JP2007029593A - Rice cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a stable reduction effect of unnecessary radiation noise by periodically varying input current so as to periodically varying the operation frequency of a heating coil so as to periodically disperse energy of the unnecessary radiation noise in a rice cooker for carrying out induction heating of a pot with the heating coil. <P>SOLUTION: A switching means 6 is connected serially with the heating coil 2 which carries out induction heating of the pot 1. An AC power source 7 is rectified by a rectification means 8 to supply power to the heating coil 2. Input current supplied from the AC power source 7 is detected by an input current detection means 12. A target value of the input current is set by an input current setting means 15. The target value of the input current is varied periodically with a prescribed amplitude by a setting current variation means 16. The on time of the switching means 6 is set by an on time setting means 17. The on time setting means 17 sets the on time of the switching means 6 according to the output values of the input current detection means 12 and the setting current variation means 16. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rice cooker that induction-heats a pan with a heating coil.

Conventionally, an induction heating cooker having a configuration similar to this type of rice cooker includes a heating coil for induction heating of a pan and a control means for controlling on / off of switching means connected in series to the heating coil. When driving, the difference between the fluctuation range when the ON time of the switching means increases and the fluctuation width when the switching means decreases so that the ON time of the switching means fluctuates irregularly, and the operating frequency of the heating coil is changed. Some have reduced unnecessary radiation noise generated more (for example, see Patent Document 1).
JP 2003-36961 A

  However, in such a conventional configuration, the fluctuation range of the input current becomes irregular, the fluctuation of the operating frequency becomes irregular, and the effect of reducing unnecessary radiation noise becomes unstable. It was.

  The present invention solves the above-described conventional problems, and periodically changes the operating frequency of the heating coil by periodically changing the input current, and periodically disperses the energy of unnecessary radiation noise, thereby stabilizing The purpose is to reduce the unnecessary radiation noise.

  In order to achieve the above object, the present invention forms a resonance circuit with a heating coil for inductively heating a pan and a resonance capacitor, a switching means is connected in series to the heating coil, and the AC power source is rectified by the rectification means to heat the heating coil. The input current supplied from the AC power source is detected by the input current detecting means, the target value of the input current is set by the input current setting means, and the target value of the input current is periodically set by the setting current fluctuation means. The on-time of the switching means is set by the on-time setting means, and the on-time setting means is controlled by the switching means according to the output values of the input current detection means and the set current fluctuation means. The on-time is set.

  Thus, by periodically changing the input current, the operating frequency of the heating coil can be periodically changed, and the energy of unnecessary radiation noise can be periodically distributed. Since the operating frequency is uniformly distributed, a stable effect of reducing unnecessary radiation noise can be obtained.

  The rice cooker of the present invention can periodically change the operating frequency of the heating coil by periodically changing the input current, and can evenly distribute the energy of unnecessary radiation noise to each operating frequency. This can stabilize the effect of reducing the quasi-peak value of unnecessary radiation noise.

  The first invention is a heating coil for inductively heating a pan, a resonance capacitor constituting a resonance circuit with the heating coil, switching means connected in series to the heating coil, rectifying an AC power source, and supplying power to the heating coil. Rectifying means to be supplied; input current detecting means for detecting an input current supplied from the AC power supply; input current setting means for setting a target value of the input current; Set current varying means for varying the amplitude of the switching means, and on-time setting means for setting the on-time of the switching means. The on-time setting means determines the output values of the input current detecting means and the set current varying means. Accordingly, the on-time of the switching means is set, and the operating frequency of the heating coil is changed by periodically varying the input current. To be able to periodically to vary the energy of equally unnecessary radiation noise to each operating frequency can be dispersed, the effect of reducing the quasi-peak of the unwanted radiation noise can be stabilized. Further, since the input current is periodically changed, it is easy to control the average value of the input current.

  According to a second aspect of the present invention, in the first aspect of the present invention, the heating coil includes a first heating coil that induction-heats the bottom of the pan, and a concentric circle formed on the first heating coil, the height of the outer end being higher than the inner end. A second heating coil formed so as to be high, and a first resonance capacitor constituting a resonance circuit and a first switching means are connected to the first heating coil and the second heating coil is connected to the second heating coil. A second resonance capacitor constituting a resonance circuit and a second switching unit are connected to the heating coil, and a set current variation unit includes a first variation period used when driving the first heating coil, A second fluctuation period used when driving the second heating coil, the second fluctuation period being longer than the first fluctuation period, and an input current of the second heating coil The fluctuation range of The fluctuation range of the operating frequency of the second heating coil can be increased, the effect of reducing the quasi-peak of the unwanted radiation noise of the second heating coil leakage flux lateral often can be stabilized.

