JP5383526B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker that supplies a high-frequency current to a heating coil to induction-heat a cooking container.

  In a conventional induction heating cooker, the capacitance of the snubber condenser (hereinafter simply referred to as “capacity”) is increased in order to reduce switching loss at high output, and the capacity of the snubber condenser is reduced at low output. There are some which are switched in this way (see, for example, Patent Document 1). By increasing the capacity of the snubber capacitor at the time of high output, the voltage fluctuation applied to the switching element can be delayed after turning off the switching element, and the switching loss (turn-off loss) due to the tail current flowing through the switching element is reduced. Can be suppressed. On the other hand, at the time of low output, when the capacity of the snubber capacitor is large, the other switching element is turned on before the snubber capacitor is charged or discharged after one switching element is turned off. At this time, a rush current for charging or discharging the snubber capacitor flows through the other switching element, resulting in a large switching loss.In this case, the time for charging or discharging the snubber capacitor is shortened by switching the capacity of the snubber capacitor to be small. Thus, it is possible to easily complete the charging or discharging of the snubber capacitor during the dead time (period in which all the switching elements are off), and the switching loss due to the rush current that flows when the switching element is turned on can be suppressed.

JP 2003-338358 A (page 5-6, FIG. 7)

  However, conversely, if the capacity of the snubber capacitor is reduced, the voltage fluctuation of the snubber capacitor becomes faster after one of the switching elements is turned on, and the current flowing through the load circuit during the dead time period is likely to commutate. If a snubber capacitor occurs, the voltage applied to the switching element that turns on increases even if the amount of electricity required for charging and discharging is small, a steep current flows in a short time, and the peak of radiation noise is Get higher. As a result, in addition to an increase in switching loss occurring in the switching element, there is a problem that the input current detection circuit, the output current detection circuit, and the like are affected as noise and cause a large error.

  The present invention has been made to solve the above-described problems, and reduces the loss of the switching element regardless of the size of the output to improve the heating efficiency, as well as the input current detection circuit, the output current detection circuit, and the like. An object of the present invention is to provide an induction heating cooker that can perform accurate heating control while suppressing generation of noise that affects the above.

  An induction heating cooker according to the present invention includes a DC power supply circuit that converts an AC voltage supplied from an AC power supply into a DC voltage, and at least two switching elements connected in series to the output terminal of the DC power supply circuit, Each of the switching elements includes a diode connected in antiparallel and a snubber capacitor connected in parallel to one of the switching elements and capable of switching a capacitance, and converts the DC voltage into a high frequency voltage. An inverter circuit, a load circuit composed of a series resonance circuit of a heating coil and a resonance capacitor connected in parallel to the switching element to which the snubber capacitor is connected in parallel, and an on / off operation of the switching element; A drive circuit for generating a drive signal having a predetermined dead time, and a capacity of the snubber capacitor; Snubber switching means for switching, a control circuit for controlling the drive circuit and the snubber switching means, and snubber current detection means for detecting a current flowing through the snubber capacitor, wherein the control circuit includes the snubber current detection means. When it is determined that the absolute value of the current detected by the current value is greater than or equal to a predetermined value after the dead time, the snubber switching means switches the snubber capacitor to a smaller capacity, and the snubber current detecting means causes the dead time to be reduced. When the peak value of the absolute value of the detected current is determined to be greater than or equal to a predetermined value, the snubber switching means switches the snubber capacitor to a large capacity, and the drive circuit causes the drive signal to For the current detected by the snubber current detection means If the commutation is determined to have occurred during the dead time, characterized in that to shorten the dead time for the drive signal to the drive circuit.

  According to the induction heating cooker according to the present invention, in the switching element of the inverter circuit, switching loss (turn-off loss) due to tail current or the like is reduced, and charging or discharging in the snubber capacitor is completed during the dead time, and Since the rush current flowing through the snubber capacitor can be reduced by avoiding commutation of the load current, switching loss and noise can be reduced.

It is a circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a figure which shows the example of a waveform of the drive signal input into the inverter circuit 22 of the induction heating cooking appliance which concerns on Embodiment 1 of this invention. In the induction heating cooking appliance which concerns on Embodiment 1 of this invention, it is a figure which shows the fluctuation | variation of the snubber voltage in the state where the capacity | capacitance of the snubber capacitor | condenser 12 is large. In the induction heating cooking appliance which concerns on Embodiment 1 of this invention, it is a figure which shows the fluctuation | variation of the snubber voltage and snubber current in case the capacity | capacitance of the snubber condenser 12 is small. It is a figure which shows the relationship between a drive frequency and input electric power (input electric current) in the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a flowchart which shows the heating control operation | movement in the induction heating cooking appliance which concerns on Embodiment 1 of this invention. It is a flowchart which shows the heating control operation | movement in the induction heating cooking appliance which concerns on Embodiment 2 of this invention. It is a circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 3 of this invention. It is a flowchart which shows the heating control operation | movement in the induction heating cooking appliance which concerns on Embodiment 3 of this invention. It is a flowchart which shows the heating control operation | movement in the induction heating cooking appliance which concerns on Embodiment 4 of this invention. It is a flowchart which shows the heating control operation | movement in the induction heating cooking appliance which concerns on Embodiment 5 of this invention. It is another example of the circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 3 of this invention. It is a circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 6 of this invention. It is a figure which shows the example of a waveform of the drive signal input into the inverter circuit 22a of the induction heating cooking appliance concerning Embodiment 6 of this invention.

Embodiment 1 FIG.
(Circuit configuration of induction heating cooker)
FIG. 1 is a circuit configuration diagram of an induction heating cooker according to Embodiment 1 of the present invention.
As shown in FIG. 1, the AC power source 1 is connected to the input side of the diode bridge circuit 2, and the choke coil 3 is connected to the output positive side of the diode bridge circuit 2. A smoothing capacitor 4 is connected between the other end of the choke coil 3 and the output negative electrode side of the diode bridge circuit 2. At least the above-described diode bridge circuit 2, choke coil 3 and smoothing capacitor 4 constitute a DC power supply circuit 21.
As shown in FIG. 1, the AC power supply 1 is a single-phase power supply, but the present invention is not limited to this, and the AC power supply 1 may have a three-phase structure. The three-phase AC voltage may be rectified.

A series circuit of a high-potential side switching element (hereinafter simply referred to as “upper switch 5”) and a low-potential side switching element (hereinafter simply referred to as “lower switch 6”) is connected to the smoothing capacitor 4 in parallel. Yes. A diode 7 is connected to the upper switch 5 in antiparallel, and a diode 8 is connected to the lower switch 6 in antiparallel.
The upper switch 5 and the lower switch 6 may use other elements such as an IGBT or a MOSFET, for example.

Further, any one of the upper switch 5 and the lower switch 6 (the lower switch 6 in the example of FIG. 1) includes a first snubber capacitor 9, a series circuit of the second snubber capacitor 10 and the disconnect switch 11, and heating. Series resonant circuits of the coil 13 and the resonant capacitor 14 are connected in parallel. The first snubber capacitor 9, the second snubber capacitor 10 and the disconnecting switch 11 constitute a snubber capacitor 12. At least the upper switch 5, the lower switch 6, the diode 7, the diode 8 and the snubber capacitor 12 constitute an inverter circuit 22. Further, a load circuit 23 is configured by the heating coil 13 and the resonance capacitor 14.
As shown in FIG. 1, the second snubber capacitor 10 is connected to the high potential side of the disconnect switch 11, but is not limited to this, and is connected to the low potential side of the disconnect switch 11. Needless to say, the configuration may be made. Moreover, what is necessary is just to use the parts which have switching functions, such as a relay circuit, IGBT, or MOSFET, for said isolation | separation switch 11, for example.

