JP4166120B2 - rice cooker - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rice cooker that performs a rice cooking operation by inductively heating a rice cooker by causing a resonance coil high-frequency current to flow through an inverter circuit.
[0002]
[Prior art]
In Patent Document 1, in an induction heating cooker, an inverter device that detects a resonance current flowing in a resonance circuit by turning on and off switching elements constituting the inverter circuit and determines an on timing of the switching element based on the resonance current. Is disclosed. Then, the switching element is turned on with the voltage applied to the switching element being always set to the minimum, thereby preventing overvoltage breakdown of the switching element.
[0003]
[Patent Literature]
JP-A-7-274534
[0004]
[Problems to be solved by the invention]
However, in Patent Document 1, since a circuit that determines the on-timing of the switching element is configured using an analog circuit, the circuit becomes very complicated. An analog circuit is easily affected by noise. For example, the oscillation frequency of an oscillation circuit or the like changes due to application of noise. As a result, the operating frequency of the inverter also changes.
[0005]
And when comprising the rice cooker which induction-heats a rice cooker using the inverter apparatus of patent document 1, when the operating frequency of an inverter changes, it is assumed that "ringing" arises in a rice cooker. In order to avoid the occurrence of the “ringing”, it is necessary to perform timing control of the switching element in more detail. However, if the control circuit is configured by an analog circuit, the circuit must be more complicated and large-scale. In addition, there is a problem in terms of cost.
[0006]
This invention is made | formed in view of the said situation, The objective is comprised so that a rice cooker which performs rice cooking operation | movement by induction-heating a rice cooker can be controlled more precisely at low cost. There is.
[0007]
[Means for Solving the Problems]
According to the rice cooker of Claim 1, the DC power supply circuit by which the smoothing capacitor was connected to the output stage,
The direct current output of the direct current power supply circuit is provided to convert the direct current output into high frequency power, the resonant coil, a resonant capacitor that forms a resonant circuit with the resonant coil, and the resonant coil interposed in series between the output terminals of the direct current power supply circuit. An inverter circuit including a switching element connected to each other and a rectifying element connected in reverse parallel to the switching element;
A rice cooker that is induction-heated by flowing a high-frequency current flowing through the resonance coil, and a control unit that controls the rice cooking operation by the rice cooker by controlling on / off of the switching element,
The control means is constituted by a RISC (Reduced Instruction Set Computer) microcomputer or a DSP (Digital Signal Processor).
[0008]
In other words, if the control means for controlling on / off of the switching element of the inverter circuit is configured by a RISC microcomputer or DSP, digital signal processing can be performed at extremely high speed, so that the on / off timing can be controlled in detail. Control that suppresses the “ringing” of the hook can be easily performed. And compared with the case where a control means is comprised with an analog circuit, it can comprise at low cost, without a circuit becoming complicated and large-scale. Further, since the oscillation signal can be generated using a built-in counter, it is possible to further reduce the influence of noise.
[0009]
  in this case, SystemThe control means is configured to fix the OFF period of the switching element and vary the ON period.The
  Here, the technique disclosed in Patent Document 1 has the following problems. That is, in Patent Document 1, since a DC power source obtained by full-wave rectification of a commercial AC power source is used as a power source for driving the inverter circuit, the phase of the power source voltage, that is, the level difference in voltage amplitude (for example, around 0V and around 140V). Accordingly, the resonance current value also changes. Then, in the phase detection circuit as the on-timing detection means, an error occurs in current detection, so that a deviation of about several microseconds occurs in the off-timing of the switching element, and the frequency of the resonance current may change. In that case, a pan or the like sometimes rang as the frequency changed.
  On the other hand,BookIn the invention, since the off period is fixed and controlled, the length of the off period does not depend on the change of the resonance current value, and the “ringing” of the rice cooker accompanying the frequency change can be suppressed.
[0010]
  Also,in frontResonant current phase detecting means for detecting a change in the resonant current flowing through the resonant capacitor when the switching element is off;
  A timing signal output means for outputting a timing signal during a period in which the voltage between the terminals when the switching element is off is a predetermined value or more based on the detection output of the resonance current phase detection means;
  When the control means defines a predetermined off period, the falling edge of the timing signal is used as a trigger signal, and when the trigger signal is output within the off period, the switching element is switched on after the off period has elapsed, When the trigger signal is output after the off period has elapsed, the switching element is turned on at the output timing of the trigger signal.And
[0011]
With such a configuration, even when the trigger signal is output at a timing earlier than the expiration of the predetermined off period, the off period is maintained constant, so even if the output timing of the trigger signal varies somewhat, It is possible to absorb a frequency change accompanying the variation. Also, during the rice cooking process, the rice cooker may float slightly due to the vibration of boiling water, but at that time, the inductance value of the resonance coil decreases, the resonance frequency increases, and the trigger signal output timing is delayed. . Therefore, when the trigger signal is output after the off period expires, the off period is exceptionally extended to cope with the resonance frequency shift due to the occurrence of “floating” in the rice cooker. it can.
