KR100302205B1 - Electromagnetic cooker - Google Patents

Abstract

The present invention relates to an electronic cooker for heating a cooking vessel by supplying a high frequency current to a heating coil, wherein the input setting unit 41a blocks the IGBT 16 when the input setting value is less than or equal to a predetermined value Wth. When the snubber capacitor 15 is charged, the snubber capacitor 15 is charged when the IGBT 6 is turned on by performing separation control for separating the capacitor 15 from the resonant circuit 14. It is possible to continuously supply high-frequency current to the heating coil 11 in a state where the short-circuit current does not flow due to insufficient capacity, and the set value is Wth or less, so that continuous heating can be performed with a weak input in a state in which switching loss can be reduced. It is characterized by providing an electronic cooker that can.

Description

Electronic cooker {ELECTROMAGNETIC COOKER}

The present invention relates to an electronic cooker for heating a cooking vessel by supplying a high frequency current to the heating coil.

BACKGROUND ART Conventional electronic cookers are widely used as cooking heaters that are safe and have excellent thermal efficiency without using fire and are assembled to a system kitchen or the like. In many cases, a plurality of electronic cookers are assembled in a system kitchen, and a half-bridge type inverter that always performs heating control at a constant frequency is adopted to prevent interference noise when the plurality of electronic cookers are used at the same time. There is.

Fig. 13 shows the electrical configuration of a half-bridge inverter employed in a conventional electronic cooker. In this FIG. 13, the AC input terminal of the rectifier circuit 1 comprised of a diode bridge is connected to the commercial AC power supply 2, and the DC output terminal is connected to the both ends of the smoothing capacitor 3. As shown in FIG. .

Both ends of the smoothing capacitor 3 are connected to the arms of the positive and negative IGBTs 6 and 7 via direct current buses 4 and 5 to form a half-bridge type inverter main circuit 8. Flywheel diodes 9 and 10 are connected between collector-emitters of the IGBTs 6 and 7, respectively.

One end of the heating coil 11 is connected to the output terminal 8a of the inverter main circuit 8, and a resonance capacitor (between the other end of the heating coil 11 and the DC bus 5) 12 and a parallel circuit of the diode 13 are connected. In addition, the heating coil 11 and the resonant capacitor 12 constitute a resonant circuit 14.

In addition, one end of the 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 through the collector-emitter of the IGBT 16. It is connected to (5). 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 losses when the IGBTs 6 and 7 are turned off.

The oscillation signal of the predetermined frequency output from the oscillator 19 is transmitted to the variable on time setting unit 20 and the fixed on time setting unit 21. The current transformer 22 is inserted into the AC input side of the rectifier circuit 1, and the output terminal of the current transformer 22 is connected to the input terminal of the input setting unit 24a through the input current detector 23. . The input current detector 23 performs A / D conversion on the input current value detected by the current transformer 22 and outputs the input current detected value Vin to the input setting unit 24a.

Although not shown in detail, the operation part 25 is provided with the key which a user selects various automatic cooking menus (control program), the key for setting heating amount to electric power, such as 1KW and 2KW. And the input setting part 24a performs feedback control based on the input current detection value Vin transmitted from the input current detection part 23 so that it may become an input current value according to the setting of the electric power amount in the operation part 25, The PWM signal is transmitted to the variable on time setting unit 20.

In addition, the heating stop part 24b outputs a heating stop command to the variable on time setting part 20 and the fixed on time setting part 21, when predetermined conditions are established. In addition, the input setting part 24a and the heating stop part 24b block and show the function of the microcomputer 24 (henceforth a microcomputer).

The output signal of the variable on time setting unit 20 is transmitted to the first and third drivers 26 and 27, and the output signal of the fixed on time setting unit 21 is transmitted to the second and third drivers 28 and 27. It is said. 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, 16, respectively.

14 shows the detailed electrical configuration of the first driver 26. In FIG. 14, the output signal of the variable on time setting unit 20 is transmitted to the photocoupler 29, and one output terminal of the photocoupler 29 is connected to the IGBT (through the series circuit of the resistors 30 and 31). It is connected to the gate of 6). The diode 32 is antiparallel connected to the resistor 30. 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, 150 Ω and 10 Ω.

The operation of the electronic cooker provided with the inverter configured as described above will be described below with reference to FIGS. 15 to 17. Heating of the container 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 alternately turned on and off in the control period Tinv of the inverter, for example, about 20 KHz.

The on period Ton1 of the IGBT 6 is changed to Tinv / 2 as the upper limit based on the output signal transmitted from the variable on time setting unit 20. On the other hand, the on time Ton2 of the IGBT 7 is fixed at about Tinv / 2 based on the output signal transmitted from the fixed on time setting unit 21. However, in order to prevent a short circuit between the IGBTs 6 and 7, the stop period TD is secured when the on periods of both are replaced.

