JP2012099347A - Induction heating cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating cooker capable of normally judging a material.SOLUTION: An induction heating cooker comprises a direct-current power supply circuit 2; switching elements 17-20; an inverter 3 for converting a direct-current voltage smoothed by the direct-current voltage circuit 2 and supplied through a booster circuit 2 into a high frequency voltage by the switching elements 17-20 and outputting it; an induction heating coil for induction heating a heated object; resonance capacitors 26, 27; a resonance circuit 4, to which the high frequency voltage of the inverter 3 is applied; temperature detection means 41 for detecting a temperature of the induction heating coil; a control circuit for controlling the inverter 3; current detection means 37 for detecting an inverter current value of a current flowing through the inverter 3; and material judging means 31 for judging the material of the heated object based on the inverter current value of the current detection means 37 while changing a driving frequency of the inverter 3 while a set-up voltage of the booster circuit 14 is changed to be higher as the high temperature of the induction heating coil is detected by the temperature detection means 41.

Description

  Embodiments of the present invention relate to an induction heating cooker.

  An induction heating cooker has advantages such as a safety and temperature control function without using fire, and is widely used as an IH cooking heater incorporated in a system kitchen. By the way, cooking pots and the like to be heated are made of various materials. For this reason, the induction heating cooker is required to be able to efficiently heat all of these materials. At present, various induction heating cookers that can heat a high-permeability pan such as an iron pan and a low-permeability pan such as an aluminum pan have been proposed.

  Such an induction heating cooker needs to determine the material of the object to be heated before induction heating cooking of food or the like. Therefore, a technique has been proposed in which the drive frequency of the high-frequency voltage is gradually changed to detect a change in the inverter current or the phase difference, and the material is determined based on the detected value. There is also provided a technique for determining the material based on the inverter current value by changing the drive frequency in a state where the operation of the active filter is stopped.

  However, for example, when the material to be heated is heated and the induction heating coil is at a high temperature, such as when the power is turned on immediately after the heated object is heated and turned off, etc. Since the temperature of the induction heating coil may rise to 200 ° C. and the resistance value of the induction heating coil increases, there is a possibility that the material cannot be normally determined.

JP 2007-095454 A JP 2007-42481 A

  Provided is an induction heating cooker that allows normal material judgment.

  The induction heating cooker shown in the embodiment includes a DC power supply circuit, an inverter, a resonance circuit, a temperature detection unit, a control circuit, a current detection unit, and a material determination unit. The DC power supply circuit supplies a DC voltage obtained by smoothing the voltage of the commercial power supply through a booster circuit.

  The inverter includes a switching element, and converts the DC voltage smoothed by the DC voltage circuit and supplied through the booster circuit into a high frequency voltage by the switching element. The resonance circuit includes an induction heating coil and an induction capacitor for induction heating of an object to be heated, and is applied with a high frequency voltage of the inverter. The temperature detecting means detects the temperature of the induction heating coil, and the control circuit controls the inverter.

  The current detection means detects an inverter current value flowing through the inverter. The material judging means is an inverter current value of the current detecting means while changing the drive frequency of the inverter in a state where the boosted voltage by the booster circuit is changed to be high in response to the temperature detecting means detecting a high temperature of the induction heating coil. Based on the above, the material judgment process of the object to be heated is performed.

The electrical block diagram of the induction heating cooking appliance which shows 1st Embodiment Block diagram showing the configuration of the inverter drive pulse generator Block diagram showing one configuration example of the multiplier circuit The figure which shows one structural example of a waveform generation circuit The figure which shows the waveform of each part of the waveform generation circuit The figure which shows one structural example of a dead time variable circuit The figure which shows the waveform of each part of the dead time variable circuit Fig. 7 equivalent when the dead time length is changed Flow chart showing a series of processing operations Flow chart showing material judgment processing Frequency characteristics diagram according to the material of the inverter current value Frequency characteristics diagram of input power FIG. 1 equivalent view showing the second embodiment Flow chart showing a part of the material judgment process

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 schematically shows an electrical configuration of the induction heating cooker. An induction heating cooker 1 shown in FIG. 1 is configured by connecting a DC power supply circuit 2, an inverter 3, a resonance circuit 4, a control circuit 5, a gate control circuit 6, and the like. The full-wave rectifier circuit 7 constitutes a DC power supply circuit 2 together with a smoothing capacitor 8, and its AC input terminal has a 200 V single-phase AC power supply (via AC power supply lines L 1, L 2 and a noise filter 9). (Commercial power supply) 10.

  The positive-side DC output terminal of the full-wave rectifier circuit 7 is connected to one terminal of the capacitor 8 via the reactor 11 and the anode-cathode of the diode 12. The negative DC output terminal of the full-wave rectifier circuit 7 is connected to the other terminal of the capacitor 8. As will be described later, the DC power supply circuit 2 outputs a DC voltage obtained by smoothing the commercial power supply 10. The DC power supply circuit 2 outputs a DC voltage through a chopper circuit (boost circuit) 14.

  The NPN transistor 13 forms a chopper circuit 14 together with the reactor 11 and the diode 12. The collector of the transistor 13 is connected to the common connection point of the reactor 11 and the anode of the diode 12, and the emitter thereof is connected to the negative side DC output terminal of the full-wave rectifier circuit 7. DC power supply lines 15 and 16 are connected to both terminals of the capacitor 8. The chopper circuit 14 outputs a DC voltage as a boosted voltage that is boosted as necessary.

  The inverter 3 converts the DC voltage VDC output from the DC power supply circuit 2 into a high frequency voltage by the switching operation, and supplies it to the resonance circuit 4. The inverter 3 includes a first half bridge circuit in which the first and second transistors 17 and 18 are connected in series between the DC power supply lines 15 and 16, and a third half and fourth transistors 19 and 20 connected in series. It is a full bridge type inverter circuit composed of two half bridge circuits.

  The first to fourth transistors 17 to 20 correspond to switching elements, and are, for example, IGBTs. Free wheel diodes 17a to 20a are connected between the collector and the emitter of the first to fourth transistors 17 to 20, respectively. The resonance circuit 4 is connected between a node N1 that is an interconnection point of the first transistor 17 and the second transistor 18 and a node N2 that is an interconnection point of the third transistor 19 and the fourth transistor 20. It is connected. Snubber capacitors 21 and 22 are connected between the nodes N1 and N2 and the DC power supply line 16 in order to reduce switching loss.