[0012]
  Further claims2As described above, when the trigger signal is not output within the allowable period set longer than the off period, the control means may be configured to switch the switching element on after the elapse of the allowable period. That is, since the resonance current in the resonance circuit tends to hardly flow during the period in which the level of the commercial AC power supply voltage is close to zero, it is assumed that the output timing of the trigger signal by the timing signal output means is greatly delayed. In such a case, the oscillating operation in the inverter circuit can be maintained by switching on the switching element up to the expiration of the allowable period.
[0013]
  Claims3As described above, the control unit performs the material determination process of the heating target before starting the induction heating of the rice cooker, and at the time of the material determination process, the control unit is switched based on the trigger signal output by the timing signal output unit. It is preferable that an off period of the element is determined, and the induction heating operation is performed based on the off time when it is determined that the material of the rice cooker is appropriate as a result of the material determination process.
[0014]
In other words, something other than the rice cooker installed in the part where induction heating is performed, for example, a fork, knife, mug or the like, or an aluminum rice cooker etc. that the user has used conventionally is set. It is possible that you forgot to set the rice cooker. Therefore, it is preferable to perform the material determination process of the heating target before starting the rice cooking process.
[0015]
When performing the material judgment processing, even if the inverter circuit oscillates in the off period set on the assumption that it is a proper rice cooker, the trigger signal is turned off if anything else is set. It may not be output within the period. Therefore, in the material determination process, according to the timing at which the trigger signal is actually output (of course, assuming that it is a target capable of induction heating), the OFF period of the switching element is determined, and in the subsequent rice cooking process, By performing induction heating based on the off period determined in the material determination process, heating can be performed at an oscillation frequency suitable for the material of interest.
[0016]
  Claims4As described above, in the case where the ON period of the switching element is changed, the control means is preferably configured in the vicinity of the zero cross point of the AC power supply voltage waveform. That is, if the ON period is changed, the oscillation frequency of the inverter circuit will change. Therefore, if the change occurs during a period when the resonance voltage level is high, the rice cooker “squeals”. Therefore, if the ON period is changed in the vicinity of the zero cross point where the resonance voltage level becomes low, the “ringing” of the rice cooker accompanying the change in the oscillation frequency can be suppressed as much as possible.
[0017]
  Claims5If the inverter circuit is composed of quasi-E class and the input power of the inverter circuit is less than or equal to a predetermined power, the inverter circuit is intermittently driven at a predetermined time ratio according to the input power. It is good to constitute so that. That is, in the quasi-E class inverter circuit, when driven with low input power, the peak of the resonance voltage decreases, and the voltage waveform averages close to the DC drive voltage level. Therefore, the switching element is turned on while the terminal voltage is high, and the switching loss, that is, the heat generation amount of the switching element increases. Therefore, in such a state, the inverter circuit is intermittently driven at a predetermined time ratio, whereby an increase in heat generation of the switching element can be suppressed.
[0018]
  Claims6As described above, the temperature sensor for detecting the temperature of the lid that covers the opening of the rice cooker is provided, and in the rice cooking process, the temperature of the lid detected by the temperature sensor is determined in advance in the cooking process. It is good to control so that it raises according to the rise degree.
[0019]
For example, when the temperature of the rice cooker is detected, the temperature near the boiling point of water is detected immediately after the start of heating, which is inappropriate for use in controlling the rice cooking process. On the other hand, the temperature of the lid that covers the opening of the rice cooker can be regarded as the temperature of water vapor rising from the heated rice cooker, and the temperature of the water vapor reflects the temperature of water in the rice cooker. Therefore, if the rice cooking process is controlled based on the temperature of the lid, the control can be performed satisfactorily.
[0020]
  Claims7As described above, since the control means sets the reference temperature increase degree based on a curve defined by a mathematical expression, it is possible to perform more diverse heating control.
[0021]
  In addition, the claims8As described above, the control means may be capable of changing the degree of increase in the reference temperature according to the user's input operation. If configured in this way, the cooked state of the cooked rice is adjusted according to the user's preference. It becomes possible.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. In FIG. 1 showing the electrical configuration, the output terminal of the commercial AC power supply 1 is connected between both terminals of the input capacitor 2 and connected between the AC input terminals of a full-wave rectifier circuit 3 formed by bridge-connecting diodes. Yes. The positive output terminal 3a of the full-wave rectifier circuit 3 is connected to the DC power supply line 5a via the choke coil 4, and the negative output terminal 3b is connected to the DC power supply line 5b. A smoothing capacitor 6 is connected between the DC power supply lines 5a and 5b. The full-wave rectifier circuit 3, the choke coil 4 and the smoothing capacitor 6 constitute a DC power supply circuit 7.
[0023]
A heating coil 8 as a resonance coil constitutes a resonance circuit 10 together with a resonance capacitor 9, and an IGBT (Insulated gate bipolar transistor) 11 as a switching element and an IGBT 11 as a switching element and a rectification element. An inverter circuit 13 is composed of the flywheel diode 12.
[0024]
In addition, an iron rice cooker A for cooking is placed on the heating coil 8 via a top plate (not shown), and is induced in the rice cooker A by a high-frequency current energized in the heating coil 8. A current flows and the rice cooker A is heated by the resistance loss. The DC power supply line 5 a is connected to the DC power supply line 5 b via the heating coil 8 and the IGBT 11, the resonance capacitor 9 is connected in parallel to the heating coil 8, and the flywheel diode 12 is connected in reverse parallel to the IGBT 11.
