JP3888132B2 - Induction heating cooker - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an induction heating cooker, and more particularly to a cooker for induction heating a load made of a low resistance metal such as aluminum or copper.
[0002]
[Prior art]
Hereinafter, a conventional induction heating cooker will be described with reference to FIGS.
[0003]
As shown in the figure, the commercial power source 1 is rectified by the rectifying element 2, the DC power is supplied to the inverter 4 by the smoothing means 3, and the inverter 4 drives the switching element 7 to generate a high frequency magnetic field in the heating coil 6. The load 5 such as a pan is induction-heated.
[0004]
Here, in order to perform power control to the load 5, either frequency control or on / off duty control of the switching element 7 has been performed. That is, in frequency control, the on / off duty of the switching element 7 is fixed and the drive frequency of the switching element 7 is varied to perform power control utilizing the frequency-input power characteristic as shown in FIG. In the control, the drive frequency is fixed and the on / off duty of the switching element 7 is varied, so that the power control is performed by utilizing the on / off duty-input power characteristic as shown in FIG.
[0005]
[Problems to be solved by the invention]
In the induction heating cooker having the conventional configuration, when the load 5 made of a low resistance metal such as aluminum or copper is induction heated, the Q of the heating coil 6 in a magnetically coupled state with the load 5 is increased due to low resistance. The change in input power with respect to frequency becomes large, and it is necessary to perform power control by frequency control. However, when the frequency is varied digitally using a microcomputer or the like, there is a problem that the input power of the inverter 4 with the minimum frequency variable width changes greatly in steps, and fine power control cannot be performed. is doing.
[0006]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and an object thereof is to provide an induction heating cooker that can perform fine power control even with digital control means such as a microcomputer.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an induction heating cooker according to the present invention includes a switching element, a heating coil, a resonance capacitor that resonates with the heating coil, and 1 / n (n of the resonance frequency of the heating coil and the resonance capacitor. Is an inverter that inductively heats a low-resistance metal such as aluminum or copper by generating a high-frequency magnetic field from the heating coil using the resonance characteristics of the switching frequency and input power in the vicinity of the frequency of any integer of 2 or more) And output control means for performing output control by digitally varying the drive frequency of the switching element and performing output control by fixing the drive frequency and digitally varying the on / off duty of the switching element. The output control means greatly changes the input power by changing the drive frequency, and on / off It is obtained to perform the fine-grained power control by changing the Yuti.
[0008]
As a result, the duty of the switching element can be reduced, and fine power control can be performed by digital control means such as a microcomputer.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The invention described in claim 1 includes a switching element, a heating coil, a resonance capacitor that resonates with the heating coil, and 1 / n of the resonance frequency of the heating coil and the resonance capacitor (n is an arbitrary integer equal to or greater than 2). an inverter for induction heating of the low-resistance metal, such as to generate a high-frequency magnetic field of aluminum or copper from the heating coil by utilizing the resonance characteristic of the drive frequency input power of the switching elements in frequency near beside), the switching element Output control means for performing output control by digitally varying the drive frequency of the output, and performing output control by digitally varying the on / off duty of the switching element by fixing the drive frequency. The control means largely changes the input power by changing the driving frequency, and sets the on / off duty. With the induction heating cooker which performs a fine power control by reduction, it can be performed quickly and fine power control in less vital digital control unit responsible for the switching element.
[0010]
Invention, the on-off duty of the switching elements (2k-1) / 2n vicinity (k is less arbitrary integer of 1 or more n) and the induction heating cooker according to claim 1, variable in according to claim 2 By doing so, zero voltage switching at the time of turn-on can be performed, and excessive stress is not applied to the switching element when induction heating by harmonics of the driving frequency is performed.
[0011]
According to a third aspect of the present invention, the on / off duty of the switching element is fixed in the vicinity of (2k-1) / 2n (k is an arbitrary integer not smaller than 1 and not larger than n) in a transition period at the time of starting or power setting. By using the induction heating cooker described in 2, a cooker with quick inverter activation can be obtained.