  The gate control circuit 6 includes an inverter drive pulse generation unit 23 and a driver 24, and controls on / off of the transistors 17 to 20. The first and second transistors 17 and 18 are on / off controlled alternately so that when one is on, the other is off. The third and fourth transistors 19 and 20 are also alternately turned on / off so that when one is on, the other is off.

  The resonance circuit 4 includes an induction heating coil 25, first and second resonance capacitors 26 and 27, and a relay switch 28. For example, an induction heating coil 25 for heating an object 29 to be heated, such as an iron pan or an aluminum pan, and a first resonance capacitor 26 are connected in series between nodes N1 and N2.

  The second resonance capacitor 27 and the relay switch 28 are connected in series, and the series circuit is connected in parallel to the first resonance capacitor 26. The relay switch 28 is provided to switch the resonance frequency of the resonance circuit 4 by switching the connection state of the resonance capacitors 26 and 27. In the present embodiment, the number of turns of the induction heating coil 25 is set to 60 turns.

  In the state where the relay switch 28 is OFF, the induction heating coil 25 and the first resonance capacitor 26 form a series resonance circuit. The capacity of the first resonance capacitor 26 is set so that the resonance frequency when heating the aluminum pan (object to be heated) in this state is about 80 kHz.

  On the other hand, when the relay switch 28 is on, the resonance capacitors 26 and 27 are connected in parallel to each other, and the capacitance and the induction heating coil 25 constitute a series resonance circuit. The parallel capacitances of the resonant capacitors 26 and 27 are set so that the resonant frequency when heating the iron pan (object to be heated) in that state is about 20 kHz.

  The control circuit 5 is constituted by, for example, a 32-bit microcomputer (reference clock = 40 MHz). The control circuit 5 includes an input power control unit 30, a load determination unit 31, a base clock generation unit 32, and a phase difference detection unit 33 as functions realized by the software.

  The input voltage detection circuit 34 detects an AC input voltage between the AC power supply lines L <b> 1 and L <b> 2 and gives the detected value to the input power control unit 30. The input current detection circuit 35 detects an AC input current via the current transformer 36 and provides the detected value to the input power control unit 30 and the load determination unit 31. The inverter current detection circuit 37 detects the current flowing through the inverter 3 via the current transformer 38 and gives the detected value to the load determination unit 31.

  The power factor improvement unit 39 includes a voltage detection circuit 39a that detects the voltage of the DC power supply line 15, and is based on detection values of the input voltage detection circuit 34 and the input current detection circuit 35 and detection results of the voltage detection circuit 39a. Thus, a base signal for driving the transistor 13 is generated so that the waveform of the AC input current follows the waveform of the AC input voltage. This base signal is given to the base of the transistor 13 through the driver 40. Thus, the chopper circuit 14 uses the set DC voltage VDC as a step-up chopper circuit for improving the power factor between the DC power supply lines 15 and 16.

  In the present embodiment, the temperature sensor 41 a is disposed below the top plate 42 to detect the temperature of the top plate 42, and the temperature sensor 41 b contacts the induction heating coil 25 to detect the temperature of the induction heating coil 25. It is installed as follows. Each of these temperature sensors 41a and 41b is constituted by an insulating and heat-resistant ceramic temperature sensor, for example.

  The temperature detection circuit (temperature detection means) 41 detects the temperature of the top plate 42 on which the object to be heated 29 is placed and the temperature of the induction heating coil 25 for heating the object to be heated 29 based on the detection signals of these temperature sensors 41a and 41b. And the detected temperature is output to the load determination unit 31.

  The temperature detection result of the temperature sensor 41a disposed below the top plate 42 is used as the temperature of the induction heating coil 25, or the temperature of the switching elements 17 to 20 of the inverter 3 is detected and the temperature of the switching elements 17 to 20 is detected. May be substituted for the temperature of the induction heating coil 25.

  The load determination unit (material determination unit) 31 of the control circuit 5 gives the base clock generation unit 32 while changing the frequency command value from a predetermined initial frequency while determining the material of the object 29 to be heated. 32 generates a base clock signal corresponding to the frequency command value and supplies it to the inverter drive pulse generator 23, and drives and controls the switching elements 17 to 20 through the driver 24.

  The zero cross detection circuit 43 is supplied with the detection signal of the inverter current detection circuit 37, detects the zero cross timing of the inverter current IQ, and supplies it to the phase difference detection unit 33. The phase difference detection unit 33 detects the phase difference between the drive pulse generated by the inverter drive pulse generation unit 23 and the zero cross timing and outputs the detected phase difference to the load determination unit 31.

  The load determination unit 31 determines the material of the object to be heated 29 using the inverter current IQ detected by the inverter current detection circuit 37 and the input current detected by the input current detection circuit 35. You may determine the material of the to-be-heated material 29 using the phase difference PQ detected by the phase difference detection part 33. FIG. In the present embodiment, the functional block using the phase difference detection unit 33 and the zero cross detection circuit 43 will be described. However, the functional block may be provided as necessary. The material of the object to be heated 29 can be determined from the inverter current IQ and the input current detected by the input current detection circuit 35. Details of the load determination process performed by the load determination unit 31 will be described later.

  The load determination unit 31 turns off the relay switch 28 via the relay switching circuit 43 when it is determined that the article 29 to be heated is made of an aluminum-based (low resistance and low magnetic permeability) material. The load determination unit 31 turns on the relay switch 28 via the relay switching circuit 44 when the object to be heated 29 is determined to be an iron-based (high resistance and high magnetic permeability) material.

  The input power control unit 30 controls the power (heating power) consumed by the induction heating coil 25 during the normal heating operation. The input power control unit 30 is a circuit that controls so that the power consumed by the induction heating coil 25 matches the target power value instructed from the outside. In the present embodiment, during the normal heating operation, the input power of the DC power supply circuit 2 is made to coincide with the input power target value calculated based on the target power value. As a result of the control, the power consumption (heating power) of the induction heating coil 25 is matched with the target power value.

  That is, the input power control unit 30 calculates input power from the AC input voltage detected by the input voltage detection circuit 34 and the AC input current detected by the input current detection circuit 35. The input power control unit 30 provides the base clock generation unit 32 with a frequency command value that indicates the target value of the heating frequency (frequency of the inverter current IQ) so that the calculated input power becomes equal to the input power target value.

  The base clock generation unit 32 includes a timer, for example. The base clock generator 32 is supplied with a reference clock signal (for example, 40 MHz) of the microcomputer. During normal driving after the material determination process of the object to be heated 29, the base clock generation unit 32 counts the reference clock signal with a timer and generates a base clock signal having a frequency corresponding to the count value. That is, the base clock generation unit 32 divides the reference clock signal to generate a base clock signal.

