JP4084615B2 - Electromagnetic induction heating cooker - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic induction heating cooker that uses an inverter to supply a high-frequency current to a heating coil and heats a cooking pan by electromagnetic induction, and more particularly to a technique for preventing the inverter from operating in a lead phase. Is.
[0002]
[Background Art and Problems to be Solved by the Invention]
Electromagnetic induction heating cookers are spreading to the food service industry and homes because they are safe without using fire types and have low fuel consumption.
FIG. 15 is a main circuit configuration diagram of this well-known electromagnetic induction heating cooker. In the figure, DR1 is a rectifier that rectifies a commercial frequency AC power supply (U, V, W) to DC, C1 is a smoothing capacitor, SW1 and SW2 are switching elements that constitute a half-bridge inverter, such as a MOSFET or IGBT. Is used. L is a heating coil that forms a single-end push-pull series resonance circuit with the resonance capacitors C2 and C3. A cooking pot is placed on the heating coil L and heating is performed by electromagnetic induction.
[0003]
By the way, in this type of inverter, when the output current advances with respect to the output voltage and operates in a phase region, there is a high possibility that a through current flows or a surge voltage is generated and the switching element breaks down. Hereinafter, the phenomenon of this defect will be briefly described. 16 shows a waveform when the output current of the inverter is delayed by the phase difference γ with respect to the output voltage, and FIG. 17 shows a waveform when the output current of the inverter advances by the phase difference γ with respect to the output voltage. Show. From both figures, the waveform of the current flowing through the upper arm (SW1) and the lower arm (SW2) is as shown in FIGS. 18A and 18B in the lag phase and the lead phase, respectively. The current below the zero base line in the figure flows through the anti-parallel diode (see FIG. 19) built in the MOSFET or IGBT that is the switching element.
[0004]
Accordingly, when the polarity of the current changes from minus to plus, in the case of a lag phase, there is no particular problem because the current of the built-in diode shifts to the forward current of the same MOSFET. On the other hand, in the lead phase, since the current of the built-in diode shifts to the forward current of the other MOSFET, the reverse recovery time of the diode exists and the current that passes through the upper and lower arms flows due to the reverse leakage current, and the short circuit state occurs. Become.
Further, a surge voltage is generated because the current change rate di / dt when the peak value of the reverse leakage current returns to 0 is large.
[0005]
For this reason, in the conventional electromagnetic induction heating cooker, the phase difference γ is detected and compared with a preset lower limit value γ0, and when γ = γ0, the output frequency of the inverter is lowered. I was trying to stop it. However, this method cannot follow the change of the resonance frequency due to the change of the load (change of the position, material, size, etc. of the pan), and there is a possibility that the operation proceeds in a transient phase. Therefore, in order to reliably prevent the operation in the lead phase, the lower limit value γ0 of the phase difference must be set to a sufficiently large value. As a result, the efficiency decreases due to a decrease in the driving power factor, and the maximum There was a problem that the output was greatly limited.
[0006]
The present invention has been made to solve the above-described problems. Electromagnetic induction that can efficiently increase the maximum output by actively realizing operation in the phase of the lagging phase by the control operation. The purpose is to obtain a cooking device.
[0007]
[Means for Solving the Problems]
An electromagnetic induction heating cooker according to the present invention includes a capacitor, this capacitor and Both A heating coil that forms a series resonance circuit, an inverter that supplies high-frequency current to the heating coil, a power calculation circuit that calculates the input power of the inverter, and a phase difference between the output voltage of the inverter and the current flowing through the heating coil is detected. A phase difference detection circuit that inputs the power calculation value and the power setting value by manual setting, amplifies the difference between the two input values, and when the power calculation value exceeds the power setting value, the polarity of the output potential is positive The differential amplifier for power control set so that the phase difference detection value and the phase of the output voltage of the inverter are set within the range of the delay phase in which the phase of the current flowing through the heating coil is delayed. Enter the phase difference lower limit setting value and amplify the difference between the two input values. Phase difference A differential amplifier for phase difference control that is set so that the polarity of the output potential becomes positive when the detected value is less than the above-mentioned phase difference lower limit set value, and both of the above differentials via a diode at the resistance-grounded input terminal Control is performed so that the output frequency of the inverter increases as the output terminal of the amplifier is connected and the potential of the input terminal increases. When the potential of the input terminal is zero (ground) potential, the inverter is controlled at the lowest frequency. A V / f converter that converts an input potential into a frequency command signal so as to output a frequency command signal for the purpose.