[0012]
The invention described in claim 4 has detection means for detecting the input or output of the inverter, and when the input or output of the inverter is small, the on / off duty of the switching element is in the vicinity of (2k-1) / 2n (k is 3. An electric power control is quickly performed by fixing at an arbitrary integer between 1 and n , and when the input or output of the inverter is large, the on / off duty of the switching element is varied in the vicinity of (2k−1) / 2n. More detailed power control can be performed by using the induction heating cooker described in 1. above.
[0013]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0014]
In FIG. 1, a commercial power source 11 is rectified by a rectifying element 12, DC power is supplied by a smoothing means 13 to an inverter 14 having a switching element 17, and the inverter 14 drives the switching element 17 to generate a high-frequency magnetic field. It is generated in the heating coil 16, and the heating coil 16 induction heats the load 15 such as a pan. In order to control the power to the load 15, the output control means 18 performs output control by varying the drive frequency and on / off duty of the switching element 17.
[0015]
A resonance capacitor is connected in series with the heating coil 16, and the inverter 14 has a half-bridge configuration.
[0016]
As shown in FIG. 2, when the resonance frequency of the heating coil 16 and the resonance capacitor in the presence of the load 15 is fc, the second harmonic and the third harmonic are generated when the drive frequency is fc / 2 and fc / 3, respectively. Resonance occurs, and the drive frequency-input power characteristic is as shown in the figure.
[0017]
Here, in order to inductively heat a low-resistance metal such as aluminum or copper as the load 15, induction heating is performed at a high frequency in order to increase the skin resistance. In this embodiment, by setting the drive frequency in the vicinity of fc / 3, the drive frequency can be lowered to about one third of the resonance frequency, and an efficient induction heating with a small switching loss is realized. Further, when the load 15 is aluminum, copper, or the like, since the resonance Q of the heating coil 16 and the resonance capacitor in a state where the load is magnetically coupled is large, the input power is steep with respect to the minimum frequency variable width as shown in FIG. Is a characteristic that changes. In addition, when the drive frequency is constant in the vicinity of the third harmonic frequency, that is, in the vicinity of fc / 3, the input power characteristics when the on / off duty of the switching element 17 is changed are as shown in FIG. That is, when the on / off duty is 1/6, 3/6, and 5/6, the input power is maximized. In this embodiment, the output is controlled by varying the on / off duty in the vicinity of 3/6, and the drive frequency is set to a larger frequency in the vicinity of fc / 3. Therefore, the current waveform of the switching element 17 is as shown in FIG. Zero voltage switching is realized at turn-on.
[0018]
Further, the output control means 18 is realized by a microcomputer in this embodiment. That is, the drive frequency is varied by changing the cycle of the control signal to the switching element 17, and the on / off duty is varied and controlled by changing the on / off time of the control signal. When the control signal cycle and on / off time are changed by the microcomputer, there is a minimum time based on the clock signal. As a result, when the drive frequency and the on / off time are changed, they change discretely. In this embodiment, the drive frequency is changed as shown in FIG. 2 and the on / off duty is changed as shown in FIG. Even when a resistive metal is used as a load, the input power is greatly changed by changing the drive frequency, and the on / off duty is changed in the vicinity of 0.5. Is also a small induction heating cooker.
[0019]
FIG. 5 shows another embodiment, and the inverter configuration is a half-bridge type that also has a step-up chopper. In other words, a filter 19 and a booster coil 20 are added to the circuit shown in FIG. In this case, since the voltage can be boosted with two stones, the input voltage of the inverter 14 can be increased, and the output of the inverter 14 can be increased. In this case, it goes without saying that the same effect can be obtained.
[0020]
Further, the embodiment of FIG. 5 is an example in which a detecting means for detecting an input or output of the inverter such as an input current, a heating coil voltage, a heating coil current, or a resonance coil voltage is used. In this example, input current control to the inverter 14 is performed by the input detection means 21. As a result, when the input of the inverter 14 is small, the output control means 18 fixes the on / off duty of the switching element 17 in the vicinity of (2k-1) / 2n (k is an arbitrary integer from 1 to n). When the drive frequency is varied and power control is performed quickly and the input of the inverter 14 is large, the on / off duty of the switching element 17 is varied in the vicinity of (2k-1) / 2n, and the drive frequency is also varied at the same time. It is possible to perform fine power control by both sides. It goes without saying that the same control can be performed even if the output of the inverter 14 is detected. The current detection can be easily realized by dividing the voltage detection with a shunt resistor, a current transformer, a magnetic sensor, or the like.
