JP5892842B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker having a function of protecting, for example, a diode bridge that rectifies commercial power, a switching element of an inverter, and the like from abnormal current.

  In the conventional induction heating cooker, for example, “a power control differential amplifier 4 that operates by inputting a power detection value W from the power calculation circuit 1 and a power setting value WA from the power setting unit 7, and a phase difference detection circuit. 2 and the phase difference lower limit set value γA from the phase difference setting unit 8 are inputted to the differential amplifier 5 for phase difference control which operates and the diodes D1 and D2 respectively. And a drive circuit 3 for driving the switching elements SW1 and SW2 of the inverter in response to a frequency command signal from the V / f converter 6, and the phase difference within the range of the lagging phase. The output frequency of the inverter is controlled so as to be maintained at the same time "(for example, see Patent Document 1).

JP 2004-71444 A (Abstract, FIG. 1)

  When induction heating the object to be heated, if the phase of the current flowing through the heating coil advances from the phase of the output voltage of the inverter depending on the state of the object to be heated (material, size, position, etc.) and the output frequency of the inverter ), A phase advance current flows through the switching element, and the element loss increases. In addition, there is a problem that it is impossible to input desired power by performing control to avoid this phase advance.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an easy-to-use induction heating cooker that can reliably protect a switching element or the like by a lead phase current. And

An induction heating cooker according to the present invention has a DC generation circuit that converts AC power into DC power, and a plurality of switching elements connected in series, and the DC current of the DC generation circuit is driven by driving the plurality of switching elements. In an induction heating cooker having an inverter for converting to a high-frequency current and a heating coil and a resonant capacitor connected to the output terminal of the inverter and forming a resonant circuit, the positive side or the negative side between the direct current generating circuit and the inverter An element current detecting means for detecting a current flowing in one of the plurality of switching elements; and a positive or negative bus between the direct current generating circuit and the inverter. a short-circuit current detecting means for detecting a short-circuit current which flows when a short-circuit at the same time, device current current value detected by the detection means in advance When the set first predetermined threshold is reached, the output of the inverter is limited so that the power of the heating coil is lower than the set power, and the current value detected by the short-circuit current detecting means is preset. And a control means for stopping the output of the inverter when a predetermined threshold value of 3 is reached .

  According to the present invention, comprising: an element current detection means for detecting a current flowing in one of the plurality of switching elements; and a short-circuit current detection means for detecting a short-circuit current flowing when the plurality of switching elements are short-circuited at the same time. A drive signal is output to the inverter in accordance with detection signals from the element current detection means and the short-circuit current detection means to control the output of the inverter. By having both the element current detection means and the short-circuit current detection means in this way, it becomes possible to detect a current that has advanced in phase and a short-circuit of the switching element of the inverter. This element can be protected.

It is a circuit diagram which shows schematic structure of the induction heating cooking appliance which concerns on Embodiment 1. FIG. FIG. 2 is an example of a waveform of a current at a normal time and a waveform of a current at a lead phase detected by the element current detection unit of FIG. 1. It is a circuit diagram which shows schematic structure of the induction heating cooking appliance which concerns on Embodiment 2. FIG. It is a flowchart which shows operation | movement of the induction heating cooking appliance which concerns on Embodiment 2. FIG.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing a schematic configuration of the induction heating cooker according to the first embodiment, and FIG. 2 shows a waveform of a current at a normal time and a waveform of a current at a lead phase detected by the element current detection means of FIG. It is an example figure.
In FIG. 1, an induction heating cooker includes a rectifier circuit 1 that rectifies AC power of a commercial power supply, a smoothing circuit 2 that smoothes the output of the rectifier circuit 1 to DC power, and a DC current of the smoothing circuit 2 that is a high-frequency current. An inverter 3 for conversion to the inverter 3, a heating coil 4 and a resonance capacitor 5 connected to the output terminal of the inverter 3 to form a resonance circuit, input current detection means 6 for detecting an input current from a commercial power source, and switching of the inverter 3 Element current detection means 7 for detecting a current flowing through the element 3a (hereinafter referred to as “element current”), short-circuit current detection means 8 for detecting a short-circuit current flowing when the switching elements 3a and 3b of the inverter 3 are short-circuited, and control means 9 and.

