JP4613687B2 - Induction heating device - Google Patents

Description

  The present invention relates to an induction heating device used in general homes, offices, restaurants, factories and the like.

  Conventionally, as an induction heating apparatus of this type, for example, for an electromagnetic cooker, there is a switching means for shaping an input current waveform, particularly when heating an object to be heated formed of a material other than a ferromagnetic material such as iron. A technique for improving the power factor is known (see, for example, Patent Document 1).

  Hereinafter, as a conventional induction heating apparatus, an induction heating apparatus (induction heating cooker) in Patent Document 1 will be described with reference to the drawings.

  FIG. 6 is a circuit diagram showing an embodiment of a conventional induction heating apparatus described in Patent Document 1, and FIG. 7 is a signal waveform diagram of each part of FIG.

  In FIG. 6, a commercial power supply 101 of AC voltage Vac is connected to the bridge circuit 105. The bridge circuit 105 is configured by bridge-connecting two thyristors 107a and 107b and two diodes 109a and 109b, and converts an alternating current of the commercial power supply 101 into a direct current.

  The capacitor 111 is set to a relatively large capacity in order to remove the ripple current, and is a smoothing means for smoothing the pulsating current rectified by the bridge circuit 105.

  The input control circuit 133 is connected to a current transformer 134 provided on the commercial power supply 101 side. The current transformer 134 detects the input current Iin input from the commercial power supply 101 and sends information corresponding to the detected current value of the input current Iin to the input control circuit 133.

  The input control circuit 133 has a built-in arithmetic processing unit such as a microcomputer, and executes optimum PWM control based on information on the actual input current Iin from the current transformer 134. That is, the input control circuit 133 performs the input control of the input current Iin. In order to improve the power factor so that the current waveform is substantially a sine wave, a pulse signal 133a as shown in FIG. 7C is output to the transistor Tr1.

  The transistor Tr1 is a switching means for shaping the waveform of the input current Iin by performing a switching operation at a predetermined waveform shaping period based on the pulse signal 133a.

The reactor L is tank means for accumulating electric power from the commercial power source 101 when the transistor Tr1 is turned on and supplying the accumulated electric power to the capacitor 111 when the transistor Tr1 is turned off.
JP-A-1-246683

  When the transistor Tr1 is turned on / off, noise accompanying switching occurs.

  Usually, when the current flowing through the reactor L does not pass through the zero point, it is called a continuous operation mode, and when it passes through the zero point, it is called a discontinuous operation mode. Whether to adopt the continuous operation mode or the discontinuous operation mode depends on the reactor L shape, loss, transistor Tr1 rating, loss, and the like.

  In the continuous operation mode, although depending on the rated output of the inverter, generally, the reactor L current flows continuously by setting the capacity of the reactor L large. Therefore, the turn-off current when the transistor Tr1 is turned off is relatively small, but a short-circuit current flows suddenly when the transistor Tr1 is turned on.

  On the other hand, in the discontinuous mode, the reactor L current peak increases because the capacity of the reactor L is set small so that the reactor L current passes through the zero point. Therefore, the turn-on current hardly flows when the transistor Tr1 is turned on, but the turn-off current is increased.

  For example, a snubber or the like may be provided to suppress dI / dt and dV / dt when the transistor Tr1 is turned off. The transistor Tr1 is PWM-controlled so that the waveform is shaped regardless of the input current. Therefore, the ON / OFF conduction ratio and timing are not constant, and it is inevitable to suppress an increase in the short-circuit current or the turn-off current peak when the transistor Tr1 is turned on.

  That is, regardless of which of the continuous operation mode and the discontinuous operation mode is adopted, a sudden current change occurs with the switching of the transistor Tr1, so that electromagnetic noise is propagated to the pattern or radiated to surrounding wiring. Become.

  Such noise makes the operation of the input control circuit 133 unstable and reduces the detection accuracy of the current transformer 134 and the like.

