JP5355442B2 - Induction heating cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating cooker which has improved precision in determining whether a pot is appropriate or not at the start of heating. <P>SOLUTION: The heating cooker includes: an inverter circuit 3 which converts an output power from a DC power circuit 2 connected to a commercial AC power supply 1 into high-frequency power and supplies the converted power to a load circuit 4; an input current detecting unit 17; an output current detecting unit 19; a temperature-detecting unit 21 which detects the temperature of a pot 16 on a top plate 15; a control circuit 24 which controls a drive signal for driving the inverter circuit 3; and a pot-appropriateness determining unit 26 which, upon determining whether the pot 16 on the top plate 15 is appropriate or not using a current detected by the input current detecting unit 17 and a current detected by the output current detecting unit 19, when the control circuit 24 drives the inverter circuit 3 under a given drive condition at the start of heating, corrects a threshold for determining whether the pot 16 is appropriate or not depending on the temperature of the pot 16 detected by the temperature-detecting unit 21. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an inverter type induction heating cooker, and more particularly, induction heating for determining whether or not a load placed on a top plate above a heating coil is appropriate and whether or not a load is placed. It relates to cookers.

  In an induction heating cooker that detects the load using the input current and the current flowing in the heating coil, the input current and output current become small at low output, so the small diameter pan that should continue the heating operation and the heating operation are stopped. It becomes difficult to determine the unloaded state to be used and the load of small items such as forks and spoons. Further, when the input voltage fluctuates, even when the inverter circuit is operated with the same load state and the same drive signal, the magnitudes of the input current and the heating coil current change. Furthermore, since the impedance of the pan changes when the temperature of the pan changes, even when the inverter circuit is operated with the same drive signal at the same input voltage, the magnitude of the input current and the heating coil current will change.

  Therefore, in the conventional induction heating cooker, if the drive signal of the inverter circuit is at a low output level and the load determination is difficult, load detection is performed by periodically increasing the load determination to a level at which load determination is possible (for example, , Refer to Patent Document 1), and there is one in which load determination is performed by periodically operating with a predetermined drive signal corresponding to an input voltage (for example, refer to Patent Document 2).

Japanese Patent Laid-Open No. 06-119968 (page 4, FIGS. 1 to 4) Japanese Patent Laid-Open No. 05-315068 (page 3-4, FIG. 1)

  In the conventional induction heating cooker described above, the inverter circuit is periodically driven by a predetermined level drive signal or input periodically so that the input current and the current flowing in the heating coil are at a level at which the load can be determined. The load is determined by changing to a predetermined drive signal corresponding to the voltage. For this reason, even if the user does not change the thermal power setting, the thermal power changes, and it becomes unnatural operation for the user, it is delayed to detect the change in the pan mounting state, or the heating output of low thermal power However, there was a problem that it becomes larger than the set firepower.

  The present invention has been made in order to solve the above-described problems, and improves the accuracy of determining whether or not the pan is appropriate at the start of heating. It aims at obtaining the induction heating cooking appliance which can determine the mounting state of a pan correctly, without adjusting.

  An induction heating cooker according to the present invention includes a load circuit having a heating coil disposed below a top plate, a DC power supply circuit that converts AC power to DC, and converts the output of the DC power supply circuit to high-frequency power. An inverter circuit to be supplied to the load circuit; a control circuit for controlling a drive signal for driving the inverter circuit; and a temperature detecting means for detecting the temperature of the pan placed on the top plate. Input current detection means for detecting current input to the circuit; input voltage detection means for detecting voltage input from the AC power supply to the DC power supply circuit; output current detection means for detecting current flowing in the load circuit; Output voltage detection means for detecting the resonance voltage generated in the circuit, and input current detection means when the inverter circuit is driven by the control circuit at a predetermined drive condition at the start of heating. A pan determining means for determining whether or not the pan placed on the top plate is appropriate using the detection values of at least two of the pressure detecting means, the output current detecting means and the output voltage detecting means, When determining whether the pan is appropriate, the determination unit corrects the determination condition as to whether the pan is appropriate according to the temperature of the pan detected by the temperature detection unit.

