JP2009259851A - Induction heating device and cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device which easily determines the type of load and carries out capacity change of a snubber circuit according to the type of the load based on the determination. <P>SOLUTION: This induction heating device is provided with: at least an inverter circuit 3 composed of a plurality of switching elements 3a-3d, and supplying a high-frequency current to a heating coil 4 to generate electromagnetic induction; a snubber capacitor 7 connected to one of the switching elements 3a-3d, and suppressing generation of a spike voltage; an input current detection means 12 detecting a current supplied to the inverter circuit 3 from a power source; a drive signal control circuit 9a outputting, to the inverter circuit 3, a drive signal creating power set by controlling the duty of a switching element of the inverter circuit based on the current detected by the input current detection means 12; and a load determination means 9e determining the type of a load 10 based on the current detected by the input current detection means 12 and the duty, and controlling the capacitance of the snubber capacitor 7. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an apparatus for heating using electromagnetic induction and an induction heating cooker using the same. In particular, the load is determined, and effective heating with less loss is performed according to the determination.

  Heating using electromagnetic induction can be performed by causing a high-frequency current to flow through a coil in which an object to be heated is placed, generating a magnetic force, and generating an eddy current in the object. Devices that use this principle have been particularly popular in cooking relations that have been performed using fire. Therefore, an electromagnetic induction cooking device will be described below as an example of a device that performs heating using electromagnetic induction.

  The electromagnetic induction heating cooker has various advantages such as safety and low fuel consumption because it does not use fire. Because of the use of electromagnetic induction, the desired heating effect cannot be obtained unless appropriate control is performed based on the material of the container or the like (load) that is the heating target of the cooker. In addition, unlike fire, the operating state of the device cannot be visually observed, so that the device may be operated without a load, consuming power wastefully, or damaging the device due to high-frequency heating. Therefore, a method for determining the presence / absence of a load, a material, and the like has been proposed (see, for example, Patent Document 1). In addition, a method is proposed in which a load is determined by variable oscillation frequency control, and the capacity of a snubber capacitor of a snubber circuit is switched based on the determined load and input current (power) (see, for example, Patent Document 2). .

JP-A-4-269488 Japanese Patent Laid-Open No. 5-94868 (page 5, FIG. 1)

  However, the method as described above has a large amount of data when determining the load, and the processing procedure, calculation, and the like become complicated. Further, the switching of the snubber capacitor is performed based on the output when the inverter circuit is controlled by the oscillation frequency variable control.

  The present invention has been made to solve the above-described problems. An induction heating apparatus that easily determines the type of load and further changes the capacity of the snubber circuit according to the type of load based on the determination, and apparatus therefor. An induction heating cooker used is provided.

  The induction heating device according to the present invention is configured by a plurality of switching elements, and is connected to one of the switching circuit and an inverter circuit that supplies a high-frequency current to the heating coil and suppresses the generation of spike voltage. The snubber circuit, the input current detecting means for detecting the current supplied from the power source to the inverter circuit, the current detected by the input current detecting means is converted into electric power, and compared with the set electric power. Drive signal control means that outputs a drive signal to the inverter circuit to set the power based on the current detected by the input current detection means by controlling the duty, and the input current detection when the set power is reached The type of load to be heated is determined based on the current and duty detected by the means, and the determined type of load and input current Based on the current detection means it has detected, in which at least comprises a load determination means for controlling the capacitance of the capacitor constituting the snubber circuit.

According to the present invention, since the load determination unit determines the type of load based on the phase difference of the drive timing between each pair of switching elements and the current detected by the input current detection unit, for example, a plurality of data The type of load can be determined without complicatedly combining (parameters), and the procedure (algorithm) for performing the processing can be simplified. Particularly in the case of an induction heating cooker, the type of load is often changed, and simplification of the processing procedure is particularly effective.
Further, based on the determined type of load and the current detected by the input current detection means, the total loss due to the switching element can be reduced, and the thermal power can be increased. Further, since the loss is small, it is possible to suppress an increase in the heat of the switching element, and to realize, for example, downsizing of the heat radiating fins, a cooling fan, etc., and a cost reduction associated therewith.

