JP4570580B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker used in general households.

  In conventional induction heating cookers, the capacity of the snubber capacitor is switched depending on the size of the input, the type of load, and the presence or absence of current flowing in the flywheel diode. In addition to reducing the turn-off loss of the element, the snubber capacitor capacity is reduced when the input is low, etc. to prevent the short-circuit current from flowing through the snubber capacitor when the switching element is turned on. (See, for example, Patent Document 1).

Japanese Patent Laid-Open No. 5-94868

  In a conventional induction heating cooker, the switching loss is reduced by switching the capacity of the snubber capacitor to be connected by the output of the input detection unit or the load detection unit or by the output of the diode current detection circuit for detecting the flywheel diode current. Therefore, when the heating thermal power is changed by the user, the snubber capacitor is disconnected or connected during the heating operation, that is, during the inverter circuit operation.

  In particular, when a snubber capacitor is connected during operation of the inverter circuit, there is a high possibility of a difference between the voltage applied to the snubber capacitor and the voltage charged to the connected snubber capacitor. In some cases, a large short-circuit current flows through the switching element of the inverter circuit via the snubber capacitor, causing a large switching loss. Therefore, when switching the capacity of the snubber capacitor, it is necessary to temporarily stop the operation of the inverter circuit, and there is a problem that the thermal power output cannot be controlled smoothly.

  The present invention has been made to solve the above-described problems, and it is possible to connect / disconnect a snubber capacitor even during heating output control, and to enable smooth heating power adjustment from low output to high output. The purpose is to obtain a cooker.

An induction heating cooker according to the present invention alternately turns on and off a DC power supply circuit that rectifies an AC power supply and converts it into DC, and first and second switching elements connected in series between positive and negative buses of the DC power supply circuit. An inverter circuit that generates a high-frequency voltage, a load circuit composed of a heating coil and a resonant capacitor connected to the output of the inverter circuit, and both ends of either the first or second switching element constituting the inverter circuit in parallel A snubber circuit comprising a connected snubber capacitor and a third switching element; and a control means for outputting a drive signal to the first and second switching elements of the inverter circuit and the third switching element of the snubber circuit;
The control means controls the heating output by changing at least one of the frequency and the conduction ratio of the drive signal for the first and second switching elements of the inverter circuit, and the first or second switching element having a snubber circuit connected in parallel The third switching element is switched between conduction and non-conduction in a state in which is conducting.

  In the present invention, the inverter control means switches the connection / disconnection state of the snubber capacitor while the switching element of the inverter circuit connected in parallel with the snubber capacitor is conducting. In addition, since there is no voltage applied to the snubber capacitor, it is possible to switch the connection state of the snubber capacitor when no charging current or discharging current flows through the snubber capacitor. Even if the snubber capacitor is connected / disconnected, an induction heating cooker can be obtained in which the short-circuit current passing through the snubber capacitor does not flow to the switching element, and the heating power can be adjusted smoothly from low to high heating power.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a circuit configuration of an induction heating cooker according to Embodiment 1 for carrying out the present invention. In the figure, reference numeral 1 is an AC power source, and 2 is a DC power source circuit. Reference numeral 6 denotes input current detection means for detecting an input current to the DC power supply circuit 2, and reference numeral 7 denotes input voltage detection means connected to the output terminal of the rectifier diode bridge 3. Reference numeral 8 denotes an inverter circuit connected to the output of the DC power supply circuit 2, and the first and second switching elements 9 and 10 connected in series between the positive and negative DC buses and the switching elements connected in antiparallel. It is composed of flywheel diodes 11 and 12.

  The inverter circuit 8 converts the DC voltage into a high-frequency voltage and outputs it by alternately turning on and off the first and second switching elements 9 and 10. The output of the inverter circuit 8 is connected to a load circuit in which a heating coil 13 and a resonance capacitor 14 are connected in series. Reference numeral 15 denotes a load current detecting means for detecting a current flowing through the load circuit. Reference numeral 16 denotes a snubber circuit 16, and a third switching element 18 and its antiparallel diode 19 are connected in series so that the snubber capacitor 17 and the snubber capacitor 17 can be disconnected.

  20 is a control means 20 for controlling the whole induction heating cooker, and outputs a drive level signal of the inverter circuit 8 and a snubber control signal for switching connection / disconnection of the snubber capacitor 17 from detected values of the input current, input voltage, and output current. Output control means 21 for performing the above operation, inverter drive signal generating means 22 for generating a drive signal for the first and second switching elements 9 and 10 of the inverter circuit 8 from the drive level signal, and driving for the second switching element 10 Snubber connection switching means 23 for generating a drive signal to the third switching element 18 from the signal and the snubber control signal.