  For example, noise can be detected by detecting the type of pan such as detecting the material of the object to be heated from the input current or inverter output, detecting small objects that detect improper heating due to movement of the object to be heated, etc. Since the accuracy is lowered and the operation is not performed normally, the heating may not be continued or a circuit failure may occur.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide an induction heating apparatus that performs a stable operation.

  In order to solve the above-described conventional problems, in the induction heating apparatus of the present invention, the inverter supplies a high-frequency current to the heating coil by the on / off of the second switching element group to induction-heat the object to be heated, and the power factor The improvement means improves the power factor by turning on / off the first switching element, and the control means controls to provide a stop period of the power factor improvement means from the start to the stop of the inverter drive.

  While the power factor improving means is operating, the influence of noise on the control means is large, but the noise generated from the power factor improving means is also stopped during the stop period of the power factor improving means. During this period, the control means performs the pot type determination, the accessory determination, and the signal reading from the detection means, thereby making it possible to suppress the influence of noise on these controls and to stabilize the operation of the induction heating device Can be.

  The induction heating apparatus of the present invention can perform a stable operation by providing a stop period of the power factor correction means during the heating operation.

  According to a first aspect of the present invention, there is provided a rectifying unit that rectifies an AC voltage from a commercial power source, a power factor improving unit connected to an output side of the rectifying unit, and a first switching element included in the power factor improving unit. A smoothing means connected to the output side of the power factor improving means; an inverter connected to the smoothing means; a plurality of second switching elements included in the inverter; and connected to the inverter; A heating coil for induction heating an object to be heated made of aluminum or copper or a low permeability material having an electric conductivity substantially equal to or higher than these, a detection means for detecting the magnitude of the output of the inverter, and the detection means And a control means for controlling the inverter, wherein the inverter generates a high-frequency current by turning on / off the second switching element group. The heating element is supplied to the heating coil to inductively heat the object to be heated, and the power factor improvement means improves the power factor by turning on / off the first switching element, and the control means stops from the start of the inverter drive. The induction heating apparatus is controlled so as to provide a stop period for the power factor improving means.

  When induction heating is performed on an object to be heated made of aluminum, copper, or a low-permeability material having an electric conductivity substantially equal to or higher than these, the object to be heated is caused by the repulsive force between the high frequency magnetic field generated from the heating coil and the object to be heated. In order to suppress the vibration noise of an object, a smoothing means that smoothes the inverter power supply voltage and makes the inverter output substantially constant is necessary.

  Further, since the input current is distorted by providing the smoothing means, a power factor improving means for shaping the input current into a sine wave and improving the power factor is also required.

  As described above, the power factor improvement means shapes the input current by turning on and off the included switching element to improve the power factor, but the operation of the power factor improvement means, that is, the first switching element. The noise generated by the switching operation affects the control means, the detection means, and the like. However, according to the present invention, by stopping the operation of the power factor improvement means for a predetermined period, the control means can read the signal of the detection means with high accuracy, so that a stable heating operation is possible.

  In a second aspect of the present invention, in particular, in any one of the first aspects, the control means controls to stop the power factor improvement means when determining the material of the object to be heated based on the output of the detection means. This is a heating device.

  The material determination of the object to be heated is performed in a state where the input current is particularly low in order to suppress the load on the device, and the output signal of the detection means is also at a low level. At that time, if the power factor improving means operates to generate noise, the control means cannot read the output signal of the detecting means with high accuracy.

  When the material determination of the object to be heated cannot be performed accurately, for example, when the object to be heated made of aluminum is determined to be an iron-based object to be heated, an excessive load is applied to the circuit component and heating cannot be continued.

  In the present invention, since the power factor improving means is stopped when determining the material of the object to be heated, the control means can suppress the influence of noise and can accurately read the output signal of the detecting means.

  In a third aspect of the invention, in particular, in any of the first and second aspects of the invention, the control means is an induction heating device that controls to stop the power factor correction means when the detection means signal becomes a predetermined value or less. Is.

  For example, when the object to be heated is moved by the user during the heating of the object to be heated, the inductance of the heating configuration including the heating coil and the object to be heated changes. That is, the state of the inverter changes suddenly. In such a case, the inverter output decreases and the input current hardly flows.

