JP2002343547A - Electromagnetic heating control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable to switch on the switching element at the best timing throughout a wide rage of heating power. SOLUTION: The electromagnetic induction heating control device can change the time from outputting a detection signal from the synchronized timing detection means 15 till switching on of the switching element 6 in accordance with the heating power of the induction heating coil 7. Thereby, however is the heating power of the induction heating coil 7 set, it becomes possible that the switching element 6 is switched on at the time when the voltage V1 between the both ends of the switching element 6 has become zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic induction heating control device for electromagnetically heating a load by a high-frequency magnetic field generated from an induction heating means.

[0002]

Conventionally, this type of electromagnetic induction heating control device converts a DC input current into a high frequency AC current by a switching element constituting a high frequency inverter, and supplies the high frequency current to an induction heating coil. Then, the load is electromagnetically heated by a high frequency magnetic field generated from the induction heating coil, but the high frequency inverter used here is a voltage resonance type inverter having a simple circuit configuration so as not to increase the cost. Used.

FIG. 5 is a circuit diagram of an electromagnetic induction heating control device provided with such a voltage resonance type inverter. In FIG. 5, reference numeral 1 denotes a rectifying stack 3 connected to an AC power supply 2 of, for example, 100 VAC. And a choke coil 4 for smoothing the voltage rectified by the rectifier stack 3 and a smoothing capacitor 5. An AC power source 2 is connected between both ends of the smoothing capacitor 5 on the output side of the DC power source 1. A DC input voltage Ed is obtained by rectifying and smoothing the AC voltage from the DC. Reference numeral 6 denotes a high-frequency inverter 10 including a transistor Q1 and a diode D1 connected in anti-parallel between the collector and the emitter of the transistor Q1.
Is a switching element. A parallel circuit of an induction heating coil 7 serving as an induction heating means and a resonance capacitor 8 is connected between the DC power supply 1 and the switching element 6. Reference numeral 9 denotes a pot as a load provided at a position facing the induction heating coil 7 and subjected to electromagnetic induction heating by a high-frequency magnetic field generated from the induction heating coil 7.

On the other hand, as power feedback control means for outputting the induction heating coil 7 at a desired constant power,
Input voltage detecting means 11 for detecting an input voltage to the induction heating coil 7, input current detecting means 12 for detecting an input current flowing through the induction heating coil 7, and these input voltage detecting means 11
And an on-time of the switching element 6 is adjusted and controlled by the respective detection signals from the input current detecting means 12 so that the heating power of the induction heating coil 7 becomes constant, and a control program for executing such control is incorporated. A control device 14 as a control means having a microcomputer 13 is provided. 15 is the switching element 6
Resistors 16 and 17 connected between both ends of the
This is a synchronous timing detecting means constituted by a comparator 19 which compares the voltage V3 at the connection point of 16 and 17 with the reference voltage Vref from the reference power supply 18 and outputs the comparison result to the control device 14. The synchronous timing detecting means 15 detects the on-time of the switching element 6 by comparing the voltage V3 at the connection point of the voltage dividing resistors 16 and 17 with the reference voltage Vref in proportion to the voltage V1 across the switching element 6. The control device 14 determines the ON timing of the switching element 6 based on the detection signal from the synchronization timing detection means 15.

[0005] In order to increase the heating power of the induction heating coil 7, it is necessary to lengthen the ON time of the switching element 6. As a result, the operating cycle becomes longer, and the operating frequency of the switching element 6 and thus the high frequency inverter 10 is increased. Becomes lower. Conversely, to reduce the heating power of the induction heating coil 7, it is necessary to shorten the ON time of the switching element 6, and in this case, the operation cycle is shortened, and the operation frequency of the high-frequency inverter 10 is increased. That is, in the high frequency inverter 10 of the voltage resonance type, the operating frequency fluctuates according to the heating power of the induction heating coil 7.

FIG. 6 shows the optimum voltage V1 across the switching element 6 and the voltage level V2 of the drive signal supplied to the switching element 6 in the above circuit configuration. In the electromagnetic induction heating control device including the voltage resonance type inverter, in order to reduce the loss in the switching element 6, the voltage V1 between both ends of the switching element 6 is reduced to zero as shown in FIG. The switching element 6
The voltage level V2 of the drive signal from L (low) to H (high)
And the switching element 6 needs to be turned on.

