JPH01143187A - Complex cooking apparatus - Google Patents

Abstract

PURPOSE:To ensure safety at the time of electromagnetic induction heating by detecting input current to an inverter circuit, judging whether a load is proper or not via comparison between the detected value and a set value, and stopping the operation of the inverter circuit when the load is judged to be improper. CONSTITUTION:When an electromagnetic induction heating process is under way, a microcomputer 62 makes a comparison between a computed value on the basis of output from a bridge rectifier 81 and a set value for detecting a load, and judges whether the load is proper or not. And when the computed value is equal to or less than the set value, the microcomputer 62 judges that the load is improper and immediately stops the operation of an inverter circuit 30. According to the aforesaid system, it is possible to ensure safety at the time of electromagnetic induction heating without causing any cost increase and difficult adjustment work.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a composite cooking device that enables high-frequency dielectric heating as a microwave oven and electromagnetic induction heating as an electromagnetic cooker.

(Prior Art) Recently, a composite cooker equipped with an inverter circuit and capable of high-frequency dielectric heating as a microwave oven and electromagnetic induction heating as an electromagnetic cooker has been developed and is being put into practical use.

In such a composite cooker, during electromagnetic induction heating, it is necessary to determine whether the load pot is appropriate, and if it is inappropriate, immediately stop the operation of the inverter circuit to ensure safety.

(Problem to be solved by the invention) Therefore, it is possible to provide a load detection circuit like a general electromagnetic cooker, but the load detection circuit has a large number of parts, is expensive, and is difficult to adjust. There is a problem.

This invention was made in view of the above circumstances,
The objective is to provide a highly reliable composite cooker that can ensure sufficient safety during electromagnetic induction heating without increasing costs or requiring difficult adjustments. It is in.

[Structure of the Invention] (Means for Solving the Problems) A means for detecting the input current to an inverter circuit, and a means for determining whether the load is suitable by comparing the detected current with a set value during electromagnetic induction heating. and means for stopping the operation of the inverter circuit when the determination result is inappropriate.

(Function) During electromagnetic induction heating, if the input terminal to the inverter circuit is below the set value, the load is judged to be inappropriate and the operation of the inverter circuit is stopped.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

In FIG. 2, reference numeral 1 denotes a main body of the composite cooking device, which has a door 2 pivotably supported on the front surface so as to be freely openable and closable, and a top plate 3 on the upper surface.

A heating chamber (not shown) is provided in the main body 1 corresponding to the door 2, and a magnetron 44 (described later) is installed in the heating chamber.
High frequency radio waves are supplied from Furthermore, a turntable (not shown) for placing food is provided in the heating chamber.

Inside the main body 1 corresponding to the top plate 3, a heating coil 50, which will be described later, is arranged spaced apart and facing the lower surface of the top plate 3.
is provided.

A corner portion where the front surface and the top surface of the main body 1 are connected serves as an operating section 4. This operation section 4 is sloped for easy viewing and operation, and includes a tack plate key 5 for setting electromagnetic induction heating, a range key 6 for setting high frequency dielectric heating, and a key 6 for setting output. Up key 7, Down key 8 for output setting, Start key 9, Cancel key 10,
A time setting knob 11 and a display 12 are provided.

The control circuit is shown in FIG.

20 is a commercial AC power supply, and a fuse 21 is connected to the power supply 20.
Door switch 22a1 A door monitor switch (short switch) 22C is connected via door switch 22b and magnetron thermal 23.

A heating indoor lighting lamp (interior lamp) 24 is connected to the power source 20 via a fuse 21, a door switch 22a1, a relay contact 72a1, a main relay contact 71a1, a door switch 22b1, and a magnetron thermal 23. A turntable drive motor 25 is connected in parallel to the heating indoor lighting lamp 24.

A blower motor 26 for cooling the magnetron and heating coil is connected to the power supply 20 via a fuse 21, a door switch 22a1, a main relay contact 71a1, a door switch 22b, and a magnetron thermal 23.

