JP3604538B2 - Electromagnetic cooker - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electromagnetic cooker for heating a cooking vessel by supplying a high-frequency current to a heating coil.
[0002]
[Prior art]
The electromagnetic cooker is safe and excellent in heat efficiency without using fire, and is becoming widespread as a cooking heater incorporated in a system kitchen or the like. A plurality of electromagnetic cookers are often incorporated in a system kitchen, and in order to prevent the generation of interference noise when the plurality of electromagnetic cookers are used at the same time, a half-heater that constantly controls heating at a constant frequency. A bridge-type inverter may be employed.
[0003]
FIG. 13 shows an electrical configuration of a half-bridge inverter used in a conventional electromagnetic cooker. In FIG. 13, an AC input terminal of a rectifier circuit 1 composed of a diode bridge is connected to a commercial AC power supply 2, and a DC output terminal is connected to both ends of a smoothing capacitor 3.
[0004]
Arms composed of positive and negative IGBTs 6 and 7 are connected to both ends of the smoothing capacitor 3 via DC buses 4 and 5, thereby forming a half-bridge type inverter main circuit 8. I have. Freewheeling diodes 9 and 10 are connected between the collector and the emitter of the IGBTs 6 and 7, respectively.
[0005]
One end of a heating coil 11 is connected to the output terminal 8a of the inverter main circuit 8, and a parallel circuit of a resonance capacitor 12 and a diode 13 is connected between the other end of the heating coil 11 and the DC bus 5. Have been. The heating coil 11 and the resonance capacitor 12 constitute a resonance circuit 14.
[0006]
Further, one end of a snubber capacitor 15 is connected to the output terminal 8a, and the other end of the snubber capacitor 15 is connected to the DC bus 5 via the collector-emitter of the IGBT16. The diode 17 is connected between the collector and the emitter of the IGBT 16. These constitute a so-called snubber circuit 18 and are provided to reduce switching loss when the IGBTs 6 and 7 are off.
[0007]
An oscillation signal of a predetermined frequency output from the oscillator 19 is given to a variable on-time setting unit 20 and a fixed on-time setting unit 21. A current transformer 22 is inserted on the AC input side of the rectifier circuit 1, and an output terminal of the current transformer 22 is connected to an input terminal of an input setting unit 24 a via an input current detection unit 23. The input current detection unit 23 performs A / D conversion on an input current value detected by the current transformer 22 and outputs the input current value to the input setting unit 24a as an input current detection value Vin.
[0008]
Although not specifically shown, the operation unit 25 includes a key for a user to select various automatic cooking menus (control programs), a key for setting a heating amount by an electric energy such as 1 KW, 2 KW, and the like. Is provided. The input setting unit 24a performs feedback control based on the input current detection value Vin given from the input current detection unit 23 so that the input current value corresponds to the setting of the electric energy in the operation unit 25, and the variable ON time A PWM signal is provided to the setting unit 20.
[0009]
The heating stop unit 24b outputs a heating stop command to the variable on-time setting unit 20 and the fixed on-time setting unit 21 when a predetermined condition is satisfied. The input setting unit 24a and the heating stop unit 24b show the functions of a microcomputer (hereinafter, referred to as a microcomputer) 24 in a block form.
[0010]
The output signal of the variable on-time setting unit 20 is supplied to first and third driving units 26 and 27, and the output signal of the fixed on-time setting unit 21 is supplied to the second and third driving units 28 and 27. I have. The output terminals of the first, second, and third drive units 26, 28, and 27 are connected to the gates of the IGBTs 6, 7, and 16, respectively.
[0011]
FIG. 14 shows a detailed electrical configuration of the first drive unit 26. In FIG. 14, the output signal of the variable on-time setting unit 20 is given to a photocoupler 29, and one output terminal of the photocoupler 29 is connected to the gate of the IGBT 6 via a series circuit of resistors 30 and 31. ing. A diode 32 is connected in anti-parallel to the resistor 30. Further, the other output terminal of the photocoupler 29 is connected to the emitter of the IGBT 6. The resistance values of the resistors 30 and 31 are set to, for example, about 150Ω and 10Ω.
[0012]
The operation of the electromagnetic cooker including the inverter configured as described above will be described below with reference to FIGS. The heating of the pot is performed by supplying a high-frequency current to the heating coil 11 by an inverter. FIG. 16 shows the signal waveform of each part in this case. As shown in FIGS. 16A and 16B, the IGBTs 6 and 7 are turned on and off alternately in a control cycle Tinv of the inverter of about 20 KHz, for example.
[0013]
The ON period Ton1 of the IGBT 6 changes based on the output signal given from the variable ON time setting unit 20, with Tinv / 2 as the upper limit. On the other hand, the ON period Ton2 of the IGBT 7 is fixed to approximately Tinv / 2 based on the output signal given from the fixed ON time setting unit 21. However, in order to prevent a short circuit between the IGBTs 6 and 7, a stop period TD is ensured for switching between the ON periods of both.
