 to 80 kHz, and the loss during the switching operation of the semiconductor switch is greatly increased. Increased challenges will arise.

  On the other hand, in order to solve this problem, there is a method of adjusting the power with the conduction time ratio of the semiconductor switch in the inverter with a constant frequency. However, as shown in FIG. 9, when the conduction ratio is 50%, the third harmonic (60 kHz in FIG. 9) occupies most as the harmonic of the drive frequency (20 kHz in FIG. 9) (FIG. 9). As shown in FIG. 9A, the second harmonic of the driving frequency (40 kHz in FIG. 9) increases as the conduction ratio deviates from 50% (see FIG. 9B). In particular, when operating a plurality of heating coils and inverters from a single smoothing capacitor as in a conventional induction heating device, the frequency components generated by the respective heating coil currents are mutually heated through the smoothing capacitor that is a common component. Will be superimposed.

  Specifically, as shown in FIG. 10, when the first inverter is driven at 20 kHz and the second inverter is driven at 44 kHz, the second harmonic of the first inverter is 40 kHz. The 4 kHz component of the difference of 44 kHz, which is the drive frequency of the inverter 2, generates a heating coil current and has a problem of being generated as an interference sound through the pan.

  In order to solve the above-described problems, an induction heating apparatus of the present invention includes a rectifier circuit that rectifies an AC power supply, a smoothing capacitor that smoothes the output of the rectifier circuit, and an output of the smoothing capacitor that has power of a predetermined frequency using a semiconductor switch. The first and second inverters arranged in parallel to convert the first and second heating coils to supply high-frequency power to the first and second heating coils, and the conduction time of the semiconductor switches in the first inverter and the second inverter And when the first inverter and the second inverter operate simultaneously, the control means determines the drive frequency of the semiconductor switch in the second inverter as the semiconductor switch in the first inverter. The induction heating device is operated at twice the frequency.

  Thereby, in the system which operates two inverters by the structure which shared the rectifier circuit, the induction heating apparatus with few generation | occurrence | production of interference sound is realizable.

  According to the present invention, in a method of operating two inverters with a configuration in which a rectifier circuit is shared, interference between heating coils is caused by operating the other inverter at a frequency twice the heating frequency of one inverter. Since the noise can be reduced, it is possible to realize a quiet induction heating device with less noise during operation.

The figure which shows the circuit structure of the induction heating apparatus in Embodiment 1 of this invention. The figure which shows the drive signal of the semiconductor switch of the 1st inverter of the induction heating apparatus in Embodiment 1 of this invention, and a 2nd inverter The figure which shows the drive signal of the semiconductor switch of the 1st inverter of the induction heating apparatus in Embodiment 1 of this invention, and a 2nd inverter The figure which shows the method of the electric power control of the induction heating apparatus in Embodiment 1 of this invention (A) The figure which shows the electric power which can be set of each inverter of the induction heating apparatus in Embodiment 2 of this invention (b) The figure which shows the control in case the drive frequency of the induction heating apparatus in Embodiment 2 of this invention changes (C) The figure which shows the control at the time of changing the conduction | electrical_connection ratio of the induction heating apparatus in Embodiment 2 of this invention. The figure which shows the structure of the induction heating apparatus in Embodiment 3 of this invention. The figure which shows the structure of the induction heating apparatus in Embodiment 3 of this invention. The figure which shows the circuit structure of the conventional induction heating apparatus The figure which shows the example of the frequency analysis of the heating coil of the conventional induction heating apparatus The figure which shows the example of the frequency analysis of the heating coil of the conventional induction heating apparatus

  According to a first aspect of the present invention, there is provided a rectifying circuit for rectifying an AC power source, a smoothing capacitor for smoothing the output of the rectifying circuit, and converting the output of the smoothing capacitor into electric power of a predetermined frequency using a semiconductor switch. First and second inverters arranged in parallel to supply high-frequency power to the heating coil, and control means for controlling the conduction time of the semiconductor switches in the first inverter and the second inverter, When the first inverter and the second inverter operate simultaneously, the control means operates the semiconductor switch in the second inverter at a drive frequency twice that of the semiconductor switch in the first inverter. Can prevent the interference sound between the second harmonic of the heating frequency of one inverter and the heating frequency of the other inverter, Those that can achieve kana induction heating device.