  The inverter drive signal generation means 22 turns off the second switching element 10 while the first switching element 9 of the inverter circuit 8 is on, and turns off the first switching element 9 when the second switching element 10 is on. It is turned off, and the first and second switching elements 9 and 10 are turned on and off alternately to be converted into a high frequency voltage. As shown in FIG. 2 (a), the inverter drive signal may be changed in drive frequency at a fixed energization rate according to the drive level signal, or fixed as shown in FIG. 2 (b). The energization rate may be changed depending on the frequency.

FIG. 3 is a diagram showing an example of the configuration of the snubber connection switching means 23, and FIG. 4 shows the drive signal and snubber control signal to the inverter circuit 8 and the third switching element 18 that switches connection / disconnection of the snubber capacitor 17. It is a time chart which shows the timing of these drive signals. In FIG. 3, when the level of the snubber control signal is switched, if the drive signal of the second switching element 10 is on, the drive signal to the third switching element 18 is immediately switched (4-2, FIG. 4). 4-3), if the drive signal of the second switching element 10 is in an off state (in the case of 4-1 and 4-4 in FIG. 4 ), the drive signal of the second switching element 10 is turned on. The driving signal to the third switching element 18 is switched at the time when it is turned on.

  This is because a voltage may be applied to the snubber circuit 16 when the second switching element 10 connected in parallel with the snubber circuit 16 is in an off state. When turned off, the charge charge remains in the snubber capacitor 17, and when the third switching element 18 is turned on, depending on the difference between the voltage applied to the snubber circuit 16 and the charge charge voltage of the snubber capacitor 17, the first or second switching is performed. A short-circuit current flows through the element 10 and the third switching element 18, and the switching loss increases. On the other hand, if the second switching element 10 connected in parallel with the snubber circuit 16 is in the ON state, the voltage applied to the snubber circuit 16 is 0, and the current flowing through the snubber circuit 16 is also 0. The snubber capacitor 17 is not charged. Even if the snubber sensor is connected or disconnected in such a state, no current flows through the snubber capacitor 17 at that time, so that the snubber capacitor is switched when the first and second switching elements 9 and 10 of the inverter circuit 8 are switched. Current through 17 does not flow, and switching loss does not increase.

  Next, output control processing in which the output control means 21 controls the drive level signal and the snubber control signal will be described with reference to the flowchart shown in FIG. In FIG. 5, the input power is calculated from the input current and the input voltage detected by the input current detecting means 6 and the input voltage detecting means 7, and compared with a preset set power (step 1). If the input power is smaller than the set power, the drive level signal is adjusted to increase the heating output (step 2). Conversely, if the input power is larger, the drive level signal is output to the heating output. Adjustment is made in the decreasing direction (step 3). This drive level signal is input to the inverter drive signal generation means 22 and converted into drive signals for the first switching element 9 and the second switching element 10 of the inverter circuit 8.

  Next, the output state of the snubber control signal is confirmed (step 4). When the snubber control signal is on, that is, when the snubber capacitor 17 is connected, the current flowing through the load circuit by the load current detecting means 15 is greater than the threshold value A1. It is determined whether or not it is small (step 5). If the load current is small, the snubber control signal is turned off (step 6). When the snubber capacitor 17 is connected and the current flowing through the load circuit is small, the snubber capacitor is used during a so-called dead time from when one switching element of the inverter circuit 8 is turned off until the other switching element is turned on. By disconnecting the snubber capacitor 17, the charging or discharging of 17 is not completed and a short-circuit current flows when the other switching element is turned on. When the snubber control signal is turned off, the snubber connection switching means 23 turns off the third switching element 18 while the second switching element 10 connected in parallel with the snubber circuit 16 is on, and the snubber capacitor 17 Can be separated without charge.

  In step 4, when the snubber control signal is off, that is, when the snubber capacitor 17 is disconnected, the load current detection means 15 determines whether or not the current flowing through the load circuit is larger than the threshold value A2 (step 7). If is larger, the snubber control signal is turned on (step 8). When the snubber capacitor 17 is disconnected and the current flowing through the load circuit is large, when one switching element of the inverter circuit 8 is turned off, the voltage applied to the switching element is rapidly changed by the large load current. The loss at the time of turn-off of the element increases. This increase in turn-off loss is prevented by connecting a snubber capacitor 17. When the snubber control signal is turned on, the snubber connection switching means 23 turns on the third switching element 18 while the second switching element 10 connected in parallel with the snubber circuit 16 is turned on, and the snubber capacitor 17 Can be connected in a state where no voltage is applied thereto. The values of the thresholds A1 and A2 are set in advance by confirming the operation using various pans.