[0014]
In addition, the IGBT 16 of the snubber circuit 18 is controlled so as to reduce the switching loss when the IGBTs 6 and 7 are turned off, and to prevent the snubber capacitor 15 from being charged during a period from when the IGBT 6 is turned off to when the IGBT 7 is turned on.
[0015]
The control cycle consists of the following four cycles. FIG. 16D shows the waveform of the current IL flowing through the heating coil 11 at this time, and FIG. 16E shows the waveform of the collector-emitter voltage Vtr2 of the IGBT 7.
(1) IGBT6: ON / IGBT7: OFF
A current is supplied to the heating coil 11 and the resonance capacitor 12 is charged through the path of the smoothing capacitor 3, the IGBT 6, the heating coil 11, the resonance capacitor 12, and the smoothing capacitor 3 (see FIG. 16D, A).
(2) IGBT6: OFF / IGBT7: OFF
In the path of the heating coil 11, the resonance capacitor 12, the freewheel diode 10, and the heating coil 11, the resonance capacitor 12 is further charged by the delay current of the heating coil 11 (see FIGS. 16D and B).
[0016]
(3) IGBT6: OFF / IGBT7: ON
The resonance capacitor 12 is discharged through the path of the resonance capacitor 12, the heating coil 11, the IGBT 7, and the resonance capacitor 12 to flow a current in the opposite direction to the heating coil 11 (see FIGS. 16D and 16C). When the resonance capacitor 12 is completely discharged, the current flows through the diode 13 connected in parallel (see FIG. 16D, C ').
(4) IGBT6: OFF / IGBT7: OFF
In the path of the heating coil 11, the freewheel diode 9, the smoothing capacitor 3, the diode 13, and the heating coil 11, the delay current of the heating coil 11 is regenerated to the power supply side through the freewheel diode 9 (FIG. 16D, D).
[0017]
By repeating the above-mentioned cycle, a high-frequency current is supplied to the heating coil 11, and an eddy current is induced in the pot 34 (see FIG. 13) placed on the top plate 33 to perform heating cooking. . The input current control is performed by changing the on-period Ton1 of the IGBT 6, and if the on-period Ton1 is lengthened, the input current increases and the amount of heating of the pot 34 increases.
[0018]
[Problems to be solved by the invention]
However, in such a conventional electromagnetic cooker, if the ON period Ton1 of the IGBT 6 is shortened in order to perform weak input heating, the following problem occurs. FIG. 17 shows the signal waveform of each part at this time. That is, as shown in FIG. 17A, when the ON period Ton1 of the IGBT 6 becomes equal to or less than a certain time, the amount of current supplied to the heating coil 11 decreases (see FIG. 17D, A). In the periods C and C 'and the cycle (4), the snubber capacitor 15 cannot be fully charged until the voltage Vtr2 between the terminals of the IGBT 7 becomes equal to the DC power supply voltage. Therefore, in the cycle (4), the regenerative current does not flow and the snubber does not flow. The capacitor 15 will continue to be charged.
[0019]
Then, the IGBT 6 is turned on in the next cycle {circle around (1)} in that state, so that a short circuit occurs in the path of the DC bus 4, the IGBT 6, the snubber capacitor 15, the IGBT 16 and the DC bus 5 due to the potential difference between the DC power supply voltage and the voltage Vtr2. Electric current flows. Here, FIG. 17F shows a current waveform Itr1 flowing through the IGBT 6, and a short-circuit current flows at a point P shown in FIG. 17F.
[0020]
In order to suppress the occurrence of such a short-circuit current as much as possible, as shown in FIG. 14, the gate of the IGBT 6 is set so as to have a large gate resistance at turn-on through a series circuit of resistors 30 and 31 as shown in FIG. As shown in FIG. 15, the rise of the gate signal VG1 is made gentle to delay the timing at which the IGBT 6 is turned on.
[0021]
However, by making the rise of the gate signal VG1 gradual in this manner, the rise of the collector-emitter voltage of the IGBT 6 becomes gradual, so that a switching loss (turn-on loss) occurs when the IGBT 6 is turned on. The switching loss at the time of turn-on increases as the set input decreases, and if continuous heating is performed while the turn-on loss is large, the temperature of the IGBT 6 rises, leading to thermal destruction in the worst case.
[0022]
Therefore, in the conventional electromagnetic cooker, for example, in the case of performing weak input heating corresponding to cooking for a long period of cooking with low heat, a low input that does not cause a turn-on loss of the IGBT 6 is set to the lower limit. For example, periodic heating such as heating for 3 seconds and then stopping for 3 seconds had to be performed.
[0023]
In such a heating method, there have been problems such as a sudden boiling state when the amount of the object to be cooked is small, and the object to be cooked when the stewed cooking is performed.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electromagnetic cooker capable of performing continuous heating with a weak input in a state where switching loss can be reduced.