[0025]
Next, the configuration of the control system will be described. The input setting unit 14 includes a current transformer 15 that detects an input current, an input current detection circuit 16, an input setting circuit 17, and an input comparison circuit 18, and detects the input current from the commercial AC power source 1. A difference from a preset input current level is calculated and output to the output side as an input setting signal. In this case, the input current detection circuit 16 detects the input current level based on the detection signal of the current transformer 15 provided in one output line of the commercial AC power supply 1. The input comparison circuit 18 compares the input level set in the input setting circuit 17 with the input current level detected by the input detection circuit 16, and outputs an input setting signal having a level corresponding to the difference. Yes.
[0026]
The oscillation control unit 19 includes a current transformer 20 as a resonance current phase detection unit, a phase detection circuit 21 as an on timing setting unit, a RISC microcomputer 22 and a drive circuit 24, and is based on the resonance current of the resonance capacitor 9. As described later, the on-timing and on-period of the IGBT 11 are set. The current transformer 20 is provided so as to detect the resonance current of the resonance capacitor 9, and the phase detection circuit 21 outputs a phase detection signal indicating a peak value of the negative current based on the detection signal of the current transformer 20. Is configured to do.
[0027]
The RISC microcomputer 22 generates and outputs a sawtooth wave signal for setting the ON timing for the IGBT 11 for each period based on the phase detection signal output from the phase detection circuit 21 inside. Then, the sawtooth wave signal is compared with the input setting signal output from the input comparison circuit 18, and a gate signal for setting the ON timing and ON period of the IGBT 11 is output to the gate of the IGBT 11 via the drive circuit 24. It has become. The RISC microcomputer 22 implements functions corresponding to the oscillation circuit 22 and the output control circuit 23 in Patent Document 1 by using control software.
[0028]
A temperature sensor 25 composed of a thermistor or the like is disposed on the lid of the rice cooker A, and a sensor signal output by the temperature sensor 25 is given to the RISC microcomputer 22. Here, the RISC microcomputer 22 is a microcomputer having a CPU core of RISC architecture. The RISC architecture CPU has the following features.
・ All decoding is realized by wired logic,
Simple instruction set that can be executed in the same time
・ Pipeline control of instruction execution processing
・ Many internal registers
・ Large capacity cache
In order to efficiently execute the program by the above architecture, the executable program is optimized by the compiler.
According to the RISC type microcomputer having such a configuration, the total processing performance is improved as compared with a CISC (Complex Instruction Set Computer) type microcomputer. In particular, the execution speed of product operations and the like is extremely increased.
[0029]
Next, the operation of the present embodiment will be described with reference to the waveform diagrams showing the time change of the current and voltage of each part shown in FIG. First, the oscillation operation of the inverter circuit 13 will be described. That is, when an “H” level gate-on signal Vj (see FIG. 2 (j)) is output from the drive circuit 24 at an on-timing Ton, which will be described later, the IGBT 11 is turned on and the output of the DC power supply circuit 7 to the heating coil 8. The voltage VDC is applied. As a result, a current Ia whose current value gradually increases flows through the heating coil 8 as shown in FIG. At this time, a current Ib (in FIG. 1, the current flowing through the IGBT 11 is Ib1 and the current flowing through the flywheel diode 12 is Ib2) shown in FIG.
[0030]
Next, in this state, when the output of the gate-on signal Vj is inverted to the “L” level at the later-described off timing Toff from the drive circuit 24 (see FIG. 6J), the IGBT 11 is turned off and the current Ia flowing from the heating coil 8 Will come to block. However, in the heating coil 8, the current Ia that has just flowed does not suddenly become zero, and the current Ia flows into the resonance capacitor 9 as the resonance current Ic (see FIG. 3C). The resonance current Ic generates a current that flows in the opposite direction because the charge charge is saturated when the terminal voltage of the resonance capacitor 9 reaches a predetermined voltage.
[0031]
At this time, the terminal voltage Vd of the IGBT 11 becomes the highest at the time T1 when the current Ic flowing from the heating coil 8 into the resonance capacitor 9 becomes zero, as shown in FIG. When the current Ic flows toward the coil 8, the terminal voltage Vd of the IGBT 11 decreases. The current Ic that flows into the heating coil 8 when the terminal voltage Vd of the IGBT 11 becomes equal to the output voltage VDC of the DC power supply circuit 7, that is, when the voltage applied between both terminals of the resonance capacitor 9 becomes zero. Becomes a negative peak value.
[0032]
Subsequently, at time T3 when the terminal voltage Vd of the IBGT 11 becomes zero, when the current Ic further flows from the resonance capacitor 9 toward the heating coil 8, the current Ic stops because the flywheel diode 12 is turned on. Instead, the regenerative current Ib2 flows from the smoothing capacitor 6 side to the heating coil 8 via the flywheel diode 12.
