JPH01313881A - Electromagnetic cooker - Google Patents

Abstract

PURPOSE:To enable the stable and proper control of heating output to the predetermined low output and the like by setting an input pulsating current for a smoothing means to a pulsating current having the predetermined frequency set after the completion of counting the pulsating current having the predetermined frequency with a count means. CONSTITUTION:When an input setting means 20 is operated and set to the predetermined level in setting and changing heating output to the predetermined level, the wave number of a pulsating current inputted to a smoothing means 5 via the control operation of a control means 13 is not set and changed to a new number until the completion of the counting operation of a count means for the pulsating current of the predetermined frequency. Then, the wave number is set to the revised predetermined number after the completion of a counting operation about the pulsating current of the predetermined frequency. It follows, therefore, that the pulsating current at the trailing end of an on-off pattern immediately before the setting and change is prevented from being superimposed on the pulsating current at the leading end of an on-off pattern after the setting and change. According to the aforesaid construction, the thermal fracture of a high-frequency transistor 7 in a high-frequency inverter 10 is not caused and heating output can be stably and properly set and controlled to the predetermined low output and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an electromagnetic cooker that heats an object to be heated, such as a metal pot, by electromagnetic induction.

(Prior Art) In general, an electromagnetic cooker has a power supply system equipped with a rectifier that rectifies AC input from a commercial power source into a pulsating current, a smoothing unit that smooths the pulsating current, and converts the pulsating current into DC power. , a high-frequency inverter that is equipped with a high-frequency transistor, a resonant capacitor, etc., and converts DC power from the power supply system into high-frequency power of a required frequency, a heating coil to which the high-frequency power from the high-frequency inverter is applied, and this heating coil. It consists of a top plate placed above.

Then, by induction heating a cooking utensil, which is an object to be heated, such as a metal pot placed on the top plate, the required cooking can be performed safely and efficiently.

(a) and (■) in FIG. 5 show a method for adjusting the heating output in such an electromagnetic cooker. In this adjustment method, by varying the on-time of the high-frequency transistor, its collector current, That is, the heating output is adjusted by controlling the input current Ic to the high frequency inverter. In the figure, Vcε indicates the resonant voltage charged to the resonant capacitor by the energy stored in the heating coil during the off-time of the high frequency transistor.

However, in this adjustment method, the heating output is set low, so if the on-time of the high-frequency transistor is controlled to a short time below the required value, the charge stored in the resonant capacitor when the high-frequency transistor is off becomes completely zero. The high-frequency transistor is turned on at the previous timing, and at this moment, a short-circuit current Is flows as shown in FIG. This short-circuit current Is becomes larger as the on-time of the high-frequency transistor is controlled to be shorter, and there is a problem in that the loss of the high-frequency transistor increases and may lead to thermal breakdown.

Figure 6 shows that in an electromagnetic cooker with a maximum heating output of, for example, 1.2 kW, if the heating output is set low to about 300 W or less, the loss of the high-frequency transistor increases due to the increase in the short-circuit current IS, resulting in heat generation. It shows how it leads to destruction.

On the other hand, as another adjustment method that can set the heating output of an electromagnetic cooker to a low level without causing thermal damage to the high-frequency transistor, the oscillation operation of the high-frequency inverter is controlled to be turned on and off at appropriate time intervals. A method is being considered.

FIGS. 7 and 8 show a method of adjusting the heating output by on/off control of this high frequency inverter. An electromagnetic cooker employing this adjustment method is provided with an input setting means for setting the wave number of the pulsating flow to be input to the smoothing means to a desired wave number among the pulsating flows of a predetermined wave number output from the rectifying means.

Then, by setting the input setting means, the wave number of the pulsating flow to be input to the smoothing means is set to a required wave number, and the high frequency inverter is turned on and off in a desired on/off pattern,
The heating output is set to a required low output without causing thermal damage to the high frequency transistor.

ω), (b), and (C) in Fig. 7 respectively show examples of on/off patterns of the high-frequency inverter when the predetermined wave number of the pulsating flow output from the rectifier is set to 8. Figure (2) shows the on-off pattern when the maximum heating output is set to PMAX and the heating output is set to (7/8) PMA 5/8) On-off pattern when set to PMAX, Figure (C) shows an on-off pattern when the heating output is set to (3/8) PMAX.

However, in this conventional heating output adjustment method using on/off control, when the on/off pattern setting is changed by operating the input setting means, the on/off pattern is immediately changed to the changed setting. As shown in Figure 8 (image) and function), the pulsating flow on the rear end side in the on-off pattern immediately before the setting change and the front flA in the on-off pattern after the setting change. The pulsating flow on the side may overlap, and in such a case, the on/off pattern will be disrupted, making it impossible to stably control the input of the pulsating flow to the smoothing means, resulting in a reduction in heating output. There was a problem in that it was difficult to reliably set the output to the required value. If the setting operation results in a pattern like that shown in FIG. 8, for example, it becomes impossible to control the desired output such as low output.