[0008]
In addition, the electromagnetic induction heating cooker according to the present invention automatically sets the power at the start of the operation of the inverter, and outputs a potential that gradually decreases to zero at a predetermined gradient at the maximum after the start of the operation. The output terminal of the soft start circuit is connected to the V / f converter via a diode, and the V / f converter controls the inverter at the maximum frequency when the potential of the input terminal is the maximum potential. For this purpose, a frequency command signal is output.
[0009]
Moreover, in the electromagnetic induction heating cooker according to the present invention, the phase difference detection value is the above A potential that gradually falls to zero at a predetermined gradient after the maximum potential is output when the phase difference is within the range of the lagging phase and becomes less than or equal to the phase difference minimum lower limit setting value set to a value smaller than the phase difference lower limit setting value. An output phase difference recovery circuit is provided, and an output terminal of the phase difference recovery circuit is connected to the V / f converter via a diode.
[0010]
Further, the phase difference recovery circuit of the electromagnetic induction heating cooker according to the present invention outputs the single pulse of the maximum potential when the phase difference detection value is equal to or lower than the phase difference lower limit setting value, and the single pulse The comparator is configured to start the soft start circuit with the output of.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
FIG. 1 is a circuit configuration diagram showing the entire electromagnetic induction heating cooker according to Embodiment 1 of the present invention, and FIG. 2 is a diagram showing an output frequency control mechanism of an inverter, which is a main part of the present invention. Since the main circuit configuration is the same as that described above, the configuration of the control circuit will be mainly described below. In the figure, reference numeral 1 denotes a signal input from a voltage detector PT1 that detects the voltage of the smoothing capacitor C1 (input voltage of the inverter) and a signal from the current detector CT1 that detects current at the input terminal of the inverter. A power calculation circuit 2 for calculating the input power W receives a signal from a drive circuit 3 described later and a signal from a current detector CT2 for detecting a current flowing through the heating coil L, and outputs an inverter output voltage and current. A phase difference detection circuit 3 for detecting the phase difference γ is a drive circuit for generating a drive signal for turning on and off the switching elements SW1 and SW2. The drive signal indicates the phase of the output voltage of the inverter. It is also sent to the circuit 2 and used for voltage phase detection.
As will be described later, in the phase difference detection circuit 2 of FIG. 1, the output phase difference γ is a signal whose potential increases as the delayed phase difference decreases.
[0012]
Reference numeral 4 denotes a power control differential amplifier, to which the input power signal W from the power calculation circuit 1 is input to the non-inverting input terminal, and the power setting value WA from the power setting unit 7 is input to the inverting input terminal. Therefore, when the input power W is smaller than the power set value WA, the differential amplifier 4 outputs a negative potential obtained by amplifying the deviation between the two, and when the input power W becomes larger than the power set value WA, the differential amplifier 4 Output amplified positive potential.
The power setting device 7 is linked to a volume that the cook adjusts appropriately according to the cooking contents.
Reference numeral 5 denotes a differential amplifier for phase difference control. A phase difference signal γ from the phase difference detection circuit 2 is provided at its non-inverting input terminal, and a phase difference lower limit setting value γA from the phase difference setting unit 8 is provided at its inverting input terminal. Each is entered. Therefore, when the phase difference signal γ is smaller than the lower limit set value γA (actually, when the phase difference detection value is greater than the set value), the differential amplifier 5 outputs a negative potential obtained by amplifying the deviation between the two. When the phase difference signal γ is larger than the lower limit set value γA (actually, this corresponds to a case where the phase difference detection value is smaller than the set value), a positive potential obtained by amplifying the difference between the two is output.
