JP5506547B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker that heats a cooking container by supplying a high-frequency current to a heating coil.

In a conventional induction heating cooker, when the input set value is below a predetermined value, a heating operation period in which the switching means of the inverter circuit repeats an on / off operation and a heating pause period in which the on / off operation is paused are set. The first control means for controlling the ratio of the length of the heating operation period and the heating pause period according to the input set value, and the load for detecting the load state by comparing the power set current with the input set value There is one provided with a detection means and a second control means for controlling the ON time of the switching means to a value corresponding to the frequency at the time of load detection when the input set value is equal to or less than the value at the time of load detection (for example, Patent Document 1). Even when the input set value is low, the oscillation frequency of the switching means can be set to a value corresponding to the frequency at the time of load detection, so the noise bandwidth can be narrowed and noise can be reduced. Moreover, the power loss of the switching means can be reduced.
However, when the input set value is low, the heating operation period and the heating pause period are repeated, so that a sound is generated from the pan as the object to be heated at the time of switching, which is harsh.

Japanese Patent Laid-Open No. 2-148685

  The present invention has been made to solve the above-described problems, and at the time of switching between the heating operation period and the heating pause period in the induction heating cooker that alternately repeats the heating operation and the heating pause at the time of low heating output. In addition to suppressing the noise generated in the pan, it can prevent the overcurrent from flowing in the inverter circuit even when the pan is moved or replaced during the heating pause period, and can accurately detect that there is no pan The purpose is to obtain.

In order to achieve the above object, an induction heating cooker according to the present invention includes a heating coil that is magnetically coupled to an object to be heated such as a pan, an inverter circuit that causes a high-frequency current to flow through the heating coil, and a drive signal to the inverter circuit. An inverter drive circuit that outputs power, power detection means for detecting input power to the inverter circuit or output power from the inverter circuit, and operation input means for setting heating power and the like for heating the object to be heated , An output current detection means for detecting an output current from the inverter circuit, and a control means for controlling the inverter drive circuit, wherein the control means is set to a heating power less than a predetermined power by the operation input means The heating operation period for outputting predetermined power from the inverter circuit and the heating pause period for stopping output alternately. An intermittent heating mode for operating the inverter circuit so as to repeat is executed, and in the intermittent heating mode, at the end of the heating operation period, a drive signal for gradually decreasing the output of the inverter circuit is output and then the output is stopped. And at the start of the heating operation period, the inverter drive circuit is feedback-controlled to output a predetermined power after outputting a drive signal for gradually increasing the output from the inverter drive circuit to the inverter circuit from a low output , At the end of the heating operation period, the control means stores drive signal information to be output from the inverter drive circuit to the inverter circuit before outputting a drive signal for gradually decreasing the output of the inverter circuit, and the heating operation At the start of the period, from the inverter drive circuit Serial is obtained by the output of the inverter circuit so as to output a driving signal according to the stored drive signal information after gradually to output the drive signal to increase from a low output.

  The induction heating cooker according to the present invention has the above-described configuration, and when the control means is in the intermittent heating mode, at the end of the heating operation period, after the drive signal for gradually reducing the output of the inverter circuit is output, the output is stopped and the heating is stopped. At the start of the operation period, the inverter drive circuit is feedback-controlled so that a predetermined power is output after outputting a drive signal that gradually increases the output from the inverter drive circuit to the inverter circuit from a low output. The sound generated in the pan when the heating pause period is switched can be suppressed.

It is a circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 1 and 2 of this invention. It is a figure which shows the example of the drive signal output to the upper switch 8 and the lower switch 9 of the inverter circuit 3 from the inverter drive circuit 18 of the induction heating cooking appliance concerning Embodiment 1 and 2 of this invention. It is a figure which shows the electricity supply pattern at the time of the low heating output of the induction heating cooking appliance which concerns on Embodiment 1 and 2 of this invention. Input current and output current for determining whether or not an appropriate pan suitable for heating is placed above the heating coil 13 at the start of heating of the induction heating cooker according to Embodiments 1 and 2 of the present invention. It is a figure which shows the relationship. The relationship between the drive signal and input power (or input current) for determining whether the appropriate pan is mounted during the heating operation of the induction heating cooking appliance which concerns on Embodiment 1 and 2 of this invention is shown. FIG. It is a flowchart which shows the whole heating control process in the control means of the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a flowchart which shows the continuous operation control process in the control means of the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a flowchart which shows the intermittent heating control process in the control means of the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a time chart which shows the example of a fluctuation | variation of the heating electric power in the intermittent heating mode of the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a figure which shows the relationship between the input current and output current for determining whether the appropriate pan is mounted during the heating operation of the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a flowchart which shows the whole heating control process in the control means of the induction heating cooking appliance which concerns on Embodiment 2 of this invention. It is a flowchart which shows the intermittent heating control process in the control means of the induction heating cooking appliance which concerns on Embodiment 2 of this invention.