  Between the AC power supply 1 and the diode bridge circuit 2, an input current detection means 31 for detecting an input current to the DC power supply circuit 21 is installed. Further, an input voltage detecting means 32 for detecting a voltage between the output terminals (hereinafter referred to as “input voltage”) is installed at the output terminal of the diode bridge circuit 2. The input current detection means 31, the input voltage detection means 32, and the operation input means 33 that receives an operation by the user and generates an operation signal are connected to the control circuit 37. In addition, a drive signal is output to the above-described upper switch 5 and lower switch 6, and a switching signal is output to the drive circuit 34 that performs the on / off operation and the disconnect switch 11, and the on / off operation is performed. A snubber switching means 35 is connected to the control circuit 37. Further, a snubber current detection means 36 for detecting a current flowing through the first snubber capacitor 9 is connected to the control circuit 37.

  The input current detection unit 31 and the snubber current detection unit 36 transmit the detected currents to the control circuit 37, respectively. Further, the input voltage detection unit 32 transmits the detected input voltage to the control circuit 37. Further, the operation input means 33 transmits the generated operation signal to the control circuit 37. Then, the control circuit 37 transmits a control signal for controlling the on / off operation of the upper switch 5 and the lower switch 6 and the separation switch 11 to the drive circuit 34 and the snubber switching unit 35, respectively.

In the above description, the input current detection means 31 is installed between the AC power supply 1 and the diode bridge circuit 2 to detect the input current to the DC power supply circuit 21, but the present invention is not limited to this. For example, it may be configured between the DC power supply circuit 21 and the inverter circuit 22 to detect a DC current output from the DC power supply circuit 21 and input to the inverter circuit 22 as an input current.
In the above description, the snubber current detection means 36 detects the current flowing through the first snubber capacitor 9, but the present invention is not limited to this, and the snubber current detection means 36 causes the first snubber capacitor 9 and The total of the currents flowing through both of the second snubber capacitors 10 may be detected.
The input current detection means 31 and the input voltage detection means 32 correspond to the “power detection means” of the present invention.

(Heating operation of induction heating cooker)
FIG. 2 is a diagram illustrating a waveform example of a drive signal input to the inverter circuit 22 of the induction heating cooker according to the first embodiment of the present invention. Hereinafter, the operation of the induction heating cooker according to the present embodiment will be described with reference to FIGS. 1 and 2.
The AC voltage output from the AC power supply 1 is full-wave rectified by the diode bridge circuit 2 in the DC power supply circuit 21 and converted into a DC voltage, and the DC voltage is smoothed by the smoothing capacitor 4. The smoothed DC voltage is applied to the inverter circuit 22.

  Further, the user places a pan or the like on a heating port (not shown) on the top plate of the induction heating cooker, performs an operation for adjusting the heating power on the operation input means 33, and operates the input means. 33 generates an operation signal including information such as set power based on the operation content, and transmits the operation signal to the control circuit 37. Based on the received operation signal, the control circuit 37 generates a control signal for controlling the on / off operation of the upper switch 5 and the lower switch 6 for the drive circuit 34, and sends the control signal to the drive circuit 34. Send. The drive circuit 34 generates a drive signal for turning on / off the upper switch 5 and the lower switch 6 based on the received control signal, and outputs the drive signal to the upper switch 5 and the lower switch 6. The upper switch 5 and the lower switch 6 perform an on / off operation based on the drive signal, and convert the DC voltage applied from the DC power supply circuit 21 into a high-frequency voltage. A high frequency current flows through the heating coil 13 and the resonance capacitor 14 by the high frequency voltage converted by the upper switch 5 and the lower switch 6. The change in magnetic flux generated by the high-frequency current flowing through the heating coil 13 induces an eddy current in a pan or the like placed above the heating coil 13 to heat the pan or the like.

  At this time, the driving frequency of the on / off operation of the upper switch 5 and the lower switch 6 of the inverter circuit 22 is set within a frequency range higher than the resonance frequency of the load circuit 23. In addition, as shown in FIG. 2, the upper switch 5 and the lower switch 6 are alternately turned on / off based on the drive signal, and the upper switch 5 and the lower switch 6 are turned on (energized state). The dead time dt in which both the upper switch 5 and the lower switch 6 are in the off state is provided for a predetermined time when switching to, and the time ratio of the on state of the upper switch 5 and the lower switch 6 excluding the dead time dt is Both the upper switch 5 and the lower switch 6 are 50%. In FIG. 2, FIG. 2 (a) is a drive signal in the case of medium output, FIG. 2 (b) is a high output, and FIG.

  The control circuit 37 uses the input current detected by the input current detection means 31 and the input power calculated based on the input voltage detected by the input voltage detection means 32 as the power set by the operation input means 33. Thus, the inverter circuit 22 is controlled via the drive circuit 34.

(Snubber voltage and snubber current behavior during switching operation)
FIG. 3 is a diagram showing variations in the snubber voltage and the snubber current when the capacity of the snubber condenser 12 is large in the induction heating cooker according to Embodiment 1 of the present invention. In FIG. 3, in order to increase the capacity of the snubber capacitor 12, it is assumed that the control circuit 37 turns off the separation switch 11 via the snubber switching means 35 and enables the second snubber capacitor 10.

  FIG. 3A is a waveform example when charging or discharging of the snubber capacitor 12 is completed by the current flowing through the load circuit 23 during the dead time dt, and FIG. 3B flows through the load circuit 23. It is an example of a waveform when the snubber capacitor 12 is not charged or discharged during the dead time dt because the current is small. In FIG. 3, “snubber voltage” means the voltage across the snubber capacitor 12, and “snubber current” means the current flowing through the snubber capacitor 12. The same applies in the following description. In FIG. 3A, when the charging or discharging of the snubber capacitor 12 is completed, the diode 7 or the diode 8 becomes conductive, and the turn-on of the upper switch 5 or the lower switch 6 becomes zero volt switching, and the switching loss is reduced. On the other hand, in FIG. 3B, the turn-on of the upper switch 5 or the lower switch 6 is performed in a state where the snubber capacitor 12 is not completely charged or discharged, so that a rush current for charging or discharging the snubber capacitor 12 is obtained. As a result, large switching loss and noise occur.

  FIG. 4 is a diagram illustrating changes in the snubber voltage and the snubber current when the capacity of the snubber condenser 12 is small in the induction heating cooker according to the first embodiment of the present invention. In FIG. 4, in order to reduce the capacity of the snubber capacitor 12, it is assumed that the control circuit 37 turns off the disconnecting switch 11 via the snubber switching means 35 and disables the second snubber capacitor 10.

  FIG. 4A shows an example of a waveform when charging or discharging of the snubber capacitor 12 is completed in a short time by a current flowing through the load circuit 23 during the dead time dt. FIG. 4B shows a waveform during the dead time dt. FIG. 4C shows an example of a waveform in which the charging or discharging of the snubber capacitor 12 is completed within an appropriate time and no commutation occurs, and FIG. 4C shows the current flowing through the load circuit 23 during the dead time dt. It is an example of a waveform where commutation occurs. In FIG. 4A, the switching loss (turn-off loss) increases due to the tail current or the like when the lower switch 6 is turned off. In FIG. 4B, the turn-on of the upper switch 5 or the lower switch 6 is zero volt switching, and the switching loss is reduced. In FIG. 4C, commutation occurs in the current flowing through the load circuit 23, so that the upper switch 5 or the lower switch 6 that is turned on cannot be switched to zero volts, and a rush current flows, so that a large switching loss and noise are generated. To do.

(Relationship between drive frequency and input power)
FIG. 5 is a diagram showing the relationship between drive frequency and input power (input current) in the induction heating cooker according to Embodiment 1 of the present invention.
In FIG. 5, the solid line indicates a state where the capacity of the snubber capacitor 12 is large, and the broken line indicates a state where the capacity of the snubber capacitor 12 is small. As shown in FIG. 5, when the large-diameter pan is placed, the area through which the induction current generated by the high-frequency current flowing in the heating coil 13 flows is large, and a relatively high driving frequency (hereinafter, this state is referred to as “ Even when the drive signal level is low, ”the input power (input current) increases to some extent. On the other hand, in the no-load state where the pan is not placed, even if the drive frequency is low (hereinafter, this state is called “the drive signal level is high”), there is no pan that generates heat due to the induction current flowing. The input power (input current) remains at a low level. And when the small diameter pan is mounted, the intermediate characteristic of the state in which the large diameter pan is mounted and a no-load state is shown.

