JPH04277487A - Induction heating cooking apparatus - Google Patents

Abstract

PURPOSE:To heat only load to be heated in an induction heating cooking apparatus including a resonance capacitor changeover means by making equal the minor object judge level before and after changing-over of the resonance capacitor, and refraining from heating when loading with a minor object such as a knife is judged irrespective of the connected condition of the resonance capacitor. CONSTITUTION:A minor object sensing circuit 119 is composed of an input current sensing circuit 116, a resonance capacitor voltage sensing circuit 117, and a microcomputer 118 which is fed with outputs of the later named two sensing circuits 116, 117. The ratio of the output of the input current, sensing circuit 116 to the output of resonance capacitor voltage sensing circuit 117 is compared with the judging criterion set in the microcomputer 118, and judgment is made to know whether the load is below a certain specified level. The criterion set in the microcomputer 118 is switched while interlocked with a relay 113.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating cooker equipped with resonant capacitor switching means.

0002

2. Description of the Related Art In recent years, a method has been proposed in which resonant capacitors are switched to efficiently heat the load using an inverter circuit suitable for the load.

[0003] A conventional induction heating cooker will be explained below. As shown in FIG. 3, a DC power source 4 is constructed by rectifying an AC power source 1 with a diode bridge 2 and smoothing it with a smoothing capacitor 3, and includes a heating coil 5, a transistor 6, a transistor 7, a diode 8, a diode 9, Resonant capacitor 1
0 and a resonant capacitor 11 constitute an inverter circuit 12. The resonant capacitor 10 and the resonant capacitor 11 are arranged in parallel, and the resonant capacitor 11 is connected to or disconnected from the inverter circuit 12 by a relay 13 which is a resonant capacitor switching means. The control circuit 14 includes a relay control section 20 that controls the relay 13 and an oscillation control section 1 that controls oscillation and stopping of the inverter circuit 12.
5, the output V+ of the input current detection circuit 16, and the output V- of the resonant capacitor voltage detection circuit 17 are compared by a comparator 18,
A small object detection circuit 19 is provided as an operating state detection means that determines that the load is a small object below the small object determination level when V- exceeds V+. Further, a manual switch 21 is provided outside the main body (not shown) for switching the connection state of the resonance capacitor 11 depending on whether the load is a magnetic pot or a non-magnetic pot. is input to the relay control section 20, and the relay control section 20 switches the connection state of the relay 13 based on this signal.

[0004] The operation of the induction heating cooker constructed as described above will be explained below. First, when the load is a magnetic pot, when the user sets the manual switch 21 to the magnetic pot side, the relay control unit 20 turns off the relay 13,
The resonant capacitor 11 is disconnected from the inverter circuit 12, and the inverter circuit 12 becomes an inverter circuit suitable for a magnetic pot and heats the load. Next, when the load is a non-magnetic pot, if the manual switch 21 remains set to the magnetic pot side, the inverter circuit 12 remains an inverter circuit suitable for a magnetic pot, so the specified input power cannot be obtained. Therefore, when the user sets the manual switch 21 to the non-magnetic pot side, the relay control unit 20 turns on the relay 13, the resonance capacitor 11 is connected to the inverter circuit 12, and the inverter circuit 12 is set to the non-magnetic pot side. It becomes an inverter circuit and heats the load with a predetermined input. Next, we will explain the operation when the load is below a predetermined size, that is, when the knife is below the accessory judgment level, and when the enamel pot (pot bottom diameter is 70 mm) is slightly larger than the accessory judgment level, using Fig. 4. . FIG. 4 shows the relationship between V+ and V- at each heating output of the knife and the enamel pot. This is a discrimination standard that distinguishes between small items below the level and non-small items. The figure (1) shows manual switch 2.
1 is set to the magnetic pot side, that is, when the resonance capacitor 11 is disconnected from the inverter circuit 12. Figure (2) shows the characteristics when the manual switch 21 is set to the non-magnetic pot side. This is the characteristic when the resonant capacitor 11 is connected to the inverter circuit 12. When the resonant capacitor 11 is connected to the inverter circuit 12, the total resonant capacitor capacity is larger than when the resonant capacitor 11 is disconnected from the inverter circuit 12, so the resonant capacitor voltage at the same input current is Therefore, V- at the same V+ with the same load becomes smaller. Now, when the user sets the manual switch 21 to the magnetic pot side and operates it, the enamel pot is heated as shown in FIG. When the manual switch 21 is set to the non-magnetic pot side and operated, the enamel pot is heated as is clear from FIG. 4(2), but the knife is also heated without being recognized as an accessory.

