JP2009272267A - Induction heating device - Google Patents

Abstract

An induction heating apparatus capable of improving the heating efficiency as compared with a conventional circuit control system is provided.
A serial connection body of a first switching element and a first diode 15 for flowing a current only in one direction, and a serial connection body of a second switching element and a second diode 16 for flowing a current only in one direction. A rectifier bridge 17 configured by connecting both ends of two series connection bodies to each other, an AC power source 18, and an inverter 26 for supplying power to a load from a power source rectified from the AC power source by the rectifier bridge, A power supply voltage supplied to the inverter by controlling the first switching element and the second switching element, and a control means 27 for controlling the conduction of the first switching element and the second switching element and the inverter 27 To control.
[Selection] Figure 1

Description

  The present invention relates to a means for improving the heating efficiency of an induction heating apparatus such as an induction heating cooker that uses induction heating.

  Conventionally, as a method of adjusting the heating power of this type of induction heating device, for example, an inverter is used so that no beat noise due to a difference in operating frequency is generated when two adjacent heating units operate at different frequencies. A duty control technique is disclosed in which conduction control is performed exclusively for the two switching elements constituting the power supply and power adjustment is performed by changing the conduction ratio of the two switching elements (see, for example, Patent Document 1).

  The circuit diagram of FIG. 7 and the waveform of FIG. 8 show the technique of the conventional induction heating apparatus disclosed in Patent Document 1. When the gate signal generated by the control circuit 9 shown in FIG. 7 is applied to the first switching element 3 and the second switching element 4, voltage waveforms such as Vce1 and Vce2 in FIG. 8, and Ic1 and Ic2 A current waveform is obtained.

  The heating power can be reduced by changing the state of FIG. 8B to the state of FIG. That is, the heating power can be controlled by changing the duty of the two switching elements.

Further, as a method for improving the heating efficiency, for example, in the power supply mode, the inverter circuit 2 is operated near the resonance frequency determined by the heating coil 5 and the resonance capacitor 6 to improve the heating efficiency. Has been disclosed (see, for example, Patent Document 2).
Japanese Patent No. 2532565 JP 2007-103049 A

  However, in the configuration of the conventional Patent Document 1, when power control is performed, the operation periods of the two switching elements are different.

  As a result, the current value at the time of cutting off the conducting current in one switching element is larger than that at the time of rating, so the turn-off loss that occurs when transitioning from the conducting state to the non-conducting state becomes large. In one switching element, the conduction period is longer than that at the time of rating, so that conduction loss is increased.

  In this control method, as the duty is further away from 50%, the distortion of the waveform of the current flowing through the heating coil increases.

  As a result, an extra high-frequency current that is n-order times the driving frequency of the switching element is caused to flow, resulting in a reduction in efficiency.

  When heating a load having a single object to be heated and having a constant resonance frequency, the efficiency during rated heating can be increased by setting the operation frequency of the inverter in the vicinity of the resonance frequency of the load.

  However, when the user changes the pan, that is, the load like an induction heating cooker, the load characteristics vary depending on the type of the pan. It is not possible to achieve a rated heating power at a constant driving frequency and 50% duty.

  Therefore, when the operating frequency is constant regardless of the type of pan, a pan having a different operating frequency and resonance frequency must be heated in a state where the duty is smaller than 50% even at the time of rated heating, that is, the heating efficiency is low. It was in the state which did not get.

  Moreover, although the structure of the said patent document 2 is also what solves the subject of the said patent document 1, since accuracy is requested | required with respect to identification of the resonant frequency of load in order to perform heating control, in order to identify There was a problem that the circuit of this became complicated.

  In addition, since maximum heating is performed instantaneously, soft start cannot be performed and the switching element may be destroyed.

  As a means for solving the above-mentioned problems, a step-down circuit is provided between the power source and the inverter, and the power source voltage supplied to the inverter is varied by the step-down circuit, so that the inverter can be driven at a constant rate regardless of the type of pan. Although a method of setting the rated heating power at a frequency and Duty of 50% is also conceivable, application to a product is not easy because the number of partial points increases and switching loss due to the step-down circuit occurs.

  The present invention solves the above-described problems, and provides an induction heating apparatus capable of improving heating efficiency by replacing parts with respect to a conventional circuit configuration and without requiring complicated control. The purpose is to provide.

