JP5877302B2 - Induction heating device - Google Patents

Description

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

  A conventional induction heating apparatus will be described by taking an induction heating cooker as an example. Attaching the switching means attached to the radiator to the printed wiring board, attaching a temperature detection element such as a thermistor to this printed wiring board, detecting the temperature in the vicinity of the switching means, and if this temperature rises to a certain value, A technique for protecting power electronic components constituting an inverter circuit such as a switching means from thermal destruction by restricting the input of the inverter circuit is disclosed.

JP-A-10-154579

  However, the conventional configuration is useful when the thermal duty of the power electronic component is also reduced in proportion to the decrease in the input of the inverter circuit, but otherwise, for example, when the switching means is normally turned on. If zero current switching is used, the inverter circuit input and switching means loss (conduction loss and turn-off loss) are almost proportional, but when turn-on current occurs instead of zero current at turn-on, the turn-on loss becomes dominant Even if the conduction time or drive time ratio of the switching means is reduced to reduce the input of the inverter circuit, the conduction loss and turn-off loss of the switching means are reduced, but the turn-on loss is not reduced, so the total loss of the switching means The range of reduction of the In the case of a cooker, the induction heating output to the load such as a pan will be lowered earlier, so it may not be possible to obtain the thermal power required for cooking, or in the worst case, the power electronic components may not be protected against thermal destruction. I had the problem of being there.

  Even if the input of the inverter circuit is limited, if the temperature detected by the temperature detector further increases, it is possible to decrease the input limit value step by step. In that case, the induction heating output to the load is further increased. Therefore, it has a problem that it is not easy to use.

  The present invention solves the above-described conventional problem. When a switching device is turned on, a turn-on current is generated, and even if the input of the inverter circuit is limited, the switching device loss cannot be greatly reduced. By grasping the change in the operation trajectory of the control element generated in the inverter circuit such as the input current versus the resonant voltage and the resonant current, the load material judgment is performed again and the switching means drive frequency is changed to the load material. Try to adapt to the shape and electrical characteristics, increase the chances that the switching means will inductively heat the load at a drive frequency that does not generate turn-on current, and ease of use by reducing the induction heating output for thermal protection of power components It aims at providing the induction heating apparatus which prevented deterioration of.

In order to solve the above conventional problems, the induction heating apparatus of the present invention, induces an AC power source, a rectifier circuit for rectifying the AC power supply into DC, a load by converting the output of the rectifier circuit to the high frequency AC heating, comprising switching means, and an inverter circuit including a heating coil and a resonance capacitor, and a control circuit for controlling the operation of the inverter circuit, the said control circuit, for detecting the input current to the inverter circuit input Current detection means, control element detection means for detecting an electrical control element generated in the inverter circuit, and determination of the presence and material of the load based on the output of the control element detection means at the start of operation of the inverter circuit a material determining means, depending on the material it is determined that the material determining means, to select the fundamental driving frequency of two or more of said inverter circuit set discretely, To drive the switching means at serial fundamental drive frequency, so that the output of said control element detecting means for the output of the input current detecting means becomes below a predetermined limit value group, the conduction time or the drive of the switching means Driving means for variably controlling the frequency, and load for detecting a state in which the output of the input current detecting means is within a predetermined range and the output of the control element detecting means is limited to the predetermined limit value group. comprising a state detection means, said control circuit, when the turn-on current at the time of turn-on of said switching means is caused by restricting the input of the inverter circuit can not be loss significantly reduced in the switching means, the load state detection And the output of the control element detection means is predetermined in the predetermined range. From the state is limited to the limit value set in operation, when detecting that change state to operating in the predetermined range of the input current detecting means, the material of the load in the material determining means In order to re-determine, the inverter circuit is restarted .

Due to this, the material and shape of the load determined at the start of heating is due to some factors, changes in the electrical characteristics of the load due to heat, changes in magnetic coupling with the heating coil due to changes in the position of the load with respect to the heating coil, etc. In order to inductively heat the load in the changed state, the operation at the basic driving frequency of the switching means that has been determined is not suitable for operation by generating a turn-on current in the switching means. Using the change in the operating characteristic curve of the output of the control element detection means relative to the output of the input current detection means, the output of the control element detection means relative to the output of the input current detection means within the output range of the predetermined input current detection means the limitation operation by the limit value group, the change of outside the limiting operation upon detecting the load condition detecting means, the inverter circuit again Basic dynamic and, if suitable conditions and the material of the current load by determining the material at material determining means may be at the start inverter operation, the switching means suitable for electrical state variation phased load By suppressing the induction heating output without changing the basic drive frequency as the drive frequency, it is possible to remove the unintentional thermal stress of the switching means that is not excluded.