  The base clock generation unit 32 determines the frequency of the base clock signal based on the frequency command given from the input power control unit 30 and based on the determination result of the load determination unit 31. The base clock signal is output from, for example, a general-purpose I / O port of a microcomputer and is supplied to the inverter drive pulse generator 23.

  The inverter drive pulse generator 23 that constitutes the gate control circuit 6 generates drive pulse signals VG1 to VG4 for driving the transistors 17 to 20 of the inverter 3 using the base clock signal supplied from the control circuit 5. . The drive pulse signals VG1 to VG4 are supplied to the gates of the transistors 17 to 20 of the inverter 3 via the driver 24, respectively.

  FIG. 2 is a block diagram showing an electrical configuration of the inverter drive pulse generator 23. The inverter drive pulse generation unit 23 includes a multiplication circuit 45, a waveform generation circuit 46, and a dead time variable circuit 47. The multiplier circuit 45 generates a multiplied clock signal obtained by multiplying the base clock signal supplied from the control circuit 5, and functions as a high-speed oscillation stabilization circuit. The waveform generation circuit 46 generates drive pulse signals VG1 'to VG4' based on the multiplied clock signal supplied from the multiplication circuit 45. The dead time variable circuit 47 changes the rising timing of the drive pulse signals VG1 ′ to VG4 ′ generated by the waveform generation circuit 46, and serves as drive pulse signals VG1 to VG4 for turning on / off the transistors 17 to 20 of the inverter 3. Output.

  FIG. 3 shows a configuration example of the multiplier circuit 45. The multiplication circuit 45 shown in FIG. 3 includes a phase comparator 48, an LPF (low pass filter) 49, a VCO (voltage controlled oscillator) 50, a NOT circuit 51, and a feedback provided with a PLL control function. It has a circuit configuration. The phase comparator 48 outputs a voltage signal corresponding to the phase difference between the base clock signal and the output signal of the frequency divider 52. The output of the phase comparator 48 is smoothed through the LPF 49 and then supplied to the VCO 50.

  The VCO 50 outputs a signal having a frequency corresponding to the voltage value of the applied voltage signal. The output of the VCO 50 is supplied to the frequency divider 52 via the inverter 51 and is output as a multiplied clock signal. The frequency divider 52 divides the multiplied clock signal by 1/64 and outputs it. With such a configuration, the multiplication circuit 45 generates a multiplied clock signal by synchronizing with the base clock signal and increasing the frequency at 64 times the frequency of the base clock signal. Since the multiplication circuit 45 is controlled by the PLL control function, the oscillation operation can be stabilized at high speed.

  4 shows an example of the configuration of the waveform generation circuit 46, and FIG. 5 shows the signal waveforms of the respective parts in the waveform generation circuit 46. As shown in FIG. The waveform generation circuit 46 shown in FIG. 4 includes a counter 53, OR circuits 54 and 55, an AND circuit 56, a NAND circuit 57, a NOR circuit 58, and NOT circuits 59 and 60. The counter 53 counts in synchronization with the falling edge of the multiplied clock signal (see FIG. 5A) applied to the CK terminal. The counter 53 outputs a signal (see (b) to (d) in FIG. 5) indicating a count value (3-bit binary data) from the QA terminal, the QB terminal, and the QC terminal.

  The output signals from the QA terminal and QB terminal of the counter 53 are given to the input terminals of the OR circuit 54, respectively. An output signal of the OR circuit 54 (see FIG. 5E) is supplied to one input terminal of the AND circuit 56, one input terminal of the NAND circuit 57, and an input terminal of the NOT circuit 59. The output signal of the NOT circuit 59 (see FIG. 5F) is applied to one input terminal of the OR circuit 55 and one input terminal of the NOR circuit 58.

  The QC terminal of the counter 53 is connected to the input of the NOT circuit 60. The output signal of the NOT circuit 60 (see (g) in FIG. 5) is obtained by using the other input terminal of the AND circuit 56, the other input terminal of the NAND circuit 57, the other input terminal of the OR circuit 55, and the other input terminal of the NOR circuit 58. It is given to the input terminal. With such a configuration, the driving pulse signals VG1 'and VG2' are output from the OR circuit 55 and the NOR circuit 58, respectively (see (h) and (i) of FIG. 5). Further, drive pulse signals VG3 'and VG4' are output from the AND circuit 56 and the NAND circuit 57, respectively (see (j) and (k) in FIG. 5).

  As shown in FIG. 5, the period (switching period) of the drive pulse signals VG1 'to VG4' is eight times the period of the multiplied clock signal. That is, the switching frequency of each of the transistors 17 to 20 in the inverter 3 is 1/8 of the frequency of the multiplied clock signal and 8 times the frequency of the base clock signal.

  Further, as shown in FIG. 5 (h), the drive pulse signal VG1 ′ turns on the first transistor 17 during the 5/8 cycle of the switching cycle and turns off during the remaining 3/8 cycle. It is supposed to be in a state. As shown in (j) of FIG. 5, the drive pulse signal VG3 ′ turns on the third transistor 20 during the 3/8 cycle of the switching period and turns off during the remaining 5/8 period. It is supposed to be. The timing for turning on the third transistor 20 is delayed by 1/8 cycle from the timing for turning on the first transistor 17.

  The drive pulse signals VG2 'and VG4' have waveforms having opposite polarities to those of the drive pulse signals VG1 'and VG3', respectively. That is, the drive pulse signal VG2 ′ causes the second transistor 18 to operate in the opposite direction to the first transistor 17, and the drive pulse signal VG4 ′ causes the fourth transistor 20 to operate as the third transistor. The operation opposite to that of 19 is performed.

  FIG. 6 shows an example of the configuration of the dead time variable circuit 47, and FIGS. 7 and 8 show signal waveforms of respective parts of the dead time variable circuit 47. FIG. The dead time variable circuit 47 shown in FIG. 6 is changed so as to delay only the rising timing of the input drive pulse signal VG1 ', and is output as the drive pulse signal VG1. Although not shown, the same configuration as that of the present circuit is provided corresponding to the drive pulse signals VG2 'to VG4'.

  The dead time variable circuit 47 shown in FIG. 6 is configured by connecting resistors 61 and 62, capacitors 63 and 64, a diode 65, Schmitt trigger type NOT circuits 66 and 67, and a switching circuit 68.