On the other hand, as shown in FIG. 7, when the voltage level V2 of the drive signal from the control device 14 to the switching element 6 rises to H before the voltage V1 across the switching element 6 falls to zero, A short-circuit current flows through the switching element 6 to cause a loss (see the symbol X in FIG. 7).
In this case, adverse effects such as a decrease in heating efficiency, heat generation of the switching element 6 and abnormal noise are caused.

Normally, the synchronization timing detecting means 15 monitors the voltage V1 across the switching element 6, and outputs a detection signal having a voltage level H to the control device 14 near the point where the voltage V1 across the terminal becomes zero. , Microcomputer
In response to this detection signal, the control signal 13 raises the voltage level V2 of the drive signal and turns on the switching element 6. However, as shown in FIG. Timing detection means 15
In some cases, a delay time td occurs between the time when the detection signal is received and the time when the drive signal for turning on the switching element 6 is output, resulting in a deviation from the optimum on timing of the switching element 6.

In order to cope with such a problem, a delay in the instruction processing time of the microcomputer 13 is expected in advance, and
The generation timing of the detection signal from the synchronization timing detection means 15 is set to a predetermined value Vt before the voltage V1 across the switching element 6 becomes zero. But,
As shown in the waveform diagrams of FIGS. 9 and 10, this type of voltage resonance type inverter has an on-time ton of the switching element 6 and a switching element which changes in a sine wave shape according to the heating power from the induction heating coil 7. 6 have different maximum values Vmax of the voltage V1 between both ends. That is, in the state where the heating power is large as shown in FIG. 9, the on-time ton of the switching element 6 is long and the maximum value Vmax of the voltage V1 across the switching element 6 is large, whereas the heating power shown in FIG. In the state, the ON time t of the switching element 6
On is short, and the maximum value Vmax of the voltage V1 across the switching element 6 is small. However, the voltage V1 across the switching element 6 at which the detection signal of the synchronization timing detection means 15 switches from H to L is constant (predetermined value Vt) regardless of the amount of heating power. The times td1 and td2 from when the signal is switched to L to when the voltage V1 across the switching element 6 becomes zero become longer as the heating power increases (td1> td2). for that reason,
When the synchronization timing detecting means 15 is adjusted so that the detection signal is switched to the optimum timing with the high heating power shown in FIG. 9, the switching timing of the detection signal from the synchronization timing detecting means 15 is reduced with the low heating power shown in FIG. Is too early, an undesired short-circuit current flows through the switching element 6 as described above, and conversely, if the synchronous timing detecting means 15 is adjusted so that the detection signal is switched to the optimal timing with the low heating power shown in FIG. With the high heating power shown in FIG. 9, the switching timing of the detection signal from the synchronization timing detection means 15 is too late. As described above, no matter how the synchronization timing detection means 15 is conventionally adjusted, the range of the heating power at which the detection signal from the synchronization timing detection means 15 is switched at the optimum timing is limited, and the heating power outside the adjusted range is limited. When the electromagnetic induction heating is performed, there is a problem that the above-mentioned adverse effects appear.

On the other hand, in the circuit diagram of FIG. 5, the DC power supply 1 rectifies the AC voltage from the AC power supply 2 to obtain a DC input voltage Ed. However, when the pan 9 is heated, a large current flows. The voltage V1 across the switching element 6 is
An envelope-shaped pulse waveform whose peak value changes along the full-wave rectified waveform of the DC input voltage Ed. FIG.
In this case, the voltage between both ends of the smoothing capacitor 5 at this time, that is, the DC input voltage Ed, and the voltage at the non-inverting input terminal of the comparator 19 constituting the synchronous timing detecting means 15, that is,
A voltage V3 at a connection point of 16 and 17, an inverting input terminal voltage of the comparator 19, that is, a reference voltage Vref, and a detection signal from the synchronization timing detecting means 15 are shown.

However, as shown in FIG. 11, when the AC voltage of the AC power supply 2 approaches the zero crossing, the voltage V3 at the connection point between the voltage dividing resistors 16 and 17 in the synchronous timing detecting means 15 does not exceed the reference voltage Vref. Then, the synchronous timing detecting means 15 does not generate a detection signal output synchronized with the high-frequency inverter 10. In this case, the switching element 6 does not turn on temporarily, and the high-frequency inverter
The oscillation of 10 was discontinuous, causing an abnormal sound.

An object of the present invention is to solve the above-mentioned problems, and a first object of the present invention is to provide an electromagnetic induction heating control device capable of turning on a switching element at an optimum timing over a wide range of heating power. And

A second object of the present invention is to provide an electromagnetic induction heating control device capable of continuously oscillating by a detection signal from a synchronous timing detecting means without stopping a high frequency inverter even near a zero crossing of an AC power supply voltage. To provide.