In addition, the IGBT 16 of the snubber circuit 18 reduces the switching loss at the time of turning off the IGBTs 6 and 7, and also the period until the IGBT 7 is turned on after the IGBT 6 is turned off. The snubber capacitor 15 is controlled on and off so that the snubber capacitor 15 is not charged.

The control cycle consists of four cycles: 16D is a waveform of the current IL flowing through the heating coil 11 at this time, and FIG. 16E is a waveform of the voltage Vtr2 between the collector and emitter of the IGBT 7. .

①IGBT (6): On / IGBT (7): Off

The current is supplied to the heating coil 11 by the path of the smoothing capacitor 3, the IGBT 6, the heating coil 11, the resonant capacitor 12, and the smoothing capacitor 3, and the resonant capacitor 12 is Charging (see Fig. 16 (d), A).

②IGBT (6): Off / IGBT (7): Off

The resonant capacitor 12 is again charged by the delay current of the heating coil 11 in the path of the heating coil 11, the resonant capacitor 12, the flywheel diode 10, and the heating coil 11 (FIG. d), see B).

③IGBT (6): Off / IGBT (7): On

The resonant capacitor 12 is discharged by the paths of the resonant capacitor 12, the heating coil 11, the IGBT 7, and the resonant capacitor 12 so that a reverse current flows in the heating coil 11 (FIG. 16). (d), C). When the resonant capacitor 12 is completely discharged, current flows through the diodes 13 connected in parallel (see Fig. 16 (d), C ').

4.IGBT (6): Off / IGBT (7): Off

The delay current of the heating coil 11 is regenerated to the power supply side through the flywheel diode 9 in the path of the heating coil 11, the flywheel diode 9, the smoothing capacitor 3, the diode 13, and the heating coil 11. (See FIG. 16 (d) and D).

By repeating the above cycle, a high frequency current is supplied to the heating coil 11, and an eddy current is induced to conduct a heating cooking to a container 34 (see FIG. 13) installed on the top plate 33. have. Input current control is performed by changing the on-period Ton1 of the IGBT 6, and when the on-period Ton1 is extended, the input current increases and the heating amount of the container 34 increases.

However, in such a conventional electronic cooker, since the weak input heating is performed, the following problem occurs when the on period Ton1 of the IGBT 6 is shortened.

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 less than a certain time, the amount of current supplied to the heating coil 11 is reduced (Fig. 17 (d), A). In the periods (C and C ′) of cycle ③ and cycle ④, the snubber capacitor 15 is not fully charged until the voltage Vtr2 between the terminals of the IGBT 7 is equal to the DC power supply voltage. In (4), the regenerative current does not flow and the snubber capacitor 15 is continuously charged.

In this state, since the IGBT 6 is turned on in the next cycle ①, the DC bus 4, the IGBT 6, the snubber capacitor 15, and the IGBT 16 are driven by the potential difference between the DC power supply voltage and the voltage Vtr2. And a short-circuit current flow in the path of the DC bus 5. Here, FIG. 17 (f) shows a current waveform Itr1 flowing through the IGBT 6, and a short circuit current flows at the point P shown in FIG. 17 (f).

In order to suppress the occurrence of such short-circuit current as much as possible, as shown in FIG. 14, the gate resistance value at turn-on is set to be large by passing the gate of the IGBT 6 through a series circuit of resistors 30 and 31. As shown in Fig. 15, the rising of the gate signal VG1 is slowed to delay the timing at which the IGBT 6 is turned on.

However, since the rise of the voltage between the collector and the emitter of the IGBT 6 is also moderated by smoothing the rise of the gate signal VG1 in this manner, the switching loss (turn-on loss) generated when the IGBT 6 is turned on. ) Occurs. The switching loss at this turn-on becomes larger as the set input becomes lower, and continuous heating with the turn-on loss becomes larger causes the temperature of the IGBT 6 to rise, leading to thermal breakdown in the worst case.

Therefore, in a conventional electronic cooker, for example, a low input such that the turn-on loss of the IGBT 6 does not occur when a weak input heating corresponding to a cooking cooked on low heat for a long time is set to a lower limit, for example. After heating for 3 seconds, periodic heating for 3 seconds was stopped.

In addition, such a heating method has a problem such that when a small amount of the cooked material suddenly boils, or when the cooked food is cooked, the cooked material burns out.

This invention is made | formed in view of the said situation, The objective is to provide the electronic cooker which can perform continuous heating with a weak input in the state which can reduce switching loss.