  The input terminal of the drive pulse signal VG 1 ′ is connected to the ground line 69 via the resistor 61 and the capacitor 63. A series circuit of a diode 65 and a resistor 62 is connected in parallel with the resistor 61. The cathode of the diode 65 is connected to the input terminal side of the drive pulse signal VG1 '. A capacitor 64 and a switching circuit 68 are connected in series between a node N3, which is an interconnection point between the resistor 61 and the capacitor 63, and the ground line 69. The switching circuit 68 includes a transistor with a built-in base-emitter resistance and a base resistance, and is configured for switching. A switching signal output from the control circuit 5 is supplied to the base.

  The control circuit 5 switches the switching signal to the H level (a level at which the switching circuit 68 can be sufficiently turned on) or the L level (a level at which the switching circuit 68 can be sufficiently turned off). The signal at the node N3 is output as a drive pulse signal VG1 through NOT circuits 66 and 67.

  Since the transistor 68 is turned off when the switching signal is at the L level, only the capacitor 61 is connected between the node N3 and the ground line 69. On the other hand, when the switching signal is at the H level, the transistor 68 is turned on, so that the capacitors 63 and 64 are connected in parallel between the node N3 and the ground line 69. In the present embodiment, the capacity of the capacitor 64 is set to about twice the capacity of the capacitor 63. The resistance value of the resistor 61 is set to about 10 times the resistance value of the resistor 62.

  According to such a configuration, when the switching signal is at the L level, the capacitor 63 is charged via the resistor 61 when the drive pulse signal VG1 ′ (see FIG. 7A) rises (time t0). Therefore, the rise of the signal at the node N3 becomes gentle (see FIG. 7B). On the other hand, when the drive pulse signal VG1 ′ falls (time t1), the charge of the capacitor 63 is discharged through the resistor 62 and the diode 65 having a resistance value sufficiently smaller than that of the resistor 61, so that the signal at the node N3 Falls sharply (see FIG. 7B). By outputting the slowly rising signal generated in this way through the NOT circuits 66 and 67, the driving pulse signal VG1 (see FIG. 7C) in which the rising timing is delayed by the time T1 is generated.

  When the switching signal is at the H level, the capacitors 63 and 64 are charged via the resistor 61 when the drive pulse signal VG1 ′ (see FIG. 8A) rises (time t0). The rise of the signal at the node N3 is very gradual (see FIG. 8B). On the other hand, when the drive pulse signal VG1 ′ falls (time t1), the fall of the signal at the node N3 becomes steep, as in the case where the switching signal is at the L level (FIG. 8 (( b)). By outputting the very slowly rising signal generated in this way through the NOT circuits 66 and 67, the driving pulse signal VG1 (FIG. 8C) in which the rising timing is delayed by a time T2 longer than the time T1. Reference) is generated.

  In this way, by delaying the rising timing of the drive pulse signals VG1 to VG4, the dead time when both the first and second transistors 17 and 18 are turned off, and the third and fourth transistors 19 and 20 are In any case, a dead time for turning off is provided. The length of the dead time can be switched in two steps according to the level of the switching signal given from the control circuit 5. The control circuit 5 outputs an L level switching signal when the input power is greater than or equal to a predetermined value, and outputs an H level switching signal when the input power is less than the predetermined value. Therefore, the length of the dead time is shortened if the input power is equal to or greater than a predetermined value, and is increased if the input power is less than the predetermined value.

Next, the operation of this embodiment will be described focusing on the material determination process. 9 and 10 show a schematic operation of the material determination process in a flowchart.
When the user places the object to be heated 29 on the top plate 42, the interaction between the induction heating coil 25 and the object to be heated 29 changes depending on the material of the object to be heated 29 and the resonance frequency of the resonance circuit 4 is changed. Change. When the material of the object to be heated 29 is aluminum, the resonance frequency of the resonance circuit 4 is high, and when the material of the object to be heated 29 is iron, the resonance frequency of the resonance circuit 4 is low. Therefore, the inverter current value IQ flowing through the induction heating coil 25 varies greatly around the resonance frequency depending on whether the material of the object to be heated 29 is iron-based or aluminum-based. The load determination unit 31 performs the material determination process mainly using this property.

  In FIG. 9, when a signal (not shown) indicating the start of heating is received from the outside (S1), the load determination unit 31 determines the type (material) of the article 29 to be heated. In making this determination, the load determination unit 31 measures the temperature of the induction heating coil 25 through the temperature detection circuit 41 (S2).

  When the user receives a heating start signal before the time has elapsed since the heat treatment of the article 29, the temperature of the induction heating coil 25 is higher than the normal temperature. When the temperature of the induction heating coil 25 increases, the gap between the induction heating coil 25 and the object to be heated 29 becomes narrower than usual due to expansion or the like, so that the capacity of the resonance circuit 4 increases and the resonance frequency of the resonance circuit 4 increases. Becomes higher. Therefore, in this embodiment, when the material determination process is performed when the temperature of the induction heating coil 25 is higher than a predetermined temperature, the process is changed.

  The load determination unit 31 sets the start frequency as the first frequency f1 when the temperature is lower than the predetermined temperature (S4), and sets the start frequency as the second frequency f2 (> f1) when the temperature is higher than the predetermined temperature (S5).

FIG. 11 shows the change in material characteristics of the inverter current value IQ according to the drive frequency, and also shows the relationship of the start frequency.
The start frequency indicates a target frequency (reciprocal of the switching period) when the load determination unit 31 starts driving determination of the material of the article 29 to be heated and controls the gates of the switching elements 17 to 20. Although the change can be set in two stages, this is not limited to the above-described processing form as long as the drive start frequency of the inverter 3 is changed according to the temperature of the induction heating coil 25. For example, there are three stages according to the temperature level. The change setting may be made possible in the above plural stages.

  Returning to FIG. 9, the load determination unit 31 performs parameter setting such as a threshold value (S6). This parameter mainly relates to material determination processing such as the upper limit value of the inverter current value IQ, the upper limit of the phase difference between the voltage VQ and the current IQ, and a predetermined range (including 0) where the phase difference is inappropriate. Parameters for preventing malfunction and parameters such as change frequency (see later) are shown. For example, when the user places an inappropriate pan on the top plate 42, the load determination unit 31 needs to interrupt the material determination process and stop the drive of the inverter 3, and set parameters for preventing malfunctions. This is done because it needs to be set in advance.