[0024]
[Means for Solving the Problems]
To achieve the above object, the electromagnetic cooker according to claim 1 rectifies an AC power supply to generate a DC power supply,
Positive and negative DC buses to which DC power generated by the rectifier circuit is supplied;
First and second switching elements connected in series between the positive and negative DC buses;
A resonance circuit connected between both terminals of any one of the first and second switching elements, the resonance circuit including a heating coil and a resonance capacitor for inductively heating the cooking container;
A snubber circuit connected between both terminals of the one switching element and configured by a series circuit of a snubber capacitor and a third switching element;
Input powerA control signal is output to the first, second, and third switching elements according to a set value to perform conduction control.Input powerThe setting value isRespond to weak inputControl means for performing disconnection control for substantially disconnecting the snubber capacitor from the resonance circuit by shutting off the third switching element when the value is equal to or less than a predetermined value.,
The control means controls the third switching element to be energized after a lapse of a predetermined time after the energization of one of the switching elements, and to shut off the third switching element after a lapse of a predetermined time after the interruption of the other switching element. OutputIt is characterized by that.
[0025]
With this configuration, the control unit substantially disconnects the snubber capacitor from the resonance circuit when the set value is equal to or less than the predetermined value.In this case, the snubber capacitor is not charged and the other switching element is turned on. In this case, no short-circuit current flows due to insufficient charging capacity of the snubber capacitor. Therefore, even when the set value is equal to or less than the predetermined value, the high-frequency current can be continuously supplied to the heating coil in a state where the switching loss in the other switching element can be reduced, and the continuous heating can be performed with a weak input. it can.Then, when one of the switching elements is turned on, a short-circuit current can be prevented from flowing through the snubber capacitor.
[0026]
In this case, as described in claim 2, the snubber circuit may be configured by connecting the snubber capacitor and the third switching element in series. With such a configuration, disconnection control can be easily performed. .
[0028]
Claim3As described in, the control means,When shifting between normal control and disconnection control,The configuration may be such that the conduction control for the first and second switching elements is temporarily stopped, and during that time, the transition between the disconnection control and the normal control is performed. According to this configuration, when transitioning between the disconnection control and the normal control, the conduction control of the first and second switching elements is stopped, thereby preventing a short-circuit current from flowing to the third switching element. can do.
[0029]
Claim4As described above, it is preferable to connect a resistor in parallel with the resonance capacitor. With such a configuration, the control unit controls the first and second switches while performing the transition between the disconnection control and the normal control for turning on and off the third switching element in accordance with the conduction control of the first and second switching elements. Even when the conduction control for the switching element is temporarily stopped, the charge charged in the resonance capacitor can be quickly discharged through the resistor.
[0030]
Claim5As described in, the control means,When shifting between normal control and disconnection control,It is preferable that the conduction control of one switching element is stopped with a delay with respect to the other switching element. With such a configuration, the claims4Similarly to the above, even when the control means temporarily stops the conduction control for the first and second switching elements, the charge charged in the resonance capacitor is changed by the switching operation by the conduction control (on / off) of one of the switching elements. Discharge can be performed more quickly.
[0031]
Claim6As described in the above, input current detection means for detecting the input current value,
Regenerative current detection means for detecting a regenerative current value,
Control means,In a state where the input power set value is set to a predetermined value or less, a regenerative current value when the third switching element is turned on and a regenerative current value when the third switching element is turned offThe function of the third switching element may be checked based on the relationship with the regenerative current value.
With such a configuration, the function of the third switching element can be confirmed by the control means, so that the occurrence of switching loss in the first and second switching elements is reliably prevented, and safety is improved. Can be.
[0032]
With such a configuration, the function of the third switching element can be confirmed by the control means, so that the occurrence of switching loss in the first and second switching elements is reliably prevented, and safety is improved. Can be.
[0033]
Claim7As described in the above, comprising a resistance value switching means configured to switch the resistance value of the resistor connected in series to the control input terminal of the other switching element, the control means,Input powerThe setting value isRespond to weak inputWhen the value falls below a predetermined value, a switching signal is output to the resistance value switching means.Decrease the resistance valueIt is good also as a structure which carries out. With such a configuration,Input powerThe setting value isSaidIf the value is equal to or less than the predetermined value, the switching loss caused when the other switching element is turned on can be reduced by reducing the resistance value of the resistor connected in series to the control input terminal of the other switching element.
[0034]
In this case, the claim8As described in the above, it is provided with temperature detecting means for detecting the heating temperature of the cooking vessel, the control means, when the heating temperature of the cooking vessel detected by the temperature detecting means is equal to or higher than a predetermined temperature, the set value is equal to or less than a predetermined value It is good also as a structure switched to. With such a configuration, in the heating and cooking that performs automatic control according to the heating temperature of the cooking container, claims 1 to7The same operation and effect as described above can be obtained.
[0035]
Claims9As described in above, a low output setting key for setting a low output may be provided, and the control unit may be configured to switch the setting value to a predetermined value or less when the low output setting key is operated. With such a configuration, in the heating cooking that performs automatic control in accordance with the operation of the low output setting key by the user, claims 1 to7The same operation and effect as described above can be obtained.
