JP2007294344A - Induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device capable of maintaining and outputting rated power in response to characteristics of a heated object. <P>SOLUTION: The induction heating device is provided with a resonance circuit including first and second switching elements 12, 13, a heating coil 14, and a resonance capacitor 15, a power supply 11, a control circuit 17, a material determination circuit 19 of the heated object 16, and a temperature detection circuit 18, and is operated by varying an operation mode of an inverter by a detection signal of the temperature detection circuit 18. Thereby, even when the material determination circuit 19 of the heated object 16 erroneously determines the operation mode, and the inverter is operated in the erroneous operation mode, temperature information of the switching elements is fed back as criteria for switching the operation mode of the inverter, and loss of the switching elements is suppressed, and the rated power can be maintained and output in response to the characteristics of the heated object. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is capable of efficiently induction-heating an object to be heated having high conductivity and low magnetic permeability such as an aluminum pot and an object to be heated having low conductivity and high permeability such as an iron pot. The present invention relates to an induction heating device used as an induction heating cooker.

Conventionally, in this type of induction heating apparatus, since the switching element control method and the resonance frequency of the resonance current differ depending on the material and thickness of the object to be heated, a material determination circuit for the object to be heated is provided, and each object to be heated is provided. What heats in the optimal state is known (for example, refer patent document 1).
JP 2004-362798 A

  However, in the above-described conventional configuration, the operation mode may be erroneously determined particularly in an object to be heated having a characteristic in the vicinity of the inverter control method, that is, the operation mode switching point. By driving in the wrong operation mode, the temperature of the switching element rises above the original normal operation temperature, and when the switching element temperature exceeds a certain threshold value, the protection circuit of the switching element is activated and heated. There is a case where control is performed so that the temperature of the switching element is lowered by reducing the heating amount to the object. On the other hand, due to an erroneous determination in the material determination circuit of the object to be heated, the temperature of the switching element may become lower than the original normal operation temperature and the amount of heating to the object to be heated may not rise to the rating. . Also, when the characteristics of the object to be heated change due to movement of the object to be heated during the operation of the inverter, the same result as when the material judgment circuit of the object to be heated has mistakenly determined the operation mode is obtained. End up. Furthermore, if the inverter is continuously operated in an incorrect operation mode, parts other than the switching element such as a heating coil also become high temperature, which may cause destruction of each part. Further, if the inverter is operated in a state where the circuit parts generate a lot of heat, the power loss in the entire circuit increases and the efficiency is lowered.

  The present invention solves the above-mentioned conventional problems, and even if the material determination circuit of the object to be heated makes an incorrect determination of the operation mode, the temperature information of the switching element is used as a determination to switch the operation mode of the inverter. An object of the present invention is to provide an induction heating device capable of maintaining and outputting a rated power according to the characteristics of an object to be heated by feedback.

  In order to solve the conventional problems, an induction heating apparatus according to the present invention includes a first switching element, a second switching element, a first reverse conducting element, a second reverse conducting element, and a heating coil. And a resonance capacitor, a power source, a control circuit, a material determination circuit, and a temperature detection circuit, and the control circuit includes a detection signal output from the temperature detection circuit to the control circuit. The control signal output to the first switching element and the second switching element is changed from the start of conduction of the first switching element to the inverter until the first switching element is turned off. The period of the resonant current that flows is changed even during driving of the inverter, and the rated output power is maintained and the temperatures of the first switching element and the second switching element are maintained. And controls to be below a certain threshold.

  As a result, the operation mode of the inverter is switched so that the temperature of the switching element falls below a certain threshold value, so that the output power does not decrease due to the erroneous operation mode discrimination of the material judgment circuit of the object to be heated. Can be controlled. In addition, since the inverter operating mode is switched so as to maintain the rated output power determined by the characteristics of the object to be heated, the temperature of the switching element is below the normal operating temperature and power is not output to the rated value. Can be. Further, by efficiently changing the drive frequency of the switching element, it is possible to heat with high output even if the characteristics of the object to be heated change.

  The induction heating device of the present invention can heat at high output according to the characteristics of the object to be heated while maximizing heat generation of circuit components such as switching elements while maintaining rated output power.

