KR900007381B1 - Electromagnetic heating cooker - Google Patents

Abstract

a resonance circuit including an induction heat coil and a resonance capaccitor; an inverter for generating high freq. magnetic field from the induction heat coil by supplying high freq. power to the resonance circuit and inducting an eddy current to an object; data providing means for controlling an inverter power level according to the relation between the high freq. power from the inverter and the repulaive force of the object and preventing the object floated on the plate surface; and a control means for feeding back the inverter power level control data to the inverter.

Description

Induction heating cooker

3A to 3D show a first embodiment of the present invention.

1 is a general block diagram.

2 is a block diagram of the main part

3A to 3D are graphs for explaining a power source voltage change and a frequency change.

4 is a general block diagram illustrating a second embodiment of the present invention corresponding to FIG.

5 is a graph showing the relationship between the power of the inverter and the repulsive force acting on the object to be heated.

6 to 8a to 8d show a third embodiment of the present invention.

6 is a general block diagram.

7 is a block diagram of the main part.

8A to 8D are graphs for explaining the power source voltage change and the frequency change.

FIG. 9 is a general block diagram showing a fourth embodiment of the present invention corresponding to FIG.

* Explanation of symbols for main parts of the drawings

1: DC power source 2: AC power source

3: choke coil 4: full-wave rectifier

6 resonant circuit 7 induction coil

10, 11: transistor 12: inverter

13: inverter controller 19: power change circuit

20: state determination circuit 21: F-V converter

22: sample-hold circuit 26: reference value setting circuit

32: comparator 33: power control circuit

35: courage.

The present invention relates to an electromagnetic induction heating apparatus capable of preventing an undesired state of a cooking utensil or a container, and more particularly, to induce electromagnetic induction to heat an object to be heated such as a cooking vessel according to a vortex current loss generated. Relates to a device.

In a conventional induction heating apparatus, an induction heating coil is constructed under an upper plate on which an object to be heated, such as a cooking vessel, is to be placed. The high frequency current is supplied to the induction heating coil by the inverter, and the high frequency magnetic field is applied to the cooking vessel so that the vortex current flows through it, thereby heating the cooking vessel.

In this type of induction heating apparatus, the cooking vessel receives a repulsion effect because the current flowing through the induction heating coil has a phase opposite to the vortex current flowing through the cooking vessel. When the cooking vessel is made of a magnetic material such as iron, the cooking vessel is attracted to the magnetic force generated by the magnetic field from the coil, and as a result, the repulsive force acting on the cooking vessel is reduced.

However, when the cooking vessel is made of a nonmagnetic material such as aluminum (Al), the attraction force due to the magnetic force becomes small. Since the Al cooking vessel has a small characteristic permeability and surface resistance, a large vortex current must flow through the Al vessel to form an input resistance with respect to the induction heating coil like the iron cooking vessel. Therefore, the repulsive force acting on the Al cooking vessel increases undesirably. As a result, when the total weight of the Al container and the material to be heated therein is small, the container is often floated from the top plate. If this state is left unchanged, the heating efficiency is considerably reduced and good induction heating cannot be performed. In the worst case, the vessel is moved along the top plate.

5 shows the relationship between the power [W] of the inverter and the repulsive force [g] acting on the vessel. In this case, the vessel is formed of Al, the number of turns of the induction heating coil is 80 times, the frequency is 50 KHz, and the distance between the vessel and the heating coil is 6 mm. As can be seen from FIG. 5, the repulsive force is increased in proportion to the power of the inverter. More specifically, as the output increases, the container is likely to float from the top plate.

In order to solve the above problem, a detection mechanism is required to detect whether the container is floating from the top plate. For example, in a detection technique, a detection element for detecting a change in magnetic flux flux density such as a hool element or a detection coil may be used. In this case, the change in the magnetic flux flux density can often not be detected depending on the position of the detection element, resulting in insufficient detection reliability. In this technique, since the magnetic flux density to be detected varies depending on the power of the inverter, the detection circuit configuration is complicated.

Accordingly, it is an object of the present invention to provide reliable and relatively easy prevention when the total weight of the object to be heated and the material to be cooked therein is small and the object is floated from the top plate by the repulsive force from the induction heating coil. Similarly, it is to provide a novel and improved electromagnetic induction heating apparatus capable of preventing undesirable conditions of cookware or vessels.

According to the present invention, there is provided an electromagnetic induction heating apparatus capable of preventing an undesired state of a cookware or a container, which includes a top plate for placing an object to be heated, such as a cookware or a container, and a bottom plate. A resonant circuit having an induction heating coil configured to and a resonant capacitor connected to the coil, and an inverter circuit for supplying high frequency power to the resonant circuit to generate a high frequency magnetic field from the induction heating coil and inducing a vortex current to an object to be heated. The inverter power level control data is output in accordance with the inverter means and the high frequency power from the inverter circuit and the repulsive force acting on the object to be heated according to the harmonic power, and the inverter power level control data is the level of the high frequency power from the inverter circuit. To control the object to be heated Inverter power level control data generating means, which is data which can prevent floating from the position surface of the upper plate, and control means for feeding back the inverter power level control data from the control data generating means to the inverter circuit. .