  Here, when the capacity of the snubber capacitor 12 is small, the input power is higher when the drive signal level such as the drive signal shown in FIG. 2B is higher than when the capacity of the snubber capacitor 12 is large. (Input current) increases slightly. This is because the output current of the inverter circuit 22 is increased, and as shown in FIG. 4A, the voltage fluctuation when the lower switch 6 is turned off becomes faster, and the switching loss (turn-off loss) due to the tail current or the like. This is because of the increase.

  Further, when the capacity of the snubber capacitor 12 is large, the input power (when the drive signal level such as the drive signal shown in FIG. 2C is low is compared with the case where the capacity of the snubber capacitor 12 is small. Input current) is slightly higher. As shown in FIG. 3B, this is because the upper switch 5 or the lower switch 6 is turned on in a state where the charging or discharging of the snubber capacitor 12 is not completed during the dead time dt. This is because a rush current for charging or discharging the battery flows to increase the switching loss. At this time, the switching loss increases, noise is generated, and the detected input power (input current) becomes larger than the actual input power (input current) due to the influence of the noise. In FIG. 5, the detected input power (input current) is indicated by a thick solid line, and the actual input power (input current) is indicated by a thin solid line. As a result, even if the drive signal level is lowered, the switching loss increases, so the input power (input current) does not drop sufficiently. As a result, when the minimum set power is set (for example, 100 W output), there is no load. There is almost no difference in input power (input current) detected in each of the state and the state where the small-diameter pan is placed, and the no-load state cannot be determined.

  Therefore, in order to discriminate the no-load state, a threshold value as shown in FIG. 5 is set, and when the drive signal level is high or the input power is large, the snubber capacitor 12 has a large capacity, and the drive signal level In a low state or a low input power, the capacity of the snubber capacitor 12 is set to a small state, and the determination may be made based on whether or not the detected input power (input current) is larger than the threshold value.

(Snubber capacitor 12 capacity switching operation)
FIG. 6 is a flowchart showing a heating control operation in the induction heating cooker according to Embodiment 1 of the present invention. Hereinafter, the heating control operation in the induction heating cooker according to the present embodiment including the switching operation of the capacity of the snubber condenser 12 will be described with reference to FIG.

(S1)
First, the control circuit 37 receives the operation signal from the operation input means 33, and determines whether or not the operation of the heating start request by the user has been performed. If the result of the determination is that a heating start request operation has been carried out, the process proceeds to step S2. On the other hand, when the operation of the heating start request is not performed, the process waits until the operation of the heating start request is performed.

(S2)
The control circuit 37 generates a control signal based on the set power included in the operation signal received from the operation input unit 33 and transmits the control signal to the drive circuit 34. The drive circuit 34 generates a drive signal based on the received control signal, and starts outputting the drive signal to the upper switch 5 and the lower switch 6.

(S3)
The control circuit 37 determines whether or not an appropriate pan or the like is placed based on the input current detected by the input current detection unit 31 and the input voltage detected by the input voltage detection unit 32. As a result of the determination, if an appropriate pan or the like is placed, the process proceeds to step S4. On the other hand, if an appropriate pan or the like is not placed, the process returns to step S1.
The control circuit 37 determines whether or not an appropriate pan or the like is placed based on the input current detected by the input current detection unit 31 and the input voltage detected by the input voltage detection unit 32. However, the present invention is not limited to this, and the determination may be made based only on the input current. Further, the determination may be made based on the above-described input current or the like and the current detected by the snubber current detection means 36.

(S4)
Next, the control circuit 37 is in a state in which the capacity of the snubber capacitor 12 is large because the second snubber capacitor 10 is enabled while the separation switch 11 is on, or in a state where the separation switch 11 is off. 2. It is determined whether the capacity of the snubber capacitor 12 is small because the snubber capacitor 10 is disabled. As a result of the determination, if the capacity of the snubber capacitor 12 is large, the process proceeds to step S5. On the other hand, when the capacity | capacitance of the snubber capacitor | condenser 12 is small, it progresses to step S8.

(S5)
The control circuit 37 determines whether or not the absolute value of the current detected by the snubber current detection means 36 is equal to or greater than a predetermined value after the dead time dt. As a result of the determination, if the value is equal to or larger than the predetermined value, the state of the snubber voltage and the snubber current shown in FIG. 3B is reached, charging or discharging of the snubber capacitor 12 is not completed during the dead time dt, and Alternatively, when the lower switch 6 is turned on, it is determined that a rush current for charging or discharging the snubber capacitor 12 flows to generate a large switching loss and noise, and the process proceeds to step S6. On the other hand, if it is less than the predetermined value, it is determined that the state of the snubber voltage and the snubber current shown in FIG.

(S6)
The control circuit 37 waits until it detects the timing at which the lower switch 6 is turned on, and proceeds to step S7 if it is detected.

(S7)
The control circuit 37 transmits a control signal to the snubber switching means 35, and the snubber switching means 35 generates a switching signal based on the received control signal, outputs it to the disconnecting switch 11, and turns it off. As a result, the second snubber capacitor 10 becomes invalid and the capacity of the snubber capacitor 12 becomes small. As a result, the time required for charging or discharging the snubber capacitor 12 can be shortened, so that the rush current when the upper switch 5 or the lower switch 6 is turned on can be reduced, and switching loss and noise can be suppressed. In step S6, the capacity of the snubber capacitor 12 is switched after waiting until the lower switch 6 is turned on. When the lower switch 6 is turned on, the snubber voltage and the snubber current of the snubber capacitor 12 are zero. Because there is. Then, the process proceeds to step S14.

(S8)
The control circuit 37 determines whether or not the peak value of the absolute value of the current detected by the snubber current detection means 36 is greater than or equal to a predetermined value during the dead time dt. As a result of the determination, if it is equal to or greater than a predetermined value, it is the state of the snubber voltage and snubber current shown in FIG. 4A, and when the lower switch 6 is turned off, the voltage applied to both ends of the lower switch 6 increases rapidly. It is determined that the switching loss (turn-off loss) due to current or the like is large, and the process proceeds to step S9. On the other hand, if it is less than the predetermined value, the process proceeds to step S12.

(S9)
The control circuit 37 waits until it detects the timing at which the lower switch 6 is turned on, and proceeds to step S10 if it is detected.

(S10)
The control circuit 37 transmits a control signal to the snubber switching means 35, and the snubber switching means 35 generates a switching signal based on the received control signal, outputs it to the disconnecting switch 11, and turns it on. As a result, the second snubber capacitor 10 becomes effective and the capacity of the snubber capacitor 12 becomes large. As a result, when the lower switch 6 is turned off, an increase in voltage applied to both ends of the lower switch 6 can be moderated, and switching loss due to tail current can be reduced. In step S9, the capacity of the snubber capacitor 12 is switched until the lower switch 6 is turned on. The lower switch 6 is turned on when the snubber voltage and the snubber current of the snubber capacitor 12 are zero. Because there is.

(S11)
Furthermore, the control circuit 37 transmits a control signal to the drive circuit 34 so that the dead time dt of the drive signal output from the drive circuit 34 becomes longer. As a result, when the upper switch 5 or the lower switch 6 is turned off, the increase or decrease in the voltage applied to both ends of the snubber capacitor 12 is moderated, so that the charging or discharging of the snubber capacitor 12 is completed during the dead time dt. It can be suppressed that it cannot be performed. Then, the process proceeds to step S14.

(S12)
The control circuit 37 determines whether or not a reverse current is generated as the current detected by the snubber current detection means 36 before the dead time dt ends. As a result of the determination, when a current in the reverse direction is generated, it is the state of the snubber voltage and the snubber current shown in FIG. 4 (c). It is determined that the switch 6 cannot perform zero volt switching, a rush current flows and a large switching loss and noise are generated, and the process proceeds to step S13. On the other hand, if no reverse current is generated, the process proceeds to step S14.