Embodiment 1 FIG.
FIG. 1 is a circuit configuration diagram of an induction heating cooker according to Embodiment 1 of the present invention.
In FIG. 1, the induction heating cooker includes a commercial AC power supply 1, a DC power supply circuit 2, an inverter circuit 3, and a load circuit 4. The 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 connected to a DC bus and is supplied to the inverter circuit 3. The inverter circuit 3 includes switching elements 8 and 9 connected in series (hereinafter, the high potential side switching element 8 is referred to as an upper switch and the low potential side switching element 9 is referred to as a lower switch), and the switching elements 8 and 9 respectively. The diodes 10 and 11 connected in anti-parallel and the snubber capacitor 12 connected in parallel with at least one of the switching elements are provided. By alternately turning on and off the switching elements 8 and 9, the connection point and the DC bus A high frequency voltage is generated between one end and supplied to the load circuit 4. The load circuit 4 is composed of a series circuit of a heating coil 13 and its resonant capacitor 14, and a magnetic flux generated by a high frequency current flowing through the heating coil 13 induces an eddy current in a pan (not shown) placed above the heating coil. Heat. The output current detection means 15 detects the current flowing through the load circuit 4, and the input current detection means 16 detects the input current from the commercial AC power source 1 to the diode bridge circuit 5, and the input voltage The detecting means 17 detects the output voltage of the diode bridge circuit 5. The input current detection means 16 and the input voltage detection means 17 constitute a power detection means. The inverter drive circuit 18 sends a drive signal to the switching elements 8 and 9 of the inverter circuit 3, the operation input means 19 sets heating power and heating start / stop, and the control means 20 cooks. The no-load detecting means 21 is a load to be heated from the output current or input current detected by the output current detecting means 15 or the input current detecting means 16 in the control means 20 ( The drive signal information storage means 22 temporarily stores the frequency information of the drive signal.

  FIG. 2 is a diagram illustrating an example of drive signals output from the inverter drive circuit 18 of the induction heating cooker according to the first embodiment of the present invention to the upper switch 8 and the lower switch 9 of the inverter circuit 3, and FIG. The upper switch 8 and the lower switch 9 of the inverter circuit 3 are alternately turned on and off at a frequency higher than the resonance frequency of the four heating coils 13 and the resonance capacitor 14 thereof. As shown in the figure, when shifting from the ON state of one switch to the ON state of the other switch, there is a dead time period in which both switches are in the OFF state. The heating output is controlled by changing the frequency of the drive signal to the inverter circuit 3. Of the drive signals (a) to (c), the lowest frequency (b) is the high output drive signal and the highest frequency. (c) is a low output drive signal.

  FIG. 3 is a diagram showing an energization pattern at the time of low heating output of the induction heating cooker according to Embodiment 1 of the present invention. In the figure, 400 W output is continuous heating, and intermittent heating is performed at 100 W to 300 W output. 300W output repeats heating operation period 1.5 seconds (400W output) and heating pause period 0.5 second, 200W output repeats heating operation period 1 second (400W output) and heating pause period 1 second, 100W output heats The operation period is 1 second (400 W output) and the heating pause period is 3 seconds. When the heating output control is performed using the drive signal shown in FIG. 2 in the circuit configuration shown in FIG. 1, the output adjustment range is limited due to an increase in loss in the switching elements 8 and 9 of the inverter circuit 3. . In particular, since driving is performed at a high frequency when the heating output is low, the switching loss is increased and the heating efficiency is greatly reduced. Therefore, by performing the low heating output by operating intermittently, the heating output in the heating operation period of the intermittent heating is set to a predetermined power (400 W in the present embodiment), thereby suppressing an increase in switching loss. A wide output adjustment range is secured. Here, it is preferable that the repetition period of the heating operation period and the heating pause period is short because the temperature fluctuation of the object to be heated (pan) is small and it is difficult to cause scorching, but if the heating operation period is extremely short, the cycle of the commercial power supply voltage is desirable. Due to fluctuations and detection delay of the input current detection means 16 and the like, it becomes difficult to control to a predetermined power (400 W in this embodiment) by power feedback control, or to determine a no-load state It becomes difficult. In the present embodiment, the heating power 200W to 300W suppresses the temperature fluctuation by setting the repetition cycle to 2 seconds, and the heating power 100W sets the heating operation time 1 second (repetition cycle 4 seconds) to achieve stable power output and no-load detection. It is possible. Note that the lower limit value of the heating operation time is not limited to 1 second, and is set in consideration of responsiveness of the input current detection means and the like.

  FIG. 4 shows an input current for determining whether or not an appropriate pan suitable for heating is placed above the heating coil 13 at the start of heating of the induction heating cooker according to the first embodiment of the present invention. It is a figure which shows the relationship of an output current. The control means 20 controls the inverter drive circuit 18 at the start of heating and outputs a predetermined drive signal to the inverter circuit 3, and in that state, the input current detection means 16, the input voltage detection means 17, and the output current detection means 15 respectively. A low-impedance load made of aluminum or the like is placed using the detected input current, input voltage, and output current values, or a no-load state in which nothing is placed or a fork, spoon, etc. It is determined whether an accessory is placed or a proper pan suitable for heating is placed. Compared to the case where a pan suitable for heating is placed, the output current increases when a pan of low impedance such as an aluminum pan is placed, and there is no load or small items such as knives and forks Output current and input current are reduced. It is assumed that the relationship between the input current and the output current for determining the proper pan shown in FIG. 4 is provided for each level of the detected input voltage (for example, for 185 V or less, for 185 V to 195 V, for 195 V to 205 V, 205 V to 215 V For 215V, etc.).