1 is a functional block diagram showing the electrical configuration of the first embodiment of the present invention;

FIG. 2 is a diagram showing signal waveforms of respective portions in a region where the input set value exceeds a predetermined value Wth; FIG.

FIG. 3 is an equivalent of FIG. 2 in a region where the input set value is equal to or less than the predetermined value Wth,

4 is a diagram showing a control state in the case of transition between separation control and normal control;

5 is a view showing a temperature change (vertical axis) of IGBT when the steel container is heated by changing an input set value (horizontal axis);

6 is a correspondence of FIG. 1 showing a second embodiment of the present invention;

7 is an equivalent of FIG. 4,

8 is an equivalent view of FIG. 1 showing a third embodiment of the present invention;

9 is a diagram showing a change in regenerative current detection value Vinv (vertical axis) when the input set value (horizontal axis) is changed;

Fig. 10 is a diagram showing the electrical configuration of main parts in the fourth embodiment of the present invention;

11 is a view showing a voltage waveform of a gate signal;

12 is an equivalent of FIG. 5,

FIG. 13 is a correspondence of FIG. 1 showing a prior art;

14 is a view showing the electrical configuration of the gate driver of the IGBT;

15 is a correspondence of FIG.

16 corresponds to the equivalent of FIG. 2 and FIG.

17 is an equivalent view of FIG. 3.

* Explanation of symbols for the main parts of the drawings

1: rectifier circuit 2: commercial AC power supply

4, 5: positive and negative DC buses 6, 7: IGBTs (first and second switching means)

8: inverter main circuit 11: heating coil

12 resonant capacitor 14 resonant circuit

15: snubber capacitor 16: IGBT (third switching element)

18: snubber circuit 22: current transformer (input current detecting means)

41, 41´: Microcomputer (control means) 41a: Input setting section

41b, 41b´: Heating stop 42: Resistance

43: capacitor (regenerative current detection means) 44: resistance (regenerative current detection means)

45: diode (regenerative current detection means) 46: resistance (resistance value switching means)

47: photocoupler (resistance value switching means)

In order to achieve the above object, the electronic cooker according to claim 1

A rectifier circuit for rectifying AC power to generate DC power,

Both side and negative side DC buses to which the DC power generated by the rectifier circuit is supplied;

First and second switching elements connected in series between the both side and the negative side DC bus lines;

A resonant circuit composed of a heating coil and a resonant capacitor connected between any one of these first and second switching elements to inductively heat the cooking vessel;

A snubber circuit connected between both terminals of the one switching element and configured of a snubber capacitor and a series circuit of the third switching element;

Conducting control by outputting a control signal to the first, second and third switching elements in accordance with a set value, and when the set value is less than or equal to a predetermined value, shuts off the snubber by cutting off the third switching element. And control means for performing separation control for substantially separating the capacitor from the resonant circuit.

In such a configuration, the control means substantially separates the snubber capacitor from the resonant circuit when the set value is less than or equal to the predetermined value. In this case, the snubber capacitor is not charged. The short-circuit current does not flow due to the insufficient charging capacity of the nuber capacitor. Therefore, even if the set value is less than or equal to the predetermined value, the high frequency current can be continuously supplied to the heating coil in a state in which switching loss can be reduced in one switching element, and continuous heating can be performed at a weak input.

In this case, as described in claim 2, the snubber capacitor and the third switching element may be connected in series to form a snubber circuit. With this configuration, separation control can be easily performed.

Further, as described in claim 3, the control means is configured to energize the third switching element after a predetermined time elapses after the energization of one switching element, and to shut off the third switching element after a predetermined time elapses after the interruption of the other switching element. It is good also as a structure which outputs a control signal. With this configuration, it is possible to prevent the short circuit current from flowing through the snubber capacitor when the other switching element is turned on.

As described in claim 4, when the control means switches the set value to a range including a predetermined value, the conduction control for the first and second switching elements is once stopped, and the separation control and the normal control therebetween. The configuration may be implemented. Such a configuration can prevent the short circuit current from flowing through the third switching element by stopping the conduction control of the first and second switching elements when transitioning between the separation control and the normal control.

As described in claim 5, a resistor may be connected in parallel with the resonant capacitor. With this arrangement, the control means controls the conduction of the first and second switching elements during the execution of the normal control of turning on and off the third switching element in accordance with the separation control and the conduction control of the first and second switching elements. Even after the power supply is stopped, the charges charged in the resonant capacitor can be quickly discharged through the resistor.

As described in claim 6, when the control means switches the set value to a range including a predetermined value, it is preferable that the conduction control of one switching element is stopped later than the other switching element. In such a configuration, similarly to claim 5, even when the control means stops the conduction control of the first and second switching elements, the conduction control (on, off) of one switching element is carried out by the charges charged in the resonant capacitor. It can be discharged more quickly by the switching operation by.

