JPH09223577A - Induction heating cooking appliance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cause the loss of switching elements to effectively utilize a range where an induction heating cooking appliance can cool so as to supply power to a pan by judging the operation frequency of the induction heating cooking appliance, and controlling so that the threshold value of both end voltages is changeable in response to the operation frequency. SOLUTION: An induction heating cooking appliance is composed of a switching element 15 which is directly connected to a heating coil 12, a resonance condenser 13 which is connected to the heating coil 12 in parallel, a reverse conduction diode 16 which is connected to the switching element 15 in parallel, and a control circuit 17 which contains a drive circuit 17a driving the switching element 15 and an operation frequency detection portion 17b. In response to the operation frequency of the switching element 15 detected by the operation frequency detection portion 17b, the threshold value of both end voltages of the switching element 15 is changeable.

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 used in general households, restaurants and the like. More specifically, the induction heating cooker characterized by the control means of the induction heating inverter circuit. It is about.

[0002]

2. Description of the Related Art In recent years, induction heating cookers as a safe heating source have been in the spotlight. In this induction heating cooker, an induction magnetic field is generated in the vicinity of the coil by turning on and off the switching element and flowing a high frequency current in the coil.Therefore, a pot made of a metal such as iron is placed near the coil, It is a device that uses the heat generated by iron loss by generating an induced current by an induction magnetic field in a pan.

In the conventional induction heating cooker, the voltage value of the switching element is constant due to the output from the voltage detecting section of the switching element, although the operating frequency changes depending on the characteristics such as the material and shape of the pot. It controlled below the threshold of. An example of the inverter circuit of the induction heating cooker using the conventional control means will be described with reference to FIGS.

FIG. 12 shows an example of a circuit of a conventional induction heating cooker. In FIG. 12, 31 is a DC power source and 32 is a heating coil, on which an object to be heated (pot etc.) is placed, although not particularly shown in the figure. A resonance capacitor 33 resonates with the heating coil 32. Reference numeral 35 denotes a switching element, which is an IGBT having a large current and a high breakdown voltage in this example. 36 is a reverse conducting diode. A control circuit 37 controls the switching element 35 and has a built-in drive circuit 37a for driving the switching element. A voltage detector 39 of the switching element detects the voltage Vce applied to both ends of the switching element 35 and outputs it to the control circuit 37. The control circuit 37 controls the voltage value of the switching element to be equal to or lower than the threshold value by the input from the voltage detection unit 39 of the switching element.

FIG. 13 shows operating waveforms of various parts of the inverter during steady operation. FIG. 13A shows a drive signal output from the drive circuit 37a incorporated in the control circuit 37, and the switching element 35 is output when this output is High.
Turns on. FIG. 13B shows the switching element 3
5 and the current Ic flowing in the reverse conducting diode 36,
(C) is the voltage V applied across the switching element 35.
It is ce.

The operation of this circuit will be described below with reference to FIGS. 12 and 13. The control circuit 37 turns on the switching element 35 for a predetermined time and then turns it off to resonate the resonance circuit including the heating coil 32 and the resonance capacitor 33. Further, the control circuit 37 detects the voltage Vce of the switching element by the voltage detection unit 39 of the switching element, and turns on the switching element 35 again when Vce becomes lower than the predetermined value. Since the above operation is repeated, Ic and Vce are as shown in FIGS. 13B and 13C with respect to the drive signal of the drive circuit 37a in FIG.
As described above, electric power is supplied to an object to be heated such as a pot placed on the heating coil 32. The power supplied to the object to be heated can be freely changed by controlling the ON time of the switching element 35.

The conventional inverter control means is generally a circuit using a means for controlling the voltage Vce of the switching element so as not to exceed a certain threshold value. However, in the induction heating cooker, even when the voltage of the switching element is controlled to a certain threshold value or less, the operating frequency varies depending on the material, shape, etc. of the object to be heated. However, there is a difference in that the loss increases as the frequency increases.