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

1 to 3, a first embodiment of the present invention will now be described. Referring to FIG. 1, reference numeral 1 denotes a DC power source. The power source 1 is made by connecting the choke coil 3, the full wave rectifier 4 and the smoothing capacitor 5 to the AC power source 2. Reference numeral 6 denotes a resonant circuit composed of an induction coil 7 and a resonant capacitor 8 for heating an object to be heated. The induction coil 7 is configured below the lower surface of the top plate 9 to place therein the object to be heated. Reference numerals 10 and 11 denote first and second switching transistors. The transistors 10 and 11 are connected to the resonant circuit 6 to constitute the inverter 12 as shown in FIG. Reference numeral 13 denotes an inverter controller. The controller 13 has an inverter drive circuit 14, a phase detection circuit 15, and a voltage controlled oscillator (VCO) 15-1. The inverter drive circuit 14 alternately turns on / off the switching transistors 10 and 11. The phase detection circuit 15 receives the output from the instrument transformer 16 in the resonant circuit 6 and feeds back the control inverter drive circuit 14 through the VCO 15-1. More specifically, the inverter driving circuit 14 controls the on / off timing of the transistors 10 and 11 based on the oscillation output from the VCO 15-1 in accordance with the phase comparison output, whereby the inverter 12 Control the output frequency. As a result, the resonant circuit 6 is controlled to maintain the frequency (resonant frequency) to be set for the object whose resonance state is to be heated.

를 검출하여, 인버터 전력 레벨 제어 데이타 및 그 검출 결과에 따라서 출력 에러 검출 신호 S

를 생성한다.As shown in FIG. 5, the power change that changes the power of the inverter 12 for a predetermined period of time and generates inverter power level control data according to the relationship between the inverter power and the repulsive force to the cooking vessel as described later. The circuit is indicated by reference numeral 19. The output from the power change circuit 19 is connected to the gate electrode of the switching thyristor 18. The main electrode of the switching thyristor 18 is connected to the DC power source 1 as shown in FIG. The power change circuit 19 phase-controls the gate of the thyristor 18 for a given period at power-on to change the output voltage from the DC power source 1, thereby powering the inverter 12 for a predetermined period of time. Change from low power to high power. The power change circuit 19 outputs the high level sampling timing signal st to the state determination circuit 20 when setting the power of the inverter 12 to low power. Determination circuit 20 is the resonant frequency of resonant circuit 6 through transformer 16.

Is detected and the output error detection signal S depends on the inverter power level control data and the detection result.

Create

를 검출하여, 이 검출된 주파수를 전압으로 변환시키는 F-V 변환기를 나타낸다. F-V 변환기(21)는 검출될 주파수를 연산증폭기(23)의 비반전 입력단자(+) 및 또한 비교기(32)(이후 설명됨)의 반전 단자(-)에 공급한다. 샘플-홀드 회로(22)는 연산증폭기(23), 아날로그 스위치(24) 및, 메모리 커패시터(25)를 갖는다. 아날로그 스위치(24)의 게이트 단자는 회로(19)가 저전력 제어모드에 있을때 전력 변화 회로(19)로부터 하이 레벨 샘플링 타이밍 신호 St를 수신한다. 메모리 커패시터(25)는 회로(19)가 저전력 제어모드에 있을 때 샘플-홀드 전압 Vs로서 공진회로(6)의 공진주파수 f, 즉 초기 주파수 f₀에 대응하는 출력전압 Vp 성분을 샘플링 및 홀링시킨다. 참조부호(26)는 연산증폭기(27), 다이오드(28)및, 저항(29,30,31)을 구비하는, 기준값 설정 회로를 나타낸다. 기준값 설정회로(26)는 샘플-홀드 전압 Vs로부터 기준전압 Vk를 감하는 것에 의해 얻어진 초기 설정 전압 Vh를 출력시킨다. 기준전압 Vk는 저항(30,31)의 전압 제산비로 다이오드(28)의 정방향 바이어스 전압을 제산함으로써 얻어진 전압이다. 기준전압 Vh는 코일(7)로부터의 반발력으로 인한 상단 플레이트(9)로부터 가열될 물건의 플로우팅에 의해 발생된 공진회로(6)의 공진주파수에서의 변화에 대한 소정의 값 f_s(제3도참조)에 대응하는 값으로 설정된다. 회로(26)로부터 출력된 초기 설정 전압 Vh는 비교기(32)의 비반전 입력단자(+)에 공급된다. 비교기(32)의 반전 단자(-)는 F-V 변환기(21)로부터 검출전압 Vp를 수신한다.In FIG. 2, the state determination circuit 20 is shown in detail. Reference numeral 2l denotes the resonant frequency of the resonant circuit 6 according to the output from the transducer 16.

Denotes an FV converter that converts the detected frequency into a voltage. The FV converter 21 supplies the frequency to be detected to the non-inverting input terminal (+) of the operational amplifier 23 and also to the inverting terminal (-) of the comparator 32 (described later). The sample-hold circuit 22 has an operational amplifier 23, an analog switch 24, and a memory capacitor 25. The gate terminal of the analog switch 24 receives the high level sampling timing signal St from the power change circuit 19 when the circuit 19 is in the low power control mode. The memory capacitor 25 samples and holds the resonant frequency f of the resonant circuit 6, that is, the output voltage Vp component corresponding to the initial frequency f ₀ as the sample-hold voltage Vs when the circuit 19 is in the low power control mode. . Reference numeral 26 denotes a reference value setting circuit having an operational amplifier 27, a diode 28, and resistors 29, 30, and 31. The reference value setting circuit 26 outputs the initial setting voltage Vh obtained by subtracting the reference voltage Vk from the sample-hold voltage Vs. The reference voltage Vk is a voltage obtained by dividing the forward bias voltage of the diode 28 by the voltage division ratio of the resistors 30 and 31. The reference voltage Vh is a predetermined value f _s for the change in the resonant frequency of the resonant circuit 6 generated by the floating of the object to be heated from the upper plate 9 due to the repulsive force from the coil 7 (third Value). The initial set voltage Vh output from the circuit 26 is supplied to the non-inverting input terminal (+) of the comparator 32. The inverting terminal (-) of the comparator 32 receives the detected voltage Vp from the FV converter 21.