  In a third aspect based on the second aspect, the maximum value of the first input current when driving the first heating coil is the maximum value of the second input current when driving the second heating coil. It is larger than the value, suppresses unnecessary radiation noise of the second heating coil with a large amount of leakage flux in the side direction, and provides sufficient high-frequency power to the pan using the first heating coil with a small amount of leakage flux in the side direction. Can be supplied.

  According to a fourth aspect of the present invention, in any one of the first to third aspects of the present invention, a zero voltage detection unit that outputs a pulse when the zero voltage of the AC power supply is detected is provided, and the set current fluctuation unit includes the zero voltage detection unit. The target value of the input current is changed with a predetermined amplitude in synchronization with the output pulse, and the target value of the input current is changed when the voltage of the AC power supply is low. Generation of noise due to change can be suppressed.

  In a fifth aspect based on the fourth aspect, when the number of output pulses of the zero voltage detection means reaches a predetermined value, the set current fluctuation means fluctuates the target value of the input current with a predetermined amplitude to obtain the frequency of the AC power supply. Accordingly, the predetermined value of the number of output pulses is changed, and it is possible to prevent a difference in unnecessary radiation noise between the region where the frequency of the AC power supply is 50 Hz and the region where it is 60 Hz.

  In a sixth aspect based on any one of the first to fifth aspects, the input current setting means has at least two input current target values, and the set current fluctuation means has a large input current target value. Sometimes the target value is fluctuated longer than when it is small, and even when the current flowing through the heating coil is large and the leakage flux from the heating coil increases, the quasi-peak value of unwanted radiation noise is reliably reduced. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a partial block diagram of a rice cooker according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the pan 1 is composed of a laminated body using a plurality of metals through which magnetic flux passes, and FIG. 1 shows an equivalent circuit. The heating coil 2 is composed of a first heating coil 3 and a second heating coil 4, and the first heating coil 3 and the second heating coil 4 are connected in series. The first heating coil 3 has a spiral shape and is arranged at a certain distance on the bottom of the pan 1 so as to be magnetically coupled to the bottom of the pan 1. The second heating coil 4 is configured concentrically with the first heating coil 3 and formed so that the height of the outer end is higher than the inner end, and is formed on the concentric side surface of the first heating coil 3. Arranged and magnetically coupled to the side of the pan 1. The 1st heating coil 3 and the 2nd heating coil 4 are comprised by the wire which twisted more than 20 litz wires which bundled a plurality of copper wires, and the current distribution when a high frequency current flows is uniform. I have to.

  The resonance capacitor 5 constitutes a resonance circuit with the heating coil 2 and is connected to the heating coil 2 in parallel. In the present embodiment, a polypropylene capacitor having a small loss even when a high-frequency current flows is used.

  The switching means 6 is composed of a semiconductor element such as a MOSFET or IGBT and a reverse connection diode reversely connected to the semiconductor element. MOSFETs and IGBTs have high withstand voltage, can switch at high frequency, and can flow a large current by applying a voltage to the gate terminal, and have an advantage that a large current can be flowed with less power than a power transistor. . In the present embodiment, an IGBT is used.

  The AC power supply 7 supplies power to the rice cooker, and the power supply frequency of the AC power supply 7 is 50 Hz in the eastern Japan region and 60 Hz in the western Japan region. The rectifying means 8 rectifies the AC power supply 7 and supplies power to the heating coil 2, and includes a diode bridge 9, a choke coil 10, and a smoothing capacitor 11. Here, the capacity of the smoothing capacitor 11 is as small as several μF, and ripple occurs when a current is passed through the heating coil 2. In the present embodiment, this ripple voltage waveform is the same as the voltage waveform of the AC power supply 9.

  The input current detection means 12 detects an input current supplied from the AC power supply 7, and is not particularly shown, but converts the input current to a current of several mA at a predetermined ratio using a current transformer, It is converted into a DC voltage using a load resistor, a rectifier diode and an electrolytic capacitor connected to the secondary side of the transformer.

  The zero voltage detecting means 13 outputs a pulse when the zero voltage of the AC power source 7 is detected. The (u) pole of the AC power source 7 is connected to the base terminal of the transistor through a resistor, and the collector terminal of this transistor is It is connected to a 5V power source supplied from the AC power source 7 via a resistor, and (u) outputs low to the microcomputer 14 when the potential of the pole is higher than the other pole, and outputs high when the potential is low. .

  The microcomputer 14 operates with a 4 MHz oscillator and a 32.728 kHz oscillator. In the present embodiment, although not shown in particular, in addition to the input current setting means 15 and the set current fluctuation means 16, an LCD display means for controlling the LCD display unit, a time measuring means for displaying the clock inside the LCD, and a rice cooking process are controlled. The rice cooking process control means to perform is comprised.

