JP6076040B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker that suppresses heating power for a small-diameter pan.

  In a conventional induction heating cooker, for example, “a small pan determination unit that determines the size of a pan from an input current detection unit and an inverter output detection unit, a temperature detection unit that detects the temperature of the pan, and a signal from the temperature detection unit And a control means for controlling the output of the inverter circuit according to the (For example, see Patent Document 1)

JP 2007-184179 A (Claim 1)

  In the technique described in Patent Document 1 described above, when the small pan determining means determines that the pan is small, the control means configures the control temperature of the temperature detecting means to be low so that the self-heating per unit area is large. The temperature rise was reduced.

  However, if the placement position of the small-diameter pan is deviated from the center position of the heating coil, or the pan-bottom of the small-diameter pan is warped, the detection temperature may not be accurate or the detection may be delayed. There was a problem of overheating the peripheral edge of the pan bottom.

  The present invention was made in order to solve the above-described problems. When the pan position of the small-diameter pan is shifted from the center position of the heating coil, or when the pan bottom is warped, the small-diameter pan is the center of the heating coil. The object is to obtain an induction heating cooker that can suppress overheating of the peripheral edge of the bottom of the small-diameter pan and control the heating density not to be too high.

An induction heating cooker according to the present invention includes a heating coil that heats a pan on a top plate, an inverter circuit that supplies high-frequency current to the heating coil, output current detection means that detects an output current from the inverter circuit, and an inverter Output power detection means for detecting output power from the circuit, and control means for controlling the inverter circuit based on the detection results of the output current detection means and the output power detection means. The control means outputs the output power from the output power. defining a first output current upper limit value becomes smaller as the output current decreases, the output current when the proper pot heating that controls the inverter circuit so as not to exceed the first output current limit.

  In the present invention, the inverter circuit is controlled so that the output current does not exceed the first output current upper limit value determined from the output power. By performing this control, it is possible to limit the output current during heating of the small-diameter pan, and thus it is possible to suppress overheating of the peripheral portion of the pan bottom of the small-diameter pan, and to suppress the heating density. Moreover, since the output current at the time of heating of a small-diameter pan is limited, even when the detection temperature of the small-diameter pan is not accurate or when the detection is delayed, overheating of the small-diameter pan can be suppressed. .

It is a figure which shows the circuit structure of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a wave form diagram which shows an example of the drive signal of the induction heating cooking appliance which concerns on Embodiment 1. FIG. It is a figure which shows the positional relationship of the magnetic flux which arises with the high frequency current which flows into the heating coil of the induction heating cooking appliance which concerns on Embodiment 1, and a pan. It is a figure which shows the output current upper limit with respect to the magnitude | size of the pan in the correlation of the input electric power of the induction heating cooking appliance which concerns on Embodiment 1, and an output current. It is a flowchart which shows the operation | movement of the heating control of the control circuit in the induction heating cooking appliance of FIG. In the control circuit in the induction heating cooker of FIG. 1, it is a figure which shows the relationship between the input current at the time of the output of the predetermined drive signal used for determination of whether it is an appropriate pan which can be heated at the time of a heating start, and an output current. . It is a figure which shows the output current upper limit with respect to the magnitude | size of a pot in the correlation of the input current of an induction heating cooking appliance which concerns on the modification 1 of Embodiment 1, and an output current. It is a figure which shows the circuit structure of the induction heating cooking appliance which concerns on the modification 2 of Embodiment 1. FIG. It is a figure which shows the output current upper limit with respect to the magnitude of the pan in the correlation with the output electric power and output current of the induction heating cooking appliance which concerns on the modification 2 of Embodiment 1. FIG. It is a flowchart which shows the operation | movement of the heating control of the control circuit in the induction heating cooking appliance which concerns on Embodiment 2. FIG. In the control circuit in the induction heating cooker of FIG. 10, it is a figure which shows the relationship between the input current at the time of the output of the predetermined drive signal used for determination of whether it is an appropriate pan which can be heated at the time of a heating start, and an output current. . It is a wave form diagram which shows an example of the drive signal of the inverter circuit of the induction heating cooking appliance which concerns on Embodiment 2. FIG. In the induction heating cooking appliance which concerns on Embodiment 2, it is a figure which shows the output current upper limit with respect to the small diameter pan of the magnetic SUS in the correlation of the input current and output current when the drive frequency f1 is output. In the induction heating cooking appliance which concerns on Embodiment 2, it is a figure which shows the output current upper limit with respect to the small diameter pan of SECC in the correlation of the input current and output current when the drive frequency f2 is output. In the induction heating cooking appliance which concerns on Embodiment 2, it is a figure which shows the output current upper limit with respect to the small diameter pan of nonmagnetic SUS in the correlation of the input current and output current when the drive frequency f3 is output. In the induction heating cooking appliance which concerns on the modification 1 of Embodiment 2, it is a figure which shows the output current upper limit with respect to the small diameter pan of the magnetic SUS in the correlation of the input current and output current when the drive frequency f1 is output. In the induction heating cooking appliance which concerns on the modification 1 of Embodiment 2, it is a figure which shows the output current upper limit with respect to the small diameter pan of SECC in the correlation of the input current and output current when the drive frequency f2 is output. In the induction heating cooking appliance which concerns on the modification 1 of Embodiment 2, it is a figure which shows the output current upper limit with respect to the small diameter pan of nonmagnetic SUS in the correlation of the input current and output current when the drive frequency f3 is output. It is a figure which shows the circuit structure of the induction heating cooking appliance which concerns on the modification 2 of Embodiment 2. FIG. It is a wave form diagram which shows an example of the drive signal at the time of the high output of the inverter circuit in the induction heating cooking appliance of FIG. It is a wave form diagram which shows an example of the drive signal at the time of the medium output of the inverter circuit in the induction heating cooking appliance of FIG. It is a wave form diagram which shows an example of the drive signal at the time of the small output of the inverter circuit in the induction heating cooking appliance of FIG. It is a figure which shows the circuit structure of the induction heating cooking appliance which concerns on Embodiment 3. FIG. It is a wave form diagram which shows an example of the drive signal of the inverter circuit of the induction heating cooking appliance which concerns on Embodiment 3. FIG. In the induction heating cooker of FIG. 23, it is a figure which shows the output current upper limit with respect to the pot in the correlation of input electric power and output current when the drive frequency f is more than the predetermined frequency fa. In the induction heating cooker of FIG. 23, it is a figure which shows the output current upper limit with respect to the pot in the correlation of input electric power and output current when the drive frequency f is less than the predetermined frequency fb. In the induction heating cooker of FIG. 23, it is a figure which shows the output current upper limit with respect to the pot in the correlation of input electric power and output current when the drive frequency f is more than the predetermined frequency fb and less than the predetermined frequency fa.

