JP5369773B2 - Induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device capable of miniaturizing a circuit. <P>SOLUTION: The induction heating device comprises an inverter converting an output of a rectifying circuit 2 into high-frequency power and applying power to a heating coil, a current detection means 3 for detecting an input current from an AC power source, and a control means 8 for controlling a conduction time of a plurality of semiconductor switches in first and second inverters according to outputs of the current detection means 3. After an input current of the first or the second inverter reaches a target value, the control means 8 can supply designated power to respective inverters even if simultaneous operations of two inverters are performed by the rectifying circuit 2 and the current detection means 3 which have their own structures, and the circuit of the induction heating device can be miniaturized. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an induction heating apparatus that heats an object to be heated using induction heating by a high-frequency magnetic field.

  Conventionally, this type of induction heating device controls a high-frequency current supplied to a heating coil in accordance with an input current from a commercial power source to an inverter (see, for example, Patent Document 1).

  FIG. 6 shows a conventional induction heating cooker described in Patent Document 1. As shown in FIG. As shown in FIG. 6, the commercial power supply 11, the first and second heating coils 16, 17, the first and second rectifier circuits 12 and 22 that rectify the commercial power supply, and the output of the rectifier circuit are converted into high-frequency power. The first and second inverters 14 and 15 for converting the current into the respective heating coils and supplying the high frequency power to the respective heating coils, the first and second current transformers 13 and 23 for detecting the current supplied to the respective inverters, The microcomputer 18 controls the operation state of the inverter according to the output of the rent transformer.

  The operation of the conventional example will be described. In FIG. 6, the microcomputer 18 includes a semiconductor switch in the first and second inverters 14 and 15 so that the input current detected by the first and second current transformers 13 and 23 becomes a preset current value. The necessary high-frequency current is supplied to the first and second heating coils 16 and 17 connected to the first and second inverters 14 and 15.

  Due to the high-frequency current supplied to the first and second heating coils 16 and 17, the high-frequency magnetic field generated from the first and second heating coils 16 and 17 is applied to a load such as a pan that is magnetically coupled to the heating coil. Applied.

  An eddy current is generated in a load such as a pan by the high-frequency magnetic field, and the pan itself generates heat due to the eddy current and the skin resistance of the pan itself.

When high frequency power is simultaneously supplied from the first and second inverters 14 and 15 to the first and second heating coils 16 and 17, the microcomputer 18 is connected to each inverter by a current transformer connected to each inverter. The semiconductor switches in the first and second inverters are independently controlled so that the input power of each inverter becomes a predetermined value.
JP 2001-267052 A

  However, in the conventional configuration, it is necessary to include a plurality of inverters for supplying high-frequency power to each of the plurality of heating coils, a rectifier circuit, and a current transformer. It had the problem of becoming difficult.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide an induction heating apparatus that can reduce the size of a circuit.

In order to solve the above-described conventional problems, an induction heating apparatus of the present invention includes a rectifier circuit that rectifies an AC power supply, and converts the output of the rectifier circuit into high-frequency power and applies power to the first and second heating coils. First and second inverters, current detection means for detecting an input current from the AC power supply, and conduction of a plurality of semiconductor switches in the first and second inverters according to the output of the current detection means Control means for controlling time, and the control means performs simultaneous operation with the other inverter after the input current of the first or second inverter reaches the target value.

  As a result, the rectifier circuit and the current detection means can be shared by two inverters, and predetermined power can be supplied to each inverter even if two independent inverters are operated simultaneously. it can.

  The induction heating device of the present invention can supply predetermined power to each inverter even if the two inverters are operated simultaneously in a configuration in which the rectifier circuit and the current detection means are shared by the two inverters. The circuit can be miniaturized, and an induction heating apparatus with a small circuit mounting volume can be realized.

  According to a first aspect of the present invention, there is provided a rectifier circuit that rectifies an AC power source, first and second inverters that convert the output of the rectifier circuit into high-frequency power and apply power to first and second heating coils, and the AC Current detection means for detecting an input current from a power supply; and control means for controlling conduction times of a plurality of semiconductor switches in the first and second inverters according to the current detection means, the control means comprising: A configuration in which the rectifier circuit and the current detection means are shared by two inverters by performing simultaneous operation with the other inverter after the input current of the first or second inverter reaches the target value. Thus, even when two independent inverters are operated simultaneously, a predetermined power can be supplied to each inverter, the inverter circuit can be downsized, and the circuit mounting volume can be reduced. It can be achieved have induction heating device.