  The input current setting means 15 is for setting a target value of the input current supplied from the AC power supply 7 and is composed of a ROM of the microcomputer 14 or the like. In this embodiment, as a plurality of current set values, a first current set value Is1 used when cooking rice, a second current set value Is2 used when cooking non-washed rice, and when keeping the rice warm The third current set value Is3 to be used is stored as 8-bit data in the ROM inside the microcomputer. In the present embodiment, the magnitude relationship between the current setting values Is1 to Is3 is Is1> Is2> Is3.

  The set current changing means 16 periodically changes the target value of the input current with a predetermined amplitude, and changes the target value of the input current with a predetermined amplitude in synchronization with the output pulse of the zero voltage detecting means 13. Further, it is constituted by a ROM of the microcomputer 14 and the like, and a fluctuation range and a fluctuation period corresponding to each current set value are stored. In the present embodiment, the fluctuation range is stored as 8-bit data, and the fluctuation period is stored as the total number of high outputs and low outputs of the zero voltage detection means 13.

  In the present embodiment, the first fluctuation range dIs1, the first fluctuation period Ts1 corresponding to the first current set value Is1, and the second fluctuation range dIs2 corresponding to the second current set value Is2. The second fluctuation period Ts2, the third fluctuation width dIs3 corresponding to the third current set value Is3, and the third fluctuation period Ts3 are stored. For example, when the first current set value Is1 is stored, the set current fluctuation means 16 causes the first current during the high output period when the number of times of high output of the zero voltage detection means 13 reaches the fluctuation period Ts1. A value obtained by subtracting the first fluctuation width dIs1 from the set value Is1 is output as 8-bit data, and is output to the on-time setting means via the DA converter. As a method of outputting 8-bit data, there are a method of using the PWM output function of the microcomputer 14 and a method of dividing the resistance by using eight output ports of the microcomputer 14 and connecting resistors to each port.

  The on-time setting means 17 sets the on-time of the switching means 6 in accordance with the output values of the input current detection means 12 and the set current fluctuation means 16, and is composed of a comparator 18, resistors 19, 20 and a capacitor 21. The voltage corresponding to the ON time is output to the pulse generating means 22. The comparator 18 compares the output voltage of the input current detection means 12 and the output voltage of the set current fluctuation means 17, and when the output voltage of the input current detection means 12 is lower, the output terminal is opened and the capacitor is connected via the resistor 19. 21 is charged and when the output voltage of the input current detection means 13 is higher, the output terminal is set to the low state and the capacitor 21 is discharged through the resistors 19 and 20.

  Although not shown in particular, the pulse generating means 22 is composed of an analog IC incorporating a sawtooth wave generating circuit and a comparison circuit, and the sawtooth wave generating circuit is composed of a charge / discharge circuit using a comparator and a capacitor, A sawtooth wave is generated using the high output of the synchronization signal generating means 23 as a trigger. The comparison circuit is composed of a comparator or the like, compares the output voltage of the sawtooth wave generation circuit with the output voltage of the on-time setting means 17, and outputs high while the output of the on-time setting means 17 is large. The configuration of the pulse generating means 22 is merely an example, and may be configured by a digital circuit using a counter, an AD converter, or the like, or a PWM circuit built in a microcomputer.

  The synchronization signal generating means 23 is constituted by a comparator or the like, and compares the voltage obtained by dividing the (C2) terminal by a predetermined ratio with the voltage obtained by dividing the (CE) terminal by a predetermined ratio, and (C2) When the divided voltage at the terminal is higher, high is output to the pulse generating means 22.

  Although not particularly shown, the drive circuit 24 is constituted by a push-pull circuit constituted by an NPN transistor and a PNP transistor, and supplies power to the IGBT constituting the switching means 6 while the output of the pulse generating means 22 is high. Turn on.

  Below, the structure of the rice cooker of this Embodiment is demonstrated, referring FIG. FIG. 2 is a cross-sectional view of the rice cooker of the present embodiment. In order to simplify the drawing, lead wires for electrical connection and screws for fixing components are omitted.

  As shown in FIG. 2, the rice cooker main body 31 is provided with a lid 32 covering the upper surface so as to be freely opened and closed. The storage unit 33 of the rice cooker body 31 includes the first heating coil 3 at the bottom, the second heating coil 4 at the side surface, and the ferrite core 34 at the outer peripheral side of the second heating coil 4. Is arranged. The first heating coil 3 and the second heating coil 4 are windings having a center substantially below the center of the bottom of the pan 1.