Embodiment 1 FIG.
1 is a diagram showing a circuit configuration of an induction heating cooker according to Embodiment 1, and FIG. 2 is a waveform diagram showing an example of a drive signal of the induction heating cooker according to Embodiment 1. FIG.
In the induction heating cooker according to Embodiment 1, a DC power supply circuit 2 is connected to a commercial AC power supply 1 as shown in FIG. The DC power supply circuit 2 includes a rectifier diode bridge 3 that rectifies AC power, a reactor 4, and a smoothing capacitor 5, and supplies DC power to the inverter circuit 6. On the input side of the DC power supply circuit 2, input current detection means 13 for detecting a current input from the commercial AC power supply 1 to the DC power supply circuit 2 is inserted. Between the output terminals of the rectifier diode bridge 3, input voltage detection means 14 for detecting the output voltage of the rectifier diode bridge 3 is connected.

  The inverter circuit 6 includes two switching elements 7 and 8 connected in series between the DC buses of the DC power supply circuit 2 (hereinafter, the high-potential side switching element is referred to as “upper switch 7”, and the low-potential side switching element. And the diodes 9 and 10 connected to the respective switches 7 and 8 in antiparallel. In the inverter circuit 6, the upper and lower switches 7, 8 connected in series are alternately turned on / off by a drive signal (drive frequency) from the drive circuit 11, and the output terminals (up / down switches 7, 8). A high frequency voltage is generated between the connection point) and one end of the DC bus. The high frequency voltage output from the inverter circuit 6 is applied to the load circuit 15, and a high frequency current (output current) flows through the heating coil 16. The output current is detected by output current detection means 12 inserted at one end of the DC bus.

  As shown in FIG. 2A, the inverter circuit 6 enters a high output state when the ON / OFF energization ratios of the drive signals for driving the upper and lower switches 7 and 8 are substantially equal, and FIG. As shown, when the energizing time of the upper switch 7 is shorter than the energizing time of the lower switch 8, the low output state is entered. Note that, during the conduction time of the upper switch 7, a period shorter than ½ of the resonance period of the heating coil 16 of the load circuit 15 and the resonant capacitor 17 is set so that commutation of the load current does not occur during that period.

  The load circuit 15 includes a series circuit of the heating coil 16 and the resonance capacitor 17 described above, and a clamp diode 18 connected in parallel with the resonance capacitor 17. The clamp diode 18 clamps the potential of the connection point between the heating coil 16 and the resonance capacitor 17 to the potential of the low potential side bus of the DC power supply circuit 2. Due to the action of the clamp diode 18, the current flowing through the heating coil 16 is not commutated when the lower switch 8 is conductive. In addition, the high frequency current which flows into the heating coil 16 induces an eddy current to the pan (not shown) mounted on the top plate (not shown), and heats the pan.

  The operation unit 19 inputs the target heating power set by the user's operation to the control circuit 20. The control circuit 20 controls the drive of the inverter circuit 6. The target heating power set by the operation unit 19 and the input current and input voltage detected by the input current detection means 13 and the input voltage detection means 14 are controlled. The drive circuit 11 is controlled based on the input power calculated from the above and the output current of the inverter circuit 6. The control circuit 20 has a function of input power detection means.

  FIG. 3 is a diagram showing the positional relationship between the magnetic flux generated by the high-frequency current flowing in the heating coil of the induction heating cooker according to Embodiment 1 and the pan, and FIG. 4 is the input power and output of the induction heating cooker according to Embodiment 1. It is a figure which shows the output current upper limit with respect to the magnitude | size of a pot in correlation with an electric current. 3A shows a state where the large-diameter pan 22a is placed on the top plate 21 above the heating coil 16, and FIG. 3B shows a state where the medium-diameter pan 22b is placed. The figure (c) has shown the state which mounted the small diameter pan 22c.