  As described above, during the dead time of the drive signal in the first switching element 9 and the second switching element 10 of the inverter circuit 8, the load circuit current is small, so that charging or discharging of the snubber capacitor 17 is not completed and switching is performed. When a short-circuit (rushing) current flows when the element is turned on, the snubber capacitor 17 can be disconnected without stopping the driving of the inverter circuit 8 and the turn-on loss of the switching element can be suppressed. In addition, when the first switching element 9 and the second switching element 10 of the inverter circuit 8 are turned off, the load circuit current is large, so that the voltage applied to the switching element changes suddenly and the turn-off loss of the switching element increases. Since the snubber capacitor 17 can be connected without stopping the drive of 8 and the turn-off loss of the switching element can be suppressed, the thermal power can be smoothly adjusted from the high thermal power output to the low thermal power output.

  Even when the timing for switching the connection / disconnection state of the snubber capacitor 17 is limited to a part of the state in which the second switching element 10 connected in parallel with the snubber circuit 16 is conductive, the same effect can be obtained. FIG. 6 is a diagram showing another configuration example of the snubber connection switching means 23. Here, an example in which the snubber connection switching means 23 is configured by a D-type flip-flop is shown. FIG. 7 is a time chart showing the timing of the drive signal and snubber control signal to the inverter circuit 8 in the snubber connection switching means 23 and the drive signal to the third switching element 18 for switching the connection / disconnection of the snubber capacitor 17. is there. In FIG. 7, when the level of the snubber control signal is switched (7-1a, 7-2a, 7-3a, 7-4a in FIG. 7), the second switching element 10 is turned on when the drive signal is turned on. 3 The drive signal to the switching element 18 is switched (7-1b, 7-2b, 7-3b, 7-4b in FIG. 7).

Embodiment 2. FIG.
The circuit configuration of the induction heating cooker according to the second embodiment of the present invention is the same as that of FIG. FIG. 8 is a flowchart showing the output control processing of the output control means 21 in the second embodiment. FIG. 9 shows the inverter switching signal generation means 22 in the second embodiment and the first switching element 9 and the first switching element 9 in the inverter circuit 8. FIG. 3 is a diagram showing the frequency of the drive signal output to the two switching elements 10 and the energization rate of the drive signal to the first switching element 9. In the second embodiment, the inverter drive signal generation means 22 outputs a drive signal according to the drive signal control line shown in FIG. 9 according to the drive level signal from the output control means 21. The higher the level of the drive level signal, the lower the frequency and the higher energization rate (first switching element 9) drive signal is output. The lower the level of the drive level signal, the higher the frequency and the low energization rate (first switching element 9). The drive signal is output. Note that the energization rate of the second switching element 10 is complementary to the energization rate of the first switching element 9. If the energization rate of the first switching element 9 decreases, the energization of the second switching element 10 is correspondingly reduced. If the rate increases and the energization rate of the first switching element 9 increases, the energization rate of the second switching element 10 decreases accordingly.

  Next, the operation of the heating output control of the output control means 21 in the induction heating cooker of the second embodiment will be described using the flowchart of FIG. Steps 8-1 to 8-4 are the same processing as steps 1 to 4 in the flowchart of FIG. In step 8-4, when the snubber control signal is on, that is, when the snubber capacitor 17 is connected, the drive level at which the energization rate of the first switching element 9 is smaller than the threshold value B1 (see FIG. 9). It is determined whether or not the signal is present (step 8-5), and if it falls below the threshold B1, the snubber control signal is turned off (step 8-6), the snubber capacitor 17 is disconnected, and the snubber capacitor 17 is entered when the switching element is turned on. Prevent increase in current.

  When the snubber control signal is off in step 8-4, that is, when the snubber capacitor 17 is disconnected, the drive level at which the energization rate of the first switching element 9 is greater than the threshold B2 (see FIG. 9). It is determined whether the signal is a signal (step 8-7). If the threshold B2 is exceeded, the snubber control signal is turned on (step 8-8), the snubber capacitor 17 is connected, and the switching element voltage change when the switching element is turned off is detected. Delay to prevent increased loss. The thresholds B1 and B2 for switching the connection / disconnection of the snubber capacitor 17 are determined by placing various pans on the induction heating cooker, checking the inverter circuit output voltage waveform with respect to the inverter drive signal, B1 is determined so as not to generate an inrush current, and B2 to which the snubber capacitor 17 is connected is determined in a range of B1 ≦ B2.