[0013]
Reference numeral 6 denotes a V / f converter connected to the differential amplifier 4 via the diode D1 and to the differential amplifier 5 via the diode D2, and a drive circuit for supplying a frequency command signal that changes in accordance with the potential at its input terminal. 3 to determine the output frequency of the inverter.
As shown in FIG. 2, the input end of the V / f converter 6 is grounded via a resistor R1. Therefore, unless the output potential a of the differential amplifier 5, the output potential b of the differential amplifier 4, or the output potential d of the soft start circuit 10 described later is a positive value, the potential at the input terminal of the V / f converter 6 is not positive. c is kept at zero potential, and the V / f converter 6 outputs a frequency signal for controlling the inverter at the lowest frequency when the input potential is zero. Here, the lowest frequency of the inverter is set to a value slightly higher than the resonance frequency of the series resonance circuit including the heating coil L including the cooking pot to be placed and the resonance capacitors C2 and C3.
[0014]
In addition to the differential amplifiers 4 and 5, a soft start circuit 10 is connected to the input end of the V / f converter 6 via a diode D3. When the cooker turns on the power of the cooker and suddenly sets a high power value with the power setter 7, if the proper cooking pan is not set at the proper position, an excessive current flows and the device stops. there's a possibility that. The soft start circuit 10 is provided for such a situation. At the start of operation, even if a high power value is suddenly set, the soft start circuit 10 operates to increase the power gradually from a small power. Let
FIG. 3 shows the internal configuration of the soft start circuit 10. When a single pulse ON signal is input from the operation command circuit 9, the switching element (MOSFET) SW3 is turned on, and the capacitor C4 is charged by the power source E. The resistor R2 is reduced and the voltage of the capacitor C4 is rapidly raised. When the single pulse from the operation command circuit 9 falls, SW3 is turned off, and the voltage of the capacitor C4 gradually decreases with a time constant determined by C4 and the resistor R3.
[0015]
Next, an operation example under a typical situation will be described with reference to a timing chart. First, in FIG. 4, after the operation starts, the electric power gradually increases by the soft start, but the phase difference γ reaches the lower limit set value γA until the electric power W reaches the set value WA, and thereafter the output of the inverter A mode that a frequency is controlled based on this phase difference is shown.
When an ON command is issued from the operation command circuit 9 at time t = t0 and a single pulse is input to the soft start circuit 10, the output potential d of the soft start circuit 10 rises sharply, and the input potential of the V / f converter 6 rises. c rises equal to the potential d. At the timing when the single pulse falls (t = t1), the output potential d of the soft start circuit 10 reaches the maximum value, and at this timing, the operation of the inverter is turned on and output at the maximum frequency is started. Then, the output frequency is reduced according to the drooping characteristic of the output potential d.
Note that the output potentials b and a of the differential amplifiers 4 and 5 up to the above timing are saturated at a negative polarity because both the input power W and the phase difference γ are sufficiently low with respect to the respective set values. After is turned on, it stands up quickly.
[0016]
As the inverter frequency decreases, both the phase difference γ and the input power W increase. In the case of FIG. 4, the rate of increase of the phase difference signal γ is faster, and at t = t2, γ = γA and the output potential a of the differential amplifier 5 becomes zero. Further, when t = t3, the value of the output potential a of the differential amplifier 5 becomes equal to the value of the output potential d of the soft start circuit 10 that is decreasing, and thereafter, the output potential a of the differential amplifier 5 becomes V This is the input potential c of the / f converter 6.
When the phase difference signal γ exceeds the set value γA, the inverter acts to increase the output frequency and lower the phase difference signal γ. When the phase difference signal γ decreases, the output potential a of the differential amplifier 5 decreases, the output frequency of the inverter decreases, and the phase difference signal γ increases. Therefore, after t = t3, both the phase difference γ and the input power W are kept substantially constant within a certain range of change.