  The induction heating cooker according to the present invention includes a load circuit having a heating coil disposed below the top plate, a DC power circuit that converts AC power to DC, and converts the output of the DC power circuit to high-frequency power. And an inverter circuit for supplying the load circuit, a control circuit for controlling a drive signal for driving the inverter circuit, and a temperature detecting means for detecting the temperature of the pan placed on the top plate, and further comprising an AC power source Input current detecting means for detecting a current input from the AC power source to the DC power supply circuit, input voltage detecting means for detecting a voltage input from the AC power supply to the DC power supply circuit, and output current detecting means for detecting a current flowing through the load circuit And the pan is placed on the top plate using at least one of the input voltage detection means, the output current detection means, and the drive signal and the current detected by the input current detection means during the heating operation. A pan presence / absence judging means for judging whether or not the pan is present, and when the pan presence / absence judging means judges whether or not the pan is placed on the top plate, the temperature of the pan detected by the temperature detecting means is determined. Accordingly, the judgment condition for the presence or absence of the pan is corrected.

  In the present invention, at the start of heating, the current detected by the input current detection means, the voltage detected by the input voltage detection means, the current detected by the output current detection means, and the resonance voltage detected by the output voltage detection means When determining whether or not the pan placed on the top plate is appropriate using at least two of them, the determination condition as to whether or not the pan is appropriate is corrected according to the temperature of the pan detected by the temperature detecting means. I am doing so. Thereby, it is possible to determine more accurately even when the difference in the input current between the state where the small-diameter pan is placed and the state where no load or small item (fork or spoon) is placed is small. .

  In the present invention, during the heating operation, at least one of the voltage detected by the input voltage detecting means, the current detected by the output current detecting means, and the drive signal and the current detected by the input current detecting means are obtained. When determining whether or not the pan is placed on the top plate, the determination condition of the presence or absence of the pan is corrected according to the temperature of the pan detected by the temperature detecting means. Thereby, even if it is a low heating output state and the temperature of a pan changes and the impedance of a pan changes, the presence or absence of a pan can be determined correctly, without adjusting a heating output.

It is a figure which shows the circuit structure of the induction heating cooking appliance which concerns on embodiment. It is a flowchart which shows the process of the heating control in the control circuit of the induction heating cooking appliance which concerns on embodiment. It is a characteristic view of the pot determination in the induction heating cooking appliance which concerns on embodiment. It is a characteristic view of the pot determination in the induction heating cooking appliance which shows the modification of embodiment. It is a characteristic view of the presence or absence determination of the pan in the induction heating cooking appliance which concerns on embodiment. It is a characteristic view of the presence or absence determination of the pan in the induction heating cooking appliance which shows the modification of embodiment.

Hereinafter, embodiments of the induction heating cooker according to the present invention will be described in detail.
Drawing 1 is a figure showing the circuit composition of the induction heating cooking appliance concerning an embodiment.
In FIG. 1, the induction heating cooker of this Embodiment is comprised, for example with the DC power supply circuit 2 connected to the commercial AC power supply 1, the inverter circuit 3, the load circuit 4, and the heat-resistant tempered glass, and the pan 16 is mounted. There is provided a top plate 15, a heating power setting unit 23 for setting heating start and stop, and heating power, and a control circuit 24 for controlling the entire cooking device.

  The aforementioned DC power supply circuit 2 includes a diode bridge circuit 5 that rectifies the AC power of the commercial AC power supply 1, and a choke coil 6 and a smoothing capacitor 7 that smooth the rectified voltage. The output of the DC power supply circuit 2 is supplied to the inverter circuit 3 through a DC bus. The inverter circuit 3 includes switching elements 8 and 9 connected in series between DC buses (hereinafter, the high-potential side switching element 8 is referred to as “upper switch 8”, and the low-potential side switching element 9 is referred to as “lower switch 9”. And diodes 10 and 11 connected in antiparallel to the upper switch 8 and the lower switch 9, respectively. In this inverter circuit 3, when the upper switch 8 and the lower switch 9 are alternately turned on and off, a high frequency voltage is generated between the connection point and one end (low potential side) of the DC bus. Supplied.