[0033]
Then, at a later-described on timing Ton during the period when the regenerative current Ib2 is flowing, the gate 11 is again turned on by the drive circuit 24 from the drive circuit 24 to the IGBT 11 and the heating coil 8 is energized. To come. Thereafter, the same operation as described above is repeated so that a high-frequency current is passed through the heating coil 8, an induction current is generated in the rice cooker A, and heating is performed by the resistance loss.
[0034]
The “timing that can be turned ON” shown in FIG. 2A corresponds to a period during which the regenerative current Ib2 flows through the flywheel diode 12. During this period, the terminal voltage Vd of the IBGT 11 is zero. Therefore, if the IBGT 11 is turned on within the period, an increase in switching loss can be suppressed.
[0035]
Thus, since the gate-on signal Vj to the IGBT 11 is given by the drive circuit 24, the on-operation is performed when the terminal voltage of the IGBT 11 is almost zero, and resonance occurs from the heating coil 8 side when the IGBT 11 is on-operated. The charging current flowing into the capacitor 9 suddenly flows between the drain and the source, or when the charge charged in the resonant capacitor 9 flows toward the heating coil 8, the charging current does not flow suddenly, leading to destruction. This is prevented.
[0036]
Now, the output timings Ton and Toff of the gate-on signal Vj given to the IGBT 11 in the above-described high-frequency oscillation operation will be described in detail below. That is, the current Ic flowing through the resonant capacitor 9 is detected by the current transformer 20, and a detection voltage Vc having the same phase as that of the current Ic is obtained between the resistance terminals (not shown) in the phase detection circuit 21 (FIG. 2 ( c)). The detected voltage Vc is phase-shifted by 90 ° by a phase shift circuit (not shown) to become a voltage Ve (see FIG. 5E).
[0037]
That is, the voltage Ve changes from a positive value to zero at the time T2 when the current Ic flowing from the resonant capacitor 9 toward the heating coil 8 becomes maximum, and the voltage Ve exhibits a negative peak value at the time T3. In a comparison circuit (not shown) inside the phase detection circuit 21, a signal Vf (see FIG. 5F) of “H” level is output during a period when the output of the voltage Ve is positive. Therefore, the output signal Vf of the comparison circuit turns to the “L” level at the time T2 when the voltage Ve becomes zero.
[0038]
Next, the RISC microcomputer 22 outputs a signal Vg based on the signal Vf output from the phase detection circuit 21 (see (g) in the figure). That is, the signal Vg becomes “L” level after securing the on period Ton according to the input power setting, and starts a predetermined set off period starting from that timing. The length of the setting off period is determined according to the result of the material determination process. For example, when heating a rice cooker made of an appropriate material, it is set to 17.5 μsec. Further, the on period Ton is variably set, for example, between 3 μm and 35 μs. Here, the falling timing of the output signal Vf is set as a trigger signal.
[0039]
Then, on the condition that the trigger signal is detected until 17.5 μsec of the set off period elapses, the RISC microcomputer 22 changes the signal Vg from the “L” level to the “H” level after the set off period elapses. Change. Further, the RISC microcomputer 22 sets a period of 40 μs exceeding the set off period of 17.5 μs as an “allowable period”.
[0040]
When the trigger signal is not detected within the set off period, the RISC microcomputer 22 waits for detection of the trigger signal until the allowable period elapses. If the trigger signal is detected within the period, the signal Vg is “ The level is changed to the “H” level (see (h) in the figure). In this case, the period Toff is extended more than the set off period. Further, when the allowable period elapses without detecting the trigger signal, the signal Vg is changed to the “H” level at the time of the elapse.
[0041]
FIG. 3 is a flowchart showing the control contents related to the output signal processing by the RISC microcomputer 22. First, the RISC microcomputer 22 performs a material determination process to be heated prior to the start of the rice cooking process (step S1). For example, as described above, the material determination processing is adjusted so that the trigger signal is finally stably detected with reference to the timing at which the trigger signal is actually output during the initially set off period. Based on off-period. A similar process also appears in the description of (Steps S7, S10, S12, S13) of this flowchart described later.
[0042]
Here, the material judgment processing is performed by putting something other than the rice cooker A provided in the part where induction heating is performed, for example, a fork, a knife, a mug or the like, or the aluminum conventionally used by the user This is because it may be possible to set a rice cooker or forget to set rice cooker A.
[0043]
And when performing a material determination process, even if it performs the oscillation operation of the inverter circuit 13 in the off period set on the assumption that it is a proper rice cooker A, if other than that is set, a trigger signal May not be output within the off period. Therefore, in the material determination process, the off-period of the IGBT 11 is determined according to the timing at which the trigger signal is actually output (assuming that it is an object capable of induction heating), and in the subsequent rice cooking process, the material determination is performed. By performing induction heating based on the off period determined in the process, heating is performed at an oscillation frequency suitable for the target material.
[0044]
In addition, although not reflected in FIG. 3, if something unsuitable for cooking rice is detected, or if forgetting to set rice cooker A is detected, the user is notified at that time (for example, , A buzzer is sounded, or an error code is displayed on a liquid crystal or LED 7-segment display).