(S13)
The control circuit 37 transmits a control signal to the drive circuit 34 so that the dead time dt of the drive signal output from the drive circuit 34 is shortened. As a result, the occurrence of commutation of the load current during the dead time dt can be avoided. Then, the process proceeds to step S14.

(S14)
And the control circuit 37 determines whether the pan etc. are mounted by the method similar to step S3. As a result of the determination, when a pan or the like is placed, the control circuit 37 proceeds to step S15 in order to adjust the heating output. On the other hand, if a pan or the like is not placed, the process returns to step S3.

(S15)
The control circuit 37 detects input power based on the input current detected by the input current detection means 31 and the input voltage detected by the input voltage detection means 32. Then, the control circuit 37 compares the detected input power with the set power set by the user via the operation input means 33. As a result of the comparison, when it is determined that the set power is smaller than the detected input power, the process proceeds to step S16. If it is determined that the set power is greater than the detected input power, the process proceeds to step S17. If it is determined that the set power is substantially the same as the detected input power, the process proceeds to step S18.

(S16)
The control circuit 37 lowers the drive signal level (increases the drive frequency) with respect to the drive circuit 34 to reduce the heating output. Then, the process proceeds to step S18.

(S17)
The control circuit 37 raises the drive signal level (lowers the drive frequency) with respect to the drive circuit 34 and increases the heating output. Then, the process proceeds to step S18.

(S18)
Based on the operation signal received from the operation input means 33, the control circuit 37 determines whether or not the operation of the heating stop request by the user has been performed. If the result of the determination is that a heating stop request operation has been carried out, the process proceeds to step S19. On the other hand, when the operation to request heating stop is not performed, the process returns to step S4 and the heating operation is continued.

(S19)
The control circuit 37 causes the drive circuit 34 to stop outputting the drive signal to stop the heating operation. And it returns to step S1 and waits until the heating start request | requirement by a user is implemented.

(Effect of Embodiment 1)
With the configuration and operation as described above, in the switching element of the inverter circuit 22, switching loss (turn-off loss) due to tail current or the like is reduced, charging or discharging of the snubber capacitor 12 is completed during the dead time dt, and Since the rush current flowing through the snubber capacitor 12 can be reduced by avoiding commutation of the load current, switching loss and noise can be reduced.
In addition, since noise in the switching operation can be reduced as described above, the current and voltage can be accurately detected by the input current detecting means 31, the input voltage detecting means 32, and the snubber current detecting means 36, and no load is applied. The state detection can also be reliably performed.
And since switching loss can be reduced as mentioned above, heating efficiency can be improved and generation | occurrence | production of the failure of a switching element can be suppressed.
Furthermore, when installing a cooling fan or the like for cooling the switching element, the output can be reduced, and the energy used for cooling and noise caused by cooling air can be suppressed.

Embodiment 2. FIG.
The induction heating cooker according to the present embodiment will be described focusing on differences from the configuration and operation of the induction heating cooker according to the first embodiment. In addition, the structure of the induction heating cooking appliance which concerns on this Embodiment is the same as the structure shown by FIG. 1 of the induction heating cooking appliance which concerns on Embodiment 1. FIG.

(Snubber capacitor 12 capacity switching operation)
FIG. 7 is a flowchart showing a heating control operation in the induction heating cooker according to Embodiment 2 of the present invention. Hereinafter, with reference to FIG. 7, the induction heating according to the present embodiment including the switching operation of the capacity of the snubber capacitor 12 will be described with a focus on differences from the operation shown in the flowchart of FIG. 6 in the first embodiment. The heating control operation in the cooking device will be described.

(S7)
The control circuit 37 transmits a control signal to the snubber switching means 35, and the snubber switching means 35 generates a switching signal based on the received control signal, outputs it to the disconnecting switch 11, and turns it off. As a result, the second snubber capacitor 10 becomes invalid and the capacity of the snubber capacitor 12 becomes small. As a result, the time required for charging or discharging the snubber capacitor 12 can be shortened, so that the rush current when the upper switch 5 or the lower switch 6 is turned on can be reduced, and switching loss and noise can be suppressed. Then, the process proceeds to step S20.

(S20)
Then, the control circuit 37 transmits a control signal to the drive circuit 34 so that the dead time dt of the drive signal output from the drive circuit 34 is shortened. This is because the time required for charging or discharging the snubber capacitor 12 is shortened by reducing the capacity of the snubber capacitor 12 in step S7, and the timing at which the load current commutates is also advanced. As a result, the occurrence of commutation of the load current during the dead time dt can be avoided. Then, the process proceeds to step S14.

(S8)
The control circuit 37 determines whether or not the peak value of the absolute value of the current detected by the snubber current detection means 36 is greater than or equal to a predetermined value during the dead time dt. As a result of the determination, if it is equal to or greater than a predetermined value, it is the state of the snubber voltage and snubber current shown in FIG. 4A, and when the lower switch 6 is turned off, the voltage applied to both ends of the lower switch 6 increases rapidly. It is determined that the switching loss (turn-off loss) due to current or the like is large, and the process proceeds to step S9. On the other hand, if it is less than the predetermined value, the process proceeds to step S14.

  Moreover, in FIG. 7, the process of step S1-step S6, step S9-step S11, and step S14-step S19 is the same as that of Embodiment 1, and in the heating control operation | movement of this Embodiment. There is no processing of step S12 and step S13 in FIG. 6 of the first embodiment.

(Effect of Embodiment 2)
The same effects as those of the first embodiment can be obtained by the operation as described above.

Embodiment 3 FIG.
The induction heating cooker according to the present embodiment will be described focusing on the differences from the configuration and operation of the induction heating cooker according to the second embodiment.

(Circuit configuration of induction heating cooker)
FIG. 8 is a circuit configuration diagram of the induction heating cooker according to the third embodiment of the present invention.
Between the resonant capacitor 14 and the inverter circuit 22, output current detection means 38 for detecting a load current flowing in the load circuit 23 is installed. The output current detection means 38 is connected to the control circuit 37 and transmits the detected load current to the control circuit 37. Further, the induction heating cooker according to the present embodiment is not provided with the snubber current detection means 36. Other configurations are the same as the circuit configuration of the induction heating cooker shown in FIG. 1 of the first embodiment.
In FIG. 8, the output current detection means 38 is installed between the resonant capacitor 14 and the inverter circuit 22, but is not limited to this, and the output current detection means 38 is between the inverter circuit 22 and the heating coil 13. Alternatively, it goes without saying that it may be installed between the heating coil 13 and the resonant capacitor 14.

(Snubber capacitor 12 capacity switching operation)
FIG. 9 is a flowchart showing a heating control operation in the induction heating cooker according to the third embodiment of the present invention. Hereinafter, with reference to FIG. 9, the induction heating according to the present embodiment including the switching operation of the capacity of the snubber capacitor 12 will be described with a focus on differences from the operation shown in the flowchart of FIG. 7 in the second embodiment. The heating control operation in the cooking device will be described.

(S3)
The control circuit 37 determines whether or not an appropriate pan or the like is placed based on the input current detected by the input current detection unit 31 and the input voltage detected by the input voltage detection unit 32. As a result of the determination, if an appropriate pan or the like is placed, the process proceeds to step S21. On the other hand, if an appropriate pan or the like is not placed, the process returns to step S1.
The control circuit 37 determines whether or not an appropriate pan or the like is placed based on the input current detected by the input current detection unit 31 and the input voltage detected by the input voltage detection unit 32. However, the present invention is not limited to this, and the determination may be made based only on the input current. Further, the determination may be made based on the input current or the like and the current detected by the output current detection means 38.

