JPH08288059A - Microwave oven - Google Patents

Abstract

PURPOSE: To provide a microwave oven capable of feeding such power as corresponding to a load by making judgement about the load with a judgement section, on the basis of input from an input current detecting section and an operating frequency detecting section, and changing input power depending on the load. CONSTITUTION: A judgement section 17c makes a comparison between input from an input current detecting section 19 and an operating frequency detecting section 17b, and preliminarily saved value, thereby making judgement about a load. Input power is limited, according to an input current limit value corresponding to the load. Also, the limit value is set at a value smaller than input power as a limit enough to cool a microwave oven, and the input power is limited to such a limit value as corresponding to the load judged with the section 17c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating cooker characterized by inverter control means.

[0002]

2. Description of the Related Art An example of an inverter circuit of an induction heating cooker using a control means for controlling an input current by an input from a conventional input current detector will be described with reference to FIGS. 7 and 8.

FIG. 7 shows an example of a circuit of a conventional induction heating cooker. Reference numeral 51 is a DC power source, and 52 is a heating coil, on which an object to be heated (pot or the like) is placed, although not particularly shown in the figure. Reference numeral 53 is a resonance capacitor, and the heating coil 52 and the resonance capacitor 53 constitute a load circuit 54. 55
Is a switching element, and in this example, a high current (60 A), high breakdown voltage (900 V) IGBT is used. 56 is a reverse conducting diode. Reference numeral 57 is a control circuit that outputs a signal for controlling the switching element 55. Although not shown in the drawing, the voltage Vce applied to both ends of the switching element 55 is shown.
The drive circuit 57a for driving the switching element 55 is incorporated.

FIG. 8 shows operation waveforms of various parts of the inverter during steady operation. FIG. 8A shows a drive signal output from the control circuit 57. When this output is High, the switching element 55 is turned on. FIG. 8A shows the current Ic flowing through the switching element 55 and the reverse conducting diode 56, and FIG. 8C shows the voltage Vce applied across the switching element 55.

The operation of this circuit will be described below with reference to FIGS. 7 and 8. The control circuit 57 is the switching element 5
5 is turned on for a predetermined time, then turned off and the heating coil 5
The load circuit 54 composed of 2 and the resonance capacitor 53 resonates. Further, the control circuit 57 detects Vce,
When the fall of ce becomes lower than the predetermined value, the switching element 55 is turned on again. In order to repeat the above operation, in response to the drive signal of FIG. 8A in the control circuit 57 of FIG. 7, Ic is as shown in FIG. 8A and Vce is as shown in FIG.
As shown in (c), power is supplied to the pan placed on the heating coil 52. The power supplied to the pan can be freely changed by controlling the on time of the switching element 55 and changing the input current of the inverter circuit 58. Therefore, the input power is Pin, the DC power supply 51
When the output voltage of Vdc is Vdc and the input current (effective value) is Iin, Pin = Vdc × Iin holds. This equation shows that by controlling the input current Iin to the limit value, P
Indicates that in is maintained at a constant value. Further, the power supplied to the pan can be detected by the signal from the input current detection circuit.

The conventional inverter control means is generally a control circuit for limiting the input current so as not to exceed a set value. However, in induction heating cookers,
Even when the input current is controlled to a constant value, the current-voltage characteristics of the switching element 55, the operating frequency, etc. differ depending on the characteristics of the object to be heated, so the power supplied to the object to be heated is constant, but There was a difference in loss.

FIG. 9 shows the characteristics of the input power and operating frequency of load a, load b and load c. Here, the load a is represented by a non-magnetic pot, the load b is an enameled pot, and the load c is represented by a magnetic pot. Further, in the case of heating each load, the input power at which the loss of the switching element becomes the limit at which the induction heating cooker can be cooled is indicated by a dot. For each load, when the input power is higher than the point, the loss of the switching element becomes larger than the cooling limit of the induction heating cooker, which may lead to destruction. Set. Therefore, in the conventional control method, the limit value of the input current is determined by the characteristics of the load in which the loss of the switching element is maximum when the same power is supplied.