  When the large-diameter pan 22a is placed as shown in FIG. 3A, since the pan bottom covers the heating coil 16, most of the high-frequency magnetic flux generated by the high-frequency current flowing through the heating coil 16 is directly above the pan bottom. Interlink with. In this case, high-frequency eddy current flows through the wide pan bottom and high heat is generated, and part of the magnetic flux generated by the current flowing through the heating coil 16 is canceled out by the magnetic flux generated by the eddy current flowing through the pan bottom. On the other hand, in the state where the small-diameter pan 22c is placed as shown in FIG. 6C, the area of the pan bottom facing the heating coil 16 is small, and the high-frequency magnetic flux generated by the high-frequency current flowing in the heating coil portion immediately below is small. Most of them are linked to the bottom of the pan immediately above, but only a part of the high-frequency magnetic flux generated by the high-frequency current flowing through the heating coil 16 outside the bottom of the pan is linked to the small-diameter pan 22c, and the others are leakage flux. Become.

  Therefore, when the same current (output current) is passed through the heating coil 16, as shown in FIG. 4, the input power is larger when the large-diameter pan 22a is placed than when the small-diameter pan 22c is placed. (Heating power). However, not only the magnetic flux generated by the high-frequency current flowing in the heating coil 16 directly under the pan bottom in the small-diameter pan 22c but also a part of the magnetic flux generated by the high-frequency current flowing in the heating coil portion directly under the small-diameter pan 22c is linked to the pan bottom. As a result, an induced eddy current flows, so that the density of the eddy current increases and the heating density also increases.

  Therefore, as shown in FIG. 4, the output current of the inverter circuit 6 is limited with the current value at which the output current decreases as the input power decreases as the output current upper limit (oblique broken line: first output current upper limit value). Then, heating the small-diameter pan 22c as compared with the case where the output current is limited by a fixed upper limit value (upper / lower switch rating (rated current) or output current upper limit value determined by the cooling state) regardless of the input power. The maximum value of electric power can be suppressed, and the heating density of the small-diameter pan 22c can be suppressed. Thereby, the danger of the overheating in the small diameter pan 22c can be suppressed. In addition, about the medium diameter pan 22b, as shown in FIG. 4, it becomes the characteristic of the middle of the large diameter pan 22a and the small diameter pan 22c. As the output current upper limit value for the medium-diameter pan 22b, the above-described output current upper limit (oblique broken line) is used. Further, as the output current upper limit value for the large-diameter pan 22a, an output current (second output current upper limit value) determined by the ratings of the upper and lower switches 7, 8 of the inverter circuit 6 and the cooling state of the inverter circuit 6 is used.

  FIG. 5 is a flowchart showing the heating control operation of the control circuit in the induction heating cooker of FIG. 1, and FIG. 6 is a proper pan that can be heated at the start of heating in the control circuit of the induction heating cooker of FIG. It is a figure which shows the relationship between the input current at the time of the output of the predetermined | prescribed drive signal used for such determination (henceforth initial load determination), and output current.

  First, the control circuit 20 determines whether or not an instruction to start heating has been issued from the operation unit 19 (step 1). For example, when the target heating power is set, the control circuit 20 determines that an instruction to start heating has been issued, and a predetermined drive signal for determining whether or not the pan is appropriate is sent from the drive circuit 11. The drive circuit 11 is controlled so as to be output to the inverter circuit 6. Then, the control circuit 20 reads the input current detected by the input current detection means 13, and also reads the output current detected by the output current detection means 12, and performs an initial load determination process (step 2).

  As shown in FIG. 6, when both the input current and the output current are small, the control circuit 20 determines that a small object such as a fork, a knife, or the like, in which no pan is placed, or is placed. In addition, when the output current is large or the ratio of the output current to the input current is large, the control circuit 20 determines that an inappropriate pan that is not suitable for induction heating such as an aluminum pan is placed. Furthermore, the control circuit 20 determines that the pan is appropriate for a pan whose input current and output current are within a predetermined range with respect to the output of the predetermined drive signal. In addition, the size (large / medium / small) of the pan is also determined from the input current and the output current.

  As a result of the initial load determination, when the control circuit 20 determines that there is no load or an inappropriate pan (aluminum pan) (step 3), the control circuit 20 determines whether or not a proper pan is determined (step 4). If not determined, the control circuit 20 returns to step 2 and repeats the initial load determination process. If the proper pan is not determined, the control circuit 20 stops driving the inverter circuit 6 (step 5) and returns to the initial state. Return to. In addition, the determination that there is no proper pan is when the state continues for a predetermined period after determining that the pan is inappropriate.