[0036]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. Note that the same parts as those in FIG. 13 are denoted by the same reference numerals and description thereof is omitted, and only different parts will be described below. FIG. 1 shows an electrical configuration. In the present embodiment, a microcomputer (control means) 41 having an input setting unit 41a and a heating stop unit 41b is arranged instead of the microcomputer 24 shown in FIG. The input setting unit 41a directly supplies the control signal VS to the third drive circuit 27.
[0037]
Further, a resistor 42 is connected in parallel with the resonance capacitor 12 and the diode 13. The resistance value of the resistor 42 is set to a value sufficiently larger than the impedance of the resonance capacitor 12 when the inverter main circuit 8 is operating. Other configurations are the same as those shown in FIG.
[0038]
Next, the operation of the present embodiment will be described with reference to FIGS.IGBT16IGBT7 (second switching) as shown in FIG.element) Is turned on after a lapse of a predetermined time Tα after being turned on, and the IGBT 6 (first switching) is turned on.element) Is turned off after a lapse of a predetermined time Tα after turning off.
[0039]
Thereby, when the IGBTs 6 and 7 shift from the on-state to the off-state, the voltage change between the collector and the emitter is moderated to prevent the occurrence of switching loss, and a short-circuit current flows through the snubber capacitor 15 when the IGBT 7 is turned on. It also prevents that. Here, the fixed time Tα is set such that a voltage change at the time of turning off the IGBTs 6 and 7 converges within the time, regardless of any load or setting input within an appropriate range.
[0040]
When the input set value (set by the power amount “W”) set by the user from the operation unit 25 is set to be equal to or smaller than the predetermined value Wth, the input setting unit 41a switches the IGBT 16 (third switching element). Is always turned off (cut off), so that the snubber capacitor 15 is controlled to be disconnected from the resonance circuit 14. As an example, when the maximum rating of the electromagnetic cooker is 3 KW, the predetermined value Wth is set to about 500 W.
[0041]
FIG. 3 is a diagram illustrating signal waveforms of the respective units when the input set value is set to a predetermined value Wth or less. That is, in this case, since the IGBT 16 is always turned off by the heating stop unit 41b as shown in FIG. 3C, the snubber capacitor 15 is not charged and is substantially separated from the resonance circuit 14. It is in.
[0042]
Therefore, even when the input current value is small, the snubber capacitor 15 is not charged, so that the regenerative current flows reliably in the above-mentioned control cycle (4), and the IGBT 6 is turned on in the next cycle (1). Even when turned on, no short-circuit current flows (see FIG. 3 (f)).
[0043]
That is, the snubber capacitor 15 is provided to reduce the turn-off loss of the IGBTs 6 and 7 when the input current value is large. When the input current value is small, the current flowing through the IGBTs 6 and 7 during the switching operation is small. Even without the capacitor 15, the turn-off loss is small. Therefore, in this case, there is no problem even if the snubber capacitor 15 is separated from the resonance circuit 14.
[0044]
FIG. 4 shows a control state in which a transition is made between the above-described disconnection control and the normal control for making the snubber capacitor 15 function according to the setting of the input current value, by controlling the inter-terminal voltage Vtr2 (a) of the IGBT 7 with the control. Signal Vs (b). In FIG. 4, when the setting of the input current value is switched from a value exceeding the predetermined value Wth (Hi, see FIG. 5) to a value less than the predetermined value Wth (Lo, see FIG. 5), that is, from normal control to disconnection control When shifting, the input setting unit 41a first supplies a control signal to the heating stop unit 41b to stop the conduction control of the IGBTs 6 and 7 (see FIG. 4A, time point A).
[0045]
Then, the electric charge remaining in the resonance capacitor 12 is discharged via the resistor 42, so that the voltage Vtr2 gradually decreases from the DC power supply voltage and becomes approximately 0 V after the lapse of the estimated time Ta (FIG. 4A, (See time point B). Further, after the waiting voltage Vtr2 becomes 0 V surely for the allowance time Tb, the input setting unit 41a outputs the control signal Vs to the third driving unit 27, thereby always turning off the IGBT 16 and performing disconnection control (FIG. 4 (b), time point C). Next, after waiting for the control system switching wait time Tc to elapse, continuous heating with a weak input (500 W or less) is started (see FIG. 4A, time point D).
[0046]
Also, when returning to the normal control from the state in which the disconnection control is being performed, the switching is performed similarly. That is, the input setting unit 41a gives a control signal to the heating stop unit 41b to stop the conduction control of the IGBTs 6 and 7 (see time point E in FIG. 4A), and the remaining of the resonance capacitor 12 during the estimated time Ta. Wait for discharge of the electric charge (see FIG. 4A, time point F).
[0047]
Further, after waiting for the margin time Tb, the input setting unit 41a stops outputting the control signal Vs to the third driving unit 27, and returns the IGBT 16 to the normal control normal state (see FIG. 4B, time point G). . Then, after waiting for elapse of the control system switching wait time Tc, continuous heating with an input current value exceeding 500 W is started (see FIG. 4A, time point H).