  In the second aspect of the invention, in particular, by setting the driving frequency of one inverter to 20 kHz or more, the driving frequency between the first inverter and the second inverter is separated by 20 kHz or more, so that interference noise between the driving frequencies is prevented. Therefore, an induction heating device with a quiet sound can be realized.

  In the third invention, in particular, the control means operates the semiconductor switches in the first and second inverters at their respective fixed frequencies and changes the conduction ratio to supply the first and second heating coils. By changing the electric power, it is possible to suppress an increase in inverter loss due to an increase in the drive frequency of the second inverter, so that an induction heating device with good heating efficiency can be realized.

  In the fourth invention, in particular, when the first and second inverters operate independently, the control means changes the power supply to the heating coils of the first and second inverters by changing the frequency. As a result, it becomes easy to increase the rated power at the same time, and thus a high heating power induction heating device can be realized.

  In the fifth aspect of the invention, in particular, when the control means increases the power supplied to the first and second heating coils, the conduction ratio of the semiconductor switch in the first and second inverters is increased, and the conduction ratio is increased. After reaching 50%, by reducing the frequency while maintaining the conduction ratio of 50%, the control method can be shared between the single operation and the simultaneous operation, thus realizing an induction heating device with good controllability. It can be done.

  In the sixth aspect of the invention, in particular, by making the outer diameter of the first heating coil larger than the outer diameter of the second heating coil, the resonance between the heating coil and the inverter can be achieved without greatly changing the configuration of the heating coil strands. Since the resonance frequency of the resonance circuit composed of capacitors can be increased, the drive frequency can be increased easily, interference noise can be reduced with a low-cost configuration, and a silent induction heating device can be realized. is there.

  In the seventh aspect of the invention, in particular, since the maximum power of the first heating coil is made larger than the maximum power of the second heating coil, the output of the heating coil having a small diameter with poor cooling efficiency is suppressed. It is possible to realize an induction heating device that can be simplified in configuration and quiet in sound.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
This embodiment relates to claims 1 to 4.

  FIG. 1 is a diagram showing a circuit configuration of an induction heating apparatus according to the first embodiment of the present invention.

In FIG. 1, an AC power source 1, a rectifier circuit 2 that rectifies the AC power source 1, a smoothing capacitor 9 that smoothes the output of the rectifier circuit 2, and first and second converters that convert the output of the smoothing capacitor 9 into high-frequency power. The inverters 4 and 5, the first and second heating coils 6 and 7 connected to the respective inverters and supplied with high-frequency current from the inverters, and the current flowing from the AC power supply 1 to the rectifier circuit 2 are detected by a current transformer or the like. The input current detection means 3 and the control means 8 for controlling the semiconductor switches in the first and second inverters so that the detection value of the input current detection means 3 becomes a set value.
The target value of the control means 8 includes, but is not particularly limited to, the heating coil current and voltage in addition to the input current.

  The first inverter 4 is connected to one end or both ends of the series connection body of the semiconductor switch 1a11 and the semiconductor switch 1b12 connected in parallel to the smoothing capacitor 9, the series connection body of the semiconductor switches 1a11 and 1b12, and the smoothing capacitor 9. In many cases, the half bridge circuit is composed of the first heating coil 6 and the resonance capacitor 1a13. However, there is no particular problem even in the case of a full bridge circuit.