  In the present invention, the power factor improvement means is stopped in a state where the inverter output in which the detection means signal is equal to or less than the predetermined value is reduced. The state in which the inverter output is reduced may be a state that is not suitable for heating, that is, a small item heating state or a state in which there is no object to be heated, but is the control unit accurately acquiring the detection unit signal and is it suitable for heating? It is possible to accurately determine whether it is inappropriate.

  In a fourth aspect of the invention, in particular, in any of the first and second aspects of the invention, the control means changes the detection means signal read timing within a half cycle of the commercial power supply by operating / stopping the power factor improvement means. It is what.

  When the power factor improving means is operating, for example, the input current waveform is substantially sinusoidal, so that the input current peak is located approximately in the middle of the commercial power supply half cycle. Therefore, it is possible to detect the input current peak if the timing at which the control means reads the detection means signal is set approximately in the middle of the commercial power supply half cycle.

  On the other hand, when the power factor correction means is stopped, the input current waveform is distorted, so that the peak is also at a position delayed from almost the middle of the commercial power supply half cycle. If the timing of reading the detection means signal of the control means remains substantially in the middle of the commercial power supply half cycle, the peak of the input current cannot be detected.

  However, in the present invention, since the reading timing can be changed, the detection can be performed at the timing when the input current reaches a peak regardless of the operation / stop of the power factor improvement means.

  Therefore, since the control means does not detect the input current, the inverter output, etc. too low, stable control is possible.

  In a fifth aspect of the present invention, in particular, in any of the first and second aspects, the control means stops the number of times of reading of the detection means signal within the half cycle of the commercial power supply with respect to when the power factor correction means is operating. The induction heating device is set to a small number when it is in operation.

  While the power factor correction means is operating, the generated noise affects the surroundings. Since noise is also superimposed on the output signal of the detection means, a signal superimposed with noise may be read instead of a normal signal at the moment when the control means reads the detection signal.

  Normally, the control means reads the output signal of the detection means a plurality of times during a half cycle of the commercial power supply, and performs internal calculation to suppress the influence of noise. Therefore, efficient control can be performed by changing the number of readings.

  That is, when the power factor improvement means is operating, the control means increases the number of times of reading the output signal of the detection means, and removes and excludes the signal affected by the noise, and calculates from the normal detection signal. . Further, when the power factor improving means is stopped, it is possible to perform efficient control by reducing the number of readings and allocating that time to another control.

  In a sixth aspect of the invention, in particular, in any of the first and second aspects of the invention, the control means is an induction heating device that changes the correction to the detection means signal by operating / stopping the power factor improvement means. is there.

  For example, when the detection means is a circuit of a peak hold system, when the power factor improvement means is operating, the overall level of the detection means signal is increased due to the influence of noise generated.

  In the present invention, when the power factor correction means is operating, the control means corrects the read detection means signal, and performs calculation based on the corrected signal from which the influence of noise has been removed.

  On the other hand, since the influence of noise is reduced when the power factor improvement means is stopped, the control means performs the calculation with a reduced correction amount, so that regardless of the operation / stop of the power factor improvement means. Highly accurate detection is possible.

  In a seventh aspect of the invention, in particular, in any of the first and second aspects of the invention, the control means is an induction heating apparatus that reads a part or all of the detection means signal at a timing when the commercial power source becomes a predetermined value or less. is there.

  Since the power factor improving means aims to shape the input current into a sine wave, both the voltage and current are low before and after the zero volt cross of the commercial power supply. Therefore, during this period, the noise generated from the power factor improving means is also lower than that near the commercial power supply peak.

  In the present invention, the control means reads the signal from the detection means before and after the zero volt cross when the commercial power supply becomes a predetermined value or less, thereby suppressing the influence of noise generated from the power factor improvement means and enabling accurate detection. Become.

  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, and is a schematic circuit diagram of a main part of an induction heating cooker in particular.

  In FIG. 1, a power factor improving means 3 is connected to an output side of a rectifying means 2 composed of a diode bridge that rectifies an AC voltage from a commercial power source 1.

