JPH07274527A - Induction heating cooker - Google Patents

Abstract

PURPOSE:To make a precise output control available under the condition of the ceiling frequency even if the ceiling value is set on the operating frequency of a switching device, a driving circuit of the switching device, etc., when the output is controlled by controlling the frequency. CONSTITUTION:The reference voltage Vref' which is obtained by amplifying the reference voltage Vref, the output of a reference voltage generator 15, by an amplifier 19, and a chopping wave for duty control which is output from a chopping wave generator 20 are compared with each other by a duty controller 21. A duty controlling signal is so output to driving circuits 13, 14 of switching transistors 10, 12 through AND gates 18a, 18b that the operation may be continued when the Vref' is higher than the chopping wave for duty control and the operation is stopped when the Vref' is lower than the chopping wave of duty control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency induction heating cooker in which the output of an inverter is adjusted by frequency control.

[0002]

2. Description of the Related Art Heretofore, in this type of cooker, it has been widely adopted to adjust its output, that is, the output of an inverter by frequency control. By the way, when cooking for a long time while keeping the output of the cooker extremely small, noise is generated due to the operation of the switching element and the drive circuit of the switching element, and power consumption increases, so the operating frequency has an upper limit. It is usually set. For this reason, conventionally, an induction heating cooker has been proposed in which the output is adjusted by duty control for changing the time ratio between operation and operation stop within the range of the upper limit value of this frequency (Japanese Patent Publication Sho 55). -15955, H02M
5/27).

[0003]

However, in the above-mentioned conventional technique, the operating frequency of the inverter is detected, and the duty controller operates and stops the cooker based on this frequency, which causes a problem that the circuit scale becomes large. there were. The present invention has been made in view of such circumstances,
It is an object of the present invention to provide an induction heating cooker which does not require frequency detection and enables fine output adjustment by duty control with a small-scale circuit configuration.

[0004]

In an induction heating cooker according to the present invention, a resonance circuit including a heating coil is connected to a commercial power source via a switching element which is controlled to be turned on and off by a drive circuit. If the operating frequency of the switching element is within a predetermined range, a circuit that controls the drive circuit to adjust the output of the heating coil accordingly, and if the operating frequency exceeds a predetermined range, supply of power to the heating coil and stop of power supply. In an induction heating cooker comprising a duty controller for controlling the drive circuit so as to perform a duty control that alternately alternates a detector with a detector that detects an input power value from the commercial power source to the resonance circuit, and the detector. A reference voltage generator that generates a reference voltage based on the detected input power value and the set power value, and a reference voltage generated by the reference voltage generator is a predetermined operating frequency. A voltage-frequency converter for converting the frequency to a frequency corresponding to the range and a constant frequency when the reference voltage is outside the predetermined range, the voltage-frequency converter and the duty controller A drive circuit that controls the switching element to be turned on and off based on the output of the switching element, and a vibration wave generator that outputs a periodic vibration wave for duty control, and the duty controller has the reference voltage outside a predetermined range. When the reference voltage is compared with the periodic vibration wave generated by the vibration wave generator when the reference voltage exceeds the periodic vibration wave, power is supplied to the heating coil. It is characterized in that each of the drive circuits is controlled so as to cut off the power supply to the heating coil in the case of less than the target vibration wave.

[0005]

In the present invention, in the range where the reference voltage generated by the reference voltage generator exceeds a predetermined voltage, the voltage-frequency converter performs frequency conversion according to the voltage value, and the reference voltage is Below a predetermined voltage, the voltage-frequency converter converts the voltage value to a predetermined frequency, and the output of the heating coil is adjusted at each of these frequencies, while the duty controller controls the reference voltage and the periodic oscillatory wave generator. The generated vibration wave is compared, and operation is performed in the range where the reference voltage exceeds the vibration wave, and duty control is performed to suspend the operation in the range where the reference voltage is less than the vibration wave.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is an electric circuit diagram showing the configuration of an induction heating cooker according to the present invention, in which 1 is a three-phase power line,
3 is a feedback diode, and 7 is a heating coil.
The three-phase power supply line 1 is connected to a feedback diode 3, and a high frequency bypass capacitor 4, a series circuit of a pair of capacitors 5 and 6 and a series circuit of switching transistors 10 and 12 are connected in parallel to the feedback diode 3. The heating coil 7 is connected between the capacitors 5 and 6 and between the switching transistors 10 and 12. An oscillation circuit is constituted by the heating coil 7 and the capacitors 5, 6, and the feedback diode 3,
An inverter is composed of the capacitors 4, 5 and 6.