It is a figure which shows the circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 1. FIG. 4 is an operation flowchart of the induction heating cooker according to the first embodiment. It is a figure showing the example of a relationship with the thermal power-phase difference of the inverter circuit 3, and a total loss characteristic. It is a figure which shows the drive waveform of the switching element at the time of drive control of the inverter 3 by a phase. It is a figure which shows the drive waveform of the switching element at the time of duty control. It is a figure which shows the circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 2. FIG. It is an operation | movement flowchart of the induction heating cooking appliance which concerns on Embodiment 2. FIG. It is a figure which shows the circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 3. FIG. It is an operation | movement flowchart of the induction heating cooking appliance which concerns on Embodiment 3. FIG. It is a load current waveform of the induction heating cooking appliance which shows Embodiment 3.

Embodiment 1 FIG.
1 is a diagram showing a circuit configuration of an induction heating cooker according to Embodiment 1 of the present invention, FIG. 2 is an operation flowchart of the induction heating cooker according to Embodiment 1 of the present invention, and FIG. FIG. 4 is a diagram showing an example of the relationship between the thermal power-phase difference / total loss characteristic of FIG. 4, FIG. 4 is a diagram showing a drive waveform of the switching element when controlling the inverter circuit 3 by phase, and FIG. FIG. The induction heating cooker in this Embodiment is demonstrated based on each figure.

  In FIG. 1, an inverter circuit 3 is connected to an output terminal of a rectifier circuit 2 that rectifies an AC current from an AC power source 1. In the present embodiment, it is assumed that the inverter circuit 3 has a full bridge configuration with the switching elements 3a to 3d, and the switching elements 3a and 3b and the switching elements 3c and 3d are in pairs. In some cases, there is a switching element to which a flywheel diode or the like is connected. The switching elements 3a to 3d of the inverter circuit 3 operate according to the drive control signal from the control means 9, so that the direct current obtained by the rectification of the rectifier circuit 2 and the smoothing of the smoothing capacitor 14 is converted into a high-frequency current having a pulse waveform. To do. Here, as long as a DC current can be supplied to the inverter circuit 3, the AC power supply 1, the rectifier circuit 2, and the smoothing capacitor 14 are not particularly required.

  By the operation of the inverter circuit 3, the load 10 disposed in the vicinity of the heating coil 4 connected to the output terminal of the inverter circuit 3 is induction-heated. One of the switching elements (for example, the switching element 3b in FIG. 1) is connected in parallel with a switchable snubber capacitor 7 provided in order to prevent generation of a spike voltage due to switching of the switching element. The capacitance is switched by the capacitor switching means 8. In addition, a resonance capacitor 5 is connected in series with the heating coil 4 to form a series resonance circuit. Here, the configuration is made only with the snubber capacitor 7, but a resistor or the like can be attached to the snubber capacitor 7 to form a snubber circuit.

  The set power generation means 11 outputs a command voltage signal corresponding to the specified set power level to the drive signal control circuit 9a. The input current detection means 12 detects the input current supplied from the AC power supply 1, converts it to a voltage signal corresponding to the magnitude of the input current, and outputs it. Here, for the signals output from each, based on the relationship between the preset input current and power, for example, the voltage of the signal based on the input current and the voltage of the signal based on the corresponding set power are the same voltage. (Hereinafter, the voltage of the signal is referred to as voltage A). Based on this input current, input power (so-called thermal power, which is determined by the input current) can be calculated. Therefore, it can also be determined whether the input power and the set power are the same based on whether the signal voltages match. Here, a signal indicating the magnitude of current and power in terms of voltage is created. However, for example, the current and power values may be converted into digital data and output to the control means 9.