[0008]

However, in the above-mentioned conventional inverter control means, there is a margin to supply more power except for the load in which the loss of the switching element becomes maximum when the same power is supplied. Nevertheless, power cannot be supplied above the set value. That is, when actually used at home, there is a problem that the object to be heated, such as a pot, which is usually used, is supplied with only the power matched to the load having the characteristic that the loss of the switching element becomes high.

The present invention is for solving the above-mentioned problems, and determines the load from the characteristics of the operating frequency and the input current,
It is a first object of the present invention to provide an induction heating cooker that limits the power supplied according to the load.

Further, the operating frequency range is preset according to the input current, and the operating frequency within the set range, that is, the loss of the switching element is larger than the limit of cooling of the induction heating cooker A second object is to provide an induction heating cooker that limits the power supplied to the object to be heated only in the operating frequency range for heating the object.

Further, if the operating frequency is preset according to the input current and the operating frequency is higher than the set value, that is, the loss of the switching element becomes larger than the cooling limit of the induction heating cooker. A third object is to provide an induction heating cooker that limits the power supplied to the object to be heated above the operating frequency for heating.

Further, when a preset input current is preset, the operating frequency range is preset, and when the operating frequency is within the preset range, that is, the loss of the switching element is lower than the limit of cooling the induction heating cooker. A fourth object is to provide an induction heating cooker that limits the power supplied to the object to be heated only at an operating frequency at which the object to be heated becomes large.

Further, when the operating frequency is preset at a preset input current and the operating frequency is higher than the set value, that is, the loss of the switching element becomes larger than the limit of cooling of the induction heating cooker. A fifth object of the present invention is to provide an induction heating cooker that limits the power supplied to the object to be heated above the operating frequency for heating the object to be heated.

[0014]

In order to achieve the first object, the first means of the present invention is to provide a heating coil, a switching element connected in series with the heating coil, a resonance capacitor connected in parallel with the heating coil, and the switching. An inverter circuit consisting of a reverse conducting diode connected in parallel to the element, an input current detection unit of the inverter circuit, an operating frequency detection unit, a determination unit that determines the load by the inputs from these detection units, and a load The induction heating cooker is characterized by being provided with a control circuit having means for controlling the input current accordingly.

In order to achieve the second object, the second aspect of the present invention
Means is an inverter circuit including a heating coil, a switching element connected in series to the heating coil, a resonance capacitor connected in parallel to the heating coil, and a reverse conducting diode connected in parallel to the switching element; and an input current detection unit of the inverter circuit. And an operating frequency detector,
An induction heating cooker is characterized in that a control circuit having a control means for presetting a range of operating frequency according to an input current value and limiting the input current at an operating frequency within the set range is provided.

In order to achieve the third object, the third aspect of the present invention
Means is an inverter circuit including a heating coil, a switching element connected in series to the heating coil, a resonance capacitor connected in parallel to the heating coil, and a reverse conducting diode connected in parallel to the switching element; and an input current detection unit of the inverter circuit. And an operating frequency detector,
An induction heating cooker is characterized in that an operating frequency is preset according to an input current value, and a control circuit having a control means for limiting the input current if the operating frequency is higher than the set value is provided.

In order to achieve the fourth object, the fourth aspect of the present invention
Means is an inverter circuit including a heating coil, a switching element connected in series to the heating coil, a resonance capacitor connected in parallel to the heating coil, and a reverse conducting diode connected in parallel to the switching element; and an input current detection unit of the inverter circuit. And an operating frequency detector,
An induction heating cooker characterized in that a control circuit having a control means for presetting a range of operating frequency at a predetermined input current and limiting the input current at the operating frequency within the set range is provided. .

In order to achieve the fifth object, the fifth aspect of the present invention
Means is an inverter circuit including a heating coil, a switching element connected in series to the heating coil, a resonance capacitor connected in parallel to the heating coil, and a reverse conducting diode connected in parallel to the switching element; and an input current detection unit of the inverter circuit. And an operating frequency detector,
Preset the operating frequency at a given input current,
An induction heating cooker is provided with a control circuit having control means for limiting an input current if the operating frequency is higher than a set value.