  The rectifier circuit 1 described above is configured by, for example, a diode bridge, and full-wave rectifies AC power. The smoothing circuit 2 includes an inductor 2a inserted into the positive bus on the rectifier circuit 1 and a smoothing capacitor 2b connected between the positive bus and the negative bus. The inverter 3 is, for example, a half-bridge type inverter, and includes a switching element 3a, 3b connected in series between the positive and negative buses, and a snubber capacitor 3c connected in parallel to the switching element 3b. Has been. The switching elements 3a and 3b of the inverter 3 are alternately turned on / off based on a drive signal from the control means 9 and supply a high-frequency current to the above-described resonance circuit.

  The element current detection means 7 is provided on the positive side bus of the rectifier circuit 1. As can be seen from FIG. 2, it is difficult to detect the element current at the leading phase from the waveform of the coil current flowing in the heating coil 4, so the element current detection means 7 is provided on the positive side bus. Thus, it is possible to accurately detect the element current at the lead phase. In addition, although it has been described that the element current detecting means 7 is provided on the positive side bus of the rectifier circuit 1, it may be a negative side bus.

  As shown in FIG. 1, the short-circuit current detection means 8 is provided on the negative pole bus. In addition, you may provide the short circuit current detection means 8 in a positive electrode side bus-line. When the current detected by the short-circuit current detection unit 8 reaches the third predetermined threshold, the control unit 9 determines that the short-circuit current has flowed through the switching elements 3a and 3b of the inverter 3, and drives the inverter 3. Stop. Further, the control means 9 determines that the phase of the element current flowing through the switching element 3a is an advanced phase when the element current detected by the element current detection means 7 reaches the first predetermined threshold value. For example, the output of the inverter 3 is limited so that the power of the heating coil 4 is lower than the set power.

  As a factor that the phase of the element current advances and becomes the phase, for example, it occurs when the pan 20 is shaken while the pan 20 is heated by the heating coil 4. That is, when the pan 20 is lifted when the pan is shaken, the inductance value of the heating coil 4 is increased, so that the resonance frequency is lowered. In the case of the current resonance type, the drive frequency is also lowered. If the pan 20 is shaken off in this state, the inductance value decreases steeply and the resonance frequency also increases steeply. Therefore, the driving frequency that has been driven immediately before reaches the phase advance state, and the switching element 3a has an excessive advance phase. An element current will flow. If this excessive element current continues to flow, the switching element will generate excessive heat, leading to failure.

  Therefore, in the present embodiment, as described above, when the element current detected by the element current detection means 7 reaches the first predetermined threshold value, the power of the heating coil 4 becomes lower than the set power. The output of the inverter 3 is limited.

The operation of the induction heating cooker configured as described above will be described with reference to FIG.
When the user places the pan 20 on the heating coil 4 via the top plate and then instructs the start of heating by a heating start switch (not shown) of the induction heating cooker, the control means 9 is connected to the inverter 3. And start initial load detection.

  At this time, the control means 9 first drives the inverter 3 with a high frequency drive signal of 40 kHz, for example. Next, the control means 9 determines that the pan 20 is appropriate based on the input current detected by the input current detection means 6 and the coil current detected by the coil current detection means (not shown) and the threshold value for inappropriate heating determination. Determine whether or not. If the control means 9 determines that the pan 20 is suitable for heating based on the determination result, the control means 9 performs the material determination of the pan 20 based on the input current and the coil current and the material determination threshold value, and starts heating. End load detection.

  Thereafter, the control means 9 starts driving the inverter 3 with a drive signal corresponding to the material determination of the pot 20 and performs power feedback control. During the power feedback control, the element current detected by the element current detection means 7 is detected. It is determined whether or not the first predetermined threshold has been reached, and whether or not the current detected by the short-circuit current detection means 8 has reached the third set threshold.