The bases of the switching transistors 10 and 12 are connected to the drive circuits 13 and 14, and the feedback diodes 9 and 1 are provided between the collectors and the emitters, respectively.
0 is connected with its cathode side to the emitter side and its anode side to the collector side. A reference voltage generator 15 has a set power value based on a detected power value from the input power detecting current transformer 2 provided in each of the three-phase power supply lines 1 and a set power value set by a setter (not shown). Is higher than the detected power value, a high reference voltage V _ref is set to reduce the operating frequency, and when the set power value is smaller than the detected power value, a lower reference voltage V _{ref is} set to increase the operating frequency.
Is output to the duty controller 21 via the voltage-frequency converter 16 and the amplifier 18.

FIG. 2 is a graph showing the relationship between the output p of the heating coil 7 and the operating frequency f, with the operating frequency f on the horizontal axis.
, And the output p is plotted on the vertical axis. As is clear from this graph, in order to increase the output p, the operating frequency f
It can be seen that the operating frequency f may be set high in order to reduce the output power p and reduce the output p. Voltage-frequency converter 1
6 is determined upper limit value of the frequency to be converted, the reference is the voltage V _ref performs frequency conversion to a value corresponding to s reference voltage V _ref husband entered in a range exceeding the predetermined voltage value V _ref1, the reference The frequency conversion value f ₁ is set to be constant in the range where the voltage V _ref is equal to or lower than the predetermined voltage value V _ref1 .

FIG. 3 is a graph showing the relationship between the reference voltage V _ref input to the voltage-frequency converter 16 and the conversion frequency. The horizontal axis represents the reference voltage V _ref and the vertical axis represents the operating frequency f. Is shown. As is apparent from this graph, frequency conversion corresponding to the reference voltage V _ref is performed in the range where the reference voltage exceeds V _ref1 , but it is understood that the frequency f ₁ is constant at the upper limit value in the range below V _ref1 .

The signal frequency-converted by the voltage-frequency converter 16 is output to the two-phase divider 17, and the two-phase divider 17 is supplied.
Is input to one of the input ends of the AND gates 18a and 18b. The output (duty control signal) from the duty controller 21 is input to the other input terminals of the AND gates 18a and 18b.

The amplifier 19 has a reference voltage V_refPredetermined
A value amplified by a predetermined amplification factor, that is, V _ref′ Is the reference voltage
Then, this is output to the duty controller 21. Figure 4
(A) is an explanatory view showing the amplification factor of the amplifier 19, and is a reference
Voltage V_refThe amplification factor for V is shown in FIG._ref1Amplifies
Reference voltage V_ref'Is output from the triangular wave generator 20
The duty control triangle wave maximum value.
Is determined.

The duty controller 21 compares the reference voltage V _ref ′, which is the output of the amplifier 19, with the output of the triangular wave generator 20, and the amplified reference voltage V _ref ′ is used for duty control as shown in FIG. 4B. When it is higher than the triangular wave, a high level duty control signal is output, and when the reference voltage V _ref ′ is lower than the maximum value of the duty controlling triangular wave as shown in FIG. _{When the ref} 'is high, when the duty control triangular wave is high, the low level duty control signals are output to the other input terminals of the AND gates 18a and 18b, respectively.