(S21)
The control circuit 37 detects input power based on the input current detected by the input current detection unit 31, the input voltage detected by the input voltage detection unit 32, and the load current detected by the output current detection unit 38. To do. Then, the process proceeds to step S22.
In the present embodiment, as shown in FIG. 8, the output current detection means 38 is installed, and the load current detected by the output current detection means 38 and the input current detection means 31 are detected as described above. The input power is detected on the basis of the input current detected and the input voltage detected by the input voltage detection means 32. However, the present invention is not limited to this, and is detected by the input current detection means 31. The input power may be detected based only on the input current and the voltage detected by the input voltage detection means 32. In this case, the output current detection means 38 may not be installed.

(S22)
The control circuit 37 compares the detected input power with a predetermined value. As a result of the comparison, when it is determined that the detected input power is less than the predetermined value, the process proceeds to step S23. On the other hand, when it determines with the detected input power being more than predetermined value, it progresses to step S24.

(S23)
The control circuit 37 is in a state where the capacitance of the snubber capacitor 12 is small because the second snubber capacitor 10 is disabled while the separation switch 11 is off, or the second snubber capacitor is present when the separation switch 11 is on. It is determined whether or not the capacity of the snubber capacitor 12 is large when 10 is enabled. As a result of the determination, when the capacity of the snubber capacitor 12 is large, charging or discharging of the snubber capacitor 12 is not completed during the dead time dt, and the snubber capacitor 12 is charged or discharged when the upper switch 5 or the lower switch 6 is turned on. Therefore, it is determined that the large rush current flows and large switching loss and noise are likely to occur, and the process proceeds to step S6. On the other hand, when the capacity | capacitance of the snubber capacitor | condenser 12 is small, it progresses to step S14.

(S24)
The control circuit 37 is in a state where the capacity of the snubber capacitor 12 is large because the second snubber capacitor 10 is enabled while the separation switch 11 is on, or the second snubber capacitor is present when the separation switch 11 is off. It is determined whether or not the capacity of the snubber capacitor 12 is small because 10 is invalid. As a result of the determination, when the capacity of the snubber capacitor 12 is small, when the lower switch 6 is turned off, the voltage applied to both ends of the lower switch 6 suddenly increases and the switching loss (turn-off loss) due to the tail current or the like increases. Determination is made, and the process proceeds to step S9. On the other hand, when the capacity | capacitance of the snubber capacitor | condenser 12 is large, it progresses to step S14.

(S15)
The control circuit 37 detects input power based on the input current detected by the input current detection unit 31, the input voltage detected by the input voltage detection unit 32, and the load current detected by the output current detection unit 38. To do. Then, the control circuit 37 compares the detected input power with the set power set by the user via the operation input means 33. As a result of the comparison, when it is determined that the set power is smaller than the detected input power, the process proceeds to step S16. If it is determined that the set power is greater than the detected input power, the process proceeds to step S17. If it is determined that the set power is substantially the same as the detected input power, the process proceeds to step S18.
In the present embodiment, as shown in FIG. 8, the output current detection means 38 is installed, and the load current detected by the output current detection means 38 and the input current detection means 31 are detected as described above. The input power is detected on the basis of the input current detected and the input voltage detected by the input voltage detection means 32. However, the present invention is not limited to this, and the first and second embodiments are not limited thereto. Similarly, the input power may be detected based only on the input current detected by the input current detection unit 31 and the input voltage detected by the input voltage detection unit 32. In this case, the output current detection means 38 may not be installed.

(S18)
Based on the operation signal received from the operation input means 33, the control circuit 37 determines whether or not the operation of the heating stop request by the user has been performed. If the result of the determination is that a heating stop request operation has been carried out, the process proceeds to step S19. On the other hand, when the operation of the heating stop request is not performed, the process returns to step S21 and the heating operation is continued.

  Further, in FIG. 9, the processes of step S1, step S2, step S6, step S7, step S9 to step S11, step S14 to step S17, step S19, and step S20 are the same as those in the second embodiment. And in the heating control operation of the present embodiment, there is no processing of step S4, step S5 and step S8 in FIG. 7 of the second embodiment.

(Effect of Embodiment 3)
As in the above configuration and operation, when the input power is less than the predetermined value, the capacity of the snubber capacitor 12 is switched to a small state and the dead time dt is shortened. When the input power is greater than the predetermined value, the snubber capacitor 12 In the switching element of the inverter circuit 22, switching loss (turn-off loss) due to tail current or the like is reduced in the switching element of the inverter circuit 22 and the dead time dt is increased in the snubber capacitor 12 during the dead time dt. Since rush current flowing through the snubber capacitor 12 can be reduced by completing charging or discharging and avoiding commutation of load current, switching loss and noise can be reduced.
In addition, since noise in the switching operation can be reduced as described above, the current and voltage can be accurately detected by the input current detecting means 31, the input voltage detecting means 32, and the output current detecting means 38, and no load is applied. The state detection can also be reliably performed.
And since switching loss can be reduced as mentioned above, heating efficiency can be improved and generation | occurrence | production of the failure of a switching element can be suppressed.
Furthermore, when installing a cooling fan or the like for cooling the switching element, the output can be reduced, and the energy used for cooling and noise caused by cooling air can be suppressed.

Embodiment 4 FIG.
The induction heating cooker according to the present embodiment will be described focusing on differences from the configuration and operation of the induction heating cooker according to the third embodiment. The configuration of the induction heating cooker according to the present embodiment is the same as the configuration shown in FIG. 8 of the induction heating cooker according to the third embodiment.

(Snubber capacitor 12 capacity switching operation)
FIG. 10 is a flowchart showing a heating control operation in the induction heating cooker according to the fourth embodiment of the present invention. Hereinafter, with reference to FIG. 10, the induction heating according to the present embodiment including the switching operation of the capacity of the snubber capacitor 12 will be described, focusing on the difference from the operation shown in the flowchart of FIG. 9 in the third embodiment. The heating control operation in the cooking device will be described.

(S3)
The control circuit 37 determines whether or not an appropriate pan or the like is placed based on the input current detected by the input current detection unit 31 and the input voltage detected by the input voltage detection unit 32. As a result of the determination, if an appropriate pan or the like is placed, the process proceeds to step S25. On the other hand, if an appropriate pan or the like is not placed, the process returns to step S1.
The control circuit 37 determines whether or not an appropriate pan or the like is placed based on the input current detected by the input current detection unit 31 and the input voltage detected by the input voltage detection unit 32. However, the present invention is not limited to this, and the determination may be made based only on the input current.

(S25)
The control circuit 37 receives the load current detected by the output current detection means 38. Then, the process proceeds to step S26.

(S26)
The control circuit 37 compares the received load current with a predetermined value. As a result of the comparison, when it is determined that the load current is greater than or equal to a predetermined value, the process proceeds to step S23. On the other hand, when it determines with the detected load current being less than a predetermined value, it progresses to step S24.

(S15)
The control circuit 37 detects input power based on the input current detected by the input current detection unit 31, the input voltage detected by the input voltage detection unit 32, and the load current detected by the output current detection unit 38. To do. Then, the control circuit 37 compares the detected input power with the set power set by the user via the operation input means 33. As a result of the comparison, when it is determined that the set power is smaller than the detected input power, the process proceeds to step S16. If it is determined that the set power is greater than the detected input power, the process proceeds to step S17. If it is determined that the set power is substantially the same as the detected input power, the process proceeds to step S18.
In the present embodiment, as shown in FIG. 8, the output current detection means 38 is installed, and the load current detected by the output current detection means 38 and the input current detection means 31 are detected as described above. The input power is detected on the basis of the input current detected and the input voltage detected by the input voltage detection means 32. However, the present invention is not limited to this, and the first and second embodiments are not limited thereto. Similarly, the input power may be detected based only on the input current detected by the input current detection unit 31 and the input voltage detected by the input voltage detection unit 32.

(S18)
Based on the operation signal received from the operation input means 33, the control circuit 37 determines whether or not the operation of the heating stop request by the user has been performed. If the result of the determination is that a heating stop request operation has been carried out, the process proceeds to step S19. On the other hand, when the operation of the heating stop request is not performed, the process returns to step S25 and the heating operation is continued.