  As described above, in the second embodiment, the connection / disconnection of the snubber capacitor 17 is switched in accordance with the drive level signal output from the output control means 21, so that the switching of the inverter circuit 8 can be performed without adding a circuit or the like. It is possible to prevent an increase in element loss. The on / off switching timing of the third switching element 18 for connecting and disconnecting the snubber capacitor 17 is the same as that of the first embodiment when the second switching element 10 connected in parallel with the snubber circuit 16 is in the on state. As a result, no voltage is applied to the snubber circuit 16 and no current flows through the snubber circuit 16. Accordingly, even during induction heating (inverter circuit operation), the connection / disconnection of the snubber capacitor 17 can be switched with low loss.

Embodiment 3 FIG.
FIG. 10 is a diagram showing a circuit configuration of an induction heating cooker according to Embodiment 3 of the present invention. The circuit configuration in the present embodiment is almost the same as that in FIG. 1 of the first embodiment, and the same or corresponding parts are denoted by the same reference numerals. The difference from FIG. 1 is that the drive signal to the first switching element 9 output from the inverter drive signal generating means 22 is input to the output control means 21, and the first switching element 9 is turned on / off in the output control means 21. It is to know when to do.

  Next, the operation will be described using the diagram showing the drive signal and load current waveform of the inverter circuit 8 in FIG. 11 and the flowchart showing the output control processing of the output control means 21 in FIG. In the third embodiment, the heating output is controlled by adjusting the energization rates of the first switching element 9 and the second switching element 10 of the inverter circuit 8. For example, in FIG. 11, (a) is a drive signal with high heating output, and (b) is a drive signal with low heating output.

  In FIG. 12, steps 12-1 to 12-4 are the same processing as steps 1 to 4 in the flowchart of FIG. If the snubber control signal is on and the snubber capacitor 17 is connected in step 12-4, the timing for turning on the first switching element 9 input from the inverter drive signal generation means 22 and the load current detection means 15 The time difference (or phase difference) of the commutation timing of the load current input from the input is checked (step 12-5), and the time from turn-on to commutation is shorter than a predetermined time (threshold C1) or the first switching If the commutation of the load current has occurred before the element 9 is turned on, the snubber control signal is turned off (step 12-6). When the snubber control signal is turned off, the snubber connection switching means 23 turns off the third switching element 18 while the second switching element 10 connected in parallel with the snubber circuit 16 is turned on, and the snubber capacitor 17 is turned on. It is possible to cut off in a state where there is no charge, and it is possible to prevent a short circuit current via the snubber capacitor 17 when the switching element is turned on.

  If the snubber capacitor 17 is disconnected while the snubber control signal is off in step 12-4, the time difference (or phase difference) between the turn-on timing of the first switching element 9 and the load current commutation timing. (Step 12-7), when the time from turn-on to commutation is longer than a predetermined time (threshold C2), or when the load current is commutated later than the turn-on of the first switching element 9, The snubber control signal is turned on (step 12-8), and the snubber capacitor 17 is connected to reduce the loss generated when the switching element is turned off.

Embodiment 4 FIG.
FIG. 13: is a figure which shows the circuit structure of the induction heating cooking appliance in Embodiment 4 of this invention. In the figure, the same or corresponding parts as in FIG. 1 of the first embodiment and FIG. 10 of the third embodiment are denoted by the same reference numerals, and description thereof is omitted. A snubber circuit voltage fluctuation detecting means 24 detects the peak of voltage fluctuation generated at the connection point of the series circuit of the capacitor 25 and the resistor 26 connected in parallel with the snubber circuit 16 and its generation timing.

  FIG. 14 shows the drive signal output to the first switching element 9 and the second switching element 10 of the inverter circuit 8 by the inverter drive signal generation means 22 in the fourth embodiment, the voltage generated in the snubber circuit 16, and the snubber circuit voltage. FIG. 15 is a time chart showing the detection output of the fluctuation detection means 24, and FIG. 15 is a flowchart showing the output control processing of the output control means 21 in the fourth embodiment.