In the figure, the state of pulsation after t = t3 is emphasized and illustrated, which is actually a smaller pulsation, and the differential amplifiers 4 and 5 have an amplification factor of several tens of times. In particular, the phase difference γ is accurately kept substantially at the set value γA.
[0017]
FIG. 5 is also a case where the control is performed based on the phase difference, but the increase rate of the phase difference signal γ is still larger. That is, as the output frequency of the inverter is reduced, the phase difference signal γ rapidly rises, at a timing t = t4 earlier than in the case of FIG. 4, and accordingly, when the input potential c of the V / f converter 6 is higher. Then, γ = γA, and then, at t = t5, the output potential a of the differential amplifier 5 is equal to the output potential d of the soft start circuit 10.
As a result, the phase difference γ is kept at the set value γA as compared with the case of FIG. 4, but the output frequency of the inverter is higher, and therefore the input power W remains at a lower value. .
[0018]
Next, FIG. 6 shows that when the cook suddenly operates the power setting knob to the maximum setting value from the state where the input power W is kept at the setting value WA, the phase difference signal γ is set in the process of increasing the power. The operation when the value γA is reached and then limited to the power value at that time will be shown.
In the figure, until the time t = t6 when the setting change is started, the output potential b of the differential amplifier 4 maintains a positive value, and the input power W is maintained at the setting value WA at that time. Further, the phase difference signal γ is sufficiently lower than the set value γA, and the output potential a of the differential amplifier 5 is a negative value.
When the power setting value increases from t = t6, the output potential b of the differential amplifier 4 starts to decrease, and the output frequency of the inverter decreases to increase the input power. Accordingly, the phase difference signal γ increases (as described above, the actual phase difference decreases), the output potential a of the differential amplifier 5 also increases, and the zero line is set at time t = t7 when γ = γA. When t exceeds t8 and further reaches t = t8, the value of the output potential a of the differential amplifier 5 becomes equal to the value of the output potential b of the differential amplifier 4 that is decreasing. Becomes the input potential c of the V / f converter 6.
As a result, the input power W does not reach the value after the setting change, but remains at the power determined when γ = γA. Of course, the phase difference is also kept substantially at the set value γA.
[0019]
As described above, in the first embodiment of the present invention, when the phase difference signal γ reaches the set value γA regardless of the control power, the phase difference signal γ is set to the set value γA in preference to the power control. Automatically switches to maintaining phase difference control. Therefore, by setting the set value γA to an appropriate small value before the phase advance region within the delay phase range, the inverter can be reliably prevented from operating in the phase advance region, and the efficiency is improved. The maximum output of the inverter also increases and the utilization rate increases.
[0020]
Embodiment 2. FIG.
During operation of the cooker, the load on the heating coil may change suddenly. For example, if the cooking pan is replaced from stainless steel (stainless pan) to aluminum (aluminum pan), if the replacement is performed very rapidly, the phase difference γ exceeds the set value γA, and temporarily the inverter There is a possibility that the operation enters the phase advance region, and there is a concern that the switching element may fail.
In the second embodiment, measures are taken to prevent the phase advance operation of the inverter even during this sudden load change.
[0021]
First, the phenomenon in which this sudden load fluctuation occurs will be described with reference to FIGS. FIG. 7 shows the cooking pan on the cooker plate being replaced. That is, during the heating operation with the stainless steel pan, the aluminum pan is sequentially replaced along the arrow in the figure.
FIG. 8 is a characteristic diagram showing the relationship between inverter output frequency (kHz) and phase difference (°) for stainless steel and aluminum. Assuming that the stainless steel pan is heated at an output frequency of 30 kHz, and if it is sequentially replaced with an aluminum pan from this state as shown in FIG. 7, the material of the pan viewed from the heating coil is from stainless steel to aluminum in FIG. The phase difference γ decreases rapidly. FIG. 9 deals with such a sudden decrease in phase difference.