  The control means 9 includes a drive signal control circuit 9a, an inverter circuit 3 driver 9b (hereinafter referred to as driver 9b), a capacitor switching means 8 driver 9c (hereinafter referred to as driver 9c), a measurement means 9d and a load determination means 9e. Is provided. The drive signal control circuit 9a generates a drive signal for controlling the drive of the inverter circuit 3 based on the phase difference or the duty based on the signal output from the set power generation means 11 and the signal output from the input current detection means 12. Output to the driver 9b. Based on the drive signal from the drive signal control circuit 9a, the driver 9b outputs a drive signal to the switching elements 3a to 3d at respective timings, and causes the inverter circuit 3 to perform a conversion operation to a high-frequency current (the driver 9b). Strictly speaking, the input drive signal and the output drive signal are not the same signal, but are the same in that they are signals for operating the inverter circuit 3. It will be described as a drive signal). Here, the drive signal control circuit 9a stores data on the upper limit value of the input current corresponding to the set power. Based on the set power set in the set power generation means 11, the upper limit value of the input current is set. It may be determined. In this case, the drive signal control circuit 9a outputs a drive signal so that the peak value of the input current becomes the upper limit value.

  On the other hand, the measuring means 9d is based on the drive signal from the drive signal control circuit 9a, and the phase difference of the drive signal output timing (hereinafter referred to as the phase difference, between 0 ° and 180 ° between the switching elements 3a and 3c. And a signal including the data is output to the load determining means 9e. The phase difference is a phase difference between the group of switching elements 3a and 3b and the group of switching elements 3c and 3d, which is caused by a difference in timing of driving signal output, for example, as shown in FIG. Here, the phase difference generated between the switching elements 3a and 3c will be described. For example, the phase difference between the switching elements 3a and 3d or 3b and 3c (3d) may be used. Here, determination and measurement are performed based on the phase difference. However, when a drive signal based on the duty is output from the drive signal control circuit 9a, the measurement means 9d includes the switching element 3a (3c) and the switching element 3b ( The duty (pulse width) of 3d) may be determined and measured. FIG. 5 shows that the determination is based on the duty of the switching element 3a (3c).

  The load determination means 9e is based on the relationship between the heating power of the inverter circuit 3 and the phase difference based on the signal including the phase difference or duty data determined and measured by the measurement means 9d and the signal output from the input current detection means 12. The type of the load 10 is determined. Then, based on the determined type of the load 10, a switching signal for performing the switching operation of the capacitor switching means 8 is output to the driver 9c. The driver 9c outputs a switching signal to the capacitor switching means 8 (here, the switching signal to be input and the switching signal to be output are not exactly the same signal for the driver 9c, but will be described as a switching signal. To do). Here, the load determination means 9e has a storage means (not shown), and data necessary for the load determination means 9e to perform processing is stored temporarily or for a long time in the storage means. Shall. As the stored data, for example, phase difference data and thermal power (input power to the inverter circuit 3) data necessary for the load 10 determination process by the load determination unit 9e are associated with each type of the load 10. It is stored in a table format (represented by FIG. 3A if it is graphed). In addition, the power reference (boundary) data of the switching timing necessary for the capacity switching timing determination processing of the snubber capacitor 7 is further stored in association with each other.

  Hereinafter, in the present embodiment, the determination of the load 10 and the determination of the capacity switching of the snubber capacitor 7 when the thermal power (input power) control by the phase difference is performed will be described. However, the drive control of the inverter circuit 3 by the duty is described. Even in the case where the load determination is performed, the load determination unit 9e is different from the phase difference control only in that the load 10 is determined based on the duty data measured by the measurement unit 9d instead of the phase difference data. The effect is obtained. In the case of drive control based on duty, it is possible to determine the load 10 and the switching of the capacity of the snubber capacitor 7 even if the inverter circuit 3 has a half-bridge configuration.