  The load determination unit 31 turns off the relay switch 28 through the relay switching circuit 44, and uses, for example, a start frequency f1 or f2 (see above) between 80 and 100 kHz as a frequency command value as a target value of the drive frequency of the inverter 3 as a base clock. The generation unit 32 is instructed (S7). In this state, the load determination unit 31 reads the detection value of the inverter current detection circuit 37 when the inverter 3 is driven (S8). In the present embodiment, a relatively high frequency (about 80 kHz to 100 kHz) is set as a start frequency by turning the relay switch 28 in an OFF state, but a relatively low frequency (about 20 to 40 kHz is set by setting the relay switch 28 to an ON state. ) May be the starting frequency.

  Next, the load determination unit 31 determines whether or not the inverter current value IQ at the initial stage of oscillation is 0 (S9). If the inverter current value IQ is 0 (S9: YES), it is determined as abnormal. (S10), the material determination process is terminated, the drive of the inverter 3 is stopped, and a notification to that effect is given. If the condition of step S9 is not satisfied, the load determination unit 31 proceeds to the material determination process (S11), and ends the material determination process on condition that the material is normally determined.

  FIG. 10 is a schematic flowchart showing the content of the material determination process in step S11. As shown in FIG. 10, in the material determination process, first, when the temperature detection circuit 41 detects the temperature of the induction heating coil 25 (T1), the load determination unit 31 detects the DC voltage corresponding to the temperature of the induction heating coil 25. Is calculated (T2).

The load determination unit 31 gives a DC voltage instruction signal to the power factor improvement unit 39, and the power factor improvement unit 39 controls the boosted voltage V _DC calculated by the load determination unit 31, and a voltage detection circuit (output voltage detection means). 39a detects the output voltage of the booster circuit 14 and determines whether or not a predetermined boosted voltage has been reached (T3). During the process of step T3, the temperature detection circuit 41 detects the temperature of the induction heating coil 25 by the temperature sensor 41b, and the chopper circuit 14 outputs a voltage according to the detected temperature of the induction heating coil 25. The reason for determining whether or not the boosted voltage has been reached is to prevent the input power input to the induction heating coil 25 from being lowered.

  FIG. 12A schematically shows the temperature change characteristic of the input power according to the drive frequency. Since the resistance value of the induction heating coil 25 increases almost in proportion to the temperature increase, the input power decreases as the temperature increases. In particular, when a material determination process is performed on an aluminum pan, the frequency range that can be used for inverter control may be narrow because of driving at a high driving frequency. In such a case, since the input power of the inverter 3 may not be sufficient, it is preferable to increase the degree of boost of the chopper circuit 14 during the material determination process. Then, the input power necessary for the material determination process can be ensured, the inverter current value IQ can be increased, the necessary accuracy can be ensured, and the accurate material determination can finally be performed.

  For example, in the induction heating cooker 1 operating at AC 200 V, the operation is guaranteed up to AC 220 V in order to guarantee the operation up to ± 10%. In this case, a boosted voltage corresponding to the temperature is output within a predetermined voltage range (320 V to 400 V) in which a margin voltage higher than 220 V × √2 = about 310 V is expected. For example, when the temperature of the induction heating coil 25 is normal temperature (25 ° C.), it is 320 V, and when it is high temperature (200 ° C.), it is 400 V. In these temperature ranges and boost voltage ranges, the voltage and the boost voltage are set proportionally. Output voltage.

  Thereafter, when it is determined that the detection result of the voltage detection circuit 39a has reached a desired boosted voltage (T3: YES), the load determination unit 31 determines the inverter current value IQ, the input current, and the drive pulse signals VG1 to VG1. The phase difference between VG4 (drive voltage) and the inverter current is detected (T4). The load determination unit 31 determines whether or not the period of the drive pulse signals VG1 to VG4 has passed a plurality of periods (for example, 5 cycles) (T5). If not, the process is repeated from step T4.

  The reason for repeating the process of step T4 for a plurality of cycles is to suppress detection errors accompanying noise as much as possible. For example, if the drive frequency is set to about 80 kHz, one cycle is obtained with a period of 6.25 microseconds, which is 1/2 of 12.5 microseconds. Step S5 is exited.

  Here, the load determination unit 31 corrects the detection value (for example, the inverter current value IQ) by proportional calculation according to the temperature detection result of the induction heating coil 25 detected by the temperature detection circuit 41. In this case, the control circuit 5 holds a data table corresponding to the temperature of the induction heating coil 25 and the boosted voltage in an internal memory (not shown), and is proportional to the reference voltage 320V at normal temperature and the detection voltage of the voltage detection circuit 39a. Calculation is performed to correct the detection result of the inverter current detection circuit 37.

  After exiting step T5, the load determination unit 31 calculates the inverter current value IQ and the average value of the phase differences (T6), and determines whether the phase difference is within a predetermined range close to 0 (T7). Next, on condition that the phase difference is determined to be within a predetermined range close to 0 (T7: YES), the load determination unit 31 determines that the pot is an improper pan (T8) and drives the base clock generation unit 32. An output stop command is output (T9), and the material determination is stopped.

  And the control circuit 5 notifies that to a user by alert | reporting that it is an improper pan via the panel etc. which are not shown in figure (T10). Even when it is determined NO in step T7, when the load determination unit 31 determines that the phase difference is equal to or greater than the predetermined value (T11: YES), it determines that there is no load (T12), and also in this case, the drive output is stopped. A command is output (T13) and the material determination is stopped. In such a case, the user is notified accordingly.

  When the load determination unit 31 determines that the detected inverter current value and phase difference satisfy the aluminum-based or iron-based condition (T14: YES), the load-determining unit 31 is aluminum-based or iron-based. The material is determined (T15), the material determination process routine is exited, and the heat treatment according to the material is performed (S12).

  In the vicinity of the resonance frequency due to the interaction between the object to be heated 29 and the induction heating coil 25, the inverter current value IQ rapidly increases. For example, the inverter current value IQ is detected as a frequency value exceeding a predetermined threshold current Ith. Thus, it can be determined whether the material is aluminum-based or iron-based.

  The load determination unit 31 determines whether the second input current value and the inverter current value are detected (T16). If the input current value and the inverter current value are detected only for the first time (T16: NO), The process proceeds to step T17. When the inverter current detection circuit 37 detects the inverter current value, the load determination unit 31 corrects the inverter current value in the same manner as described above. In step T17, the load determination unit 31 stores the input current value and the average value of the inverter current values in an internal memory (not shown) (T17), and lowers the frequency command value by a predetermined first step (T18). ), Returning to step T4, the process is repeated. In this way, if the process does not exit midway, the processes of steps T4, T5, T6, T7, T11, T14, and T16 are repeated twice.