(Problems to be Solved by the Invention) Conventional electromagnetic cookers use on/off control of a high frequency inverter to adjust the heating output without causing thermal damage to the high frequency transistor. The pulsating flow on the rear end side of the pattern and the pulsating flow on the front end side of the on/off pattern after the setting change may overlap, and in such cases, the heating output may be stabilized at the required output. There was a problem in that it was difficult to control reliably.

This invention was made based on the above circumstances, and an object thereof is to provide an electromagnetic cooker that can stably and reliably control the heating output to a required low output without causing thermal damage to the high frequency transistor. shall be.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention rectifies alternating current using a rectifying means to produce a pulsating current, and smoothes this pulsating current using a smoothing means to generate direct current power. In an electromagnetic cooker that converts this DC power into high-frequency power using a high-frequency inverter and applies this high-frequency power to a heating coil to induction heat the object to be heated, the wave number of the pulsating current rectified by the rectifying means is counted. a counting means; an input setting means for setting the wave number of the pulsating flow to be input to the smoothing means to a required wave number among the pulsating flows of a predetermined wave number output from the rectifying means; and changing the setting of the input pulsating flow by the input setting means. and a control means for setting the input pulsating flow to the smoothing means to the pulsating flow having the changed desired wave number after the counting means finishes counting the pulsating flow having a predetermined wave number.

(Function) When changing the setting of the heating output to a required low output, etc., when the input setting means is set, the wave number of the pulsating flow input to the smoothing means is changed by the counting operation of the pulsating flow of a predetermined wave number by the counting means. The setting is not changed to the new setting number until the counting operation is completed, and after the counting operation of the pulsating flow of the predetermined wave number is completed, the setting is set to the required wave number after the setting change.

Therefore, the pulsating flow on the rear end side in the on-off pattern immediately before the setting change and the pulsating flow on the front end side in the on-off pattern after the setting change are prevented from overlapping, and the heating output is reduced to the required low output, etc. Stable and reliably set. Furthermore, since the heating output is adjusted by on/off control of the high frequency inverter, thermal destruction of the high frequency transistors in the high frequency inverter is prevented.

(Example) Embodiments of the present invention will be described below based on the drawings.

1 to 3 are diagrams showing one embodiment of the present invention.

First, to explain the configuration of an electromagnetic cooker, in Fig. 1, 1 is a commercial power source, and this commercial power source 1 is converted into a full-wave rectifier consisting of a diode bridge as a rectifier via a triac 2 as a switching element. Connected to circuit 4. As will be described later, the trigger timing of the triac 2 by the ignition circuit 3 is synchronized with a half cycle (one waveform of pulsating current) of the AC input from the commercial power supply 1 and operates at zero cross, and The AC input from the commercial power supply 1 is switched and controlled for an integral multiple of the period.

Further, a smoothing capacitor 5 is connected to the output terminal of the full-wave rectifier circuit 4 as a smoothing means for smoothing the pulsating output and converting it into DC power.

6 is a heating coil for inductively heating a cooking device which is an object to be heated (not shown) such as a metal pot; 7 is a high frequency transistor; 8 is a resonant capacitor; 9 is a damper diode; these elements including the heating coil 6; Thus, a high frequency inverter 10 for converting DC power into high frequency power and driving the heating coil 6 is configured. 11 is a drive circuit for driving a high frequency transistor.

In addition to the above configuration, the electromagnetic cooker of this embodiment is further provided with the following means. That is, first, a microcomputer 13 including a zero cross detector 12 that detects zero crosses of alternating current from the commercial power supply 1 and a counter that counts zero crosses detected by the zero cross detector 12 is provided. The counter and zero-cross detector 12 included in the microcomputer 13 constitute a counting means for counting the half cycle of the alternating current from the commercial power supply 1, in other words, the wave number of the pulsating current that is full-wave rectified by the full-wave rectifier circuit 4. has been done. Further, the microcomputer 13 is connected to the above-mentioned ignition circuit 3 and drive circuit 11, respectively, and an input setting device 14 is connected to the A/D converter 15.
connected via. This input setting device 14, A/D
The converter 15, the triac 2, and the ignition circuit 3 constitute an input setting means 20 that sets the wave number of the pulsating flow to be input to the smoothing capacitor 5 to a required wave number among the pulsating currents of a predetermined wave number output from the full-wave rectifier circuit 4. has been done.

Furthermore, when the input setting means 20 changes the setting of the input pulsating flow to the smoothing capacitor 5, the microcomputer 13 is programmed to input the information to the smoothing capacitor 5 after the counting means finishes counting the pulsating flow of a predetermined wave number. A control means is included for setting and controlling the input pulsating flow to the pulsating flow of the desired wave number whose setting has been changed.