[0022]
In the following, FIG. 9 will be described with a focus on the differences from FIG. 1 of the first embodiment. Reference numeral 11 denotes a comparator that outputs the phase difference signal γ from the phase difference detection circuit 2 in accordance with the comparison result between the phase difference lower limit setting value γB from the phase difference setting unit 12. Here, the set value γB is set to a value smaller than the set value γA within the range of the delay phase. However, as described above, the phase difference signal γ that is the detection output of the phase difference detection circuit 2 is a signal that increases as the actual phase difference decreases, and therefore, in the circuit operation described later, a relationship of γB> γA is set. Has been. When the phase difference signal γ reaches the set value γB, the comparator 11 applies a single pulse output potential having a predetermined width (for example, about 1 second) to the V / f converter 6 via the diode D4 and the software. The data is sent to the start circuit 10 and further to a flip-flop circuit 15 to be described later.
A comparator 13 compares the phase difference signal γ from the phase difference detection circuit 2 with the phase difference lower limit setting value γA from the phase difference setting unit 14, and when γ ≧ γA, an H level signal is expressed as γ <γA. In this case, an L level signal is sent to the flip-flop circuit 15.
The flip-flop circuit 15 detects the falling edge of the single pulse signal from the comparator 11 and sends an inverter stop signal to the operation command circuit 9 if the output signal from the comparator 13 at that time remains H level. To do.
FIG. 10 shows a portion related to output frequency control extracted from the circuit of FIG.
[0023]
Next, as an operation, an overall operation when the load fluctuates in the output frequency control mechanism shown in FIGS. 9 and 10 will be described with reference to the flowchart of FIG.
When the load fluctuation occurs (step S1) and the phase difference signal γ exceeds the set value γA, the output frequency a of the differential amplifier 5 is inverted to be positive and the output frequency of the inverter is controlled so that γ = γA is maintained. (Step S2). When the comparator 11 performs a phase difference comparison operation and the phase difference signal γ maintains its state and does not exceed the phase difference set value γB (NO in step S3), the operation is continued as it is (step S4). When γ exceeds γB (YES in step S3), the comparator 11 outputs a single pulse, the diode D4 is turned ON, the input potential c of the V / f converter 6 becomes the level of the single pulse, and the inverter sets the output frequency. The frequency is raised to the highest frequency (step S5). The single pulse from the comparator 11 is also sent to the soft start circuit 10, and the soft start circuit 10 starts charging the capacitor C4 at the rising edge of the single pulse (see FIG. 3).
[0024]
Separately, the comparator 13 compares the magnitude of the phase difference signal γ and the set value γA. When a predetermined time elapses, that is, when a single pulse from the comparator 11 falls, the flip-flop circuit 15 The timing is detected, and a comparison output between the phase difference signal γ and the set value γA at that time is input from the comparator 13 (step S6). If γ exceeds γA (YES in step S7), a stop command signal is sent from the flip-flop circuit 15 to the operation command circuit 9 to stop the inverter (step S8). This is because there is a possibility of entering the advance phase region and preventing a failure of the switching element. If γ does not exceed γA (NO in step S7), the output frequency of the inverter gradually decreases according to the drooping characteristic of the output potential d of the soft start circuit 10 (step S9), and the original operation is restored.
[0025]
9 and 10, the output of the comparator 11 is sent to the V / f converter 6 via the diode D4. This is because the capacitor C4 (see FIG. 3) in the soft start circuit 10 is charged. This is because the output frequency of the inverter is immediately raised to the maximum value regardless of the time delay required for the above. Therefore, if the voltage generation mechanism in the soft start circuit 10 can be made to be able to instantaneously raise the voltage, the output of the comparator 11 need only be sent to the soft start circuit 10 and need not be sent to the V / f converter 6 separately. .
If the comparator 11 determines that γ exceeds γB without using the soft start circuit 10, a phase difference that generates a potential that gradually increases to a maximum value and then gradually decreases with a predetermined gradient based on the determination output. A recovery circuit may be provided separately, and the output of the phase difference recovery circuit may be sent to the V / f converter 6 via a diode. Regardless of the power increase characteristic at the start, there is an advantage that the optimum power increase characteristic can be set when the operation is restored after a sudden load change occurs.