  The pan 1 is made of a magnetic material such as stainless steel, iron, copper, etc., has a flange 35 protruding outward at the upper end opening, and is placed in a state where the flange 35 is lifted from the upper end of the storage portion 33. The storage unit 33 is detachably stored. Therefore, the pan 1 has a gap with the storage portion 33 during storage.

  A detachable lid heating plate 36 is disposed on the lid 32. The lid heating plate 36 is made of a metal such as stainless steel. The lid heating coil 37 is built in the lid 32 and induction-heats the lid heating plate 35.

  The first circuit board 38 includes a switch, an LCD, a microcomputer 14 and the like. Although not shown in particular, the second circuit board 39 includes an IGBT constituting the switching means 6, a resonant capacitor 5 connected in series or in parallel with the heating coil 2, a diode bridge 9 constituting the rectifying means 8, a choke coil 10, A smoothing capacitor 11, a current transformer constituting the input current detecting means 12, an analog IC constituting the on-time setting means 17 and the like are mounted.

  The wind-up type power cord storage unit 40 is electrically connected to the second circuit board 39 via a lead wire. The power cord storage unit 40 can wind up the power cord using a stopper and a spring.

  The temperature detection means 41 is composed of a thermistor and is arranged at the approximate center of the bottom of the pan 1. Since the resistance value of the thermistor changes with temperature, a voltage dividing circuit is configured with this thermistor and a resistor having a predetermined resistance value, and the resistance value of the thermistor is analogized by supplying a predetermined voltage to both ends of the voltage dividing circuit. Can be converted to voltage. The microcomputer 14 shown in FIG. 1 estimates the temperature from this analog voltage using a built-in AD converter.

  The cooling means 42 is constituted by a fan motor in which a fan is attached to a rotor of a DC brushless motor. This fan motor is on / off controlled by the microcomputer 14 shown in FIG.

  Although not particularly shown, the first circuit board 37 and the second circuit board 38 are electrically connected by lead wires, and the input current setting means 15 and the setting current fluctuation means configured inside the microcomputer 14. The on-time setting means 17 mounted on the second circuit board 38 receives the signal from 16 to turn on / off the IGBT and cause a high-frequency current to flow through the first heating coil 3 and the second heating coil 4. The first heating coil 3 and the second heating coil 4 generate an alternating magnetic field when a high-frequency current flows, and this alternating magnetic field causes an eddy current to flow through the pan 1 and the pan 1 generates heat.

  Thus, the rice cooker of this Embodiment induction-heats the pan 1, and heats the food in the pan 1. Here, the cooked product is rice before cooking rice, water, cooked rice, or the like.

  The operation of the above configuration will be described with reference to FIG. FIG. 3 shows an operation waveform of the main part of the rice cooker of the present embodiment.

  3A shows the voltage waveform across the AC power supply 7, FIG. 3B shows the pulse waveform output from the zero voltage detection means 13 to the microcomputer 14, and FIG. 3C shows the set current fluctuation means 16. 3 (d) shows an analog voltage waveform output from the set current fluctuation means 16 to the on-time setting means 17, and FIG. 3 (e) shows an on-time setting by the input current detection means 12. 3A shows an analog voltage waveform output to the means 17, FIG. 3F shows an analog voltage waveform output by the on-time setting means 17 to the pulse generating means 22, and FIG. 3G shows an input supplied from the AC power source 7. 3 shows a current waveform (waveform input to the input current detection means 12), FIG. 3 (h) shows an envelope waveform of the collector voltage CE terminal of the switching means 6, and FIG. 3 (i) shows the operating frequency of the heating coil 2. Strange The shows.

  As shown in FIG. 3, at time T1, when the high output of the zero voltage detection means 13 is input to the microcomputer 14 as shown in FIG. 3B, the microcomputer 14 is configured as shown in FIG. The set current changing means 16 sets the count number to zero, subtracts dIs1 from the output Is1 of the input current setting means 15 as shown in FIG. 3D, and outputs (Is1−dIs1) to the on-time setting means 17. . At this time, since the output of the set current fluctuation means 16 becomes smaller than the output of the input current detection means 12 as shown in FIG. 3E, the comparator 18 becomes low, and the resistors 19 and 20 as shown in FIG. The output voltage is lowered with the time constant set by the capacitor 21. The pulse generation means 22 outputs a high pulse with a pulse width corresponding to the output voltage of the on-time setting means 17. In the present embodiment, the output voltage of the on-time setting means 17 and the pulse width of the pulse generation means 22 are in a proportional relationship, and the pulse width is set longer as the output voltage increases. That is, since the on-time is reduced, the operating frequency of the heating coil 2 is increased as shown in FIG.