  The load circuit 4 includes a series circuit of a heating coil 12 disposed below the top plate 15 and its resonance capacitor 13, and a clamp diode 14 connected in parallel to the resonance capacitor 13. In the load circuit 4, the magnetic flux generated by the high-frequency current flowing in the heating coil 12 induces an eddy current in the pan 16 placed on the top plate 15 and heats it. The clamp diode 14 may be connected to the heating coil 12 in parallel.

  The input current detection unit 17 detects an input current flowing from the commercial AC power supply 1 to the diode bridge circuit 5. The input voltage detector 18 detects the voltage output from the diode bridge circuit 5. The output current detector 19 detects a current flowing from the inverter circuit 3 to the load circuit 4. The output voltage detector 20 detects a resonance voltage generated in the resonance capacitor 13. The temperature detection unit 21 is disposed so as to be in close contact with the lower surface of the top plate 15 and indirectly detects the temperature of the pan 16 via the top plate 15. The inverter drive circuit 22 generates a drive signal based on the control from the control circuit 24, outputs the drive signal to the upper switch 8 and the lower switch 9 of the inverter circuit 3, and alternately turns on / off.

  The control circuit 24 described above is provided with a pan presence / absence determination unit 25 and a pan determination unit 26. The pan presence / absence determination unit 25 determines whether or not the pan 16 placed on the top 15 has been removed from the detected value of the input current and the level of the drive signal of the inverter circuit 3 during the heating operation. When the inverter circuit 3 is driven at the level of a predetermined drive signal by the control circuit 24 at the start of the heating operation, the pan determination unit 26 determines whether the proper pan 16 is placed on the top plate 15 or not. Judgment is made from the detected value.

The heating control process in the induction heating cooker configured as described above will be described with reference to the flowchart of FIG.
FIG. 2 is a flowchart showing a heating control process in the control circuit of the induction cooking device according to the embodiment.
First, the control circuit 24 determines whether or not a heating start request based on the setting of the heating power is input from the heating power setting unit 23 (step 1). When the control circuit 24 detects the heating start request, it controls the inverter drive circuit 22 and starts outputting predetermined drive signals to the upper switch 8 and the lower switch 9 of the inverter circuit 3 (step 2). Thereafter, the control circuit 24 receives the input current via the input current detector 17, the input voltage via the input voltage detector 18, the output current flowing through the load circuit 4 via the output current detector 19, and The resonant voltage generated in the resonant capacitor 13 via the output voltage detector 20 is detected, and the temperature of the top 15 (pan 16) is detected via the temperature detector 21 (step 3).

  At this time, the pan determination unit 26 of the control circuit 24 determines whether or not the proper pan 16 is placed on the top board 15 based on the detected value such as the detected input current (step 4). On the other hand, when the pan determining unit 26 determines that the proper pan 16 is not placed, the control circuit 24 stops outputting a predetermined drive signal, returns to step 1, and waits for a heating start request. The control circuit 24 also detects the input current detected by the input current detection unit 17 and the input detected by the input voltage detection unit 18 when the pan determination unit 26 determines that the proper pan 16 is placed. The input power is calculated from the voltage and compared with the set power set by the heating power setting unit 23 (step 5). When the input power is larger, the control circuit 24 controls the inverter drive circuit 22 to increase the drive frequency of the inverter circuit 3, lowers the heating output (step 6), and proceeds to step 8. Further, when the set power is larger in Step 5, the control circuit 24 controls the inverter drive circuit 22 to lower the drive frequency of the inverter circuit 3, increase the heating output (Step 7), and proceed to Step 8. . Further, the control circuit 24 proceeds to step 8 as it is without controlling the inverter drive circuit 22 when the set power and the input power are substantially equal in step 5.

  Thereafter, the control circuit 24 determines whether or not a heating stop request due to the heating stop operation of the heating power setting unit 23 has been detected (step 8). When the control circuit 24 does not detect the heating stop request, the control circuit 24 inputs the input current via the input current detector 17, the input voltage via the input voltage detector 18, and the load circuit 4 via the output current detector 19. Further, the temperature of the top plate 15 (pan 16) is detected via the temperature detector 21 and the resonant voltage generated in the resonant capacitor 13 via the output voltage detector 20 and the temperature of the top plate 15 (pan 16), respectively. .