  FIG. 5 shows the relationship between the drive signal and input power (or input current) for determining whether or not the proper pan is placed during the heating operation of the induction heating cooker according to Embodiment 1 of the present invention. FIG. Using this relationship, the control means 20 is in a state in which the pan placed above the heating coil 13 should be continuously heated during the heating operation, or in a state where the heating operation should be stopped due to movement or the like. It is judged whether or not.

  In the no-load state in which the pan is removed, the induced eddy current does not flow through the pan and power is not consumed, so the input power is smaller than when the pan is placed. Therefore, a threshold is provided according to the drive signal, and a state where the pan is placed and a state where there is no pan are discriminated. In the low heating power state where the heating power is low, the input power is small even when the pan is placed, so the difference from the input power in the no-load state is small, especially when a small-diameter pan is placed and no load It becomes difficult to determine the state. In the present embodiment, the intermittent heating operation is performed in the low heating power state, and the heating power during the heating operation period is set to a predetermined power (400 W), so that the pan is placed and the no-load state. The difference in input power is set to a predetermined value or more, and the heating operation period is secured for a predetermined time (1 second), so that the state where the pan is placed and the no-load state can be reliably determined. If correction is made according to the input voltage, the accuracy of determination is improved.

  Next, the heating control process in the control means 20 of the induction heating cooker according to the present embodiment will be described using the flowcharts shown in FIGS. FIG. 6 is a flowchart showing the entire heating control process in the control means of the induction heating cooker according to the first embodiment of the present invention, and FIGS. 7 and 8 are respectively the induction heating cooking according to the first embodiment of the present invention. It is the flowchart which shows the continuous operation control process in the control means of a container, and the flowchart which shows an intermittent heating control process.

  In FIG. 6, first, the control means 20 determines whether or not a heating start request such as setting of a heating power to be heated is input from the operation input means 19 (step 1), and when there is a heating start request, the inverter is driven. The circuit 18 is controlled to start outputting predetermined drive signals to the upper switch 8 and the lower switch 9 of the inverter circuit 3 (step 2). And the control means 20 acquires the output current, the input current, and the input voltage detected by the output current detection means 15, the input current detection means 16, and the input voltage detection means 17, and the detected value and the heating shown in FIG. It is determined whether or not the proper pan is placed using the relationship of the load determination at the start (step 3). As a result, if the proper pan is not placed, the control means 20 stops the drive signal to the inverter circuit 3 (step 4) and returns to step 1. In addition, when the proper pan is placed in Step 3, the control means 20 continues the heating operation, but the thermal power control state is a transient state, and the state of the presence or absence of the pan cannot be accurately determined. Since there is a possibility, the control means 20 sets a no-load non-detection state in which it is not determined whether or not there is no pan (step 5), and starts by setting a predetermined time in a no-load non-detection timer (step 6). ). Next, the control unit 20 acquires the output current, the input current, and the input voltage detected by each of the output current detection unit 15, the input current detection unit 16, and the input voltage detection unit 17, and the acquired input current and input. Input power (detected power) is calculated from the voltage (step 7). Thereafter, the control means 20 determines whether it is a no-load detection state or a no-load non-detection state (step 8), and if it is a no-load non-detection state, determines whether the no-load non-detection timer has expired ( Step 9). If the no-load detection state is detected in step 8 or if the no-load non-detection timer has timed out in step 9, the control means 20 uses the drive signal and input power (or input power) shown in FIG. Using the relationship with the current, it is determined whether the proper pan is placed, the no-load state where the pan is removed, or the like (step 10), and the process branches depending on the result (step 11). In the case of a no-load state where the proper pan is not placed, the control means 20 stops the drive signal output from the inverter drive circuit 18 to the inverter circuit 3 (step 12) and returns to step 2 The initial load detection process at the start of heating is performed.

  If the proper pan is placed in step 11, the process proceeds to step 13. Further, if the no-load non-detection timer has not timed out in step 9, the inverter circuit 3 is in a transient heating output control state, and there is a possibility that the presence / absence of the pan cannot be accurately determined. The means 20 proceeds to step 13 without performing the no-load discrimination process.

  In step 13, the control means 20 determines whether or not the heating power set by the operation input means 19 is equal to or greater than a predetermined heating power, and executes the continuous heating control process shown in FIG. Step 14) and the process proceeds to Step 16. If the set thermal power is less than the predetermined thermal power in step 13, the control means 20 executes the intermittent heating control process shown in FIG. 8 (step 15), and proceeds to step 16.

