JP2002151242A - Electromagnetic induction heating control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a high frequency inverter in a desirable operation frequency range whatever the state of load. SOLUTION: An operation frequency of a switching element 5 is monitored by a trigger timing detection means 14. A control device 15 controls the operation time, that is, an on-time so that the operation frequency be in the range over 20 kHz and under 40 kH, which allows to achieve abiding by the Radio Law as well as avoidance of adverse effects on the standard radiowave signal of 40 kHz unaffected by conditions of a pan 8.

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

Incidentally, the high frequency inverter of the electromagnetic induction heating control device has an operating frequency of 2 according to the radio law.
It is regulated in the range of 0.0 kHz to 100 kHz, and is often operated at an operating frequency of about several tens kHz in terms of efficiency. In addition, since the standard radio wave transmitting station transmits a telegraphic Morse code at a frequency of 40 kHz, the upper limit of the operating frequency of the high-frequency inverter is preferably set to less than 40 kHz in order to avoid the influence on the standard radio signal.

On the other hand, in order to control the electromagnetic induction heating control device with a constant power required by a user, the ON time of the switching element is adjusted and controlled by feedback control. The frequency does not become a fixed frequency depending on the load, for example, the temperature of the pot, the material, the shape, etc., and if the required power is not reached, the ON time of the switching element is lengthened,
Feedback control is performed to increase the high-frequency current flowing through the induction heating coil. At this time, the operating frequency of the high-frequency inverter fluctuates depending on the load, and depending on the load, the frequency may fall below 20.0 kHz. Conversely, if it exceeds the required power,
Feedback control is performed so as to reduce the high-frequency current flowing through the induction heating coil by shortening the on-time of the switching element. At this time, however, depending on the load, the frequency may be as high as 40 kHz as the standard radio signal.

An object of the present invention is to provide an electromagnetic induction heating control device capable of controlling a high-frequency inverter within a desired operating frequency range regardless of a load state. For that purpose.

[0006]

According to the present invention, there is provided an electromagnetic induction heating control apparatus comprising: a high frequency inverter; a detecting means for detecting an operating frequency of the high frequency inverter; an induction heating means connected to the high frequency inverter; A load that is electromagnetically heated by a high-frequency magnetic field generated from the heating means, and the operating frequency of the high-frequency inverter is 2
Control means for controlling the high-frequency inverter so as to be limited to a range of more than 0 kHz and less than 40 kHz.

According to the above configuration, the operating frequency of the high-frequency inverter is monitored by the frequency detecting means, and the operating time of the high-frequency inverter is controlled so that the operating frequency is in the range of more than 20 kHz and less than 40 kHz. Compliance with the Radio Law and 40kHz
Can be avoided at the same time.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the accompanying drawings. In FIG. 1 showing the configuration of the entire device,
Reference numeral 1 denotes an AC power supply 2 of, for example, AC 100 V, a rectifying stack 3 for rectifying an AC voltage from the AC power supply 2, and a smoothing capacitor 4 for smoothing the voltage rectified by the rectifying stack 3.
A DC input voltage Ed obtained by rectifying and smoothing the AC voltage from the AC power supply 2 is generated at both ends of the smoothing capacitor 4 on the output side of the DC power supply 1. Reference numeral 5 denotes a switching element constituting a high-frequency inverter including a transistor Q1 and a diode D1 connected in anti-parallel between the collector and the emitter of the transistor Q1. A parallel circuit of an induction heating coil 6 serving as induction heating means and a resonance capacitor 7 is connected between the DC power supply 1 and the switching element 5. 8 is provided at a position facing the induction heating coil 6,
It is a pot as a load that is subjected to electromagnetic induction heating by a high-frequency magnetic field generated from the induction heating coil 6.

On the other hand, reference numeral 11 denotes feedback control means for outputting the induction heating coil 6 at a desired constant power.
This is because the input voltage detecting means 12 for detecting the input voltage to the induction heating coil 6, the input current detecting means 13 for detecting the input current flowing through the induction heating coil 6, the ON timing of the switching element 5, The output power of the induction heating coil 6 is kept constant by the trigger timing detecting means 14 as a frequency detecting means for detecting the operating frequency of the element 5 and the detection signals from the input voltage detecting means 12 and the input current detecting means 13. The ON time of the switching element 5 is adjusted and controlled so that the operation frequency of the switching element 5 is controlled so that the operating frequency of the switching element 5 is limited to a range of more than 20 kHz and less than 40 kHz by a detection signal from the trigger timing detection means 14. The control unit 15 is a control unit for controlling the operation of the element 5.