  At this time, the pan presence / absence determination unit 25 of the control circuit 24 determines whether the pan 16 is continuously placed on the top plate 15 based on the detected value of the detected input current or the like, or the pan 16 is removed. Then, it is determined whether or not it is not on the top 15 (step 10). On the other hand, when it is determined by the pan presence / absence determination unit 25 that the pan 16 is continuously placed on the top plate 15, the control circuit 24 proceeds to step 5 and continues the heating operation. Further, when it is determined in step 10 that the pan 16 has been moved and is not on the top plate 15 in step 10, the control circuit 24 temporarily stops outputting the drive signal (step 11). Then, the control circuit 24 proceeds to step 2 and restarts from the output of a predetermined drive signal for detecting the initial load, and causes the pot determination unit 26 to determine whether or not the pot 16 is appropriate. When the control circuit 24 detects the heating stop request in step 8, the control circuit 24 controls the inverter drive circuit 22 to stop the drive signal to the inverter circuit 3 (step 12), and returns to step 1 to request the heating start request. wait.

  As described above, the control circuit 24 performs the heating control process. In step 4 of FIG. 2, the determination as to whether or not the proper pan 16 performed by the pan determination unit 26 at the start of heating is placed is shown in FIG. As shown in FIG. 6, the inverter circuit 3 is driven by a predetermined drive signal, and the relationship between the input current and the output current is used.

  The pan determination unit 26 is input when the output current is larger than a predetermined value in a predetermined driving state (low impedance pan such as an aluminum pan or copper pan), or when the input current or output current is small (no load or small item). When the output current is larger than the current (small impedance pan with low impedance), it is determined that the pan 16 is inappropriate. At that time, when the temperature of the pan 16 rises, its impedance characteristic changes, and even when the same pan 16 is placed at the same position, the relationship between the input current and the output current in the low temperature state, and in the high temperature state The relationship between input current and output current changes.

  Therefore, in the present embodiment, the threshold value which is the determination condition is corrected according to the temperature of the pan 16. For example, as shown in FIG. 3, the threshold value is corrected to be indicated by a solid line when the temperature of the pan 16 is low, and the threshold value is indicated by a broken line when the temperature is high, as shown in FIG. To do. As a result, it is possible to accurately determine whether or not the pot 16 is appropriate.

  In addition, not only the relationship between the input current and the output current but also the input voltage is taken into account, and it is determined whether or not the proper pan 16 is determined from the relationship between (input current / input voltage) and (output current / input voltage). May be. In this case, it can be determined whether or not the pot 16 is suitable considering the influence of variations in input voltage.

  Further, for example, as shown in FIG. 4, the determination as to whether or not the proper pan 16 placed by the pan determination unit 26 is placed is performed with the input current in a state where the inverter circuit 3 is driven with a predetermined drive signal. It can also be determined from the relationship of the resonance voltage.

  This is because in a predetermined drive state, the resonance voltage generated in the resonance capacitor 13 detected by the output voltage detection unit 20 also varies depending on the state of the pan 16 on the top plate 15. When a low impedance pan such as an aluminum pan or a copper pan is placed, the resonance voltage is high, and when no load or small items are placed, the resonance voltage or input current is low, resulting in a low impedance. When the small-diameter pan is placed, the resonance voltage becomes higher with respect to the input current. Therefore, when the resonance voltage detected by the output voltage detection unit 20 is higher than a predetermined value, when the resonance voltage or the input current is small, or when the resonance voltage is high with respect to the input current, the pot 16 is determined to be inappropriate. To do. Also in this case, when the temperature of the pan 16 rises, its impedance characteristic changes, and even in the same pan 16, the relationship between the input current and the resonance voltage in the low temperature state and the relationship between the input current and the resonance voltage in the high temperature state change.