  The induction heating device according to the present invention has a change in which the limiting operation deviates from the limiting operation by the limit value group of the output of the control element detecting unit with respect to the output of the input current detecting unit within the output range of the predetermined input current detecting unit. By providing a load state detection means to detect, the material and shape of the load determined at the start of heating is some factor, the electrical characteristics of the load change due to heat, the magnetism with the heating coil due to the change in the position of the load with respect to the heating coil In order to inductively heat the load in which the driving frequency of the switching means, which was initially determined due to a change in coupling or the like, is changed to a state in which the switching means is operated by generating a turn-on current, From the limit operation by the limit value group of the output of the control element detection means for the output of the input current detection means within the output range of the predetermined input current detection means, When the load state detection means detects that the change is out of the limit operation of the load, the material determination operation of the load by the material determination means is performed again to drive the switching means suitable for the changed electrical state of the load. Reduce the frequency of suppressing the induction heating output to the load for thermal protection of power components by removing the thermal stress of the switching means that is not excluded by lowering the induction heating output without changing the drive frequency without changing the frequency By doing so, deterioration in usability can be prevented.

(A) Block diagram of cooking device in Embodiment 1 of the present invention (b) Operating characteristic curve diagram in Embodiment 1 of the present invention Load material determination region diagram in the first embodiment of the present invention (A) Current waveform diagram during operation in a state where the iron material load is deviated from the specified position and the non-magnetic stainless steel is deviated from the specified position at the basic drive frequency of 23 kHz of the switching means in Embodiment 1 of the present invention (b) Implementation of the present invention (C) Current waveform diagram during operation in a state where the nonmagnetic stainless steel is in a specified position at the basic driving frequency of 23 kHz of the switching means in the first embodiment (c) The nonmagnetic stainless steel at the basic driving frequency of 30 kHz of the switching means in the first embodiment of the present invention Current waveform during operation in the specified position Flowchart of operation of load state detection means in Embodiment 1 of the present invention

A first aspect of the present invention is an AC power source, a rectifier circuit for rectifying the AC power to DC, an output induction heating the load is converted into a high frequency alternating current of the rectifier circuit, the switching means, the heating coil, and the resonance capacitor includes an inverter circuit including a, and a control circuit for controlling the operation of the inverter circuit, the said control circuit, an input current detecting means for detecting an input current to said inverter circuit, electricity generated in the inverter circuit A control element detection means for detecting a static control element, a material determination means for determining presence / absence and material of the load based on an output of the control element detection means at the start of operation of the inverter circuit, and the material determination means depending on the material, select the fundamental driving frequency of two or more of the inverter circuits set discretely, said switching means at the fundamental drive frequency Driving means for variably controlling the conduction time or the driving frequency of the switching means so that the output of the control element detection means with respect to the output of the input current detection means is less than or equal to a predetermined limit value group. and a load condition detecting means output for detecting a state in which output is operating is limited to the predetermined limit value group of the control element detecting means within a predetermined range of the input current detector, said control In the case where the circuit generates a turn-on current when the switching means is turned on, and the loss of the switching means cannot be greatly reduced even if the input of the inverter circuit is limited, the load state detection means outputs the output of the input current detection means. From the state where the output of the control element detection means is limited to the predetermined limit value group within the predetermined range. Configuration upon detecting the changes in state of said operating within predetermined range of the input current detecting means, in order to re-determine the material of the load in the material determining means, to restart the inverter circuit It is what.

  As a result, the switching means of the inverter circuit is normally driven by the drive means, and the direct current rectified by the rectifier circuit is converted into the high frequency alternating current to generate the high frequency current in the resonance circuit formed by the resonance capacitor and the heating coil. The high frequency current is supplied to the heating coil, and the load is induction heated by the magnetic flux generated from the heating coil.