  In the second invention, in particular, when the first and second inverters of the first invention operate simultaneously, at least one of the inverters performs duty control in which the ON state and the OFF state continue for a certain period of time. Even when two independent inverters are operated simultaneously in a configuration in which a rectifier circuit and current detection means are shared, the input current of each inverter can be accurately detected, and predetermined power is accurately supplied to each inverter. be able to.

  In the third invention, in particular, when the duty control of the second invention is performed, by preventing the mutual OFF state from overlapping, the two rectifier circuits and the current detecting means are shared, and the two independent inverters are configured. Even if the simultaneous operation is performed, the input current of each inverter can be accurately detected, so that predetermined power can be accurately supplied to each inverter.

  According to a fourth aspect of the invention, in particular, when the first and second inverters of any one of the first to third aspects of the invention operate simultaneously, the control means determines the current after the detection value of the current detection means reaches the target value. A configuration in which the rectifier circuit and the current detection unit are shared by stopping at least one of the first and second inverters when a difference between the detection value of the detection unit and the target value exceeds a predetermined value within a predetermined time. Even if two inverters are operated at the same time, the heating operation can be stopped when the heating conditions are changed by moving the load placed on each heating coil. Can do.

In the fifth aspect of the invention, in particular, when the first and second inverters of any one of the first to fourth aspects of the invention are simultaneously operated, the control means is provided when the detection value of the current detection means reaches the target value. By setting the conduction time of the semiconductor switch in the first and second inverters as the conduction time at the time of stability, if there is no change in the target value, by providing a maximum conduction time that does not increase from the conduction time at the time of stability to a conduction time of a certain time If the load placed on each burner shifts even if simultaneous operation of two independent inverters is performed with a configuration in which the rectifier circuit and current detection means are shared, the input power will change as the load deviates from the center of the burner. Therefore, it is possible to prevent a large amount of input power from being supplied when the load is deviated.

  According to a sixth aspect of the invention, in particular, when the control means of the fifth aspect of the invention reaches the maximum conduction time of either one of the first and second inverters, the conduction time of both the first and second inverters is determined. By prohibiting the increase, if the load placed on each heating coil is moved even if independent inverters are operated simultaneously in a configuration in which the rectifier circuit and current detection means are shared, the center of the heating coil Accordingly, the input power is reduced as the pan moves away from the pan, and it is possible to prevent a large input power from being supplied when the pan is displaced.

  In the seventh invention, in particular, the control means of the fifth invention stops at least one of the first and second inverters when either one of the first and second inverters reaches the maximum conduction time. As a result, even if simultaneous operation of independent inverters is performed with a configuration in which the rectifier circuit and the current detection means are shared, the heating operation is stopped when the load placed on each heating coil is moved, which is unnecessary. You can suppress the movement.

  Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 shows a circuit configuration diagram of an induction heating apparatus according to a first embodiment of the present invention.

  In FIG. 1, an AC power source 1, a rectifier circuit 2 that rectifies the AC power source, first and second inverters 4 and 5 that convert the output of the rectifier circuit 2 into high-frequency power, First and second heating coils 6 and 7 to which a high-frequency current is supplied from an inverter, current detection means 3 for detecting an input current from an AC power source, and first and second outputs according to an output from the current detection means 3 It is comprised with the control means 8 which controls the semiconductor switch in an inverter.

  The first inverter 4 and the first heating coil 6 constitute a first burner 9, and the second inverter 5 and the second heating coil 7 constitute a second burner 10, and each heating coil. A load such as a pan is arranged in the vicinity of.

  About the induction heating apparatus comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  FIG. 2 shows a flowchart of the operation of the induction heating apparatus in the first embodiment of the present invention.

  When the control means 8 receives an operation command for the first or second burner 9, 10 (Step 1 or Step 11), the control means 8 starts the operation of the first or second burner 9, 10 (Step 2 or 12).

  First, it is determined whether or not a load such as a pan placed on the first or second burner 9 or 10 is a heating compatible load using electrical characteristics or the like. (Step 4 or Step 14), the operation of the other burner is permitted (Step 7 or Step 17).

  At this time, when there is an operation command for the burner, the control means 8 starts heating the burner (Step 12 or Step 2).

  On the other hand, the control means 8 sequentially increases the heating power when the load is considered suitable, and determines that the corresponding burner has reached the target value when the input current reaches the set value by the current detection means 3. (Step 5 or Step 15) When the simultaneous operation is not performed (Step 6 or Step 16), the heating operation of the other burner is permitted (Step 7 or Step 17).

