JP6779369B2 - Electromagnetic induction heating cooker - Google Patents

Description

The present invention relates to an electromagnetic induction heating cooker.

Conventionally, an induction heating cooker that forms a pot holder for arranging a pot for holding food in a magnetic field generated by an electromagnetic induction heating coil, and induces heating the pot placed in the pot holder to perform cooking. There is. In such an induction heating cooker, a magnetic field is generated by energizing an electromagnetic induction heating coil to generate an induced electromotive force in a pot, and the pot itself is heated to perform cooking.
That is, in such an electromagnetic induction heating cooker, a load current is generated due to the presence of a pot serving as a resistance load in the magnetic field generated by the induction heating coil, and the pot generates heat to perform cooking. Is.

In such an electromagnetic induction heating type heating cooker, there is no resistance load in the magnetic field generated by the electromagnetic induction heating coil, that is, when the pot that becomes the load resistance is not arranged in the pot holder. It is in a load state and no load current is generated.
Conventionally, using such a phenomenon, it is detected whether or not a load current is generated when the electromagnetic induction heating coil is energized, and when the load current cannot be detected, a pot is placed in the pot holder. It is controlled to stop the heating operation by judging that there is no such thing.
Then, as a method for detecting the presence or absence of this load current, there is a method using a low-frequency AC detecting means having a current transformer (for example, Patent Document 1).

Japanese Patent No. 3314124

However, in the method of detecting the presence or absence of such a load, it is necessary to use a current transformer, and the configuration of the electric circuit becomes complicated. Further, since a current transformer is used, there is a problem that the parts constituting the electric circuit become expensive.

The present invention is for solving the above-mentioned problems, and provides an electromagnetic induction heating cooker capable of detecting the presence or absence of a load without using a current transformer.

In order to solve the above problems, in the electromagnetic induction heating cooker, an inverter circuit provided with a pot holder, an electromagnetic induction heating coil for generating a magnetic field in the pot holder, and a switching element to supply power to the electromagnetic induction heating coil. The timing output circuit that generates the output control timing waveform of the inverter circuit from the input voltage and the voltage of the switching element, the input voltage fluctuation detection circuit that detects the fluctuation of the input voltage and generates the input voltage fluctuation waveform, and the input voltage. It is equipped with a load detection circuit that detects the load based on the fluctuation waveform and the output control timing waveform, and a main control circuit that determines whether or not the pot is placed on the pot holder based on the load detection. The load detection circuit performs load detection based on the input voltage fluctuation waveform during which the output control timing waveform is at the High level among the input voltage fluctuation waveforms, and the switching element is turned off in the output control timing waveform. The high level is configured during the period during which the regenerative current is not flowing through the switching element .

According to the present invention, among the input voltage fluctuation waveforms, the load detection is performed based on the input voltage fluctuation waveform whose output control timing waveform is between the High levels, so that the presence or absence of a load can be accurately determined without using a current transformer. An electromagnetic induction heating cooker that can be detected well can be provided.

The block diagram which shows the structure of the electric circuit S of the electromagnetic induction heating cooker which concerns on Embodiment 1. A graph showing an operation waveform when there is a pan during the heating operation of the electromagnetic induction heating cooker according to the first embodiment. A graph showing an operation waveform when there is no pot during the heating operation of the electromagnetic induction heating cooker according to the first embodiment. Perspective view of the electromagnetic induction heating cooker according to the second embodiment AA sectional view of FIG. 4

Embodiment 1.
The first embodiment will be described with reference to FIGS. 1 to 3.
FIG. 1 is a block diagram showing a configuration of an electric circuit S of an electromagnetic induction heating cooker.
The commercial low-frequency AC power supply 1 is connected to the full-wave rectifier circuit 2. The output of the full-wave rectifier circuit 2 is smoothed by a smoothing capacitor 3 and a choke coil (not shown).

The smoothed output passes through an electromagnetic induction heating coil 4 for high-frequency induction heating, and is connected to a parallel circuit including a resonance capacitor 5, a switching element 6, and a diode 7 connected in series with the electromagnetic induction heating coil 4. These constitute an inverter circuit that converts direct current into alternating current, and supplies electric power to the electromagnetic induction heating coil 4. In the magnetic field generated by the electromagnetic induction heating coil 4 that receives electric power from the inverter circuit, a pot holder P for arranging the pot N for holding the cooked food is provided inside.