  Similarly, the second inverter 5 is connected to one end or both ends of the series connection body of the semiconductor switch 2a14 and the semiconductor switch 2b15 connected in parallel to the smoothing capacitor 9, the series connection body of the semiconductor switches 2a14 and 2b15, and the smoothing capacitor 9. This is a half-bridge circuit composed of the second heating coil 7 and the resonant capacitor 1a13.

  The first inverter 4 and the first heating coil 6 and the second inverter 5 and the second heating coil 7 supply a high-frequency current of about 20 kHz to each heating coil in accordance with a command from the control means 8. A high frequency magnetic field generated from the heating coil by the high frequency current is supplied to a load such as a pan.

  An eddy current is generated on the surface of the pan by the high frequency magnetic field, and the pan is heated by the resistance of the eddy current and the load itself such as the pan.

  On the other hand, in the first inverter 4 using the series resonance circuit of the first heating coil 6 and the resonant capacitor 1a13 as shown in FIG. 1, the control means 8 has placed a pan in order to change the material or input power of the pan. In many cases, the semiconductor switches 1a11 and 1b12 are controlled so that the input current or the like becomes a predetermined value by changing the drive frequency with respect to the resonance frequency determined by the inductance of the first heating coil 6 and the capacitance of the resonance capacitor 1a13. .

  At that time, when the first heating coil and the second heating coil are simultaneously operated, if they operate at different frequencies and the difference in driving frequency is within 20 kHz, the user can hear the interference sound. It will be.

  Therefore, a method for designing and operating each inverter so as to be separated from each other by 20 kHz or more as in the prior art has been proposed. However, in the configuration in which the smoothing capacitor 9 is shared as in the present embodiment, the first is used. In addition to the driving frequency of the heating coil 6, the harmonic component is also superimposed on the second heating coil 7, and is between the second harmonic of the first heating coil 6 and the driving frequency of the second heating coil 7. Interference sound will be generated.

  FIG. 2 is a diagram showing drive signals for the semiconductor switches of the first inverter and the second inverter of the induction heating apparatus according to the first embodiment of the present invention.

In FIG. 2, the drive signal of the semiconductor switch 1a11 in the first inverter 4 is (a).
The drive signal for the semiconductor switch 1b12 is shown in (b), the drive signal for the semiconductor switch 2a14 in the second inverter 5 is shown in (c), and the drive signal for the semiconductor switch 2b15 is shown in (d).

  The control means 8 supplies electric power to the heating coil by alternately conducting the semiconductor switches connected in series.

  As shown in FIG. 2, when operating simultaneously, the first inverter 4 operates at 20 kHz, and the second inverter 5 operates at 40 kHz. That is, the second heating coil 7 is operated at a frequency twice that of the first heating coil 6, and the second harmonic of the first heating coil and the drive frequency of the second heating coil are made to coincide with each other, thereby causing interference sound. Will be reduced.

  By setting the drive frequency of the first inverter 4 to 20 kHz or more, the difference in drive frequency between the first heating coil 6 and the second heating coil 7 can be always 20 kHz or more, and interference between the drive frequencies. No sound is generated.

  FIG. 3 is a diagram showing drive signals for the semiconductor switches of the first inverter and the second inverter of the induction heating apparatus according to the first embodiment of the present invention.

  In FIG. 3, the drive signal for the semiconductor switch 1 a 11 in the first inverter 4 is shown in (a), the drive signal for the semiconductor switch 1 b 12 in (b), and the drive signal for the semiconductor switch 2 a 14 in the second inverter 5. (C), the drive signal for the semiconductor switch 2b15 is shown in (d).

  The control means 8 supplies electric power to the heating coil by alternately conducting the semiconductor switches connected in series.

  As shown in FIG. 3, both the first inverter 4 and the second inverter 5 can obtain the same effect as changing the driving frequency by changing the conduction ratio of the semiconductor switch. The second heating coil can be operated at a frequency twice that of the first heating coil 6 for changing the value.