  At time T2, when the low output of the zero voltage detection means 13 is input to the microcomputer 14, the set current fluctuation means 16 increases the count number by 1 as shown in FIG. 3 (c), and as shown in FIG. 3 (d). The output Is1 of the input current setting means 15 is output. At this time, since the output of the set current fluctuation means 16 becomes larger than the output of the input current detection means 12 as shown in FIG. 3 (e), the output of the comparator 18 becomes high, and as shown in FIG. The output voltage rises with the time constant set by the capacitor 21. Since the pulse generator 22 increases the pulse width in accordance with the output voltage, the operating frequency of the heating coil 2 decreases.

  From time T2 to time T6, every time the zero voltage detection means 13 outputs high or low as shown in FIG. 3C, the set current fluctuation means 16 increases the count number by one. However, the output Is1 of the input current setting means 15 is output as it is as shown in FIG. At this time, since the output of the setting current fluctuation means 16 becomes larger than the output of the input current detection means 12, the output of the comparator 18 becomes high, and the output voltage with the time constant set by the resistor 19 and the capacitor 21 in FIG. Rises. The pulse generating means 22 increases the pulse width according to this output voltage, so that the operating frequency of the heating coil 2 continues to decrease.

  At time T7, when the high output of the zero voltage detecting means 13 is input to the microcomputer 14 as shown in FIG. 3B, the count number of the set current changing means 16 is set to the predetermined number Ts1 as shown in FIG. Is reached, the count is reset to zero, and the set current fluctuation means (Is1-dIs1) is output to the on-time setting means 17 as shown in FIG. Thereafter, the operation from time T1 to time T7 is repeated.

  As described above, by changing the set value of the input current, the output of the on-time setting means 17 for setting the on-time of the switching means 6 is changed, so that the operating frequency of the heating coil 2 can be changed. it can. Further, since the fluctuation is periodically performed, the fluctuation of the operating frequency can be made regular.

  As shown in FIG. 3, it is preferable that the output of the input current detection means 12 does not reach Is1 during the period from time T2 to time T7. When Is1 is reached, the output of the on-time setting means 17 becomes substantially constant, so that the operating frequency of the heating coil 2 does not fluctuate. Therefore, energy concentrates on one operating frequency, and unnecessary radiation noise increases.

  Next, FIG. 4 is a waveform showing the operation of the rice cooker in a part of the period between time T0 and time T1 in FIG. In general, in a rice cooker using induction heating, the on / off frequency of the switching means 6 is 20 kHz or more and 400 times or more of the frequency of the AC power supply 7 (50 Hz or 60 Hz). 4A shows an analog output voltage waveform of the on-time setting means 17, FIG. 4B shows an output waveform of the pulse generating means 22, and FIG. 4C shows a current waveform flowing through the switching means 6. FIG. 4D shows the voltage waveform of the (CE) terminal and the voltage waveform of the (C2) terminal, FIG. 4E shows the output waveform of the synchronization signal generating means 23, and the voltage of the (CE) terminal. Is output when the voltage is lower than the voltage at the (C2) terminal, and the pulse generating means 22 becomes high after a predetermined time. FIG. 4 (f) shows a current waveform flowing through the heating coil 2.

  As shown in FIG. 4, in the rice cooker of this Embodiment, since the setting time of the ON time setting means 17 changes little by little, the high pulse period of the pulse generation means 22 will change, and it fixes to one frequency. And unnecessary radiation noise can be dispersed.

  FIG. 5 is a graph showing the relationship between the input current of the rice cooker of the present embodiment and the operating frequency of the heating coil 2. At this time, the power supply voltage of the AC power supply 7 is constant at 100 VAC. As shown in FIG. 5, since the input current and the operating frequency of the heating coil 2 are in a substantially proportional relationship, the operating current of the heating coil 2 is changed by periodically changing the input current by the set current changing means 16. be able to.

  FIG. 6 is a graph showing the relationship between the frequency and the quasi-peak value of unwanted radiation noise in the rice cooker of the present embodiment. In this graph, the target value of the input current is Is1. (A) shows no change, (b) shows the case where the change period Ts1 is set to 4 times, (c) shows the case where the change period Ts1 is set to 8 times, and (d) shows the case where the change period Ts1 is set to 12 times. ing.

  When the fluctuation period Ts1 is increased with respect to the case where there is no fluctuation in FIG. 6A, the frequency range becomes large and unnecessary radiation noise decreases. However, when the fluctuation period Ts1 is set to 12 times, unnecessary radiation noise increases at a lower operating frequency than when the fluctuation period Ts1 is set to 12. As described with reference to FIG. 3, since the output of the input current detection means 12 has reached Is1 during the period from time T2 to time T7, the output of the on-time setting means 17 becomes substantially constant, and the heating coil 2 It shows that the operating frequency is not changed. That is, energy is concentrated on one operating frequency, and unnecessary radiation noise is increased. The phenomenon shown in FIG. 6D can be countered by increasing the fluctuation range dIs1. That is, it is possible to prevent the input current from reaching the set value Is1 during the fluctuation period Ts1 by providing a sufficiently large fluctuation width with respect to the time constant provided in advance by the on-time setting means 17. .