Next, the switching element 6 is controlled by the switching control circuit 10. The switching control circuit 10 is connected to the main control circuit 11 and is controlled by a switching control signal from the main control circuit 11. The main control circuit 11 has a microprocessor and a memory, and is a main control circuit that controls the heating operation of the electromagnetic induction heating cooker, controls various notifications, and controls each of the above parts.

Next, the timing output circuit 12 and the input voltage detection circuit 14 are connected to the smoothing capacitor 3 via the resistor 8. Then, the input voltage detected by the input voltage detection circuit 14 is input to the main control circuit 11 to detect the power supply voltage level of commercial low-frequency AC. The timing output circuit 12 is also connected to the collector terminal of the switching element 6, and the collector-emitter voltage Vce of the switching element 6 changes from 0V or 0V based on the power supply voltage of commercial low-frequency AC. The timing is detected, an output control timing waveform is generated, and the output control timing waveform is input to the main control circuit 11. The voltage detection circuit 13 is connected to the collector terminal of the switching element 6, detects the collector-emitter voltage Vce of the switching element 6, and inputs it to the main control circuit 11.

An input voltage fluctuation detection circuit 9 that detects fluctuations in the input voltage and generates an input voltage fluctuation waveform is connected to the smoothing capacitor 3. Then, the input voltage fluctuation waveform from the input voltage fluctuation detection circuit 9 and the output control timing waveform from the timing output circuit 12 are input to the load detection circuit 15. The load detection circuit 15 detects the presence or absence of a load current based on the input voltage fluctuation waveform from the input voltage fluctuation detection circuit 9 and the output control timing waveform from the timing output circuit 12. Then, the main control circuit 11 determines the presence / absence of the pot in the pot holder P based on the detection signal of the presence / absence of the load current from the load detection circuit 15.

Although not shown, the main control circuit 11 adjusts the pulse width of the switching control signal by the operation input to the operation unit provided in the electromagnetic induction heating cooker, and selects the strength of heating. Alternatively, the strength of heating is controlled to be constant or the strength is changed by a built-in control program. Further, the main control circuit 11 determines the presence or absence of the pan based on the detection signal from the load detection circuit 15, and controls the strength or stop of heating.

FIG. 2 shows the operation waveforms of the electromagnetic induction heating cooker with a pot during the heating operation, which are (a) collector-emitter voltage Vce of the switching element, (b) output control timing waveform, and (c) switching element, respectively. The current, (d) input voltage fluctuation waveform, and (e) switching element drive signal are shown. The state with a pot is a state in which the pot N is placed on the pot holder P.

Upon receiving the switching control signal from the main control circuit 11, the switching control circuit 10 outputs a switching element drive signal. When the switching element drive signal is ON (High level), the switching element 6 becomes conductive and the switching element current Ic flows. While the switching element 6 is conducting, the collector-emitter voltage Vce of the switching element 6 is 0V.

When the switching element drive signal is turned OFF (Low level) by the switching control circuit 10 that receives the switching control signal from the main control circuit 11, the switching element current Ic does not flow, while the collector-emitter voltage Vce of the switching element 6 Begins to rise. The collector-emitter voltage Vce of the switching element 6 generated at this time changes in magnitude in proportion to the switching element current Ic that flows when the switching element 6 is ON.

The timing for turning off the switching element 6 is controlled by the main control circuit 11 depending on the strength of heating. The period of the collector-emitter voltage Vce of the switching element 6 is determined by the reactance component of the electromagnetic induction heating coil 4 and the pot for induction heating, and the resonance frequency of the resonance capacitor 5.

The collector-emitter voltage Vce of the switching element 6 becomes 0V in a period determined by the resonance frequency. The timing when the collector-emitter voltage Vce of the switching element 6 changes from 0V and the timing when the voltage becomes 0V is detected, and the timing output circuit 12 detects the output control timing synchronized with the collector-emitter voltage waveform of the switching element 6. A waveform is generated and input to the main control circuit 11.

The main control circuit 11 that detects the falling edge of the output control timing waveform, that is, the collector-emitter voltage Vce of the switching element 6 becomes 0V, outputs a switching control signal after a certain period of time, and the switching control circuit 10 Turns on the switching element drive signal.

As for the switching element current Ic, when the collector-emitter voltage Vce of the switching element 6 becomes 0V, the regenerative current Ir by the inverter circuit flows in the opposite direction. This regenerative current is for a certain period from when the collector-emitter voltage Vce of the switching element 6 becomes 0V until the main control circuit 11 outputs the switching control signal and the switching control circuit 10 turns on the switching element drive signal. It is desirable that the Ir is settled.