[0014]

According to the electromagnetic induction heating control device of the first aspect of the present invention, a switching signal is output from the synchronous timing detection unit in accordance with the heating power of the induction heating unit, and then the switching element is turned on. The time until turning on can be changed. Therefore, no matter how the heating power of the induction heating means is set, the switching element can be turned on when the voltage between both ends of the switching element becomes zero, and the switching element can be turned on over a wide range of heating power. It can be turned on at the optimal timing.
Therefore, it is possible to reduce adverse effects such as a decrease in heating efficiency due to an increase in the loss of the switching element and heat generation and abnormal noise of the switching element.

According to the electromagnetic induction heating control device of the second aspect of the present invention, in proportion to the input voltage of the induction heating means,
Since the reference voltage of the synchronous timing detecting means fluctuates, even if the AC voltage of the AC power supply is near zero crossing, the synchronous timing detecting means outputs a detection signal synchronized with the high-frequency inverter, and the high-frequency inverter is continuously stopped without stopping. And oscillate. Therefore, it is possible to reduce adverse effects such as abnormal sounds generated from the switching elements.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings. In these embodiments, the same parts as those of the conventional example are denoted by the same reference numerals, and detailed description of common parts will be omitted because they are duplicated.

FIGS. 1 and 2 correspond to the first embodiment of the present invention, and FIG.
The difference from FIG. 5 in the conventional example is that the microphone computer 13 constituting the control device 14 is provided with a time delay adjusting means 21 having a built-in delay timer. That is, the time delay adjusting means 21 varies the time delay td from when the detection signal is output from the synchronization timing detecting means 15 to when the switching element 6 is turned on, according to the heating power of the induction heating coil 7. Specifically, as the heating power of the induction heating coil 7 is larger, the set time of the delay timer and, consequently, the time delay td are shorter.
Is set such that the smaller the heating power is, the longer the set time of the delay timer and thus the time delay td. Other configurations are the same as those of the conventional example shown in FIG.

Next, the operation of the above configuration will be described with reference to the flowchart of FIG. The AC voltage from the AC power supply 2 is rectified and smoothed by the DC power supply 1, and a DC input voltage Ed in the form of a full-wave rectified wave is generated between both ends of the smoothing capacitor 5 as an input voltage to the induction heating coil 7. When the switching element 6 is turned on and off by a drive signal from the control device 14, a high-frequency current flows through the induction heating coil 7 to generate an alternating magnetic field.
Is heated by electromagnetic induction heating. The control device 14 includes an input voltage detecting means 11 for detecting an input voltage to the induction heating coil 7 so that the set power preset by the user and the actual heating power of the induction heating coil 7 are equal to each other; Current detection means for detecting the input current flowing through the circuit 7
By monitoring each detection signal from 12, the ON time of the switching element 6 is adjusted and controlled. That is, the induction heating coil 7
If the heating power of the switching element 6 is longer than the set power, the ON time of the switching element 6 is lengthened, and the operating frequency of the switching element 6 and thus the high-frequency inverter 10 is reduced. If it is also smaller, the on-time of the switching element 6 is lengthened to increase the operating frequency of the high-frequency inverter 10.

On the other hand, the synchronous timing detecting means 15 comprises a voltage dividing resistor 1 proportional to the voltage V1 across the switching element 6.
The voltage V3 at the connection point between the switching elements 6 and 17 is monitored.
When the voltage V3 at the connection point exceeds the reference voltage Vref of the reference power supply 18, the voltage level of the detection signal from the synchronous timing detection means 15 switches from L to H, and conversely, the voltage V1 across the switching element 6 decreases. Then, when the voltage V3 at the connection point of the voltage dividing resistors 16 and 17 becomes lower than the reference voltage Vref of the reference power supply 18, the voltage level of the detection signal from the synchronization timing detection means 15 switches from H to L. As a result, it is possible to perform the generation timing of the detection signal from the synchronization timing detection unit 15 at the predetermined value Vt before the voltage V1 across the switching element 6 becomes zero.