  As described above, in the present embodiment, the on-time setting unit 17 is configured to set the on-time of the switching unit 6 according to the output values of the input current detection unit 12 and the set current fluctuation unit 16. By periodically changing the input current, the operating frequency of the heating coil 2 can be changed periodically, and the energy of unnecessary radiation noise can be evenly distributed to each operating frequency, and unnecessary radiation noise can be distributed. The effect of reducing the quasi-peak value can be stabilized. Further, since the input current is periodically changed, it is easy to control the average value of the input current.

  Further, since the set current changing means 16 changes the target value of the input current with a predetermined amplitude in synchronization with the output pulse of the zero voltage detecting means 13, the input current is changed when the voltage of the AC power supply 7 is low. Since the target value is changed, it is possible to suppress the generation of noise due to a sharp change in frequency.

(Embodiment 2)
FIG. 7 is a partially block circuit diagram of the rice cooker according to Embodiment 2 of the present invention.

  As shown in FIG. 7, the 1st heating coil 81 and the 2nd heating coil 82 are divided | segmented so that it can heat separately. Although not particularly illustrated, the first heating coil 81 has a spiral shape, is arranged at a certain distance from the bottom of the pan 1, and is magnetically coupled to the bottom of the pan 1. The second heating coil 82 is disposed on the concentric outer side of the first heating coil 2 and is magnetically coupled to the side surface portion of the pan 1.

  The first resonance capacitor 83 is connected in parallel to the first heating coil 81, and the second resonance capacitor 84 is connected in parallel to the second heating coil 82. In the present embodiment, the first resonant capacitor 83 and the second resonant capacitor 84 are polypropylene capacitors with little loss even when a high frequency current flows.

  The first switching means 85 and the second switching means 86 are composed of a semiconductor element such as a MOSFET or an IGBT and a reverse connection diode reversely connected to the semiconductor element. MOSFETs and IGBTs have high withstand voltage, can switch at high frequency, and can flow a large current by applying a voltage to the gate terminal, and have an advantage that a large current can be flowed with less power than a power transistor. . In the present embodiment, an IGBT is used.

  The microcomputer 87 constitutes input current setting means 88 and set current fluctuation means 89. The input current setting means 88 stores the set value Is81 of the input current when driving the first heating coil 81 and the set value Is82 of the input current when driving the second heating coil 82 in the ROM inside the microcomputer 87 in advance. It consists of memorizing. The setting current fluctuation means 89 has a first fluctuation width dIs81 and a first fluctuation period Ts81 of the input current when driving the first heating coil 81, and a second fluctuation of the input current when driving the second heating coil 82. The fluctuation range dIs82 and the second fluctuation period Ts82 are stored in the ROM inside the microcomputer 87 in advance. Here, the second fluctuation cycle Ts82 is longer than the first fluctuation cycle Ts81.

  Further, the maximum value of the first input current when driving the first heating coil 81 is larger than the maximum value of the second input current when driving the second heating coil 82. Since the first drive circuit 90 and the second drive circuit 91 have the same configuration as the drive circuit 24 in FIG. 1, they are omitted here. Other configurations are the same as those of the first embodiment, and the same reference numerals are given and description thereof is omitted.

  The operation in the above configuration will be described. Since the 2nd heating coil 82 is arrange | positioned at the side part of the pan 1, unnecessary radiation noise leaks from the side surface side, and unnecessary radiation noise becomes large. On the other hand, as shown in FIG. 6, the quasi-peak value of the unwanted radiation noise becomes smaller as the quasi-peak value of the unwanted radiation noise becomes smaller as the fluctuation period becomes longer. Unnecessary radiation noise can be more effectively reduced by lengthening the second fluctuation period Ts82 when the larger second heating coil 82 is driven.

  In addition, the setting value Is82 when driving the second heating coil 82 is made smaller than the setting value Is81 when driving the first heating coil 81, and the current of the second heating coil 82 having a large unnecessary radiation noise. By suppressing the above and increasing the current of the first heating coil 81 having a small unnecessary radiation noise, it is possible to sufficiently obtain energy for heating the pot while suppressing the unnecessary radiation noise.

