JPH0495383A - Induction heating cooker - Google Patents

Abstract

PURPOSE:To discriminate that a cooker is under the no-load condition or not, and discriminate the material of a metal vessel by detecting a resonance frequency with a resonance frequency detecting means on the basis of the current flowing to a heating coil, and discriminating the material of a metal vessel with a discriminating means on the basis of the detected resonance frequency. CONSTITUTION:The current flowing to a heating coil 6 is detected by a current transformer 10 to be given to a phase detecting circuit 3, and the phase detecting circuit 3 detects the phases shift between the current from the current transformer 10 and the output signal from a driving frequency variable circuit 2, and the described operation is repeated till a phase difference becomes 0. At a point that a phase difference is 0, the pulse signal of the phase difference detecting circuit 3 is given to a micro computer 5, and a resonance frequency detecting unit 5c detects this pulse signal as a resonance frequency. A discriminating unit 5e compares the detected resonance frequency with the resonance frequency data stored in a memory unit 5d to discriminate the material of a metal vessel and that a cooker is under the no-load condition or not.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to induction heating cooking in which a heating coil is arranged to generate an eddy current in a metal container and heat an object to be heated stored in the metal container. The present invention relates to an induction heating cooker that can determine whether it is in an unloaded state and the material of a metal container.

[Prior Art and Problems to be Solved by the Invention] FIG. 4 is a schematic block diagram of a conventional induction heating cooker. In the figure, this induction heating cooker includes an inverter circuit 51 that switches a DC voltage to generate a high frequency signal, and a heating coil 52 that heats a metal container 57 in response to the high frequency signal generated by the inverter circuit 51. A resonant capacitor 53, a current transformer 54 for detecting the current flowing through the heating coil 52, and a microcomputer that generates a signal for driving the inverter circuit 51 at a resonant frequency based on the current value detected by the current transformer 54. 55, and a drive circuit 56 that drives the inverter circuit 51 in response to a control signal generated by the microcomputer 55.

In the induction heating cooker shown in FIG. 4, the metal container 57 is detected in the following manner. That is, the peak value of the current flowing through the heating coil 52 by the current transformer 54 is compared with a threshold value set based on the peak value in the no-load state, and the metal container is determined depending on whether the peak value exceeds the threshold value. It determines whether the vehicle is on board or not. This is because when the metal container is placed on top of the heating coil, the impedance due to electromagnetic coupling between the heating coil 52 and the metal container 57 is reduced, and the peak value of the current flowing through the heating coil 52 is the peak value when there is no load. It takes advantage of the fact that it increases more than the value.

However, when a metal container made of a non-magnetic material is mounted, the electromagnetic coupling between the heating coil 52 and the metal container 57 is weak. lower compared to formed metal containers. As a result, the peak value of the current flowing through the heating coil 52 becomes high. The peak current value in this case is almost equal to the peak current value under no load (
(see FIG. 3), it becomes difficult to determine whether or not there is a no-load state.

For this reason, there is a possibility that the drive of the inverter circuit 51 may be stopped because it is determined that there is no load even though a non-magnetic metal container is placed on the container. Further, there is a problem in that the cook cannot be informed that a non-magnetic metal container is placed on top of the cooking device, and cooking cannot be performed in a way that is compatible with the non-magnetic container.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an induction heating cooker that can determine whether it is in a no-load state or not and determine the material of the metal container.

[Means for Solving the Problems] To achieve the above object, an induction heating cooker according to the present invention includes a heating coil that generates an eddy current in a metal container to heat an object to be heated stored in the metal container. In the induction heating cooker in which the heating coil is arranged, a resonant frequency detection means detects the resonant frequency in a state where the heating coil and the metal container are electromagnetically coupled or in a no-load state based on the current flowing through the heating coil; The present invention is characterized in that it has a determining means for determining whether there is no load or not and determining the material of the metal container based on the resonant frequency detected by the resonant frequency detecting means.

[Function] The present invention described above focuses on the fact that the resonant frequencies differ when the metal containers are made of different materials or are in an unloaded state.

Therefore, the resonance frequency detection means can detect the resonance frequency based on the current flowing through the heating coil, and the discrimination means can discriminate the material of the metal container based on the resonance frequency detected by the resonance frequency detection means.

[Embodiments of the Invention] Hereinafter, embodiments of the induction heating cooker according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a frequency distribution diagram for explaining the present invention in detail. In the figure, the resonant frequency is the lowest when there is no load, the highest when a non-magnetic metal container is the load, and the resonant frequency is the highest when a magnetic metal container is the load. It is located between the resonant frequency of and the resonant frequency under no-load condition. In this way, since the resonant frequency differs depending on the material of the metal container, by detecting the resonant frequency and searching for the material or state (no load) that corresponds to the detected resonant frequency, it is possible to determine the material of the metal container. It is possible to determine whether there is no load or not.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, an input variable circuit 1 is a circuit that rectifies and smoothes an alternating current voltage to generate a direct current voltage, and changes this direct current voltage using a chopper type inverter or the like (not shown). Further, phase control may be performed using a thyristor or the like. The DC voltage generated here is supplied to a single-ended push-pull type inverter circuit 11.

This inverter circuit 11 includes a pair of transistors 11a
and llb, and flywheel diodes llc and lid. Here, as the transistors lla and llb, it is possible to use bipolar type M08FETs (also known as IGBTs) that can perform high-speed switching operations.

The inverter circuit 11 is driven by an inverter drive circuit 8, generates a high frequency signal, and supplies this high frequency signal to a series resonant circuit consisting of a heating coil 6 and a resonant capacitor 7. As a result, an eddy current is generated in the metal container 9 placed on the heating coil 6, and the metal container 9 generates heat due to this eddy current.