Next, the operation of the electromagnetic induction heating control apparatus according to the present embodiment will be described with reference to the waveform diagram of FIG. 2 and the flowcharts of FIGS. In FIG. 2, what is at the top is the collector current IQ1 of the transistor Q1. Hereinafter, the current ID1 flowing through the diode D1, the current IL1 flowing through the induction heating coil 6, the current IC1 flowing through the resonance capacitor 7, the transistor Q1 and the diode D1
At the voltage VQ1 between 1, the direction indicated by each arrow in FIG. 1 appears on the plus side in the waveform diagram shown in FIG.

The pulse drive signal from the control device 15
The operation of the switching element 5, the induction heating coil 6, and the resonance capacitor 7 transitions in one cycle in the following three modes. The first mode I is a mode in which the transistor Q1 of the switching element 5 is turned on. In this case, since the voltage VQ1 between the transistors Q1 is short-circuited to zero volt, the DC input voltage Ed is applied to the induction heating coil 6. ,
The current IL1 flowing through the induction heating coil 6 increases linearly from zero. At this time, the same DC input voltage Ed as that of the induction heating coil 6 is applied to the resonance capacitor 7, but the current IC1 does not flow because the resonance capacitor 7 is already charged.

Next, when the transistor Q1 of the switching element 5 is turned off, a transition is made to mode II. This mode II is a mode in which a resonance current flows between the induction heating coil 6 and the resonance capacitor 7. When the transistor Q1 is switched from on to off, the induction heating coil 6 maintains the continuity of the current IL1. The current IL1 flows through the resonance capacitor 7 as the current IC1. As a result, the current IL1 flowing through the induction heating coil 6 and the current IC1 (resonance current) flowing through the resonance capacitor 7 both change sinusoidally and gradually decrease after reaching a maximum. Becomes zero when all of the energy has been transferred to the induction heating coil 6 from the resonance capacitor 7 again.
When the energy moves to this point, it flows in the opposite direction (negative). At this time, the voltage across the resonance capacitor 7 changes in a sinusoidal manner, gradually decreases from the DC input voltage Ed, reaches a minimum value (negative) when the resonance current becomes zero, and then increases again to increase the DC input voltage. It returns to the voltage Ed. Therefore,
The transistor Q1 and the diode D1 connected in anti-parallel to the transistor Q1 include (DC input voltage Ed-resonant capacitor 7
Is applied as a voltage VQ1.
Q1 changes sinusoidally. When the voltage between both ends of the resonance capacitor 7 returns to the DC input voltage Ed, the next mode II
Move to I.

Mode III is a mode in which the diode D1 is turned on. That is, when the voltage between both ends of the resonance coil 7 tries to exceed the DC input voltage Ed, the diode D1
, A diode D1 turns on and a current ID1 flows. At this time, a DC input voltage Ed is applied across the induction heating coil 6, but this voltage acts to reduce the current ID1 flowing through the diode D1, so that the current ID1 decreases linearly to zero. If the transistor Q1 of the switching element 5 is turned on at the time when the value becomes zero, the mode returns to the mode I described above.

In this series of operations, if the time of mode I, that is, the ON time of the switching element 5 is lengthened, the peak value of the current IL1 flowing through the induction heating coil 6 increases, so that the heating power from the induction heating coil 6 ( If the ON time of the switching element 5 is shortened, the peak value of the current IL1 flowing through the induction heating coil 6 decreases, and the heating power from the induction heating coil 6 decreases. Mode II and mode III, which are the off periods of the switching element 5, are substantially constant time depending on the resonance frequency of the induction heating coil 6 and the resonance capacitor 7, so that the operating frequency of the switching element 5 changes with the time of the mode I, The temperature decreases as the heating power of the induction heating coil 6 increases, and conversely increases as the heating power of the induction heating coil 6 decreases.

Here, the procedure of the control program built in the microcomputer of the control device 15 will be described with reference to the flowcharts of FIGS. The control device 15 first multiplies the values of the input voltage and the input current of the induction heating coil 6 detected by the input voltage detection means 12 and the input current detection means 13 in step S1, and Find the heating power. Then, a power difference between the actual heating power and the power required by the user is obtained in the next step S2.