  According to a first aspect of the present invention, there is provided a serial connection body of a first switching element and a second switching element, a first reverse conducting element connected in parallel to the first switching element, and the second switching element. Including a second reverse conducting element connected in parallel and a resonant circuit including a heating coil and a resonant capacitor connected in parallel to the first switching element or the second switching element; An inverter that supplies a resonance current to the resonance circuit by exclusive conduction between the switching element and the second switching element, a power source that supplies power to the inverter, the first switching element, and the second switching element A control circuit for controlling conduction, a material determination circuit for determining characteristics of the object to be heated, and the first switching element or the second switching element. A temperature detection circuit that directly or indirectly detects the temperature of the element and outputs the detection signal to the control circuit, the control circuit being accompanied by a detection signal output from the temperature detection circuit to the control circuit The control signal output from the control circuit to the first switching element and the second switching element is changed, and the first switching element is turned off after the first switching element is turned on. By changing the period of the resonance current flowing through the inverter by the time the inverter is being driven to maintain the rated output power, the temperature of the first switching element and the second switching element is set to a certain threshold value. The induction heating device is controlled to be lower. As a result, the operation mode of the inverter is switched so that the temperature of the switching element falls below a certain threshold value, so that the output power does not decrease due to the erroneous operation mode discrimination of the material judgment circuit of the object to be heated. Can be controlled. In addition, since the inverter operating mode is switched so as to maintain the rated output power determined by the characteristics of the object to be heated, the temperature of the switching element is below the normal operating temperature and power is not output to the rated value. Can be. Further, by efficiently changing the drive frequency of the switching element, it is possible to heat with high output even if the characteristics of the object to be heated change.

  According to a second aspect of the invention, in particular, in the first aspect of the invention, when the temperature of the first switching element or the second switching element exceeds a certain threshold value, after the conduction of the first switching element starts By controlling so that the period of the resonance current flowing from 1 increases by one period, the temperature of the switching element can be lowered, and heating can be maintained at an output corresponding to the characteristics of the object to be heated. Further, since the period of the resonance current flowing during one switching operation is increased, the number of switching times of the switching element is reduced with respect to the frequency of the resonance current applied to the object to be heated, and the switching loss can be reduced.

  In a third aspect of the invention, in particular, in the first aspect of the invention, when the output power is lower than the rated value, the control circuit controls the period of the resonance current that flows after the conduction of the first switching element is reduced by one period. As a result, the power is driven with a higher power factor than before reducing the period of the resonance current by one period, so that the output power can be increased.

  According to a fourth aspect of the invention, in particular, in any one of the first to third aspects of the invention, the control circuit may be configured so that a current flows through the first switching element after the conduction of the first switching element. By changing the drive stop timing of the first switching element, the resonance current at the start of conduction of the switching element flows through the reverse conduction element connected in parallel to the switching element. Loss generated in the element can be eliminated. Further, since it can be turned off at an arbitrary timing as long as the current flows in the switching element, the output power can be arbitrarily varied.

  In the fifth invention, in particular, in any one of the first to fourth inventions, the power supply for supplying power to the inverter is boosted and smoothed by the boost smoothing means and supplied to the inverter to change the supply voltage. Thus, even if the period of the resonance current flowing through the inverter changes from the start of conduction of the switching element to the non-conduction state, the output power can be adjusted by adjusting the power supply voltage.

  In a sixth aspect of the invention, in particular, in any one of the first to fifth aspects of the invention, the resonant capacitor is formed by changing the resonant frequency of the resonant circuit by switching two or more values. Since the period of the resonance current flowing through the inverter can be changed from the start of conduction of the switching element to the non-conduction state without greatly changing the drive frequency, the switching loss of the switching element can be changed without much change. The inverter can be operated in an operation mode according to the characteristics of the heated object.