  The power factor improving means 3 includes a first switching element 4, a first choke coil 5, and a first diode 6. One of the first choke coils 5 is connected to the diode bridge 2 high potential output side. The other is connected to the first switching element 4 high potential terminal (collector in the case of IGBT, drain in the case of MOSFET).

  The low potential terminal (emitter in the case of IGBT, source in the case of MOSFET) of the first switching element 4 is connected to the low potential output side of the diode bridge 2.

  The cathode of the first diode 6 is connected to the high potential terminal of the first switching element 4.

  Between the anode of the first diode 6 on the output side of the power factor improving means 3 and the first switching element 4 low potential terminal, a smoothing means 7 made of a large capacity electrolytic capacitor is connected. In this embodiment, two electrolytic capacitors having a capacity of 820 μF are connected in parallel, and the voltage is boosted by the power factor improving means 3 so that it becomes approximately 350 V in a normal case (when the commercial power source 1 is AC 200 V and peak is about 280 V). Will be.

  An inverter 8 is connected to the smoothing means 7, and the smoothing means 7 serves as a power source for the inverter 8 when viewed from the inverter 8 side.

  In the inverter 8, the smoothing means 7 is connected in parallel to the boosting means 9 that boosts the voltage, the second smoothing means 10 that smoothes the boosted voltage, and the second smoothing means 10. A series connection of a resonant capacitor 13 and a heating coil 12 connected in parallel to a high potential terminal and a low potential terminal of a second switching element group 11 composed of a plurality of IGBTs and a low potential side switching element 11a of the second switching element group 11 The body is contained.

  Each second switching element group 11 includes a reverse conducting diode.

  Similar to the smoothing means 7, the second smoothing means 10 serves as a power source for the inverter 8 when viewed from the inverter 8.

  Both ends of the second smoothing means 10 are connected to a first voltage detecting means 14 made of a resistor so as to detect the voltage of the second smoothing means 10. The divided voltage divided by this resistor is input at a voltage division ratio so as to be equal to or lower than the power supply voltage (5 V in the present embodiment) of the control means 15 comprising a microcomputer.

  Similarly, the second voltage detector 16 is connected to both ends of the resonant capacitor 13 in order to detect the voltage of the resonant capacitor 13. The detected detection voltage is input at a voltage division ratio that is equal to or lower than the power supply voltage (5 V in the present embodiment) of the control means 15 formed of a microcomputer.

  The circuit configuration of the boosting means 9 is the same as that of the power factor improving means 3, and is composed of a third switching element 17, a second choke coil 18, and a second diode 19. Similar to the second switching element group 11, the third switching element 17 includes a reverse conducting diode.

  One end of the second choke coil 18 is connected to the high potential side of the smoothing means 7 and the other end is connected to the high potential terminal of the third switching element 17. The low potential terminal of the third switching element 17 is connected to the low potential side of the smoothing means 7. The second diode 19 has an anode connected to the third switching element 17 high potential terminal and a cathode connected to the second smoothing means 10 high potential side.

  Further, since the second smoothing means 10 voltage is boosted to about 700 V by increasing the smoothing means 7 voltage (350 V), a film capacitor is used instead of an electrolytic capacitor in which the withstand voltage cannot be set high. In the present embodiment, the capacitance of the film capacitor 10 is set to 5 μF.

  Tempered glass is disposed above the heating coil 12 (not shown), and an object to be heated 20 made of a low magnetic permeability material having an electric conductivity substantially equal to or higher than aluminum or copper is disposed thereon. It is burned.

  Further, the heating coil 12 is configured by winding a stranded wire bundled with strands on a flat plate in order to suppress loss.

  As described above, the control unit 15 receives signals from the first voltage detection unit 14 and the second voltage detection unit 16 and also includes an input including a current transformer that detects an input current from the commercial power source 1. A signal from the current detection means 21 is also input.

  Further, the control unit 15 is configured to control the first switching element 4 so that a predetermined output can be obtained based on signals from the first voltage detection unit 14, the second voltage detection unit 16, the input current detection unit 21, and the like. The operation and the operation of the second switching element group 11 and the third switching element 17 are controlled.