[0048]
FIG. 5 is a measurement example performed by the inventor of the present invention, and shows a temperature change (vertical axis) of the IGBT 6 when the iron pot 34 is heated while changing the input set value (horizontal axis). Although the temperature of the IGBT 6 also decreases in accordance with the decrease in the input set value, when the IGBT 16 is continuously controlled as usual, as shown by the solid line in FIG. 5, when the input power amount falls below the predetermined value Wth, the temperature of the IGBT 6 decreases. Rises sharply. On the other hand, when the disconnection control is performed in the area where the predetermined value is equal to or less than the predetermined value Wth, the temperature of the IGBT 6 decreases as the input set value decreases, as indicated by the broken line in FIG.
[0049]
As described above, according to the present embodiment, when the input setting value becomes equal to or less than the predetermined value Wth, the input setting unit 41a performs the disconnection control for disconnecting the snubber capacitor 15 from the resonance circuit 14 by shutting off the IGBT 16. . Accordingly, the snubber capacitor 15 is no longer charged, and when the IGBT 6 is turned on, a short-circuit current does not flow due to insufficient charging capacity of the snubber capacitor 15, and a high-frequency current is supplied to the heating coil 11 with the set value being equal to or less than Wth. Can be supplied continuously. Thus, since the continuous heating by the weak input can be performed while the switching loss of the IGBT 6 is suppressed, unlike the conventional method, for example, the cooked food may be scorched or boiled for a long time such as stew cooking. Can be performed without any problems.
[0050]
Further, according to the present embodiment, the input setting unit 41a outputs the control signal so that the IGBT 16 is turned on after a predetermined time has elapsed since the IGBT 7 was turned on, and the IGBT 16 is turned off after the predetermined time has elapsed since the IGBT 6 was turned off. Therefore, the switching loss of the IGBTs 6 and 7 can be suppressed, and the short circuit current can be prevented from flowing through the snubber capacitor 15 when the IGBT 7 is turned on.
[0051]
Further, according to the present embodiment, when the resistor 42 is connected in parallel to the resonance capacitor 12 and the input setting unit 41a switches the set value in a range including the predetermined value Wth, the input control unit 41a controls the IGBTs 6 and 7 to conduct. Since the control is temporarily stopped and the transition between the disconnection control and the normal control is performed during that time, it is possible to prevent a short-circuit current from flowing through the IGBT 16 when transitioning between the disconnection control and the normal control. Even if the conduction control of the resonance capacitor 12 is stopped, the electric charge charged in the resonance capacitor 12 can be quickly discharged via the resistor 42.
[0052]
FIGS. 6 and 7 show a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted. Only the different parts will be described below. In FIG. 6 showing the electrical configuration, in the second embodiment, the resistor 42 is removed, and the microcomputer 41 is replaced by a microcomputer (control means) 41 '. The microcomputer 41 'is obtained by replacing the heating stop section 41b of the microcomputer 41 with a heating stop section 41b'. Other configurations are the same as in the first embodiment.
[0053]
Next, the operation of the second embodiment will be described with reference to FIG. The second embodiment is different from the first embodiment in the control state in which a transition is made between the disconnection control and the normal control according to the setting of the input current value. That is, as shown in FIG. 7, when shifting from the normal control to the disconnection control, the input setting unit 41a first supplies a control signal to the heating stop unit 41b 'to stop the conduction control of only the IGBT 6, and the IGBT 7 Is stopped after continuing for the time Ta '(see FIG. 7A, time point A).
[0054]
Then, the charge remaining in the resonance capacitor 12 is discharged and consumed within a very short time (for example, about three or four cycles) by the switching operation of the IGBT 7 having a frequency of 21.5 KHz. After that, as in the first embodiment, the input setting unit 41a outputs the control signal Vs to the heating stop unit 41b after waiting for the lapse of the margin time Tb (see FIG. 7A, time point B). (See FIG. 7 (b), time point C), wait for the elapse of the switching waiting time Tc, and start continuous heating with a weak input (500 W or less) (see FIG. 7 (a), time point D). Also, when returning to the normal control from the state in which the disconnection control is being performed, the switching is performed similarly.
[0055]
As described above, according to the second embodiment, when switching the input set value within the range including the predetermined value Wth, the heating stop unit 41b 'stops the conduction control of the IGBT 7 with a delay with respect to the IGBT 6, so that the resonance is stopped. The charge charged in the capacitor 12 can be discharged and consumed more quickly by the switching operation by the conduction control (on / off) of the one IGBT 7, and the time required for switching the control state can be reduced. Further, since the resistor 42 required in the first embodiment can be eliminated, the number of parts can be reduced.
[0056]
8 and 9 show a third embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Only different parts will be described below. 8, in the third embodiment, in the third embodiment, a series circuit of a capacitor 43 and a resistor 44 is connected in parallel to the smoothing capacitor 3, and the resistor 44 has a diode 45Are connected in anti-parallel. The capacity of the capacitor 43 is set to, for example, about 1/100 of the capacity of the smoothing capacitor 3.
[0057]
The capacitor 43, the resistor 44, and the diode 45 constitute a regenerative current detecting unit. A common connection point of the capacitor 43 and the resistor 44 is a regenerative current detection unit.50Is connected to the input terminal of the input setting unit 41a via the. Other configurations are the same as in the first embodiment.