  In a seventh aspect of the invention, in particular, in any one of the first to sixth aspects of the invention, a current detection circuit that detects the current of the heating coil and outputs the detection signal to the control circuit, and a voltage of the resonance capacitor are detected. And at least one of a voltage detection circuit that outputs the detection signal to the control circuit, and the control circuit includes the detection signal output from the current detection circuit or the voltage detection circuit to the control circuit, and By changing the control signal output from the control circuit to the first switching element and the second switching element, and controlling so as not to exceed the withstand current of the heating coil and the withstand voltage of the resonant capacitor, If circuit components are destroyed by changing the inverter operating mode, do not switch the inverter operating mode even if the output power is below the rated value. It is possible to prevent breakage of the circuit component to. On the other hand, if the switching element temperature exceeds a certain threshold, if the operation mode of the inverter is changed and the circuit components are destroyed, the switching element becomes non-conductive after the start of conduction. By changing the period of the resonant current flowing through the inverter until the switching element temperature falls, the circuit is controlled so that the output is lowered without switching the inverter operation mode and the switching element temperature is lowered. Can prevent destruction.

  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 an induction heating apparatus according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the induction heating apparatus according to the present embodiment includes a series connection body of a first switching element 12 and a second switching element 13, and a first connected in parallel to the first switching element 12. The reverse conducting element 12a, the second reverse conducting element 13a connected in parallel to the second switching element 13, and the heating coil connected in parallel to the first switching element 12 or the second switching element 13 14 and a resonance circuit including a resonance capacitor 15 and an inverter that includes the resonance circuit and supplies a resonance current to the resonance circuit by exclusive conduction between the first switching element 12 and the second switching element 13. . In addition, a power source 11 that supplies power to the inverter, a control circuit 17 that controls conduction of the first switching element 12 and the second switching element 13, an object to be heated 16 such as a pot heated by the heating coil 14, A temperature at which the temperature of the first switching element 12 or the second switching element 13 is detected directly or indirectly and the detection signal is output to the control circuit 17. A detection circuit 18 is also provided. And the control circuit 17 changes the control signal output to the 1st switching element 12 and the 2nd switching element 13 from the control circuit 17 with the detection signal output to the control circuit 17 from the temperature detection circuit 18, The period of the resonance current flowing through the inverter from the start of conduction of the first switching element 12 to the non-conduction state of the first switching element 12 is changed even during driving of the inverter to maintain the rated output power. However, the temperature of the first switching element 12 and the second switching element 13 is controlled to fall below a certain threshold value.

  Also, a snubber capacitor 20 is connected in parallel with the second switching element 13 so as to suppress switching loss that occurs when the first switching element 12 and the second switching element 13 transition from on to off. Yes.

  Next, operation | movement of the induction heating apparatus in the said structure is demonstrated.

  The inverter is of a single end push pull type, and operates under control as is generally known in a steady state.

  Immediately after the operation of the inverter, the period of the resonance current flowing through the inverter from the start of conduction of the first switching element 12 to the non-conduction state is determined by the discrimination of the material judgment circuit 19 of the object to be heated 16 (see FIG. 2), in this operation mode, if the temperature of the first switching element 12 or the second switching element 13 exceeds a certain threshold value, the first switching element 12 is turned off after the start of conduction. The temperature of the switching element is lowered by setting the period of the resonance current flowing through the inverter to 3 periods until the temperature reaches (see FIG. 3). On the other hand, if the temperature of the first switching element 12 and the second switching element 13 is not more than the normal operation temperature and the power cannot be output to the rated value, the first switching element 12 starts to conduct. The rated power is output by changing the period of the resonance current flowing through the inverter from 3 periods to 2 periods until it becomes a non-conductive state later.

  In the above control method, the amount of heating to the object to be heated 16 can be adjusted by changing the period of the resonance current that flows during one switching operation of the first switching element 12. When the temperature of the first switching element 12 or the second switching element 13 exceeds a certain threshold value, the period of the resonance current that flows after the start of conduction of the first switching element 12 is increased by one period. The temperature of the element can be lowered, and heating can be maintained with an output corresponding to the characteristics of the article to be heated 16. Further, since the period of the resonance current that flows during one switching operation is increased, the switching frequency of the switching element is reduced with respect to the frequency of the resonance current applied to the object to be heated 16, and the switching loss can be reduced. . That is, as the period of the resonance current that flows during one switching operation increases, the number of times the first switching element 12 and the second switching element 13 are switched with respect to the frequency of the resonance current that appears in the article to be heated 16 decreases. , Switching loss can be reduced.