[0019]

With the above construction, an induction heating cooker capable of determining a load, setting an input power according to the load, and supplying power to a pan up to a limit where the loss of a switching element can cool the induction heating cooker is provided. be able to.

In addition, the operating frequency range is set in advance according to the input current, and when the operating frequency is within the set range, the input power is set according to the load and the switching element loss is induced. You can power the pot to the limit where the cooker can cool.

Further, the operating frequency is preset according to the input current, and when the operating frequency is equal to or higher than the set value,
By setting the input power according to the load, power can be supplied to the pan until the loss of the switching element can cool the induction cooking device.

When a preset input current is preset, the operating frequency range is preset. When the operating frequency is within the preset range, the input power is set according to the load and the switching element The pan can be powered up to the point where the loss can cool the induction cooker.

When the preset input current is preset, the operating frequency is preset, and when the operating frequency is equal to or higher than the set value, the input power is set according to the load.
The pan can be powered to the extent that the switching element loss can cool the induction cooker.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an example of a circuit of an induction heating cooker according to the present invention. Reference numeral 11 is a DC power source, and 12 is a heating coil, on which an object to be heated (pot or the like) is placed, although not particularly shown in the figure. Reference numeral 13 denotes a resonance capacitor, and the heating coil 12 and the resonance capacitor 13 constitute a load circuit 14. Reference numeral 15 is a switching element, and in this example, a high current (60 A), high breakdown voltage (900 V) IGBT is used. Reference numeral 16 is a reverse conducting diode. Reference numeral 17 denotes a control circuit that outputs a signal for controlling the switching element 15. Although not particularly shown in the figure, the voltage Vce applied to both ends of the switching element 15 is detected,
It has a built-in drive circuit 17a for driving. Also,
The load is determined by comparing the value input in advance by the determination unit 17c with the input from the input current detection unit 19 and the operating frequency detection unit 17b, and the input power is limited by the input current limit value according to the load. .

The limit value is shown in FIG. The load a,
The characteristics of the input power and the operating frequency of the load b and the load c are shown.
The load a is represented by a non-magnetic pot, the load b is an enameled pot, and the load c is represented by a magnetic pot. Further, in the case of heating each load, the input power at which the loss of the switching element becomes the limit at which the induction heating cooker can be cooled is indicated by a dot. For each load, when the input power is larger than the point, the loss of the switching element becomes larger than the limit of cooling the induction heating cooker, which may lead to destruction. Therefore, for each load, set the limit value to a value where the input power is lower than the point,
The input power is limited by the limit value according to the load determined by the determination unit 17c. Therefore, in the conventional control method,
Although it was possible to supply only constant power regardless of the load, it is possible to supply power according to the load.

Next, a second embodiment of the present invention will be described with reference to FIG. Whether or not the input current detection unit 19 and the operating frequency detection unit 17b in FIG. 1 are within the range of the operating frequency preset according to the input current value by the input from both the detection units. judge. Here, it is set within the range of the operating frequency of the load as shown in FIG.

FIG. 3 shows the characteristics of the input power and operating frequency of load a, load b, and load c. Load a is a non-magnetic pan, load b
The load c such as an enameled pot is represented by a magnetic pot. Also,
In the case of heating each load, the input power at which the loss of the switching element is the limit at which the induction heating cooker can be cooled is indicated by a dot. For each load, when the input power is larger than the point, the loss of the switching element becomes larger than the limit of cooling the induction heating cooker, which may lead to destruction. In FIG. 3, since only the characteristic of the load a is the operating frequency range for heating the object to be heated, the loss of the switching element at the maximum input power value is larger than the cooling limit of the induction heating cooker. Only in this case, the switching element is protected by controlling with the limit value of the load a.