Furthermore, the power supply 20, a fuse 21, a door switch 22
a1 main relay contact 71a1 door switch 22b,
Inverter circuit 30 via magnetron thermal 23
is connected.

The inverter circuit 30 includes a diode bridge 31, a choke coil 32 . It has a rectifier circuit consisting of a smoothing capacitor 33, and one end of each of the primary coil 40a and heating coil 50 of the high voltage transformer 40 is connected to the output end of the rectifier circuit. Then, the other end of the secondary coil 40 is connected to one end of the resonant capacitor 34 via the normally closed side of the relay contact (bidirectional contact) 73a, and the other end of the resonant capacitor 34 is connected to the other end of the rectifier circuit. are doing. Further, the other end of the heating coil 50 is connected to one end of the resonant capacitor 34 via the normally open side of the relay contact 73a.

In other words, when the relay contact 73a is not activated, the negative coil 4
A series resonant circuit is formed by Oa and the resonant capacitor 34. When relay contact 73a is activated, heating coil 50 and resonant capacitor 34 form a series resonant circuit.

The resonant capacitor 34 includes a switching element such as NP.
The collector and emitter of the N-type power transistor 35 are connected in parallel, and a damper diode (flywheel) 36 is connected in parallel. Note that the power transistor 35 and damper diode 36 are packaged into one.

The power transistor 35 excites the resonant circuit by turning on and off, thereby causing the primary coil 40a to
Alternatively, a high frequency current is caused to flow through the heating coil 50.

The anode and cathode of the magnetron 44 are connected to the secondary coil 40b of the high voltage transformer 40 via a voltage doubler rectifier circuit consisting of a high voltage capacitor 41 and high voltage diodes 42 and 43. The anode of the magnetron 44 is grounded, and the heater (cathode) is connected to the high voltage transformer 40.
is connected to the secondary coil 40c.

On the other hand, a primary coil of a step-down transformer 27 is connected to the power source 20 via a fuse 21 and a magnetron thermal 23, and a control unit 60 is connected to the secondary coil.

The control unit 60 controls the entire cooking device, and includes a power supply circuit 61, a microcomputer 62, a relay drive circuit 63, a D/A (digital/analog) converter 64, a timing circuit 65, an oscillation circuit 66, and a pulse width modulation circuit. A comparator 67 which is a circuit (PWM circuit),
It has a base drive circuit 68.

Relay drive circuit 63 drives main relay 71 and relays 72 and 73.

The D/A converter 64 issues an output setting signal of a voltage level corresponding to an output setting command from the microcomputer 62.

The timing circuit 65 is designed to minimize loss due to switching of the inverter circuit 30.
The voltage of the smoothing capacitor 33 and the collector voltage of the power transistor 35 are taken in, and the oscillation timing of the oscillation circuit 66 is determined accordingly.

Oscillator circuit 66 generates a sawtooth signal.

The comparator 67 pulse-width modulates the sawtooth wave signal generated from the oscillation circuit 66 using the output setting signal from the D/A converter 64.

The base drive circuit 68 turns on and off the transistor 35 of the inverter circuit 30 based on the output of the comparator 67.

Thus, the operating section 4 is connected to the microcomputer 62.

Furthermore, a current transformer 80 is provided on the input line to the inverter circuit 30. This current transformer 80
constitutes input current detection means together with a bridge rectifier 81 that rectifies its output, and the output of the bridge rectifier 81 is supplied to the microcomputer 62.

Next, the operation of the above configuration will be explained with reference to FIG.

The pot 51 is placed on the top plate 3, and the tack plate key 5 of the operating section 4 is pressed. Further, a desired cooking time is set using the time setting knob 11, and a desired output is set using the up key 7 or the down key 8.

At this time, the characters "tack plate" are displayed on the display 4, and the set cooking time is displayed numerically. Further, on the display 4, a number of light emitting elements corresponding to the set output light up.