  Further, an operation means 22 that outputs a signal to heat / stop the article to be heated 20 by an operation by the user is connected to the control means 15. The operation means 22 includes a display means 23 composed of a liquid crystal for displaying information on the state of the apparatus, that is, a thermal power display, a timer display, a temperature display, etc., and a ringing sound constituted by a buzzer or a speaker for generating a notification sound or a sound. Means 24 are included.

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

  First, when the commercial power source 1 is turned on and the user performs a heating start operation of the article to be heated 20 by the operation means 22, a heating start signal is output from the operation means 22 to the control means 15. At the same time, signals are output from the operation means 22 to the display means 23 and the sounding means 24, and the start of heating is notified by sounding such as display and sound according to the user's operation.

  The control means 15 having received the heating start signal from the operation means 22 outputs a drive signal to operate the second switching element group 11. At that time, control is performed so that the ON time of the low potential side switching element 11a of the second switching element group 11 is minimized, the ON time of the high potential side switching element 11b is maximized, and each is exclusively turned on. I do.

  The control means 15 is a low-potential-side switching element that maintains a constant drive frequency (period) of 33 kHz that is about 1/3 of the resonance frequency of about 90 kHz of the resonance element composed of the resonance capacitor 13, the heating coil 12, and the object to be heated 20. While continuing the exclusive drive of 11a and the high potential side switching element 11b, the ON time of the low potential side switching element 11a is gradually extended. When the on-time of the low-potential side switching element 11a reaches 1/2 of the driving cycle, the control means 15 keeps the on-time ratio between the low-potential side switching element 11a and the high-potential side switching element 11b constant. Decrease (cycle).

  2A is an input current waveform when the power factor improving means 3 is stopped, FIG. 2B is an input current waveform when the power factor improving means 3 is operating, and FIG. The drive signal for the first switching element 4 in FIG. 5B, FIG. 4D shows the commercial power supply 1 voltage.

  The control means 15 controls to provide a stop period of the power factor improvement means 3 between the start of driving of the inverter 8 and the stop thereof. In the present embodiment, the initial stage of heating corresponds to the stop period.

  As shown in FIG. 2, the input current waveform at the beginning of heating is distorted because the power factor correction means 3 is stopped.

  The peak of the input current is at a position delayed from the middle of one half cycle of the commercial power source.

  In order to detect the input current peak, the control means 15 reads the input current detection means 21 signal reading timing, which is a detection means signal, at a position (indicated by an arrow A in FIG. 2) that is delayed from the middle in one half cycle of the commercial power supply. Set.

  FIG. 3 is an enlarged view of the input current detection means 21 signal at the moment when the control means 15 detects the input current, and shows an enlargement of arrows A and B in FIG.

  Depending on the operation / stop of the power factor improving means 3, the noise level superimposed on the signal of the input current detecting means 21 is different. In order to eliminate the influence of such noise as much as possible, the control means 15 reads the input current detection means 21 signal a plurality of times, and then performs an internal calculation (excludes values that change more than a predetermined value) Etc.).

  However, during the period when the power factor improving means 3 is stopped as in the material determination of the article to be heated 20, there is little noise to be superimposed as shown in FIG. Therefore, the control means 15 reduces the number of times of reading of the detection means signal within one half cycle of the commercial power source, that is, the input current detection means 21 signal, when the power factor improvement means 3 is stopped ( In this embodiment, by setting 6 times during operation and 4 times during stoppage, reading time is shortened and efficient control is possible.

  When the output of the second voltage detection means 16 for detecting the voltage of the resonant capacitor 13 exceeds a threshold set according to the output from the input current detection means 21 during a series of operations, the control means 15 Then, it is determined that an object to be heated 20 is placed above the heating coil 12, and the driving of the first switching element 4 is started so that the voltage of the smoothing means 7 becomes 350V, and further the third switching The driving of the element 17 is started.