[0045]
When the RISC microcomputer 22 determines the set off period according to the material to be heated based on the adjustment result in step S1 (step S2), the RISC microcomputer 22 determines the on period according to the input power set by the user (step S3). . If the input power setting is 500 W or less, an intermittent ON period and an intermittent OFF period for intermittently driving the inverter circuit 13 are also set (details will be described later).
[0046]
Here, the input setting signal VS generated by the above-described input setting unit 14 is set as follows. The output signal of the current transformer 15 that detects the input current is input to the input current detection circuit 16, and the level of the current input from the commercial AC power supply 1 to the DC power supply circuit 7 side is detected. The input setting circuit 17 is given a signal of a level corresponding to the set heating amount by the heating coil 8 based on the user's operation input.
[0047]
When the user selects and inputs the amount of rice cooked (the total number of rice) and the rice cooking course (white rice, brown rice, red rice, rice porridge, cooked rice, hard / soft setting, etc.), the input result A signal corresponding to the set heating amount appropriately determined based on the output is output from the input setting circuit 17.
[0048]
The input comparison circuit 18 compares the levels of the detection signal of the input current detection circuit 16 and the setting signal of the input setting circuit 17 and outputs the input setting signal VS corresponding to the difference between them. As a result, the input comparison circuit 18 outputs an input setting signal VS corresponding to the deviation of the actual heating amount with respect to the set heating amount to the RISC microcomputer 22. Of course, the function of the input setting unit 14 can also be realized by the RISC microcomputer 22.
[0049]
Next, when the output port level of the signal Vg is set to “H” (step S4), the RISC microcomputer 22 waits until the on period determined in step S3 elapses (step S5), and when the on period elapses. ("YES") The output port level of the signal Vg is set to "L" (step S6).
[0050]
Subsequently, the RISC microcomputer 22 waits until the set off period elapses in step S7, but determines whether or not a trigger signal is output during the standby (step S8). When the trigger signal is output (“YES”), the flag FTR indicating the event is set to “1” (step S9), and the setting off period is awaited.
[0051]
When the set off period elapses in step S7 ("YES"), the RISC microcomputer 22 determines whether or not the flag FTR is set to "1" (step S10), and if it is set ("YES"). ) The flag FTR is reset to “0” (step S11), and the process proceeds to step S14.
[0052]
On the other hand, if the trigger signal is not output at the time when the set off period has elapsed and the determination is “NO” in step S10, the RISC microcomputer 22 waits for the above-described allowable period to elapse (step S12). It is determined whether or not a trigger signal is output even during the waiting (step S13). Then, whether the trigger signal is output before the allowable period elapses (step S13, “YES”), or when the allowable period elapses without the trigger signal being output (step S12, “YES”). Also proceeds to step S14.
[0053]
By controlling in this way, even if the trigger signal is output at a timing earlier than the expiration of the set off period, the set off period is maintained constant, so even if the output timing of the trigger signal varies somewhat, Frequency changes due to variations are absorbed.
[0054]
In addition, during the rice cooking process, the rice cooker A may float slightly due to the vibration of boiling water. At this time, the inductance value of the heating coil 8 decreases, the resonance frequency increases, and the trigger signal output timing. May be delayed. Therefore, when the trigger signal is output before the allowable period elapses after the set off period expires, the off period is extended exceptionally, and the resonance frequency due to the occurrence of “floating” in the rice cooker A is increased. It corresponds to the deviation.
[0055]
Furthermore, since the resonance current in the resonance circuit 10 tends to hardly flow during a period in which the level of the commercial AC power supply voltage is close to zero, a case where the output timing of the trigger signal is greatly delayed is assumed. In such a case, the oscillation operation in the inverter circuit 13 is maintained without stopping by switching on the IGBT 11 with the expiration of the allowable period as a limit.
[0056]
Here, in the case where the trigger signal is not output at the time when the set off period has elapsed and the trigger signal is output even after waiting for the allowable period to elapse, the material determination process in step S1 described above. Is the same as the case where the heating target is not the rice cooker A assumed in advance, and the time measured from the time when it is determined “YES” in step S13 is set according to the material. It will be an off period.
[0057]
In step S14, the RISC microcomputer 22 determines whether there is an intermittent ON period setting. If the input power set by the user exceeds 500 W, the intermittent ON / OFF period is not set in step S3 ("NO"), and the process returns to step S3. The intermittent drive of the inverter circuit 13 at the time of setting low input power is, for example, alternately repeating a period in which the inverter circuit 13 is continuously turned on (switching drive) and a period in which the inverter circuit 13 is continuously turned off (completely stopped) within a period of 30 seconds. is there. For example, if the input power setting is 400 W, each period is determined such that it is ON for 24 seconds and OFF for 6 seconds, and if the input power setting is 300 W, it is ON for 18 seconds and OFF for 12 seconds.
[0058]
If the set input power is 500 W or less, since the intermittent ON (and OFF) period is set (step S14, “YES”), the RISC microcomputer 22 determines the elapse of the intermittent ON period from step S4. (Step S15) If it has not elapsed ("NO"), the process returns to Step S3.
[0059]
When the intermittent ON period elapses (step S15, “YES”), the process waits for the intermittent OFF period to elapse (step S16), and when elapses (“YES”), the process returns to step S3.