As described in claim 7, the apparatus includes an input current detecting means for detecting an input current value and a regenerative current detecting means for detecting a regenerative current value.

The control means may be configured to perform a function check of the third switching element based on the relationship between the input current value and the regenerative current value.

With this arrangement, since the function of the third switching element can be confirmed by the control means, it is possible to reliably prevent the occurrence of switching losses in the first and second switching elements, thereby improving safety.

As set forth in claim 8, further comprising resistance value switching means configured to switch resistance values of the resistors connected in series to the control input terminal of the other switching element, wherein the control means sets the control value when the set value is equal to or less than the predetermined value. It is good also as a structure which outputs a switching signal to a resistance value switching means. In this configuration, when the set value is less than or equal to the predetermined value, the switching loss caused at the turn-on of the other switching element can be reduced by reducing the resistance value of the resistor connected in series with the control input terminal of the other switching element. have.

In this case, as described in Claim 9, it is provided with the temperature detection means which detects the heating temperature of a cooking container, and sets a control value when a heating temperature of the said cooking container which the said temperature detection means detects a control means becomes more than predetermined temperature. It is good also as a structure which switches to below predetermined value. When comprised in this way, in the heating cooking which performs automatic control according to the heating temperature of a cooking container, the effect similar to Claim 1 thru | or 8 can be acquired.

In addition, as described in claim 10, a low output setting key for setting a low output may be provided, and the control means may be configured to switch the setting value to a predetermined value or less when the low output setting key is operated. According to this arrangement, the same effects as those of claims 1 to 8 can be obtained in the heating cooking which performs automatic control in accordance with the operation of the user's low power setting key.

Embodiment of the Invention

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 5. In addition, the same code | symbol is attached | subjected to the same part as FIG. 13, and description is abbreviate | omitted and only a different part is demonstrated below. 1 shows an electrical configuration. In this embodiment, a microcomputer (control means) 41 having an input setting section 41a and a heating stop section 41b is disposed in place of the microcomputer 24 shown in FIG. The input setting section 41a is configured to directly transmit the control signal VS to the third drive circuit 27.

In addition, a resistor 42 is connected in parallel to the resonant capacitor 12 and the diode 13. The resistance value of the resistor 42 is set to a sufficiently large value with respect to the impedance of the resonance capacitor 12 when the inverter main circuit 8 is operating. The other structure is the same as that shown in FIG.

Next, the operation of this embodiment will be described with reference to FIGS. 2 to 4. As shown in Fig. 2C, the input setting unit 41a is turned on after a predetermined time Tα has passed after the IGBT 7 (second switching means) turns on, and the IGBT 6 (first The switching means is turned off after the predetermined time Tα is passed after the switching means is turned off.

As a result, when the IGBTs 6 and 7 transition from the on state to the off state, the voltage change between the collector and the emitter is smoothed to prevent the occurrence of switching loss, and the snubber is turned on when the IGBT 7 is turned on. The short circuit current is prevented from flowing to the capacitor 15. Here, the constant time Tα is set so that the voltage change at the time of turn-off of the IGBTs 6 and 7 converges in any load or setting input within an appropriate range.

In addition, when the input setting value (set as the amount of power “W”) set by the user at the operation unit 25 is set to be smaller than or equal to the predetermined value Wth, the input setting unit 41a performs the IGBT 16 (third switching element). ), The snubber capacitor 15 is separated from the resonant circuit 14 by always turning off (blocking). As an example, when the maximum rating of the electronic cooker is 3KW, the predetermined value Wth is set to about 500W.

3 is a diagram illustrating signal waveforms of respective portions when the input set value is set to the predetermined value Wth or less. That is, in this case, since the IGBT 16 is always turned off by the heating stop 41b as shown in Fig. 3 (c), the snubber capacitor 15 is not charged and is substantially separated from the resonant circuit 14. Is in a state of being.

Therefore, even when the input current value is small, the snubber capacitor 15 is not charged. Therefore, the regenerative current flows reliably in the control cycle ④ described above, and the short circuit current flows even when the IGBT 6 is turned on in the next cycle ①. There is no work (see FIG. 3 (f)).

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, and when the input current value is small, the IGBTs 6 and 7 are used during the switching operation. Since the current flowing through the C1 is small, the turn-off loss is small even without the snubber capacitor 15. In this case, therefore, there is no problem even if the snubber capacitor 15 is separated from the resonant circuit 14.