  In addition, when the control circuit 20 determines that the pot 22 is appropriate as a result of the initial load determination (step 3), the control circuit 20 passes the drive circuit 11 so that the target heating power set by the operation unit 19 is obtained. The inverter circuit 6 is controlled. Then, the control circuit 20 reads the input current and the input voltage detected by the input current detection means 13 and the input voltage detection means 14, respectively, and calculates the input power (step 6). Next, as shown in FIG. 4, the control circuit 20 calculates a first output current upper limit value from the input power (step 7). As described above, the first output current upper limit value is a current value at which the output current decreases as the input power decreases, and the heating density does not increase when the loaded pot 22 is the small diameter pot 22c. Is set to

  Thereafter, the control circuit 20 reads the output current detected by the output current detecting means 12, and determines whether or not the output current exceeds the calculated output current upper limit value (step 8). When the output current exceeds the output current upper limit value, the control circuit 20 controls the drive circuit 11 so as to reduce the energization time ratio of the upper switch 7 and lowers the output of the inverter circuit 6 (step 11). When the output current is less than or equal to the output current upper limit value, the calculated input power is compared with the target heating power set by the operation unit 19 (step 9).

  When the control circuit 20 determines in step 9 that the calculated input power is smaller, the control circuit 20 controls the drive circuit 11 so that the energization time ratio of the upper switch 7 is large (however, 50% or less), and the inverter circuit 6 (Step 10). Further, when the input power calculated in step 6 is larger than the target heating power, the control circuit 20 controls the drive circuit 11 so that the energization time ratio of the upper switch 7 becomes small, and the output of the inverter circuit 6 is controlled. Lower (step 11). Further, when the calculated input power and the target heating power are substantially equal, the control circuit 20 proceeds to step 12 as it is and determines whether or not a heating end instruction is input from the operation unit 19. If there is no instruction to end heating, the control circuit 20 returns to step 6 and continues control of the heating power. If there is an instruction to end heating, the control circuit 20 stops the control of the drive circuit 11 and stops the output of the inverter circuit 6 ( Step 13), returning to the initial state.

  As described above, according to Embodiment 1, the first output current upper limit value is set to a lower value as the input power becomes smaller. For this reason, the output current at the time of the heating of the small diameter pan 22c where input power becomes small with respect to the output current of the same magnitude can be limited, and overheating (heating density) of the small diameter pan 22c can be suppressed. Moreover, since the output current at the time of heating of the small-diameter pan 22c is limited, even when the detection temperature of the small-diameter pan 22c is not accurate or when the detection is delayed, the overheating of the small-diameter pan 22c is suppressed. be able to.

In the first embodiment, the upper limit value of the output current is determined based on the input power obtained from the input current and the input voltage. However, instead of the input power, the upper limit of the output current is determined based on the input current. A value may be set.
Since the voltage of the commercial AC power supply 1 is generally constant, as shown in FIG. 7, the current value at which the output current decreases as the input current input to the induction heating cooker decreases becomes the output current upper limit value (output current Upper limit value = input current × a + b (a> 0)). Also in this case, similarly to Embodiment 1, the maximum value of the heating power of the small-diameter pan 22c can be suppressed, and the heating density of the small-diameter pan 22c can be suppressed. In this case as well, the output current upper limit value for the medium-diameter pan 22b is set to a current value at which the output current decreases as the input current decreases. Further, the output current upper limit value for the large-diameter pan 22a uses an output current determined by the ratings of the upper and lower switches 7 and 8 of the inverter circuit 6 and the cooling state of the inverter circuit 6. FIG. 7 described above is a diagram showing an output current upper limit value for the size of the pot in the correlation between the input current and the output current of the induction heating cooker according to the first modification of the first embodiment.

  Moreover, you may make it consider the influence of the fluctuation | variation of the input voltage (voltage of the commercial alternating current power supply 1) at the time of inputting fixed electric power. When the input voltage is high, the input current becomes small (for example, when the input power is 900 W, the power factor is 90%, and the input voltage is 200 V, the input current is 5 A, but when the input voltage is 220 V, the input current is about 4. 5A), the higher the input voltage is, the higher the upper limit value of the output current is corrected. For example, the output current upper limit value is set to (output current upper limit value = (input current × a + b) × input voltage / reference input voltage (220 V)), or (output current upper limit value = (input current × a + b) + ΔV × c. -By using one of the equations (ΔV = input voltage−reference input voltage, c> 0)), it is possible to suppress the variation in the heating density due to the increase in the input voltage.

Further, the upper limit value of the output current may be determined based on the output power of the inverter circuit 6 instead of the input power and input current of the induction heating cooker.
For example, as shown in FIG. 8, the output voltage detection means 23 for detecting the output voltage of the inverter circuit 6 (voltage applied to the load circuit 15), the output current detected by the output current detection means 12, and the output voltage detection means 23 Is provided with a multiplication circuit 24 (output power detection means) for calculating the output power of the inverter circuit 6 from the output voltage detected by the above. As shown in FIG. 9, the current value at which the output current decreases as the output power calculated by the multiplication circuit 24 decreases is set as the output current upper limit value. Also in this case, similarly to Embodiment 1, the maximum value of the heating power of the small-diameter pan 22c can be suppressed, and the heating density of the small-diameter pan 22c can be suppressed. 8 is a diagram illustrating a circuit configuration of the induction heating cooker according to the second modification of the first embodiment, and FIG. 9 illustrates output power and output current of the induction heating cooker according to the second modification of the first embodiment. It is a figure which shows the output current upper limit with respect to the magnitude | size of the pan in the correlation.