Therefore, when the detected voltage Vp is higher than the initial set voltage Vh, that is, when the voltage change Vs-Vp corresponding to the frequency change is equal to or less than the reference voltage Vk corresponding to the predetermined value f _s , the comparator 32 is low. Outputs the (LOW) level signal. When the detected voltage Vp is lower than the initial voltage Vh, that is, when the voltage change Vs-Vp corresponding to the frequency change exceeds the reference voltage Vk corresponding to the predetermined value f _s , the comparator 32 is high. The level error detection signal Se is output and supplied to the power control circuit 33. When the power control circuit 33 receives the signal Se, it forcibly turns off the switching thyristor 18 to stop the power output of the inverter 12.

), 여기서 L은 유도 코일(7)의 인덕턴스, C는 커패시터(8)의 커패시턴스). 이때, 전력 변화 회로(19)로부터의 샘플링 타이밍 신호 St는 상태 결정회로(20)의 아날로그 스위치(24)에 공급된다.The effect of the above configuration will now be described. An example in which the cooking vessel 35 is formed of iron as an object to be heated will be described with reference to FIGS. 3A and 3B. 3a and 3b show the power change of the inverter 12 and the frequency change of the resonant circuit 6. After the container 35 is placed on the top plate 9 as an object to be heated, the power change circuit 19 cycles when turning on the power switch or a switch (both not shown) for detecting the state of the container 35. Phase control of the Lister 18 sets the inverter 12 in a low power mode for a predetermined period of time. Therefore, the resonance circuit 6 is set to the resonance frequency f corresponding to the container 35 (f = 1/2 (2π +)

), Where L is the inductance of the induction coil (7), C is the capacitance of the capacitor (8). At this time, the sampling timing signal St from the power change circuit 19 is supplied to the analog switch 24 of the state determination circuit 20.

는 제3b도에 도시된 바와같이 공진주파수 f1까지 감소한다. 그러나, 주파수 변화는 작다. 그러므로, 변화 f1은 소정의 값 foo보다 더 크고, 따라서 주파수 변화(fo-f1)는 소정의 값 f_s이하이다. 결정회로(20)에서의 검출전압 Vp는 초기 설정 전압 Vh보다 더 높다. 결국, 비교기(32)의 출력단자는 결정회로(20)에의해 로우레벨에서 유지된다. 이 상태에서, 에러 검출신호 Se가 출력되지는 않는다.As a result, the resonant frequency f of the resonant circuit 6, that is, the sample-hold voltage Vs corresponding to the initial voltage f ₀ in the low power mode, is sampled and held by the sample-hold circuit 22 of the circuit 20. The reference voltage Vk (corresponding to the predetermined value f _s for the frequency change) is subtracted from the sample-hold voltage Vs to determine the initial set voltage Vh. The frequency corresponding to the voltage Vh is indicated as foo in FIG. 3B. When the power mode of the inverter 12 is continuously changed by the power change circuit l9 from the low power mode to the high power mode, the repulsive force from the coil 7 to the container 35 increases. When the container 35 is formed of iron, its weight is large, and the container 35 is made of magnetic material. Therefore, the attraction force from the coil 7 to the container 35 is increased. Eventually, the repulsive force is canceled by the attraction force and virtually small. The container 35 is thus located on the top plate 9 in a fixed state. In this case, the resonant frequency of the resonant circuit 6

Decreases to the resonant frequency f1 as shown in FIG. 3B. However, the frequency change is small. Therefore, the change f1 is greater than the predetermined value foo, so the frequency change fo-f1 is less than or equal to the predetermined value f _s . The detection voltage Vp in the determination circuit 20 is higher than the initial set voltage Vh. As a result, the output terminal of the comparator 32 is held at the low level by the decision circuit 20. In this state, the error detection signal Se is not output.

가 fo'로 지시되어 있다. 이 경우에서 샘플-홀드 전압이 Vs'로 주어진다면, 초기설정 전압은 전압 Vs'로부터 기준전압 Vk를 감하는 것에 의해 얻어진 전압 Vh'이다. 초기 설정 전압 Vh'에 대응하는 주파수는 주파수 foo'로 주어진다. 이 경우에서, 인버터(l2)의 전력모드가 전력 변화 회로(19)에 의해 저전력 모드로부터 고전력 모드로 변화될 경우, 코일(7)로부터의 반발력은 상술된 제5도로부터 볼수 있듯이 증가한다. 코일(7)로부터 A1과 같은 비자성 물질로 형성된 용기(35)로의 인력은 작아지고, 용기(35)와 그안에서 조리될 물질의 전체 무게에 따라서 용기(35)가 플로우팅 될 수 있다. 그러나, 이 경우에 있어서 용기(35)가 플로우팅될 경우 용기(35)와 유도코일(7)간의 틈이 증가되는데, 즉 자력 선속 누설이 커지게 되고 코일(7)의 인덕턴스 L이 증가된다. 그 결과로서, 공진 주파수

의 변화(fo'-f2)가 제3D에서 소정의 값 f_s를 초과한다(foo'＞f2). 결국, 결정회로(20)에서의 검출전압 Vp'는 초기 설정 전압 Vh'보다 더 작게되고, 에러 검출신호 Se가 출력된다. 따라서, 용기(35)가 플로우팅 상태에 있다는 것이 검출된다. 에러 검출신호 Se는 전력제어회로(33)에 공급된다. 전력제어회로(33)는 강제적으로 스위칭 싸이리스터(18)를 오프시키고 인버터(12)로부터의 전력 출력을 중단시킨다.Referring to FIGS. 3C and 3D, an example will be described in which the container 35 is made of a material that is relatively non-magnetic and has a relatively small weight, such as aluminum. In this case, the resonance frequency when the inverter 12 is set in the low power mode by the power change circuit 19.