  In step 16, the control means 20 determines whether or not the heating power set by the operation input means 19 has been changed. If there is no change, the control means 20 returns to step 7 and continues the power control process. If there is a change in the set thermal power in step 16, the control means 20 determines whether or not the change in the set thermal power is a heating stop (step 17), and if it is a heating stop, the inverter drive circuit 18 to the inverter circuit. 3 is stopped (step 18), the process returns to step 1 and waits for a heating start request to be input from the operation input means 19. If the heating is not stopped in step 17 but the heating power setting is changed to another thermal power setting, the thermal power control state becomes a transitional state, and there is a possibility that the presence / absence of the pan cannot be accurately determined. Is set to a no-load non-detection state in which it is not determined whether or not there is a panless state (step 19), a predetermined value is set in a no-load non-detection timer (step 20), and the process returns to step 7 and heating power feedback Continue control.

Next, the continuous heating control process of step 14 will be described based on the flowchart of FIG.
First, the control means 20 determines whether or not the output current detected by the output current detection means 15 in step 7 (FIG. 6) exceeds a predetermined threshold (step 101). When the output current is large, the temperature of the switching elements 8 and 9 of the inverter circuit 3 may increase, which may cause a failure. Therefore, when the output current is larger than the threshold value, the control means 20 Control to reduce the inverter output, such as increasing the frequency of the drive signal (step 102), set to a no-load detection state for determining whether there is no pan (step 103), continuous operation control processing Exit. In step 102, the detected value of the output current exceeds the threshold value, and the detected values in the output current detecting means 15, the input current detecting means 16, and the input voltage detecting means 17 are considered to be sufficiently large. Even if you set the no-load detection state and execute the no-load discrimination process, there is little possibility of misjudging that there is no pan even though the proper pan is placed, and the value of the no-load non-detection timer Regardless, since it sets to the state which performs a no-load discrimination | determination process, the quickness and certainty of a panless detection can be improved.

  If the output current does not exceed the threshold value in step 101, the control means 20 compares the detected power calculated in step 7 with the set power corresponding to the thermal power set by the operation input means (step 104), and the detected power If it is larger, a no-load detection state for determining whether there is no pan is set (step 105). Next, the control means 20 determines whether or not the drive signal is an adjustable lower limit (frequency upper limit) (step 106). If the drive signal is not the lower limit, the control means 20 adjusts the drive signal so as to reduce the inverter output (the drive frequency is increased). (Step 107), and the continuous operation control process ends. Further, when the detected power and the set power are substantially equal in step 104, the control means 20 is set to a no-load detection state for performing a determination process as to whether or not there is a panless state (step 108). The operation control process is terminated. When the detected power is approximately equal to or greater than the set power, the values detected by the output current detecting means 15, the input current detecting means 16, and the input voltage detecting means 17 have already increased, so that the no-load detection state is entered. Even if it is set and no-load discrimination processing is executed, the detected power exceeds the threshold value for discriminating the loaded / unloaded state shown in FIG. 5 and no load is loaded even though the pan is placed. In addition, since it is set to the no-load detection state regardless of the value of the no-load non-detection timer, it is possible to improve the quickness and certainty of the no-pan detection.

  In step 104, if the detected power is smaller than the set power, it is necessary to increase the input power. Therefore, the control means 20 first determines whether or not the drive signal is an adjustable upper limit (frequency lower limit) (step 109), and if it is not the upper limit, the drive frequency is lowered so as to increase the inverter output (step 110). ), The continuous operation control process is terminated. In step 109, when the drive signal is an adjustable upper limit, the control means 20 is set to a no-load detection state for determining whether or not there is no pan (step 111), and a continuous operation control process is performed. Exit. The state where the drive signal is at the upper limit is a heating state in which the input power can be maximized, and there is a large difference in input power between the no-load state and the loaded state, so that the no-load state can be easily determined. By setting to the no-load detection state in step 111 which is such a state, the reliability of detection of no pan can be improved.

Next, the intermittent heating control process in step 15 of FIG. 6 will be described using the flowchart of FIG.
The control means 20 first determines whether the heating operation period of intermittent heating or the heating pause period is in effect (step 201), and if it is in the heating pause period, it determines the drive state of the inverter circuit 3 (step 202). If the inverter circuit 3 is already stopped, the control means 20 ends the intermittent heating control process. If the inverter circuit 3 is heating, it is the time when the heating operation period ends, and therefore the control means 20 stores the information of the drive signal being output in the drive signal information storage means 22 (step 203). Then, a no-load non-detection state in which it is not determined whether or not there is no pan is set (step 204), and a no-load non-detection timer is set (step 205) so that no-load determination processing is not executed. Then, the control means 20 sets the inverter drive state to the stop transition state (step 206), and proceeds to step 207.

  If it is determined in step 202 that the inverter drive state is in the stop transition, the process proceeds to step 207 and the control means 20 determines whether or not the drive signal has reached a level at which the drive is stopped. The control means 20 adjusts the level of the drive signal by controlling the drive frequency. If the drive signal level has not reached the stop level, the drive frequency is increased so as to decrease the inverter output (step 208), and intermittently. The heating control process ends. If the drive signal has reached the level at which the drive is stopped in step 207, the control means 20 stops the drive signal output from the inverter drive circuit 18 to the inverter circuit 3 (step 209), and changes the inverter drive state. The stopped state is set (step 210), and the intermittent heating control process is terminated.