  In order to solve the above-described conventional problems, an induction heating apparatus according to the present invention includes a first connection element that allows current to flow only in one direction and a series connection body of a first diode, and a second current that flows only in one direction. A switching element and a series connection body of a second diode, a rectification bridge configured by connecting both ends of the two series connection bodies to each other, an AC power source, and a power source obtained by rectifying the AC power source by the rectification bridge An inverter for supplying electric power, and a first switching element, conduction control of the second switching element, and control means for controlling the inverter, by controlling the first switching element and the second switching element The power supply voltage supplied to the inverter is controlled.

  As a result, the rectified power source can be provided with a period that does not contribute to heating, so even if the inverter is operated at a constant frequency and a duty of 50%, the average power per unit time can be kept below the rated value. At the time of supply, the inverter can be operated at a constant frequency and a duty of 50% regardless of the set heating power.

  According to the induction heating device of the present invention, even if the load characteristics differ by changing the pan, the inverter operates at a constant operating frequency by controlling the conduction timing of the switching element connected as part of the rectifier bridge. Since the rated heating power can be obtained at a duty of 50%, the heating efficiency can be improved.

The first invention is a series connection body of a first switching element and a first diode that flows current only in one direction, and a series connection body of a second switching element and a second diode that flows current only in one direction. A rectifier bridge configured by connecting both ends of the two series connection bodies to each other, an AC power source, an inverter for supplying power to a load from a power source rectified from the AC power source by the rectifier bridge, Control means for controlling the conduction of the first switching element and the second switching element and the inverter, and supplying the inverter by controlling the first switching element and the second switching element By controlling the power supply voltage, even if the load characteristics differ by changing the pan, By controlling the conduction timing of the switching elements, the inverter will be rated heating power at a constant operating frequency and Duty 50%, it is possible to improve the heating efficiency.

  According to a second aspect of the invention, in the first aspect of the invention, when heating a load made of a material having a low resistivity, the first switching element and the first switching element when the absolute value of the instantaneous voltage of the AC power source is greater than or equal to a threshold value By making the second switching element non-conductive, the peak value of the voltage and current generated in the inverter can be suppressed, so that parts with a small rating can be used and can be realized at low cost. .

  According to a third aspect of the invention, in particular, the heating power of the first or second aspect of the invention is a pan having a characteristic that is easy to heat by changing and adjusting a non-conduction period of the first switching element and the second switching element. In the case of heating, the rated heating power can be made constant by providing a period that does not contribute to heating, and even if the heating power is low, the operating frequency of the inverter is near the resonance frequency and the duty is 50%. Since it can be operated, the heating efficiency can be improved.

  According to a fourth aspect of the present invention, in particular, the first switching element and the second switching element according to any one of the first to third aspects of the present invention are configured such that the AC power supply changes from a non-conductive state to a conductive state in the vicinity of a zero cross point. By making the transition, the output voltage of the rectifying bridge 17 gradually increases from the zero voltage at the power supply frequency, so that it is possible to prevent the destruction of the circuit components including the switching elements constituting the inverter 26. .

  In a fifth aspect of the present invention, in particular, in any one of the first to fourth aspects, when the heating power is reduced, the operations of the first switching element and the second switching element are shorter than the period of the AC power supply. By making the cycle longer, it is possible to suppress not only the IGBT 19 and IGBT 20 used in the inverter but also the switching elements of the IGBT 11 and IGBT 13 used in the rectifier bridge.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, this invention is not limited by this embodiment.

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

  In FIG. 1, a first switching element that enables current conduction only in one direction, which includes an IGBT 11 and a diode 12 connected in series with the IGBT 11, an IGBT 13, and a unidirectional direction that includes a diode 14 connected in series with the IGBT 13. Only a rectifying bridge 17 composed of a second switching element, a first diode 15 and a second diode 16 capable of conducting current only, an AC power source 18, an LC filter 19, a rectifying bridge 17 and An inverter 26 composed of IGBTs 21 and 22, a heating coil 23, a resonant capacitor 24, and a snubber capacitor 25, and IGBTs 11, IGBTs 13, IGBTs 21, and IGBTs 22, for supplying power to the pan 20 from a power source obtained by rectifying the AC power source 18 using the LC filter 19. Continuity control Is composed of a control means 27.

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

  FIG. 2 shows the gate signal of each IGBT and the output voltage of the rectifier bridge when the IGBT 11 and IGBT 13 of the rectifier bridge of the induction heating device according to the first embodiment of the present invention are not switched between the conductive state and the non-conductive state. It is a figure which shows the relationship of heating electric power.

  FIG. 3 shows the gate signal of each IGBT, the output voltage of the rectifier bridge, and the heating when the IGBT 11 and IGBT 13 of the rectifier bridge of the induction heating device according to the first embodiment of the present invention are switched between the conductive state and the non-conductive state. It is a figure which shows the relationship of electric power.

  Here, in order to make the change in power easy to understand, the operating frequency and duty of the inverter 26 are constant, and the power supply voltage and heating power of the inverter 26 have a one-to-one relationship in the same pan.

  As shown in FIG. 3, when the IGBT 11 or the IGBT 13 is changed from the conductive state to the non-conductive state at a certain timing, the circuit of the rectifier bridge 17 is opened, and the output voltage of the rectifier bridge 17 becomes zero. As a result, the pan 20 is not heated regardless of the operation of the inverter 26.

  If the system of this development is used, even if the inverter 26 is operated at a constant frequency and a duty of 50%, a period that does not contribute to heating can be provided, so that the average power per unit time can be kept below the rating.

  Therefore, when the power is supplied, the heating efficiency can be improved by operating the inverter 26 at a constant frequency and a duty of 50% regardless of the set heating power.

  Moreover, in the conventional system, when the characteristics of the load change by changing the type of the pan, if the inverter 26 is operated at a constant frequency and a duty of 50%, the heating power changes and the rated heating power can be made constant. Although it was not possible, when using the method of this development, the rated heating power can be made constant by providing a long period of time that does not contribute to heating when heating a pan that is easy to heat (see FIG. 2). A = B in FIG.

  By heating the inverter 26 at a drive frequency near the resonance frequency of the load and a duty of 50% without heating the IGBT 11 and the IGBT 13, the pot 20 having a low resistivity is heated compared to a pot whose heating power is rated. In this case, in order to give the rated heating power to the pan 20, the value of the current flowing through the circuit becomes large.

  As the current increases, the voltage applied to the components of the inverter 26 and the like increases due to resonance. As a result, it is necessary to increase the current resistance and voltage resistance of the components. The voltage and current generated in the inverter 26 are correlated with the power supply voltage supplied to the inverter 26, and the voltage and current increase as the power supply voltage increases.

  As described above, in the present embodiment, when a material having a low resistivity is heated, the timing at which the IGBT 11 and the IGBT 13 are made non-conductive is set at a place where the instantaneous voltage of the AC power supply 18 is large, so that the inverter 26 Since the peak value of the generated voltage and current can be suppressed, parts with a small rating can be used, and the cost can be reduced.

In addition, the power adjustment in the developed system has a lower operating frequency than the system in which a step-down circuit is provided between the rectifier bridge 18 and the inverter 26, so that the loss in the switching element can be reduced.

(Embodiment 2)
FIG. 4 is a diagram showing the heating power control means of the induction heating apparatus according to the second embodiment of the present invention, and is a diagram in which the non-conduction periods of the IGBT 11 and the IGBT 13 are adjusted.

  In FIG. 4, since the average power is the heating amount per unit time, the heating power can be adjusted by controlling the non-conduction period when the pan is not heated (C in FIG. 4> C in FIG. 4). D).

  When the power is adjusted by the method of this development, even if the heating power is low, the operation frequency of the inverter 26 can be operated in the vicinity of the resonance frequency and at a duty of 50%, so that the heating efficiency can be improved.

  FIG. 5 is a diagram illustrating the timing at which the IGBT 11 and the IGBT 13 which are components of the clear current bridge of the induction heating device according to the second embodiment of the present invention transition from the non-conduction period to the conduction period.

  In FIG. 5, since the inverter 26 operates at a constant frequency and in the vicinity of 50% Duty regardless of the type of pan, the IGBT 11 and the IGBT 13 are transitioned from a non-conducting state to a conducting state when the power supply voltage of the AC power source 18 is large. Then, a large current / large voltage is instantaneously applied to the inverter 26, and the switching element may be destroyed.

  Therefore, the timing at which the IGBT 11 and the IGBT 13 transition from the non-conducting state to the conducting state is such that the power supply voltage of the AC power supply 18 is near zero.

  As a result, the output voltage of the rectifier bridge 17 gradually increases from the zero voltage at the power supply frequency, so that it is possible to prevent the destruction of circuit components including the switching elements constituting the inverter 26.

  FIG. 6 shows the relationship between the gate signal of the IGBT, which is a component of the rectifier bridge, and the output voltage of the rectifier bridge when the heating power of the induction heating device in the second embodiment of the present invention is reduced.

  When the power supply voltage supplied to the inverter 26 is almost unnecessary, it is not necessary to control the IGBT 11 and the IGBT 13 for every power supply cycle of the AC power supply 18, so that the operation cycle of the IGBT 11 and IGBT 13 is longer than the power supply cycle of the AC power supply 18. As a result, the power supply voltage can be switched near zero both when the IGBT 11 and the IGBT 13 transition from conduction to non-conduction and when the IGBT 11 and IGBT 13 transit from the non-conduction to the conduction state. The destruction of the switching elements of the IGBT 11 and the IGBT 13 used in the rectifier bridge 17 as well as the IGBT 19 and the IGBT 20 that are used can be suppressed.

  Further, during the operation period of the inverter 26, the phase difference between the voltage of the AC power supply 18 and the current flowing from the AC power supply 18 becomes zero, so that the power is supplied to the load with high efficiency by operating with the power factor of 1. Can be supplied.

  In the first and second embodiments, the duty of the IGBT 21 and the IGBT 22 in the inverter 26 is always 50% constant. However, when it is desired to finely control the heating power, the duty control may be used together.

  In the first and second embodiments, the IGBT is used as the switching element constituting the rectifying bridge 17. However, any switching element that can be controlled so that current flows in only one direction can be used. Since such a switching element can also be applied to the present invention, for example, a switching element suitable for low-frequency driving such as a thyristor and a mechanical switching element such as a relay can be applied, and it is necessary to limit the switching element to only an IGBT. Absent.

  As described above, the induction heating device according to the present invention can adjust the power without changing the drive frequency and duty of the inverter and can improve the heating efficiency of the induction heating device. It is effective for equipment that performs

The circuit diagram of the induction heating apparatus in Embodiment 1 of this invention The figure which shows the relationship between the gate signal of each IGBT, the output voltage of a rectification bridge, and heating power when not switching IGBT11 and IGBT13 of the rectification bridge of the induction heating apparatus in Embodiment 1 of this invention to a conduction | electrical_connection state and a non-conduction state. The figure which shows the relationship between the gate signal of each IGBT, the output voltage of a rectification bridge, and heating power when switching IGBT11 and IGBT13 of the rectification bridge of the induction heating apparatus in Embodiment 1 of this invention to a conduction | electrical_connection state and a non-conduction state. The figure which shows the control means of the heating electric power of the induction heating apparatus in Embodiment 2 of this invention. The figure which shows the timing which IGBT11 and IGBT13 which are the components of the rectification bridge | bridging of the induction heating apparatus in Embodiment 2 of this invention change from a non-conduction period to a conduction | electrical_connection period. The figure which shows the relationship between the gate signal of IGBT which is a structural component of a rectification bridge when reducing the heating power of the induction heating apparatus in Embodiment 2 of this invention, and the output voltage of a rectification bridge. The figure which shows the example of a circuit structure of the conventional induction heating apparatus The figure which shows each part waveform of the conventional induction heating apparatus

Explanation of symbols

11 IGBT
12 Diode 13 IGBT
14 diode 15 first diode 16 second diode 17 rectifier bridge 18 AC power supply 19 LC filter 20 pan (load)
21 IGBT
22 IGBT
23 Heating coil 24 Resonance capacitor 25 Snubber capacitor 26 Inverter 27 Control means

Claims (6)

A series connection body of a first switching element and a first diode that allows current to flow only in one direction, a series connection body of a second switching element and a second diode that flows current only in one direction, and the two series A rectification bridge configured by connecting both ends of a connection body to each other, an AC power supply, an inverter for supplying power to a load from a power supply obtained by rectifying the AC power supply using the rectification bridge, and the first switching element And control means for controlling the conduction of the second switching element and the inverter, and the power supply voltage supplied to the inverter is controlled by controlling the first switching element and the second switching element. Induction heating device. When heating a load made of a material having a low resistivity, the first switching element and the second switching element are brought into a non-conductive state when the absolute value of the instantaneous voltage of the AC power source is equal to or greater than a certain threshold value. The induction heating apparatus according to claim 1. The induction heating apparatus according to claim 1 or 2, wherein the heating power is adjusted by changing a non-conduction period of the first switching element and the second switching element. The induction heating device according to any one of claims 1 to 3, wherein the first switching element and the second switching element transition from the non-conducting state to the conducting state near the zero cross point of the AC power supply. The induction heating device according to any one of claims 1 to 4, wherein when the heating power is reduced, an operation period of the first switching element and the second switching element is made longer than a period of the AC power supply. . The induction heating apparatus according to any one of claims 1 to 5, wherein the control of the heating power uses a duty control means of the inverter in combination.