  Next, operation | movement of the induction heating cooking appliance centering on the control means 9 is demonstrated based on FIGS. FIG. 2 shows a flowchart that takes into account the flow of signals input to and output from the control means 9. First, when the power is turned on (power on) by an operation of the induction heating cooker user or the like, the drive signal control circuit 9a of the control means 9 outputs a drive signal for activation to the driver 9b (P1). A drive signal is output from the driver 9b to each of the switching elements 3a to 3d, and the inverter circuit 3 having a full bridge configuration starts operating. As a result, the input current from the AC power source 1 is converted into a DC current by the rectifier circuit 2, and the DC current is further converted into a high-frequency current having a pulse waveform, for example. The input current detection means 12 detects an input current from the AC power source 1 and outputs a voltage signal based on the input current (P2). The high-frequency current obtained by the operation of the inverter circuit 3 flows as a resonance current through the heating coil 4 by a resonance circuit including the heating coil 4 and the resonance capacitor 5. The load 10 disposed near the heating coil 4 is induction-heated.

  Next, when the set power is further instructed by the operation of the induction heating cooker user, the set power generating means 11 generates a signal of the command voltage A based on the instructed set power (P3), and the control means 9 It outputs to the drive signal control circuit 9a (P4). The drive signal control circuit 9a determines whether the set power and the input power match (P5). For this reason, the input current is converted into input power and compared with the set power, or the input current upper limit value is determined based on the set power and compared with the input current. Further, as described above, when the voltage A of the signal of the input current detection unit 12 and the voltage A of the signal of the set power generation unit 11 are associated with each other, the input current is not compared with the value (data) represented by the signal. You may make it judge whether the voltage A of the signal from the detection means 12 and the command voltage A from the setting electric power generation means 11 correspond. Then, a drive signal for operating the inverter circuit 3 is output so that the peak value becomes the input current upper limit value. Thereby, the desired heating output or heating output upper limit value is obtained. Therefore, depending on the type of the load 10, in the initial stage, the input power does not necessarily match the set power set by the user's operation.

  Based on the drive signal, the driver 9b of the control means 9 outputs a drive signal as shown in FIG. 4 to the switching elements 3a to 3d at respective timings to operate the inverter circuit 3. Here, the drive signal control circuit 9a controls the drive of the inverter 3 by changing the phase difference between the high-frequency current by the switching element 3a (3b) and the high-frequency current by the switching element 3c (3d) when outputting the drive signal. I do. Regarding the phase difference, as the phase difference is increased, the power supplied to the load 10 (resonance circuit) is increased, and the thermal power (input power) is increased.

  Next, the peak value of the input current detected by the input current detection unit 12 matches the input current upper limit value, or the voltage A of the signal from the input current detection unit 12 and the command voltage based on the signal from the set power generation unit 11 If it is determined that A matches, the drive signal control circuit 9a continues to output a drive signal for maintaining the phase difference. The inverter circuit 3 continues to supply a high-frequency current based on the heating power (input power) based on the phase difference to the resonance circuit, thereby inductively heating the load 10.

  On the other hand, the measuring means 9d determines and measures the phase difference between the switching element 3a (3b) and the switching element 3c (3d) based on the drive signal output from the drive signal control circuit 9a, and obtains the data of the phase difference. A signal including this is output (P6).

  A signal including phase difference data is input to the load determination unit 9e. 3A shows the relationship between the thermal power and the phase difference for each type of load 10, and FIG. 3B shows the relationship between the thermal power and the total loss characteristic of the load 10 and the snubber capacitor. FIG. The load determination unit 9e determines the thermal power (input power) based on the output from the input current detection unit 12. Then, based on the determined thermal power and the phase difference measured by the measuring means 9d, the type of the load 10 is determined (P7). For example, according to FIG. 3A, if the phase difference when supplying 0.6 kW of thermal power is about 37 °, it is determined that the load 10 is the “pan D” group, and about 60 °. If it is a “pan A” group.