Embodiment 2. FIG.
In the second embodiment, the drive frequency of the inverter circuit 6 is selected from the material of the pan (small diameter pan), and the upper limit value of the output current (first output current upper limit) is obtained from the input power obtained by driving at the selected drive frequency. Value).
FIG. 10 is a flowchart showing the heating control operation of the control circuit in the induction heating cooker according to the second embodiment, and FIG. 11 is an appropriate heating capable of heating at the start of heating in the control circuit in the induction heating cooker of FIG. The figure which shows the relationship between the input current at the time of the output of the predetermined drive signal used for determination whether it is a pan, and an output current, FIG. 12 shows an example of the drive signal of the inverter circuit of the induction heating cooking appliance which concerns on Embodiment 2. FIG. Waveform diagram, FIG. 13 is a diagram showing an output current upper limit value for a small diameter pan of magnetic SUS in the correlation between the input current and the output current when the drive frequency f1 is output in the induction heating cooker according to the second embodiment. 14 is the induction heating cooker according to the second embodiment, and shows the upper limit value of the output current for the SECC small-diameter pan in the correlation between the input current and the output current when the drive frequency f2 is output. FIG. 15 is a diagram showing an output current upper limit value for a non-magnetic SUS small-diameter pan in the correlation between the input current and the output current when the drive frequency f3 is output in the induction heating cooker according to the second embodiment. . In addition, the circuit structure of the induction heating cooking appliance of Embodiment 2 is the same as that of Embodiment 1 shown in FIG.

  Hereinafter, the heating control operation of the control circuit 20 will be described based on the flowchart of FIG. 10 with reference to FIGS. 13 shows the output current and the output current upper limit value for the input power when the inverter circuit 6 is driven at the driving frequency f1 for the small diameter pan 22c of magnetic SUS, and FIG. 14 shows the small diameter pan 22c of SECC. An output current and an output current upper limit value with respect to input power when the inverter circuit 6 is driven at the drive frequency f2 are shown. FIG. 15 shows the output current and the output current upper limit value with respect to the input power when the inverter circuit 6 is driven at the driving frequency f3 for the non-magnetic SUS small-diameter pan 22c.

  First, the control circuit 20 determines whether or not an instruction to start heating has been issued from the operation unit 19 (step 1). For example, when the target heating power is set, the control circuit 20 determines that an instruction to start heating has been issued, and a predetermined drive signal for determining whether or not the pan is appropriate is sent from the drive circuit 11. The drive circuit 11 is controlled so as to be output to the inverter circuit 6. Then, the control circuit 20 reads the input current detected by the input current detection means 13, and also reads the output current detected by the output current detection means 12, and performs an initial load determination process (step 2).

  As shown in FIG. 11, when both the input current and the output current are small, the control circuit 20 determines that a no-load state where the pan is not placed and small items such as a fork and a knife are placed. In addition, when the output current is large or the ratio of the output current to the input current is large, the control circuit 20 determines that an inappropriate pan that is not suitable for induction heating such as an aluminum pan is placed. Further, the control circuit 20 determines that the pan having the input current and the output current within a predetermined range is an appropriate pan with respect to the predetermined driving signal. For example, when the output current is relatively small with respect to the input current, the magnetic SUS pan is determined, and when the output current is relatively large with respect to the input current, the non-magnetic SUS pan is determined. Further, when the output current is positioned approximately in the middle of the input current, it is determined that the SECC pan is used. In addition, the size (large / medium / small) of the pan is also determined from the input current and the output current.

  As a result of the initial load determination, when the control circuit 20 determines that there is no load or an inappropriate pan (step 3), the control circuit 20 determines whether or not the proper pan is confirmed (step 4). If not determined, the control circuit 20 returns to step 2 and repeats the initial load determination process. If the proper pan is not determined, the control circuit 20 stops driving the inverter circuit 6 (step 5) and returns to the initial state. Return to. In addition, as described above, the determination that there is no proper pan is when the state continues for a predetermined period after it is determined that the pan is inappropriate.

  Further, when the control circuit 20 determines that the pot 22 is appropriate as a result of the initial load determination (step 3), the control circuit 20 selects the drive frequency of the inverter circuit 6 based on the material of the proper pot (step 3-1). . For example, the control circuit 20 selects the drive frequency f1 when the pan 22 is magnetic SUS (see FIG. 12A), and controls the drive circuit 11 so that the inverter circuit 6 is driven at the drive frequency f1. (Step 3-2). The control circuit 20 selects the drive frequency f2 when the pan 22 is SECC (see FIG. 12B), and controls the drive circuit 11 so that the inverter circuit 6 is driven at the drive frequency f2 (see FIG. 12B). Step 3-3). Further, the control circuit 20 selects the driving frequency f3 when the pan 22 is nonmagnetic SUS (see FIG. 12C), and controls the driving circuit 11 so that the inverter circuit 6 is driven at the driving frequency f3. (Step 3-4).

  Then, the control circuit 20 reads the input current and the input voltage detected by the input current detection means 13 and the input voltage detection means 14, respectively, and calculates the input power (step 6). Next, as shown in FIGS. 13 to 15, the control circuit 20 calculates the first output current upper limit value from the selected drive frequency and input power (step 7). As described above, the first output current upper limit value is a current value at which the output current decreases as the input power decreases, and is set so that the heating density of the small-diameter pan 22c does not increase. Therefore, the upper limit value of the output current for the same input power is higher than the upper limit value at the driving frequency f1 of the small diameter pan 22c of the magnetic SUS having a large resistance value, and the upper limit value at the driving frequency f3 of the small diameter pan 22c of the nonmagnetic SUS having a small resistance value. Will be higher.