[0005]

[Problems to be Solved by the Invention] In such a conventional induction heating cooker, as shown in FIGS. 16 output V+ and resonant capacitor voltage detection circuit 17
The relationship between the output V- and the output V- at the same V+ is smaller when the manual switch 21 is set to the non-magnetic pot side than when it is set to the magnetic pot side under the same load. The detection circuit 19 detects the same load when the manual switch 21 is set to the non-magnetic pot side, because it is harder to distinguish it from a small object when the manual switch 21 is set to the non-magnetic pot side, compared to when it is set to the magnetic pot side. If it is set to the side, the knife, which is originally under a load below the accessory judgment level, will be heated,
It was dangerous. Conversely, the circuit constants of the input current detection circuit 16 and the resonant capacitor voltage detection circuit 17 of the small object detection circuit 19 are changed so that a knife can be determined as a small object when the manual switch 21 is set to the non-magnetic pot side. If the V+ and V- characteristics of the knife and enamel pot are as shown in Figure 5 (2), when the manual switch 21 is set to the magnetic pot side, the same characteristics will become as shown in Figure 5 (1), There was a problem in that enamel pots, which had a load higher than the small item determination level, were judged as small items.

The present invention solves the above-mentioned problem, and regardless of the connection state of the resonant capacitor with the inverter circuit, a knife, which is a load to be determined as a small object, is determined to be a small object, and a enamel pot, which is a load to be heated, is determined to be a small object. aims to provide an induction heating cooker capable of heating.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a heating coil provided at a predetermined distance from a load, an inverter circuit that supplies a high frequency current to the heating coil, and an inverter circuit that supplies a high frequency current to the heating coil. the inverter circuit includes a plurality of resonant capacitors, and resonant capacitor switching means for connecting at least one of the resonant capacitors to or disconnecting from the inverter circuit; The circuit includes an operating state detecting means for detecting an operating state of the inverter circuit, and the operating state detecting means determines a ratio between an input current of the inverter circuit and a voltage or current applied to the inverter circuit, and a preset value. When the load is determined to be a predetermined size, that is, below the accessory determination level, the inverter circuit stops operating, and the resonant capacitor switching means changes the connection state of the resonant capacitor. The discrimination criterion is switched in conjunction with the switching of the resonant capacitor, so that the small object discrimination level is made almost equal before and after the resonant capacitor switching means switches the connection state of the resonant capacitor.

[0008]

According to the present invention, with the above-described configuration, the resonant capacitor switching means can switch the connection state of the resonant capacitor, so that the load can be efficiently heated by an inverter circuit suitable for each material. Also,
The operating state detection means compares the ratio of the input current of the inverter circuit to the voltage or current applied to the inverter circuit with a preset discrimination criterion, and detects a predetermined magnitude, that is, a small object detection level or less. load, or
An unsuitable load corresponding to this can be determined, and this preset discrimination criterion is switched in conjunction with the resonant capacitor switching means switching the connection state of the resonant capacitor. The means can be made almost equal before and after switching the connection state of the resonant capacitor.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a DC power supply 104 is constructed by rectifying an AC power supply 101 with a diode bridge 102 and smoothing it with a smoothing capacitor 103, and includes a heating coil 105, a transistor 106, a transistor 107, and a diode 1.
08, a diode 109, a resonant capacitor 110, and a resonant capacitor 111 constitute an inverter circuit 112. Resonant capacitor 110 and resonant capacitor 1
11 are arranged in parallel, and the resonant capacitor 111 is connected to or disconnected from the inverter circuit 112 by a relay 113 which is a resonant capacitor switching means. The control circuit 114 includes a relay control section 120 that controls the relay 113, an oscillation control section 115 that controls oscillation/stop of the inverter circuit 112, an input current detection circuit 116, a resonant capacitor voltage detection circuit 117, and a microcomputer 118. The small object detection circuit 11 is a means for detecting the operating state of
9. Further, a manual switch 121 is provided outside the main body (not shown) for switching the connection state of the resonance capacitor 111 depending on whether the load is a magnetic pot or a non-magnetic pot. is input to the relay control unit 120, and the relay control unit 120 switches the connection state of the relay 113 based on this signal.