  Further, in order to reduce the total loss of the inverter circuit 3 (switching loss due to the switching elements 3a to 3d), the timing for switching the capacity of the snubber capacitor 7 is determined based on the type of the load 10 and the thermal power. For example, as shown in the thermal power-total loss characteristic of FIG. 3B, the total loss of the inverter circuit 3 with respect to the thermal power (switching loss due to the switching elements 3a to 3d) differs depending on the type of the load 10. Further, the total loss of the inverter circuit 3 varies depending on the capacity of the snubber capacitor 7 in the same type of load 10. This is because if the capacity of the snubber capacitor 7 is small, the turn-off loss at the time of high heating power increases, and if the capacity of the snubber capacitor 7 is large, the switching loss at the time of low heating power increases. If the loss is large, the efficiency of induction heating is poor and the inverter circuit has heat. Therefore, in order to reduce the loss, it is better to reduce the capacity of the snubber capacitor at low heating power and increase the capacity of the snubber capacitor at high output.

  Here, when the type of the load 10 can be discriminated, the reference of the thermal power (electric power) for switching the capacity of the snubber capacitor 7 that can minimize the total loss of the inverter circuit 3 from the high thermal power to the low thermal power ( Threshold) can be determined for each load type. For example, according to FIG. 3 (b), in the “pan D” group, the heating power (electric power) serving as a reference for switching the snubber capacitor 7 that can be switched between two capacities is about 0.8 kW, and “pan A” “The heating power as a reference for switching in the group can be set to about 1.6 kW. The load discriminating means 9e stores in advance the above-described switching by type of load 10 (hereinafter referred to as thermal power reference). Here, the thermal power reference for switching the capacity of the snubber capacitor 7 is determined only at one location, but a plurality of locations may be determined according to the thermal power. Further, if the capacity of the snubber capacitor 7 can be continuously changed, the capacity of the snubber capacitor 7 may be continuously changed according to the thermal power so that the total loss is minimized.

  After determining the type of the load 10, the load determination unit 9 e determines the operating thermal power (input power) based on the input current data detected by the input current detection unit 12. When it is determined that the thermal power is equal to or higher than the power reference based on the power reference data set for each type of the load 10 (P8), the capacity of the snubber capacitor 7 is set to X (in the example of FIG. 3B, 0. If it is determined that the snubber capacitor 7 is smaller than the power reference, the capacitance of the snubber capacitor 7 is set to Y lower than X (0.064 μF in the example of FIG. 3B), and a switching signal based on the determination is output. Further, based on the output, the driver 9c outputs a switching signal corresponding to the capacitor switching means 8, and causes the capacitor switching means 8 to switch the capacity of the snubber capacitor 7. Thereby, it becomes possible to reduce the total loss of the inverter circuit 3 from the time of high thermal power to the time of low thermal power.

  As described above, according to the first embodiment, in the induction heating apparatus including the induction heating cooker, based on the signal based on the set power from the set power generation unit 11 and the input current from the input current detection unit 12. From the signal, the drive signal control circuit 9a controls the inverter circuit 3 by the phase difference of the timing at which the switching element 3a (3c) and the switching element 3a (3d) are driven or the duty (pulse width) of the switching element 3a (3b). The load determination means 9e outputs the drive signal for performing the load 10 based on the phase difference or duty measured by the measurement means 9d and the input current (the thermal power (input power) determined thereby). Since the determination is made, the type of the load 10 can be determined without performing a complicated calculation, and the procedure for performing the processing (algorithm) Beam) can be simplified. In particular, in the case of an induction heating cooker, the type of the load 10 such as a pan is often changed, and simplification of the processing procedure is particularly effective.