When the start key 9 is pressed, the microcomputer 6
2 operates relays 71.73. When the relay 71 operates, the contact 71a is turned on, and an energizing path to the inverter circuit 30 and the blower motor 26 is formed. relay 7
3 operates, the normally open side of the contact 73a closes and the heating coil 50 is selected.

Furthermore, the microcomputer 62 issues an output setting command based on the above setting output. This output setting command is D/
The A converter 64 converts the output setting signal into an analog value output setting signal, and supplies the signal to the comparator 67.

Further, an oscillation circuit 66 generates a sawtooth wave signal, which is pulse width modulated by a comparator 67.

That is, when the voltage of the output setting signal is higher than the voltage of the sawtooth wave signal, the output voltage of the comparator 67 is at a high level.

When the voltage of the output setting signal is lower than the voltage of the sawtooth signal, the output voltage of the comparator 67 is at a low level.

The output of the comparator 67 is amplified by a base drive circuit 68 and applied between the base and emitter of the power transistor 35.

When the power transistor 35 is turned on, current flows into the heating coil 50 through the collector and emitter of the power transistor 35. When the power transistor 35 is turned off, the current flowing through the heating coil 50 begins to charge the resonant capacitor 34. Then, current flows from the resonant capacitor 34 to the heating coil 50.

In this way, a high frequency current flows through the heating coil 50 by turning on and off the power transistor 35, and a high frequency magnetic field is emitted from the heating coil 50.

The high frequency magnetic field is applied to the pot 51 through the top plate 3, causing eddy currents to be generated in the pot 51. When eddy currents occur,
The pot 51 self-heats due to eddy current loss, and the food inside is heated. In other words, cooking begins.

The timing circuit 65 generates a trigger pulse at the intersection of the voltage of the smoothing capacitor 33 (rectified voltage) and the collector voltage of the power transistor 35, and triggers the oscillation circuit 66. As a result, the power transistor 35 is turned on with its own collector voltage being low, and the switching loss of the power transistor 35 can be reduced.

When the set cooking time has elapsed, the microcomputer 62
stops the operation of relays 71 and 73.

When the operation of the relay 71 stops, the contact 71a turns off,
The energizing path to the inverter circuit 30 is cut off. In other words,
This is the end of cooking.

Meanwhile, place the food on the turntable inside the heating chamber and open the door 2.
At the same time, the range key 6 of the operating section 4 is pressed. Further, a desired cooking time is set using the time setting knob 11, and a desired output is set using the up key 7 or the down key 8.

At this time, the characters "range" are displayed on the display 4, and the set cooking time is displayed numerically.

Further, on the display 4, a number of light emitting elements corresponding to the set output light up.

When the start key 9 is pressed, the microcomputer 6
2 operates relays 71.72.

When relays 71 and 72 operate, contact 71a.

72a is turned on, and the inverter circuit 30. Heating indoor lighting lamp 24. An energizing path is formed between the turntable drive motor 25 and the blower motor 26.

Note that since the relay 73 does not operate, the normally closed side of the contact 73a is closed, and the primary coil 40 of the high voltage transformer 40
a is selected.

Thus, the inverter circuit 30 operates in the same way as electromagnetic induction heating, and a high frequency current flows through the secondary coil 40a. Then, the voltage generated in the secondary coil 40b is voltage doubled and rectified and applied to the magnetron 44, so that the magnetron 44 performs an oscillating operation. When the magnetron 44 oscillates, high-frequency radio waves are supplied into the heating chamber, and high-frequency dielectric heating starts.

When the set cooking time has elapsed, the microcomputer 62
stops the operation of relays 71 and 72.

When the operation of the relay 71 stops, the contact 71a turns off,
The energizing path to the inverter circuit 30 is cut off. In other words,
This is the end of cooking.

By the way, when the inverter circuit 30 is in operation, the input current to the inverter circuit 30 is detected by the current transformer 80, and a DC voltage at a level corresponding to the detected current is supplied from the bridge rectifier 81 to the microcomputer 62.