  FIG. 4 is a diagram showing a method of controlling the power of the induction heating device according to the first embodiment of the present invention, and shows an example of a change in input power when the conduction ratio of the semiconductor switch is changed. As shown in FIG. 4, the maximum power is reached when the conduction ratio is 50%.

  Since the interference sound is generated when the first heating coil 4 and the second heating coil 5 operate simultaneously, there is no problem even if the heating coils are controlled independently by frequency.

  In addition, when the rated power at the time of single operation of each inverter is larger than the rated power at the time of simultaneous operation, it is possible to perform frequency control at the same time and cope with high output.

  As described above, in the present embodiment, in a method of operating two inverters with a configuration in which the rectifier circuit 2 is shared, by operating the other inverter at a frequency twice the heating frequency of one inverter, Since the interference sound generated between the heating coils can be reduced, it is possible to realize a quiet induction heating apparatus with less noise during operation.

(Embodiment 2)
This embodiment relates to claim 5. The configuration of the present embodiment is the same as that of the first embodiment.

  FIG. 5 (a) is a diagram showing the settable power of each inverter of the induction heating apparatus in the second embodiment of the present invention. FIG. 5 (b) shows the drive frequency of the induction heating apparatus in the second embodiment of the present invention. FIG. 7C showing the control when changing is a diagram showing the control when changing the conduction ratio of the induction heating device in the second embodiment of the present invention.

  As shown in FIG. 5 (a), in the configuration in which the rectifier circuit 2 is shared by a plurality of inverters (FIG. 1), when the two inverters are simultaneously heated, the rated power is exceeded when the single inverter is operated. By avoiding this, the rating of parts in the shared part is not increased.

  For this reason, in this embodiment, a “P” setting that allows only a single operation is provided.

  On the other hand, as shown in FIG. 5C, when the drive frequency is constant and the conduction ratio is used, the maximum power is obtained when the conduction ratio is 50% as shown in FIG. Therefore, if the control can be performed at a constant driving frequency with the “P” setting even with a load of different materials, the load C reaches the rated power with a small conduction ratio, so that the power fluctuation is large with respect to the change in the conduction ratio. The problem of becoming will arise.

  Further, when switching to frequency control when setting the single operation, there are two types of control methods, and the control method becomes complicated.

  Therefore, as shown in FIG. 5 (c), the maximum power of the individual inverters at the time of simultaneous operation can be controlled by the conduction ratio, and after the conduction ratio exceeds 50% for more outputs, By shifting to frequency control as shown in FIG. 5B, it is possible to control without distinguishing between control during single operation and simultaneous operation, and without increasing power fluctuation.

  As described above, in the present embodiment, when increasing the power supplied to the first and second heating coils, the control means increases the conduction ratio of the semiconductor switches in the first and second inverters, After the conduction ratio reaches ½, the frequency can be reduced while maintaining the conduction ratio ½, so that the control method can be shared between the single operation and the simultaneous operation. A heating device can be realized.

(Embodiment 3)
This embodiment relates to claims 6-7. The configuration of this embodiment is different from that of the first embodiment in that the outer diameter of the first heating coil is larger than the outer diameter of the second heating coil.

  FIG. 6 is a diagram showing the configuration of the induction heating apparatus in the third embodiment of the present invention.

  In FIG. 6, among the heating coils disposed under the top plate 18, the first heating coil 6 having a large shape is disposed on the front side, and the second heating coil 7 having a small shape is disposed on the back. An operation / display unit 17 for displaying the operation of the induction heating device and the state of the device is disposed in front of the heating coil.

  In a half-bridge or full-bridge inverter in which the heating coil and resonant capacitor are connected in series, the drive frequency is set higher than the resonant frequency determined by the inductance of the heating coil including the load such as a pan and the capacity of the resonant capacitor. By shifting the drive frequency from the frequency, the load material and shape can be handled and the power adjusted. Therefore, the resonance frequency and the drive frequency at the maximum power are often close to each other.