Next, a third embodiment of the present invention will be described with reference to FIG. Based on the input from both the input current detection unit 19 and the operation frequency detection unit 17b in FIG. 1, the determination unit 17c determines whether or not the operation frequency is equal to or higher than a preset operation frequency according to the input current value. . Here, the operating frequency of the load is set as shown in FIG.

FIG. 4 shows the characteristics of the input power and the operating frequency of the load a, the load b, and the load c. Load a is a non-magnetic pan, load b
The load c such as an enameled pot is represented by a magnetic pot. Also,
In the case of heating each load, the input power at which the loss of the switching element is the limit at which the induction heating cooker can be cooled is indicated by a dot. For each load, when the input power is larger than the point, the loss of the switching element becomes larger than the limit of cooling the induction heating cooker, which may lead to destruction. In FIG. 4, only the characteristic of the load a is equal to or higher than the operating frequency for heating an object to be heated, in which the loss of the switching element at the maximum input power value is larger than the cooling limit of the induction heating cooker. Only, the load a is controlled by the limit value to protect the switching element.

Next, a fourth embodiment of the present invention will be described with reference to FIG. Whether the input current detection unit 19 and the operating frequency detection unit 17b in FIG. 1 are within the preset operating frequency range at the preset predetermined input current in the determination unit 17c by the input from both the detection units. Determine whether or not. Here, the load operating frequency range is set as shown in FIG. FIG. 5 shows the characteristics of the input power and the operating frequency of the load a, the load b, and the load c. The load a is represented by a non-magnetic pot, the load b is an enameled pot, and the load c is represented by a magnetic pot. Further, in the case of heating each load, the input power at which the loss of the switching element becomes the limit at which the induction heating cooker can be cooled is indicated by a dot. For each load, when the input power is larger than the point, the loss of the switching element becomes larger than the limit of cooling the induction heating cooker, which may lead to destruction. In FIG. 5, since only the characteristic of the load a is the operating frequency range for heating the object to be heated, the loss of the switching element at the maximum input power value is larger than the limit of cooling of the induction heating cooker. Only in this case, the switching element is protected by controlling with the limit value of the load a.

Next, a fifth embodiment of the present invention will be described with reference to FIG. Whether or not the input current detection unit 19 and the operating frequency detection unit 17b in FIG. 1 are at or above the preset operating frequency at the time of the preset input current in the determination unit 17c, based on the inputs from both the detection units. judge. Here, the operating frequency of the load as shown in FIG. 6 is set. FIG. 6 shows the characteristics of the input power and the operating frequency of the loads a, b, and c. The load a is represented by a non-magnetic pot, the load b is an enameled pot, and the load c is represented by a magnetic pot. Further, in the case of heating each load, the input power at which the loss of the switching element becomes the limit at which the induction heating cooker can be cooled is indicated by a dot. For each load, when the input power is larger than the point, the loss of the switching element becomes larger than the limit of cooling the induction heating cooker, which may lead to destruction. In FIG. 6, only the characteristic of the load a is equal to or higher than the operating frequency for heating the object to be heated, in which the loss of the switching element at the maximum input power value is larger than the cooling limit of the induction heating cooker. Only, the load a is controlled by the limit value to protect the switching element.

[0032]

As is apparent from the above embodiments, the first means of the present invention determines the load, sets the input power according to the load, and the loss of the switching element causes the cooling of the induction heating cooker. It provides an induction heating cooker that can supply power to a pan to the maximum possible.

Further, according to the second means of the present invention, the operating frequency range is preset according to the input current,
If the operating frequency is within the set range, set the input power according to the load and use an induction cooker that can supply power to the pan until the loss of the switching element can cool the induction cooker. It is provided.

According to the third means of the present invention, the operating frequency is preset according to the input current, and when the operating frequency is equal to or higher than the set value, the input power is set according to the load and the switching element is set. It provides an induction cooker that can power a pan to the extent that the loss of the induction cooker can cool it.