The microcomputer 62 calculates the average value or actual value of the input current to the inverter circuit 30 from the output of the bridge rectifier 81, and changes the level of the output setting signal when the calculated value becomes smaller than the set value (corresponding to the set output). This increases the on-period of the power transistor 35. Conversely, when the calculated value becomes larger than the set value, the level of the output setting signal is lowered and the on period of the power transistor 35 is shortened.

When the on period of the power transistor 35 becomes longer, the high frequency current flowing through the heating coil 50 or the primary coil 40a becomes larger, and the output increases.

When the on period becomes shorter, the high frequency current flowing through the heating coil 50 or the primary coil 4.0a becomes smaller, and the output decreases.

Therefore, during electromagnetic induction heating, even if the pot 51 is different from a standard pot, the output can be maintained at the set output regardless of the difference. That is, the elements of the inverter circuit 30 are not overloaded, and the life of the elements is improved. Furthermore, proper heating is possible and reliability can be improved.

Furthermore, during high-frequency dielectric heating, the output can be maintained at the set output regardless of temperature changes in the magnetron 44.
Appropriate heating can be performed.

In addition, since the heating coil 50 is connected to the normally open side of the relay contact 73a, for example, if a disconnection failure occurs in the coil of the relay 73, the power to the heating coil 50 is immediately cut off, which is safe. .

By the way, during electromagnetic induction heating, the microcomputer 62
compares the calculated value (average value or actual value of input current) based on the output of the bridge rectifier 81 with the load detection setting value Vs, and determines whether the load is appropriate.

That is, as shown in FIG. 4, a weak output operation for load detection is performed for a time t det from tl to t2 when the start key 9 is pressed. At this time, if there is no pot 51 on the top plate 3, the input current to the inverter circuit 30 is small, and the output voltage of the bridge rectifier 81 is
The level is low as shown in the figure. Furthermore, if an inappropriate aluminum pot is placed on the top plate 3, or a small metal object such as a fork or knife is placed on the top plate 3, the input current to the inverter circuit 30 will still be small.
The output voltage of the bridge rectifier 81 becomes a low level as shown in FIG.

The microcomputer 62 sets a set value Vs for load detection.
The set value Vs is initially maintained at a low level. Then, the calculated value of the input current and the set value Vs are compared at time t2, and if the calculated value is lower than the set value Vs, it is determined that the load is inappropriate.

After that, the same (
Weak output operation for load detection is repeated for tdet time. Note that this weak output is set to a value that does not cause small items such as forks and knives to generate heat.

Assume, however, that the proper pot has already been placed at time t3, which is between time t2 and time t4.

At this time, the input current to the inverter circuit 30 increases in accordance with the weak output operation at time t2, and the bridge rectifier 81
The output voltage becomes a high level as shown in FIG.

In this way, when the calculated value exceeds the set value Vs at time t5, the microcomputer 62 gradually increases the level of the output setting signal to the target value corresponding to the set output,
Start substantial electromagnetic induction heating.

Note that the non-operating tol'f' time is set to about 1.5 seconds to 2 seconds, which does not feel unnatural to the user. Also, t of'f' time of non-operation and t d of weak output operation.
The ratio to et time is set to such an extent that small items such as forks and knives are not heated.

At the start of heating, as the output increases, the inverter circuit 30
The input current to increases. At this time, the microcomputer 62 causes the set value Vs to follow the increase in the calculated value.

Then, when the output reaches the set output and stabilizes (time t6), the set value Vs at that time is maintained as it is.

When the user shifts the pot on the top plate 3 at time t7 during cooking, the state approaches a state where there is no pot, and the input current to the inverter circuit 30 decreases.

When the input current becomes smaller (when the calculated value becomes smaller), the microcomputer 62 tries to increase the level of the output setting signal by performing the original output control. However, this is an attempt to forcibly increase the output even in a nearly no-load state, and this results in stress (overvoltage) being applied to the power transistor 35 of the inverter circuit 30.