Is indicated by fo '. In this case, if the sample-hold voltage is given by Vs', the initialization voltage is the voltage Vh 'obtained by subtracting the reference voltage Vk from the voltage Vs'. The frequency corresponding to the initial set voltage Vh 'is given by the frequency foo'. In this case, when the power mode of the inverter 12 is changed from the low power mode to the high power mode by the power change circuit 19, the repulsive force from the coil 7 increases as can be seen from FIG. 5 described above. The attractive force from the coil 7 to the container 35 formed of a nonmagnetic material such as A1 becomes small, and the container 35 can be floated according to the total weight of the container 35 and the material to be cooked therein. However, in this case, when the container 35 is floated, the gap between the container 35 and the induction coil 7 is increased, that is, the magnetic flux flux increases and the inductance L of the coil 7 is increased. As a result, the resonant frequency

The change fo'-f2 exceeds the predetermined value f _s in 3D (foo '> f2). As a result, the detection voltage Vp 'in the determination circuit 20 becomes smaller than the initial set voltage Vh', and the error detection signal Se is output. Thus, it is detected that the container 35 is in the floating state. The error detection signal Se is supplied to the power control circuit 33. The power control circuit 33 forcibly turns off the switching thyristor 18 and stops the power output from the inverter 12.

Assume that the container 35 is shifted from an appropriate position on the top plate 9 when the container 35 is made of iron or A1. In this case, the magnetic flux leakage becomes large and the inductance L also increases. Therefore, an inappropriate position of the container 35 can be detected.

를 검출하고, 변화(fo-f1, fo'-f2)가 소정의 값(f_s)을 초과할 경우의 에러 검출신호 Se를 출력시킨다. 이들 회로 성분들을 가지고서, 공진회로(6)의 공진주파수

에서의 변화 정도가 인버터(12)의 전력모드에서의 변화가 상당히 커지는데, 즉 조리 용기에 대한 반발력이 그것을 플로우팅하기에 충분히 크고, 에러 검출신호 Se가 발생된다. 그 결과로서, 용기(35)가 상단 플레이트(9)로부터 플로우팅 상태에서 있는지의 여부가 신뢰성있고도 쉽게 검출될 수있고, 용기(35)의 적절하지 않은 위치가 또한 검출될 수 있다. 검출결과에 따라서, 인버터(l2)의 전력출력은 용기가 풀로우팅하는 것을 막도륵 중단된다. 본 장치는 용기(35)가 상단 플레이트(9)를 따라서 이동되는것을 막을 수 있고, 유도 가열 조리기는 가열조리 불가능 상태에서 사용되는 것으로부터 방지될 수 있다. 인버터(12)의 전력레벨은 다음의 실시예에서와 같이 용기의 무게 검출 데이타에 따라서 제어될 수 있다. 따라서, 신뢰가능한 가열 조리가 수행될 수 있다.According to this embodiment, a power change circuit for changing the output mode of the inverter l2 from the low power mode to the high power mode in order to generate inverter power level control data in accordance with the relationship between the repulsive force on the container 35 and the inverter output. 19 is constituted. In addition, the determination circuit 20 is a resonance frequency of the resonance circuit 6.

Is detected and an error detection signal Se is outputted when the changes fo-f1 and fo'-f2 exceed a predetermined value f _s . With these circuit components, the resonant frequency of the resonant circuit 6

The degree of change in is significantly greater in the power mode of the inverter 12, ie the repulsive force on the cooking vessel is large enough to float it, and an error detection signal Se is generated. As a result, whether or not the container 35 is in the floating state from the top plate 9 can be detected reliably and easily, and an inappropriate position of the container 35 can also be detected. According to the detection result, the power output of the inverter 1 2 is stopped even if the container is not pulled down. The apparatus can prevent the vessel 35 from moving along the top plate 9 and the induction cooker can be prevented from being used in a non-cookable state. The power level of the inverter 12 can be controlled according to the weight detection data of the container as in the following embodiment. Thus, reliable heating cooking can be performed.

4 shows a second embodiment of the present invention. Like reference numerals in the second embodiment denote like parts in FIG. The difference between the first and second embodiments (FIGS. 1 and 4) will be described below. Reference numeral 36 denotes an inverter used in place of the inverter 12, which has a resonant circuit 39 consisting of an induction coil 37 and a resonant capacitor 38. Instead of the first and second switching transistors, one switching transistor 40 and a dumper diode 41 are configured. In the second embodiment, the terminal voltage of the resonant capacitor 38 is output to the phase detection circuit 42 without configuring the instrument transformer, and the phase difference is detected in accordance with the change of the output voltage. Inverter drive circuit 46 that configures inverter control circuit 45 together with phase detection circuit 42 controls switching transistor 40.

