JP5369878B2 - Induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device capable of miniaturizing a circuit. <P>SOLUTION: In the case a detected value of a current detection means 3 and a target value are different in more than a prescribed value within a fixed time in a constitution which has a rectifying circuit 2 and the current detection means 3 in common, by stopping at least one of first and second inverters 4, 5, the inverter circuit can be operated stably even if a load variation occurs, and can be miniaturized. <P>COPYRIGHT: (C)2011,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. 5 shows a conventional induction heating apparatus described in Patent Document 1. In FIG. As shown in FIG. 5, the commercial power supply 11, the first and second heating coils 16 and 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 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. 5, 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 inverters 14 and 15 first and second.

  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.

  Further, when supplying high-frequency power from the first and second inverters 14 and 15 to the first and second heating coils 16 and 17 at the same time, the microcomputer 18 is connected to each inverter by a current transformer. The inverter input current is detected, and 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 times of a plurality of semiconductor switches in the first and second inverters according to the current detection means And when the first and second inverters operate at the same time, after the detection value of the current detection means reaches the target value, the control means detects the detection value and the target value of the current detection means. This is an induction heating device that stops at least one of the first and second inverters when a difference of a predetermined value or more occurs within a certain time.

  As a result, even if two inverters are operated simultaneously in a configuration in which the rectifier circuit and the current detection means are shared, predetermined power can be supplied to each inverter and the state of the load on the heating coil varies. Therefore, stable operation of the inverter circuit is possible, and the mounting volume of the inverter circuit is reduced.

  The induction heating device of the present invention is configured to share the rectifier circuit and the current detection means for the two inverters, and supplies predetermined power to each inverter even if the two inverters are operated simultaneously. In addition, since fluctuations in the load on the heating coil can be detected, stable operation of the inverter circuit is possible, and a compact induction heating device with a small mounting volume of the inverter circuit can be realized.

The circuit block diagram of the induction heating apparatus in Embodiment 1 of this invention Input current change graph at the time of load fluctuation of induction heating device in Embodiment 1 of the present invention Input current change graph of induction heating device in Embodiment 2 of the present invention The graph which shows the maximum conduction time of the semiconductor switch of the induction heating apparatus in Embodiment 3 of this invention Circuit diagram of a conventional induction heating device

  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, When the second inverter operates simultaneously, the control means has a difference between the detection value of the current detection means and the target value within a predetermined time after the detection value of the current detection means reaches the target value. In addition, by using an induction heating device that stops at least one of the first and second inverters, even if two inverters are operated simultaneously in a configuration in which the rectifier circuit and the current detection means are shared, In addition to being able to supply a certain amount of power to the inverter, it is possible to detect fluctuations in the state of the load on the heating coil, enabling stable operation of the inverter circuit, and compact induction with a small mounting volume of the inverter circuit A heating device can be realized.

According to a second 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, When the second inverter operates simultaneously, the control means has a difference between the detection value of the current detection means and the target value within a predetermined time after the detection value of the current detection means reaches the target value. In addition, by setting the conduction time of at least one of the first and second inverters to the minimum conduction time, the two inverters can be operated simultaneously in a configuration in which the rectifier circuit and the current detection means are shared. Predetermined power can be supplied to the inverter, and when the load on the heating coil fluctuates, the time until reheating can be shortened, so the inverter circuit supplies power stably. Thus, a compact induction heating apparatus with a small mounting volume of the inverter circuit can be realized.

  According to a third aspect of the invention, in particular, when the inverter operates simultaneously, the control means of the first and second aspects of the first and second inverters when the detection value of the current detection means reaches the target value When the conduction time of the semiconductor switch is the stable conduction time, and there is no change in the target value, a rectifier circuit and current detection means are provided by providing a maximum conduction time that does not increase the conduction time for a certain time or more from the stable operation time. Even if simultaneous operation of two independent inverters is performed in a configuration in which the two are shared, if the load placed on each heating coil shifts, the input power can be reduced as the load deviates from the center of the heating coil. Therefore, it is possible to prevent a large input power from being supplied in a state where the load is shifted.

  The fourth aspect of the invention relates to the control means of the fourth aspect of the invention, particularly when either one of the first and second inverters reaches the maximum conduction time, the conduction time of both the first and second inverters. By prohibiting the increase, if the load placed on each heating coil is moved even if the independent inverter is operated simultaneously in a configuration in which the rectifier circuit and the current detection means are shared, the center of the heating coil Since the input power can be reduced as the pan deviates, it is possible to prevent a large input power from being supplied with the pan deviated.

  In the fifth aspect of the invention, in particular, the control means of the third aspect of the invention stops at least one of the first and second inverters when one of the first and second inverters reaches the maximum conduction time. As a result, the heating operation can be stopped when the load placed on each heating coil is moved even if the independent inverters are operated simultaneously in a configuration in which the rectifier circuit and the current detection means are shared. Unnecessary operations can be suppressed.