In addition, Fig. 4 shows the control state in the case of shifting between the separation control and the normal control functioning of the snubber capacitor 15 in accordance with the setting of the input current value, the voltage Vtr2 between terminals of the IGBT 7 (a). ) And the control signal Vs (b). In FIG. 4, when the setting of the input current value is changed from a value exceeding the predetermined value Wth (Hi, see FIG. 5) to a value (Lo, FIG. 5) below the predetermined value Wth, that is, In the case of shifting from normal control to separate control, the input setting unit 41a first transmits a control signal to the heating stop unit 41b, and stops the conduction control of the IGBTs 6 and 7 (Fig. 4 (a)). , See point A).

When stopped as described above, since the charge remaining in the resonant capacitor 12 is discharged through the resistor 42, the voltage Vtr2 gradually decreases from the DC power supply voltage to become about 0V after the lapse of the assumed time Ta. (See Fig. 4 (a), time point B). In addition, after waiting for the allowance time Tb, the voltage Vtr2 is surely 0V, the input setting section 41a always turns off the IGBT 16 by outputting the control signal Vs to the third drive section 27. Separation control is performed (see FIG. 4B and time C). Next, after waiting for the elapse of the switching waiting time Tc of a control system, continuous heating is started at the weak input (500 W or less) (refer FIG. 4 (a), time D).

In addition, when returning to normal control in the state which isolate | separation control is being performed, it switches similarly. That is, the input setting part 41a transmits a control signal to the heating stop part 41b, and stops the conduction control of the IGBTs 6 and 7 (refer FIG. 4 (a), time point E), and assumes the assumed time Ta The discharge of the residual charge of the resonant capacitor 12 is waited for a while (see FIG. 4A and time F).

In addition, after waiting for the allowance time Tb, the input setting unit 41a stops output of the control signal Vs to the third drive unit 27, and returns the IGBT 16 to the normal control state (Fig. 4). (B), point in time G). Then, after waiting for the change of the switching wait time Tc of the control method, continuous heating is started at an input current value exceeding 500 W (see FIG. 4A and time H).

Fig. 5 is a measurement example performed by the inventor of the present invention, and shows the temperature change (vertical axis) of the IGBT 6 when the steel container 34 is heated by changing the input set value (horizontal axis). The temperature of the IGBT 6 also decreases as the input set value decreases. However, when the control of the IGBT 16 is normally performed, as shown by the solid line in FIG. 5, when the input power amount is lower than the predetermined value Wth. The temperature of the IGBT 6 rises rapidly. On the other hand, when separation control is performed in the area | region which becomes predetermined value Wth or less, as shown by the broken line in FIG. 5, the temperature of the IGBT 6 will fall according to the fall of an input setting value.

As described above, according to the present embodiment, the input setting unit 41a disconnects the snubber capacitor 15 from the resonance circuit 14 by blocking the IGBT 16 when the input setting value becomes less than the predetermined value Wth. Separation control to separate is performed. Therefore, when the snubber capacitor 15 is not charged and the IGBT 6 is turned on, no short-circuit current flows due to insufficient charging capacity of the snubber capacitor 15, and heating is performed in a state where the set value is Wth or less. The high frequency current can be continuously supplied to the coil 11. Therefore, since the switching loss of the IGBT 6 can be suppressed and continuous heating can be performed by the weak input, unlike the conventional art, for example, cooking for a long time can be performed well without burning or suddenly boiling the food. have.

In addition, according to the present embodiment, the input setting unit 41a turns on the IGBT 16 after a predetermined time has elapsed since the IGBT 7 is turned on, and after the predetermined time has elapsed since the IGBT 6 is turned off. Since the control signal is output to turn off, switching losses of the IGBTs 6 and 7 can be suppressed, and a short circuit current can be prevented from flowing to the snubber capacitor 15 when the IGBT 7 is turned on.

In addition, according to the present embodiment, when the resistor 42 is connected in parallel to the resonant capacitor 12, and the input setting section 41a switches the set value to a range including the predetermined value Wth, IGBT ( Since the conduction control for 6 and 7 is once stopped and the separation control and the normal control are executed in the meantime, the short-circuit current is prevented from flowing to the IGBT 16 when transitioning between the separation control and the normal control. Further, even when the conduction control to the IGBTs 6 and 7 is stopped, the charges charged in the resonant capacitor 12 can be quickly discharged through the resistor 42.

6 and 7 show a second embodiment of the present invention. The same parts as those of the first embodiment will be denoted by the same reference numerals, and description thereof will be omitted. In Fig. 6 showing the electrical configuration, in the second embodiment, the resistor 42 is removed, and the microcomputer 41 is replaced with a microcomputer (control means) 41 '. The microcomputer 41 'replaces the heating stop part 41b of the microcomputer 41 with the heating stop part 41b'. The rest of the configuration is the same as in the first embodiment.