[0026]
Next, a series of operations assuming that YES is obtained in step S3 of FIG. 11 due to a sudden change in the load, that is, the phase difference signal γ exceeds the set value γB will be described with reference to the timing chart of FIG.
From the state where the input power W is balanced with the set value WA, load fluctuation occurs at time t = t9, the phase difference signal γ increases rapidly, and the input power W decreases. In response to this change, the output potential a of the differential amplifier 5 also rises, but the phase difference signal γ becomes the set value γB before the effect of suppressing the sudden increase in the phase difference signal γ from the delay between the input and output of the differential amplifier. Reach (t = t10).
When γ = γB, the comparator 11 determines this and generates a single pulse output potential e. The output potential e that rises steeply becomes the input potential c of the V / f converter 6 as it is, and the output frequency of the inverter immediately rises to the maximum frequency, and both the phase difference signal γ and the input power W rapidly decrease. The soft start circuit 10 receives the pulse output from the comparator 11 and rapidly raises the potential.
[0027]
When the pulse output from the comparator 11 falls at time t = t11, the input potential c of the V / f converter 6 is soft-started through the diode D3 from the output potential e of the comparator 11 that has passed through the diode D4. After switching to the output potential d of the circuit 10, the output frequency of the inverter decreases along the potential d, and the input power W increases. In this case, since the phase difference signal γ does not exceed the set value γA at the timing t = t11 when the potential e falls, there is no inverter stop operation shown in step S8 of FIG.
As the output frequency of the inverter decreases, the phase difference signal γ gradually increases, reaches the set value γA at t = t12, and immediately thereafter, the value of the output potential a of the differential amplifier 5 becomes the output of the soft start circuit 10 at t = t13. When it becomes equal to the value of the potential d, thereafter, as described with reference to FIG. 4, the operation shifts to a steady operation maintaining substantially γ = γA.
[0028]
As described above, in the second embodiment of the present invention, even if the load suddenly changes and the phase difference suddenly decreases and the inverter operates and may enter the phase region, the output frequency is immediately increased to the maximum frequency. It is possible to prevent entry into the advance phase region. In addition, the inverter is automatically stopped when the phase difference remains below the lower limit setting even after the frequency is raised to the maximum frequency, so switching element failures are prevented even during such abnormal sudden load changes. Reliability is improved.
[0029]
Embodiment 3 FIG.
FIG. 13 is a circuit configuration diagram showing an electromagnetic induction heating cooker according to Embodiment 3 of the present invention, and FIG. 14 is a flowchart for explaining the operation thereof. The difference from the second embodiment is only that a timer circuit 16 is added. That is, in the third embodiment, the flip-flop circuit 15 outputs an inverter stop command signal to the operation command circuit 9 and simultaneously sends a command signal to the timer circuit 16, and the timer circuit 16 starts its counting operation. When a predetermined time (for example, set to about several seconds) elapses, the timer circuit 16 sends a command signal to the operation command circuit 9 to soft-start the inverter at the maximum frequency (step S10 in FIG. 14). Then, a comparison operation between the phase difference signal γ and the set value γA at that time is performed, and when γA is not exceeded (NO in step S7), the output frequency is gradually decreased to return to normal operation (step). S9). Of course, if γA is exceeded (YES in step S7), the inverter is stopped again (step S8), and the operations after step S10 are repeated.
[0030]
As described above, in the third embodiment of the present invention, for example, when a proper cooking pot is returned to the cooker even after the load suddenly changes due to sudden replacement of the cooking pot and the inverter stops. Detecting this and automatically returning to the original cooking and heating operation further improves the convenience of the cooker.
[0031]
The phase difference detection circuit 2 in each of the above embodiments outputs a phase difference signal γ whose output potential increases as the actual delay phase difference decreases in relation to the subsequent control circuit using the output. Of course, the output characteristics are not limited to the above-mentioned output characteristics in the application of the present invention.