[0058]
In the third embodiment, a regenerative current regenerated from the load side to the power supply side and flowing into the smoothing capacitor 3 is divided into a series circuit of the capacitor 43 and the resistor 44. Then, the regenerative current detection unit 45 detects the terminal voltage of the resistor 44 at the timing when the regenerative current flows and performs A / D conversion, and outputs the result to the input setting unit 41a as a regenerative current detection value Vinv. .
[0059]
Next, the operation of the third embodiment will be described with reference to FIG. FIG. 9 shows a change in the regenerative current detection value Vinv (vertical axis) when the input set value (horizontal axis) is changed. As described in the first embodiment, if the snubber circuit 18 is continuously operated even in the region where the input set value is reduced to around the predetermined value Wth, the short-circuit current flows through the snubber capacitor 15 and the regenerative current hardly flows. As shown by the solid line in FIG. 9, the regenerative current detection value Vinv decreases.
[0060]
Therefore, the threshold value is set as shown by the one-dot chain line in FIG. Then, for example, the microcomputer 41 is switched to the test mode, and the function test is performed as follows. For example, the control signal Vs is output to turn off the IGBT 16, and then the input set value is set to a predetermined value Wth or less. The regenerative current detection value Vinv at this time isThresholdIf the regenerative current detection value Vinv is smaller than the threshold value, the switching control function or the IGBT 16 may be determined to be normal. Can be determined.
[0061]
Further, after the IGBT 16 performs the disconnection control, the input set value is set to a predetermined value Wth or less. If the regenerative current detection value Vinv at this time is larger than the threshold value, it can be determined that the switching control function is abnormal or that the IGBT 16 is open or not mounted.
[0062]
As described above, according to the third embodiment, the input of the microcomputer 41PowerThe setting unit 41a performs the control switching function and the function test of the IGBT 16 based on the relationship between the input set value and the regenerative current value Vinv. Therefore, for example, in the manufacturing process before product shipment, or in the service center after shipment, the microcomputer 41 is switched to the test mode to perform the test, thereby reliably preventing the occurrence of switching loss in the IGBTs 6 and 7. As a result, safety can be enhanced, or a check at the time of failure can be easily performed.
[0063]
FIGS. 10 to 12 show a fourth embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, only different parts will be described. In FIG. 10 showing the electrical configuration of the main part, in the fourth embodiment, the gate resistance value of the IGBT 6 is configured to be switched according to the input set value.
[0064]
That is, one end of a resistor 46 having a resistance value of 10Ω is connected to a common connection point of the resistors 30 and 31, and the other end of the resistor 46 is connected to one end of an output terminal of a photocoupler 47. The other end of the output terminal of the photocoupler 47 is connected to a common connection point between the output terminal of the photocoupler 29 and the resistor 30. An output signal is supplied from the microcomputer 41 to an input terminal of the photocoupler 47. Note that the resistor 46 and the photocoupler 47 constitute resistance value switching means, and the other configuration is the same as that of the first embodiment.
[0065]
Next, the operation of the fourth embodiment will be described with reference to FIGS. In the first to third embodiments, the short-circuit current can be prevented from flowing through the snubber capacitor 15 in the region where the input set value is smaller than the predetermined value Wth. Since the short-circuit current may flow when the IGBT 6 is connected to the IGBT 6, the gate resistance of the IGBT 6 is set to be large at the time of turn-on, similarly to the conventional configuration shown in FIG.
[0066]
That is, in an area where the input set value is smaller than or equal to the predetermined value Wth, a short-circuit current does not occur when the IGBT 6 is turned on. However, since the terminal voltage Vtr1 falls slowly, it occurs in that part. Switching losses still exist. Therefore, in the fourth embodiment, in a region where the input set value is smaller than the predetermined value Wth, the microcomputer 41 outputs a high-level signal to the photocoupler 47 to connect the resistor 46 to the resistor 30 in parallel. Control.
[0067]
Then, the gate resistance value at the time of turn-on is switched from 160Ω to (150/10 + 10) Ω.1As shown in the figure, the rise of the gate voltage VG115, the fall of the inter-terminal voltage Vtr1 becomes steep. As a result, the turn-on loss of the IGBT 6 is further reduced, and as shown in FIG. 12, for example, as compared with FIG. 5 in the first embodiment, the temperature rise of the IGBT 6 is further suppressed.
[0068]
As described above, according to the fourth embodiment, the microcomputer 41 outputs a switching signal to the photocoupler 47 when the input set value becomes equal to or less than the predetermined value Wth, and is connected in series to the gate (control input terminal) of the IGBT 6. Since the resistor 46 is connected in parallel with the resistor 30 to switch the gate resistance value, by reducing the gate resistance value of the IGBT 6, the switching loss that occurs at the time of turn-on can be further reduced.
[0069]
The present invention is not limited to the embodiment described above and shown in the drawings, and the following modifications or extensions are possible.