At this time, however, since the set value Vs is maintained at a high value, the calculated value quickly falls below the set value Vs as the input current becomes smaller. When the calculated value becomes less than or equal to the set value Vs, the microcomputer 62 determines that the load is inappropriate and immediately stops the operation of the inverter circuit 30. Therefore, problems such as stress being applied to the transistor 35 can be prevented.

In this way, when there is no pot 51 on the top plate 3,
If small metal objects such as forks or knives are placed, or if an unsuitable aluminum pot is placed, it is automatically detected and electromagnetic induction heating is not performed. It is safe because the elements of the circuit 30 are not overloaded. Also, a fork and a knife.

Unnecessary heating of empty cans, etc. can be prevented, and the user will not get burned.

In particular, since the microcomputer 62, which controls the entire cooker, determines whether the load is appropriate, it is only necessary to provide the current transformer 80 and the bridge rectifier 81 as components for detecting the load. The number of points is small and the cost is low. Moreover, difficult adjustments are not required.

Substantially, the current transformer 80 and the bridge rectifier 81, which are input detection means for output control, are also used, so the cost is very low.

In addition, since the set value Vs for load detection is made to follow the increase in input current after the start of heating, and the operation of the inverter circuit 30 is immediately stopped when the pot 51 is moved, the power transistor 35 of the inverter circuit 30 is No stress is applied, and damage to the power transistor 35 can be prevented.

Note that the present invention is applicable not only to a composite cooker capable of high-frequency dielectric heating and electromagnetic induction heating, but also to a general electromagnetic cooker dedicated to electromagnetic induction heating.

In addition, the present invention is not limited to the above-mentioned embodiments, and various modifications can be made without changing the gist.

[Effects of the Invention] As described above, according to the present invention, there is provided a means for detecting the input current to the inverter circuit, and a method for determining whether the load is appropriate by comparing the detected current with a set value during electromagnetic induction heating. Since the method is provided with a means and a means for stopping the operation of the inverter circuit when the determination result is inappropriate, there is no increase in cost or the need for difficult adjustments.
It is possible to provide a highly reliable composite cooker that can ensure sufficient safety during electromagnetic induction heating.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a control circuit in an embodiment of the present invention, FIG. 2 is an external perspective view of the same embodiment, and FIG.
Diagrams showing the voltage waveforms of each part in the figure, Figures 4 to 7
Each figure is a diagram for explaining the operation of the same embodiment. DESCRIPTION OF SYMBOLS 1...Main body, 2...Door, 3...Top plate, 4...Operation unit, 30...Inverter circuit, 40...
... High voltage transformer, 44... Magnetron, 50...
- Heating coil, 60...control unit, 80...current transformer. Applicant's agent Patent attorney Takehiko Suzue Figure 2 Time opening -m-- Figure 3 7゛Pano; l :MJ# 8 i output 77 voltage ridge adjustment 5 rough 1 81 output 77 voltage grff darkness - ya Fig. 5 time □ Fig. 6 time M - Fig. 7

Claims (4)

[Claims] (1) In a composite cooker equipped with an inverter circuit and capable of performing high-frequency dielectric heating and electromagnetic induction heating, a means for detecting the input current to the inverter circuit, and a means for detecting the input current to the inverter circuit and a set value between the detected current and the set value during electromagnetic induction heating. A composite cooking appliance characterized by comprising means for determining whether the load is appropriate by comparison, and means for stopping the operation of the inverter circuit when the result of this determination is inappropriate. (2) The composite cooking device according to claim 1, wherein the set value follows an increase in the detected current after the start of electromagnetic induction heating. (3) The composite cooking appliance according to claim 1 or 2, wherein the means for detecting the input current also serves as an input current detecting means for output control. (4) It has a relay that switches between high-frequency dielectric heating and electromagnetic induction heating, and the primary coil of a high-voltage transformer for high-frequency dielectric heating is connected to the normally closed side of the relay contact, and the heating coil for electromagnetic induction heating is connected to the normally open side of the relay contact. A composite cooking device according to claim 1, 2, or 3, characterized in that: