JP2006294436A - Induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device having a simple structure and capable of preventing element destruction caused by turn-on loss increase of a switching element in a wide power voltage range. <P>SOLUTION: This induction heating device includes: an input current detection means for detecting an input current or an input power detection means for detecting input power; a heating coil current detection means for detecting a heating coil current; and a turn-on mode determination means for determining that the device is in a turn-on mode when heating coil current determination output is below a predetermined value according to the input current detection output or input power detection output, and input voltage detection output; and is characterized by being controlled so as to suppress turn-on loss of the switching element when it is determined that the device is in a turn-on mode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an induction heating apparatus such as an induction heating cooker, an induction heating type water heater, a humidifier, or an iron.

  Conventionally, this type of induction heating device generates a high-frequency magnetic field from a heating coil and heats a load such as a pan by an eddy current due to electromagnetic induction (see, for example, Patent Document 1).

  FIG. 3 is a diagram showing a circuit configuration of a conventional induction heating device (induction heating cooker) described in Patent Document 1. In FIG. In FIG. 3, 11 is an AC power source, 12 is a rectifier circuit for converting the AC power source 11 into DC, 13 is a heating coil for heating the load pan, 14 is a resonance capacitor, 15 is a switching element, 16 is a reverse conducting diode, 13, the resonance capacitor 14, the switching element 15, and the reverse conducting diode 16 constitute an inverter circuit 17. Reference numeral 18 denotes input power detection means for detecting input power from the AC power supply 11, reference numeral 19 denotes input power setting means for setting power supplied to the load pan, and reference numeral 20 denotes turn-on voltage detection for detecting a voltage at both ends when the switching element 15 is turned on. Means 21 is a turn-on voltage determination means 22 that determines that the detection result of the turn-on voltage detection means 20 is valid when the detection voltage of the turn-on voltage detection means exceeds a preset threshold value continuously for a predetermined time or more. A drive circuit for driving the element, 23 is a control means for controlling the ON time of the switching element 15 so that the detected power of the input power detection means 18 becomes the power set by the input power setting means 19, and 24 is the duty of the input power. Duty control means 25 for realizing the power set by the input power setting means 19 by control, 25 is input Load detecting means for detecting the presence or absence of heatable load pot from the voltage across the sensing power and the switching element 15 of the power sensing means 18, display means for displaying the operating state of the cooker 26, 27 is a notifying means. FIG. 4 is a diagram showing the relationship between the current flowing through the switching element 15 and the reverse conducting diode 16 and the voltage at both ends during the operation of the inverter circuit 17. In FIG. 4, (a) shows the respective relationships when the input power is small, and (b) shows the respective relationships when the input power is large. FIG. 5 shows the characteristics of the voltage Von across the switching element 15 generated when the switching element 15 is turned on and the power supplied to the load pan. In FIG. 5, a load A and a load C are load pans with good magnetic coupling with a heating coil 13 typified by an enamel pan or a copper clad pan, and a load B is poor with magnetic coupling with a heating coil 13 typified by a non-magnetic pan. Indicates a load pan. Further, Von at which the loss of the switching element 15 becomes the cooling limit of the induction heating cooker when the load pan is heated is indicated by a point, and the threshold value of Von is set at a lower voltage. About the induction heating cooking appliance comprised as mentioned above, the operation | movement is demonstrated. When the load pan is placed above the heating coil 13 and heating is started, the drive circuit 22 drives the switching element 15 by a signal from the control means 23, and a high-frequency current is supplied to the heating coil 13 by the on / off operation of the switching element 15. Then, the load pan placed above the heating coil 13 is induction-heated. The electric power supplied to the load pan can be freely changed by changing the ON time of the switching element 15. When the input power is small in a load pan having good magnetic coupling with the heating coil 13 such as an enamel pan or a copper clad pan, the on-time of the switching element 15 is short and flows to the heating coil 13 as shown in FIG. Since the current is small, the amplitude of the voltage generated by the resonance of the heating coil 13 and the resonance capacitor 14 while the switching element 15 is off is small, and the voltage across the switching element 15 does not reach 0 V or less. When the switch is turned on, an excessive current flows through the switching element 15. At the start of heating, the power supplied to the load pan is reduced, and then the supplied power is gradually increased to perform a soft start to control the power to a predetermined level. Therefore, the turn-on voltage initially exceeds the threshold value as in load A and load C in FIG. 5, but the power supplied to the load increases and the turn-on voltage is generated within the time set by the turn-on voltage determination means 21. When it becomes lower than the threshold value, the turn-on voltage determination means 21 determines that the detection result of the turn-on voltage detection means 20 is invalid, so that the control means 23 becomes the power set by the input power setting means 19 in the continuous heating control. The on-time of the switching element 15 is controlled. Now, when the load A is placed above the heating coil 13 and the power supplied to the load pan is set to P1 by the input power setting means, the soft start ends as shown in FIG. Even when the supplied power reaches P1, the turn-on voltage exceeds the threshold value, so that the turn-on voltage becomes higher than the threshold value continuously for a predetermined time or more. The detection result is determined to be valid, and duty control of the input power larger than P1 is performed by the duty control means 24 so that the power supplied to the load pan becomes P1. Next, when the power supplied to the load pan is changed from P1 to P2 by the input power setting means 19, the duty control means 24 cancels the duty control so that the power supplied to the load becomes P2 by the continuous heating control. The on-time of the switching element 15 is controlled. As shown in FIG. 5, when the power supplied to the load pan is P2, the turn-on voltage is lower than the threshold value. Therefore, even after the supplied power reaches P2, it is continuously heated by the continuous heating control. Next, when the power supplied to the load pan is set to P1 again and the load A is removed from above the heating coil 13 during heating by duty control, the load detection means 25 determines that there is no load pan and heats up. Stop. After that, when the load B is placed on the heating coil 13, the load detection means 25 determines that the heatable load pan is placed, and the duty control means 24 cancels the duty control and continues. Heating is resumed by heating control. As shown in FIG. 5, in the load B, even if the electric power supplied to the load pan is P1, the turn-on voltage is lower than the threshold value. Therefore, even after the supplied electric power reaches P1, it is continuously heated by the continuous heating control. Next, when the load pan is changed to the load C and the power supplied to the load pan is set to P4 by the input power setting means 19, the load C is supplied to the load pan as shown in FIG. Since the turn-on voltage exceeds the threshold even when the power is P4, the turn-on voltage becomes higher than the threshold continuously for a predetermined time or more, and the turn-on voltage determination means 21 determines that the detection result of the turn-on voltage detection means 20 is valid. Since the heating power is set to stop when the power supplied to the load pan is P3 or more and the turn-on voltage exceeds the threshold value, the turn-on voltage determination means 21 at P4 when the power supplied to the load pan is larger than P3. In this state where the detection result of the turn-on voltage detection means 20 is determined to be valid, heating is stopped.

In the induction heating cooker configured as described above, even if the turn-on voltage of the switching element 15 exceeds the threshold value, the turn-on voltage determination means 21 detects the turn-on voltage detection means if it is due to soft start at the start of heating. The detection result is determined to be invalid, and desired input power can be obtained by continuous heating control. If the turn-on voltage of the switching element 15 exceeds the threshold value when the power is stable, the turn-on voltage determination means 21 determines that the detection result of the turn-on voltage detection means 20 is valid, and realizes the desired input power by duty control. The loss of the switching element can be reduced.
Japanese Patent No. 3168756

  However, the conventional configuration has a problem that the configuration becomes complicated, such as the need for a turn-on voltage detection means, and is difficult to implement.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide an induction heating apparatus that can be determined to be in a turn-on mode in an easy configuration and in a wide power supply voltage range.

  In order to solve the conventional problem, the induction heating apparatus of the present invention has a heating coil, a resonant capacitor, a switching element, and a control means, the heating coil and the switching element are connected in series, and the resonant capacitor is heated. Connected in parallel to a coil or a switching element, the control means controls the on-time of the switching element and drives it on and off at high frequency to cause a high-frequency current to flow through the heating coil to induce induction heating in the vicinity of the heating coil The input current detection means for detecting the input current or the input power detection means for detecting the input power, the heating coil current detection means for detecting the heating coil current, the input voltage detection means for detecting the input voltage, and the input current detection output or input The heating coil current detection output is below a predetermined value according to the power detection output and the input voltage detection output. Has a turn-on mode determining means determines that the turn-on mode, if it is determined that the turn-on mode, and configured to control so as to suppress the turn-on loss of the switching element. With this configuration, the turn-on mode can be detected with a simple configuration and in a wide power supply voltage range, so that an induction heating device that can suppress the turn-on loss of the switching element in a wide power supply voltage range can be provided.

  The induction heating device of the present invention can prevent element destruction due to an increase in turn-on loss of the switching element in an easy configuration and in a wide power supply voltage range.

  1st invention has a heating coil, a resonance capacitor, a switching element, and a control means, the heating coil and the switching element are connected in series, the resonance capacitor is connected in parallel to the heating coil or the switching element, The control means controls the on-time of the switching element and performs on-off driving at a high frequency, thereby causing a high-frequency current to flow through the heating coil to inductively heat a load installed in the vicinity of the heating coil, thereby detecting an input current. Or the input power detection means for detecting the input power and the heating coil current detection means for detecting the heating coil current and the input voltage detection means for detecting the input voltage and the input current detection output or the input power detection output and the heating according to the input voltage detection output The turn-on mode that determines the turn-on mode when the coil current detection output is below a certain value. Has a de determination means determines that the turn-on mode, and configured to control so as to suppress the turn-on loss of the switching element. With this configuration, it is possible to provide an induction heating device that has an easy configuration and can suppress the turn-on loss of the switching element in a wide power supply voltage range.

  According to a second aspect of the invention, in particular, when the induction heating device of the first aspect of the invention is determined to be in the turn-on mode, power control is performed by duty control. With this configuration, it is possible to provide an induction heating device that has an easy configuration and can suppress the turn-on loss of the switching element in a wide power supply voltage range.

  3rd invention has a heating coil, a resonance capacitor, a switching element, and a control means, the heating coil and the switching element are connected in series, the resonance capacitor is connected in parallel to the heating coil or the switching element, The control means controls the on-time of the switching element and performs on-off driving at a high frequency, thereby causing a high-frequency current to flow through the heating coil to inductively heat a load installed in the vicinity of the heating coil, thereby detecting an input current. Alternatively, the input power detection means for detecting the input power, the input voltage detection means for detecting the input voltage, the heating coil current detection means for detecting the heating coil current, and the input current detection output or the input power detection output and the heating according to the input voltage detection output The turn-on mode is determined to be the turn-on mode when the coil current detection output is below a certain value. Has a de determination means determines that the turn-on mode, and configured to control so as to stop the driving of the switching element. With this configuration, it is possible to provide an induction heating device that has an easy configuration and can prevent element destruction due to increase in turn-on loss of the switching element in a wide power supply voltage range.

  4th invention has a heating coil, a resonance capacitor, a switching element, a control means, and a cooling means, the heating coil and the switching element are connected in series, and the resonance capacitor is connected in parallel to the heating coil or the switching element. The control means controls the on-time of the switching element to drive on and off at a high frequency, thereby flowing a high-frequency current to the heating coil to inductively heat a load installed in the vicinity of the heating coil, and the cooling means at least the Input current detecting means for cooling the switching element and detecting input current or input power detecting means for detecting input power, heating coil current detecting means for detecting heating coil current, input voltage detecting means for detecting input voltage, and input current Heating coil current detection output according to detection output or input power detection output and input voltage detection output Has a turn-on mode determining means for determining is not more than a predetermined value and the turn-on mode in which there is, determines that the turn-on mode, and configured to control so as to increase the ability of the cooling means. With this configuration, it is possible to provide an induction heating device that has an easy configuration and can prevent element destruction due to increase in turn-on loss of the switching element in a wide power supply voltage range.

  According to a fifth aspect of the present invention, in particular, the capacity of the cooling means of the induction heating device according to the fourth aspect of the present invention is changed according to the heating coil current detection output. With this configuration, it is possible to provide an induction heating device that has an easy configuration and can prevent element destruction due to increase in turn-on loss of the switching element in a wide power supply voltage range.

  In the sixth aspect of the invention, in particular, the cooling means of the induction heating device of the fourth or fifth aspect is a cooling fan, and the rotation speed of the cooling fan is increased. With this configuration, it is possible to provide an induction heating device that has an easy configuration and can prevent element destruction due to increase in turn-on loss of the switching element in a wide power supply voltage range.

  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 is a block diagram of an induction heating cooker according to the first embodiment of the present invention, and FIG. 2 is a characteristic diagram of a turn-on mode determination unit of the induction heating cooker.

  In FIG. 1, a power source 11 is a commercial power source. The commercial power source is converted into direct current by a rectifying means 12 formed of a diode bridge, converted into a high frequency by an inverter, and a high frequency magnetic field is generated in the heating coil 13. Reference numeral 10 denotes a pan as a load, which is installed facing the heating coil 13. A resonance capacitor 14 is connected to the heating coil 13 to form a resonance circuit. The inverter is connected to the switching element 15 so as to have the one-tone voltage resonance type inverter configuration. The switching element 15 has a diode connected in reverse parallel as the reverse conducting element 16. When the switching element 15 is driven by the control means 30 and the output is increased, the switching element is driven by the control means 30 so that the drive frequency of the switching element is lowered, and the input current detection means 18 comprising a current transformer is used to input current. This is a frequency controlled inverter that detects the above and obtains a predetermined heating output. Reference numeral 32 denotes a heating coil current detection means, which comprises a current transformer. Reference numeral 33 denotes an input voltage detection means which is based on resistance division. The detection output of the heating coil current detection unit 32, the detection output of the input current detection unit 18, and the detection output of the input voltage detection unit 33 are input to the turn-on mode determination unit 31.

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

  FIG. 2 is a characteristic diagram of the turn-on mode determination means 31 at a predetermined heating power. Depending on the degree of load coupling such as the material of the load and the area of the load facing the heating coil, when the load is poorly coupled or the load is made of non-magnetic stainless steel, the heating coil current for a given heating output increases. In addition, when the coupling is good or the material is an iron load such as an enamel pan, the heating coil current becomes smaller. In these cases, since the amplitude of the resonance voltage is large, the switching element 15 is turned on, that is, zero voltage switching is realized when the switching element voltage is zero. Furthermore, the heating coil current becomes smaller when the load is very good, such as a copper clad pan with thin copper. Further, when the commercial power supply voltage is increased, the resonance origin of the resonance voltage is increased, which is equivalent to a relatively small amplitude of the resonance voltage, and the zero voltage switching of the switching element becomes more difficult. In the region indicated by the oblique lines in FIG. 2, a turn-on mode occurs and zero voltage switching cannot be performed. In addition, the slanted straight line portion in the region shown by the slanted line in FIG. 2 is designed to be an equiloss line of the switching element. The nominal voltage of household AC power supply voltage in the world is as wide as 100 to 120V in the 100V system and 200 to 240V in the 200V system, and corresponds to a wide power supply voltage range, that is, depending on the degree of load coupling and the power supply voltage level In this embodiment, when the input voltage and the heating coil current are in the region indicated by the oblique lines in FIG. 2, the turn-on mode determining means 31 determines that the turn-on mode has occurred, and the control means 30 The heating output is increased and power control is performed by duty control so that the average heating output becomes a predetermined value. When the instantaneous heating output is increased, the amplitude of the resonance voltage increases and zero voltage switching can be performed, so that the turn-on loss of the switching element can be suppressed. Although not shown in the figure, the switching element is forcibly cooled by a cooling fan as a cooling means, and the temperature of the switching element is lowered to prevent thermal destruction by discharging lost heat. In this case, when a load having a very good coupling is heated, a turn-on loss of the switching element that exceeds the capacity of the cooling fan occurs instantaneously. In this case, the turn-on mode determination means 31 stops driving the switching element. Thus, the device can be safely protected by driving the control means 30 and stopping the heating.

  In this embodiment, the resonance capacitor is connected in parallel to the heating coil, but the same effect can be obtained even if it is connected in parallel to the switching element.

  In the present embodiment, a one-stone voltage resonance type inverter is used, but it goes without saying that even an active clamp type two-stone inverter to which a switching element for clamping the resonance voltage is added can prevent element destruction due to an increase in turn-on loss.

  Furthermore, the same effect can be obtained by detecting input power or heating output instead of the input current.

  Further, although the input voltage detection means detects the voltage after rectification, it is of course possible to directly detect the power supply voltage.

  Although the determination threshold value of the turn-on mode determination means is one, it is needless to say that the provision of a plurality of turn-on mode determination means makes it possible to provide an induction heating device with higher heating efficiency and lower noise, such as being able to change the rotation speed of the cooling fan more finely. Absent.

  As described above, in the present embodiment, element destruction due to increase in turn-on loss of a switching element can be prevented with an easy configuration and a wide power supply voltage range.

  As described above, since the induction heating device according to the present invention can perform heating according to the load and the power supply voltage with an easy configuration, it can also be applied to uses such as industrial induction heating.

The block diagram of the induction heating cooking appliance in Embodiment 1 of this invention Characteristic diagram of turn-on mode determination means of the induction heating cooker Block diagram of a conventional induction heating cooker Operation waveform diagram of the inverter circuit of the induction heating cooker Characteristics diagram of turn-on voltage and power supplied to load of the induction heating cooker

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Load 13 Heating coil 14 Resonance capacitor 15 Switching element 18 Input current detection means 30 Control means 31 Turn-on mode determination means 32 Heating coil current detection means 33 Input voltage detection means

Claims (6)

A heating coil, a resonant capacitor, a switching element, and control means; the heating coil and the switching element are connected in series; the resonant capacitor is connected in parallel to the heating coil or the switching element; and the control means is the switching element By controlling the on-time of the coil and driving it on and off at a high frequency, a high-frequency current is passed through the heating coil to inductively heat a load installed in the vicinity of the heating coil, and an input current detecting means for detecting the input current or input power is detected. There is a heating coil current detection output according to the input power detection means and the heating coil current detection means for detecting the heating coil current and the input voltage detection means for detecting the input voltage and the input current detection output or the input power detection output and the input voltage detection output. Turn-on mode determination means for determining that the turn-on mode is below a predetermined value And, when it is determined that the turn-on mode, the induction heating device is controlled so as to suppress the turn-on loss of the switching element. The induction heating apparatus according to claim 1, wherein when the turn-on mode is determined, power control is performed by duty control. A heating coil, a resonant capacitor, a switching element, and control means; the heating coil and the switching element are connected in series; the resonant capacitor is connected in parallel to the heating coil or the switching element; and the control means is the switching element By controlling the on-time of the coil and driving it on and off at a high frequency, a high-frequency current is passed through the heating coil to inductively heat a load installed in the vicinity of the heating coil, and an input current detecting means for detecting the input current or input power is detected. There is an input power detection means, an input voltage detection means for detecting the input voltage, a heating coil current detection means for detecting the heating coil current, and an input current detection output or a heating coil current detection output according to the input power detection output and the input voltage detection output. Turn-on mode determination means for determining that the turn-on mode is below a predetermined value And, when it is determined that the turn-on mode, the induction heating device for controlling to stop the driving of the switching element. A heating coil, a resonant capacitor, a switching element, a control means, and a cooling means; the heating coil and the switching element are connected in series; the resonant capacitor is connected in parallel to the heating coil or the switching element; By controlling the on-time of the switching element to drive on and off at a high frequency, a high-frequency current is passed through the heating coil to inductively heat a load installed in the vicinity of the heating coil, and the cooling means cools at least the switching element, Input current detection means for detecting input current or input power detection means for detecting input power, heating coil current detection means for detecting heating coil current, input voltage detection means for detecting input voltage, and input current detection output or input power detection Predetermined value with heating coil current detection output according to output and input voltage detection output Has a turn-on mode determining means for determining the turn-on mode when there below, if it is determined that the turn-on mode, the induction heating device for controlling to increase the capacity of the cooling unit. The induction heating apparatus according to claim 4, wherein the capacity of the cooling means is changed in accordance with the heating coil current detection output. 6. The induction heating apparatus according to claim 4, wherein the cooling means is a cooling fan, and the cooling fan is rotated at a higher speed.

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