  Further, in FIG. 10, the processing of step S1, step S2, step S6, step S7, step S9 to step S11, step S14 to step S17, step S19, step S20, step S23, and step S24 is described in the embodiment. 3 and in the heating control operation of the present embodiment, there is no processing of step S21 and step S22 in FIG. 9 of the third embodiment.

(Effect of Embodiment 4)
As in the above configuration and operation, when the load current is less than the predetermined value, the capacity of the snubber capacitor 12 is switched to a small state and the dead time dt is shortened. When the load current is greater than the predetermined value, the snubber capacitor 12 In the switching element of the inverter circuit 22, switching loss (turn-off loss) due to tail current or the like is reduced in the switching element of the inverter circuit 22 and the dead time dt is increased in the snubber capacitor 12 during the dead time dt. Since rush current flowing through the snubber capacitor 12 can be reduced by completing charging or discharging and avoiding commutation of load current, switching loss and noise can be reduced.
In addition, since noise in the switching operation can be reduced as described above, the current and voltage can be accurately detected by the input current detecting means 31, the input voltage detecting means 32, and the output current detecting means 38, and no load is applied. The state detection can also be reliably performed.

Embodiment 5 FIG.
The induction heating cooker according to the present embodiment will be described focusing on differences from the configuration and operation of the induction heating cooker according to the third embodiment. The configuration of the induction heating cooker according to the present embodiment is the same as the configuration shown in FIG. 8 of the induction heating cooker according to the third embodiment.

(Snubber capacitor 12 capacity switching operation)
FIG. 11 is a flowchart showing a heating control operation in the induction heating cooker according to the fifth embodiment of the present invention. Hereinafter, with reference to FIG. 11, the induction heating according to the present embodiment including the switching operation of the capacity of the snubber capacitor 12 will be described, focusing on the difference from the operation shown in the flowchart of FIG. 9 in the third embodiment. The heating control operation in the cooking device will be described.

(S3)
The control circuit 37 determines whether or not an appropriate pan or the like is placed based on the input current detected by the input current detection unit 31 and the input voltage detected by the input voltage detection unit 32. As a result of the determination, if an appropriate pan or the like is placed, the process proceeds to step S27. On the other hand, if an appropriate pan or the like is not placed, the process returns to step S1.
The control circuit 37 determines whether or not an appropriate pan or the like is placed based on the input current detected by the input current detection unit 31 and the input voltage detected by the input voltage detection unit 32. However, the present invention is not limited to this, and the determination may be made based only on the input current.

(S27)
The control circuit 37 detects input power based on the input current detected by the input current detection unit 31, the input voltage detected by the input voltage detection unit 32, and the load current detected by the output current detection unit 38. To do. Then, the process proceeds to step S22.
In the present embodiment, as shown in FIG. 8, the output current detection means 38 is installed, and the load current detected by the output current detection means 38 and the input current detection means 31 are detected as described above. The input power is detected on the basis of the input current detected and the input voltage detected by the input voltage detection means 32. However, the present invention is not limited to this, and is detected by the input current detection means 31. The input power may be detected based only on the input current and the input voltage detected by the input voltage detection means 32.

(S22)
The control circuit 37 compares the detected input power with a predetermined value. As a result of the comparison, when it is determined that the detected input power is less than the predetermined value, the process proceeds to step S23. On the other hand, when it determines with the detected input power being more than predetermined value, it progresses to step S28.

(S28)
The control circuit 37 compares the load current received from the output current detection means 38 with a predetermined value. As a result of the comparison, when it is determined that the load current is less than the predetermined value, the process proceeds to step S23. On the other hand, when it determines with load current being more than predetermined value, it progresses to step S24.

(S15)
The control circuit 37 detects input power based on the input current detected by the input current detection unit 31, the input voltage detected by the input voltage detection unit 32, and the load current detected by the output current detection unit 38. To do. Then, the control circuit 37 compares the detected input power with the set power set by the user via the operation input means 33. As a result of the comparison, when it is determined that the set power is smaller than the detected input power, the process proceeds to step S16. If it is determined that the set power is greater than the detected input power, the process proceeds to step S17. If it is determined that the set power is substantially the same as the detected input power, the process proceeds to step S18.
In the present embodiment, as shown in FIG. 8, the output current detection means 38 is installed, and the load current detected by the output current detection means 38 and the input current detection means 31 are detected as described above. The input power is detected on the basis of the input current detected and the input voltage detected by the input voltage detection means 32. However, the present invention is not limited to this, and the first and second embodiments are not limited thereto. Similarly, the input power may be detected based only on the input current detected by the input current detection unit 31 and the input voltage detected by the input voltage detection unit 32.

(S18)
Based on the operation signal received from the operation input means 33, the control circuit 37 determines whether or not the operation of the heating stop request by the user has been performed. If the result of the determination is that a heating stop request operation has been carried out, the process proceeds to step S19. On the other hand, when the operation of the heating stop request is not performed, the process returns to step S27 and the heating operation is continued.

  Moreover, in FIG. 11, the process of step S1, step S2, step S6, step S7, step S9 to step S11, step S14, step S16, step S17, step S19, step S20, step S23, and step S24 is It is the same as that of Embodiment 3, and in the heating control operation of this embodiment, there is no processing of step S21 in FIG. 9 of Embodiment 3.

(Effect of Embodiment 5)
As in the above configuration and operation, when the input power is less than the predetermined value or the load current is less than the predetermined value, the capacity of the snubber capacitor 12 is switched to a small state and the dead time dt is shortened so that the input power is predetermined. When the load current is equal to or greater than the predetermined value and the load current is equal to or greater than the predetermined value, the switching capacity of the snubber capacitor 12 is switched to a large state and the dead time dt is lengthened. (Turn-off loss) is reduced, and charging or discharging in the snubber capacitor 12 is completed during the dead time dt, and commutation of the load current can be avoided, so that the rush current flowing through the snubber capacitor 12 can be reduced. Reduce switching loss and noise It can be.
In addition, since noise in the switching operation can be reduced as described above, the current and voltage can be accurately detected by the input current detecting means 31, the input voltage detecting means 32, and the output current detecting means 38, and no load is applied. The state detection can also be reliably performed.

In the present embodiment, the input power is detected based on the input current detected by the input current detection means 31 and the input voltage detected by the input voltage detection means 32, and based on this input power, The determination of the placement of the pan or the like, and the control of the drive signal level, the capacity of the snubber condenser 12 and the length of the dead time dt are implemented, but the present invention is not limited to this. For example, in FIG. It is good also as a circuit structure as shown. That is, the heating coil voltage detecting means 39 for detecting the voltage across the heating coil 13 (hereinafter referred to as output voltage), and the output voltage and the output current detecting means 38 detected by the heating coil voltage detecting means 39 are detected. The output power detection means 40 for detecting the output power based on the load current thus provided may be installed, and the input current detection means 31 and the input voltage detection means 32 may not be installed. At this time, the output power detection means 40 transmits the detected output power to the control circuit 37. The control circuit 37 determines the placement of the pan or the like based on the output power instead of the input power, and Control of the drive signal level, the capacity of the snubber capacitor 12, and the length of the dead time dt may be performed. The output power detection means 40 is not configured to detect the output power based on the load current detected by the output current detection means 38 and the output voltage detected by the heating coil voltage detection means 39, but the heating coil The voltage detection means 39 transmits the detected output voltage to the control circuit 37 that transmits the output power, and the control circuit 37 outputs the output power based on the received output voltage and the load current detected by the output current detection means 38. It is good also as a structure to calculate. In this case, the output power detection means 40 need not be installed.
The output power detection means 40 corresponds to the “power detection means” of the present invention.