  If it is determined in step 201 that the heating period is intermittent heating, the control unit 20 determines the inverter drive state in step 211. As a result, when the inverter circuit 3 is stopped, it is the time when the heating pause period ends, so the control means 20 starts outputting a high-frequency drive signal at which the inverter circuit 3 has a low output (step 212). The inverter drive state is set to a starting state (step 213), and the intermittent heating control process is terminated.

  If the inverter drive state is being activated in step 211, the control means 20 determines whether the detected output current is less than a threshold value for protection of the inverter circuit 3 (step 214). For example, the frequency of the drive signal output from the inverter drive circuit 18 to the inverter circuit 3 is compared with the drive frequency based on the information stored in the drive signal information storage means 22 (step 215). Is a high frequency (the drive output level is low), the drive frequency during the output is compared with a predetermined frequency (a predetermined frequency so that the output current does not become excessive) (step 216). As a result, when the output drive frequency is higher, the control means 20 sets the detection power calculated in step 7 and a predetermined power (for example, a setting corresponding to the heating power set by the operation input means 19). (Step 217), the frequency of the drive signal to the inverter circuit 3 is lowered so that the output increases if the detected power does not reach the set power (step 218), and the intermittent heating control process is terminated. . The control means 20 performs a small adjustment so that the output of the drive signal in step 218 does not increase the inverter output too rapidly.

  When the output current exceeds the threshold value in step 214, the control means 20 sets the inverter driving state to the heating state (step 221) to end the intermittent heating start-up state, and proceeds to step 223. . Further, when the driving frequency being output in step 215 is equal to or lower than the driving frequency based on the information stored in the driving signal information storage unit 22 (when the driving signal level is equal to or higher than the stored driving signal level), If the drive frequency being output in step 216 is equal to or lower than a predetermined frequency (a frequency determined in advance so that the output current does not become excessive) (when the drive signal level is equal to or higher than a predetermined drive signal level); If the detected power is greater than or equal to the predetermined power in step 217, the control means 20 ends the starting state of intermittent heating. Next, the control means 20 sets the inverter drive state to the heating state (step 219), starts the no-load non-detection timer (step 220), and proceeds to step 225.

  If the inverter drive state is heating in step 211, the control means 20 compares the detected output current with a threshold value for protection of the inverter circuit 3 (step 222). As a result, when the output current exceeds the threshold value, the control means 20 increases the drive frequency to the inverter circuit 3 so as to suppress the output current (step 223), and determines whether or not there is a panless state. A no-load detection state in which the process is performed is set (step 224), and the intermittent heating control process is terminated. If the detected value of the output current exceeds the threshold value in step 222, it is considered that the detected values in the output current detecting means 15, the input current detecting means 16, and the input voltage detecting means 17 have already become sufficiently large. Therefore, even if the no-load detection state is set, there is little possibility of misjudgment that there is no pan even though the proper pan is placed, and no-load detection state regardless of the value of the no-load non-detection timer Therefore, the quickness and certainty of the detection without pan can be improved.

  If the output current is equal to or smaller than the threshold value in step 222, the control means 20 compares the detected power calculated in step 7 with the set power corresponding to the heating power set in the operation input means 19 (step 225). If the detected electric power is larger, it is set to a no-load detection state in which a process for determining whether or not there is a panless state is performed (step 226). Next, the control means 20 determines whether or not the drive signal is an adjustable lower limit (frequency upper limit) (step 227). If it is not the lower limit, the drive frequency is increased so as to decrease the inverter output (step 228). The intermittent heating control process is terminated. When the drive signal reaches an adjustable lower limit in step 227, the control means 20 ends the intermittent heating control process. Further, when the detected power and the set power are substantially equal in step 225, the control means 20 is set to a no-load detection state for performing a determination process as to whether or not there is a panless state (step 229), and intermittently. The heating control process ends. When the detected power is substantially equal to or higher than the set power, the value detected by the input current detection means 16 and the like has already increased, so even if the no-load detection state is set, the no-load state shown in FIG. It is less than the threshold value to be determined, and there is little possibility of misjudging that the pan is placed but no load, and it is possible to reliably detect no pan.

  In step 225, if the detected power is smaller than the set power, it is necessary to increase the input power. Therefore, the control means 20 first determines whether or not the drive signal is at the upper limit (adjustable lower limit frequency at which the drive signal frequency is adjustable) (step 230). If it is not the upper limit, the control means 20 lowers the frequency of the drive signal so as to increase the output of the inverter circuit 3 (step 231), and ends the intermittent heating control process. In step 230, if the frequency of the drive signal is an adjustable lower limit frequency, the control means 20 is set to a no-load detection state for determining whether or not there is a panless state (step 232). Then, the intermittent heating control process ends. The state where the drive signal is at the upper limit is a heating state in which the input power can be maximized, and there is a large difference in input power between the no-load state and the loaded state, so that the no-load state can be easily determined. If no-load detection is performed in such a state, reliable detection without a pan can be performed.