Further, according to the fourth means of the present invention, the range of operating frequency is preset at the time of preset input current, and when the operating frequency is within the set range, it is determined according to the load. Provided is an induction heating cooker capable of supplying power to a pan by setting the input power to a limit at which a loss of a switching element can cool the induction heating cooker.

According to the fifth means of the present invention, the operating frequency is preset at a predetermined input current preset, and when the operating frequency is equal to or higher than the set value, the input power corresponding to the load is set. The present invention provides an induction heating cooker capable of supplying power to a pan until the switching element loss reaches the limit at which the induction heating cooker can be cooled.

[Brief description of drawings]

FIG. 1 is a block diagram of an inverter circuit of an induction heating cooker according to the present invention.

FIG. 2 is a diagram showing a relationship between operating frequency and input power in the first embodiment of the induction heating cooker of the present invention.

FIG. 3 is a diagram showing a relationship between operating frequency and input power in the second embodiment of the induction heating cooker of the present invention.

FIG. 4 is a diagram showing the relationship between operating frequency and input power in the third embodiment of the induction heating cooker of the present invention.

FIG. 5 is a diagram showing the relationship between operating frequency and input power in the fourth embodiment of the induction heating cooker of the present invention.

FIG. 6 is a diagram showing the relationship between operating frequency and input power in a fifth embodiment of the induction heating cooker of the present invention.

FIG. 7 is a schematic configuration diagram of an inverter circuit using control means of a conventional induction heating cooker.

FIG. 8 is an operation waveform diagram of the inverter circuit.

FIG. 9 is a diagram showing a relationship between operating frequency and input power in a conventional induction heating cooker.

[Explanation of symbols]

 11, 51 DC power supply 12, 52 Heating coil 13, 53 Resonant capacitor 14, 54 Load circuit 15, 55 Switching element 16, 56 Reverse conduction diode 17, 57 Control circuit 17a, 57a Drive circuit 17b Discrimination unit 17c Operating frequency detection unit 18 , 58 Inverter circuit 19, 59 Input current detector

Claims (5)

[Claims] 1. An inverter circuit comprising a heating coil, a switching element connected in series to the heating coil, a resonance capacitor connected in parallel to the heating coil, and a reverse conducting diode connected in parallel to the switching element, and an input current detection of the inverter circuit. Section, an operating frequency detection section, a determination section for determining a load based on inputs from both detection sections, and a control circuit having means for controlling an input current according to the load. vessel. 2. An inverter circuit comprising a heating coil, a switching element connected in series to the heating coil, a resonant capacitor connected in parallel to the heating coil, and a reverse conducting diode connected in parallel to the switching element, and an input current detection of the inverter circuit. A control circuit that has a control section and an operating frequency detection section, and that sets a range of the operating frequency according to the input current value in advance and that has a control means that limits the input current at the operating frequency within the set range. Induction heating cooker characterized by. 3. An inverter circuit comprising a heating coil, a switching element connected in series to the heating coil, a resonant capacitor connected in parallel to the heating coil, and a reverse conducting diode connected in parallel to the switching element, and an input current detection of the inverter circuit. And an operating frequency detecting unit, the operating frequency according to the input current value is preset, and a control circuit having a control means for limiting the input current if the operating frequency is higher than the set value is provided. And induction heating cooker. 4. An inverter circuit comprising a heating coil, a switching element connected in series to the heating coil, a resonant capacitor connected in parallel to the heating coil, and a reverse conducting diode connected in parallel to the switching element, and an input current detection of the inverter circuit. A control circuit having a control section for presetting a range of the operating frequency at a predetermined input current and limiting the input current at the operating frequency within the set range. An induction heating cooker characterized by the following. 5. An inverter circuit comprising a heating coil, a switching element connected in series to the heating coil, a resonance capacitor connected in parallel to the heating coil, and a reverse conducting diode connected in parallel to the switching element, and an input current detection of the inverter circuit. A control circuit having a control section and an operating frequency detection section, presetting an operating frequency at a predetermined input current, and limiting the input current if the operating frequency is higher than the set value. Characteristic induction heating cooker.