  At this time, when the switching means is driven, the inverter circuit is operated, and the load starts to be inductively heated, an electrical control element generated in the inverter circuit detected by the control element detection means, for example, the voltage or current across the resonance capacitor Based on the voltage and current at both ends of the heating coil, based on the electrical characteristics of the load to be heated, the material and shape are determined by the material determination means, and the basic drive frequency of the switching means corresponding to the predetermined material by this The inverter circuit is operated by driving at the determined basic drive frequency.

  Control of the induction heating output to the load is performed by varying the conduction time of the switching means so that the output of the control element detection means with respect to the output of the input current detection means is equal to or less than a predetermined limit value group. .

  In addition, while the inverter circuit is operating, the switching means generates heat due to switching loss, but the generated heat is dissipated through the radiator with the switching means attached to suppress the temperature rise of the switching means and radiator. ing.

  Here, the basic drive frequency of the switching means determined at the start of the inverter circuit operation due to some cause, change in electrical characteristics of the load due to heat, change in magnetic coupling with the heating coil due to change in position of the load with respect to the heating coil, etc. Then, since the mutual inductance due to the magnetic coupling of the heating coil and the load and the resonant frequency of the resonant capacitor change, when the switching means is operating by generating a turn-on current, compared to the case where there is no turn-on current. As the switching loss of the switching means increases, the amount of heat generation also increases, and if the heat generation exceeds the heat dissipation capability of the radiator, the thermal stress of the switching means increases and may be destroyed.

In order to avoid this, the operation at the basic drive frequency of the switching means, which was initially determined for the above-mentioned reason, operates by generating a turn-on current in the switching means in order to inductively heat the load in a changed state. Input current within the output range of the predetermined input current detection means using the change in the operating characteristic curve of the output of the control element detection means relative to the output of the input current detection means when an unsuitable state occurs. When the load state detection means detects a change that the control element detection means outputs relative to the output of the detection means by the limit value group, the deviation from the limit operation is detected by the load state detection means, the operation of the inverter circuit is temporarily stopped. The
After stopping and operating again, and determining the material of the load by the material determining means, the operation ratio of the switching means or the driving time ratio or When the drive frequency is fixed to a predetermined value and the load material is re-determined with another discrimination threshold, the time difference until the original induction heating output is restored is large, but another discrimination threshold is set. There is no need to provide the same threshold value used for the material judgment performed at the start of the inverter circuit operation, so that the design factor for determining the judgment threshold can be reduced and the judgment threshold value can be stored. It is possible to reduce the storage area of a microcomputer or the like.

  As a result, by reselecting the basic drive frequency of the switching means and operating at a drive frequency suitable for the electrical characteristics of the load whose state has changed and the magnetic coupling with the heating coil, an operation in which no turn-on current is generated. The mode can be switched to reduce the switching loss of the switching means and reduce the thermal duty of the switching means.

According to a second aspect of the present invention, there is provided an AC power source, a rectifier circuit that rectifies the AC power source into direct current, a switching means, a heating coil, and a resonant capacitor that inductively heat a load by converting the output of the rectifier circuit into high frequency alternating current Including an inverter circuit, and a control circuit for controlling the operation of the inverter circuit. The control circuit includes an input current detection means for detecting an input current to the inverter circuit, and an electric current generated in the inverter circuit. Control element detection means for detecting a control element, material determination means for determining the presence / absence and material of the load based on the output of the control element detection means at the start of operation of the inverter circuit, and material determined by the material determination means In accordance with the above, the basic drive frequency of two or more of the inverter circuits set discretely is selected, and the switching means at the basic drive frequency Driving means for variably controlling the conduction time or the driving frequency of the switching means so that the output of the control element detection means with respect to the output of the input current detection means is less than or equal to a predetermined limit value group. Load state detecting means for detecting a state in which the output of the input current detecting means is operating within a predetermined range and the output of the control element detecting means is limited to the predetermined limit value group, and the control In the circuit, the load state detection unit operates from a state in which the output of the input current detection unit is within the predetermined range and the output of the control element detection unit is limited to the predetermined limit value group. When it is detected that the input current detecting means has changed to a state of operating outside the predetermined range, the conduction ratio or driving time ratio or driving frequency of the switching means is set to a predetermined value. Fixed to, as well as re-determine the material of the load in the material determining means, the predetermined value is set to the output side is less than the induction heating output of the load before changing to the predetermined value It is a configuration.