In this embodiment, unlike in the first embodiment, the power mode of the inverter does not change from the low power mode to the high power mode for a predetermined period of time in order to detect a change in the resonance frequency and obtain inverter power level control data. More specifically, in this embodiment, the weight of the container 35 or the repulsive force against it is detected by the sensor 44 for a predetermined period of time. As shown in FIG. 5, the state determination memory 43 previously stores inverter power control level data according to the relationship between the repulsive force for the cooking vessel and the inverter power. The power control circuit 47 controls the inverter drive circuit 46 in accordance with the inverter power level control data read out from the determination memory 43 according to the tare weight or the repulsive force detection data from the sensor 44.

According to the second embodiment, the inverter power level control data is stored in advance in the memory 43 according to the relationship between the power of the inverter 36 and the repulsive force on the container 35. The inverter power level control data is read from the memory 43 according to the weight data of the container 35 or the repulsive force detection data from the sensor 44 to control the power of the inverter 36. Therefore, in this embodiment, the weight of the vessel and the repulsive force on the vessel generated by the inverter power at that time are balanced so that an appropriate inverter power can always be provided that can prevent the vessel from floating.

A third embodiment of the present invention will now be described with reference to FIGS. 6 to 8. In Fig. 6, reference numeral 101 denotes a DC power source. The DC power source 101 is configured by connecting the choke coil 103, the full-wave rectifier 104, and the smoothing capacitor 105 to the AC power source 102. Reference numeral 106 denotes a resonant circuit composed of an induction coil 107 and a resonant capacitor 108 for heating an object to be heated.

Induction coil 107 is configured below the lower surface of the top plate 109 for placing the object to be heated. Reference numerals 110 and 111 denote first and second switching transistors. Transistors 110 and 111 are connected to resonant circuit 106 to construct inverter 112 as shown in FIG. Reference numeral 113 denotes an inverter controller. The controller 113 has an inverter driving circuit 114, a phase detection circuit 115, and a voltage controlled oscillator (VCO) 115-1. The inverter driving circuit 114 alternately turns on / off the switching transistors 1010 and 111. The phase detection circuit 115 receives the output from the instrument transformer 116 in the resonant circuit 106 and feedback-controls the inverter drive circuit 114 through the VCO 115-1. More specifically, the inverter driving circuit 114 controls the on / off timing of the transistors 110 and 111 according to the oscillation output from the VCO 115-1 according to the phase comparison output, whereby the inverter 112 Control the output frequency. As a result, the resonant furnace 106 is controlled to maintain the frequency (resonant frequency) at which the resonant state is set for the object to be heated.

Reference numeral 119 denotes a voltage change circuit for changing the output voltage as the power source voltage of the DC power source 110 to be supplied to the inverter 112. The voltage change circuit 119 periodically phase-controls the switching thyristor 118 and the gate electrode according to the oscillation signal from the oscillator circuit 120. The switching thyristor 118 is connected to the DC power source 101 as shown in FIG. The voltage change circuit 119 periodically functions in accordance with an oscillation signal having a predetermined period T1 (see FIGS. 8A to 8D) supplied from the oscillator circuit 120. More specifically, the voltage change circuit 119 changes the output period and the output period of the gate signal supplied to the switching thyristor 118 during the predetermined function time T2 (see FIGS. 8A to 8D) during each period T1. Thus, the on / off time interval of the thyristor 118 is changed. Therefore, the power source voltage supplied to the inverter 112 is changed from the low voltage V1 to the high voltage V2. When the voltage change circuit 117 is set to the low voltage V1 control mode, the gate signal output circuit 119 outputs the high level sampling timing signal St to the same state determination circuit 121 as in the first embodiment. The determination circuit 121 periodically or continuously changes the resonant frequency f of the resonant circuit 106 according to the output from the instrument transformer 116 in order to obtain inverter power level control data in the same manner as in the first embodiment. Detect. Therefore, the normal detection signal Sn or the error detection signal Se is output.

7 shows the state determination circuit 121 in detail. Reference numeral 122 denotes an F-V converter which detects the resonant frequency f of the resonant circuit 106 from the output of the instrument transformer 116 and converts it into a voltage. The FV converter 122 supplies the detected voltage Vp corresponding to the detected frequency to the non-inverting input terminal (+) of the operational amplifier 124 of the sample-hold circuit 123, and compares it with the comparator 133 (described later). To the inverting terminal (-). The sample-hold circuit 123 has an operational amplifier 124, an analog switch 125, and a memory capacitor 126. The gate terminal of the analog switch 125 receives the sampling timing signal St from the voltage change circuit 119 when the circuit 119 is set to the low voltage control mode. The memory capacitor 126 generates an output voltage Vp component corresponding to the resonant frequency f of the resonant circuit 106, that is, the initial frequency fo, when the circuit 119 is in the low voltage control mode such as the sample-hold voltage Vs. Reference numeral 127 denotes a reference value setting circuit. The reference value setting circuit 127 includes an operational amplifier 128, a diode 129, and resistors 130, 131, and 132. The reference value setting circuit 127 subtracts the reference voltage Vk determined by the resistors 130 to 132 from the sample-hold voltage Vs supplied to the non-inverting input terminal (+) of the operational amplifier 128, thereby initial setting voltage Vh. Outputs