The AND gates 18a and 18b have an input power detecting current transformer 2 from the two-phase divider 17 at one input end thereof.
A high-level signal or a low-level signal is input according to the polarity of the detected power, and the duty control signal from the duty controller 21 is input to the other input end. Drive circuit 13,
When a high-level signal is input from the AND gates 18a and 18b, 14 outputs a predetermined signal to each base of the switching transistors 10 and 12 to control it on, and when a low-level signal is input. The other signals are output to the bases of the switching transistors 10 and 12 to turn them off.

Next, the operation of such a device of the present invention will be described. Now, if the set power to the reference voltage generator 15 is increased to increase the output of the heating coil 7 and the set power value is decreased to decrease the output of the heating coil, the reference voltage generator 15 detects the set power value and the input power detection. The reference voltage V _ref is generated based on the power detected by the current transformer 2.

That is, as shown in FIG. 2, the operating frequency f is decreased to increase the output p, conversely the operating frequency f is increased to decrease the output p, and the operating frequency is decreased as shown in FIG. To increase the reference voltage V _ref and conversely increase the operating frequency, the reference voltage V _ref may be decreased. Therefore, when the output p is increased, the reference voltage generator 15 has a large reference voltage to decrease the operating frequency f. V
_{When ref} is decreased, and conversely, when the output p is decreased, a small reference voltage V _ref is output to increase the operating frequency f.
The voltage-frequency converter 16 outputs a small frequency conversion output for a large reference voltage V _ref , and a small reference voltage V _ref .
_{For ref} , a large frequency conversion output is output in the relationship shown in FIG. The output from the voltage-frequency converter 16 is input to the AND gates 18a and 18b via the two-phase divider 17.

On the other hand, the duty controller 21 compares the duty controlling triangular wave output from the triangular wave generator 20 with the amplified reference voltage V _ref ′ output from the amplifier 19, and the reference voltage V _ref is V _{ref. In the} range larger than _{ref1, the} relationship shown in FIG. 4 (b) is established, so a high-level signal is output to the AND gates 18a, 18b. From the AND gates 18a, 18b, the input power detecting current transformer 2 is output. A high level signal or a low level signal corresponding to the polarity of the detected power value is output to each drive circuit 13, 14. Each drive circuit 13 and 14 gives a signal corresponding to each to the bases of the switching transistors 10 and 12, and controls ON / OFF of the switching transistors 10 and 12 to perform continuous operation at the output p according to the conversion frequency value.

FIG. 5 shows switching transistors 10 and 1.
2 is an explanatory diagram of the operation of FIG. 2, and when the switching transistor 10 is turned on, the current I _L flowing in the resonance circuit of the capacitors 5 and 6 and the heating coil 7 passes through the switching transistor 10 as shown in FIG. An electric current flows. When the switching transistor 10 changes from the ON state to the OFF state, an induced electromotive force is generated in the heating coil 7, but at this time, the current I _L flows through the diode 10 as shown in FIG. 5 (b).

At this time, the switching transistor 12 is turned on, but the direction of the current I _L is opposite and no current flows through the switching transistor 12. On the other hand, when the polarity changes, the switching transistor 12 is turned on, so that the current I _L flows through the switching transistor 12 as shown by an arrow in FIG. 5C.

When the switching transistor 12 changes from the ON state to the OFF state, an induced electromotive force is generated in the heating coil 7. At this time, the current I _L flows through the diode 9 as shown in FIG. 5 (d). , Does not flow to the switching transistor 10.

On the other hand, the reference voltage V_refIs the voltage as shown in Fig.
The frequency converter 16 has an upper limit frequency f ₁Voltage value V
_ref1If the following occurs, the duty controller 21 is activated.
Energize the heating coil 7, that is, operate and heat
De-energizing the coil 7, that is, stopping the coil 7 for a predetermined time ratio
The duty control is performed alternately with.