Thereby, without stopping the operation of the inverter circuit, the driving means is fixed for a predetermined time after the change, and during that time, at a predetermined determination threshold different from the material determination performed when the inverter circuit starts operating. After the material determination of the load by the material determination means, the operation of the inverter circuit is controlled so that a desired input current is obtained. This operation restarts the inverter circuit.
When determining the material of a moving load, there is a time difference between the induction heating temporarily stopping and reaching the desired induction heating output. Therefore, it is possible to quickly return to a desired induction heating output and to minimize the interruption of the induction heating output. Further, the predetermined value is configured to be set on the side where the output is smaller than the induction heating output of the load before the change to the predetermined value. This makes it possible to determine the material of the load in a reduced state without increasing the electrical and thermal responsibilities of the power components such as the switching means constituting the inverter circuit compared to the current operation.

A third invention is the first or second invention, in particular, the switching means of the inverter circuit comprises a first switching means and a second switching means,
The driving means alternately drives the first switching means and the second switching means, and increases or decreases a conduction ratio or a driving time ratio of the first switching means and the second switching means, or A limit value group in which the driving frequency is increased or decreased within a predetermined frequency range with respect to the selected basic driving frequency, the output of the input current detecting means is within a predetermined range, and the output of the control element detecting means is predetermined. In other cases, the induction heating output to the load is controlled by making the value detected by the input current detection means constant .

Thereby, the output of the input current detection means is within a predetermined range, and the output of the control element detection means is limited to a predetermined limit value group. For example, the pan is placed out of the center of the heating coil or has a small diameter. When heating a load that requires thermal power restriction such as a pot, the desired induction heating output to the load can be obtained as much as possible by making the value detected by the input current detection means constant, except for By alternately driving the two switching means, the drive time ratio can be varied at a predetermined basic drive frequency, or the drive frequency can be varied within a predetermined frequency range with respect to the basic drive frequency. By switching the basic drive frequency without switching the inductance of the heating coil or the capacitance of the resonance capacitor, the operation mode suitable for the load material is achieved and the same material is used. Since the basic drive frequency can be made substantially the same when heating the load, the frequency of interference noise due to the frequency difference of the high-frequency magnetic field applied to the load when operated simultaneously by multiple induction heating devices is suppressed. Thus, the induction heating output to the load of the inverter circuit can be easily controlled.

A fourth invention is, in particular, in any one invention of the first to 3 electrical control element generated in the inverter circuit, wherein the control element detecting means detects, and both ends voltage or current of said resonant capacitor It is a configuration.

  As a result, the detection circuit can be simply configured with relatively small and inexpensive electronic components such as resistors and current transformers.

A fifth invention is, in particular, in any one invention of the first to 3 electrical control element generated in the inverter circuit, wherein the control element detecting means detects, and both ends voltage or current of the heating coil It is a configuration.

  As a result, the detection circuit can be simply configured with relatively small and inexpensive electronic components such as resistors and current transformers.

  Embodiments of the induction heating apparatus of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
Hereinafter, an embodiment of the present invention will be described with reference to the drawings, taking an induction heating cooker as an example. FIG. 1A is a block diagram showing the configuration of the embodiment of the present invention. FIG. 1 (b) is an operating characteristic curve diagram according to the embodiment of the present invention, FIG. 2 is a load material determination region diagram according to the embodiment of the present invention, and FIGS. 3 (a), (b) and (c) are according to the present invention. FIG. 4 is an operation flowchart of the load state detection means in the embodiment of the present invention.

  In FIG. 1A, a rectifier circuit 2 comprising a bridge-connected diode for rectifying an AC power supply 1, a smoothing circuit 3 comprising a choke coil 3a and a capacitor 3b, a first switching means 4a and a second switching means 4d An inverter circuit 4 including a resonant capacitor 4b and a heating coil 4c is provided, and induction heating is performed by applying a high-frequency alternating magnetic field to a load 5 such as a pan when a high-frequency current is supplied from the heating coil 4c.