  Further, based on the determined type of the load 10, a thermal power standard for switching the capacity of the snubber capacitor 7 corresponding to the load is determined, and when the thermal power is higher than the thermal power standard, the thermal power standard is switched to a larger capacity side and the thermal power is low. In this case, the total loss due to the switching elements 3a to 3d can be reduced by switching to the smaller capacity side. Therefore, the thermal power can be increased. In addition, since the loss is small, it is possible to suppress an increase in the heat of the switching element, and to realize, for example, downsizing of the radiating fins, a cooling fan, etc., and a cost reduction associated therewith. Even when determining the load and determining the capacitance switching timing of the snubber capacitor 7, in the case of control by duty, the inverter circuit 3 can be configured in a half-bridge configuration. Reduction, space saving, etc. can be achieved. Here, the drive signal control circuit 9a, the measurement means 9d, and the load determination means 9e are configured separately, but for example, the drive signal control circuit 9a performs the processing in the measurement means 9d and the load determination means 9e. May be.

Embodiment 2. FIG.
In the first embodiment, the load determination unit is based on the phase difference (or duty) data measured by the measurement unit 9d and the thermal power (input power) data based on the input current detected by the input current detection unit 12. 9e determined the type of the load 10. In the present embodiment, a case where the induction heating cooker user gives an instruction regarding the type of load 10 will be described focusing on the control means 9.

  FIG. 6 is a diagram showing a circuit configuration of the induction heating cooker according to the second embodiment, and FIG. 7 shows an operation flowchart of the induction heating cooker according to the second embodiment. In FIG. 6, the point where the load determination switch 13 is provided is different from the first or second embodiment described above. The induction heating cooker user operates the load determination switch 13 provided in the operation unit (not shown) of the induction heating cooker together with the set power instruction to the set power generation means 11. The load determination switch 13 is provided with, for example, a plurality of switches according to the type of the load 10. Based on the pressed switch, a signal including the data of the type of the load 10 is sent to the drive signal control circuit 9 a of the control means 9. Is output.

  In the present embodiment, unlike the first embodiment, the measurement means 9d and the load determination means 9e are not provided. Therefore, the drive signal control circuit 9a performs the load 10 determination processing, the capacitance switching timing determination processing of the snubber capacitor 7 and the switching signal output to the driver 9c, which were performed by the load determination means 9e in the first embodiment. The power reference (boundary) data of the switching timing is stored for each type of load 10. Except for the drive signal control circuit 9a that performs processing to be described later, the other components having the same reference numerals as those in FIG.

  Next, operation | movement of the induction heating cooking appliance of this Embodiment centering on the control means 9 is demonstrated based on FIG.6 and FIG.7. The components denoted by the same reference numerals as those in FIG. 2 are basically the same as the operations described in the first embodiment, and therefore description thereof will be simplified or omitted. When the power is turned on (power is turned on), the set power is instructed by the operation of the induction heating cooker user or the like (P3). In the present embodiment, the user of the induction heating cooker further operates the load determination switch 13 to instruct the type of the load 10 (P9), and the load determination switch 13 outputs a signal including the data of the type of the load 10 Is output to the drive signal control circuit 9a (P4).

  The drive signal control circuit 9a controls the inverter circuit 3 by the output drive signal, and when the voltage A based on the input current matches the command voltage A based on the set power, or when the input current matches the input current upper limit value (P5) ), The output of the drive signal for maintaining the phase difference is continued.

  In addition, the drive signal control circuit 9 a determines the type of the load 10 based on the data of the type of the load 10 included in the signal from the load determination switch 13. Then, based on the power reference data associated with the load 10, as described in the first embodiment, it is determined whether or not the capacity of the snubber capacitor 7 is switched (P8), and the switching signal is determined based on the determination. Output. The driver 9c outputs a switching signal from the capacitor switching means 8.

  Here, in the case of the present embodiment, for example, although the load 10 of the “pan D” group is used, the induction heating cooker user selects the “pan A” group in the load determination switch 13, There is a possibility that data of the wrong type of load 10 is input to the drive signal control circuit 9a. In such a case, depending on the set power, the capacity of the snubber capacitor 7 becomes inappropriate, the total loss of the inverter circuit 3 increases, and the switching element may be destroyed (about 0.8 kW or more in FIG. 3). If set to).