  When the element current detected by the element current detection means 7 reaches the first predetermined threshold, the control means 9 determines that the element current flowing through the switching element 3a is in an advanced phase, and The output of the inverter 3 is limited so that the power is lower than the set power. Further, when the current detected by the short-circuit current detection unit 8 reaches the third set threshold, the control unit 9 determines that both of the switching elements 3a and 3b of the inverter 3 are short-circuited at the same time, and the inverter 3 Stop driving.

  As described above, according to the first embodiment, when the element current detected by the element current detecting means 7 reaches the first predetermined threshold, the inverter 3 is configured such that the power of the heating coil 4 is lower than the set power. So that the inverter 3 is shifted to a safe operation, and when the current detected by the short-circuit current detection means 8 reaches the third set threshold, the drive of the inverter 3 is stopped. . Thus, by having both the element current detection means 7 and the short circuit current detection means 8, it is possible to reliably protect the switching elements 3a, 3b of the inverter 3, the diode bridge of the rectifier circuit 1, and the substrate elements such as the current fuse.

  In the first embodiment, when the element current detected by the element current detecting means 7 reaches the first predetermined threshold, the output of the inverter 3 is limited so that the power of the heating coil 4 becomes lower than the set power. However, the present invention is not limited to this. As described above, when the element current reaches the first predetermined threshold, the operation may be shifted to the operation of detecting the initial load with low power. Also in this case, the drive of the inverter 3 can be shifted to a safer side, and the substrate elements such as the switching elements 3a and 3b of the inverter 3 and the diode bridge of the rectifier circuit 1 can be reliably protected.

  In the first embodiment, when the element current detected by the element current detection means 7 reaches the first predetermined threshold, the phase of the element current is determined to be a lead phase. As described above, when the change amount dI / dt per unit time of the element current (collector current) detected by the element current detection means 7 reaches the second predetermined threshold value set in advance, the power of the heating coil 4 is reduced. The output of the inverter 3 may be limited so as to be lower than the set power, or the operation may be shifted to an initial load detection operation with low power.

  Also in this case, since an excessive current due to the advance of the phase of the element current can be kept low, the substrate elements such as the switching elements 3a and 3b of the inverter 3 and the diode bridge of the rectifier circuit 1 can be reliably protected.

Embodiment 2. FIG.
In the second embodiment, for example, when the element current detected by the element current detection unit 7 reaches the first predetermined threshold, the detection signal from the short-circuit current detection unit is invalidated using this as a trigger. It is a thing.
FIG. 3 is a circuit diagram showing a schematic configuration of the induction heating cooker according to the second embodiment, and FIG. 4 is a flowchart showing the operation of the induction heating cooker according to the second embodiment. In the second embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals.

  In FIG. 3, the short-circuit current detection means 10 shown in the figure is divided by a shunt resistor 11 inserted in the negative bus of the rectifier circuit 1, resistors 12 and 13 that divide, for example, a 5 V power supply, and resistors 12 and 13. The comparator 14 uses the pressed voltage as a reference voltage. The reference voltage is input to the (+) input terminal of the comparator 14, and the voltage obtained by the shunt resistor 11 is input to the (−) input terminal. When a short-circuit current flows through the negative-side bus of the rectifier circuit 1 due to a short circuit of the switching elements 3a and 3b of the inverter 3, the comparator 14 inputs a voltage equal to or lower than the reference voltage to the (−) input terminal, and from the output terminal to Lo The detection signal inverted to Hi is output to the control means 9a. The above-described reference voltage is set according to the third predetermined threshold value.

  The control means 9a determines that the switching elements 3a and 3b are short-circuited when the detection signal from the short-circuit current detection means 10 is inverted from Lo to Hi, and stops driving the inverter 3.

  Further, the control unit 9a determines whether or not the element current detected by the element current detection unit 7 has reached the first predetermined threshold value. When the element current reaches the first predetermined threshold value, the control means 9a makes the detection signal from the short-circuit current detection means 10 invalid by using it as a trigger. As described in the first embodiment, the element current that reaches the first predetermined threshold is an element current that has a phase more advanced than the user's panning, and is an excessive element current.