The switching from the continuous operation state to the duty control operation state is performed by amplifying the reference voltage V _ref so that the reference power V _ref ′ which is non-inverted and amplified by the amplifier 19 has a relationship shown in FIG. 4 (a). Since the ratio is set, when the reference voltage V _ref becomes smaller than the voltage value V _ref1 that becomes the upper limit frequency f ₁ , the duty control triangular wave and the amplified reference voltage V _ref ′ are as shown in FIG. 4 (c). Therefore, the duty control is automatically switched to a high level signal in a range where the duty control triangular wave is lower than the reference voltage V _ref ′ from the duty controller 21, and a low level signal in a range where the duty control triangular wave is high. Are output respectively.

High-level or low-level signals are output from the AND gates 18a and 18b, respectively. When high-level signals are output, the switching transistors 10 and 12 are polarized via the drive circuits 13 and 14, respectively. Accordingly, the switching transistor 10 is turned on and off alternately to enter the operating state. On the other hand, when the low level signal is output, the switching transistor 10 and
Both 12 are turned off, and the operation is stopped.

As is apparent from FIG. 4 (c), the reference voltage V
_{As ref} ′ becomes lower, the area below the duty control triangle wave becomes wider, and conversely, the area above the duty control triangle wave becomes narrower, and the ratio of operation time / operation time + stop time becomes smaller and the output p is reduced. Therefore, even if the reference voltage V _ref ′ is in the range of V _ref1 or less, the output p can be precisely controlled. In the embodiment, the duty control triangular wave is used as the object to be compared with the reference voltage V _ref ′ by the duty controller 21, but the present invention is not limited to this, and for example, a oscillating wave that periodically changes such as a sine wave may be used. Of course, it is good.

[0024]

As described above, in the induction heating cooker according to the present invention, when the upper limit value of the operating frequency is set, the periodic vibration wave and the reference power value are set even in the range exceeding the upper limit value. According to the present invention, there is no need to detect the frequency of the input power as in the conventional case, and the output can be finely adjusted with a simple configuration.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing a relationship between an operating frequency f and an output p.

FIG. 3 is an explanatory diagram of a conversion operation of the voltage-frequency converter.

FIG. 4 is an operation explanatory diagram of a duty controller.

FIG. 5 is an operation explanatory diagram of a switching element and an inverter.

[Explanation of symbols]

 1 Three-Phase Power Line 2 Input Detection Current Transformer 3 Feedback Diode 4 Capacitor 5,6 Capacitor 7 Heating Coil 8 Heated Object 9,10 Diode 10,12 Switching Transistor 13,14 Drive Circuit 15 Reference Voltage Generator 17 2 Phase division circuit 19 Amplifier 20 Triangular wave generator 21 Duty controller

Claims (1)

[Claims] 1. A resonance circuit including a heating coil is connected to a commercial power source through a switching element which is controlled to be turned on and off by a drive circuit, and the operating frequency of the switching element responds to this within a predetermined range. And a circuit for controlling the drive circuit to adjust the output of the heating coil, and a drive circuit for performing duty control for alternately supplying power to the heating coil and stopping power supply when the operating frequency exceeds a predetermined range. In an induction heating cooker including a duty controller, a detector that detects an input power value from the commercial power source to the resonance circuit, and a reference based on the input power value and the set power value detected by the detector A reference voltage generator for generating a voltage and a frequency corresponding to the reference voltage generated by the reference voltage generator if the reference voltage is within a range corresponding to the predetermined range of the operating frequency. A voltage-frequency converter that converts to a constant frequency when the reference voltage is out of a predetermined range,
The duty control includes: a drive circuit that turns on and off the switching element based on outputs of the voltage-frequency converter and the duty controller; and a vibration wave generator that outputs a periodic vibration wave for duty control. The device compares the periodic oscillatory wave generated by the oscillatory wave generator with the reference voltage when the reference voltage is out of a predetermined range, and the heating coil when the reference voltage exceeds the periodic oscillatory wave. The induction heating cooker is configured to control the drive circuits to supply power to the heating coil and to cut off power supply to the heating coil when the reference voltage is less than the periodic vibration wave.