[0060]
That is, in the quasi-E class inverter circuit 13, when driven with low input power, the peak of the resonance voltage decreases, and the voltage waveform averages close to the DC drive voltage VDC level. Accordingly, the IGBT 11 is turned on while the terminal voltage is high, and the switching loss, that is, the amount of heat generated by the IGBT 11 increases. Therefore, in such a state, the inverter circuit 13 is intermittently driven at a predetermined time ratio to suppress an increase in heat generation of the IGBT 11.
[0061]
FIG. 4 is a flowchart showing the contents of the rice cooking process controlled by the RISC microcomputer 22. In addition, the control concerning the flowchart of FIG. 3 is performed in parallel during control of the rice cooking process of FIG. The RISC microcomputer 22 performs initial power setting according to the amount of cooked rice and determines a reference temperature increase rate according to the cooked hardness (step S21).
[0062]
Then, the RISC microcomputer 22 waits until a predetermined rice cooking control cycle time elapses (step S22), and calculates a reference temperature that should be reached when the control cycle time elapses (step S23). That is, it is calculated by multiplying the reference temperature increase rate determined in step S21 by the elapsed time.
[0063]
Next, when the temperature of the lid of the rice cooker A is detected by the temperature sensor 25 (step S24), the RISC microcomputer 22 compares the temperature of the lid with the reference temperature calculated in step S23 (step S25). When the lid temperature is low, control is performed so as to increase the input power by PID (Proportional-Integral-Differential) control (step S26). When the lid temperature is high, the input power is decreased by PID control. Control is performed as follows (step S27). If the cooking process does not reach the end point (step S28, "NO"), the process returns to step S22.
[0064]
Here, the temperature sensor 25 detects the temperature of the lid of the rice cooker A for the following reason. For example, in the case of directly detecting the temperature of the rice cooking pot A, the temperature near the boiling point of water is detected immediately after heating is started, so that it is inappropriate for use in controlling the rice cooking process. On the other hand, the temperature of the lid can be regarded as the temperature of water vapor rising from the heated rice cooker A, and the temperature of the water vapor reflects the temperature of water in the rice cooker A. Therefore, if the rice cooking process is controlled based on the temperature of the lid, the control can be performed satisfactorily.
[0065]
Also, the PID control is used for the temperature control because the PID control is suitable for controlling the temperature so as to increase according to the reference temperature increase rate, for example, to increase 5 degrees per minute. Because.
[0066]
Moreover, Fig.5 (a) shows the example of heating control of the rice cooking process in the conventional rice cooker. In the conventional heating control, even when the rate of increase in the heating temperature corresponding to the ideal rice cooking process is set, the control executed for it does not change even when the total number of cooked rice changes. It was constant. As a result, the actual temperature increase rate may deviate from the ideal temperature increase rate.
[0067]
On the other hand, as shown in FIG. 5B, according to the present embodiment, even when the total number of cooked rice changes (for example, 1 go, 2 go), high-speed digital computation by the RISC microcomputer 22 Depending on the case, the actual temperature rise rate is controlled so as to be as close as possible to the ideal temperature rise rate depending on the case, so it is possible to realize a more ideal rice cooking process and improve the cooking quality. It has become.
[0068]
In other words, the actual cooking process consists of three steps of “dipping”, “cooking”, and “steaming”, but since the state of cooking is solely dependent on “cooking”, the “cooking” Since it is possible to perform the heating control in detail, even when the rice cooking course is set in various ways, it is possible to improve the respective cooking quality.
[0069]
As described above, according to the present embodiment, when the high frequency power is supplied to the heating coil 8 of the resonance circuit 10 by the inverter circuit 13 and the rice cooker A is induction-heated, the inverter circuit 13 is controlled by the RISC microcomputer 22. I made it. Therefore, since digital signal processing can be performed at an extremely high speed, the on / off timing can be controlled in detail, and control for suppressing the “ringing” of the rice cooker A can be easily performed.
[0070]
And compared with the case where a control means is comprised with an analog circuit like patent document 1, it can comprise at low cost, without a circuit becoming complicated and large-scale. Further, since the oscillation signal can be generated using a built-in counter, it is possible to further reduce the influence of noise. Further, since the RISC microcomputer 22 performs control to fix the off-period of the IGBT 11 and vary the on-period, the length of the off-period does not depend on the change of the resonance current value, and the “ringing of the rice cooker accompanying the frequency change” Can be suppressed.
[0071]
Further, the phase detection circuit 21 outputs a timing signal based on the detection output of the current transformer 22 during a period in which the voltage between the terminals when the IGBT 11 is off exhibits a positive polarity, and the RISC microcomputer 22 causes the falling edge of the timing signal. When the trigger signal that is an edge is output within the set off period, the IGBT 11 is turned on after the set off period elapses. When the trigger signal is output after the set off period elapses, the trigger signal is output at the timing of the trigger signal. The IGBT 11 is switched on. Therefore, even if the output timing of the trigger signal varies somewhat, it is possible to absorb the frequency change due to the variation. Further, it is possible to cope with a shift in resonance frequency due to the occurrence of “floating” in the rice cooker.