  The control means 15 controls the power factor improvement means 3 to stop when determining the material of the article to be heated 20 based on the output of the detection means, thereby suppressing the influence of noise generated from the power factor improvement means 3. This makes it possible to accurately determine the material.

  The control means 15 includes an oscillation circuit therein, and drives the first switching element 4 in synchronization with the oscillation frequency. Further, the control means 15 calculates from the detection results of the smoothing means 7 voltage detection means (not shown) and the input current detection means 21, changes the ON time of the first switching element 4, and the input current is substantially sine. PWM control as shown in FIG. 2 is performed so that the power factor is improved in a wave shape and the voltage of the smoothing means 7 becomes a set value.

  At this time, the peak of the input current is almost in the middle of one half cycle of the commercial power source. In order to detect the input current peak, the control means 15 changes the input current detection means 21 signal reading timing, which is a detection means signal, to substantially the middle (indicated by arrow B in FIG. 2) within one half cycle of the commercial power source.

  That is, the control means 15 changes the detection means signal reading timing within one half cycle of the commercial power supply by operating / stopping the power factor improvement means 3, and can detect it at the timing when the input current peaks. .

  In addition, when the power factor improving means 3 is in operation, the control means 15 performs an internal correction to reduce the level in anticipation that the overall level of the detection means signal will increase due to the influence of the generated noise.

  That is, the control unit 15 changes the correction performed on the detection unit signal by operating / stopping the power factor improvement unit 3, thereby suppressing the influence of noise and enabling highly accurate detection.

  Initially after the material determination of the object to be heated 20, the ON time of the third switching element 17 is set to be a minimum, but the voltage of the second smoothing means 10 is set to about 700 V by the first voltage detecting means 14. The on-time is gradually extended until it is detected that this has been reached. Thereafter, the ON time of the third switching element 17 is controlled by the control means 15 so that the voltage of the second smoothing means 10 is maintained at about 700V.

  A current for short-circuiting the smoothing means 7 flows in the second choke coil 18 during the ON time of the third switching element 17, and energy is accumulated in the second choke coil 18. When the third switching element 17 is turned off, the energy accumulated in the second choke coil 18 charges the second smoothing means 10 via the second diode 19. As a result, the second smoothing means 10 voltage is boosted with respect to the smoothing means 7 voltage.

  This boosting operation is also the same in the power factor improving means 3. The first switching element 4 corresponds to the third switching element 17 and the smoothing means 7 corresponds to the output of the rectifying means 2 and the second choke. The first choke coil 5 for the coil 18, the first diode 6 for the second diode 19, and the smoothing means 7 for the second smoothing means 10.

  Note that the third switching element 17 is controlled to operate at a constant frequency of about 20 kHz.

  After starting the driving of the third switching element 17, the control means 15 compares the output of the input current detection means 21 with the heating output setting by the operation means 22, and appropriately drives the driving frequency of the second switching element group 11, and The on-time of the third switching element 17 is controlled.

  That is, the inverter 8 turns on / off the second switching element group 11 under the control of the control means 15, supplies a high frequency current to the heating coil 12, and inductively heats the object to be heated 20.

  FIG. 4 shows an operation waveform of each part in a state where a predetermined input current is obtained in the present embodiment.

  4A shows the voltage (Vce) between the high potential terminal and the low potential terminal of the low potential side switching element 11a, FIG. 4B shows the current (Ic) of the low potential side switching element 11a, and FIG. The voltage (Vce) between the high potential terminal and the low potential terminal of the high potential side switching element 11b, FIG. 4 (d) shows the high potential side switching element 11b current (Ic), and FIG. 4 (e) shows the heating coil 12 current (IL). 4 (f) shows the voltage (Vce) between the high potential terminal and the low potential terminal of the third switching element 17, and FIG. 4 (g) shows the third switching element 17 current (Ic).

  In the present embodiment, the control unit 15 operates the second switching element group 11 at a frequency that is about 1/3 of the resonance frequency of the resonance element including the resonance capacitor 13, the heating coil 12, and the article to be heated 20. This is related to the object to be heated 20 being a material having high electrical conductivity and low magnetic permeability such as aluminum.