  Moreover, the circuit configuration shown in FIG. 12 can be applied to the induction heating cooker according to the first embodiment, the second embodiment, or the fourth embodiment. In this case, in the flowchart shown in FIG. 6, FIG. 7 or FIG. 10, the control circuit 37 performs the determination of placing the pan or the like in step S <b> 3 and step S <b> 14 and the control of the drive signal level in steps S <b> 15 to S <b> 17. What is necessary is just to implement based on the above-mentioned output electric power. Similarly, the circuit configuration shown in FIG. 12 can also be applied to the induction heating cooker according to the third embodiment. In this case, in the flowchart shown in FIG. 9, the control circuit 37 determines the placement of the pan or the like in step S3 and step S14, the calculation of the input power in step S21, and the control of the drive signal level in steps S15 to S17. May be implemented based on the output power described above.

Embodiment 6 FIG.
The induction heating cooker according to the present embodiment will be described focusing on differences from the configuration and operation of the induction heating cooker according to the third embodiment.

(Circuit configuration of induction heating cooker)
FIG. 13: is a circuit block diagram of the induction heating cooking appliance which concerns on Embodiment 6 of this invention.
As shown in FIG. 13, the lower switch 6 is connected in parallel with the first lower snubber capacitor 9a and the series circuit of the second lower snubber capacitor 10a and the lower disconnect switch 11a. The upper switch 5 is connected in parallel with a first upper snubber capacitor 9b and a series circuit of a second upper snubber capacitor 10b and an upper disconnect switch 11b. The first lower snubber capacitor 9a, the second lower snubber capacitor 10a, the lower disconnect switch 11a, the first upper snubber capacitor 9b, the second upper snubber capacitor 10b, and the upper disconnect switch 11b constitute a snubber capacitor 12a. At least the upper switch 5, the lower switch 6, the diode 7, the diode 8, and the snubber capacitor 12a constitute an inverter circuit 22a. Further, a clamp diode 41 is connected in parallel to the resonance capacitor 14, and the load circuit 23 a is configured by the heating coil 13, the resonance capacitor 14, and the clamp diode 41.

As shown in FIG. 13, the second lower snubber capacitor 10a is connected to the high potential side of the lower disconnect switch 11a, and the second upper snubber capacitor 10b is connected to the high potential side of the upper disconnect switch 11b. However, the present invention is not limited to this, and the second lower snubber capacitor 10a is connected to the lower potential side of the lower disconnect switch 11a, or the second upper snubber capacitor 10b is connected to the lower potential side of the upper disconnect switch 11b. Needless to say.
Moreover, what is necessary is just to use components which have switching functions, such as a relay circuit, IGBT, or MOSFET, for example for the said lower separation switch 11a and the upper separation switch 11b.
The snubber capacitor 12a corresponds to the “second snubber capacitor” of the present invention.

  A snubber switching means 35 a for outputting a switching signal to each of the lower disconnect switch 11 a and the upper disconnect switch 11 b and controlling the on / off operation is connected to the control circuit 37.

(Operation of induction heating cooker)
The snubber switching unit 35a generates a switching signal based on the control signal received from the control circuit 37, outputs the switching signal to the lower disconnecting switch 11a and the upper disconnecting switch 11b, and performs the on / off operation. Thereby, the capacity of the snubber capacitor 12a is switched to a large state or a small state.

FIG. 14 is a diagram illustrating a waveform example of a drive signal input to the inverter circuit 22a of the induction heating cooker according to the sixth embodiment of the present invention.
As shown in FIG. 13, the clamp diode 41 is connected in parallel to the resonance capacitor 14, so that the potential at the connection point between the resonance capacitor 14 and the heating coil 13 is increased even when the lower switch 6 is on. Is clamped to the low potential side of the DC bus by the clamp diode 41, the reverse voltage is not applied to the heating coil 13, and the load current does not commutate. Therefore, in the induction heating cooker according to the present embodiment, the output can be adjusted by changing the conduction time ratio between the upper switch 5 and the lower switch 6 while keeping the drive frequency of the inverter circuit 22a constant. . At this time, as shown in FIG. 14, FIG. 14A shows a drive signal in the case of medium output, FIG. 14B shows a high output, and FIG. 14C shows a drive signal in the case of low output. Thus, in this Embodiment, even if a some heating coil is arrange | positioned adjacently by being able to drive with a constant driving frequency, the interference sound in the heating coil 13 and a pan can be suppressed.

  The control circuit 37 controls the on / off operation of the upper switch 5, the lower switch 6, and the lower disconnect switch 11a via the drive circuit 34 and the snubber switching unit 35a, and the drive circuit according to the third or fourth embodiment. The control is performed in the same manner as the on / off operation control in the upper switch 5, the lower switch 6, and the disconnecting switch 11 via 34 and the snubber switching means 35.

(Effect of Embodiment 6)
Since the clamp diode 41 is connected in parallel to the resonant capacitor 14 as in the above configuration, no reverse voltage is applied to the heating coil 13, and the occurrence of commutation of the load current can be suppressed. Switching loss can be reduced.
Further, when the input power is less than a predetermined value, the capacity of the snubber capacitor 12a is switched to a small state, and when the input power is equal to or greater than the predetermined value, the capacity of the snubber capacitor 12a is switched to a large state. In the switching element 22a, the switching loss (turn-off loss) due to the tail current or the like is reduced, the charging or discharging in the snubber capacitor 12a is completed during the dead time dt, and the commutation of the load current can be avoided. Since the rush current flowing through the capacitor 12a can be reduced, switching loss and noise can be reduced.
In addition, since noise in the switching operation can be reduced as described above, the current and voltage can be accurately detected by the input current detecting means 31, the input voltage detecting means 32, and the output current detecting means 38, and no load is applied. The state detection can also be reliably performed.

In the present embodiment, the output current detection means 38 is provided and the load current is detected. However, the present invention is not limited to this, and as in the first embodiment, the output current detection means 38 Instead, the snubber current detection means 36 may be provided. At this time, the control circuit 37 may perform the heating control operation based on the flowchart shown in FIG. 7 in the first embodiment or the flowchart shown in FIG. 8 in the second embodiment. With the above configuration and operation, the same effects as described above can be obtained.
In the present embodiment, the input current detection means 31 and the input voltage detection means 32 are provided to detect the input voltage. However, the present invention is not limited to this, and FIG. 12 in the fifth embodiment. As in the circuit configuration diagram shown, instead of the input current detection means 31 and the input voltage detection means 32, a heating coil voltage detection means 39 and an output power detection means 40 may be provided to detect the output power. At this time, the control circuit 37 performs the heating control operation based on the output power detected by the output power detection means 40 based on the flowchart shown in FIG. 11 in the fifth embodiment and instead of the input power. That's fine. As described above, the control circuit 37 calculates the output power based on the load current detected by the output current detection means 38 and the output voltage detected by the heating coil voltage detection means 39. In this case, the output power detection means 40 may not be installed.

  1 AC power source, 2 diode bridge circuit, 3 choke coil, 4 smoothing capacitor, 5 upper switch, 6 lower switch, 7, 8 diode, 9 first snubber capacitor, 9a first lower snubber capacitor, 9b first upper snubber capacitor, 10 Second snubber condenser, 10a Second lower snubber condenser, 10b Second upper snubber condenser, 11 Disconnect switch, 11a Lower disconnect switch, 11b Upper disconnect switch, 12, 12a Snubber condenser, 13 Heating coil, 14 Resonance condenser, 21 DC Power circuit, 22, 22a Inverter circuit, 23, 23a Load circuit, 31 Input current detection means, 32 Input voltage detection means, 33 Operation input means, 34 Drive circuit, 35 Snubber switching means, 36 Snubber current detection Stage, 37 control circuit, 38 an output current detecting means, 39 heating coil voltage detector, 40 an output power detection unit, 41 clamp diodes.