  Thereafter, the control circuit 20 reads the output current detected by the output current detection means 12, and determines whether or not the output current exceeds the obtained output current upper limit value (step 8). When the output current exceeds the output current upper limit value, the control circuit 20 controls the drive circuit 11 so as to reduce the energization time ratio of the upper switch 7 and lowers the output of the inverter circuit 6 (step 11). When the output current is less than or equal to the output current upper limit value, the calculated input power is compared with the target heating power set by the operation unit 19 (step 9).

  When the control circuit 20 determines in step 9 that the calculated input power is smaller, the control circuit 20 controls the drive circuit 11 so that the energization time ratio of the upper switch 7 is large (however, 50% or less), and the inverter circuit 6 (Step 10). Further, when the input power calculated in step 6 is larger than the target heating power, the control circuit 20 controls the drive circuit 11 so that the energization time ratio of the upper switch 7 becomes small, and the output of the inverter circuit 6 is controlled. Lower (step 11). Further, when the calculated input power and the target heating power are substantially equal, the control circuit 20 proceeds to step 12 as it is and determines whether or not a heating end instruction is input from the operation unit 19. If there is no instruction to end heating, the control circuit 20 returns to step 6 and continues control of the heating power. If there is an instruction to end heating, the control circuit 20 stops the control of the drive circuit 11 and stops the output of the inverter circuit 6 ( Step 13), returning to the initial state.

  As described above, in the second embodiment, the current value that decreases as the input power obtained when the inverter circuit 6 is driven at the drive frequency (drive signal) set in accordance with the material of the pot 22 is reduced. The upper limit is set. For this reason, compared with the case where it restrict | limits with the upper limit of the constant current determined by the rated current of the up / down switches 7 and 8 and the cooling state, the output current at the time of heating the small-diameter pan 22c can be suppressed, and the heating of the small-diameter pan 22c An increase in density can be suppressed. Moreover, since the output current at the time of the heating of the small diameter pan 22c is restrict | limited, even if detection of the temperature of the small diameter pan 22c is delayed in time, overheating can be suppressed.

  In the second embodiment, the first output current upper limit value is determined based on the input power obtained according to the drive frequency shown in FIGS. 13 to 15 so that the heating density of the small-diameter pan 22c does not become too high. However, as shown in FIGS. 16 to 18, a constant output current upper limit value determined by the rated current of the upper and lower switches 7 and 8 constituting the inverter circuit 6 and the cooling state of the inverter circuit 6 and the heating coil 16. (Second output current upper limit value) may also be considered.

  FIG. 16 is a diagram showing an output current upper limit value for a small-diameter pan of magnetic SUS in the correlation between the input current and the output current when the drive frequency f1 is output in the induction heating cooker according to the first modification of the second embodiment. FIG. 17 is a diagram showing an output current upper limit value for the SECC small-diameter pan in the correlation between the input current and the output current when the drive frequency f2 is output in the induction heating cooker according to the first modification of the second embodiment. 18 is a diagram illustrating an output current upper limit value for a small-diameter pan of nonmagnetic SUS in the correlation between the input current and the output current when the drive frequency f3 is output in the induction heating cooker according to the first modification of the second embodiment. is there.

  For example, as shown in FIG. 16, the driving frequency f1 (driving frequency less than the first predetermined value) for the magnetic SUS having a large resistance value of the pan 22 is higher than the first output current upper limit value based on the input power. The second output current upper limit value based on the ratings of the lower switches 7 and 8 is increased. On the other hand, as shown in FIG. 18, at the driving frequency f3 (driving frequency equal to or higher than the second predetermined value) for the nonmagnetic SUS having a small resistance value of the small-diameter pan 22c, the first output current upper limit value based on the input power is exceeded. However, the constant second output current upper limit value based on the rated current of the upper / lower switches 7 and 8 is lower. Therefore, when the non-magnetic SUS small-diameter pan 22c is heated at a driving frequency f3 higher than the driving frequency f1, the resistance value is small and the heating density is not high. Therefore, the output current of the inverter circuit 6 is not dependent on the input power. In both cases, overheating does not occur even when the output current upper limit is constant.

  On the contrary, the output current upper limit value is lowered based on the input power in the same manner as the small-diameter pan 22c of the magnetic SUS having a large resistance value with respect to the small-diameter pan 22c of the non-magnetic SUS having a small resistance value (the output shown in FIG. 16). Current upper limit value), the input power becomes smaller (heating is weaker). Therefore, when the drive frequency f3 is higher than the second predetermined frequency, by not performing control to lower the output current upper limit value as the input power decreases, overheating is caused when the small-diameter pan 22c of magnetic SUS is heated. While suppressing, it can avoid that the small diameter pan 22c of nonmagnetic SUS becomes low heating power and cannot be heated.