  Hereinafter, embodiments of the present invention will be described 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.

  Here, the first inverter 4 and the first heating coil 6, and the second inverter 5 and the second heating coil 7 are in accordance with instructions from the control means 8, such as pots placed on the respective heating coils. The load will be heated.

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

  FIG. 2 is an input current change graph when the load of the induction heating apparatus according to the first embodiment of the present invention varies.

  First, when the control means 8 receives an operation command to the first or second heating coils 6, 7, a load such as a pan placed on the first or second heating coils 6, 7 is adapted for heating. Whether it is a load or not is discriminated using electrical characteristics, etc. If it is a non-conforming pan, heating is stopped.

  On the other hand, when the control means 8 considers that the load is suitable, the control means 8 sequentially increases the heating power until the input current detected by the current detection means 3 reaches a set value.

  When power is supplied only to a single heating coil, the target value of the input current is an input current value for supplying predetermined power to each heating coil. The target value at the time of simultaneous heating is the total value of the respective input current values for supplying predetermined power to both heating coils.

  Here, when the heating coils are simultaneously heated, the current detection means 3 detects the total current of the input currents supplied to the respective inverters. For example, when the load is removed from the heating coils. As shown in FIG. 2, a state occurs in which the input current is smaller than the set value (target value).

  Therefore, when the input current continues to be small (ΔI) with respect to the target value for a certain time (Δt), the control means 8 considers that the load has fluctuated and stops the operation of each inverter.

  Note that FIG. 2 shows a case where the input current is smaller than the target value by a certain amount. However, even when the input current is larger than the certain amount continues for a certain period of time, it is desirable that the load is changed and stopped.

  Further, by setting the time (Δt) for detecting the fluctuation to be shorter than the correction time for the control means 8 to detect that the input current is small and increase the conduction time or frequency of the semiconductor switch in each inverter, It is possible to increase the detection speed.

  Furthermore, when the load fluctuation is detected, it is possible to identify the heating coil in which the load fluctuation has occurred by stopping the inverter in order. That is, when the inverter having a load change is stopped, the input current does not change, and when the inverter having no load change is stopped, the input current is reduced. Here, when the side where there was no load fluctuation is stopped, the cooking operation can be continued without feeling uncomfortable by quickly returning to the predetermined power.

  In addition, when it is possible to detect which inverter has a load change based on a change in the current flowing through the heating coil, the generated resonance voltage, or the like, the inverter can be preferentially stopped.

  Note that an inverter that has undergone load fluctuation (such as running out of load) performs a normal restart operation, and when the load is placed again at a normal position, it shifts to a simultaneous operation state.

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 a difference of a predetermined value or more occurs within a certain time, at least one of the first and second inverters 4 and 5 is stopped, so that two rectifier circuits and input current detecting means are shared. Even if simultaneous operation of the inverter is performed, fluctuations in the load placed on each heating coil can be detected, enabling stable operation of the inverter and realizing a compact induction heating device with a small mounting volume of the inverter circuit It is.

(Embodiment 2)
FIG. 3 is an input current change graph of the induction heating apparatus in the second embodiment of the present invention. The configuration of the present embodiment is the same as that of the first embodiment.

  When the heating coils are simultaneously heated, the current detection means 3 detects the total current of the input currents supplied to the respective inverters. For example, when a load is taken from the heating coil, As shown in FIG. 3, a state occurs in which the input current is less than the set value (target value).

  Therefore, when the input current continues to be small (ΔI) with respect to the target value for a certain time (Δt), the control means 8 considers that the load has fluctuated and determines the conduction time of each inverter as the minimum conduction time. To decrease.

  Although FIG. 3 shows a case where the input current is smaller than the target value by a certain amount, even when the input current is larger than the certain amount continues for a certain time, it is considered that there is a load fluctuation and the conduction time of each inverter is minimized. It is desirable to reduce it to time.

  Further, by setting the time (Δt) for detecting the fluctuation to be shorter than the correction time for the control means 8 to detect that the input current is small and increase the conduction time or frequency of the semiconductor switch in each inverter, It is possible to increase the detection speed.

  Furthermore, when the load fluctuation is detected, it is possible to identify the heating coil in which the load fluctuation has occurred by performing an operation of sequentially reducing the conduction time of each inverter to the minimum conduction time.

  In other words, if the conduction time of the inverter with load fluctuation is set to the minimum, the input current does not change, and if the conduction time of the inverter without load fluctuation is reduced to the minimum conduction time, the input current is reduced. .

  Here, when the conduction time of the inverter on the side where there is no load fluctuation is reduced to the minimum conduction time, the cooking operation can be continued without feeling uncomfortable by quickly returning to the predetermined power.

  Alternatively, it is possible to identify the inverter having the load fluctuation by sequentially increasing the conduction time after decreasing the conduction time of the inverter to the minimum conduction time when the load fluctuation is detected.