  In order to control the operation of the inverter circuit 4, the control circuit 6 drives the first switching means 4a and the second switching means 4d alternately on and off, and changes the drive time ratio or drive frequency to the heating coil 4c. Control corresponding to induction heating output to a load 5 such as a pot to be heated, a driving means 7 for controlling a high frequency current to be supplied, an input current detection means 8 for detecting an input current (Iin) of the inverter circuit 4 A control element detecting means 9 for detecting an element value, a material determining means 10 for determining the presence / absence and material of the load 5 from the output of the control element detecting means 9, and an output of the input current detecting means 8 within a predetermined range. There is provided a load state detection means 11 for detecting a state in which the output of the detection means is limited to a predetermined limit value group.

  In the present embodiment, a case will be described in which the control element detection means is the resonance voltage detection means 9 that detects the voltage (Vc1) across the resonance capacitor 4b.

  The driving means 7 drives the first switching means 4a and the second switching means 4d of the inverter circuit 4, rectifies the AC power source 1 with the rectifier circuit 2, and converts the direct current smoothed with the smoothing circuit 3 into high-frequency alternating current. The high frequency current is supplied to the heating coil 4c, and the pan as the load 5 is induction-heated by the magnetic flux generated from the heating coil 4c. The heating thermal power of the load 5 is controlled by changing the driving timing of the first switching means 4a and the second switching means 4d by the output of the driving means 7 and changing the high-frequency current supplied to the heating coil 4c. .

  At this time, the output of the input current detection means 8 is within a predetermined range, and the output of the resonance voltage detection means 9 is limited to a predetermined limit value group or less. For example, the pan is placed out of the center of the heating coil. The value detected by the input current detection means 8 is not the case (operation b in FIG. 1 (b)) except when the load requiring heating power restriction such as a small-diameter pan is heated (operation a in FIG. 1 (b)). Increase or decrease the drive time ratio of the first switching means 4a and the second switching means 4d or increase or decrease the drive frequency within a predetermined frequency range with respect to the selected basic drive frequency so that a desired value is obtained. By controlling the induction heating output to the load 5, the desired induction heating output to the load can be obtained as much as possible.

  In the present embodiment, the drive time ratio of the first switching means 4a and the second switching means 4d is the ratio of the conduction time of the first switching means 4a to the conduction time of the second switching means 4d. By increasing the time ratio from the predetermined minimum value to the maximum value, the capacitance of the resonance capacitor 4b, the inductance of the heating coil 4c, the heating coil 4c and the load 5 are increased so that the induction heating output of the load 5 also increases monotonously. The distance between and is set.

The basic drive frequency is obtained when the operation of the inverter circuit 4 is started (at the time of start-up). In this embodiment, the drive frequency of the first switching means 4a and the second switching means 4d is 23 kHz, and the drive time ratio is minimized. Based on the output of the resonance voltage detection means 9 caused by the material and shape of the load 5 when set, depending on a predetermined material judgment region as shown in FIG. If the load 5 has low magnetic permeability and low conductivity, the first basic operating frequency is 23 kHz. If the load 5 has low magnetic permeability and low conductivity such as nonmagnetic stainless steel, the second basic operating frequency is 30.
Inductive heating as kHz, and even with the above two materials, the magnetic coupling with the heating coil 4c is weak, such as a knife, small diameter pan, a small diameter pan, or a low permeability, high conductivity load 5 such as aluminum, or no load Therefore, it is determined that there is no load, and induction heating is not performed. In the case of induction heating, the induction heating output to the load 5 is controlled by increasing / decreasing the drive time ratio of the first switching means 4a and the second switching means 4d at the determined basic drive frequency. Even if the drive time ratio between the means 4a and the second switching means 4d is maximized, if the desired input current is not reached, in this embodiment, the drive frequency is subtracted from the basic drive frequency to an upper limit of 2 kHz. Control is performed as close as possible to the input current. This is because when a plurality of loads 5 of the same material are simultaneously induction-heated by a plurality of inverter circuits 4, the frequency of the high-frequency magnetic field applied to each load is made substantially the same, and the audible range due to the frequency difference is reduced. It suppresses the frequency of occurrence of interference sound. In addition, the basic drive frequency is switched depending on the material of the load 5 determined to be capable of induction heating. The capacitance of the resonance capacitor 4b and the inductance of the heating coil 4c are switched by a large-capacity contact such as a relay. Without changing the basic drive frequency, the operation suitable for the material of the load 5 is realized. With the load 5 of a high magnetic permeability and high conductivity material such as iron or magnetic stainless steel, the heating coil 4c Since the mutual inductance with the heating coil 4c increases and the maximum induction heating output decreases at a high driving frequency, the desired induction heating output can be obtained by setting the driving frequency as low as possible above the audible range. It is easy to get.