In step S1, the microcomputer 13 constituting the control device 14 detects a detection signal (synchronization timing detection signal) from the synchronization timing detection means 15.
Is changed from H to L. When the voltage level of the synchronization timing detection signal is H
Then, the microcomputer 13 determines in step S2 whether or not the set power preset by the user is high heating power. If the set power is the high heating power, the process proceeds to step S3 to set the delay timer incorporated in the time delay adjusting means 21 to 0 μsec.
Then, the process goes to step 4 to set the delay timer to 2 μsec. Then, if the delay timer is 0 in the next step S5, that is, if the set power is high heating power, a drive signal for turning on the switching element 6 immediately without counting the delay timer is output (step S7). . On the other hand, if the delay timer is not 0 in step S5, that is, if the set power is other than the high heating power, the process proceeds to step S6 to count the delay timer,
After 2 μsec in the next step S7, the switching element 6
And outputs a drive signal for turning on.

In this way, the generation timing of the detection signal from the synchronization timing detection means 15 is performed at the predetermined value Vt before the voltage V1 across the switching element 6 becomes zero, and the induction heating coil 7 set by the user. As the heating power decreases, the heating power of the induction heating coil 7 is set by increasing the time td from when the detection signal is output from the synchronization timing detection means 15 to when the switching element 6 is turned on. Also the switching element 6
When the voltage V1 between both ends becomes zero, the switching element 6 can be turned on.

As described above, according to the present embodiment, the switching element 6 controlled by the control device 14 as the control means is provided.
, An induction heating coil 7 as an induction heating means connected to the high frequency inverter 10, a pan 9 as a load subjected to electromagnetic induction heating by a high frequency magnetic field generated from the induction heating coil 7, a high frequency inverter
The synchronous timing detecting means 15 sends a detection signal synchronized with the operation state of the control signal 10 to the control device 14, and the time td from when the detection signal is output from the synchronous timing detecting means 15 to when the switching element 6 is turned on is derived. It is configured to be variable according to the heating power of the heating coil 7.

In this manner, the time td from when the synchronous timing detecting means 15 outputs a detection signal to when the switching element 6 is turned on can be varied according to the heating power of the induction heating coil 7. Therefore, no matter how the heating power of the induction heating coil 7 is set, when the voltage V1 across the switching element 6 becomes zero,
The switching element 6 can be turned on, and the switching element 6 can be turned on at an optimum timing over a wide range of heating power. Therefore, it is possible to reduce a decrease in the heating efficiency due to an increase in the loss of the switching element 6, and to reduce adverse effects such as heat generation and abnormal noise of the switching element 6.

In this embodiment, the time td from when the detection signal is output from the synchronization timing detection means 15 to when the switching element 6 is turned on is varied with the power set by the user as the heating power. The time td may be varied by using feedback power in power feedback control by the means 11 and the input current detection means 12 as heating power. Further, the time td may be varied continuously instead of stepwise according to the heating power.

Next, a second embodiment of the present invention will be described with reference to FIGS. In FIG. 3 showing a circuit diagram of the entire apparatus, an AC power supply 2 is used instead of the reference power supply 18.
A voltage dividing resistor 3 for dividing a DC input voltage Ed which is a power supply voltage of an induction heating coil 7 obtained by full-wave rectification of an AC voltage from
By connecting the connection point of the voltage dividing resistors 31 and 32 to the inverting input terminal of the comparator 19, a voltage proportional to the input voltage of the induction heating coil 7 can be detected by the synchronous timing detecting means 15. The comparator 19 compares the reference voltage Vref with the voltage V3 at the connection point between the voltage dividing resistors 16 and 17 as the reference voltage Vref. Other configurations are the same as those of the conventional example shown in FIG.

Next, the operation of the above configuration will be described with reference to the waveform diagram of FIG. In FIG. 4, the waveform at the top is the voltage between both ends of the smoothing capacitor 5, that is, the DC input voltage Ed. Hereinafter, the non-inverting input terminal voltage of the comparator 19 constituting the synchronization timing detecting means 15, that is, the divided voltage The voltage V3 at the connection point of the resistors 16 and 17, the inverting input terminal voltage of the comparator 19, that is, the reference voltage Vref, and the detection signal from the synchronization timing detecting means 15 are shown.

Synchronous timing detecting means in this embodiment
Reference numeral 15 indicates that since the reference voltage Vref is not a fixed voltage but fluctuates in proportion to the amplitude of the voltage V1 across the switching element 6, the reference voltage Vref also decreases near the zero crossing of the AC voltage of the AC power supply 2, and the voltage dividing resistor Voltage V3 at the connection point of 16, 17
Becomes higher than the reference voltage Vref.
Therefore, even if the AC voltage of the AC power supply 2 is near the zero crossing, a detection signal synchronized with the high-frequency inverter 10 is output from the synchronous timing detection means 15, and the high-frequency inverter 10 can continuously oscillate.