Next, feedback control during normal operation of this induction heating cooker will be explained. The value of the current flowing through the heating coil 6 is detected by a current transformer 10 coupled between an inverter circuit 11 and the heating coil 6, and the detected value is given to a peak current detection circuit 4 and a phase detection circuit 3. . The peak current detection circuit 4 detects the peak value based on the detection signal from the current transformer 10,
The peak value is given to the microcomputer 5. The phase detection circuit 3 detects the phase difference between the current value (current waveform) detected by the current transformer 10 and the signal generated by the variable drive frequency circuit 2, and provides the detected phase difference to the microcomputer 5. The microcomputer 5 sets a frequency for driving the inverter circuit 11 in a resonant state based on the peak current value and the phase difference, and provides data regarding this frequency to the variable drive frequency circuit 2. Inverter drive circuit 8 drives inverter circuit 11 based on the variable frequency. By performing such control, the inverter circuit 11 can be switched at the resonant frequency.

Next, the operation of determining the material of the metal container will be explained. Here, the microcomputer 5 has the following configuration in order to perform material discrimination. That is, the microcomputer 5 is connected to the power source O.
The input variable circuit control section 5a that controls the input variable circuit 1 in response to N and the sweep command 8 to the drive frequency variable circuit 2
A sweep command unit 5b that performs the detection, a resonant frequency detection unit 5c, a memory unit 5d that stores resonant frequencies in advance in correspondence with the material of the metal container 9, and a resonant frequency that is detected and the stored resonant frequency data. A determining unit 5e determines the material of the metal container and determines whether or not it is in an unloaded state based on the comparison.
including. First, when starting up the induction heating cooker, the input control section 5a of the microcomputer 5 controls the input variable circuit 1 in response to a power ON signal.
Keep the DC voltage output from the DC voltage constant and low potential. This constant DC voltage is supplied to the inverter circuit 11.

The sweep command section 5b of the microcomputer 5 issues a sweep command to the variable frequency circuit 2 in response to the power ON signal. In response to this sweep command, variable drive frequency circuit 2 uniformly changes the switching frequency of inverter drive circuit 8. According to this frequency change, the frequency of the high frequency output of the inverter circuit 5 also changes. The current flowing through the heating coil 6 is detected by a current transformer 10, and the detected current is applied to a phase detection circuit 3. The phase detection circuit 3 detects a phase shift between the current from the current transformer 10 and the output signal from the variable drive frequency circuit 2. This detection of the phase difference is repeated until the phase difference becomes 0, and at the time the phase difference becomes 0, the phase detection circuit 3 gives a pulse signal to the microcomputer 5. The resonant frequency detection section 5C of the microcomputer 5 sets the driving frequency when this pulse signal is applied as the resonant frequency. In the manner described above, the resonant frequency can be found from the frequency being scanned. The determination unit 5e determines the material of the metal container 7 and whether or not it is in an unloaded state by comparing the detected resonance frequency with the resonance frequency data stored in the memory unit 5d. Then, the determination result can be notified or the heating control can be switched to one that is appropriate for the material of the metal container 7 based on the determination result.

Now, if we convert the equivalent circuit between the heating coil and the pot shown in Fig. 2(a) as shown in Fig. 2(b), we get τ2 as 2 L3=L+ (1) L3: The difference between the heating coil and the metal container. The equivalent inductance τ of the coupling circuit, the time constant f of the metal container, and the driving frequency: the coupling coefficient between the load and the heating coil. Here, L3 is a function of the time constant τ of the metal container, and is the resonant frequency f of the series resonant circuit composed of L3 and the capacitance C of the resonant capacitor.

is, and since the time constant τ according to the material of the metal container can be approximately determined from the resonance frequency detected by this scanning, it is possible to determine the material of the metal container and the load state based on the resonance frequency. can.

[Effects of the Invention] According to the present invention, the resonant frequency in the state where the heating coil and the metal container are magnetically coupled and the resonant frequency in the no-load state are detected by the resonance frequency detection means, so that the resonant frequency in the no-load state is detected. It becomes possible to determine whether the metal container is present or not and to determine the material of the metal container. Therefore,
It is possible to inform the cook of the material of the metal container and the no-load state.

In addition, cooking can be carried out in accordance with the material of the metal container.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an equivalent circuit of a heating coil and a metal container, Fig. 3 is a frequency distribution diagram for explaining the present invention in detail, and Fig. 4 is a block diagram showing an embodiment of the present invention. FIG. 1 is a schematic block diagram of a conventional induction heating cooker. In the figure, 1 is a variable input circuit, 2 is a variable drive frequency circuit, 3 is a phase detection circuit, 4 is a peak current detection circuit, 5 is a microcomputer, 5a is a variable input circuit control section, 5
b is a sweep command section, 5C is a resonance frequency detection section, 5d is a memo section 9, 5e is a discrimination section, 6 is a heating coil, 7 is a resonance capacitor, 8 is an inverter drive circuit, 9 is a metal container, 1
0 is a current transformer, and 11 is an inverter circuit. Earth 1 Map 27 (0) R1 Heating Fill Odata Ll Near DQ Fuinoshi no Ishita 2 Terjin R2', 4 Mouse Table of Contents J Daikage 2 Diagram FB) Yusonji 11 Makimi 4 Diagram

Claims (1)

[Scope of Claims] In an induction heating cooker in which a heating coil is arranged that generates an eddy current in a metal container to heat an object to be heated stored in the metal container, based on the current flowing through the heating coil, Resonant frequency detection means for detecting a resonant frequency in a state in which a heating coil and a metal container are electromagnetically coupled or in a no-load state; 1. An induction heating cooker characterized by having a determination means for determining the determination and determining the material of the metal container.