  FIG. 9 is a time chart showing a variation example of the heating power in the intermittent heating operation of the induction heating cooker according to Embodiment 1 of the present invention. A predetermined heating operation period and a heating pause period are alternately repeated according to the set thermal power. The control means 20 controls the inverter drive circuit 18 so as to have a predetermined heating power (400 W in the present embodiment) during the heating operation period, and the inverter circuit so as to smoothly reduce the heating output when the heating operation period ends. After the drive signal to 3 is gradually increased in frequency, the drive signal output is stopped (soft stop). When the heating pause period ends, the control means 20 gradually lowers the drive signal from the low output drive signal having a predetermined high frequency to a predetermined heating power (400 W) (soft start). As described above, when heating is stopped, the heating power is smoothly reduced and then stopped (soft stop), and when heating is started, the heating power is increased smoothly from the low heating output state (soft start). And the sound generated from the pan at the start of heating can be suppressed. In the case of performing no-load detection, the control means 20 detects the state of the drive signal to the inverter circuit 3, the detected value of the input current or the output current after the elapse of a predetermined time from the restart of the output of the inverter circuit 3. The no-load detection is started in accordance with the state, so that the no-load state can be detected quickly while suppressing erroneous detection.

  In the above-described embodiment, the example in which the output power of the inverter circuit 3 is controlled by changing the drive frequency has been described. However, the present invention is not limited to this. For example, it may be performed by changing the conduction ratio (duty) of the upper switch and the lower switch of the inverter circuit 3.

  Further, in the above embodiment, no-load detection during heating is determined from the relationship between the drive signal and input power shown in FIG. 5, but the output current and input current flowing through the heating coil 13 as shown in FIG. It is also possible to discriminate using this relationship. When a high-frequency current flows through the heating coil 13, an induced eddy current flows through the pan magnetically coupled to the heating coil 13 and power is consumed, and the input current increases accordingly. In a no-load state without a magnetically coupled load, even if a high-frequency current flows through the heating coil, power consumption does not occur in the pan, so the input current is small, and even when small items such as spoons are placed, the power consumption is small. Therefore, the input current is not so large. In addition, when a large-diameter pan made of nonmagnetic material is placed, an excessive output current may flow due to a sudden change in load impedance due to a pan shake or the like. In such a case, the drive of the inverter circuit 3 is stopped. By controlling using the relationship between the input current and the output current during the heating operation as described above, it is possible to detect the no-load state and prevent the inverter circuit 3 from being driven while preventing the overcurrent from flowing through the inverter circuit 3. By stopping, it is possible to obtain an induction heating cooker that protects the inverter circuit 3 and consumes unnecessary electric power for heating and quickly stops the emission of unnecessary electromagnetic waves.

  As described above, in the induction heating cooker according to the present embodiment, low-power heating is intermittently performed while suppressing the generation of pan noise, and even if there is a pan replacement or the like, an overcurrent is generated in the inverter circuit 3. In addition to being able to prevent flow, it is possible to detect and stop a no-load state quickly and reliably, thereby suppressing wasteful power consumption and unnecessary electromagnetic wave emission.

Embodiment 2. FIG.
1 to 5 are also used in the second embodiment.
11 and 12 are a flowchart showing the entire heating control process in the control means of the induction heating cooker according to the second embodiment of the present invention, and a flowchart showing the intermittent heating control process. The circuit configuration of the induction heating cooker according to the present embodiment, the flowchart of the continuous heating control process in the control means 20, and the like are the same as those in the first embodiment, and will be omitted. 11 and 12, the same reference numerals are given to the same processing as or equivalent processing in the flowcharts of FIGS. 6 and 8 of the first embodiment.

  In the induction heating cooker according to the present embodiment, at the time of intermittent heating control with a low heating output, after the drive signal output to the inverter circuit 3 is restarted, whether the drive signal reaches a predetermined drive signal level (step) 214) or detecting that the input current or output current has exceeded a predetermined level (step 216, step 213), and restarting the feedback control (step 225) for comparing the detected power with the set power, and returning the feedback. Since no-load determination is performed after a predetermined time has elapsed after restarting the control (steps 8a to 10), the influence of detection delay of the input current detection means 16 and the like is avoided, and stable no-load detection is performed. Can do.

  In addition, the drive signal information such as the drive frequency stored at the end of the heating operation period of intermittent heating is set to the upper limit of the drive frequency at which overcurrent does not flow through the inverter circuit 3 even when there is a change in load conditions such as pan movement when heating is resumed. The frequency of the drive signal output to the inverter circuit 3 is stored in the drive signal information storage means 22 (steps 202a to 203a), and the inverter drive circuit 18 starts the inverter while the inverter drive state is activated during the heating operation period. Only by comparing the drive signal level being output to the circuit 3 with the drive signal information stored in the drive information storage means 22 (step 214), it is possible to prevent an overcurrent from flowing through the switching elements 8 and 9 of the inverter circuit 3. However, the heating power can be smoothly and quickly supplied regardless of the detection delay of the input current detection means and the output current detection means.