  As described above, in the present embodiment, the set current fluctuation means 16 is used when the first fluctuation coil Ts 81 used when driving the first heating coil 81 and the second heating coil 82 are driven. Since the second fluctuation cycle Ts82 is longer than the first fluctuation cycle Ts81, the fluctuation range of the input current of the second heating coil 82 can be increased. The fluctuation range of the operating frequency of the second heating coil 82 can be increased, and the effect of reducing the quasi-peak value of the unwanted radiation noise of the second heating coil 82 having a large amount of leakage magnetic flux in the side surface direction can be stabilized.

  In addition, since the maximum value of the first input current when driving the first heating coil 81 is larger than the maximum value of the second input current when driving the second heating coil 82, Sufficient high-frequency power can be supplied to the pan using the first heating coil 81 with less leakage magnetic flux in the side surface direction while suppressing unnecessary radiation noise of the second heating coil 82 with much leakage magnetic flux.

(Embodiment 3)
1 changes the target value of the input current with a predetermined amplitude when the number of output pulses of the zero voltage detecting means 13 reaches a predetermined value, and the number of output pulses according to the frequency of the AC power supply 7. The predetermined value is changed. Other configurations are the same as those in the first or second embodiment.

  The operation in the above configuration will be described. The microcomputer 14 counts the number of times of high output of the zero voltage detection means 13 and when it is input 60 times per second, the microcomputer 14 determines that the frequency of the AC power source 7 is 60 Hz and inputs 50 times per second. In this case, it is determined that the frequency of the AC power supply 7 is 50 Hz.

  The set current fluctuation means 16 has two data of a first fluctuation width dIs1, a first fluctuation period Ts1, a fourth fluctuation width dIs4, and a fourth fluctuation period Ts4 with respect to the first current setting device Is1. Is remembered. When the microcomputer 14 determines that the frequency of the AC power supply 7 is 60 Hz, the number of times of high output of the zero voltage detection means 13 is determined according to the data of the first fluctuation width dIs1 and the first fluctuation period Ts1. When the current reaches the first fluctuation period Ts1, the value obtained by subtracting the first fluctuation width dIs1 from the first current setting device Is1 is output as 8-bit data during the high output period, and the on-time is set via the DA converter. Output to means 17.

  On the contrary, when the microcomputer 14 determines that the frequency of the AC power supply 7 is 50 Hz, the high output of the zero voltage detection means 13 is output according to the data of the fourth fluctuation range dIs4 and the fourth fluctuation period Ts4. When the number of times reaches the fourth fluctuation cycle Ts4, during the period of high output, the value obtained by subtracting the fourth fluctuation width dIs4 from the first current setting device Is1 is output as 8-bit data, and the on-time is passed through the DA converter. Output to the setting means 17.

  Here, the number of high outputs of the zero voltage detection means 13 is 60 times per second when the frequency of the AC power supply 7 is 60 Hz, and 50 times per second when the frequency of the AC power supply 7 is 50 Hz. The time until the high output at 60 Hz is output six times is equal to the time until the high output at 50 Hz is output five times.

Therefore, the values of the first fluctuation width dIs1 and the fourth fluctuation width dIs4 are made equal, and the relationship between the first fluctuation period Ts1 and the fourth fluctuation period Ts4 is
Ts4 = 5/6 × Ts1
By doing so, the time until the number of high outputs of the zero voltage detection means 13 when the frequency of the AC power supply 7 is 60 Hz becomes the first fluctuation period Ts1, and zero when the frequency of the AC power supply 7 is 50 Hz. The time until the number of high outputs of the voltage detection means 13 becomes the fourth fluctuation period Ts4 becomes equal.

  Therefore, since the fluctuation range and the fluctuation cycle are the same when the frequency of the AC power supply 7 is 60 Hz and 50 Hz, the set current fluctuation means 16 sets the input current at a constant period regardless of the frequency of the AC power supply 7. Can be varied.

  As described above, in the present embodiment, the set current changing unit 16 changes the target value of the input current with a predetermined amplitude when the number of output pulses of the zero voltage detecting unit 13 reaches a predetermined value, and the AC power source 7 Since the predetermined value of the number of output pulses is changed according to the frequency, it is possible to prevent a difference in unnecessary radiation noise between the region where the frequency of the AC power supply 7 is 50 Hz and the region where the frequency is 60 Hz.

(Embodiment 4)
The input current setting means 15 shown in FIG. 1 has at least two target values for the input current, and the set current fluctuation means 16 makes the cycle for changing the target value longer when the target value of the input current is large than when it is small. ing. Other configurations are the same as those in the first or second embodiment.

  The operation of the above configuration will be described with reference to FIG. FIG. 8 shows the relationship between the frequency and the quasi-peak value of unwanted radiation noise in the rice cooker of the present embodiment. In FIG. 8, the fluctuation ranges dIs1, dIs2, and dIs3 are all zero.