  In addition, when it is possible to detect which inverter has a load change based on a change in the current flowing through the heating coil, the generated resonance voltage, or the like, the inverter can be preferentially stopped.

  Note that an inverter that has undergone load fluctuation (such as running out of load) performs a normal restart operation, and when the load is placed again at a normal position, it shifts to a simultaneous operation state.

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 difference in value exceeds a predetermined value within a certain time, the conduction time of at least one of the first and second inverters 4 and 5 is set to the minimum conduction time, so that the rectifier circuit and the input current detection means are shared. Even if the two inverters are operated simultaneously in a simplified configuration, the heating operation can be stopped without a sense of incongruity when the heating conditions change by moving the load placed on each heating coil. It is possible to realize an induction heating device that suppresses an unnecessary operation.

(Embodiment 3)
FIG. 4 is a graph showing the maximum conduction time of the semiconductor switch of the induction heating apparatus in the third embodiment of the present invention. The configuration of the present embodiment is the same as that of the first embodiment.

  During simultaneous heating of both heating coils, the current detection means 3 detects the total current of the input currents supplied to the respective inverters, so that a load such as a pan is placed out of the initial placement state. In this case, the control means 8 controls the semiconductor switch in the first or second inverter 4 or 5 to have a longer conduction time (Ton) so that the input current becomes a set value. Here, the control means 8 detects the conduction time in the stable state (conduction time A in FIG. 4), and conducts further by setting the constant conduction time (Δα) from the conduction as the maximum conduction time (conduction time B in FIG. 4). I try not to increase the time.

  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 Tonmax, so the input power decreases as the coupling between the heating coil and the load such as the pan deteriorates. become.

  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 either one of the first inverter 4 and the second inverter 5 reaches the maximum conduction time (Tonmax), the increase in the conduction time of both inverters is limited, so that a load such as a pan When the power of the inverter different from the inverter in which the deviation occurs is increased, it is possible to prevent the power from being concentrated and supplied to one of the inverters.

  Alternatively, when the conduction time of one of the first inverter 4 and the second inverter 5 reaches the maximum conduction time (Tonmax), at least one of the inverters is stopped, so that a load such as a pan is shifted. It is possible to increase the current of an inverter different from the generated inverter and prevent electric power from concentrating on one inverter.

  In this 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. It is possible to perform similar control.

  As described above, in the present embodiment, when the first and second inverters 4 and 5 operate simultaneously when the two burners are simultaneously heated, 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 conduction time during the stable state. When the target value is not changed, the conduction time is longer than a certain time from the stable operation time. By providing the maximum conduction time that does not increase, the load placed on each heating coil is shifted from the center even when two independent inverters are operated simultaneously in a configuration in which the rectifier circuit and the current detection means are shared. In this case, since the input power can be reduced as the load deviates from the center of the heating coil, 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 enables the downsizing of the inverter circuit and reduces the circuit mounting volume, and thus is effective for a cooker that performs heating with a plurality of burners.

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 12 1st rectifier circuit 13 1st current transformer 18 Microcomputer 22 Second rectifier circuit 23 Second current transformer

Claims (5)

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 conduction times of a plurality of semiconductor switches in the first and second inverters according to the current detecting means, wherein the first and second inverters are when operating at the same time, the control means after reaching the target value as a sum current of the input current detection value of said current detecting means is supplied to each of the first and second inverters, said current detecting means when the target value and the detected value is above a predetermined value the difference is generated within a predetermined time, at least one of said first and second inverters is stopped, the first and second inverters With specifying the inverter Chi load variation occurs, when stopping the load fluctuation was not the inverter is an induction heating device attempting to bring to a predetermined power. 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 conduction times of a plurality of semiconductor switches in the first and second inverters according to the current detecting means, wherein the first and second inverters are when operating at the same time, the control means after reaching the target value as a sum current of the input current detection value of said current detecting means is supplied to each of the first and second inverters, said current detecting means when the target value and the detected value is above a predetermined value the difference is generated within a predetermined time, the minimum conduction time of the inverter at least one of conduction time of the first and second inverters is not stopped To the with load variations of the first and second inverters to identify the inverter occurs, if the load change was not the inverter is stopped, the induction heating to a minimum conduction time of returning to the predetermined power apparatus. When the first and second inverters operate simultaneously, the control means determines the conduction time of the semiconductor switch in the first and second inverters when the detection value of the current detection means reaches the target value. The induction heating apparatus according to claim 1 or 2, wherein when the target value is not changed, a maximum conduction time is provided in which the conduction time does not increase for a predetermined time or more from the stable running time. The induction heating apparatus according to claim 3, wherein the control means prohibits an increase in conduction time of both the first and second inverters when either one of the first and second inverters reaches a maximum conduction time. . The induction heating apparatus according to claim 3, wherein the control means stops at least one of the first and second inverters when either one of the first and second inverters reaches a maximum conduction time.

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