[0021]
In this embodiment, the inverter configuration is a so-called SEPP, but needless to say, it is not necessary to stick to this. In the present embodiment , the third harmonic of the drive frequency is used. However, the on / off duty can be set to (2k−1) even if the fundamental wave or other n-order harmonics (n is an arbitrary integer of 2 or more) are used. A similar effect can be obtained by setting the value in the vicinity of / 2n (k is an arbitrary integer from 1 to n). Further, the present invention is not limited to a low-resistance metal having a large Q such as aluminum or copper, but may be used when the change in the driving frequency of the switching element is large, such as when the clock frequency of the microcomputer is low, even when the load is a small Q such as iron. The effect of can be obtained.
[0022]
In addition, it is not always necessary to vary both the drive frequency and the on / off duty during inverter operation. If it is varied during so-called steady-state heating, the object of the present invention can be achieved, and the transition period during start-up and power resetting can be achieved. For example, if the on / off duty is fixed where stationary heating is not performed, the target power can be quickly reached by sequentially changing only the drive frequency.
[0023]
【The invention's effect】
As described above, according to the present invention, the resonance characteristic of the switching element drive frequency and input power in the vicinity of 1 / n (n is an arbitrary integer of 2 or more) of the resonance frequency of the heating coil and the resonance capacitor is used. It has an inverter that generates a high-frequency magnetic field from the heating coil and induction-heats low resistance metals such as aluminum and copper, and controls the output of the switching element by varying the drive frequency and on / off duty of the switching element. An induction heating cooker that can be made small and can be easily finely controlled by a digital control means such as a microcomputer is realized.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an induction heating cooker according to an embodiment of the present invention. FIG. 2 is a drive frequency-input power characteristic diagram in the induction heating cooker. FIG. 3 is an on-duty in the induction heating cooker. Characteristic diagram of input power [FIG. 4] Current waveform diagram of switching element in the same induction heating cooker [FIG. 5] Circuit diagram of induction heating cooker which is another embodiment of the present invention [FIG. 6] Conventional induction heating cooking Circuit diagram of the cooker [Fig. 7] Characteristic diagram of drive frequency vs. input power of the induction heating cooker [Fig. 8] Characteristic diagram of on-duty vs. input power in the induction heating cooker [Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Commercial power supply 14 Inverter 15 Load 16 Heating coil 17 Switching element 18 Output control means 21 Input detection means

Claims (4)

A switching element, a heating coil, and a resonant capacitor which resonates with the heating coil, wherein the switching at frequencies near vicinity of 1 / n of the resonance frequency of the heating coil and the resonant capacitor (n is an integer of 2 or greater) An inverter that generates a high-frequency magnetic field from the heating coil by using the resonance characteristics of the driving frequency of the element and input power and induction-heats a low-resistance metal such as aluminum or copper, and the driving frequency of the switching element is digitally varied. Output control means for fixing the drive frequency and digitally varying the on / off duty of the switching element to control the output, and the output control means changes the drive frequency. By finely changing the input power and changing the on-off duty Induction heating cooker which performs a power control.   The induction heating cooker according to claim 1, wherein the on / off duty of the switching element is variable in the vicinity of (2k-1) / 2n (k is an arbitrary integer of 1 to n).   The induction heating cooker according to claim 2, wherein the on / off duty of the switching element is fixed in the vicinity of (2k-1) / 2n (k is an arbitrary integer not less than 1 and not more than n) in a transition period during startup or power setting.   It has detection means for detecting the input or output of the inverter, and when the input or output of the inverter is small, the on / off duty of the switching element is in the vicinity of (2k-1) / 2n (k is an arbitrary integer between 1 and n) The induction heating cooker according to claim 2, wherein the on / off duty of the switching element is varied in the vicinity of (2k-1) / 2n when the input or output of the inverter is large.

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