  Therefore, as a modification of the present embodiment, for example, as shown in FIG. 4, when the temperature of the pan 16 is low with respect to the threshold value before correction (two-dot chain line), the threshold value as a determination condition is indicated by a solid line. When the temperature is high, the threshold is corrected as indicated by a broken line. As a result, it is possible to accurately determine whether or not the pot 16 is appropriate.

  In addition, not only the relationship between the input current and the resonance voltage, but also the input voltage is considered, and it is determined whether or not the pot 16 is appropriate from the relationship between (input current / input voltage) and (resonance voltage / input voltage). May be. In this case, it is possible to accurately determine whether or not the pot 16 is appropriate considering the influence of variations in input voltage.

  In step 10 in FIG. 2, whether the pan 16 has been placed is determined by the pan presence / absence determination unit 25, or whether the pan 16 has been removed and the pan is left (no load determination). For example, as shown in FIG. 5, the relationship between the level of the drive signal and the input current is used.

  For example, the drive signal level is adjusted by adjusting the drive frequency of the inverter circuit 3. However, when the drive frequency is lowered (approaching the resonance frequency of the load circuit), the drive signal level is increased (heating output is increased) and the drive signal is driven. When the frequency is increased (away from the resonance frequency of the load circuit), the drive signal level is lowered (heating output is reduced). The input current detected by the input current detector 17 varies depending on the state (size, material, etc.) of the pan 16 placed on the top plate 15 above the heating coil 12 and the level of the drive signal. In the no-load state where 16 is not placed, the input current does not increase much even if the drive signal level is increased. On the other hand, in the case of a large-diameter low impedance pan (aluminum pan, copper pan, etc.), the input current increases at a relatively low drive signal level. In such a case, it is determined that the proper pan 16 is not placed, and heating is stopped.

  When the pan presence / absence determination unit 25 is heated with a low heating power (low-level drive signal), the determination when the small-diameter pan is placed and when there is no load is performed by placing the small-diameter pan. The difference between the input current in the case of being unloaded and the input current in the no-load state is small, and the impedance characteristic changes when the temperature of the pan 16 rises, so that the determination may be difficult.

  Therefore, in the present embodiment, in consideration of the fact that the relationship between the level of the drive signal and the input current in the low temperature state and the relationship between the input current and the output current in the high temperature state change even in the same pan 16. The threshold that is the determination condition is corrected according to the temperature of 16. For example, as shown in FIG. 5, the threshold value is corrected to be indicated by a solid line when the temperature of the pan 16 is low, and the threshold value is indicated by a broken line when the temperature is high, as shown in FIG. To do. When the temperature is high, the threshold of the input current is lowered with respect to the same drive signal level. Thus, by considering the temperature of the pan 16, it can be accurately determined whether or not the pan 16 is placed on the top plate 15.

  Whether the pan 16 is placed on the top plate 15 based on the relationship between the drive signal and (input current / input voltage) in consideration of not only the relationship between the level of the drive signal and the input current but also the input voltage. You may make it determine. In this case, it is possible to accurately determine the presence / absence of an appropriate pan 16 in consideration of the influence of variations in input voltage.

  In the above description, an example in which the drive signal level (heating output) is changed by adjusting the drive frequency of the inverter circuit 3 has been described. The level of the drive signal (heating output) can be changed by adjusting the energization ratio of the lower switch 9.

  When the inverter circuit 3 is driven at a constant drive frequency, the heating output increases as the ratio of the energizing time of the upper switch 8 and the lower switch 9 approaches 50%: 50%, and the energizing time of the upper switch 8 is decreased. The heating output decreases as the energization time becomes shorter.

  When the inverter circuit 3 is driven at a constant drive frequency, the determination of whether the pan 16 is placed or no pan is performed by the pan presence / absence determination unit 25 is performed, for example, as shown in FIG. The determination may be made based on the relationship between the output current detected by the above and the input current detected by the input current detection unit 17. However, even when the same pan 16 is placed at the same position, the relationship between the output current and the input current differs depending on the driving state (driving frequency) of the inverter circuit 3, so the output current for each driving frequency. And the input current relationship.