  If the load determination unit 31 detects the second input current value and the inverter current value in step T16 (T16: YES), the average value of the inverter current values is stored in the internal memory as described above (T19). . At this time, the voltage detection circuit 39a detects the output voltage of the chopper circuit 14, but when it is detected that the output voltage of the chopper circuit 14 is higher than a predetermined specified voltage, the DC voltage and voltage detection of the DC power supply circuit 2 are detected. The inverter current value IQ is corrected according to the result of the proportional calculation process with the detection voltage of the circuit 39a.

  For example, when the boost voltage of the chopper circuit 14 is 350 V and the DC voltage of the DC power supply circuit 2 is about 310 V, the proportional calculation is performed to obtain 1.13 times. Therefore, the inverter current value IQ detected by the inverter current detection circuit 37 is corrected according to this ratio.

Then, the inverter current value IQ corrected according to the reference DC voltage can be obtained. As shown in an embodiment described later, it is possible to complete the process more quickly without taking a time than waiting for the boosted voltage V _DC to reach the target boosted voltage by providing a discharge function.

  Next, the load determination unit 31 calculates the ratio of the previous and current inverter current values (T20). When the ratio of inverter current values is calculated for the first time in step T20, the ratio of the average value of the first inverter current value and the average value of the second inverter current value is calculated. In the Nth routine, the ratio of the average value of the Nth inverter current value and the average value of the N + 1th inverter current value is calculated.

  When the ratio (change rate) is smaller than a predetermined ratio (for example, 1.5) (T21: NO), the load determining unit 31 sets the change frequency (change rate) to a rough second step (for example, about 0.02 kHz step). Change (T22) and change. On the other hand, when the ratio (change rate) is equal to or higher than the predetermined ratio (T21: YES), the load determining unit 31 changes the change frequency (change rate) to a fine first step (for example, about 0.01 kHz step) ( T23) Change. And it returns to step T4 and repeats a process. In this way, the load determination unit 31 and the like repeat the processing.

  In the present embodiment, a multiplication circuit 45 that controls the oscillation frequency of the VCO 50 by a PLL control function is provided. Since the multiplication circuit 45 controls the signal by the PLL control function, the oscillation operation can be quickly stabilized. Therefore, even if the load determination unit 31 changes the drive frequency of the inverter 3, the waiting time until the drive frequency signal is stabilized can be shortened. For example, even if a half period of about 80 kHz (12.5 microseconds ÷ 2 = 6.25 microseconds) or an average value of the five cycles is obtained, the material can be determined with a period of 31.25 microseconds. Compared to the material, the material can be determined with a much finer period.

  When the material determination process is completed, a heating process is performed (S12). After the material of the object 29 to be heated is determined, the load determination unit 31 switches the relay switch 28 of the resonance circuit 4 according to the material. When the material is aluminum, the relay switch 28 is turned off to set the resonance frequency to about 80 kHz. If the material is iron, the relay switch 28 is turned on to set the resonance frequency to about 20 kHz.

  Next, when it is determined that the object to be heated 29 is an aluminum-based material, the frequency dependency (that is, the Q value) of the input power is increased, and when the object to be heated 29 is an iron-based material, low input power is obtained. When performing the heating control, since the frequency-dependent Q value of the input power is particularly low, the input power control unit 30 of the control circuit 5 has a predetermined input power when it is determined that the object to be heated 29 is a ferrous material. When performing control of lower input power than (300 W input), the boost operation by the chopper circuit 14 is performed when the heating control of input power higher than the predetermined input power is performed without performing the boost operation by the chopper circuit 14. Then, desired control according to the material of the article 29 to be heated can be performed.

  Then, the input power control unit 30 gives the target value of the heating frequency to the base clock generation unit 32 so that the calculated input power becomes equal to the set input power set by the user. The base clock generation unit 32 outputs a base clock signal having a frequency that is 1/32 of the instructed heating frequency to the inverter drive pulse generation unit 25.

  In this embodiment, when the target value of the heating frequency when the material is aluminum is about 80 kHz to about 90 kHz, the base clock signal is about 2.5 kHz to about 2.8 kHz. When the target value of the heating frequency when the material is iron-based is about 25 kHz to about 35 kHz, the base clock signal can be set to about 0.78 kHz to about 1.09 kHz.

  The inverter drive pulse generator 23 generates drive pulse signals VG1 to VG4 for turning on / off the transistors 17 to 20 so that a high-frequency current matching the instructed heating frequency flows through the induction heating coil 27. These drive pulse signals VG1 to VG4 are given as control signals to the gates of the transistors 17 to 20 through the driver 24, respectively, and drive the inverter 3 constituted by the transistors 17 to 20.

  The high-frequency voltage VQ output from the inverter 3 is twice the switching frequency of each of the transistors 17 to 20, and the inverter current IQ flowing through the induction heating coil 29 is four times the switching frequency. In this embodiment, the switching frequency at the time of 2 kW heating of the aluminum-based material pan is set to 22 kHz. Thereby, the frequency of the inverter current IQ is 88 kHz, which is four times the switching frequency. When the material of the object to be heated 29 is iron-based, except that the first and second resonance capacitors 26 and 27 are connected in parallel in the resonance circuit 4 and the target value of the heating frequency is different. For example, the inverter 3 operates in the same manner as in the case where the above-described material is aluminum.

  Note that the base clock generation unit 32 of the control circuit 5 is changed according to the count number of the timer. One count of this timer is 0.025 μs when the reference clock is 40 MHz. Therefore, when the switching frequency is varied in the range of 20 kHz to 22.5 kHz, that is, when the frequency of the base clock signal is varied in the range of 2.5 kHz to 2.8 kHz, the timer count is in the range of 16000 to 14285. It will be changed in the range of (count number = 1715). Therefore, the switching frequency of the inverter 3 can be changed in units of about 1.5 Hz (= 2.5 kHz / 1715). Such control is performed.

  In the present embodiment, the material of the object to be heated 29 in a state where the temperature of the object to be heated 29 is high and the temperature of the induction heating coil 25 is high, for example, when the power is turned on again immediately after the object to be heated 29 is heated and turned off. When performing the determination process, the material determination process is performed in a state where the temperature of the induction heating coil 25 is increased.