  As a countermeasure against such misuse, for example, temperature detection means such as a temperature sensor (not shown) is provided, and the drive signal control circuit 9a monitors the surface temperatures of the switching elements 3a to 3d. When it is determined that the set threshold value has been reached within a certain time (for example, about 4 to 10 minutes) after the power is turned on, the drive signal control circuit 9a stops outputting the drive signal and stops the operation of the inverter circuit 3. I will let you. At the same time, a sign (for example, lamp lighting display, warning sound generation, etc.) that prompts the user of the induction heating cooker to review the selection of the load 10 to be heated by the load determination switch 13 is posted. Also good.

  As described above, according to the second embodiment, the load determination switch 13 is provided, the drive signal control circuit 9a determines the load 10 based on the instruction of the induction heating cooker user, and the determined load Since the capacitance of the snubber capacitor 7 is switched based on the above, in addition to the effects of the first embodiment, the configuration in the control means 9 can be simplified, and the processing procedure of the control means 9 and the like can be simplified. Design can be made easy.

Embodiment 3 FIG.
FIG. 8 is a diagram showing a circuit configuration of the induction heating cooker according to the third embodiment, FIG. 9 is an operation flowchart of the induction heating cooker according to the third embodiment, and FIG. 10 shows a load current waveform in the induction heating cooker. It is shown.

  In FIG. 8, the point that the load current detection means 6 is connected to the resonance circuit in order to detect the current flowing through the resonance circuit of the heating coil 4 and the resonance capacitor 5 is different from the above-described first or second embodiment. The load current detection means 6 outputs a signal based on the detected load current to the drive signal control circuit 9 a in the control means 9. In the present embodiment, the storage means (not shown) of the drive signal control circuit 9a stores the thermal power data and the load current peak value data in association with each type of the load 10, for example, in a table format. It shall be. Except for the drive signal control circuit 9a, the other components having the same reference numerals as those in FIGS. 1 and 6 are described in detail in the first or second embodiment, and the description thereof is omitted. To do.

  Next, operation | movement of the induction heating cooking appliance of this Embodiment centering on the control means 9 is demonstrated based on FIGS. 2 and 7 are basically the same as the operations described in the first or second embodiment, and thus the description thereof will be simplified or omitted. When the power is turned on (power on) by the operation of the induction heating cooker user or the like, the drive signal control circuit 9a of the control means 9 outputs a drive signal for activation to the driver 9b (P1). Drive signals are output from the driver 9b to the switching elements 3a to 3d, respectively, and the inverter circuit 3 starts operating. When the operation of the inverter circuit 3 starts, the load current starts to flow (P10).

  Even if the thermal power is the same, the value taken by the load current differs depending on the type of the load 10. For example, when the input power is 1.5 kW, the load current waveforms of the “pan A” group and the “pan D” group are as shown in FIG. In FIG. 10, the load current waveform of the “pan A” group is indicated by a drive frequency f1 kHz, and the load current waveform of the “pan D” group is indicated by a drive frequency f2 kHz (f2> f1). Here, the peak value of the load current differs between the “pan A” group and the “pan D” group due to the difference in load impedance. Therefore, the drive signal control circuit 9 a determines the load current peak value based on the signal from the load current detection means 6. Then, the type of the load 10 is determined based on the data of the thermal power (input power) by the input current detected by the input current detection means 12 at that time (P7). Here, the peak value of the load current detected by the load current detection means 6 is determined and used to determine the type of the load 10. For example, the effective value of the load current is determined and the type of the load 10 is determined. There is no difference even if it is used for discrimination.