  Further, since the operation mode of the inverter is changed so that the temperature of the first switching element 12 and the second switching element 13 is lower than a certain threshold value, the erroneous operation mode of the material determination circuit 19 of the object to be heated 16 Therefore, it is possible to control so that the output power does not decrease due to the determination.

  Further, if the temperature of the first switching element 12 and the second switching element 13 is equal to or lower than the temperature during normal operation and the power is not output to the rated value, the inverter is maintained so as to maintain the rated output power. The operation mode can be changed and the output power can be increased.

  Further, when the output power is lower than the rated value, the power factor is higher than before reducing the period of the resonance current by reducing the period of the resonance current by one period by reducing the period of the resonance current flowing after the first switching element 12 is turned on. Since it is driven in a state, the output power can be increased.

  Further, the control circuit 17 changes the drive stop timing of the first switching element 12 during the period in which the current flows through the first switching element 12 after the first switching element 12 starts to conduct, Since the resonance current at the start of conduction of the second switching element 13 flows through the reverse conduction element 13a connected in parallel with the second switching element 13, the switching loss generated in the switching element 13 at the start of conduction is eliminated. Can do.

  Further, the output power can be arbitrarily varied by turning off the first switching element 12 within an arbitrary period during which a current flows through the first switching element 12.

  As described above, in the present embodiment, not only the result of the material determination circuit 19 of the object to be heated 16 but also the temperatures of the first switching element 12 and the second switching element 13 during the driving of the inverter are the operations of the inverter. By reflecting the change in the mode, the maximum power can be output according to the object 16 to be heated. Further, by devising the drive stop timing, the output power can be arbitrarily changed, and the switching loss generated in the first switching element 12 and the second switching element 13 can be reduced.

(Embodiment 2)
FIG. 4 shows an induction heating device according to Embodiment 2 of the present invention. The same elements as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The present embodiment is different from the first embodiment in that a boosting smoothing circuit 21 is provided so that the power supply 11 of the inverter can be boosted and smoothed, and a signal generated from the control circuit 17 causes the resonance capacitor 15 to The capacity can be switched between two or more values, and the current detection circuit 22 is provided to detect the current of the heating coil 14 and output the detection signal to the control circuit 17. Although not shown, a voltage detection circuit that detects the voltage of the resonance capacitor 15 and outputs the detection signal to the control circuit 17 is provided in place of the current detection circuit 22 or is used in combination.

  In the above induction heating device, even if the period of the resonance current flowing through the inverter changes from the start of conduction of the first switching element 12 to the non-conduction state by changing the supply voltage to the inverter, the output power Can be adjusted to any value.

  The resonance capacitor 15 changes the resonance frequency of the resonance circuit by switching two or more capacitors, so that the driving frequency of the first switching element 12 and the second switching element 13 is not significantly changed. Since the period of the resonance current flowing in the inverter can be changed from the start of conduction of the first switching element 12 to the non-conduction state, the switching loss of the first switching element 12 and the second switching element 13 is not much. The inverter can be operated in an operation mode according to the characteristics of the article to be heated 16 without being changed.

  Further, the control circuit 17 includes at least one of a current detection circuit 22 of the heating coil 14 or a voltage detection circuit of the resonance capacitor 15, and the control circuit 17 is accompanied by a detection signal output from the current detection circuit 22 or the voltage detection circuit to the control circuit 17. By changing the control signal output from the control circuit 17 to the first switching element 12 and the second switching element 13 and controlling so as not to exceed the withstand current of the heating coil 14 and the withstand voltage of the resonant capacitor 15, If circuit components are destroyed by changing the operation mode of the inverter, the circuit components can be prevented from being destroyed by not switching the operation mode of the inverter even if the output power is lower than the rated value. On the other hand, if the temperature of the first switching element 12 or the second switching element 13 exceeds a certain threshold value, if the circuit components are destroyed by changing the operation mode of the inverter, Even if the temperature of the first switching element 12 or the second switching element 13 is lowered by changing the period of the resonance current flowing through the inverter from the start of conduction of the first switching element 12 to the non-conduction state, the inverter Without switching the operation mode, it is possible to prevent the circuit components from being destroyed by lowering the output and controlling the temperature of the first switching element 12 and the second switching element 13 to decrease.