For example, the input setting unit 41a is configured such that, for example, among the keys for selecting a cooking (control) program provided on the operation unit 25, the “dent” key (low output setting key) is turned on by the user. Alternatively, the normal control and the disconnection control may be automatically switched in accordance with a control program in which heating is first performed at a high input to boil the object to be cooked, and thereafter heating at a low input is continuously performed. Further, when the "heat keeping key" is turned on during the high input heating, the control may be switched so that the weak input heating is continuously performed from that point.
Alternatively, a temperature sensor (temperature detecting means) for detecting the temperature of the pot 34 is provided on the top plate 33, and when the temperature detected by the temperature sensor reaches a predetermined value (predetermined temperature), the temperature is slightly reduced from that point. The control may be switched so that input heating is performed continuously.
[0070]
Even if the snubber capacitor 15 is electrically connected to the resonance circuit 14, it may be substantially separated from the resonance circuit 14 in the separation control. For example, a series circuit of a resistor having a very high resistance value and an electronic or mechanical normally open switch is connected between the collector and the emitter of the IGBT 16, the switch is closed during the disconnection control, and the snubber capacitor is connected. 15 may be connected to the DC bus 5 via a resistor.
The resonance circuit 14 may be connected to the IGBT 6 side.
The switching element is not limited to the IGBT, but may be a power transistor or a power MOSFET.
[0071]
【The invention's effect】
Since the present invention is as described above, the following effects are obtained.
According to the electromagnetic cooker according to the first aspect, when the set value becomes equal to or less than the predetermined value, the control circuit cuts off the third switching element, so that the snubber capacitor inductively heats the cooking vessel with the snubber capacitor. In this case, the snubber capacitor is not charged, and when one of the switching elements is turned on, a short-circuit current does not flow due to the shortage of the charging capacity of the snubber capacitor.
[0072]
Therefore, in a state where the set value is equal to or less than the predetermined value, it is possible to continuously supply a high-frequency current to the heating coil and perform continuous heating with a weak input, thereby performing good heating control such as cooking for a long time. be able to.Then, the control means energizes the third switching element after a lapse of a predetermined time after the energization of one of the switching elements, and shuts off the third switching element after a lapse of a predetermined time after the interruption of the other switching element. When the switching element is turned on, short-circuit current can be prevented from flowing through the snubber capacitor.
[0073]
According to the electromagnetic cooker of the second aspect, since the snubber circuit is configured by connecting the snubber capacitor and the third switching element in series, disconnection control can be easily performed.
[0075]
Claim3According to the electromagnetic cooker described above, when switching the set value within the range including the predetermined value, the control unit temporarily stops the conduction control for the first and second switching elements, during which the disconnection control and the normal control are performed. Therefore, it is possible to prevent a short-circuit current from flowing through the third switching element when performing the transition between the disconnection control and the normal control.
[0076]
Claim4According to the electromagnetic cooker described above, since the resistor is connected in parallel to the resonance capacitor, the control unit controls the conduction of the first and second switching elements during the transition between the disconnection control and the normal control. Even if the operation is temporarily stopped, the electric charge charged in the resonance capacitor can be quickly discharged via the resistor.
[0077]
Claim5According to the electromagnetic cooker described above, when the control unit switches the set value in a range including the predetermined value, the control unit stops the conduction control of one switching element with a delay with respect to the other switching element. Even when the conduction control for the first and second switching elements is temporarily stopped, the charge charged in the resonance capacitor is discharged more quickly by the switching operation by the conduction control of one of the switching elements, and the switching control is performed. The time required can be reduced.
[0078]
Claim6According to the described electromagnetic cooker, the control means includes:In a state where the input power set value is set to a predetermined value or less, a regenerative current value when the third switching element is turned on and a regenerative current value when the third switching element is turned offSince the function of the third switching element is checked based on the relationship with the regenerative current value, it is possible to reliably prevent the occurrence of switching loss in the first and second switching elements and to enhance safety.
[0079]
Claim7According to the electromagnetic cooker described above, when the set value becomes equal to or less than the predetermined value, the control unit outputs a switching signal to the resistance value switching unit, and the resistance connected in series to the control input terminal of the other switching element. The resistance ofTo decreaseSince the switching is performed, when the set value is equal to or less than the predetermined value, it is possible to reduce the switching loss that occurs when the other switching element is turned on.
[0080]
Claim8According to the electromagnetic cooker described above, the control unit switches the set value to a predetermined value or less when the heating temperature of the cooking container detected by the temperature detection unit is equal to or higher than the predetermined temperature, and thus automatically controls according to the heating temperature of the cooking container. Claims 1 to 3 in the heating cooking for performing7The same effect can be obtained.
[0081]
Claim9According to the electromagnetic cooker described above, when the low output setting key is operated, the control unit switches the set value to a predetermined value or less, so that the heating unit performs automatic control according to the operation of the low output setting key by the user. In cooking, claims 1 to7The same operation and effect as described above can be obtained.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing an electrical configuration of a first embodiment of the present invention.
FIG. 2 is a diagram showing a signal waveform of each unit in a region where an input set value exceeds a predetermined value Wth.