The input voltage fluctuation waveform fluctuates in proportion to the magnitude of the switching element current Ic. When the switching element 6 is turned on, the switching element current Ic flows. The switching element current Ic is supplied from the current stored in the commercial low-frequency alternating current power supply 1 and the smoothing capacitor 3. At this time, the current supplied from the smoothing capacitor 3 is supplied to the smoothing capacitor 3 from the commercial low-frequency AC power supply 1 during the period B when the switching element 6 is turned off.

In the period (B) when the switching element 6 is OFF, in addition to the period (C) in which the collector-emitter voltage Vce of the switching element 6 is generated, a certain period (D) until the switching element drive signal is turned on. Is included. During this fixed period (D), the regenerative current Ir is generated, and the regenerative current Ir from the resonance capacitor 5 flows into the smoothing capacitor 3, so that the input voltage fluctuation waveform becomes large. After that, the current is gradually stored in the smoothing capacitor 3 and the input voltage is smoothed, so that the input voltage fluctuation waveform does not change.

The load detection circuit 15 uses the output control timing waveform, and while the output control timing waveform is at the LOW level (the period when it is turned off), the input voltage fluctuation waveform is dropped to LOW, so that the regenerative current Ir flows (H). ) And the input voltage fluctuation during the period (I) when the switching element 6 is ON are not detected, and the input voltage fluctuation during the period (C) is input to the main control circuit 11. .. That is, the load detection is performed based on the size of the area K of the input voltage fluctuation waveform during the high level (ON period) of the output control timing waveform.

Next, a state in which the pot N is not placed on the pot holder P will be described. FIG. 3 shows the operation waveforms of the electromagnetic induction heating cooker of the present invention without a pot during the heating operation, which are (a) collector-emitter voltage Vce of the switching element, (b) output control timing waveform, and (b), respectively. c) Switching element current, (d) Input voltage fluctuation waveform, and (e) Switching element drive signal are shown. Note that no pot means that the pot N is not placed on the pot holder P.

The size of the input voltage fluctuation waveform changes in proportion to the switching element current Ic when the switching element 6 is turned on. Therefore, in the state without the pot N, the input voltage fluctuation waveform is smaller than in the state with the pot N. The load detection circuit 15 uses the output control timing waveform, and while the output control timing waveform is at the LOW level (the period when it is turned off), the input voltage fluctuation waveform is dropped to LOW, so that the regenerative current Ir flows (L ) And the period (M) in which the switching element 6 is ON, the input voltage fluctuation amount is not detected, and the input voltage fluctuation amount during the period (N) is input to the control circuit. That is, the load is detected by the area Q of the input voltage fluctuation waveform while the output control timing waveform is at the High level (period of being turned ON).

As described above, when performing load detection to determine the presence or absence of pot N, while the output control timing waveform is at the LOW level, the input voltage fluctuation waveform is dropped to LOW, so that the period during which the regenerative current Ir flows and the switching element The input voltage fluctuation waveform is configured so as not to detect the input voltage fluctuation during the period when 6 is ON, and the input voltage fluctuation waveform during the period when the regenerative current Ir is not flowing and the switching element 6 is OFF. Since the load is detected by the area Q (integrated value), the influence of the fluctuation of the input voltage due to the regenerative current Ir can be reduced.

That is, during the period when the regenerative current Ir is not flowing and the switching element 6 is OFF, there is a large difference in the input voltage fluctuation waveform when the pot N is present and when the pan N is not present. It is possible to make an accurate judgment and improve the accuracy of load detection. In the actual load detection judgment, if the area Q and the area K are larger than a certain threshold value X, it is determined that there is a load (there is a pot N), and if it is less than the threshold value X, there is no load (pot). There is no N). The threshold value X is set to a value between the value of the area Q and the value of the area K.

Embodiment 2.
The second embodiment will be described with reference to FIGS. 4 and 5. FIG. 4 is a perspective view of the electromagnetic induction heating cooker 50 provided with the electric circuit S of the first embodiment. FIG. 5 is a cross-sectional view taken along the line AA of FIG. The same configuration as that of the first embodiment is designated by the same reference numerals and the description thereof will be omitted.

The electromagnetic induction heating cooker 50 has a main body 51, a lid 52, and a pot N. A pot holder P is formed on the main body 51. The pot holder P is a recess that opens upward in the main body 51, and is configured to be able to store the cooked food in a state where the pot N holds the cooked food inside.

