JPH09257256A - Induction heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To retain resonance while following the fluctuation of a composite resonance frequency. SOLUTION: A driving circuit 4 supplies a high-frequency power to a resonance circuit 1. An output detecting circuit 5 detects the output of the resonance circuit 1 and a control circuit 8 controls the frequency of the high-frequency power based on the detecting signal of the output detecting circuit 5. The condition of resonance is maintained as much as possible while following the change of a composite resonance frequency by the frequency control effected by the control circuit 8. According to this method, the efficiency of induction heating is improved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an induction heating device.

[0002]

In the conventional induction heating device, a resonance circuit is formed by arranging an induction heating coil and a capacitor in parallel, and a high frequency current is applied to the induction heating coil by utilizing the resonance phenomenon of the resonance circuit. And a cooking utensil made of iron or stainless steel is placed above the induction heating coil to perform induction heating. In this case, the composite resonance frequency of the resonance circuit is determined by the characteristics of the induction heating coil and the capacitor, the material such as the load of the cooking utensil, the shape or size of the cooking utensil, and the heating temperature of the cooking utensil. . The output characteristic of the resonance circuit is a mountain-shaped curve that maximizes the output around a certain frequency. Therefore, the optimum frequency of resonance in the resonance circuit is the maximum value of the frequency-output characteristic of the resonance circuit. Frequency.
Therefore, the frequency as shown by a characteristic curve A in FIG. 4 - when the frequency of the maximum output value of the output characteristic is obtained in the resonant circuit is f _a, when supplying a high-frequency current having a frequency f _a to the resonant circuit, that is heated Optimal heating can be efficiently realized when the oscillation frequency of the current supplied to the resonance circuit for driving is made to coincide with the composite frequency. However, when the cooking utensil is placed on the induction heating coil, the combined resonance frequency of the resonance circuit is a value f _b different from the resonance frequency f _a before the cooking utensil is placed, as shown by the characteristic curve B in FIG. Changes to.

As described above, in order to efficiently perform induction heating of the cooking utensil, the oscillation frequency of the current supplied to the resonance circuit for heating drive may be made to coincide with the composite resonance frequency of the resonance circuit. However, when actually using an induction heating device,
Since cooking utensils having different materials, shapes, and sizes are placed on the induction heating coil, the combined impedance changes each time. In addition, since the temperature of the cooking utensil changes during use, the synthetic resonance frequency deviates from the initially set oscillation frequency, and there is a problem that the cooking utensil cannot be efficiently induction-heated.

The present invention has been made in view of the above points, and it is possible to efficiently induction-heat a pot by matching the oscillation frequency of the current supplied to the resonance circuit with the combined resonance frequency as much as possible. Another object of the present invention is to provide a simple induction heating device.

[0005]

An induction heating device according to claim 1 of the present invention is a resonance circuit having an induction heating coil and a capacitor, a drive circuit for supplying high-frequency power to the resonance circuit, and the resonance circuit. An output detection circuit for detecting the output,
A control circuit that generates a frequency signal based on the detection signal of the output detection circuit and supplies the frequency signal to the drive circuit to control the frequency of the high frequency power.

With this structure, even if the composite resonance frequency is changed by placing cooking utensils having different materials, shapes, sizes, etc. on the induction heating coil, the temperature of the cooking utensil changes due to use. Even if the combined resonance frequency changes, the resonance circuit can always be driven in the resonance state by feeding back the strength of the output of the induction heating coil to the control means to control the oscillation frequency of the high frequency power. Therefore, the resonance state is maintained as much as possible by following the change in the composite resonance frequency by the frequency control by the control circuit.

Further, in the induction heating device of the present invention according to claim 2, in addition to the configuration of claim 1, the control circuit changes the frequency in time series to decrease the output value of the resonance circuit from an increase. Is determined as the resonance frequency, and when the output value decreases as a result of first varying the frequency by a predetermined amount, the frequency is returned to twice the predetermined amount, and
It is characterized in that the frequency variation and the resonance frequency are determined based on the detected output values of the induction heating coils at three points.