  Here, when there is a heating operation command for the other burner (Step 11 or Step 1), the heating operation of the corresponding burner is started (Step 12 or Step 2).

  It is determined whether the pan on the burner is a heating compatible load using electrical characteristics (Step 13 or Step 3). If it is a non-conforming pan, heating is stopped (Step 14 is Step 4). When the heating power is sequentially increased and the current detection means 3 determines that the corresponding burner has reached the target value when the input current reaches the set value (Step 15 or Step 5), and at the same time (Step 16 or Step 6), It moves to the next process such as power adjustment.

  The target value of the input current of the single burner is the set current of each burner, and the target value of simultaneous heating is the total value of the set currents of both burners.

  In addition, the load suitability determination can be performed by combining input current, heating coil current, heating coil voltage, and the like, but is not particularly limited.

  As described above, in the present embodiment, the rectifier circuit 2 and the current detection means 3 are shared by the two inverters, and the first and second burners 9 and 10 have an input current of one burner. By performing simultaneous heating with the other burner after reaching the set value in advance by each power setting, it is possible to supply predetermined power to each inverter even if simultaneous operation of two independent inverters is performed. The inverter circuit can be miniaturized, and an induction heating apparatus with a small circuit mounting volume can be realized.

(Embodiment 2)
FIG. 3 is a power qualitative change graph when two burners are heated in the induction heating device according to the second embodiment of the present invention. The configuration of the present embodiment is the same as that of the first embodiment.

In FIG. 3, both burners perform duty control that repeats ON / OFF in a certain period, and the average power is determined by the ratio of the ON time and the OFF time.

  The control means 8 operates the semiconductor switches in the first and second inverters 4 and 5 so that the electric power of the first and second burners 9 and 10 becomes a set value.

  Here, since the current detection means 3 detects the total current of the first and second burners 9 and 10 during simultaneous heating, the individual power of each burner may not be known.

  Therefore, duty control is performed so that at least one of the burners is repeatedly turned ON / OFF for a certain time, and the control means 8 detects the other input current when one of the burners is OFF, and both burners are operating. Sometimes, by detecting the total input current, the power of each burner can be reliably set to a set value.

  Note that, when both of the two burners are duty controlled, the control means 8 can more accurately control the input power of each burner by preventing the OFF times from overlapping.

  As described above, in the present embodiment, when performing simultaneous heating of two burners, at least one inverter performs duty control in which the ON state and the OFF state continue for a certain period of time, whereby the rectifier circuit 2 and the input current are Even if the two inverters are simultaneously operated in the configuration in which the detection means 3 is shared, the input current of each inverter can be accurately detected, and predetermined power can be accurately supplied to each inverter.

(Embodiment 3)
FIG. 4 is an input current change graph when the load fluctuates when two burners are heated in the induction heating device according to the third embodiment of the present invention. The configuration of the present embodiment is the same as that of the first embodiment.

  In FIG. 4, since the current detection means 3 detects the total current during simultaneous heating of both burners, for example, when the load is removed from the heating coil, the input current becomes the set value (target value). On the other hand, fewer states will occur.

  Therefore, when the state where the input current is less than the target value (ΔI) continues for a certain time (Δt), the control means 8 considers that the load has fluctuated and stops each burner. The action can be performed.

  Note that FIG. 4 shows a case where the input current is smaller than the target value by a certain amount, but even when the input current is larger than the certain amount continues for a certain period of time, it is desirable that the load be varied and stopped.

  Further, the detection time (Δt) is detected in a shorter time than the correction time in which the control means 8 detects that the input current is small and increases the conduction time or frequency of the semiconductor switch in each inverter, thereby further improving the detection accuracy. Can be raised.

  As described above, in the present embodiment, when performing simultaneous heating of the two burners, the control means 8 detects the detected value of the current detection value 3 and the target after the detection value of the current detection means 3 reaches the target value. When the value differs by a predetermined value or more within a certain time, at least one of the first and second inverters 4 and 5 is stopped.

  As a result, even when the two inverters are operated simultaneously in a configuration in which the rectifier circuit and the input current detection means are shared, heating is performed when the heating conditions change by moving the load placed on each heating coil. The operation can be stopped and unnecessary heating operation can be suppressed.

(Embodiment 4)
FIG. 5 is a graph showing a change in conduction time of the semiconductor switch when two burners are heated in the induction heating device according to the fourth embodiment of the present invention. The configuration of the present embodiment is the same as that of the first embodiment.