  Also in the second embodiment, similarly to the first embodiment, even if the first output current upper limit value is decreased as the input current is decreased, the heating density for the small-diameter pan 22c can be suppressed. Moreover, even if it makes a 1st output current upper limit fall so that output electric power becomes small, the heating density with respect to the small diameter pan 22c can be suppressed, and the overheating in the small diameter pan 22c can be suppressed. Further, when the first output current upper limit value is determined based on the input current, similarly to the first embodiment, the same value is obtained by performing correction to increase the first output current upper limit value as the input voltage is higher. The upper limit of the heating power entering the small-diameter pan 22c can be avoided as the input voltage increases with respect to the small-diameter pan 22c.

In the first and second embodiments described above, the half-bridge type is shown as the inverter circuit 6, but a full-bridge type may be used as shown in FIG. FIG. 19 is a diagram illustrating a circuit configuration of an induction heating cooker according to the second modification of the second embodiment.
In FIG. 19, two DC upper / lower switches 7a and 8a and two diodes 9a and 10a connected in reverse parallel to the respective switches 7a and 8a are connected between the DC buses that are the output of the DC power supply circuit 2. Full bridge type from arm A constituted and two arms 9b and 10b connected in reverse parallel to the upper and lower switches 7b and 8b in series and the switches 7b and 8b, respectively. The inverter circuit 6a is configured.

  The output adjustment in the inverter circuit 6a can be performed by adjusting the drive phase difference between the two arms A and B at a constant drive frequency. An example of the drive signal is shown in FIGS. 20 is a waveform diagram showing an example of a drive signal at the time of high output of the inverter circuit in the induction heating cooker of FIG. 19, and FIG. 21 is an example of a drive signal at the time of medium output of the inverter circuit in the induction heating cooker of FIG. FIG. 22 is a waveform diagram showing an example of a drive signal at the time of a small output of the inverter circuit in the induction heating cooker of FIG.

In the case of the full-bridge type inverter circuit 6a, the drive frequency may be selected according to the pan 22 placed, similarly to the half-bridge type inverter circuit 6. For the non-magnetic SUS pan 22 having a small resistance value, a high frequency is selected as the driving frequency, and the non-magnetic SUS small-diameter pan 22c is used as a constant output current upper limit value regardless of the input power (or input current or output power). The heating output of the is avoided to be too small. On the other hand, for the magnetic SUS pan 22 having a large resistance value, a driving frequency lower than that of the nonmagnetic SUS is selected as the driving frequency, and the first output current upper limit value decreases as the input power (or input current or output power) decreases. Is reduced, overheating of the magnetic SUS with respect to the small-diameter pan 22c is suppressed.
Further, as described above, the control of the heating output of the full-bridge type inverter circuit 6a may be performed by adjusting the phase difference between the arms A and B at a constant driving frequency. May be kept constant and the heating output may be controlled by adjusting the driving frequency.

Embodiment 3 FIG.
The third embodiment is an induction heating cooker that adjusts the output by changing the drive frequency of the inverter circuit 6.
FIG. 23 is a diagram illustrating a circuit configuration of an induction heating cooker according to Embodiment 3, FIG. 24 is a waveform diagram illustrating an example of a drive signal of an inverter circuit of the induction heating cooker according to Embodiment 3, and FIG. 23 shows an output current upper limit value for the pan in the correlation between the input power and the output current when the drive frequency f is equal to or higher than the predetermined frequency fa (second predetermined value) in FIG. FIG. 27 shows the output current upper limit value for the pan in the correlation between the input power and the output current when the drive frequency f is less than the predetermined frequency fb (first predetermined value) in FIG. In an induction heating cooker, it is a figure which shows the output current upper limit with respect to the pan in the correlation of input electric power and output current when the drive frequency f is more than the predetermined frequency fb and less than the predetermined frequency fa.

The circuit configuration of FIG. 23 is the same as that of the circuit of FIG. 1 shown in Embodiment 1 except that there is no clamp diode. Moreover, about the operation | movement of the heating control of the control circuit 20 in the induction heating cooking appliance which concerns on Embodiment 3, it is the same as that of the flowchart of FIG.
As described above, the load circuit 15 according to the third embodiment includes only the series circuit of the heating coil 16 and the resonance capacitor 17. Therefore, the conduction time of any of the upper switch 7 and the lower switch 8 constituting the inverter circuit 6 is driven within a range not exceeding 1/2 of the resonance period of the heating coil 16 and the resonance capacitor 17. As shown in FIGS. 24 (a), (b), and (c), the drive signal alternately turns on and off the upper switch 7 and the lower switch 8 at a frequency higher than the resonance frequency of the load circuit 15. A high frequency voltage is applied to the circuit 15, but the drive signal (a) close to the resonance frequency has a higher output, (b) has a medium output, and (c) has a lower output.

  The output control of the inverter circuit 6 of the induction heating cooker according to the third embodiment is performed by adjusting the drive frequency of the inverter circuit 6. In addition, when the drive frequency f is in a range equal to or higher than a predetermined frequency (fa: second predetermined value), as shown in FIG. 25, it is equal to or lower than a certain output current upper limit value regardless of input power (or input current or output power). The heating is controlled within the range. The upper limit value of the output current is a value set in consideration of the rated current and cooling of the upper switch 7 and the lower switch 8 of the inverter circuit 6.