  While the inverter circuit 4 is operating, each switching means generates heat due to the conduction loss and switching loss of the first switching means 4a and the second switching means 4d, but the first switching means 4a and the second switching means. The means 4d is attached to and thermally connected to a radiator (not shown) made of aluminum or the like, so that heat is radiated through the radiator.

  Further, when the operation of the inverter circuit 4 continues, the heat generation of the first switching means 4a and the second switching means 4d continues, and the temperature of the radiator increases. If this state continues and the temperature of the first switching means 4a and the second switching means 4d continues to rise and exceeds the allowable heat-resistant temperature of the first switching means 4a and the second switching means 4d, the first switching means 4a And the second switching means 4d causes thermal runaway or thermal destruction, and the inverter circuit 4 becomes inoperable. Therefore, during the operation of the inverter circuit 4, in order to suppress the temperature rise of the first switching means 4a and the second switching means 4d, the cooling air (not shown) is mainly used as the cooling air by the cooling fan (not shown). And the first switching means 4a and the second switching means 4d.

  Generally, as the input power of the inverter circuit 4 increases, the loss of the heating coil 4c and the resonance capacitor 4b and the switching loss of the first switching means 4a and the second switching means 4d also increase, and the heat generated thereby. Will also increase. Conversely, if the input power of the inverter circuit 4 decreases, the loss of the heating coil 4c and the resonance capacitor 4b, the switching loss of the first switching means 4a and the second switching means 4d also decrease, and the heat generation associated therewith also decreases. To do.

However, as in the present embodiment, the inverter circuit 4 corresponding to the material and shape of the load 5 determined by the material determination means 10 based on the value detected by the resonance voltage detection means 9 at the start of the operation of the inverter circuit 4. Since the operating state, that is, whether to heat or not, and which basic driving frequency to use when heating is determined, for example, the relative position between the heating coil 4c and the load 5 is determined at the start of the operation of the inverter circuit 4. If the relative position differs immediately after and after that, or if the relative position of the heating coil 4c and the load 5 does not change, the electrical characteristics of the load 5 change due to heat from heating, etc. When the heating is continued, there is a case where it is not a basic driving frequency for operating the inverter circuit 4 which is originally suitable for the material and shape of the load 5 to be heated.

  For example, if the heating coil 4c and the load 5 are in specified positions, the load 5 is suitable to be operated at a basic drive frequency of 30 kHz with a nonmagnetic stainless steel load 5 having low permeability and high resistance. Even if the heating coil 4c and the load 5 are deviated or separated from the specified position by a certain degree or more, it is determined that the load 5 is made of high magnetic permeability, high resistance iron or magnetic stainless steel, and the basic drive is performed. FIG. 3A shows a point a that intersects with a resonance voltage limit value group in a section c that is a predetermined output range of the input current detection means 8 shown in operation a of FIG. Works with waveforms. If it remains in this state, the electrical characteristics of the load 5 seen from the heating coil 4c are iron or magnetic stainless steel, and it does not operate by generating a turn-on current. When 5 is returned to the specified position, the point b outside the interval c shown in the operation b in FIG. 1B intersects the set input current control value as shown in FIG. 3B. One switching means 4a may operate with a turn-on current.

  At this time, since the turn-on loss of the first switching means 4a is remarkably increased, if the heating is continued beyond the capacity of the cooling fan (not shown), the first switching means 4a is thermally destroyed. In order to avoid this, in the present embodiment, the induction heating output is limited by the resonance voltage limit value group in the interval c of the output range of the input current detection means determined in advance in the operation a of FIG. If the load state detection unit 11 detects that the operation has changed from the state in which the output current of the input current detection unit is out of the predetermined state to the operation b in FIG. Is temporarily stopped and restarted after about 2 seconds, and the material and shape determination of the load 5 in the material determination means 10 is performed again.