Claims (13)

A DC power supply circuit that converts an AC voltage supplied from the AC power source into a DC voltage;
At least two switching elements connected in series to the output terminal of the DC power supply circuit, a diode connected in antiparallel to each switching element, and a capacitance connected in parallel to one of the switching elements A snubber capacitor that can be switched, and an inverter circuit that converts the DC voltage into a high-frequency voltage;
A load circuit constituted by a series resonance circuit of a heating coil and a resonance capacitor connected in parallel to the switching element to which the snubber capacitor is connected in parallel;
A drive circuit for turning on / off the switching element and generating a drive signal having a predetermined dead time;
Snubber switching means for switching the capacity of the snubber capacitor;
A control circuit for controlling the drive circuit and the snubber switching means;
Snubber current detection means for detecting the current flowing through the snubber capacitor;
With
The control circuit includes:
If it is determined that the absolute value of the current detected after the dead time by the snubber current detection means is greater than or equal to a predetermined value, the snubber switching means switches the capacity of the snubber capacitor to a small state,
When it is determined that the peak value of the absolute value of the current detected during the dead time by the snubber current detection means is greater than or equal to a predetermined value, the snubber switching means is switched to a large capacity of the snubber capacitor, And increasing the dead time for the drive signal in the drive circuit,
An induction heating cooker characterized by causing the drive circuit to shorten the dead time for the drive signal when it is determined that commutation has occurred in the current detected by the snubber current detection means during the dead time. A DC power supply circuit that converts an AC voltage supplied from the AC power source into a DC voltage;
At least two switching elements connected in series to the output terminal of the DC power supply circuit, a diode connected in antiparallel to each switching element, and a capacitance connected in parallel to one of the switching elements A snubber capacitor that can be switched, and an inverter circuit that converts the DC voltage into a high-frequency voltage;
A load circuit constituted by a series resonance circuit of a heating coil and a resonance capacitor connected in parallel to the switching element to which the snubber capacitor is connected in parallel;
A drive circuit for turning on / off the switching element and generating a drive signal having a predetermined dead time;
Snubber switching means for switching the capacity of the snubber capacitor;
A control circuit for controlling the drive circuit and the snubber switching means;
Snubber current detection means for detecting the current flowing through the snubber capacitor;
With
The control circuit includes:
When it is determined that the absolute value of the current detected after the dead time by the snubber current detection means is greater than or equal to a predetermined value, the snubber switching means switches the capacity of the snubber capacitor to a small state, and the driving Causing the circuit to shorten the dead time for the drive signal;
When it is determined that the peak value of the absolute value of the current detected during the dead time by the snubber current detection means is greater than or equal to a predetermined value, the snubber switching means is switched to a large capacity of the snubber capacitor, And the said induction circuit makes the said dead time long about the said drive signal. The induction heating cooking appliance characterized by the above-mentioned. A DC power supply circuit that converts an AC voltage supplied from the AC power source into a DC voltage;
At least two switching elements connected in series to the output terminal of the DC power supply circuit, a diode connected in antiparallel to each switching element, and a capacitance connected in parallel to one of the switching elements A snubber capacitor that can be switched, and an inverter circuit that converts the DC voltage into a high-frequency voltage;
A load circuit constituted by a series resonance circuit of a heating coil and a resonance capacitor connected in parallel to the switching element to which the snubber capacitor is connected in parallel;
A drive circuit for turning on / off the switching element and generating a drive signal having a predetermined dead time;
Snubber switching means for switching the capacity of the snubber capacitor;
A control circuit for controlling the drive circuit and the snubber switching means;
Power detection means for detecting input power or output power in the cooker;
With
The control circuit includes:
If it is determined that the input power or the output power detected by the power detection means is greater than or equal to a predetermined value, the snubber switching means switches the snubber capacitor to a larger capacity, and the drive circuit is longer the dead time for the drive signal,
When it is determined that the input power or the output power detected by the power detection means is less than the predetermined value, the snubber switching means switches the capacity of the snubber capacitor to a small state, and the drive circuit The induction heating cooker characterized in that the dead time is shortened for the drive signal. A DC power supply circuit that converts an AC voltage supplied from the AC power source into a DC voltage;
At least two switching elements connected in series to the output terminal of the DC power supply circuit, a diode connected in antiparallel to each switching element, and a capacitance connected in parallel to one of the switching elements A snubber capacitor that can be switched, and an inverter circuit that converts the DC voltage into a high-frequency voltage;
A load circuit constituted by a series resonance circuit of a heating coil and a resonance capacitor connected in parallel to the switching element to which the snubber capacitor is connected in parallel;
A drive circuit for turning on / off the switching element and generating a drive signal having a predetermined dead time;
Snubber switching means for switching the capacity of the snubber capacitor;
A control circuit for controlling the drive circuit and the snubber switching means;
Output current detection means for detecting a load current flowing in the load circuit;
With
The control circuit includes:
When it is determined that the load current detected by the output current detection means is greater than or equal to a predetermined value, the snubber switching means is switched to a large capacity of the snubber capacitor, and the drive circuit It was long the dead time for,
When it is determined that the load current detected by the output current detection means is less than the predetermined value, the snubber switching means is switched to a state where the capacity of the snubber capacitor is small , and the drive circuit causes the drive to An induction heating cooker characterized in that the dead time is shortened for a signal. A DC power supply circuit that converts an AC voltage supplied from the AC power source into a DC voltage;
At least two switching elements connected in series to the output terminal of the DC power supply circuit, a diode connected in antiparallel to each switching element, and a capacitance connected in parallel to one of the switching elements A snubber capacitor that can be switched, and an inverter circuit that converts the DC voltage into a high-frequency voltage;
A load circuit constituted by a series resonance circuit of a heating coil and a resonance capacitor connected in parallel to the switching element to which the snubber capacitor is connected in parallel;
A drive circuit for turning on / off the switching element and generating a drive signal having a predetermined dead time;
Snubber switching means for switching the capacity of the snubber capacitor;
A control circuit for controlling the drive circuit and the snubber switching means;
Power detection means for detecting input power or output power in the cooker;
Output current detection means for detecting a load current flowing in the load circuit;
With
The control circuit includes:
It is determined that the input power or the output power detected by the power detection means is less than a first predetermined value, or the load current detected by the output current detection means is a second predetermined value. If determined to be less than, let the snubber switching means to switch the capacity of the snubber capacitor to a small state, and let the drive circuit reduce the dead time for the drive signal,
The input power or the output power detected by the power detection means is determined to be greater than or equal to the first predetermined value, and the load current detected by the output current detection means is the second power When it is determined that the value is equal to or greater than a predetermined value, the snubber switching unit is caused to switch the capacity of the snubber capacitor to a large state, and the drive circuit is caused to increase the dead time for the drive signal. Cooking device. Power detection means for detecting input power or output power in the cooker;
The control circuit determines whether or not a pan or the like is placed based on the input power or the output power detected by the power detection means. The induction heating cooker according to claim 4. The said control circuit determines whether the pan etc. are mounted based on the said input electric power or the said output electric power detected by the said electric power detection means. The Claim 3 or Claim 5 characterized by the above-mentioned. Induction heating cooker. The control circuit causes the drive circuit to generate the drive signal based on a result of comparing the input power or the output power detected by the power detection unit with a set power, and a heating output by the heating coil The induction heating cooker according to any one of claims 3 and 5 to 7, wherein the induction heating cooker is adjusted. The induction heating cooker according to claim 8, further comprising operation input means for setting the set power by an operation by a user or the like. The control circuit causes the drive circuit to generate the drive signal such that the conduction time ratio of the two switching elements is approximately 50%, respectively, and the two switching elements are alternately turned on, The induction heating cooker according to claim 8 or 9, wherein the heating output is adjusted by changing a driving frequency of the driving signal. The inverter circuit has a second snubber capacitor connected in parallel to the switching element not connected in parallel to the snubber capacitor;
The control circuit causes the drive circuit to generate a drive signal with a constant drive frequency and to turn on the two switching elements alternately, and to vary the conduction time ratio of the drive signal. The induction heating cooker according to claim 8 or 9, wherein the heating output is adjusted accordingly. The said control circuit makes the said snubber switching means switch the capacity | capacitance of the said snubber capacitor when the said switching element to which the said snubber capacitor is connected in parallel is an ON state. The induction heating cooking appliance in any one of. The induction heating cooker according to any one of claims 1 to 12, further comprising a clamp diode connected in parallel to the resonant capacitor.

Images