  On the other hand, when the drive frequency f of the inverter circuit 6 is less than the predetermined frequency fb (fb <fa), as shown in FIG. 26, the current value at which the output current decreases as the input power (or input current or output power) decreases. Is the upper limit of output current. Note that this output current upper limit value may be set to be equal to or less than a certain output current upper limit value in consideration of the rated current and cooling of the upper switch 7 and the lower switch 8 of the inverter circuit 6. In addition, as shown in FIG. 27, the output current upper limit value may be set approximately in the middle of the output current upper limit values shown in FIGS.

  In the third embodiment, when the output current upper limit value is determined based on the input current, the same correction is made by increasing the output current upper limit value as the input voltage is higher, as in the first embodiment. The upper limit of the heating power entering the small-diameter pan 22c can be avoided as the input voltage increases with respect to the small-diameter pan 22c.

  As described above, in the third embodiment, when the drive frequency f of the inverter circuit 6 is equal to or higher than the predetermined frequency fa (second predetermined value), heating control is performed with the output current upper limit value being constant, and the drive frequency f is predetermined. In a range lower than the frequency fb (first predetermined value), the output current upper limit value is lowered and the output control is performed as the input power is reduced. Therefore, the low-resistance non-magnetic element driven only in the range of the high drive frequency f is used. An induction heating cooker that can suppress overheating of the magnetic small-diameter pan 22c while avoiding further suppression of the heating output of the small-diameter pan 22c can be obtained.

  1 commercial AC power supply, 2 DC power supply circuit, 3 rectifier diode bridge, 4 reactor, 5 smoothing capacitor, 6 inverter circuit, 7 upper switch, 8 lower switch, 9, 10 diode, 11, 11a, 11b drive circuit, 12 output current Detection means, 13 Input current detection means, 14 Input voltage detection means, 15 Load circuit, 16 Heating coil, 17 Resonance capacitor, 18 Clamp diode, 19 Operation unit, 20 Control circuit, 21 Top plate, 22 Pan, 23 Output voltage detection Means, 24 multiplication circuit, A and B arms.

Claims (7)

A heating coil to heat the pan on the top plate;
An inverter circuit for supplying a high-frequency current to the heating coil;
Output current detecting means for detecting an output current from the inverter circuit;
Output power detection means for detecting output power from the inverter circuit;
Control means for controlling the inverter circuit based on the detection results of the output current detection means and the output power detection means,
The control means determines a first output current upper limit value in which the output current decreases as the output power decreases from the output power, and the output current is the first output current upper limit value when the pan is suitable for heating. induction heating cooker according to claim and Turkey controls the inverter circuit so as not to exceed the. A heating coil to heat the pan on the top plate;
An inverter circuit for supplying a high-frequency current to the heating coil;
Input power detection means for detecting input power from an AC power supply;
Output current detecting means for detecting an output current from the inverter circuit;
Control means for controlling the inverter circuit based on detection results of the input power detection means and the output current detection means,
The control means determines a first output current upper limit value in which the output current decreases as the input power decreases from the input power, and the output current is the first output current upper limit value when the pan is suitable for heating. induction heating cooker according to claim and Turkey controls the inverter circuit so as not to exceed the. A heating coil to heat the pan on the top plate;
An inverter circuit for supplying a high-frequency current to the heating coil;
An input current detecting means for detecting an input current from an AC power supply;
Output current detecting means for detecting an output current from the inverter circuit;
Control means for controlling the inverter circuit based on detection results of the input current detection means and the output current detection means,
The control means determines a first output current upper limit value that lowers the output current as the input current becomes smaller than the input current, and the output current is the first output current upper limit value when the pan is suitable for heating. induction heating cooker according to claim and Turkey controls the inverter circuit so as not to exceed the. Provide input voltage detection means to detect the input voltage from the AC power supply,
The induction heating cooker according to any one of claims 1 to 3 , wherein the control unit corrects the first output current upper limit value to be higher as the detection voltage of the input voltage detection unit is higher. . A second output current upper limit value determined from at least the rated current of the inverter circuit is set, and the control means outputs any one of the first output current upper limit value and the second output current upper limit value. The induction heating cooker according to any one of claims 1 to 4 , wherein the inverter circuit is controlled so as not to exceed a current upper limit value. The control means selects the drive frequency of the inverter circuit from the material when determining the material of the pan, and adjusts the heating output by controlling the energization ratio or phase difference of the inverter circuit with the selected drive frequency. In addition, when the selected drive frequency is less than the first predetermined value, the inverter circuit is controlled so that the output current does not exceed the first output current upper limit value, and the selected drive frequency is the first drive frequency. The induction heating cooker according to claim 5 , wherein the inverter circuit is controlled so that the output current does not exceed the second output current upper limit value when the output current is equal to or higher than a second predetermined value higher than a predetermined value. The control means controls the drive frequency of the inverter circuit to adjust the heating output, and when the drive frequency is less than a first predetermined value, the output current does not exceed the first output current upper limit value. And controlling the inverter circuit so that the output current does not exceed the second output current upper limit when the drive frequency is equal to or higher than a second predetermined value higher than the first predetermined value. The induction heating cooker according to claim 5 , wherein the induction heating cooker is used.

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