  14A shows an example in which the connection of the snubber capacitor 17 is suitable. The snubber circuit voltage, that is, the inverter, is set between the turn-off time of the second switching element 10 and the dead time when the first switching element 9 is turned on. The output voltage of the circuit 8 has risen to the DC bus potential. In this example, the speed of the voltage increase is not large, and the detection value of the snubber circuit voltage fluctuation detecting means 24 does not increase.

  FIG. 14B shows an example in which the capacity of the connected snubber capacitor 17 is insufficient. Since the snubber circuit voltage increases rapidly after the second switching element 10 is turned off, the turn-off loss increases. In this case, as shown in the figure, the detected value peak of the snubber circuit voltage fluctuation detecting means 24 becomes large, and the timing at which the peak occurs is before the first switching element 9 is turned on (during the dead time).

  FIG. 14C shows an example in which the capacity of the connected snubber capacitor 17 is too large. The snubber circuit voltage is DC between the turn-off time of the second switching element 10 and the dead time when the first switching element 9 is turned on. It has not risen to the bus potential. As a result, when the first switching element 9 is turned on, a short-circuit current is generated via the snubber capacitor 17 to generate a large turn-on loss, and the snubber circuit voltage rise rate is increased. Therefore, in this case, as shown in the drawing, the snubber circuit voltage fluctuation detecting means 24 detects a large peak value after the first switching element 9 is turned on (after the dead time is finished).

  Next, the operation of the fourth embodiment will be described using the flowchart of FIG. In the figure, steps 15-1 to 15-4 are the same as steps 1 to 4 in FIG. If the snubber control signal is ON in step 15-4, it is determined that the snubber capacitor 17 is connected, and whether the snubber voltage fluctuation speed is greater than a predetermined value based on the output of the snubber circuit voltage fluctuation detecting means 24. (Step 15-5). If it is determined that it is larger, it is determined whether or not the timing at which the peak of the snubber voltage fluctuation occurs is later than the timing at which the first switching element 9 is turned on (step 15-6). After that, when the first switching element 9 is turned on, a short circuit current flows through the snubber capacitor 17 (FIG. 14C). In this case, the snubber control signal is turned off and the snubber capacitor 17 is disconnected (step 15-7).

  If the snubber control signal is OFF in step 15-4, the snubber capacitor 17 is disconnected. In this case as well, the first and second inverter circuits 8 are output by the output of the snubber circuit voltage fluctuation detecting means 24. It is determined whether the fluctuation rate of the voltage applied to the switching elements 9 and 10 is greater than a predetermined value (step 15-8). If it is determined that it is large, it is determined whether the timing at which the peak of the voltage fluctuation occurs is before the timing when the first switching element 9 is turned on (immediately after the second switching element 10 is turned off) (step 15-9). When a peak occurs immediately after the second switching element 10 is turned off (for example, FIG. 14B), since the switching element has a large turn-off loss, the snubber control signal is turned on and the snubber capacitor 17 is connected (step) 15-10). Also in the fourth embodiment, the snubber capacitor 17 is in a state in which the second switching element 10 connected in parallel with the snubber circuit 16 is turned on by the snubber connection switching means 23 as shown in FIG. Since the ON / OFF state of the third switching element 18 connected to is switched, the snubber capacitor 17 can be connected and disconnected even during operation of the inverter circuit.

  In the first to fourth embodiments, a load circuit in which only the series circuit of the heating coil 13 and the resonance capacitor 14 is connected is used, but a diode 27 is connected in parallel with the resonance capacitor 14 as shown in FIG. A load circuit configured such that the load circuit current does not commutate when the second switching element is conductive may be used.