In each of the above embodiments, the soft start circuit 10 is provided. However, depending on the application example of the present invention, the input power adjustment is based on the operation of the power setting unit 7 only. Also good.
[0032]
【The invention's effect】
As described above, the electromagnetic induction heating cooker according to the present invention includes a capacitor, this capacitor and Both A heating coil that forms a series resonance circuit, an inverter that supplies high-frequency current to the heating coil, a power calculation circuit that calculates the input power of the inverter, and a phase difference between the output voltage of the inverter and the current flowing through the heating coil is detected. A phase difference detection circuit that inputs the power calculation value and the power setting value by manual setting, amplifies the difference between the two input values, and when the power calculation value exceeds the power setting value, the polarity of the output potential is positive The differential amplifier for power control set so that the phase difference detection value and the phase of the output voltage of the inverter are set within the range of the delay phase in which the phase of the current flowing through the heating coil is delayed. Enter the phase difference lower limit setting value and amplify the difference between the two input values. Phase difference A differential amplifier for phase difference control that is set so that the polarity of the output potential becomes positive when the detected value is less than the above-mentioned phase difference lower limit set value, and both of the above differentials via a diode at the resistance-grounded input terminal Control is performed so that the output frequency of the inverter increases as the output terminal of the amplifier is connected and the potential of the input terminal increases. When the potential of the input terminal is zero (ground) potential, the inverter is controlled at the lowest frequency. Since the V / f converter for converting the input potential into the frequency command signal is output so as to output the frequency command signal, the above-mentioned phase difference lower limit set value is appropriately small before becoming the phase advance region within the delay phase range. Even if it is set to a value, the inverter can be operated reliably in the range of the delay phase, ensuring reliability, improving efficiency, increasing the maximum output of the inverter, and increasing the utilization rate. Round.
[0033]
In addition, the electromagnetic induction heating cooker according to the present invention automatically sets the power at the start of the operation of the inverter, and outputs a potential that gradually decreases to zero at a predetermined gradient at the maximum after the start of the operation. The output terminal of the soft start circuit is connected to the V / f converter via a diode, and the V / f converter controls the inverter at the maximum frequency when the potential of the input terminal is the maximum potential. Therefore, even if the cook suddenly sets a high power value, a smooth operation start characteristic is obtained in which the power smoothly rises.
[0034]
Moreover, in the electromagnetic induction heating cooker according to the present invention, the phase difference detection value is the above A potential that gradually falls to zero at a predetermined gradient after the maximum potential is output when the phase difference is within the range of the lagging phase and becomes less than or equal to the phase difference minimum lower limit setting value set to a value smaller than the phase difference lower limit setting value. Since an output phase difference recovery circuit is provided and the output terminal of this phase difference recovery circuit is connected to the V / f converter via a diode, the inverter maintains delayed phase operation even when the load changes suddenly.
[0035]
Further, the phase difference recovery circuit of the electromagnetic induction heating cooker according to the present invention outputs the single pulse of the maximum potential when the phase difference detection value is equal to or lower than the phase difference lower limit setting value, and the single pulse Therefore, a smooth phase difference recovery operation using the soft start circuit is realized.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram showing an electromagnetic induction heating cooker according to Embodiment 1 of the present invention.
FIG. 2 is a diagram showing an output frequency control mechanism of an inverter in FIG.
FIG. 3 is a diagram showing an internal configuration of the soft start circuit 10 of FIG. 1;
4 is a timing chart illustrating an example of a control operation according to the first embodiment. FIG.
FIG. 5 is a timing chart showing an example of a control operation under a situation different from that in FIG.
6 is a timing chart showing an example of a control operation under a situation different from those in FIGS. 4 and 5. FIG.
FIG. 7 is a diagram for explaining a specific example of load fluctuation in the second embodiment of the present invention.
FIG. 8 is a diagram showing the relationship between frequency and phase difference in the case of stainless steel and aluminum as the material of the cooking pan.