[0072]
Furthermore, since the RISC microcomputer 22 switches the IGBT 11 on after the elapse of the allowable period when the trigger signal is not output within the allowable period set longer than the set off period, the level of the commercial AC power supply voltage is Even if the resonance current hardly flows in a period close to zero and the output timing of the trigger signal is greatly delayed, the oscillation operation in the inverter circuit 13 can be maintained.
[0073]
Further, the RISC microcomputer 22 performs the material determination process of the heating object before starting the induction heating of the rice cooker A. At the time of the material determination process, the set off period of the IGBT 11 is determined based on the trigger signal, and the material determination process is performed. As a result, when it was determined that the material of the rice cooker A was appropriate, the induction heating operation was performed based on the set off time. Therefore, after confirming the set of the rice cooking pot A, it is possible to perform heating at an oscillation frequency suitable for the material to be heated.
[0074]
Further, since the RISC microcomputer 22 intermittently drives the inverter circuit 13 at a predetermined time ratio according to the input power when the input power is equal to or lower than the predetermined power, it is possible to suppress an increase in heat generation of the IGBT 11. .
[0075]
Moreover, since the RISC microcomputer 22 controls the temperature of the lid of the rice cooker A detected by the temperature sensor 25 to increase in accordance with a predetermined reference temperature increase degree in the rice cooking process, The rice cooking control can be satisfactorily performed based on the temperature of the water vapor reflecting the temperature of the water.
[0076]
(Second embodiment)
6 to 8 show a second embodiment of the present invention. The same parts as those of the first embodiment are denoted by the same reference numerals and the description thereof will be omitted. Only different parts will be described below. As shown in FIG. 6, in the second embodiment, a cycle flag generator 31 is added to the input setting unit 14A. The cycle flag generator 31 is a cycle flag indicating a predetermined period for each half cycle of the AC power supply based on the input current detected by the input current detection circuit 16.
FP (see FIG. 7B) is generated. The cycle flag FP is referred to by the RISC microcomputer 22A.
[0077]
Next, the operation of the second embodiment will be described with reference to FIG. FIG. 8 corresponds to a part of the flowchart of FIG. 3 in the first embodiment, and shows only the portion according to the second embodiment. When the RISC microcomputer 22A executes step S3, it determines whether or not the input power has been changed from the previous setting (step S31). If it has not been changed ("NO"), the process proceeds to step S4. If it has been changed ("YES"), the process proceeds to step S32.
[0078]
In step S32, the RISC microcomputer 22A refers to the cycle flag FP output from the cycle flag generator 31. Then, it waits until it is determined that the AC power supply voltage is at a level near the zero cross point (“YES”), and the process proceeds to step S4. That is, as shown in FIG. 7B, the period in which the cycle flag FP is reset corresponds to the vicinity of the zero cross point of the AC power supply voltage. If the cycle flag FP is reset, the process goes to step S4. Transition.
[0079]
That is, if the input power setting is changed, the ON period of the IGBT 11 changes accordingly, and as a result, the oscillation frequency of the inverter circuit 13 changes. Accordingly, if the change occurs during a period when the resonance voltage level is high, the “ringing” of the rice cooker A is greatly generated. Therefore, if the ON period is changed near the zero cross point where the resonance voltage level is low, the oscillation frequency changes. The “ringing” of the accompanying rice cooker A is extremely small.
[0080]
As described above, according to the second embodiment, the RISC microcomputer 22A changes the ON period of the IGBT 11 in the vicinity of the zero cross point of the AC power supply voltage waveform. The “sounding” of A can be suppressed as much as possible.
[0081]
The present invention is not limited to the embodiments described above and shown in the drawings, and the following modifications or expansions are possible.
The material determination process may be performed based on a regenerative current value generated when the inverter circuit 13 is driven with a predetermined input power, for example.
The control means may be configured using a DSP or a combination of a DSP and a CISC microcomputer.
In the first embodiment, the RISC microcomputer 22 may set the reference temperature increase degree based on a curve defined by a mathematical expression. In other words, the ideal degree of temperature rise is not necessarily linear. For example, if the setting is based on a quadratic curve or a cubic curve, more diverse and more ideal heating control can be performed. Is also possible.
[0082]
Further, the RISC microcomputer 22 may be capable of changing the reference temperature rise degree in accordance with the user's input operation, and if configured in this way, the cooked state of the cooked rice can be adjusted according to the user's preference. It becomes.
When the cycle flag generating unit 31 is provided as in the second embodiment, the following control may be performed instead of the processes of steps S10, S12, and S13 in the first embodiment. That is, in the vicinity of the zero cross of the AC power supply voltage, the trigger signal becomes difficult to be detected as described above, and the oscillation cycle of the inverter circuit 13 may be greatly reduced. Therefore, if the trigger signal is not detected even after the set off period has elapsed, the cycle flag FP is referred to in the same manner as in the second embodiment, and the predetermined on period Ton and off period Toff are switched in the vicinity of the zero cross. Control. Even in such a control, it is possible to suppress the “ringing” of the rice cooker A by suppressing a significant decrease in the oscillation frequency.
You may apply to a half bridge type inverter circuit.