The reference voltage Vk is set at a voltage value corresponding to the change fs of the resonant frequency (Figs. 8A to 8D) of the resonant circuit 106 generated so that the object to be heated floats from the upper plate 109. The initial set voltage Vh output from the set circuit 127 is supplied to the non-inverting input terminal (+) of the comparator 133. The inverting terminal (-) of the comparator 133 receives the output voltage Vp from the F-V converter 122. Therefore, if the output voltage Vp is higher than the initial set voltage Vh, the comparator 133 outputs the low level steady detection signal Sn to the voltage control circuit 134. When the output voltage Vp is lower than the voltage Vh, the comparator 133 outputs the error detection signal Se to the control circuit 134. When the voltage control circuit 134 receives the normal detection signal Sn, the voltage control circuit 134 controls the switching thyristor 118 to supply the high voltage V2 to the inverter 112 to set the inverter 112 in the high voltage mode. When the circuit 134 receives the error detection signal Se, the circuit l34 supplies the low voltage V1 to the inverter 112 so that the inverter 112 is set in the low voltage mode by controlling the thyristor 11.

), 여기서 L은 유도코일(107)의 인덕턴스, C는 커패시터(108)의 커패시턴스)으로 설정된다. 이때, 전압변화회로(119)로부터의 샘플링 타이밍신호 St가 결정회로(121)에 공급된다. 그 결과로서, 공진회로(106)의 공진주파수 f, 즉 초기조파수 f0에 대응하는 샘플-홀드 전압 Vs가 결정회로(121)의 샘플-홀드회로(123)에 의해 샘플링 및 홀딩된다. 기준전압 Vk(주파수 변화 fs에 대응함)는 샘플-홀드 전압 Vs로부터 감산되어, 이에의해 초기설정 전압 Vh를 결정한다. 초기 설정전압 Vh에 대응하는 주파수(소정값)는 제8b도에서 f00로 주여진다. 인버터(112)에 공급된 전력원 전압이 전압변화회로(119)에 의해 저전압 V1로 부터 고전압 V2로 바뀔때, 용기(135)에 대한 반발력이 증가된다.The effect of the above configuration will now be described. An example in which the cooking vessel 135 is formed of iron as an object to be heated will be described with reference to FIGS. 8A and 8B. 8A and 8B show the change in power source voltage of inverter 112 and the frequency change of resonant circuit 106 associated therewith. After the container 135 is placed on the top plate 109 as the object to be heated, the voltage change circuit 119 supplies the low voltage V1 as the power source voltage to the inverter 112 for a predetermined period of time from the oscillation circuit 120. The inverter 112 is set to the low power mode for a predetermined period of time in accordance with the oscillation signal of T1. Therefore, in the inverter 112, the resonant frequency f of the resonant circuit 106 corresponding to the container 135 is (f = 1 / (2π.

Where L is the inductance of the induction coil 107 and C is the capacitance of the capacitor 108). At this time, the sampling timing signal St from the voltage change circuit 119 is supplied to the determination circuit 121. As a result, the resonant frequency f of the resonant circuit 106, that is, the sample-hold voltage Vs corresponding to the initial frequency f0, is sampled and held by the sample-hold circuit 123 of the decision circuit 121. The reference voltage Vk (corresponding to the frequency change fs) is subtracted from the sample-hold voltage Vs, thereby determining the initialization voltage Vh. The frequency (predetermined value) corresponding to the initial set voltage Vh is given as f00 in FIG. 8B. When the power source voltage supplied to the inverter 112 is changed from the low voltage V1 to the high voltage V2 by the voltage change circuit 119, the repulsive force on the container 135 is increased.

However, when the container 135 is made of iron, its weight is large and the container is made of magnetic material. Therefore, the attraction to the container 135 is increased. As a result, the repulsive force is canceled by the attractive force and reduced small. Thus, the container 135 is divided while positioned on the top plate 109 in a steady state. Although the resonant frequency f of the resonant circuit 106 is reduced to the frequency f1, the change f1 is larger than the predetermined value f00 as shown in FIG. 8B. More specifically, in this state, the output voltage Vp of the decision circuit 121 is higher than the initial set voltage Vh. As a result, the output terminal of the comparator 133 is held at the low level by the decision circuit 121. In this state, the normal detection signal Sn is output and supplied to the voltage control circuit 134. The control circuit 134 controls the thyristor 118 to supply the high voltage V2 to the inverter 11, thereby setting the inverter 112 in the high power mode. In this way, the power source voltage is optimized. The position state detection of the container 135 is periodically performed during cooking in accordance with the oscillation signal from the oscillator circuit 120.

When a user puts a substance to be cooked into or stirs the substance in the container 135, the container 135 may be shifted from an appropriate position. In this case, the magnetic flux flux is increased, and the inductance L of the induction coil 107 is increased. As a result, the resonance frequency f of the resonance circuit 106 can be reduced, and the induction heating efficiency can be lowered. Assume the container 135 is shifted in this manner at time T3 in FIGS. 8A and 8B. After the time T3, since the voltage change circuit 119 functions periodically, the power source voltage for the inverter 112 is thereby reduced to the low voltage V1, at which time the low voltage V1 changes to the high voltage V2. In this voltage change, when the resonance frequency f of the resonance circuit 106 is reduced to f2 below the frequency f00 as a predetermined value as shown in FIG. 8B, the output voltage Vp corresponding to the resonance frequency f2 is determined by the determination circuit ( It becomes smaller than the initial set voltage Vh corresponding to the frequency f00 of 121). Therefore, the error detection signal Se is output. In this manner, it is detected that the container 135 has been shifted from its proper position. The error detection signal Se is supplied to the voltage control circuit 134. The control circuit 134 controls the switching thyristor 118 to supply the low voltage V1 as the power source voltage supplied to the inverter 112 to set the inverter 112 in the low power mode. In this way, the power source voltage is optimized and the resonant frequency f is increased, thus obtaining a good heating efficiency. If the container 135 is initially shifted from the proper position, it is similarly detected and the power source voltage is controlled.