  The specific load state detection means 11 at this time determines the change in the operation state by making the condition determination shown in FIG. As a result, the basic drive frequency corresponding to the state of the load 5 is selected again, and if the load 5 is at a substantially prescribed position, 30 kHz is selected as the basic drive period, and the operation shown in FIG. This eliminates the opportunity to operate with a turn-on current thereafter. Thereafter, an operation of adjusting the drive time ratio or the drive frequency of the first switching means 4a and the second switching means 4d is performed so that the value detected by the input current detection means 8 becomes a desired value.

  By performing this material determination operation, the same determination threshold value as shown in FIG. 2 used for the material determination performed at the start of the inverter circuit operation is used, and the design factor for determining the determination threshold is reduced, and this determination threshold value is stored. The amount of storage area of a microcomputer or the like is reduced.

  In the flowchart of FIG. 4, the time condition of “1 second or more” is added to the second conditional branch, because the user shakes the pan during cooking and satisfies the condition A in a short time. This is to avoid unnecessary re-material determination operation, and this time is set as an appropriate amount.

  However, at this time, in the case where the interruption time of the induction heating operation due to the restart of the inverter circuit 4 becomes a problem, the operation of the inverter circuit 4 is not stopped and the desired setting to the inverter circuit 4 is desired. The first switching means 4a and the second switching means 4a and the second switching means 4d are adjusted by adjusting the driving time ratio of the first switching means 4a and the second switching means 4d in a direction to be smaller than the input current. The switching means 4d has a low electrical and thermal duty, and its driving time ratio is a fixed time, which is about 1 second in this embodiment (a time shorter than a standby time of about 2 seconds when the inverter circuit is restarted). ) Fixed, and in the meantime, the material determination of the load 5 is performed based on the material determination region separately determined by the material determination means 10, and the basic drive frequency suitable for the load 5 is reselected. By performing the operation, the induction heating operation is interrupted, and the induction heating output can be reduced by a specified amount from the original output. It is possible to accelerate the return to the induction heating output.

  Further, if the material is determined with the driving frequency of the first switching means 4a and the second switching means 4d being 23 kHz and the driving time ratio being minimized, the same material determination region as that at the start of the inverter circuit operation is used. it can.

  In the present embodiment, the inverter circuit 4 includes two switching means, but includes one and three or more. The inverter circuit 4 includes one resonance capacitor. However, the inverter circuit 4 includes two or more, and one heating coil. Needless to say, the same effect can be obtained even with a configuration including two or more.

  Further, the temperature detecting means may be installed anywhere on the printed wiring board as long as the heat generation state of the switching means can be estimated based on the relative correlation. In addition, the present embodiment includes one temperature detecting means. Although it is configured, it goes without saying that as a configuration having two or more, temperature detection is performed at a plurality of temperature measurement points, so that finer temperature detection is possible.

  Furthermore, although the control element obtained from the inverter circuit used for load material judgment is the voltage across the resonance capacitor, the same applies to elements that can define the operating state of the inverter circuit, such as the resonance capacitor current, the heating coil voltage, and the heating coil current. The effect is obtained.

  In the present embodiment, the load of a material having a low magnetic permeability and high conductivity such as aluminum is set not to be heated, but the same effect can be obtained as a setting for heating. In the present embodiment, the resonance voltage detection means 9 caused by the material and shape of the load 5 when the drive frequency of the first switching means 4a and the second switching means 4d is 23 kHz and the drive time ratio is set to the minimum. Based on the output, the material of the load 5 is determined and the basic drive frequency suitable for it is determined. For example, the drive frequency of the first switching means 4a and the second switching means 4d is changed from 60 kHz to 30 kHz. Therefore, the method of determining the material of the load 5 based on the output value of the resonance voltage detecting means 9 is also useful, and the same effect can be obtained regardless of the material determining method of the load 5.

  As described above, the induction heating device according to the present invention is useful when heating a metal load with a desired induction heating power using induction heating. It is effective for cookers and induction heating rice cookers.