  With the occurrence of this excessive element current (steep surge current), the GND potential of the short-circuit current detection means 10 may fluctuate, and the short-circuit current detection means 10 may malfunction. That is, no short circuit current actually flows, but the short circuit current detection means 10 outputs a detection signal. In order to prevent the control means 9a from stopping the drive of the inverter 3 due to this malfunction, when the element current detected by the element current detection means 7 reaches the first predetermined threshold, the short-circuit current detection means 10 The detection signal is invalidated to avoid malfunction of the short-circuit current detection means 10.

Next, the operation of the second embodiment will be described based on the flowchart of FIG.
Similarly to the first embodiment, when the user places the pan 20 on the heating coil 4 via the top plate, and then instructs the start of heating by a heating start switch (not shown) of the induction heating cooker. The control means 9a starts driving the inverter 3 and executes initial load detection (S1).

  At this time, the control means 9a first drives the inverter 3 with a high-frequency drive signal of 40 kHz, for example. Next, the control means 9a determines that the pan 20 is appropriate based on the input current detected by the input current detection means 6 and the coil current detected by the coil current detection means (not shown) and the threshold value for inappropriate heating determination. Determine whether or not. When the controller 9a determines that the pan 20 is suitable for heating from the determination result, the controller 9a determines the material of the pan 20 based on the input current, the coil current, and the material determination threshold, and ends the initial load detection.

  Thereafter, the control means 9a starts driving the inverter 3 with a drive signal corresponding to the material determination of the pot 20, and performs power feedback control. During the power feedback control, the element current detected by the element current detection means 7 is detected. It is determined whether or not the first predetermined threshold has been reached (S2). When the element current has not reached the first predetermined threshold, the control means 9a continues to drive the inverter 3 (S5). Further, when the element current reaches the first predetermined threshold value, the control means 9a uses that as a trigger to invalidate the detection signal from the short-circuit current detection means 10 (S3), and shifts to the above-described initial load detection operation. Then, the drive of the inverter 3 is continued (S5).

  Although not shown in FIG. 4, the control means 9a determines whether or not the short-circuit current has reached the third predetermined threshold when no element current reaching the first predetermined threshold is detected. When the short-circuit current reaches the third predetermined threshold, it is determined that the switching elements 3a and 3b are short-circuited, and the drive of the inverter 3 is stopped.

  As described above, in the second embodiment, the detection signal from the short-circuit current detection unit 10 is invalidated with the timing at which the element current reaches the first predetermined threshold as a trigger. As a result, even if it is considered that the short-circuit current detecting unit 10 malfunctions due to an element current reaching the first predetermined threshold, that is, an excessive element current (surge current) due to the advance phase, the short-circuit current detecting unit 10 is detected. Since the detection signal from is invalidated, the drive of the inverter 3 due to malfunction of the short-circuit current detection means 10 is not stopped. For this reason, it is possible to prevent the usability of the induction heating cooker from being deteriorated, and it is possible to prevent the board from being erroneously replaced.

  In the second embodiment, when the device current detected by the device current detection means 7 reaches the first predetermined threshold, the operation shifts to the initial load detection operation with low power. However, the present invention is not limited to this. Is not to be done. As described above, when the element current reaches the first predetermined threshold, the output of the inverter 3 may be limited so that the power of the heating coil 4 becomes lower than the set power. Also in this case, the drive of the inverter 3 can be shifted to a safer side, and the substrate elements such as the switching elements 3a and 3b of the inverter 3 and the diode bridge of the rectifier circuit 1 can be reliably protected.

  In the second embodiment, when the element current detected by the element current detection unit 7 reaches the first predetermined threshold, the detection signal from the short-circuit current detection unit 10 is invalidated using that as a trigger. However, the present invention is not limited to this. For example, when the change amount dI / dt per unit time of the element current (collector current) detected by the element current detection means 7 reaches a second predetermined threshold value set in advance (see FIG. 2), As a trigger, the detection signal from the short-circuit current detection means 10 may be invalidated. Also in this case, in order to protect the above-described substrate element, the operation of the initial load detection with low power is shifted, or the output of the inverter 3 is limited so that the power of the heating coil 4 is lower than the set power.