FIG. 14 shows the characteristics of the peak value of the voltage of the switching element and the operating frequency when the objects to be heated are load a and load b. Here, load a is a non-magnetic pan, load b
It is represented by enameled pots. Further, when heating each load, the voltage of the switching element of each load where the loss of the switching element is constant is shown by a dot. For each load, if the voltage of the switching element becomes higher than this point, the heat generation of the switching element becomes larger than the cooling limit of the induction heating cooker, which may lead to damage. Sets the threshold to a low value. Therefore, in the conventional control method,
The threshold value of the voltage value of the switching element is set according to the object to be heated (the load a in this case) having a low threshold value of the voltage value of the switching element.

[0009]

However, in the above conventional induction heating cooker, when the same power is supplied to the object to be heated, the loss of the switching element becomes large because the operating frequency is high, except for the object to be heated. Cannot increase the voltage value of the switching element above the threshold value, although the loss of the switching element has a margin. In other words, when actually used at home, the object to be heated, such as a pot that is normally used, supplies only the electric power controlled to the threshold voltage of both ends of the switching element that matches the object to be heated, which causes high loss of the switching element. There was a problem that was not done.

[0010]

In order to solve the above problems, the present invention provides 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 element. A reverse conducting diode connected in parallel to the switching element and a control circuit for driving and controlling the switching element, wherein the control circuit changes the threshold voltage of both ends of the switching element in accordance with the operating frequency of the switching element. It is controlled as follows.

[0011]

According to the first and second aspects of the present invention, the operating frequency of the induction heating cooker is determined, and the threshold voltage of both ends of the switching element is controlled to be variable according to the operating frequency. By effectively utilizing the cooling range of the induction heating cooker, the power loss can be effectively supplied to the pan.

According to the third aspect of the present invention, since the threshold value of the voltage across the switching element with respect to the operating frequency is corrected in accordance with the fluctuation of the power supply voltage detected by the power supply voltage detector, the actual induction heating cooker is used. It becomes possible to perform control corresponding to the conditions.

[0013]

【Example】

Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to FIG.
2 and FIG. FIG. 1 is an example of a circuit of an induction heating cooker according to the present invention. In the figure, 11 is a DC power supply, 14 is a power supply voltage detection unit, and the power supply voltage detection unit 14 is a DC power supply 11
Is detecting the voltage. Reference numeral 12 denotes a heating coil on which an object to be heated (pot or the like) is placed, although not particularly shown in the figure. A resonance capacitor 13 resonates with the heating coil 12. Reference numeral 15 is a switching element, and in this example, a high current, high breakdown voltage IGBT is used. Reference numeral 16 is a reverse conducting diode. Reference numeral 17 denotes a control circuit that outputs a signal that controls the switching element 15, and includes a drive circuit 17a that drives the switching element 15 and an operating frequency detection unit 17b of the switching element 15. Further, the switching element is controlled by the voltage value detected by the voltage detection section 19 of the switching element and the operating frequency detected by the operating frequency detection section 17b.

FIG. 2 shows the threshold value of the voltage value of the switching element with respect to the operating frequency detected by the operating frequency detector 17b. FIG. 2 shows the characteristics of the operating frequencies of the loads a and b and the peak value of the voltage of the switching element. The load a is represented by a non-magnetic pan, a load b enameled pan, and the like. Also,
In the case where each load is heated, the voltage of the switching element, which is the limit at which the heat generated by the loss of the switching element can be cooled by the configuration of the induction heating cooker, is indicated by a dot. For each load, if the voltage of the switching element becomes higher than this point, the heat generated by the switching element becomes larger than the limit that can be cooled, and there is a risk of destruction. Therefore, for each load, the threshold value is set to a value at which the voltage of the switching element is lower than this point, and the voltage value of the switching element is controlled to be equal to or less than the threshold value. Therefore, in the conventional control method, only the electric power controlled so as to be equal to or lower than the threshold value of the load a having a low threshold value of the voltage value of the switching element can be supplied to the object to be heated regardless of the operating frequency. By providing the threshold value of the voltage value of the switching element correspondingly set, the load b can be supplied with electric power up to the threshold value of the voltage value of the switching element of the load b.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIGS. The operating frequency detected by the operating frequency detector 17b of FIG. 1 is compared with a preset operating frequency, and when the operating frequency is lower than the set operating frequency, a threshold value of the voltage value of the switching element is set high. When the operating frequency is higher than the set operating frequency, the threshold value of the voltage value of the switching element is set low. With this configuration, the control method depending on the operating frequency can be realized most easily.