The lid 52 is attached to the main body 51 with its rear end portion axially supported so as to open and close the opening of the pot holder P of the main body 51. When the lid 52 is open with respect to the main body 51, the pot N can be attached to and detached from the pot holder P. Further, in a state where the pot N is provided in the pot holder P and the lid 52 is closed with respect to the main body 51, the pot N is covered with the main body 51 and the lid 52, and is an electromagnetic induction heating cooker. It is held inside the 50.

Therefore, the pot N is held inside the electromagnetic induction heating cooker 50 in a state where the electromagnetic induction heating cooker 50 cannot be visually recognized from the outside. That is, in such an electromagnetic induction heating cooker 50, when the lid 52 is closed with respect to the main body 51, it is possible to recognize from the outside whether or not the pot N is provided inside the main body 51. It becomes impossible.

Next, an electromagnetic induction heating coil 4 constituting the electric circuit S is provided below the pot holder P and inside the main body 51. The electric circuit S has a power plug 51a. The power plug 51a is led out to the outside of the main body 51, and the electromagnetic induction heating cooker 50 obtains electric power by connecting to the commercial low-frequency AC power supply 1.

Further, the bottom surface of the pot N provided in the pot holder P is located in the magnetic field generated by the electromagnetic induction heating coil 4. That is, the pot N is induced and heated by the change of the magnetic field generated by the electromagnetic induction heating coil 4, and the cooked food held inside can be cooked. Further, an electric circuit S is provided inside the main body 51.

By configuring each part as described above, the presence or absence of load detection can be determined more accurately, and the accuracy of load detection can be improved. Therefore, the pot N is placed inside the electromagnetic induction heating cooker 50. It is possible to accurately determine whether or not it is held. Therefore, even if the user forgets to put the pot N in the electromagnetic induction heating cooker 50 and starts the heating operation, the load can be detected accurately, the state without the pot N is detected, and the heating is useless. The cooking operation can be stopped. The electromagnetic induction heating cooker 50 of the present embodiment includes, for example, an electric rice cooker for cooking rice or an electric cooking pot for cooking simmered dishes.

1 Commercial low frequency AC power supply, 2 Full wave rectifier circuit, 3 Smoothing capacitor, 4 Electromagnetic induction heating coil, 5 Resonant capacitor, 6 Switching element, 7 Diode, 8 Resistance, 9 Input voltage fluctuation detection circuit, 10 Switching control circuit, 11 Main control circuit, 12 Timing output circuit, 13 Voltage detection circuit, 14 Input voltage detection circuit, 15 Load detection circuit, N pot, P pot holder, S electric circuit, 50 Electromagnetic induction heating cooker, 51a power plug.

Claims (4)

The pot holder and
An electromagnetic induction heating coil that generates a magnetic field in the pot holder,
An inverter circuit equipped with a switching element and supplying electric power to the electromagnetic induction heating coil,
A timing output circuit that generates an output control timing waveform of the inverter circuit from the input voltage and the voltage of the switching element, and
An input voltage fluctuation detection circuit that detects fluctuations in the input voltage and generates an input voltage fluctuation waveform, and
A load detection circuit that performs load detection based on the input voltage fluctuation waveform and the output control timing waveform.
Based on the load detection, a main control circuit that determines whether or not a pot is placed in the pot holder, and
With
The load detection circuit performs the load detection based on the input voltage fluctuation waveform whose output control timing waveform is among the input voltage fluctuation waveforms during the High level .
The output control timing waveform is an electromagnetic induction heating cooker that reaches a high level during a period in which the switching element is OFF and a period in which a regenerative current does not flow through the switching element . The main control circuit according to claim 1, wherein said output control timing waveform when the integral value of the input voltage fluctuation waveform between the High level is above the threshold, it is determined that the pot to the pot every part is placed electromagnetic induction heating cooker according to. A switching control circuit that gives a drive signal to the inverter circuit,
A voltage detection circuit for detecting the voltage of the switching element is further provided.
The electromagnetic induction heating cooker according to claim 1 or 2 , wherein the main control circuit gives a switching control signal for controlling the switching control circuit. It has a main body and a lid,
The pot holder is formed on the main body.
The electromagnetic induction heating cooker according to any one of claims 1 to 3 , wherein the lid body is attached to the main body so as to open and close the pot holder.

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