  Here, since the drive frequency of the first inverter 4 and the second inverter 5 is doubled, it is desirable that the resonance frequency is also different by about twice.

  Here, in order to double the resonance frequency, since the resonance frequency is inversely proportional to the square root of the product of the inductance of the heating coil and the capacitance of the resonance capacitor, it is necessary to reduce the product of the inductance of the heating coil and the capacitance of the resonance capacitor. There is.

  On the other hand, since the inductance of the heating coil increases in proportion to the square of the number of turns and the outer diameter, a small heating coil having a small outer diameter and a small number of turns tends to have a smaller inductance.

  Therefore, it is possible to provide a frequency difference without difficulty by setting the resonance frequency on the side of the small heating coil to be high.

  Further, by increasing the maximum power of the first heating coil 6 having a large shape, the maximum power of the second heating coil 7 that performs high-frequency operation that increases the loss of the inverter is suppressed, and the loss is prevented from increasing. be able to.

  FIG. 7 is a diagram showing a configuration of an induction heating device according to the third embodiment of the present invention.

  In FIG. 7, although the induction heating apparatus in the case of four heating parts is shown, it constitutes one inverter shared in the front and rear. Even in this configuration, even when four units are operating simultaneously, the interference sound can be greatly reduced because they operate at the same frequency or twice the frequency.

  As described above, in the present embodiment, by making the outer diameter of the first heating coil larger than the outer diameter of the second heating coil, the heating coil and the inverter are not changed largely without changing the configuration of the strands of the heating coil. Since the resonance frequency of the resonance circuit composed of the resonance capacitor can be increased, the drive frequency can be increased easily, the interference noise can be reduced with a low-cost configuration, and a quiet induction heating device can be realized. Is.

  As described above, the induction heating device according to the present invention is effective for a cooker using induction heating because it generates less interference noise between the heating coils and can reduce noise during operation. .

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectifier circuit 4 1st inverter 5 2nd inverter 6 1st heating coil 7 2nd heating coil 8 Control means 9 Smoothing capacitor 11 Semiconductor switch 1a
12 Semiconductor switch 1b
13 Resonant capacitor 1a
14 Semiconductor switch 2a
15 Semiconductor switch 2b
16 Resonant capacitor 2a

Claims (7)

A rectifier circuit for rectifying an AC power source, a smoothing capacitor for smoothing the output of the rectifier circuit, and converting the output of the smoothing capacitor to power of a predetermined frequency using a semiconductor switch, and supplying high-frequency power to the first and second heating coils First and second inverters arranged in parallel for supply, and control means for controlling conduction time of semiconductor switches in the first inverter and the second inverter, the first inverter; When the second inverter operates at the same time, the control means operates the induction heating device so that the drive frequency of the semiconductor switch in the second inverter is double the frequency of the semiconductor switch in the first inverter. The induction heating device according to claim 1, wherein the drive frequency of the first inverter is 20 kHz or more. The control means operates the semiconductor switches in the first and second inverters at respective fixed frequencies, and changes the power supplied to the first and second heating coils by changing the conduction ratio. 2. The induction heating device according to 2. The control means changes the power supply to the heating coils of the first and second inverters by changing the frequency when the first and second inverters operate independently. The induction heating apparatus according to item 1. When increasing the power supplied to the first and second heating coils, the control means increases the conduction ratio of the semiconductor switch in the first and second inverters, and after the conduction ratio reaches 50%. The induction heating apparatus according to any one of claims 1 to 4, wherein the frequency is decreased while maintaining a conduction ratio of 50%. The induction heating device according to any one of claims 1 to 5, wherein an outer diameter of the first heating coil is made larger than an outer diameter of the second heating coil. The induction heating device according to any one of claims 1 to 6, wherein the maximum power of the first heating coil is made larger than the maximum power of the second heating coil.

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