[0083]
【The invention's effect】
  According to the rice cooker of the present invention, since the control means for performing the induction heating control of the rice cooker by the inverter circuit is configured by the RISC microcomputer or the DSP, the digital signal processing can be performed at extremely high speed, and the on / off timing is detailed. Is possible to controlWhen the resonant current frequency changesControl that suppresses the “ringing” of the rice cooker can be easily performed. And compared with the case where a control means is comprised with an analog circuit, it can comprise at low cost, without a circuit becoming complicated and large-scale. Further, since the oscillation signal can be generated using a built-in counter, it is possible to further reduce the influence of noise.
  Further, when the trigger signal is output at a timing earlier than the expiration of the predetermined off period, even if the output timing varies somewhat, it is possible to absorb the frequency change due to the variation. In addition, during the rice cooking process, it is possible to cope with a shift in resonance frequency due to the occurrence of “floating” in the rice cooking pot.
[Brief description of the drawings]
FIG. 1 is a diagram showing an electrical configuration according to a first embodiment of the present invention.
FIG. 2 is a timing chart showing signal waveforms.
FIG. 3 is a flowchart showing control contents related to output signal processing by a RISC microcomputer.
FIG. 4 is a flowchart showing the contents of the rice cooking process controlled by the RISC microcomputer.
5A is an example of heating control for a rice cooking process in a conventional rice cooker, and FIG. 5B is a diagram illustrating an example of heating control for a rice cooking process in a rice cooker according to the present embodiment.
FIG. 6 is a view corresponding to FIG. 1 showing a second embodiment of the present invention.
7A is a current waveform of a commercial AC power supply, and FIG. 7B is a diagram showing the output timing of a period flag FP.
FIG. 8 corresponds to a part of the flowchart of FIG. 3 in the first embodiment, and shows only a portion according to the second embodiment.
[Explanation of symbols]
1 is a commercial AC power supply, 6 is a smoothing capacitor, 7 is a DC power supply circuit, 8 is a heating coil (resonance coil), 9 is a resonance capacitor, 10 is a resonance circuit, 11 is an IGBT (switching element), 12 is a flywheel diode ( Rectifier element), 13 is an inverter circuit, 20 is a current transformer (resonant current phase detection means), 21 is a phase detection circuit (timing signal output means), 22 is a RISC microcomputer (control means), 23 is an output control circuit, 24 Is a drive circuit, 25 is a temperature sensor, and A is a rice cooker.

Claims (8)

A DC power supply circuit with a smoothing capacitor connected to the output stage;
The direct current output of the direct current power supply circuit is provided to convert the direct current output into high frequency power, the resonant coil, a resonant capacitor that forms a resonant circuit with the resonant coil, and the resonant coil interposed in series between the output terminals of the direct current power supply circuit. An inverter circuit including a switching element connected to each other and a rectifying element connected in reverse parallel to the switching element;
A rice cooker that is induction-heated by flowing a high-frequency current flowing through the resonance coil;
Control means for controlling the rice cooking operation by the rice cooker by controlling on and off of the switching element ,
Resonance current phase detection means for detecting a change in resonance current flowing in the resonance capacitor when the switching element is off;
A timing signal output means for outputting a timing signal during a period in which the voltage between the terminals when the switching element is off is a predetermined value or more based on the detection output of the resonance current phase detection means;
The control means is constituted by a RISC microcomputer or DSP ,
The control means controls the switching element so that the off-period is fixed and the on-period is variable, and when the predetermined off-period is determined, the trigger signal is turned off using the falling edge of the timing signal as a trigger signal. If it is output within the period, the switching element is turned on after the lapse of the off period, and when the trigger signal is output after the lapse of the off period, the switching element is turned on at the output timing of the trigger signal. A featured rice cooker. 2. The rice cooker according to claim 1 , wherein when the trigger signal is not output within an allowable period set longer than the off period , the control unit switches the switching element on after the allowable period elapses . The control means
Before starting induction heating of the rice cooker, perform the material judgment process of the heating target,
At the time of the material determination process, the switching element OFF period is determined based on the trigger signal output by the timing signal output means,
3. The rice cooker according to claim 1, wherein when it is determined that the material of the rice cooker is appropriate as a result of the material determination process, induction heating operation is performed based on the off time . 4. The rice cooker according to claim 1 , wherein the control means changes the ON period of the switching element in the vicinity of a zero cross point of the AC power supply voltage waveform . 5. The inverter circuit is composed of quasi-E class,
Control means, wherein when the input power of the inverter circuit is less than a predetermined power, according to any of claims 1 to 4, characterized in that intermittently drives the inverter circuit at a predetermined time ratio according to the input power Rice cooker. It has a temperature sensor that detects the temperature of the lid that covers the opening of the rice cooker,
Control means, in the cooking process, any one of claims 1 to 5, characterized in that the temperature of the lid to be detected by the temperature sensor is controlled so as to rise in response to the reference temperature rise predetermined degree Rice cooker as described in. 7. The rice cooker according to claim 6, wherein the control means sets the reference temperature increase degree based on a curve defined by a mathematical expression . The rice cooker according to claim 6 or 7, wherein the control means is capable of changing the degree of increase in the reference temperature in accordance with a user input operation .

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