  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 upper switch (switching element), 9 lower switch (switching element), 10 diode, DESCRIPTION OF SYMBOLS 11 Diode, 12 Snubber capacitor, 13 Heating coil, 14 Resonance capacitor, 15 Output current detection means, 16 Input current detection means, 17 Input voltage detection means, 18 Inverter drive circuit, 19 Operation input means, 20 Control means, 21 No load Detection means, 22 Drive signal information storage means.

Claims (9)

A heating coil that is magnetically coupled to a heated object such as a pan; an inverter circuit that causes a high-frequency current to flow through the heating coil; an inverter drive circuit that outputs a drive signal to the inverter circuit; and an input power to the inverter circuit or the inverter Power detection means for detecting output power from the circuit; operation input means for setting heating power for heating the object to be heated; output current detection means for detecting output current from the inverter circuit; Control means for controlling the inverter drive circuit,
The control means repeats alternately a heating operation period in which a predetermined power is output from the inverter circuit and a heating pause period in which the output is stopped when a heating power of a predetermined power or less is set by the operation input means. An intermittent heating mode for operating the inverter circuit is executed, and in the intermittent heating mode, at the end of the heating operation period, a driving signal for gradually decreasing the output of the inverter circuit is output and then the output is stopped, and the heating is performed. At the start of the operation period, the inverter drive circuit is feedback-controlled to output a predetermined power after outputting a drive signal that gradually increases the output from the inverter drive circuit to the inverter circuit from a low output ,
At the end of the heating operation period, the control means stores drive signal information to be output from the inverter drive circuit to the inverter circuit before outputting a drive signal for gradually decreasing the output of the inverter circuit, and Induction heating characterized in that at the start of an operation period, a drive signal according to the stored drive signal information is output after a drive signal for gradually increasing the output from the inverter drive circuit to the inverter circuit from a low output is output. Cooking device. A heating coil that is magnetically coupled to a heated object such as a pan; an inverter circuit that causes a high-frequency current to flow through the heating coil; an inverter drive circuit that outputs a drive signal to the inverter circuit; and an input power to the inverter circuit or the inverter Power detection means for detecting output power from the circuit; operation input means for setting heating power for heating the object to be heated; output current detection means for detecting output current from the inverter circuit; Control means for controlling the inverter drive circuit,
The control means repeats alternately a heating operation period in which a predetermined power is output from the inverter circuit and a heating pause period in which the output is stopped when a heating power of a predetermined power or less is set by the operation input means. An intermittent heating mode for operating the inverter circuit is executed, and in the intermittent heating mode, at the end of the heating operation period, a driving signal for gradually decreasing the output of the inverter circuit is output and then the output is stopped, and the heating is performed. At the start of the operation period, the inverter drive circuit is feedback-controlled to output a predetermined power after outputting a drive signal that gradually increases the output from the inverter drive circuit to the inverter circuit from a low output ,
No-load detection means for detecting that the object to be heated has been removed during the heating operation and stopping the heating operation, and the no-load detection means detects no-load only during the feedback control in the intermittent heating mode. An induction heating cooker characterized by performing . A heating coil that is magnetically coupled to a heated object such as a pan; an inverter circuit that causes a high-frequency current to flow through the heating coil; an inverter drive circuit that outputs a drive signal to the inverter circuit; and an input power to the inverter circuit or the inverter Power detection means for detecting output power from the circuit; operation input means for setting heating power for heating the object to be heated; output current detection means for detecting output current from the inverter circuit; Control means for controlling the inverter drive circuit,
The control means repeats alternately a heating operation period in which a predetermined power is output from the inverter circuit and a heating pause period in which the output is stopped when a heating power of a predetermined power or less is set by the operation input means. An intermittent heating mode for operating the inverter circuit is executed, and in the intermittent heating mode, at the end of the heating operation period, a driving signal for gradually decreasing the output of the inverter circuit is output and then the output is stopped, and the heating is performed. At the start of the operation period, the inverter drive circuit is feedback-controlled to output a predetermined power after outputting a drive signal that gradually increases the output from the inverter drive circuit to the inverter circuit from a low output ,
The control means makes the sum of the heating operation period and the heating pause period constant when the ratio of the heating operation period to the heating pause period is a predetermined value or more, and the ratio of the heating operation period to the heating pause period is less than the predetermined value. In this case, the induction heating cooker is characterized in that only the heating pause period is adjusted with a constant heating operation period . A heating coil that is magnetically coupled to a heated object such as a pan; an inverter circuit that causes a high-frequency current to flow through the heating coil; an inverter drive circuit that outputs a drive signal to the inverter circuit; and an input power to the inverter circuit or the inverter Power detection means for detecting output power from the circuit; operation input means for setting heating power for heating the object to be heated; output current detection means for detecting output current from the inverter circuit; Control means for controlling the inverter drive circuit,
The control means repeats alternately a heating operation period in which a predetermined power is output from the inverter circuit and a heating pause period in which the output is stopped when a heating power of a predetermined power or less is set by the operation input means. An intermittent heating mode for operating the inverter circuit is executed, and in the intermittent heating mode, at the end of the heating operation period, a driving signal for gradually decreasing the output of the inverter circuit is output and then the output is stopped, and the heating is performed. At the start of the operation period, the inverter drive circuit is feedback-controlled to output a predetermined power after outputting a drive signal that gradually increases the output from the inverter drive circuit to the inverter circuit from a low output ,