  As described above, in the present embodiment, the maximum power can be output according to the object to be heated 16 by changing the power supply voltage of the inverter and the capacity of the resonance capacitor 15. Further, by providing the current detection circuit 22 or the voltage detection circuit, it is possible to prevent the circuit components from collapsing by pursuing the optimum operation mode of the article to be heated 16.

  The control method in the first and second embodiments can be applied to any inverter as long as it is an inverter type using a series connection body of two switching elements. Further, the present invention can be applied to a full bridge type, and the inverter system is not limited.

  As described above, the induction heating device according to the present invention is capable of heating at a high output according to the characteristics of the object to be heated while maximizing the heat generation of circuit components such as switching elements while maintaining the rated output power. As a result, the object to be heated may have several characteristics, which can be utilized in all inverter systems that change the operating mode of the inverter. Therefore, it can be applied to all induction heating apparatuses including business appliances as well as household appliances and household appliances in which the object to be heated changes like an IH cooking heater.

The circuit diagram which shows the induction heating apparatus in Embodiment 1 of this invention The figure which shows the control signal waveform and current waveform in the same induction heating device The figure which shows the other control signal waveform and current waveform in the same induction heating apparatus The circuit diagram which shows the induction heating apparatus in Embodiment 2 of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Power supply 12 1st switching element 12a 1st reverse conducting element 13 2nd switching element 13a 2nd reverse conducting element 14 Heating coil 15 Resonance capacitor 16 Heated object 17 Control circuit 18 Temperature detection circuit 19 Material determination circuit 21 Boosting smoothing circuit 22 Current detection circuit

Claims (7)

A series connection body of a first switching element and a second switching element, a first reverse conducting element connected in parallel to the first switching element, and a first connected in parallel to the second switching element Two reverse conducting elements and a resonant circuit including a heating coil and a resonant capacitor connected in parallel to the first switching element or the second switching element, the first switching element and the first switching element An inverter that supplies a resonance current to the resonance circuit by exclusive conduction of two switching elements, a power source that supplies power to the inverter, and a control circuit that controls conduction of the first switching element and the second switching element And a material determination circuit for determining the characteristics of the object to be heated, and the temperature of the first switching element or the second switching element. A temperature detection circuit that detects the contact signal indirectly or indirectly and outputs the detection signal to the control circuit, and the control circuit includes a detection signal output from the temperature detection circuit to the control circuit. The control signal output to the first switching element and the second switching element is changed from the start of conduction of the first switching element to the inverter until the first switching element is turned off. Controlling the temperature of the first switching element and the second switching element to be lower than a certain threshold value while maintaining the rated output power by changing the period of the flowing resonant current even during driving of the inverter. Induction heating device. When the temperature of the first switching element or the second switching element exceeds a certain threshold value, the control circuit controls to increase the period of the resonant current that flows after the first switching element starts to conduct by one period. The induction heating apparatus according to claim 1. 2. The induction heating device according to claim 1, wherein when the output power is less than a rated value, the control circuit controls the period of the resonance current that flows after the first switching element starts to conduct to be reduced by one period. 4. The control circuit according to claim 1, wherein the control circuit changes a drive stop timing of the first switching element within a period in which a current flows through the first switching element after the conduction of the first switching element. The induction heating apparatus according to any one of the above. The induction heating apparatus according to any one of claims 1 to 4, wherein a power source that supplies power to the inverter is boosted and smoothed by a boosting and smoothing means, supplied to the inverter, and the supply voltage is changed. The induction heating device according to any one of claims 1 to 5, wherein the resonance capacitor changes the resonance frequency of the resonance circuit by switching between two or more values. At least one of a current detection circuit that detects the current of the heating coil and outputs the detection signal to the control circuit, and a voltage detection circuit that detects the voltage of the resonance capacitor and outputs the detection signal to the control circuit. The control circuit outputs a control signal output from the control circuit to the first switching element and the second switching element in accordance with a detection signal output from the current detection circuit or the voltage detection circuit to the control circuit. The induction heating device according to any one of claims 1 to 6, wherein the induction heating device is controlled so as not to exceed a withstand current of the heating coil and a withstand voltage of the resonance capacitor.

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