  According to the present embodiment, the load determination unit 31 drives the inverter 3 in a state where the boosted voltage by the chopper circuit 14 is changed to be high in response to the temperature detection circuit 41 detecting the temperature of the induction heating coil 25 high. Based on the inverter current value IQ, the material determination process for the object to be heated 29 is performed while changing the frequency.

  For this reason, even when the resistance value of the induction heating coil 25 increases when performing the material determination process of the object to be heated while the temperature of the induction heating coil 25 is high, the boost voltage is changed to be high through the chopper circuit 14. The material determination process for the object to be heated 29 can be performed in a state where the input power is increased, and the resolution of the detected value of the inverter current IQ can be increased, whereby the material can be determined accurately. The chopper circuit 14 is boosted during the material determination process, and is boosted according to the target input power level when the input power control unit 30 of the control circuit 5 controls the heating. Therefore, desired control can be realized.

The load determination unit 31 corrects the inverter current value IQ according to a proportional calculation between a predetermined reference voltage and the detection voltage of the voltage detection circuit 39a, and the object to be heated 29 is based on the corrected inverter current value IQ. Therefore, the inverter current value IQ corrected according to a predetermined reference voltage can be obtained. In this case, as shown in an embodiment described later, it is possible to complete the processing quickly without taking a time compared to waiting until the boost voltage V _DC reaches the target voltage by providing a discharge function.

  The multiplication circuit 45 oscillates a frequency according to the frequency command value by the VCO 50, controls the oscillation frequency by the PLL control function, and multiplies the base clock signal as a drive frequency signal of the inverter 3 according to the frequency of the multiplied clock signal. Yes. Since the multiplication circuit 45 controls the signal by the PLL control function, the oscillation operation can be quickly stabilized. Therefore, even if the load determination unit 31 changes the drive frequency of the inverter 3, the waiting time until the drive frequency signal is stabilized can be shortened. Thereby, the drive frequency of the inverter 3 can be stabilized quickly and a material determination process can be performed quickly.

  Note that the resolution of the switching frequency can be easily changed only by changing the multiplication number of the multiplication circuit 45, and the resolution of the drive frequency can be increased as the multiplication number of the multiplication circuit 45 is increased. If the multiplication number of the multiplication circuit 45 is increased, the frequency of the base clock signal can be lowered. That is, the control circuit 5 can be configured by a relatively inexpensive microcomputer that operates with a low reference clock (for example, an 8-bit microcomputer with a reference clock of 20 MHz). As a result, power consumption in the microcomputer is reduced, and the burden on the power supply circuit that supplies power to the control circuit 5 can be reduced.

  The base clock signal generated by the base clock generation unit 32 is a square wave signal (a signal having a duty of 50%) generated based on the count value of the timer. For this reason, it is not necessary to configure the control circuit 5 using a microcomputer having a function of generating a special output waveform (for example, a function of generating a PWM signal for three-phase motor control). Therefore, it is possible to use a relatively inexpensive microcomputer having a standard function.

  The load determination unit 31 changes the drive frequency and performs the material determination process while changing the change rate of the drive frequency of the inverter 3 according to the previous and current current detection ratios of the inverter current value detected by the inverter current detection circuit 37. Is going. For example, when the ratio (rate of change) between the previous inverter current value and the current inverter current value is 1.5 or more, the first step is fine, and when the ratio is less than 1.5, the second step is coarse. Even if the determination starts with the frequency region where the current value IQ is detected as low as the start frequency, the frequency can be quickly changed by roughening the change frequency to the second step, and the determination time can be shortened.

  Since the load determination unit 31 stops the material determination on the condition that the phase difference detected by the phase difference detection unit 33 is within a predetermined range close to 0, the load determination unit 31 can prevent a capacitive load. Moreover, safety can be enhanced.

  Since the load determination unit 31 determines that the circuit is abnormal on the condition that the inverter current value is determined to be 0 at the initial stage of oscillation, for example, when a connection error occurs in the induction heating coil 25 such as during assembly, a connection failure can be immediately found. It can be determined whether or not there is an abnormality. The load determination unit 31 can determine the abnormality even if other function units such as the inverter current detection circuit 37 and the zero cross detection circuit 43 have an abnormality.

The load determination unit 31 changes and sets the drive start frequency of the inverter 3 when performing the material determination process for the object to be heated 29 according to the temperature detected by the temperature detection circuit 41 when the material determination is started. Specifically, the load determination unit 31 sets the start frequency when performing the determination process of the object to be heated 29 on the condition that the temperature detected by the temperature detection circuit 41 is equal to or lower than a predetermined temperature, as a predetermined first frequency f1, Since the material determination process of the object to be heated 29 is performed using the second frequency f2 higher than the first frequency f1 as a start frequency on condition that the temperature is higher than the predetermined temperature, the temperature characteristics of the induction heating coil 25 are taken into consideration when driving. Can be set, and the material determination process can be performed accurately.
The load determination unit 31 can calculate the inverter current value IQ and the phase difference stably because the calculated inverter current value IQ and the phase difference are averaged over a plurality of periods and this calculation result is used.

(Second Embodiment)
FIG. 13 and FIG. 14 show a second embodiment, which is different from the previous embodiment in that it includes discharging means for discharging the boosted voltage of the booster circuit and reducing the voltage, and the output voltage of the booster circuit is When it is detected that the voltage is higher than the predetermined voltage, the discharge means lowers the output voltage of the booster circuit, and then the material determination process for the object to be heated is performed. The same parts as those in the previous embodiment are denoted by the same reference numerals and the description thereof is omitted.

  As shown in FIG. 13, a resistance element 45 as a discharging means is connected in parallel to the capacitor 8 at the output of the chopper circuit 14. The resistance element 45 is set to a resistance value of about several hundred k to 1 MΩ, for example, and has a function of reducing the boosted voltage of the chopper circuit 14.

  FIG. 14 shows the material determination processing operation corresponding to steps T1 to T3 in FIG. As shown in FIG. 14, after the load determination unit 31 performs the processes of steps T1 and T2, the boost voltage actually detected is calculated as a result of calculating the DC voltage corresponding to the detected temperature in the material determination process. When it is detected that the voltage is higher than the DC voltage (corresponding to a predetermined voltage) (T3a), the step-up operation of the chopper circuit 14 is stopped, and the built-in timer of the control circuit 5 waits for, for example, 100 ms (T3b). Then, the accumulated charge of the capacitor 8 flows as a current to the resistance element 45, so that power is consumed and the voltage gradually decreases. Then, after the detection voltage of the voltage detection circuit 39a becomes equal to or lower than the calculated predetermined voltage, the process proceeds to the material determination process after step T4.