The induction heating cooker characterized in that the control means stores the predetermined drive signal level when the drive signal information stored at the end of the heating operation period exceeds a predetermined drive signal level . A heating coil that is magnetically coupled to a heated object such as a pan; an inverter circuit that causes a high-frequency current to flow through the heating coil; an inverter drive circuit that outputs a drive signal to the inverter circuit; and an input power to the inverter circuit or the inverter Power detection means for detecting output power from the circuit; operation input means for setting heating power for heating the object to be heated; output current detection means for detecting output current from the inverter circuit; Control means for controlling the inverter drive circuit,
The control means repeats alternately a heating operation period in which a predetermined power is output from the inverter circuit and a heating pause period in which the output is stopped when a heating power of a predetermined power or less is set by the operation input means. An intermittent heating mode for operating the inverter circuit is executed, and in the intermittent heating mode, at the end of the heating operation period, a driving signal for gradually decreasing the output of the inverter circuit is output and then the output is stopped, and the heating is performed. At the start of the operation period, the inverter drive circuit is feedback-controlled to output a predetermined power after outputting a drive signal that gradually increases the output from the inverter drive circuit to the inverter circuit from a low output ,
In the intermittent heating mode, after restarting the inverter drive output, the no-load detection means performs no-load detection after the detected power by the power detection means reaches the predetermined power . A heating coil that is magnetically coupled to a heated object such as a pan; an inverter circuit that causes a high-frequency current to flow through the heating coil; an inverter drive circuit that outputs a drive signal to the inverter circuit; and an input power to the inverter circuit or the inverter Power detection means for detecting output power from the circuit; operation input means for setting heating power for heating the object to be heated; output current detection means for detecting output current from the inverter circuit; Control means for controlling the inverter drive circuit,
The control means repeats alternately a heating operation period in which a predetermined power is output from the inverter circuit and a heating pause period in which the output is stopped when a heating power of a predetermined power or less is set by the operation input means. An intermittent heating mode for operating the inverter circuit is executed, and in the intermittent heating mode, at the end of the heating operation period, a driving signal for gradually decreasing the output of the inverter circuit is output and then the output is stopped, and the heating is performed. At the start of the operation period, the inverter drive circuit is feedback-controlled to output a predetermined power after outputting a drive signal that gradually increases the output from the inverter drive circuit to the inverter circuit from a low output ,
In the intermittent heating mode, after restarting the inverter drive output, the no-load detection means performs no-load detection after the current detected by the output current detection means reaches a predetermined current . A heating coil that is magnetically coupled to a heated object such as a pan; an inverter circuit that causes a high-frequency current to flow through the heating coil; an inverter drive circuit that outputs a drive signal to the inverter circuit; and an input power to the inverter circuit or the inverter Power detection means for detecting output power from the circuit; operation input means for setting heating power for heating the object to be heated; output current detection means for detecting output current from the inverter circuit; Control means for controlling the inverter drive circuit,
The control means repeats alternately a heating operation period in which a predetermined power is output from the inverter circuit and a heating pause period in which the output is stopped when a heating power of a predetermined power or less is set by the operation input means. An intermittent heating mode for operating the inverter circuit is executed, and in the intermittent heating mode, at the end of the heating operation period, a driving signal for gradually decreasing the output of the inverter circuit is output and then the output is stopped, and the heating is performed. At the start of the operation period, the inverter drive circuit is feedback-controlled to output a predetermined power after outputting a drive signal that gradually increases the output from the inverter drive circuit to the inverter circuit from a low output ,
In the intermittent heating mode, the no-load detection means performs no-load detection after a predetermined time has elapsed after the control means starts feedback control of the heating period . A heating coil that is magnetically coupled to a heated object such as a pan; an inverter circuit that causes a high-frequency current to flow through the heating coil; an inverter drive circuit that outputs a drive signal to the inverter circuit; and an input power to the inverter circuit or the inverter Power detection means for detecting output power from the circuit; operation input means for setting heating power for heating the object to be heated; output current detection means for detecting output current from the inverter circuit; Control means for controlling the inverter drive circuit,
The control means repeats alternately a heating operation period in which a predetermined power is output from the inverter circuit and a heating pause period in which the output is stopped when a heating power of a predetermined power or less is set by the operation input means. An intermittent heating mode for operating the inverter circuit is executed, and in the intermittent heating mode, at the end of the heating operation period, a driving signal for gradually decreasing the output of the inverter circuit is output and then the output is stopped, and the heating is performed. At the start of the operation period, the inverter drive circuit is feedback-controlled to output a predetermined power after outputting a drive signal that gradually increases the output from the inverter drive circuit to the inverter circuit from a low output ,
In the intermittent heating mode, after restarting inverter drive output, the no-load detection means performs no-load detection after outputting a drive signal of a predetermined level or more . Wherein, in the intermittent heating mode, according to any one of claims 1 to 8, wherein the adjusting according to the length of the ratio setting heating power of the heating operation period and the heating pause period Induction heating cooker.

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