FIG. 3 is a diagram corresponding to FIG. 2 in an area where an input set value is equal to or less than a predetermined value Wth.
FIG. 4 is a diagram showing a control state when a transition is made between disconnection control and normal control.
FIG. 5 is a diagram showing a temperature change (vertical axis) of the IGBT when an iron pot is heated by changing an input set value (horizontal axis).
FIG. 6 is a view corresponding to FIG. 1, showing a second embodiment of the present invention;
FIG. 7 is a diagram corresponding to FIG. 4;
FIG. 8 is a view corresponding to FIG. 1, showing a third embodiment of the present invention.
FIG. 9 is a diagram showing a change in a regenerative current detection value Vinv (vertical axis) when an input set value (horizontal axis) is changed.
FIG. 10 is a diagram showing an electrical configuration of a main part according to a fourth embodiment of the present invention.
FIG. 11 is a diagram showing a voltage waveform of a gate signal.
FIG. 12 is a diagram corresponding to FIG. 5;
FIG. 13 is a diagram corresponding to FIG. 1 showing a conventional technique.
FIG. 14 is a diagram showing an electrical configuration of a gate drive unit of the IGBT.
FIG. 15 is a diagram corresponding to FIG. 11;
FIG. 16 is a diagram corresponding to FIG. 2;
FIG. 17 is a diagram corresponding to FIG. 3;
[Explanation of symbols]
1 is a rectifier circuit, 2 is a commercial AC power supply, 4 and 5 are positive and negative DC buses, 6 and 7 are IGBTs (first and second switchingelement), 8 is an inverter main circuit, 11 is a heating coil, 12 is a resonance capacitor, 14 is a resonance circuit, 15 is a snubber capacitor, 16 is an IGBT (third switching element), 18 is a snubber circuit, and 22 is a current transformer (input). Current detecting means), 41 and 41 'are microcomputers (control means), 41a is an input setting section, 41b and 41b' are heating stop sections, 42 is a resistor, 43 is a resistor (regeneration current detecting means), and 44 is a capacitor ( Regenerative current detecting means), 45 is a diode (regenerating current detecting means), 46 is a resistor (resistance switching means), and 47 is a photocoupler (resistance switching means).

Claims (9)

A rectifier circuit that rectifies an AC power supply to generate a DC power supply;
Positive and negative DC buses to which DC power generated by the rectifier circuit is supplied;
First and second switching elements connected in series between the positive and negative DC buses;
A resonance circuit connected between both terminals of any one of the first and second switching elements, the resonance circuit including a heating coil and a resonance capacitor for inductively heating the cooking container;
A snubber circuit connected between both terminals of the one switching element and configured by a snubber capacitor and a third switching element;
When a control signal is output to the first, second, and third switching elements in accordance with the input power set value to perform conduction control, and when the input power set value is equal to or less than a predetermined value corresponding to a weak input, Control means for performing disconnection control for substantially disconnecting the snubber capacitor from the resonance circuit by shutting off the third switching element ,
The control means controls the third switching element to be energized after a lapse of a predetermined time after the energization of one of the switching elements, and to shut off the third switching element after a lapse of a predetermined time after the interruption of the other switching element. induction cooker, wherein also be output from the. The electromagnetic cooker according to claim 1, wherein the snubber circuit is configured by connecting a snubber capacitor and a third switching element in series. When transitioning between the normal control and the disconnection control , the control means temporarily stops the conduction control for the first and second switching elements, and performs the transition between the disconnection control and the normal control during that time. The electromagnetic cooker according to claim 1 or 2, wherein The electromagnetic cooker according to claim 3, wherein a resistor is connected in parallel with the resonance capacitor . 5. The electromagnetic device according to claim 3, wherein the control unit delays the conduction control of one of the switching elements with respect to the other switching element and stops the control when switching between the normal control and the disconnection control. Cooking device. Input current detecting means for detecting an input current value;
Regenerative current detection means for detecting a regenerative current value,
The control means, based on the relationship between the regenerative current value when the third switching element is turned on and the regenerative current value when the third switching element is turned off, with the input power set value set to a predetermined value or less. The electromagnetic cooker according to any one of claims 1 to 5, wherein the function of the third switching element is checked . A resistance value switching unit configured to switch a resistance value of a resistor connected in series to a control input terminal of the other switching element,
The control means outputs a switching signal to the resistance value switching means to reduce the resistance value when the input power set value becomes equal to or less than a predetermined value corresponding to the weak input . An electromagnetic cooker according to claim 1. It has a temperature detecting means for detecting a heating temperature of the cooking vessel,
Control means, the heating temperature of the cooking container in which the temperature detecting means detects becomes equal to or higher than a predetermined temperature, according to claim 1, wherein the switching Rukoto below a predetermined value corresponding to the weak input the input power set value An electromagnetic cooker according to any one of the above. Equipped with a low output setting key for setting low output,
The electromagnetic cooker according to any one of claims 1 to 8, wherein the control means switches the input power set value to a predetermined value or less corresponding to a weak input when the low output setting key is operated .

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