Next, the operation of the electromagnetic cooker configured as described above will be explained using FIGS. 2 and 3.

ω), (b), and (C) in FIG. 2 are set by the input setting means 20 when the predetermined wave number of the pulsating flow output from the full-wave rectifier circuit 4 is set to 8. The pattern of input pulsating current to the smoothing capacitor 5, that is, the high frequency inverter 1
Examples of on/off patterns of 0 are shown. Figure (a) shows the on-off pattern when the heating output is set to the maximum power PMA Figure (C) shows on/off patterns when the heating output is set to (3/8) PMAX.

Then, the oscillation operation of the high-frequency inverter 10 is controlled on and off according to the above-described on-off pattern by the setting operation of the input setting means 20, and the heating output is adjusted to the required level without causing thermal damage to the high-frequency transistor 7. The setting is controlled to a low output, etc.

Next, when heating the object to be heated, in order to perform appropriate cooking, etc., the input setting means 20 is operated to change the setting of the on/off pattern.
As shown in (2), the wave number of the pulsating flow input to the smoothing capacitor 5 is not changed to a new set number until the counting operation of eight pulsating flows, which are the predetermined wave number, is completed by the counting means. When the counting operation of eight pulsating flows of the predetermined wave number is completed, at the end of the counting operation, the setting is performed to the required wave number after the setting change.

Therefore, the pulsating flow on the rear end side in the on/off pattern immediately before the setting change is prevented from overlapping with the pulsating flow on the front end side in the on/off pattern after the setting change, and the heating output is stabilized at the required output. Settings are reliably controlled.

Next, FIG. 4 shows another embodiment of the present invention. In this embodiment, the input setting means 30 is composed of a plurality of setting switches 16a to 16e. Each of the setting switches 16a to 16e sets the heating output, for example, (2
/8) PMAX, (3/8) pH4AX - Corresponds to be set to PMAX. Then, by turning on the desired setting switches 16a to 16e,
The desired on/off pattern can be set. The other configurations are the same as those of the previous embodiment. Furthermore, the operation is almost the same as that of the above embodiment.

[Effects of the Invention] As explained above, according to the present invention, when the setting operation of the input setting means is performed when changing the setting of the heating output to the required output, the input to the smoothing means is changed by the control operation of the control means. The wave number of the pulsating flow to be generated is not changed to a new set number until the counting operation of the pulsating flow of the predetermined wave number is completed by the counting means, and after the counting operation of the pulsating flow of the predetermined wave number is completed,
It is set to the required wave number after the setting change. Therefore, the pulsating flow on the rear end side in the on/off pattern immediately before the setting change and the pulsating flow on the front end side in the on/off pattern after the setting change are prevented from overlapping, leading to thermal damage to the high frequency transistors in the high frequency inverter. There is an advantage that the heating output can be stably and reliably set and controlled to a required low output without causing any problems.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an embodiment of the electromagnetic cooker according to the present invention, FIGS. 2 and 3 are for explaining the operation of the same embodiment, and FIG. 2 is an input setting means. FIG. 3 is a timing chart showing an example of the on/off pattern of the high frequency inverter set by the input setting means; FIG. 5 is a circuit configuration diagram showing another embodiment of the present invention, and FIG. 5 is a timing chart showing the current flowing through the heating coil in a conventional electromagnetic cooker that adopts a heating output adjustment method by controlling the on-time of a high-frequency transistor. Figure 6 is a characteristic diagram showing the relationship between heating output and loss of high-frequency transistors in the conventional example, and Figure 7 is a characteristic diagram showing the relationship between heating output and loss of high-frequency transistors in the conventional example. FIG. 8 is a timing chart showing the on/off pattern of the inverter. FIG. 8 is a timing chart for explaining the disturbance of the on/off pattern when the setting of the on/off pattern is changed in the conventional example same as above. 1: Commercial power supply, 2: Triac, 3: Ignition circuit, 4: Full wave rectifier circuit (rectifying means), 5: Smoothing capacitor (smoothing means), 6: Heating coil, 10: High frequency inverter, 12:
20.30: Input setting means; 20.30: Zero-cross detector constituting counting means; 13 microcomputer including counter and control means constituting dual force counting means;

Claims (1)

[Scope of Claims] AC is rectified by a rectifying means to produce a pulsating current, this pulsating current is smoothed by a smoothing means to produce DC power, this DC power is converted to high frequency power by a high frequency inverter, and this high frequency power is heated. An electromagnetic cooker that induction heats an object to be heated by applying voltage to a coil, comprising: a counting means for counting the number of waves of the pulsating current rectified by the rectifying means; input setting means for setting the wave number of the pulsating flow to be input to the smoothing means to a required wave number; An electromagnetic cooking device comprising: a control means for setting an input pulsating flow to a pulsating flow having a desired wave number whose setting has been changed.