As described above, according to the present embodiment, the switching element 6 controlled by the control device 14 as the control means is provided.
, An induction heating coil 7 as an induction heating means connected to the high frequency inverter 10, a pot 9 as a load subjected to electromagnetic induction heating by a high frequency magnetic field generated from the induction heating coil 7, and a switching element. 6 is compared with a voltage V3 proportional to the voltage V1 across the terminal 6 and a reference voltage Vref proportional to the input voltage of the induction heating coil 7 (DC input voltage Ed) to control a detection signal synchronized with the operation state of the high-frequency inverter 10. And a synchronous timing detecting means 15 for sending out to the device 14.

In this case, since the reference voltage Vref of the synchronous timing detecting means 15 fluctuates in proportion to the input voltage of the induction heating coil 7, even if the AC voltage of the AC power supply 2 is near zero cross, the synchronous timing A detection signal synchronized with the high-frequency inverter 10 is output from the detection unit 15,
The high-frequency inverter 10 can oscillate continuously without stopping. Therefore, adverse effects such as abnormal sound generated from the switching element 6 can be reduced.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention.

[0031]

According to the electromagnetic induction heating control apparatus of the first aspect of the present invention, the switching element can be turned on at an optimum timing over a wide range of heating power.

According to the electromagnetic induction heating control apparatus of the second aspect of the present invention, it is possible to continuously oscillate by the detection signal from the synchronous timing detection means without stopping the high frequency inverter even near the zero crossing of the AC power supply voltage. Become.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an electromagnetic induction heating control device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing an operation procedure of the microcomputer.

FIG. 3 is a circuit configuration diagram of an electromagnetic induction heating control device according to a second embodiment of the present invention.

FIG. 4 is a waveform diagram showing a relationship among a DC input voltage, a voltage at a connection point of a voltage dividing resistor, a reference voltage, and a voltage level of a detection signal from a synchronous timing detection unit.

FIG. 5 is a circuit configuration diagram of an electromagnetic induction heating control device showing a conventional example.

FIG. 6 is a waveform diagram showing a voltage between both ends of the switching element and a voltage level of a drive signal supplied to the switching element when an operation timing of the switching element is appropriate.

FIG. 7 is a waveform diagram showing a voltage between both ends of the switching element and a voltage level of a drive signal supplied to the switching element when operation timing of the switching element is inappropriate.

FIG. 8 is a waveform diagram illustrating a relationship between a voltage between both ends of a switching element, a voltage level of a detection signal from a synchronization timing detection unit, and a voltage level of a drive signal supplied to the switching element.

FIG. 9 is a waveform diagram showing a voltage between both ends of a switching element and a voltage level of a detection signal from a synchronous timing detecting means when a large amount of heating power is used in a conventional example.

FIG. 10 is a waveform diagram showing a voltage between both ends of a switching element and a voltage level of a detection signal from a synchronous timing detection unit when heating power is small in a conventional example.

FIG. 11 is a waveform diagram showing a relationship between a DC input voltage, a voltage at a connection point of a voltage dividing resistor, a reference voltage, and a voltage level of a detection signal from a synchronization timing detection unit in a conventional example.

[Explanation of symbols]

 6 Switching element 7 Induction heating coil (Induction heating means) 9 Pot (load) 10 High frequency inverter 14 Control device (Control means) 15 Synchronous timing detection means

Claims (2)

[Claims] A high-frequency inverter including a switching element controlled by a control means; an induction heating means connected to the high-frequency inverter; a load subjected to electromagnetic induction heating by a high-frequency magnetic field generated from the induction heating means; A synchronization timing detection unit that sends a detection signal synchronized with an operation state of the high-frequency inverter to the control unit, and a time from when the synchronization timing detection unit outputs the detection signal to when the switching element is turned on is set as heating power. An electromagnetic induction heating control device characterized in that it is configured to be variable in response to the change. 2. A high-frequency inverter including a switching element controlled by a control means, an induction heating means connected to the high-frequency inverter, a load subjected to electromagnetic induction heating by a high-frequency magnetic field generated from the induction heating means, Synchronous timing detecting means for comparing a voltage proportional to a voltage across the switching element with a reference voltage proportional to an input voltage of the induction heating means, and sending a detection signal synchronized with an operation state of the high-frequency inverter to the control means. And an electromagnetic induction heating control device.