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectifier circuit 4 Inverter circuit 4a 1st switching means 4b Resonance capacitor 4c Heating coil 4d 2nd switching means 5 Load 6 Control circuit 7 Drive means 8 Input current detection means 9 Resonance voltage detection means (control element detection means) )
10 Material determining means 11 Load state detecting means

Claims (5)

AC power source, a rectifier circuit that rectifies the AC power source into direct current, an inverter circuit including a switching means, a heating coil, and a resonant capacitor that converts the output of the rectifier circuit into high-frequency alternating current to inductively heat the load, A control circuit for controlling the operation of the inverter circuit,
The control circuit includes an input current detection means for detecting an input current to the inverter circuit, a control element detection means for detecting an electrical control element generated in the inverter circuit, and the control at the start of the operation of the inverter circuit. Based on the output of the element detection means, the material determination means for determining the presence / absence and material of the load, and the basic drive frequencies of the two or more inverter circuits set discretely according to the material determined by the material determination means And the switching means is driven at the basic drive frequency, and the output of the control element detection means with respect to the output of the input current detection means is less than a predetermined limit value group. Drive means for variably controlling the conduction time or drive frequency, and the output of the input current detection means within a predetermined range of the control element detection means Comprising a load condition detecting means for detecting a state where the force is operating is limited to the predetermined limit value group, and
In the case where the control circuit generates a turn-on current when the switching means is turned on, and the loss of the switching means cannot be greatly reduced even if the input of the inverter circuit is limited, the load state detecting means is connected to the input current detecting means. Operating from outside the predetermined range of the input current detecting means from a state in which the output is within the predetermined range and the output of the control element detecting means is limited to the predetermined limit value group. When it is detected that the state has changed,
The Beku the material of the load again determine Teisu in the material determining means, the induction heating device configured to restart the inverter circuit. An AC power source, a rectifier circuit for rectifying the AC power supply into DC, and converts the output of the rectifier circuit to the high frequency AC induction heating a load, an inverter circuit including switching means, a heating coil, and a resonant capacitor, and a control circuit for controlling the operation of said inverter circuit,
The control circuit includes an input current detection means for detecting an input current to the inverter circuit, a control element detection means for detecting an electrical control element generated in the inverter circuit, and the control at the start of the operation of the inverter circuit. Based on the output of the element detection means, the material determination means for determining the presence / absence and material of the load, and the basic drive frequencies of the two or more inverter circuits set discretely according to the material determined by the material determination means select, to drive the switching means at the fundamental drive frequency, so that the limit value or less group output is preset of the control element detecting means for the output of the input current detecting means, said switching means Drive means for variably controlling the conduction time or drive frequency, and the output of the input current detection means within a predetermined range of the control element detection means Comprising a load condition detecting means for detecting a state where the force is operating is limited to the predetermined limit value group, and
The control circuit is configured such that the load state detection unit operates while the output of the input current detection unit is within the predetermined range and the output of the control element detection unit is limited to the predetermined limit value group. When detecting that the input current detecting means has changed to a state of operating outside the predetermined range, the conduction ratio or the driving time ratio or the driving frequency of the switching means is fixed to a predetermined value, While re-determining the material of the load by the material determination means ,
Wherein the predetermined value, the load induction heating output induction heating device having the configuration set on the output side is less than in prior to changing to the predetermined value. The said switching means of said inverter circuit comprises a first switching means, second switching means, and
It said drive means to drive the said first switching means and said second switching means alternately increase or decrease the conduction ratio or the driving time ratio of the first switching means and said second switching means, or Increases or decreases the driving frequency within a range of a predetermined frequency width for the selected fundamental drive frequency limit value group output is preset of the control element detecting means output is within a predetermined range of the input current detecting means 3. The induction heating device according to claim 1, wherein the induction heating output to the load is controlled by making the value detected by the input current detection means constant in a case other than the case where it is limited to . An electrical control element generated in the inverter circuit, wherein the control element detecting means for detecting, the induction heating apparatus according to any one of claims 1 to 3, the voltage across or current and the configuration of the resonant capacitor. An electrical control element generated in the inverter circuit, wherein the control element detecting means for detecting, the induction heating apparatus according to any one of claims 1 to 3, the voltage across or current and the configuration of the heating coil.

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