With this configuration, it becomes possible to drive the resonance circuit in a resonance state quickly and to drive it.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, 1 is a resonance circuit,
The induction heating coil 2 and the capacitor 3 are arranged in parallel. Reference numeral 4 is a drive circuit for supplying the resonance circuit 1 with a drive current of a high frequency pulse shown as T2 in FIG.
Reference numeral 5 denotes an output detection circuit provided near the induction heating coil 2. The output detection circuit 5 is electromagnetically connected to the induction heating coil 2 and is an output signal of the induction heating coil 2 shown as T3 in FIG. Output detection element 6 for detecting the size of
And a smoothing circuit 7 for smoothing the output signal of the output detection element 6 shown as T4 in FIG. As shown in FIG. 5, the output detection element 6 has a frequency equal to the high frequency current flowing in the induction heating coil 2 by electromagnetic induction,
In addition, the high-frequency AC signal having the strength according to the strength change of the output of the induction heating coil 2 is output. The smoothing circuit 7 smoothes the high frequency AC signal output from the output detection element 6 into a DC signal T5 and outputs the DC signal T5, as shown in FIG. 8 is a control circuit, which is based on the output level from the smoothing circuit 7,
The control signal T1 shown in FIG. 5 is supplied to the drive circuit 4.
Reference numeral 9 is a rectifier circuit that rectifies and smoothes the AC current of the AC power supply 10. Reference numeral 11 is an operation switch, and 12 is a setting switch for setting the heat power, the operation time, and the like. Reference numeral 13 is a cooking device such as a pot, a kettle, or a frying pan made of iron or stainless steel.

When the cooking utensil 13 is placed above the induction heating coil 2 and the operation switch 11 is operated, the control circuit 8 generates an initial frequency signal F _o as shown in step S1 of FIG. Step S2 shown as P1 in FIG.
Then, the initial frequency signal F _o is supplied to the drive circuit 4 as a control signal. This initial frequency signal F _o is a pulse signal of frequency f _o . The drive circuit 4 supplies a drive current I _o of a high frequency pulse having a frequency f _o based on the initial frequency signal F _o . The frequency f _o is set to a sufficiently lower frequency than the combined resonant frequency f _b of the cooking apparatus 13 and the resonance circuit 1. When the drive current I _o flows through the resonance circuit 1, a high frequency alternating current having the same frequency as the drive current flows through the induction heating coil 2, and the output of the induction heating coil 2 is detected by the output detection element 6. This output signal T4 is an alternating current in this case the frequency f _o, the analog output signal T which was smoothed
The control circuit 8 converts the signal 5 into a digital signal X _o , and the signal level is detected. When it is determined to be equal to or less than a certain value the signal level in step S3, the control circuit 8 frequency signals F ₁ frequency f ₁ plus Δf is a positive value f _o at step S4 To generate. The above operation repeated t times, it compares the signal level of the digital signal X _t is equal to or greater than the certain value a signal level of X _t at step S5 and before one sampling of the digital signal X _t-1 signal level. At this time, if X _t ≧ X _t−1 , the frequency f _t of the frequency signal F _t generated next in step S4 is set to f
Set higher than _t-1 . The above operation is sequentially repeated in time series, and when X _t <X _t−1 in step S5,
In step S6, the frequency f _t of the frequency signal F _t generated next is set to be lower than f _t-1 . In step S7, the control circuit 8 determines that this frequency f _t is the combined resonance frequency f _b of the resonance circuit 1 and the cooking device 13, and supplies the frequency signal F _t to the drive circuit 4 for a certain period of time. After the elapse of a certain time, the control circuit 8 restarts the control of the frequency signal in step S8. This time,
Since the temperature of the cooking utensil 13 changes due to heating, the combined resonance circuit impedance also changes, and the combined resonance frequency f
_b has moved to the combined resonance frequency f _b ′ of the characteristic curve C in FIG. After detecting the output of the induction heating coil 2, the control circuit 8 generates the frequency signal F _t of the frequency f _t shown in the following equation in step S9 in FIG.

[0011]

[Equation 1]

Next, in step S10, the frequency signal F _t is supplied to the drive circuit 4 to drive the induction heating coil 2 and its output is detected. Here, if X _t ≧ X _t−1 in step S11, the control circuit 8 proceeds to step S12.
At, a frequency signal F _t having a frequency f _t shown in the following equation is generated.

[0013]

[Equation 2]

These series of operations are repeated in time series according to step S13, and X _t <
If it is X _t-1 , the frequency signal F _t of the frequency f _t shown in the following equation is generated in step S15.

[0015]

(Equation 3)

The control circuit 8 uses this frequency f _t as the resonance circuit 1
And the composite resonance frequency f _b ′ of the cooking device 13 is determined, and the frequency signal F _t is supplied to the drive circuit 4 for a certain period of time in step S16. On the other hand, when X _t <X _t−1 in step S11, the frequency f _{t expressed by the} following equation is calculated in step S17.
To generate a frequency signal F _t .

[0017]

(Equation 4)

Then, through step S18, step S
In X 19, X _t is compared with X _t-2 , and if X _t ≧ X _t-2 , a frequency signal F _t having a frequency f _t shown in the following equation is generated in step S20.

[0019]

(Equation 5)

These series of operations are repeated in time series according to step S21, and X _t <X _{t-1 in} step S22.
If so, the frequency signal F _t of the frequency f _t shown in the following equation is generated in step S23.