Next, the operation of the second embodiment will be described with reference to FIG. In the second embodiment, the control state in the case of shifting between the separation control and the normal control in accordance with the setting of the input current value is different from that in the first embodiment. That is, as shown in FIG. 7, when shifting from normal control to separate control, the input setting part 41a first transmits a control signal to the heating stop part 41b ', and stops the conduction control of only the IGBT 6, The conduction control of the IGBT 7 continues to stop for the time Ta '(see Fig. 7 (a), time point A).

When stopped as described above, the charge remaining in the resonant capacitor 12 is discharged and consumed within a very short time (for example, about 3 or 4 cycles) by the switching operation of the IGBT 7 having a frequency of 21.5 KHz. Thereafter, similarly to the first embodiment, the input setting section 41a waits for the elapse of the allowable time Tb (see FIG. 7 (a) and the time point B) to apply the control signal Vs to the heating stop section 41b. It does not output and performs separate control (refer FIG.7 (b), time point C), waits for progress of switching waiting time Tc, and starts continuous heating by a weak input (500W or less) (FIG.7 ( a), see point D). In addition, the switchover is similarly performed when the control is returned to the normal control while the separation control is being performed.

As described above, according to the second embodiment, the heating stop portion 41b 'performs conduction control of the IGBT 7 with respect to the IGBT 6 when the input set value is switched within the range including the predetermined value Wth. Since it stops later, the electric charge charged in the resonant capacitor 12 can be discharged and consumed more quickly by the switching operation by conduction control (on, off) of one IGBT 7, and it is necessary to change the control state. It can save time. In addition, in the first embodiment, since the necessary resistor 42 can be eliminated, the component score can be reduced.

8 and 9 show a third embodiment of the present invention, in which the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Only the other parts will be described below. In Fig. 8 showing the electrical configuration, in the third embodiment, a series circuit of the capacitor 43 and the resistor 44 is connected in parallel to the smoothing capacitor 3, and the diode 44 is connected to the resistor 44. Inverse parallel connection. The capacity of the capacitor 43 is set at about 1/100 of the capacity of the smoothing capacitor 3, for example.

The capacitor 43, the resistor 44, and the diode 45 constitute a regenerative current detecting means. The common connection point of the capacitor 43 and the resistor 44 is connected to the input terminal of the input setting section 41a via the regenerative current detector 45. The rest of the configuration is the same as in the first embodiment.

In the third embodiment, the regenerative current flowing from the load side to the power supply side and flowing into the smoothing capacitor 3 is classified into a series circuit of the capacitor 43 and the resistor 44. The regenerative current detector 45 detects the terminal voltage of the resistor 44 at the timing at which the regenerative current flows and outputs the A / D conversion to the input setter 41a as the regenerative current detection value Vinv. .

Next, the operation of the third embodiment will be described with reference to FIG. Fig. 9 shows the change of 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 continues to operate even in an area where the input set value is reduced to the vicinity of the predetermined value Wth, a short circuit current flows through the snubber capacitor 15 so that the regenerative current is increased. It becomes difficult to flow and as shown by a solid line in FIG. 9, the regenerative current detection value Vinv falls.

Therefore, as shown by a dashed-dotted line in FIG. 9, a threshold value is set. Then, for example, the microcomputer 41 is switched to the test mode to perform a function test as follows. For example, the control signal Vs is output so that the IGBT 16 is turned off, and the input set value is set below the predetermined value Wth. If the regenerative current detection value Vinv at this time is larger than the determined value, the switching control function or IGBT 16 can be determined to be normal. If the regenerative current detection value Vinv is smaller than the threshold value, the switching control function is abnormal or It can be determined that the IGBT 16 is shorted.

In addition, separation control by the IGBT 16 is performed to set the input set value to the predetermined value Wth or less. If the regenerative current detection value Vinv at this time is larger than the threshold value, it is possible to determine that the switching control function is abnormal or that the IGBT 16 is open or unmounted.

As described above, according to the third embodiment, the input current setting unit 41a of the microcomputer 41 performs the control switching function and the function test of the IGBT 16 based on the relationship between the input setting value and the regenerative current value Vinv. I made it. Therefore, for example, the microcom 41 is switched to the test mode for testing at a manufacturing process before shipment or at a service center after shipment, and the switching loss is surely prevented from occurring in the IGBTs 6 and 7. Safety can be improved or a check at the time of failure can be performed easily.

10 to 12 show a fourth embodiment of the present invention. The same parts as those of the first embodiment will be denoted by the same reference numerals, and description thereof will be omitted. Only the other parts will be described below. 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 in accordance with the input set value.