FIG. 9 is a circuit configuration diagram showing an electromagnetic induction heating cooker according to Embodiment 2 of the present invention.
FIG. 10 is a diagram showing an output frequency control mechanism of an inverter in FIG.
FIG. 11 is a flowchart illustrating a control operation according to the second embodiment.
FIG. 12 is a timing chart illustrating an example of a control operation according to the second embodiment.
FIG. 13 is a circuit configuration diagram showing an electromagnetic induction heating cooker according to Embodiment 3 of the present invention.
FIG. 14 is a flowchart illustrating a control operation according to the third embodiment.
FIG. 15 is a diagram showing a main circuit configuration of an electromagnetic induction heating cooker.
FIG. 16 is a diagram showing voltage and current waveforms of an inverter in the case of a lag phase.
FIG. 17 is a diagram illustrating voltage and current waveforms of an inverter in the case of a lead phase.
FIG. 18 is a diagram illustrating a waveform of a current flowing through the upper and lower arms of an inverter.
FIG. 19 is a diagram illustrating a configuration of a switching element of an inverter.
[Explanation of symbols]
1 power calculation circuit, 2 phase difference detection circuit, 3 drive circuit, 4 differential amplifier for power control, 5 differential amplifier for phase difference control, 6 V / f converter, 7 power setting device,
8, 12, 14 Phase difference setting device, 9 operation command circuit, 10 soft start circuit,
11, 13 comparator, 15 flip-flop circuit, 16 timer circuit,
SW1, SW2 switching element (MOSFET), L heating coil,
C2, C3 resonant capacitors.

Claims (4)

Capacitors, heating coils forming together a series resonant circuit with the capacitor, inverter for supplying a high-frequency current to the heating coil, power calculating circuit for calculating the input power of the inverter, the output voltage of the inverter and the current flowing through the heating coil A phase difference detection circuit for detecting a phase difference between the power calculation value and a power setting value by manual setting to amplify a difference between the two input values and output when the power calculation value exceeds the power setting value A differential amplifier for power control that is set so that the polarity of the potential is positive, and a phase of a delay phase in which the phase of the current flowing through the heating coil is delayed with respect to the phase of the phase difference detection value and the output voltage of the inverter. inputs the phase difference lower limit set value set in a range to the phase difference detection value is smaller than the retardation limit set value amplifies the difference between the two input values Then, the differential amplifier for phase difference control set so that the polarity of the output potential becomes positive, and the output terminals of both the differential amplifiers are connected to the input terminals grounded by resistors through the diodes, respectively. The output frequency of the inverter is controlled to increase as the potential of the inverter increases. When the potential of the input terminal is zero (ground) potential, an input is made to output a frequency command signal for controlling the inverter at the lowest frequency. An electromagnetic induction heating cooker provided with a V / f converter that converts a potential into a frequency command signal. In order to automatically set the power at the start of operation of the inverter, a soft start circuit that outputs a potential that gradually decreases to zero at a predetermined gradient after the start of operation is provided, and an output terminal of the soft start circuit is connected to a diode. The V / f converter outputs a frequency command signal for controlling the inverter at the maximum frequency when the potential at the input terminal is the maximum potential. The electromagnetic induction heating cooker according to claim 1, wherein When the phase difference detection value falls below the phase difference lower limit setting value set within a range of the delayed phase and smaller than the phase difference lower limit setting value, the maximum potential is output and thereafter a predetermined value is output. 3. The electromagnetic induction according to claim 2, further comprising a phase difference recovery circuit that outputs a potential that gradually decreases to zero with a gradient, and an output terminal of the phase difference recovery circuit is connected to the V / f converter via a diode. Cooking cooker. The phase difference recovery circuit outputs a single pulse of the maximum potential when the phase difference detection value is equal to or lower than the phase difference minimum lower limit setting value, and starts the soft start circuit by the output of the single pulse. The electromagnetic induction heating cooking device according to claim 3, wherein the cooking device is constituted by a cooker.

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