An example in which the container 135 is made of A1 material, which is small in weight and has a specific transmittance will be described with reference to FIGS. 8C and 8D. In this case, the power source voltage applied to the inverter 112 is indicated at low voltage V1 at the nominal frequency f as f0 ', and the frequency (predetermined value) corresponding to the initial set voltage Vh is given as the frequency f00'. In this case, as can be seen from FIG. 5 described above, when the power source voltage is changed from the low voltage V1 to the high voltage V2, the repulsive force on the container 135 is increased. Since the attraction to the container 135 is reduced, the container 135 can be floated in accordance with the total weight of the container 135 and its contents. In this case, the spacing between the container 135 and the guide coil 107 is increased due to the floating, thus increasing the magnetic flux leakage. Therefore, the inductance L of the induction coil 107 is increased. As a result, the resonant frequency f of the resonant circuit 106 is remarkably reduced to the resonant frequency f2 (which is less than or equal to the frequency f00 'as a predetermined value) in FIG. 8b, and the detection voltage Vp of the determination circuit 121 is set voltage Vh. Becomes smaller than Therefore, the error detection signal Se is output. In this manner, it is detected that the container 135 is in a floating state. The error detection signal Se is supplied to the voltage control circuit 134. In response to this signal, the control circuit 134 controls the switching thyristor 118 and sets the power source voltage supplied to the inverter 112 to the low voltage V1. Thus, the power source voltage applied to the inverter 112 is optimized. In this way, the floating of the container 135 can be prevented and the resonance frequency f is increased, thereby obtaining a good heating efficiency.

Assume that at time T4 in FIGS. 8C and 8D, the overall weight of the container 135 is increased such that new material to be heated is set in the container 135. In other words, assume that the container 135 is not floating even if the power source voltage supplied to the inverter 112 is changed to the high voltage V2 to set the inverter 112 to the high power mode. In this case, when the voltage change circuit 119 functions after the time T4, the position state of the container 135 can be detected. More specifically, when the power source voltage is reduced to the low voltage V1 and then changed to the high voltage V2, the resonant frequency f of the resonant circuit 106 is reduced to the frequency f4 as shown in FIG. 8d. The resonance frequency f4 detected at that time is higher than the predetermined frequency f00 '. As a result, the determination circuit 121 outputs the normal detection signal Sn and supplies it to the voltage control circuit 134. The control circuit 134 controls the switching thyristor 118 to supply the high voltage V2 as the power source voltage to the inverter 112, and sets the inverter 112 to the high power mode. Thus, the power source voltage is optimized according to the state of the vessel 135.

According to this embodiment, in order for the inverter controller 113 to obtain the inverter power level control data in the same manner as in the first embodiment, the inverter 112 is set such that the resonant circuit 106 is set to the resonance state with respect to the container 135. It is configured to control the feedback of the output frequency. Thus, even if the positional state of the container 135 changes, the resonant circuit 106 is controlled to resonate normally. The voltage change circuit 119 is configured to change the power source voltage from the low voltage V1 to the fixed voltage V2, thereby periodically setting the inverter 112 in the low power mode to the high power mode. In addition, the state determination circuit 1121 is configured. The determination circuit 12l detects the resonance frequency f of the resonance circuit 106 when the voltage changes. In the case of the low voltage V1, when the change from the initial frequency exceeds a predetermined value, the determination circuit 121 outputs the normal detection signal Sn, otherwise outputs the error detection signal Se. Therefore, since the apparatus of this embodiment outputs the normal detection signal Sn or the error detection signal Se, it can be reliably and easily detected whether the container 135 is floated from the top plate 109 or located at an appropriate position. . Since the voltage change circuit 119 is periodically operated to periodically perform the detection, the power source voltage applied to the inverter 112 is controlled according to the detection result to control the power level of the inverter 112. When the vessel 135 is floated according to its material or weight, an appropriate power source voltage may be supplied to the inverter 112 to prevent the vessel 135 from floating. When the vessel 135 is shifted from its proper position on the top plate 109, an appropriate power source voltage (low voltage V1) can be supplied to the inverter 112 to increase the resonant frequency f. Therefore, cooking can always be performed stably.

9 shows a fourth embodiment of the present invention, wherein like reference numerals in FIG. 9 denote the same parts as in the third embodiment. Only the differences from FIG. 6 will be described below. Reference numeral 136 denotes an inverter used instead of the inverter 112, which includes a resonant circuit 139 consisting of an induction coil 137 and a resonant capacitor 138. One switching transistor 140 and a dumper diode 141 are configured instead of the first and second switching transistors 110 and 111. The terminal voltage of the capacitor 138 is output to the phase detection circuit 142 without configuring the instrument transformer. The phase difference is detected in accordance with the change of the output voltage. The voltage change circuit 144 includes an oscillator circuit for periodic operation. The inverter driving circuit 146 constitutes a feedback control circuit 145 together with a phase detection circuit 142 including a voltage controlled oscillator (VCO). The driving circuit 146 controls the switching transistor 140. The voltage control circuit 147 corresponds to the weight or repulsive force of the container 135 and to the inverter power level control data read out from the determination memory 143 according to the periodic container weight or repulsive force detection data from the sensor 144. The inverter drive circuit 146 is controlled based on this.