  In FIG. 8, (a) shows when the current set value is Is1, (b) shows when the current set value is Is2, (c) shows when the target value of the input current is Is3, and Is1, Is2 The magnitude relationship of Is3 is Is1> Is2> Is3.

  In the rice cooker of the present embodiment, the unnecessary radiation noise increases as the input current increases. Therefore, as shown in FIG. 8, the quasi-peak value of the unwanted radiation noise can be reduced uniformly by setting the relationship between the fluctuation periods Ts1, Ts2, and Ts3 of the target value of the input current to Ts1> Ts2> Ts3. .

  Moreover, in the rice cooker using induction heating, it has been experimentally confirmed that the pan 2 generates noise in a part of the frequency range of the operating frequency (20 kHz to 40 kHz) of the heating coil 2 (this embodiment). Then, this frequency region will be called a pan or frequency region). Since the range of the operating frequency of the heating coil 2 can be made narrower than by changing the fluctuation period according to the target value of the input current, the operation of the heating coil 2 can be performed in the pan frequency range. It is possible to prevent the frequency from entering.

  As described above, in the present embodiment, the input current setting means 15 has at least two target values for the input current, and the set current fluctuation means 16 has a target value that is smaller when the target value of the input current is large than when it is small. Since the period for changing the value is lengthened, the quasi-peak value of the unwanted radiation noise can be reliably reduced even when the current flowing through the heating coil 2 is large and the leakage magnetic flux from the heating coil 2 increases.

  As described above, the rice cooker according to the present invention can periodically change the operating frequency of the heating coil by periodically changing the input current, and the unnecessary radiation noise can be evenly distributed to each operating frequency. Since energy can be disperse | distributed and the reduction effect of the quasi-peak value of unnecessary radiation noise can be stabilized, it is useful as a rice cooker which induction-heats a pan with a heating coil.

The circuit diagram which made the block diagram of the rice cooker in Embodiment 1 of this invention Cross section of the rice cooker Main part operation waveform diagram of the rice cooker Another main part operation waveform diagram of the rice cooker Characteristic diagram showing the relationship between the input current of the rice cooker and the operating frequency of the heating coil Characteristic diagram showing the relationship between operating frequency and unwanted radiation noise when changing the fluctuation period of the input current of the rice cooker The circuit diagram which made the block diagram of the rice cooker in Embodiment 2 of this invention The characteristic view which shows the relationship between the operating frequency at the time of changing the setting value of the input current of the rice cooker in Embodiment 4 of this invention, and unnecessary radiation noise

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pan 2 Heating coil 5 Resonance capacitor 6 Switching means 7 AC power supply 8 Rectification means 12 Input current detection means 15 Input current setting means 16 Setting current fluctuation means 17 On time setting means

Claims (6)

A heating coil for inductively heating the pan, a resonant capacitor that constitutes a resonance circuit with the heating coil, a switching means connected in series to the heating coil, a rectifying means for rectifying an AC power source and supplying power to the heating coil, Input current detection means for detecting an input current supplied from the AC power supply, input current setting means for setting a target value of the input current, and setting for periodically changing the target value of the input current with a predetermined amplitude An on-time setting unit configured to set an on-time of the switching unit, and the on-time setting unit is configured to switch the switching unit according to output values of the input current detection unit and the set current variation unit. Rice cooker configured to set the on-time. The heating coil includes a first heating coil that induction-heats the bottom of the pan, and a second heating coil that is concentrically formed in the first heating coil and has a height at the outer end that is higher than the inner end. A first resonance capacitor that constitutes a resonance circuit to the first heating coil and a first switching means, and a second resonance capacitor that constitutes a resonance circuit to the second heating coil And the second switching means are connected, and the set current fluctuation means is a first fluctuation period used when driving the first heating coil and a first fluctuation period used when driving the second heating coil. 2. The rice cooker according to claim 1, wherein the second fluctuation period is longer than the first fluctuation period. The rice cooker according to claim 2, wherein the maximum value of the first input current when driving the first heating coil is larger than the maximum value of the second input current when driving the second heating coil. A zero voltage detecting means for outputting a pulse when a zero voltage of the AC power supply is detected is provided, and the set current changing means changes the target value of the input current with a predetermined amplitude in synchronization with the output pulse of the zero voltage detecting means. The rice cooker according to any one of claims 1 to 3. The set current changing means changes the target value of the input current with a predetermined amplitude when the number of output pulses of the zero voltage detecting means reaches a predetermined value, and changes the predetermined value of the output pulse number according to the frequency of the AC power supply. The rice cooker according to claim 4. The input current setting means has at least two target values of the input current, and the set current fluctuation means has a longer period for changing the target value when the target value of the input current is large than when it is small. The rice cooker of any one of.