[0021]

(Equation 6)

The control circuit 8 proceeds to step S15 and determines that this frequency f _t is the combined resonance frequency f _b ′ of the resonance circuit 1 and the cooking device 13 and supplies the frequency signal F _t to the drive circuit 4 for a certain period of time. . When X _t <X _t-1 and X _t <X _t-2 , it is determined that X _t and X _t-1 are located at positions sandwiching the resonance frequency f _b ′, and shown by the following equation. A frequency signal F _t having a frequency f _t is generated.

[0023]

(Equation 7)

The above control is repeated to make the frequency f of the frequency signal F coincide with the synthetic resonance frequencies f _{b to} f _b ′,
The resonance circuit 1 is kept in a resonance state.

Thus, as shown in the above embodiment, the resonance circuit 1 having the induction heating coil 2 and the capacitor 3,
A drive circuit 4 for supplying a high-frequency current to the resonance circuit 1,
An output detection circuit 5 that detects the output of the resonance circuit 1 and a control circuit 8 that controls the frequency of the high-frequency power based on the detection signal of the output detection circuit 5 are provided to follow changes in the composite resonance frequency. The resonance state can be maintained as much as possible, and highly efficient induction heating is possible. Therefore, even if the composite resonance frequency changes by placing the cooking utensils 13 having different materials, shapes, sizes, etc. on the induction heating coil 2, the control circuit 8 controls the output strength of the induction heating coil 2.
By controlling the oscillating frequency of the drive current by feeding back to the resonance circuit 1, the resonance circuit 1 can be driven in the resonance state as much as possible, and the cooking utensil and the food to be cooked therein can be efficiently heated.

Further, the frequency at which the output value of the resonance circuit 1 changes from increasing to decreasing is determined as the resonance frequency by changing the frequency in time series, and the output value decreases as a result of first changing the frequency by a predetermined amount. In this case, the frequency is returned twice as much as the fluctuation amount, and the fluctuation of the frequency and the judgment of the resonance frequency are performed based on the detected output values of the induction heating coils at three points, so that the resonance circuit 1 resonates promptly. You can

The present invention is not limited to the above embodiment, and various modifications can be made. For example, although the initial frequency f _o is set to a frequency sufficiently lower than the resonance frequency f _a and the combined resonance frequency f _b, it may be set to a sufficiently high frequency. In this case, if X _t ≧ X _t−1 , the frequency signal F _t having the frequency ft _expressed by the following equation is generated.

[0028]

(Equation 8)

If X _t <X _t-1 , the frequency signal F _t having the frequency f _t shown in the following equation is generated.

[0030]

[Equation 9]

Further, although the magnitude of the current flowing through the induction heating coil 2 is detected in the above embodiment, the voltage may be detected.

[0032]

The induction heating device according to the first aspect of the present invention detects a resonance circuit having an induction heating coil and a capacitor, a drive circuit for supplying high frequency power to the resonance circuit, and an output of the resonance circuit. An output detection circuit and a control circuit that generates a frequency signal based on a detection signal of the output detection circuit and supplies the frequency signal to the drive circuit to control the frequency of the high frequency power are configured. If
By making the oscillation frequency of the current supplied to the resonance circuit as close as possible to the combined resonance frequency, it becomes possible to efficiently induction-heat the pot.

Further, in the induction heating device according to a second aspect of the present invention, in addition to the configuration according to the first aspect, the control circuit changes the frequency in time series so that the output value of the resonance circuit decreases from an increase. Is determined as the resonance frequency, and when the output value decreases as a result of first varying the frequency by a predetermined amount, the frequency is returned to twice the predetermined amount, and
It is characterized in that the fluctuation of the frequency and the judgment of the resonance frequency are performed based on the detected output values of the induction heating coil at three points. In this case, not only the action and effect of claim 1 but also the resonance circuit can be realized. It becomes possible to drive the device in a resonance state promptly.

[Brief description of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a flow chart of the same control.

FIG. 3 is a flow chart of the same control.

FIG. 4 is a graph showing the characteristics of the above resonance circuit.

FIG. 5 is a graph showing an output signal of the same.

[Explanation of symbols]

 1 Resonance Circuit 2 Induction Heating Coil 3 Capacitor 4 Drive Circuit 5 Output Detection Circuit 8 Control Circuit

Claims (2)

[Claims] 1. A resonance circuit having an induction heating coil and a capacitor, a drive circuit for supplying high-frequency power to the resonance circuit, an output detection circuit for detecting an output of the resonance circuit, and a detection signal of the output detection circuit. And a control circuit for controlling the frequency of the high frequency power by supplying the frequency signal to the drive circuit. 2. The control circuit determines the frequency at which the output value of the resonant circuit changes from increasing to decreasing as a resonant frequency by varying the frequency in time series, and at the same time, the control circuit first varies the frequency by a predetermined amount. When the output value is reduced, the frequency is returned to twice the predetermined amount, and the frequency variation and the resonance frequency are determined based on the detected output values of the induction heating coils at the three points. The induction heating device according to claim 1.