  Even when it is determined whether the proper pan 16 is placed or the pan is in the no-pot state using the relationship between the output current and the input current, the impedance characteristics of the pan 16 change and change. Therefore, the presence / absence of the proper pan 16 can be accurately determined by correcting the threshold value which is the determination condition according to the temperature (see FIG. 6).

  As described above, in the present embodiment, the determination as to whether or not the proper pan 16 is placed at the start of heating performed by the pan determination unit 26 is performed using the threshold value corrected according to the temperature of the pan 16. Like to do. Thereby, it is possible to determine more accurately even when the difference in the input current between the state where the small-diameter pan is placed and the state where no load or small item (fork or spoon) is placed is small. . Moreover, the variation in the determination of whether heating is possible for the same pot 16 can be suppressed by the temperature of the pot 16 at the start of heating.

  Further, whether or not the proper pan 16 performed by the pan presence / absence determining unit 25 in the heating output state continues to be placed or whether the pan 16 is removed and is in an unloaded state depends on the temperature of the pan 16. The determination is made using the corrected threshold value. This makes it possible to determine more accurately even when the difference in input current between the state in which the small-diameter pan is placed in the low heating output state and the state in which no load or small items (forks or spoons) are placed is small can do. For this reason, the induction heating cooking appliance which does not use safer and useless energy can be obtained. Moreover, it can suppress that heating is stopped as the improper pan 16 in the middle of heating by the temperature rise of the pan 16, etc.

  1 commercial AC power supply, 2 DC power supply circuit, 3 inverter circuit, 4 load circuit, 5 diode bridge circuit, 6 choke coil, 7 smoothing capacitor, 8, 9 switching element, 10, 11 diode, 12 heating coil, 13 resonance capacitor, 14 clamp diode, 15 top plate, 16 pan, 17 input current detector, 18 input voltage detector, 19 output current detector, 20 output voltage detector, 21 temperature detector, 22 inverter drive circuit, 23 heating power setting unit , 24 control circuit, 25 pan presence / absence determination unit, 26 pan determination unit.

Claims (2)

A load circuit having a heating coil disposed below the top plate;
A DC power circuit that converts AC power to DC, and
An inverter circuit that converts the output of the DC power supply circuit into high-frequency power and supplies it to the load circuit;
A control circuit for controlling a drive signal for driving the inverter circuit;
Temperature detecting means for detecting the temperature of the pan placed on the top plate,
further,
An input current detecting means for detecting a current input from the AC power source to the DC power source circuit;
An input voltage detecting means for detecting a voltage input to the DC power supply circuit from an AC power supply;
Output current detection means for detecting current flowing in the load circuit;
Output voltage detecting means for detecting a resonance voltage generated in the load circuit;
Detection of at least two of the input current detection means, the input voltage detection means, the output current detection means, and the output voltage detection means when the inverter circuit is driven by the control circuit at a predetermined drive condition at the start of heating. A pan determining means for determining whether or not the pan placed on the top plate is appropriate using the detected value of the means,
When the pan determining means determines whether or not the pan is proper, the induction heating is characterized by correcting a determination condition as to whether or not the pan is appropriate according to the temperature of the pan detected by the temperature detecting means. Cooking device. A load circuit having a heating coil disposed below the top plate;
A DC power circuit that converts AC power to DC, and
An inverter circuit that converts the output of the DC power supply circuit into high-frequency power and supplies it to the load circuit;
A control circuit for controlling a drive signal for driving the inverter circuit;
Temperature detecting means for detecting the temperature of the pan placed on the top plate,
further,
An input current detecting means for detecting a current input from the AC power source to the DC power source circuit;
An input voltage detecting means for detecting a voltage input to the DC power supply circuit from an AC power supply;
Output current detection means for detecting current flowing in the load circuit;
Whether or not the pan is placed on the top plate using at least one of the input voltage detection means, the output current detection means and the drive signal and the current detected by the input current detection means during the heating operation And a pan presence / absence judging means for judging
The pan presence / absence determining means corrects the determination condition of the presence / absence of a pan according to the temperature of the pan detected by the temperature detecting means when determining whether or not the pan is placed on the top plate. Induction heating cooker.

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