(Embodiment 3) Next, a third embodiment of the present invention will be described with reference to FIGS. The operating frequency detected by the operating frequency detector 17b in FIG. 1 is compared with a preset operating frequency range, and control is performed using the threshold value of the voltage value of the switching element provided in the operating frequency range corresponding to the operating frequency. . With this configuration, in detecting the operating frequency and controlling the voltage value of the switching element, the operating frequency range corresponding to the operating frequency detecting ability or the minimum necessary operating frequency range is set, which is easier and cheaper than the first embodiment. In addition, it is possible to realize the control method adapted to the control capability as compared with the second embodiment.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIGS. 1, 5, and 6. Fig. 6 shows a load a and a load b when the power supply voltage of the induction heating cooker drops.
The characteristics of the operating frequency and the peak value of the voltage of the switching element are shown. In FIG. 6, when the power supply voltage drops,
It shows that the peak value of the voltage of the switching element at the same frequency is reduced even if the load does not change.
This is because when the power supply voltage decreases, the rising slope of Ic decreases as indicated by the dotted line on the operation waveform of FIG. 5, so that the peak value of Ic decreases even for the same on-time. Therefore, in the resonance circuit in which the current of the heating coil becomes the voltage of the resonance capacitor, the decrease in the current results in the decrease in the voltage, and the peak value of the voltage of the switching element represented by Vce also decreases. In order to deal with this phenomenon, Example 4
1 detects the power supply voltage 11 by the power supply voltage detection unit 14 of FIG. 1 and uses the threshold value of the voltage value of the switching element with respect to the operating frequency set in accordance with the fluctuation of the power supply voltage to perform the control shown in the first embodiment. I do. With this configuration, it is possible to realize the control corresponding to the actual use condition of the induction heating cooker, as compared with the first embodiment.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described with reference to FIGS. The power supply voltage detection unit 14 in FIG. 1 detects the power supply voltage, and the control shown in the second embodiment is performed using the set operating frequency set according to the fluctuation of the power supply voltage. With this configuration, the control method in which the operating frequency is detected according to the change in the power supply voltage is described in the fourth embodiment.
It can be realized more easily.

(Sixth Embodiment) Next, a sixth embodiment of the present invention will be described with reference to FIGS. The power supply voltage detection unit 14 in FIG. 1 detects the power supply voltage, and the control shown in the third embodiment of the present invention is performed using the set operating frequency range set in accordance with the fluctuation of the power supply voltage. With this configuration, it is possible to realize a control method adapted to the control capability more easily and cheaply than the fourth embodiment, as compared with the fourth embodiment.

(Embodiment 7) Next, a seventh embodiment of the present invention will be described with reference to FIGS. The power supply voltage detection unit 14 in FIG. 1 detects the power supply voltage, compares the power supply voltage with a preset power supply voltage range, and sets the threshold value of the voltage value of the switching element for the operating frequency determined for each corresponding power supply voltage range. Then, the control shown in the first embodiment is performed.
With this configuration, a control method of detecting the operating frequency and controlling the voltage value of the switching element according to the detection capability of the fluctuation of the power supply voltage or the minimum required voltage range is easier and cheaper than the fourth embodiment. Can be realized.