  When the material of the object to be heated 20 is aluminum or the like, since the high frequency resistance of the object to be heated 20 viewed from the heating coil 12 is very low, sufficient Joule heat is generated even if an induced current is induced in the object to be heated 20. Does not occur.

  In order to inductively heat the object to be heated 20, there is a method in which the strength of the high frequency magnetic field generated by the high frequency current flowing in the heating coil 12 is increased or the frequency is increased to increase the high frequency resistance of the object to be heated 20. It is valid.

  In the present embodiment, the strength of the high frequency magnetic field generated by increasing the number of turns of the heating coil 12 is increased, and the magnetic field frequency is increased from about 20 kHz to about 90 kHz, thereby inducing the object to be heated 20 such as aluminum with sufficient thermal power. Heating is possible.

  However, increasing the magnetic field frequency increases the drive frequency of the second switching element group 11, which increases the number of times of switching, leading to an increase in loss. Therefore, in the present embodiment, the resonance frequency is used to select the second switching element group 11 driving frequency that can obtain three resonances during one driving period of the second switching element group 11. . That is, the second switching element group 11 is operated at a frequency that is about 1/3 of the resonance frequency of the resonance element including the resonance capacitor 13, the heating coil 12, and the article to be heated 20.

  Thereby, while increasing the magnetic field frequency, it is possible to suppress an increase in the number of switching of the second switching element group 11 and to suppress an increase in the loss of the second switching element group 11.

  When the material to be heated 20 is aluminum or the like, since the electrical conductivity is high, the induced current induced during induction heating is larger than that of a material such as iron. Since this induced current is generated so as to repel the high-frequency magnetic field generated from the heating coil 12, the article to be heated 20 can move easily.

  When the capacity of the smoothing means 7 or the second smoothing means 10 is small, the instantaneous output of the inverter 8 fluctuates in synchronism with the commercial power source 1, and vibration noise is generated from the article to be heated 20 due to this fluctuation. .

  In the present embodiment, the capacity of the smoothing means 7 is set to two 820 μF, and the capacity of the second smoothing means 10 is set to 5 μF, so that a sufficient capacity is secured and the output of the inverter 8 synchronized with the commercial power source 1 is output. Fluctuation has been greatly reduced.

  FIG. 5 shows an overall view of the operation waveform of each part in the present embodiment.

  5A shows the smoothing means 7 voltage (VC2), FIG. 5B shows the second smoothing means 10 voltage (VCc), and FIG. 5C shows the resonance capacitor 13 voltage (VC1) correlated with the output of the inverter 8. FIG. 5D shows the commercial power supply 1 voltage. 5E, 5F, and 5G show VC2, VCc, and VC1 when the capacities of the smoothing means 7 and the second smoothing means 10 are not sufficient.

  By setting the capacity of the smoothing means 7 large, the input current flowing from the commercial power source 1 is distorted and the power factor is lowered. However, since the input current is shaped by the power factor improving means 3, a high power factor is obtained. Can be maintained.

  An arrow A indicates the timing when the control unit 15 reads the output signals from the first voltage detection unit 14 and the second voltage detection unit 16. That is, the control unit 15 reads a part of the detection unit signal at a timing when the commercial power source 1 becomes a predetermined value or less.

  During the period when the commercial power source 1 is below a predetermined value, the voltage and current applied to the power factor improving means 3 are small, so that the generated noise is small. That is, the control means 15 reads the detection signal during a period when the influence of noise is small.

  The first voltage detection means 14 and the second voltage detection means 16 are for detecting VCc and VC1, but do not peak at the reading timing. However, since the capacities of the smoothing means 7 and the second smoothing means 10 are set to be sufficiently large, VCc and VC1 at the read timing have little difference from the peak as a result of smoothing.

  In the present embodiment, by correcting the detection signals of VCc and VC1 and estimating the peak value, it is possible to detect with high accuracy during a period when the influence of noise is small.

  During such a series of heating operations, the resonance frequency of the resonant element including the heated object 20, the heating coil 12, and the resonant capacitor 13 may fluctuate greatly due to the movement of the heated object 20 by the user. .