It is a figure which shows the circuit structure of the induction heating cooking appliance in Embodiment 1 of this invention. It is a figure which shows the input / output relationship of the inverter drive signal generation means in Embodiment 1 of this invention. It is a figure which shows the example of 1 structure of the snubber connection switching means in Embodiment 1 of this invention. It is a time chart explaining the timing of the inverter drive signal and snubber connection / disconnection in one structural example of a snubber connection switching means. It is a flowchart which shows the output control process in Embodiment 1 of this invention. It is a figure which shows the other structural example of the snubber connection switching means in Embodiment 1 of this invention. It is a time chart explaining the timing of the inverter drive signal and snubber connection / disconnection in another configuration example of the snubber connection switching means. It is a flowchart which shows the output control process in Embodiment 2 of this invention. It is a figure explaining the drive signal which the inverter drive signal production | generation means in Embodiment 2 of this invention outputs. It is a figure which shows the circuit structure of the induction heating cooking appliance in Embodiment 3 of this invention. It is a figure which shows the drive signal of the inverter circuit in Embodiment 3 of this invention, and the commutation timing of load current. It is a flowchart which shows the output control process in Embodiment 3 of this invention. It is a figure which shows the circuit structure of the induction heating cooking appliance in Embodiment 4 of this invention. It is a figure which shows the drive signal of the inverter circuit in Embodiment 4 of this invention, and the commutation timing of load current. It is a flowchart which shows the output control process in Embodiment 4 of this invention. It is a figure which shows the other circuit structure of the induction heating cooking appliance in implementation of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AC power supply, 2 DC power supply circuit, 6 Input current detection means, 7 Input voltage detection means, 8 Inverter circuit, 9 1st switching element, 10 2nd switching element, 13 Heating coil, 14 Resonance capacitor, 15 Load current detection means , 16 snubber circuit, 17 snubber capacitor, 18 third switching element, 20 control means, 24 snubber circuit voltage fluctuation detection means.

Claims (5)

A DC power supply circuit that rectifies an AC power supply and converts it to DC, and an inverter circuit that alternately turns on and off first and second switching elements connected in series between positive and negative buses of the DC power supply circuit to generate a high-frequency voltage; A load circuit comprising a heating coil and a resonant capacitor connected to the output of the inverter circuit, a snubber capacitor connected in parallel to either end of either the first or second switching element constituting the inverter circuit, and a first A snubber circuit with three switching elements, and a control means for outputting a drive signal to the first and second switching elements of the inverter circuit and the third switching element of the snubber circuit,
The control means controls the heating output by changing at least one of the frequency and the conduction ratio of the drive signal for the first and second switching elements of the inverter circuit, and the snubber circuit is connected in parallel to the first or second An induction cooking device, wherein the third switching element is switched between conduction and non-conduction in a state where the second switching element is conductive. Providing a load current detecting means for detecting a current flowing in the load circuit;
The control means determines to disconnect the snubber capacitor when the current detected by the load current detection means is smaller than a threshold when the snubber capacitor is connected;
Further, it is determined that the snubber capacitor is connected when the current detected by the load current detecting means is larger than a threshold when the snubber capacitor is disconnected,
The control means executes connection or disconnection of the snubber capacitor based on this determination in a state where the first or second switching element connected to the snubber circuit in parallel is conducting. Item 1. An induction heating cooker according to item 1. The control means determines to disconnect the snubber capacitor when the energization rate of at least one of the first and second switching elements is smaller than a threshold value;
Further, it is determined that the snubber capacitor is connected when the energization ratio of any one of the first and second switching elements is larger than a threshold value,
The control means executes connection or disconnection of the snubber capacitor based on this determination in a state where the first or second switching element connected to the snubber circuit in parallel is conducting. Item 1. An induction heating cooker according to item 1. Providing a load current detecting means for detecting a current flowing in the load circuit;
The control means includes
The timing after the elapse of a predetermined time from the turn-on of the first and second switching elements is compared with the commutation timing of the current detected by the load current detecting means, and the timing after the elapse of the predetermined time from the turn-on of at least one of the switching elements. When the commutation timing is earlier, it is decided to disconnect the snubber capacitor,
In addition, when the commutation timing is later than the timing after a predetermined time has elapsed from the turn-on of any switching element, it is determined to connect the snubber capacitor,
The control means executes connection or disconnection of the snubber capacitor based on this determination in a state where the first or second switching element connected to the snubber circuit in parallel is conducting. Item 1. An induction heating cooker according to item 1. A snubber circuit voltage fluctuation detecting means is provided,
The control means includes
Based on the output of the snubber circuit voltage fluctuation detecting means, it is determined that the fluctuation speed of the snubber voltage is larger than a predetermined value, and the timing at which the peak of the snubber voltage fluctuation occurs is one of the first and second switching elements. When the switching element is turned on later, it is determined that the snubber capacitor is disconnected,
The snubber circuit voltage fluctuation detecting means determines that the fluctuation speed of the snubber voltage is greater than a predetermined value and the timing at which the peak of the snubber voltage fluctuation occurs is one of the first and second switching elements. If it is before the turn-on timing of one switching element, it is determined that the snubber capacitor is connected,
The control means executes connection or disconnection of the snubber capacitor based on this determination in a state where the first or second switching element connected to the snubber circuit in parallel is conducting. Item 1. An induction heating cooker according to item 1.

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