  Based on the power reference data associated with the determined load 10, as described in the first embodiment, it is determined whether to switch the capacity of the snubber capacitor 7 (P8), and a switching signal is output based on the determination. To do. Further, based on the output, the driver 9c outputs a switching signal corresponding to the capacitor switching means 8, and causes the capacitor switching means 8 to switch the capacity of the snubber capacitor 7. Thereby, it becomes possible to reduce the total loss of the inverter circuit 3 from the time of high thermal power to the time of low thermal power.

  As described above, according to the third embodiment, the load current detection means 6 detects the load current flowing in the resonance circuit by the heating coil 4 and the resonance capacitor 5, and the drive signal control circuit is based on the load current and the thermal power. 9a determines the load 10 and switches the capacity of the snubber capacitor 7 based on the determined load. In addition to the effects of the first embodiment, the configuration in the control means 9 is further simplified. The algorithm design such as the processing procedure of the control means 9 can be facilitated. Further, the type of the load 10 need not be determined by the induction heating cooker user, and erroneous selection, erroneous setting, and the like can be prevented.

  In the above-described embodiment, the induction heating cooker has been described. However, the present invention is, for example, a cooking device such as a rice cooker or a water heater using an induction heating equipped with an inverter circuit having a full bridge configuration or a half bridge configuration, In addition, it can be applied to equipment using electromagnetic induction heating.

  DESCRIPTION OF SYMBOLS 1 AC power supply, 2 Rectifier circuit, 3 Inverter circuit, 3a-3d Switching element, 4 Heating coil, 5 Resonance capacitor, 6 Load current detection means, 7 Snubber capacitor, 8 Capacitor switching means, 9 Control means, 9a Drive signal control circuit , 9b Inverter circuit driver, 9c Capacitor switching means driver, 9d Measuring means, 9e Load determining means, 10 Load, 11 Set power generating means, 12 Input current detecting means, 13 Load determining switch, 14 Smoothing capacitor.

Claims (5)

An inverter circuit composed of a plurality of switching elements and supplying high-frequency current to the heating coil to cause electromagnetic induction;
A snubber circuit connected to one of the switching elements to suppress spike voltage generation;
An input current detecting means for detecting a current supplied from a power source to the inverter circuit;
The current detected by the input current detection means is converted into power and compared with the set power, the duty of the switching element of the inverter circuit is controlled, and the power based on the current detected by the input current detection means is set Drive signal control means for outputting to the inverter circuit a drive signal for generating the generated power;
The type of load to be heated is determined based on the current detected by the input current detection means and the duty when the set power is reached, and the detected load type and the input current detection means are detected. An induction heating apparatus comprising at least load determination means for controlling a capacity of a capacitor constituting the snubber circuit based on a current. An inverter circuit composed of a plurality of switching elements and supplying high-frequency current to the heating coil to cause electromagnetic induction;
A snubber circuit connected to one of the switching elements to suppress spike voltage generation;
An input current detecting means for detecting a current supplied from a power source to the inverter circuit;
The upper limit value of the current is determined based on the set power, the current detected by the input current detecting means is compared with the upper limit value, the duty of the switching element of the inverter circuit is controlled, and the drive signal is Drive signal control means for outputting to the inverter circuit;
The type of load to be heated is determined based on the current detected by the input current detection unit and the duty when the current detected by the input current detection unit reaches the upper limit, and the type of the determined load and An induction heating apparatus comprising at least load determination means for controlling a capacity of a capacitor constituting the snubber circuit based on a current detected by the input current detection means.   3. The induction heating apparatus according to claim 1, wherein the load determination unit performs control so that the capacitance of the capacitor decreases as the current detected by the input current detection unit decreases. The snubber circuit has a plurality of capacitors having different capacities,
The load determination unit selects a capacitor having a capacity satisfying the criterion based on one or more criteria related to the current detected by the input current detection unit, which is determined for each type of the load. The induction heating apparatus according to any one of claims 1 to 3.   An induction heating cooker comprising the induction heating device according to claim 1 and heating a cooking utensil.

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