[0011] The operation of the induction heating cooker constructed as described above will be explained below. First, when the load is a magnetic pot, when the user sets the manual switch 121 to the magnetic pot side, the relay control unit 120 turns off the relay 113, the resonance capacitor 111 is disconnected from the inverter circuit 112, and the inverter circuit 112 is set to the magnetic pot side. It becomes an inverter circuit suitable for pots and heats the load. Next, if the load is a non-magnetic pot, if the manual switch 121 remains set to the magnetic pot side, the inverter circuit 112 will remain an inverter suitable for magnetic pots, so the specified input power will not be obtained. When the user sets the manual switch 121 to the non-magnetic pot side, the relay control unit 120 switches the relay 113
is turned on, and the resonant capacitor 111 is connected to the inverter circuit 11.
2, the inverter circuit 112 becomes an inverter circuit suitable for a non-magnetic pot and heats the load with a predetermined input power. Next, the operation in the case of a knife whose load is below the accessory judgment level and the case of an enamel pot (pot bottom diameter 70 mm) whose load is slightly larger than the accessory judgment level will be explained using FIG. Figure 2 shows the relationship between V+ and V- at each heating output of the knife and the enamel pot, and the broken line in the figure shows the microcomputer that uses the ratio of V+ and V- to determine whether the load is a small item below the small item judgment level or a non-small item. This is a discrimination standard set in advance by 118. Figure (1) shows the characteristics when the manual switch 21 is set to the magnetic pan side, that is, when the resonance capacitor 11 is disconnected from the inverter circuit 12, and Figure (2) shows the characteristics when the manual switch 21 is set to the non-magnetic pot side. When set to the magnetic pot side, that is, the resonance capacitor 11
is the characteristic when connected to the inverter circuit 12. Now, when the user sets the manual switch 121 to the magnetic pot side and operates it, the relay control section 120 turns off the relay 113, and the resonance capacitor 111 turns off the inverter circuit 112.
The inverter circuit 112 becomes an inverter circuit suitable for magnetic pots, and as is clear from FIG. 2(1), the enamel pot is heated, but the knife is determined to be an accessory and is not heated. Next, when the user sets the manual switch 121 to the non-magnetic pot side, the relay control unit 120 turns on the relay 113, the resonance capacitor 111 is connected to the inverter circuit 112, and the (V-/V+) of the same load is Although the size is smaller than when the manual switch 121 is set to the magnetic pot side, the microcomputer 118 that constitutes the small object detection circuit 119 uses preset discrimination criteria for distinguishing the load from small objects to non-small objects. In conjunction with switching from the magnetic pot side to the non-magnetic pot side, that is,
As the resonant capacitor 111 is connected to the inverter circuit 112, the line changes from the dotted line shown in FIG.
Since the switch is switched to the dotted line shown in , the enamel pot will be heated even if the manual switch 121 is set to the non-magnetic pot side, and the knife will be determined to be an accessory and will not be heated.

As described above, according to this embodiment, the small object detection circuit 119 is activated in conjunction with the change in (V-/V+) of each load due to the switching of the resonant capacitor 111, that is, the change in the state of the inverter circuit 112. Configuring microcontroller 1
Since the discrimination criteria preset in the inverter circuit 118 is also changed as shown in FIG. 2, it is possible to prevent the same load from being heated or not being heated due to a change in the state of the inverter circuit 112.

[0013]

As described above, in the present invention, since the connection state of the resonant capacitor can be switched by the resonant capacitor switching means, the load can be efficiently heated by an inverter circuit suitable for each material. In addition, the operating state detection means can switch the preset discrimination criteria for determining whether the load is below the accessory judgment level in conjunction with the switching of the connection state of the resonant capacitor. Regardless of the connection status, the accessory judgment level can be kept almost constant. Therefore, when using the same load in the connection state of a resonant capacitor, there is a risk that the user may get burned if the load does not heat up in one connection state but heats up in another connection state, or conversely, It is possible to eliminate cooking inconveniences such as being able to heat in one connection state but not being able to heat and cook in another state using the same load, and to provide an induction heating cooker that is safe and has good cooking performance.

[Brief explanation of the drawing]

FIG. 1: Circuit diagram of an induction heating cooker according to an embodiment of the present invention.

FIG. 2 is a diagram explaining the operation of the induction heating cooker in the embodiment of the present invention.

[Fig. 3] Circuit diagram of an induction heating cooker in a conventional embodiment

FIG. 4 is a diagram explaining the operation of an induction heating cooker in a conventional example.

[Fig. 5] A diagram explaining the problems of the induction heating cooker in the conventional example.

[Explanation of symbols]

105 Heating coil 112 Inverter circuit 114 Control circuit 110, 111 Resonance capacitor

Claims (1)

[Claims] 1. A heating coil provided at a predetermined distance from a load, an inverter circuit that supplies a high-frequency current to the heating coil, and a control circuit that controls the inverter circuit, the inverter circuit comprising a plurality of inverter circuits. a resonant capacitor; and resonant capacitor switching means for connecting at least one of the resonant capacitors to or disconnecting from the inverter circuit, and the control circuit includes an operating state detecting means for detecting an operating state of the inverter circuit. The operating state detecting means compares the ratio of the input current of the inverter circuit to the voltage or current applied to the inverter circuit with a preset determination standard, and determines whether the load is of a predetermined size. That is, when it is determined that the level is below the small object determination level, the operation of the inverter circuit is stopped, and the determination criterion is switched in conjunction with the resonant capacitor switching means switching the connection state of the resonant capacitor, and the resonant An induction heating cooker in which the small object determination level is approximately equal before and after the capacitor switching means switches the connection state of the resonance capacitor.