  According to the present embodiment, for example, when the power is turned on again immediately after the power is turned off, when the chopper circuit 14 is boosted and the output voltage of the chopper circuit 14 is detected to be higher than the predetermined voltage, the resistance element 45 Since the process waits for discharge and waits for a predetermined voltage before the material determination process is performed, the material determination process can be performed in substantially the same manner as in the above-described embodiment.

(Other embodiments)
The present invention is not limited to the above embodiment, and for example, the following modifications or expansions are possible.
Although the embodiment has been described in which the predetermined reference voltage is set to the boosted voltage of 320 V at room temperature, the smoothed DC voltage output from the DC power supply circuit 2 may be set as the reference voltage or other reference. DC voltage can be applied.

  Immediately after the chopper circuit 14 starts to operate and the boosting function starts to operate, when the input voltage fluctuates, the DC voltage VDC is unstable, so that the load determination unit 31 particularly uses the boosted voltage of the chopper circuit 14. Accordingly, the material current determination process for the object to be heated 29 may be performed by correcting the detection current value of the inverter current detection circuit 37. In this case, the inverter current value may be corrected by the proportional calculation shown in the above embodiment.

  On the condition that the ratio between the inverter current value IQ detected last time and the inverter current value IQ detected this time is equal to or greater than a predetermined ratio, the change frequency is set to a fine first step. Although the embodiment with steps is shown, this condition is not limited to two current detection ratios. That is, the change rate of the detected current value three times or more may be calculated by, for example, second order approximation, and the change frequency (change rate) of the drive frequency of the inverter 3 may be changed according to this change rate. Although the embodiment in which the change frequency of the drive frequency of the inverter 3 is two types of the first step (0.01 kHz) and the second step (0.02 kHz) has been shown, this change frequency may be changed as appropriate.

  The multiplication number of the multiplication circuit 45 may be changed as necessary. For example, the multiplication number of the multiplication circuit 45 may be set to a power of 2 such as 128 times or 256. The frequency dividing number of the frequency divider 52 may be another numerical value (for example, 1 / (power of 2)). Any combination of values may be applied as long as the drive frequency of the inverter 3 can be changed in a cycle corresponding to the oscillation frequency of the multiplied clock signal of the multiplication circuit 45.

  In step T2, the drive frequency is changed for each of a plurality of predetermined cycles of the drive frequency of the inverter 3, but this cycle may be any number of cycles. In the material determination process shown in FIG. 10, for example, if the noise reduction (oscillation stabilization) effect is not required, the process of step T2 can be completed in a cycle of about 1 cycle = 6.25 microseconds in the above-described embodiment. The material determination process can be completed.

  Although the embodiment in which the control circuit 5 is configured by a microcomputer has been shown, a gate array, ASIC (Application) together with a part of the inverter drive pulse generation unit 23 and / or other functional units (zero cross detection circuit 43 and the like). A specific integrated circuit (FPGA), a field programmable gate array (FPGA), or a programmable logic device (PLD) may be used. As a result, the circuit configuration can be simplified, and effects such as a reduction in the board area and the number of parts can be obtained.

  While several embodiments have been described above, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof. For example, the shape, arrangement, material, numerical value, time, and the like of the configuration described in the above embodiment are merely examples.

  In the drawings, 1 is an induction heating cooker, 2 is a DC power supply circuit, 3 is an inverter, 4 is a resonance circuit, 5 is a control circuit, 14 is a chopper circuit (boost circuit), 10 is a commercial power supply, and 17 to 20 are switching elements. , 25 is an induction heating coil, 26 and 27 are resonance capacitors, 29 is an object to be heated, 30 is an input power control unit (heating control unit), 31 is a load determination unit (material determination unit), and 37 is an inverter current detection circuit ( Current detection means), 39a is a voltage detection circuit (output voltage detection means), 41 is a temperature detection circuit (temperature detection means), and 45 is a multiplication circuit.

Claims (5)

A DC power supply circuit that supplies a DC voltage obtained by smoothing the voltage of the commercial power supply through a booster circuit;
An inverter that includes a switching element, converts the DC voltage smoothed by the DC voltage circuit and supplied through the booster circuit into a high-frequency voltage by the switching element, and
A resonance circuit configured to include an induction heating coil and a resonance capacitor for induction heating of an object to be heated and to which a high-frequency voltage of the inverter is applied;
Temperature detecting means for detecting the temperature of the induction heating coil;
A control circuit for controlling the inverter;
Current detecting means for detecting an inverter current value flowing through the inverter;
Inverter current value of the current detection means while changing the drive frequency of the inverter in a state where the boost voltage by the boost circuit is changed to be high in response to the temperature detection means detecting a high temperature of the induction heating coil An induction heating cooker comprising: material determination means for performing a material determination process of the object to be heated based on the above. After the material determination process is performed by the material determination unit, a heating control unit that performs heating control is provided,
The boosting circuit performs a boosting operation at least when a material determination process is performed by the material determination unit, and performs a boosting operation according to the level of the target input power when the heating control unit performs heating control. Item 1. An induction heating cooker according to item 1. Output voltage detecting means for detecting the output voltage of the booster circuit;
The material determining means corrects an inverter current value of the current detecting means according to a proportional calculation between a predetermined reference voltage and an output voltage of the output voltage detecting means that is boosted through the booster circuit, and the corrected inverter current The induction heating cooker according to claim 1 or 2, wherein a material determination process of the object to be heated is performed based on a value. Discharging means for discharging the boosted voltage of the booster circuit to reduce the voltage;
Output voltage detection means for detecting the output voltage of the booster circuit,
The material determination means performs the material determination processing of the object to be heated after the output voltage is reduced by the discharge means when the output voltage detection means detects that the output voltage of the booster circuit is higher than a predetermined voltage. The induction heating cooker according to any one of claims 1 to 3, wherein A multiplication circuit for increasing the frequency of a reference signal, comprising a VCO that oscillates a frequency according to a frequency command value and a PLL control function for controlling the oscillation frequency of the VCO, and a multiplication circuit for outputting a control signal to the inverter Prepared,
The material determination means performs the material determination processing of the object to be heated based on the inverter current value of the inverter current detection means while changing the drive frequency of the inverter at a cycle corresponding to the oscillation frequency of the multiplication circuit. The induction heating cooker according to any one of claims 1 to 4, characterized in that:

Images