That is, one end of the resistor 46 having a resistance value of 10? Is connected to a common connection point of the resistors 30 and 31, and the other end of the resistor 46 is an output terminal of the photocoupler 47. It is connected to one end of. The other end of the output terminal of the photocoupler 47 is connected to the common connection point of the output terminal of the photocoupler 29 and the resistor 30. The output signal from the microcomputer 41 is transmitted to the output terminal of the photocoupler 47. In addition, the resistor 46 and the photocoupler 47 constitute a resistance value switching means, and are otherwise the same as in the first embodiment.

Next, the operation of the fourth embodiment will be described with reference to FIGS. 11 and 12. In the first to third embodiments, the short-circuit current can be prevented from flowing through the snubber capacitor 15 in a small region where the input set value is less than or equal to the predetermined value Wth. Since the short-circuit current may also flow when connected to 14), the gate resistance value of the IGBT 6 is set in the same manner as in the conventional configuration shown in Fig. 14 so as to increase at turn-on.

That is, in the region where the input set value is smaller than or equal to the predetermined value Wth, the short-circuit current does not occur during the turn-on of the IGBT 6, but the voltage Vtr1 between the terminals decreases slowly, so it occurs at that portion. There is still a switching loss. Therefore, in the fourth embodiment, the microcomputer 41 outputs a high level signal to the photocoupler 47 in the region where the input set value is smaller than or equal to the predetermined value Wth. Control to connect in parallel.

In the control as described above, since the gate resistance value at turn-on is switched from 160 Ω to (150 // 10 + 10) Ω, as shown in FIG. 12, the increase in the gate voltage VG1 is more steep compared with FIG. 5. As a result, the drop of the terminal voltage Vtrl is also steep. As a result, the turn-on loss of the IGBT 6 is further reduced, and as shown in FIG. 12, for example, the temperature rise of the IGBT 6 is further suppressed as compared with FIG. 5 in the first embodiment.

As described above, according to the fourth embodiment, the microcomputer 41 outputs a switching signal to the photocoupler 47 when the input setting value becomes less than or equal to the predetermined value Wth, and to the gate (control input terminal) of the IGBT 6. Since the resistors 46 are connected in parallel to the resistors 30 connected in series to switch the gate resistance values, the switching losses occurring at turn-on can be further reduced by reducing the gate resistance value of the IGBT 6. .

The present invention is not limited to the embodiments described above and described in the drawings, and the following modifications or extensions are possible.

For example, the input setting unit 41a firstly selects a cooking (control) program installed in the operation unit 25, for example, when the “boiling” key (low output setting key) is turned on. Normal control-separation control may be automatically switched according to the control program which heats a high temperature and heats a to-be-cooked object, and performs weak input heating continuously after that. If the "heating key" is turned on during the high input heating, the control may be switched to continuously perform the weak input heating at that time.

Alternatively, a temperature sensor (temperature detecting means) for detecting the temperature of the container 34 is provided on the top plate 33, and when the temperature detected by the temperature sensor reaches a predetermined value (predetermined temperature) at that time, You may switch control so that weak input heating may be performed continuously.

Even if the snubber capacitor 15 is electrically connected to the resonant circuit 14, the snubber capacitor 15 may be substantially separated from the resonant circuit 14 in separation control. For example, a series circuit between a very high resistance value resistor and an electrical or mechanical normally open switch is connected between the collector-emitter of the IGBT 16 and the switch is closed while the snubber capacitor 15 is closed. May be connected to the DC bus 5 through a resistor.

The resonant circuit 14 may be connected to the IGBT 6 side.

The switching element is not limited to IGBT but may be a power transistor or a power MOSFET.

Since this invention is as having demonstrated above, it has the following effects.

According to the electronic cooker according to claim 1, the control means performs separation control for substantially separating the snubber capacitor from the resonant circuit for induction heating of the cooking vessel by shutting off the third switching element when the set value is less than or equal to the predetermined value. Therefore, in that case, the snubber capacitor is not charged, and when one switching element is turned on, no short-circuit current flows due to insufficient charging capacity of the snubber capacitor.

Therefore, it is possible to continuously supply a high frequency current to the heating coil in a state where the set value is less than or equal to the predetermined value, to perform continuous heating at a weak input, and to perform heating control such as cooking for a long time in a good manner.

According to the electronic cooker of Claim 2, since the snubber circuit was comprised by connecting the snubber capacitor and the 3rd switching element in series, separation control can be performed easily.

According to the electronic cooker according to claim 3, the control means energizes the third switching element after a predetermined time has passed since the energization of one switching element, and blocks the third switching element after a predetermined time has elapsed since the blocking of the other switching element. Short circuit current can be prevented from flowing to the snubber capacitor when the switching element is turned on.