(Embodiment 8) Next, an eighth embodiment of the present invention will be described with reference to FIGS. The power supply voltage detection unit 14 of FIG. 1 detects the power supply voltage, compares the power supply voltage with a preset power supply voltage range, and uses the set operating frequency determined for each corresponding power supply voltage range in the second embodiment. Perform the indicated control. With this configuration, a control method for detecting the operating frequency and controlling the voltage value of the switching element according to the fluctuation of the power supply voltage can be realized more easily and cheaper than the fifth and seventh embodiments.

(Ninth Embodiment) Next, a ninth embodiment of the present invention will be described with reference to FIGS. The power supply voltage detection unit 14 of FIG. 1 detects the power supply voltage, compares the power supply voltage with a preset power supply voltage range, and uses the set operating frequency range determined for each corresponding power supply voltage range to implement the third embodiment. Perform the control shown in. With this configuration, when the operating frequency is detected and the voltage value of the switching element is controlled in accordance with the fluctuation of the power supply voltage, the operating frequency range is set according to the operating frequency detection capability or the minimum necessary operating frequency range is set. It is possible to realize a control method adapted to the control capability more easily and cheaper than the seventh embodiment, as compared with the eighth embodiment.

[0023]

As described above, according to the first and second aspects of the present invention, the operating frequency of the induction heating cooker is determined, and the threshold voltage of both ends of the switching element is made variable according to the operating frequency. (EN) Provided is an induction heating cooker capable of supplying power to a pan by effectively utilizing a cooling range of an induction heating cooker for controlling loss of a switching element.

According to the third aspect of the present invention, the power supply voltage detected by the power supply voltage detector changes, and
Since the threshold value of the voltage across the switching element with respect to the operating frequency is corrected, it is possible to realize control corresponding to the actual use condition of the induction heating cooker.

[Brief description of drawings]

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

FIG. 2 is a diagram showing the operating characteristics of the induction cooking device.

FIG. 3 is an operation characteristic diagram of the induction heating cooker according to the second embodiment of the present invention.

FIG. 4 is an operation characteristic diagram of the induction heating cooker according to the third embodiment of the present invention.

FIG. 5 is a diagram of an operation waveform of the induction heating cooker.

FIG. 6 is an operation characteristic diagram of the induction heating cooker according to the fourth embodiment of the present invention.

FIG. 7 is an operational characteristic diagram of the induction heating cooker according to the fifth embodiment of the present invention.

FIG. 8 is an operation characteristic diagram of the induction heating cooker according to the sixth embodiment of the present invention.

FIG. 9 is an operational characteristic diagram of the induction heating cooker according to the seventh embodiment of the present invention.

FIG. 10 is an operational characteristic diagram of the induction heating cooker according to the eighth embodiment of the present invention.

FIG. 11 is an operation characteristic diagram of the induction heating cooker according to the ninth embodiment of the present invention.

FIG. 12 is a block diagram of a conventional induction heating cooker.

FIG. 13 is a waveform diagram of the same operation of the induction heating cooker.

FIG. 14 is a diagram showing an operating characteristic of the induction heating cooker.

[Explanation of symbols]

 11 DC Power Supply 12 Heating Coil 13 Resonant Capacitor 14 Power Supply Voltage Detector 15 Switching Element 16 Reverse Conducting Diode 17 Control Circuit 17a Drive Circuit 17b Operating Frequency Detector 19 Voltage Detector of Switching Element

Front page continued (72) Inventor Hiroshi Tominaga 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Hideki Ryukaku, 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A heating coil, a switching element connected in series with the heating coil, a resonance capacitor connected in parallel with the heating coil, a reverse conducting diode connected in parallel with the switching element, and a driving element for the switching element. A control circuit for controlling the induction heating cooker, wherein the control circuit makes a threshold value of a voltage across the switching element variable according to an operating frequency of the switching element. 2. The threshold value of the voltage across the switching element in two stages is set according to a predetermined operating frequency.
The induction heating cooker described. 3. The induction cooking apparatus according to claim 1, further comprising a power supply voltage detection unit, wherein the control circuit corrects the threshold voltage of both ends of the switching element according to the detection voltage of the power supply voltage detection unit. vessel.