According to the present invention as described above, the case where the object to be heated is floated from the top plate can be reliably and easily prevented.

Unlike in the third embodiment, in this embodiment, the power mode of the inverter is not periodically changed from the low power mode to the high power mode to detect a change in the resonance frequency in order to obtain inverter power level control data. More specifically, in this embodiment, the weight of the container 135 or the repulsive force thereto is periodically detected by the sensor 1144. As shown in FIG. 5, the state determination memory 143 previously stores the inverter power control level data according to the relationship between the inverter power and the repulsive force for the cooking vessel. The voltage control circuit 147 corresponds to the weight or repulsive force of the container 135 and the inverter power level control data read out from the determination memory 143 according to the periodic container weight or the repulsive force detection data from the sensor l44. The inverter drive circuit 146 is controlled based on the above. In the fourth embodiment, the same effects as in the second embodiment can be provided.

According to the present invention as described above, the case where the object to be heated is floated from the top plate can be reliably and easily prevented.

The present invention is not limited to the above embodiments and may be modified as follows. Instead of the switching thyristors 18 and 118, a plurality of diodes of the full-wave rectifiers 4 and 104 may be replaced by the switching thyristors. The power change circuit and the voltage change circuit can change the power and the voltage according to the change of the resistance, respectively. The determination circuit can detect the resonance frequency of the resonance circuit according to the output frequency of the VCO of the inverter control circuit. In this case, the F-V converters 21 and 122 can be omitted from the decision circuits 20 and 121 in the first and third embodiments. The decision circuit can detect the resonance frequency by the number of pulses in which the frequency is pulse-converted. The power change and voltage change of the power change circuit and the voltage change circuit may be stepped. In addition, the control power and control voltage of the power control circuit and the voltage control circuit can be changed to various levels.

In the first and third embodiments, the power change circuit 19 and the output control circuit 33, the voltage change circuit 119, the voltage control circuit 134 and the oscillation circuit 120 are each a microprocessor (CPU). (17,117).

Many other changes and modifications may be made within the spirit and scope of the invention.

Claims (10)

A resonant circuit 6 comprising a top plate 9 for placing an object to be heated, such as a cookware or a container, an induction heating coil 7 configured below the top plate and a resonant capacitor 8 connected to the coil. And supply a high frequency power to the resonant circuit to automatically generate a high frequency magnetic field from the induction heating coil and automatically prevent an undesired state of a cooking utensil or container having an inverter circuit 12 for inducing a vortex current to the article. An electromagnetic induction heating apparatus, comprising: an inverter power level control data generation circuit for outputting inverter power level control data according to a relationship between a high frequency power from the inverter circuit and a repulsive force acting on the object according to the high frequency power; And the inverter power level control data from the control data generation circuit. And a control circuit for feeding back to the butter circuit to control the high frequency power level from the inverter circuit to prevent the object from floating from the surface of the top plate due to the repulsive force in accordance with the inverter power level control data. Electromagnetic induction heating apparatus, characterized in that. 2. The power supply circuit of claim 1, wherein the inverter power level control data generation circuit is connected to the inverter circuit, and is connected to the resonance circuit and a power change circuit 19 for changing high frequency power from low to high power for a predetermined operation period. Receiving a resonant frequency detecting circuit for detecting the resonant frequency of the resonant circuit in the low power mode and the high power mode, and the resonant frequency detecting outputs in the low power mode and the high power mode detected by the resonant frequency detecting circuit, And a state determination circuit (20) for comparing a difference between detection outputs with a predetermined reference value when an object is floated from the located surface of the top plate due to the repulsive force. 2. The state determination memory according to claim 1, wherein said inverter power level control data generating circuit pre-stores inverter power level data according to a relationship between high frequency power from said inverter circuit and a repulsive force acting on said object in accordance with this high frequency power. (43), a sensor (44) for detecting the weight of the object, and means for reading inverter output level data corresponding to the detection output from the sensor from the memory. Device. 3. An electromagnetic induction heating apparatus according to claim 2, wherein said determination circuit comprises a converter circuit (21) for converting frequency data into voltage data as a detection output from said resonance frequency detection circuit. 3. A circuit according to claim 2, characterized in that the decision circuit comprises a sample-hold circuit 22 for sampling and holding the detection output from the resonance frequency detection circuit at a timing synchronized with the operation period of the power change circuit. Electromagnetic induction heating device. 3. The inverter control according to claim 2, wherein the inverter circuit is connected to a switching element 18, an output terminal connected to the resonant circuit, a DC power source connected to an input terminal of the switching element, and an inverter connected to a control terminal of the switching element. An electromagnetic induction heating apparatus comprising a circuit. The electromagnetic induction heating apparatus according to claim 6, wherein said power change circuit (19) controls the DC output voltage of said DC power source. 8. The inverter according to claim 6, wherein the inverter control circuit receives a phase detection circuit (15) for comparing the detection output from the resonance frequency detection circuit with a reference phase, and outputs the oscillation signal for a predetermined period. And an inverter drive circuit (14) for receiving an output from the voltage controlled circuit and supplying a drive output to the control terminal of the switching element. Induction heating device. 3. The electromagnetic induction heating apparatus according to claim 2, wherein an operation period of the power change circuit is set when the power source is turned on. 3. The electromagnetic induction heating apparatus according to claim 2, wherein the electromagnetic induction heating apparatus is set repeatedly during a small period of the operation period of the power change circuit.

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