  At this time, when the driving frequency (or an integer multiple thereof) of the second switching element group 11 and the resonance frequency are greatly different, a sufficient resonance current does not flow through the heating coil 12, so that the input current and the output of the inverter 8 are reduced. To do.

  If the state of the inverter 8 is not suitable for heating the article to be heated 20, in order to reduce the load applied to the inverter 8, heating should be stopped immediately and reheating should be started after a predetermined period. However, if the user's cooking operation is being performed, it is not convenient to repeatedly stop heating.

  In the present embodiment, when the output signal of the second voltage detection means 16, that is, the voltage of the resonant capacitor 13 having a correlation with the output of the inverter 8 becomes a predetermined value or less, the control means 15 causes the power factor improvement means 3 to Whether or not the state is suitable for continuing heating is determined comprehensively with high accuracy from detection signals from the first voltage detection means 14, the second voltage detection means 16, the input current detection means 21, and the like.

  Thereby, when the output of the inverter 8 is reduced and the detection signal is also at a low level, the influence of noise due to the operation of the power factor improving means 3 is suppressed.

  That is, the control means 15 controls the power factor improvement means 3 to stop when the detection means signal becomes a predetermined value or less, and performs accurate detection.

  As described above, in the present embodiment, it is possible to provide an induction heating device that reduces the load on components and has little influence on other devices by detecting the operating state of the power factor improving means. It becomes.

  In this embodiment, the control unit 15 controls the drive of all of the first switching element 4, the second switching element group 11, and the third switching element 17. However, the present invention is not limited to this. is not. For example, the same effect can be obtained by using a dedicated control means (such as an IC) for controlling the driving of the first switching element 4.

  As described above, the induction heating device according to the present invention provides an induction heating device that reduces the load on components and has little influence on other devices by detecting the operating state of the power factor correction means. Therefore, it is useful not only as an induction heating cooker, but also as an induction heating water heater, induction heating iron, or other induction heating heating apparatus.

Main part schematic circuit diagram of induction heating apparatus (induction heating cooker) in Embodiment 1 of the present invention Schematic diagram of input current shaping by power factor improvement means 3 of the same induction heating device (induction heating cooker) Schematic diagram showing the input current detection means 21 signal reading timing by the control means 15 of the induction heating device (induction heating cooker). Operation waveform diagram of each part in a state where a predetermined input current of the same induction heating device (induction heating cooker) is obtained Overall view of the operation waveform of each part of the induction heating device Circuit diagram showing an embodiment of a conventional induction heating device Signal waveform diagram of each part in the same induction heating device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Rectification means 3 Power factor improvement means 4 1st switching element 7 Smoothing means (electrolytic capacitor)
8 Inverter 11 Second switching element group 12 Heating coil 14 First voltage detecting means 15 Control means 16 Second voltage detecting means 20 Object to be heated

Claims (3)

Rectifying means for rectifying an AC voltage from a commercial power supply, power factor improving means connected to the output side of the rectifying means, a first switching element included in the power factor improving means, and the power factor improving means Smoothing means connected to the output side, an inverter connected to the smoothing means, a plurality of second switching elements included in the inverter, aluminum or copper connected to the inverter and these A heating coil for inductively heating an object to be heated made of a low permeability material having an electric conductivity substantially equal to or higher, a detection means for detecting the magnitude of the output of the inverter, and a signal from the detection means Control means for controlling the inverter, wherein the inverter supplies a high-frequency current to the heating coil by turning on / off the second switching element group. Supplied by heating induces the object to be heated, the said power factor improving means with improving the power factor by turning on / off the first switching element, said control means the object to be heated based on the detection means output An induction heating device that controls to stop the power factor improvement means when judging the material . The induction heating apparatus according to claim 1 , wherein the control means controls to stop the power factor improvement means when the small object is heated or there is no object to be heated . The induction heating apparatus according to claim 1 or 2, wherein the control means delays the detection means signal reading timing within a half cycle of the commercial power source when the power factor improvement means is stopped relative to the operation of the power factor improvement means .

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