  In FIG. 5, when the two burners are simultaneously heated, the current detection means 3 detects the total current of the two burners, so that, for example, when a load such as a pan is shifted from the initial placement state. The control means 8 performs control so that the conduction time (Ton) of the semiconductor switch in the first or second inverter 4 or 5 becomes longer so that the input current becomes a set value (target value).

  Here, the control means 8 detects the conduction time in the stable state when the input current reaches the set value (target value) (conduction time A in FIG. 5), and sets that time as the conduction time in the stable state.

  The conduction time that is longer than the stable conduction time by a certain time (Δα) is defined as the maximum conduction time (conduction time B in FIG. 5) so that the conduction time does not increase any further.

  As a result, even if the load such as the pan further deviates from the center of the burner, the conduction time does not increase beyond the maximum conduction time (Tonmax). Therefore, as the coupling between the heating coil and the load such as the pan becomes worse, the input power is reduced. It will decrease.

  Therefore, it is possible to prevent unnecessarily large power from being supplied to the load in a state where the load such as the pan is shifted from the center of the burner.

  Further, when the conduction time of one of the first burner 9 and the second burner 10 reaches the maximum conduction time (Tonmax), the increase in the conduction time of both burners is limited.

  Thereby, when the electric power of the burner different from the burner in which the load such as the pan is shifted is increased, it is possible to prevent the electric power from being concentrated and supplied to one of the burners.

  In addition, when the conduction time of one of the first burner 9 and the second burner 10 reaches the maximum conduction time (Tonmax), by stopping at least one of the burners, the load on the pan or the like is shifted. It is possible to prevent the electric power obtained by increasing the current of the burner different from the generated burner from being concentrated on one of the burners.

  In the present embodiment, a limit value related to Ton is provided. However, when control is performed based on a change in frequency, a minimum frequency (f−Δα: fmin) allowable for the stable frequency (f) is provided. Similar control can be performed.

  As described above, in the present embodiment, when the two burners are simultaneously heated, when the first and second inverters 4 and 5 are simultaneously operated, the control unit 8 detects the detected value of the current detection unit 3. The conduction time of the semiconductor switches in the first and second inverters 4 and 5 when the target value is reached is defined as the stable conduction time, and when the target value is not changed, the conduction time of a certain time or more from the stable conduction time. If the load placed on each burner deviates from the center even when two independent inverters are operated simultaneously in a configuration in which the rectifier circuit and current detection means are shared by providing a maximum conduction time that does not increase Furthermore, since the input power can be reduced as the load deviates from the center of the burner, it is possible to prevent a large input power from being supplied when the load deviates from the center.

  As described above, the induction heating device according to the present invention can reduce the size of the inverter circuit, and can reduce the volume of the circuit mounting. Therefore, the induction heating device is effective for a cooker that performs heating with a plurality of burners. .

The circuit block diagram of the induction heating apparatus in Embodiment 1 of this invention Flow chart of operation of induction heating apparatus in Embodiment 1 of the present invention Power qualitative change graph at the time of two burner heating of induction heating device in Embodiment 2 of the present invention Input current change graph at the time of load fluctuation at the time of two burner heating of induction heating device in Embodiment 3 of the present invention Conductive time change graph of semiconductor switch during heating of two burners of induction heating device in embodiment 4 of the present invention Circuit diagram of a conventional induction heating cooker

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectifier circuit 3 Current detection means 4 1st inverter 5 2nd inverter 6 1st heating coil 7 2nd heating coil 8 Control means 9 1st burner 10 2nd burner

Claims (3)

A rectifier circuit for rectifying an AC power supply, first and second inverters for converting the output of the rectifier circuit into high-frequency power and applying power to the first and second heating coils, and an input current from the AC power supply Current detecting means for detecting, and control means for controlling the conduction time of the plurality of semiconductor switches in the first and second inverters according to the output of the current detecting means, wherein the control means is the first or the second After the input current of the second inverter reaches the target value, the induction heating device performs simultaneous operation with the other inverter, and when the first and second inverters operate simultaneously, the control means When the target value is not changed, the conduction time of the semiconductor switch in the first and second inverters when the detection value of the detection means reaches the target value is defined as the conduction time at the time of stability. It provided the maximum conduction time does not increase from stable during conduction time to a predetermined time or more conduction time induction heating device. 2. The induction heating apparatus according to claim 1, wherein when one of the first and second inverters reaches a maximum conduction time, the control means prohibits an increase in conduction time of both the first and second inverters. . Control means, when one of the first and second inverters has reached the maximum conduction time, the induction heating apparatus according to claim 1 for stopping at least one of the first and second inverters.

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