According to the electronic cooker of Claim 4, when switching a set value to the range containing a predetermined value, a control means stops conduction control with respect to a 1st and 2nd switching element once, and performs separation control and normal control in the meantime. In this way, it is possible to prevent the short-circuit current from flowing to the third switching element when transitioning between the separation control and the normal control.

According to the electronic cooker according to claim 5, when the resistor is connected in parallel to the resonant capacitor, the control means once stops the conduction control of the first and second switching elements during the separation control and the execution of the normal control. The charge charged in the resonant capacitor can be quickly discharged through the resistor.

According to the electronic cooker of Claim 6, when a control means switches a setting value to the range containing a predetermined value, the control means stops conduction control of one switching element late with respect to the other switching element, and a control means makes the 1st and 2nd Even when the conduction control to the switching element is once stopped, the charges charged in the resonant capacitor can be discharged more quickly by the switching operation by the conduction control of one switching element to shorten the time required for the switching control.

According to the electronic cooker of Claim 7, since a control means confirms the function of a 3rd switching element based on the relationship of an input current value and a regenerative current value, generation | occurrence | production of the switching loss in a 1st and 2nd switching element is carried out. It can be prevented reliably to increase safety.

According to the electronic cooker according to claim 8, the control means outputs a switching signal to the resistance value switching means when the set value is less than or equal to the predetermined value, thereby switching the resistance value of the resistor connected in series to the control input terminal of the other switching element. Therefore, when the set value is less than or equal to the predetermined value, the switching loss caused when the other switching element is turned on can be reduced.

According to the electronic cooker of Claim 9, since a control means switches a set value below a predetermined value when the heating temperature of the cooking container which a temperature detection means detects becomes more than predetermined temperature, it performs automatic control according to the heating temperature of a cooking vessel. In the heating cooking described, the same effects as in Claims 1 to 8 are obtained.

According to the electronic cooker of Claim 10, since a control means switches a set value below a predetermined value when a low output setting key is operated, it is the heating cooking which performs automatic control according to operation of a low output setting key of a user, Claim 1 thru | or Claim The same effect as 8 is obtained.

Claims (11)

Rectifier circuit for rectifying AC power to generate DC power, Both side and negative side DC buses to which the DC power generated by the rectifier circuit is supplied; First and second switching elements connected in series between the both side and the negative side DC bus lines, A resonant circuit connected between any one of the first and second switching elements, the resonant circuit comprising a heating coil and a resonant capacitor for inductively heating the cooking vessel; A snubber circuit connected between both terminals of the one switching element, the snubber capacitor comprising a snubber capacitor and a third switching element; The conduction control is performed by outputting a control signal to the first, second and third switching elements in accordance with a set value, and when the set value is equal to or less than a predetermined value, the snubber is cut off by cutting off the third switching element. And control means for performing separation control to substantially separate the capacitor from the resonant circuit. The method of claim 1, The snubber circuit is configured by connecting the snubber capacitor and the third switching element in series. The method according to claim 1 or 2, And the control means energizes the third switching element after a predetermined time elapses after the energization of one switching element, and outputs a control signal to shut off the third switching element after a predetermined time elapses after the interruption of the other switching element. Cooker. The method according to claim 1 or 2, The control means stops the conduction control for the first and second switching elements once when the set value is switched to a range including a predetermined value, during which the separation control and the normal control are executed. Electronic cooker. The method of claim 4, wherein An electronic cooker, wherein a resistor is connected in parallel with the resonant capacitor. The method of claim 4, wherein And the control means stops the conduction control of one switching element later with respect to the other switching element when switching the set value to a range including a predetermined value. The method according to claim 1 or 2, Input current detection means for detecting an input current value; A regenerative current detecting means for detecting a regenerative current value; And the control means checks the function of the third switching element based on the relationship between the input current value and the regenerative current value. The method according to claim 1 or 2, A resistance value switching means configured to switch a resistance value of a resistor connected in series with the control input terminal of the other switching element, And the control means outputs a switching signal to the resistance value switching means when the set value is equal to or less than a predetermined value. The method according to claim 1 or 2, It is provided with the temperature detection means which detects the heating temperature of a cooking container, And the control means switches the set value to a predetermined value or less when the heating temperature of the cooking vessel detected by the temperature detecting means becomes a predetermined temperature or more. The method according to claim 1 or 2, Equipped with a low power setting key for setting low power, And the control means switches the setting value to a predetermined value or less when the low power setting key is operated. The method of claim 3, wherein The control means stops the conduction control for the first and second switching elements once when the set value is switched to a range including a predetermined value, during which the separation control and the normal control are executed. Electronic cooker.