  1 rectifier circuit, 2 smoothing circuit, 2a inductor, 2b smoothing capacitor, 3 inverter, 3a, 3b switching element, 3c snubber capacitor, 4 heating coil, 5 resonance capacitor, 6 input current detection means, 7 element current detection means, 8 short circuit Current detection means, 9, 9a control means, 10 short-circuit current detection means, 11 shunt resistance, 12, 13 resistance, 14 comparator, 20 pan.

Claims (4)

A direct current generating circuit for converting alternating current power into direct current power;
An inverter that has a plurality of switching elements connected in series, and that converts a direct current of the direct current generation circuit into a high-frequency current by driving the plurality of switching elements;
In an induction heating cooker having a heating coil and a resonance capacitor connected to the output terminal of the inverter and forming a resonance circuit,
An element current detecting means provided on a bus on the positive electrode side or the negative electrode side between the direct current generating circuit and the inverter, and detecting a current flowing in one of the plurality of switching elements;
A short-circuit current detection means for detecting a short-circuit current that is provided on a positive-side or negative-side bus between the DC generation circuit and the inverter, and that flows when the plurality of switching elements are simultaneously short-circuited;
When the current value detected by the element current detection means reaches a first predetermined threshold value set in advance, the output of the inverter is limited so that the power of the heating coil is lower than the set power, and the short circuit An induction heating cooker comprising: control means for stopping the output of the inverter when the current value detected by the current detection means reaches a preset third predetermined threshold value . A direct current generating circuit for converting alternating current power into direct current power;
An inverter that has a plurality of switching elements connected in series, and that converts a direct current of the direct current generation circuit into a high-frequency current by driving the plurality of switching elements;
In an induction heating cooker having a heating coil and a resonance capacitor connected to the output terminal of the inverter and forming a resonance circuit,
An element current detecting means provided on a bus on the positive electrode side or the negative electrode side between the direct current generating circuit and the inverter, and detecting a current flowing in one of the plurality of switching elements;
A short-circuit current detection means for detecting a short-circuit current that is provided on a positive-side or negative-side bus between the DC generation circuit and the inverter, and that flows when the plurality of switching elements are simultaneously short-circuited;
Control means for limiting the output of the inverter to decrease when the current value detected by the element current detection means reaches a first predetermined threshold value set in advance;
With
Wherein, when a current detected by the device current detection means reaches the first predetermined threshold value, you characterized in that it is not accepted the detection signal from the short-circuit current detecting means derivative Induction heating cooker. A direct current generating circuit for converting alternating current power into direct current power;
An inverter that has a plurality of switching elements connected in series, and that converts a direct current of the direct current generation circuit into a high-frequency current by driving the plurality of switching elements;
In an induction heating cooker having a heating coil and a resonance capacitor connected to the output terminal of the inverter and forming a resonance circuit,
An element current detecting means provided on a bus on the positive electrode side or the negative electrode side between the direct current generating circuit and the inverter, and detecting a current flowing in one of the plurality of switching elements;
A short-circuit current detection means for detecting a short-circuit current that is provided on a positive-side or negative-side bus between the DC generation circuit and the inverter, and that flows when the plurality of switching elements are simultaneously short-circuited;
Control means for limiting the output of the inverter to decrease when the amount of change per unit time of the current detected by the element current detection means reaches a preset second predetermined threshold;
With
The control means is configured not to accept a detection signal from the short-circuit current detection means when the amount of change per unit time of the current detected by the element current detection means reaches the second predetermined threshold value. induction cooker you wherein a. Wherein, when the current value detected by the short-circuit current detecting means reaches a third predetermined threshold value set in advance, according to claim 2 or 3, wherein the stopping the output of the inverter Induction heating cooker.

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