Subsequently, the control device 15 determines in step S3 whether or not the operating frequency of the switching element 5 detected by the trigger timing detecting means 14 is 22 kHz or more, and determines whether or not the operating frequency is 38 kHz or less. The determination is made in step S4. If the operating frequency of the switching element 5 is equal to or higher than 22 kHz and equal to or lower than 38 kHz, it is determined that the operating frequency is within a normal operating frequency range. In the next step S5, the power difference from the set power obtained in step S2 is determined. In step S6, it is determined whether or not the power difference is less than -10W. If the power difference is within ± 10W, then in step S7, it is determined. The on-time increase / decrease permission flag is set to 0. The control device 15 performs switching when the operating frequency of the switching element 5 is less than 22 kHz in step S3 or when the power difference from the set power of the induction heating coil 6 exceeds +10 W in step S5. In order to shorten the ON time of the element 5 (the heating power decreases), the ON time increase flag is set to 0 (step S8). If the operating frequency of the switching element 5 exceeds 38 kHz in step S4, or if the power difference from the set power of the induction heating coil 6 is less than -10 W in step S6, To increase the on-time (heating power increases), set the on-time increase flag to 1
(Step S9). Then, in either case after the procedure of step S8 and step S9, the on-time increase / decrease permission flag is set to 1 (step S10).

Thereafter, in step S11, when a trigger signal indicating that the current flowing from the switching element 5 to the induction heating coil 6 has become zero is input from the trigger timing detecting means 14 to the control device 15, the trigger signal is input last time. The operating frequency is obtained from the measurement value of the frequency measurement timer that measures the time difference from the trigger signal. This is calculated from the reciprocal of the value measured by the frequency measurement timer (step S12).
At the same time, clear this frequency measurement timer to 0,
Timing is started for the next operation frequency calculation.

Then, as shown in step S21 of the flowchart of FIG. 4, the control device 15 determines whether or not the on-time increase / decrease permission flag is "1". If the on-time increase / decrease permission flag is not 1 but 0, it is determined that the operating frequency of the switching element 5 does not need to be changed, and step S to be described later
25, but if the on-time increase / decrease permission flag is 1, it is determined whether or not the on-time increase flag is 1 in the next step S22. In this case, if the on-time increase flag is 1, the on-time of the switching element 5 is increased by a predetermined time, that is, 5 μSec longer than before (step S23). Conversely, if the on-time increase flag is 0, the on-time of the switching element 5 is reduced by a predetermined time, that is, 5 μSec, as compared with that before (step S 2
4). Then, in both cases of step S23 and step S24, the process proceeds to the next step S25.

In step S25, the control device 15 turns on the transistor Q1 of the switching element 5, clears the on-time count timer to 0 in the next steps S26 and S27, and starts timekeeping therefrom. In step S28, when the ON time count timer becomes equal to or longer than the ON time set in steps S21 to S24, the switching element 5
Is turned off, and the procedure returns to the step S1 in the flowchart of FIG.

Thus, feedback control is achieved in consideration of the actual operating frequency of the switching element 5 in addition to the heating power of the induction heating coil 6. Thereby, the operating frequency of the switching element 5 is limited to the range of 22 kHz to 38 kHz regardless of the condition of the pot 8 as a load. Further, the induction heating coil 6 operates stably with a power difference within ± 10 W with respect to the set power required by the user.

As described above, according to the present embodiment, the switching element 5 constituting the high-frequency inverter, the trigger timing detecting means 14 as detecting means for detecting the operating frequency of the switching element 5, and the connection to the switching element 5 An induction heating coil 6 as an induced induction means,
Pot 8 as a load that is electromagnetically heated by a high-frequency magnetic field generated from induction heating coil 6, and switching element 5
And a control device 15 as control means for controlling the switching element 5 so that the operating frequency of the switching element 5 is limited to a range of more than 20 kHz and less than 40 kHz.

As described above, the operating frequency of the switching element 5 is monitored by the trigger timing detecting means 14, and the operating time, that is, the ON time of the switching element 5 is controlled so that the operating frequency is in the range of more than 20 kHz and less than 40 kHz. Therefore, compliance with the Radio Law and avoidance of the influence on the standard radio signal of 40 kHz can be achieved at the same time without being affected by the condition of the pot 8 as the load. Therefore, the switching element 5 can be controlled in a desired operating frequency range regardless of the state of the pot 8.

In this embodiment, input voltage detecting means is used as power detecting means for detecting the heating power of the induction heating coil 6.
12 and an input current detecting means 13. The control device 15 controls the switching element 5 according to the heating power of the induction heating coil 6.
Of the induction heating coil 6
, The operating frequency of the switching element 5 is limited to a range of more than 20 kHz and less than 40 kHz.

In this case, regardless of the heating power of the induction heating coil 6, the operating frequency of the switching element 5 is limited to a range from more than 20 kHz to less than 40 kHz in any situation. It is possible to reliably control.

Further, as apparent from the flowchart of FIG. 3, the control device 15 of the present embodiment
In the case where the heating power range of the induction heating coil 6 exceeds the upper limit and is less than the lower limit, the flag for increasing or decreasing the on-time of the induction heating coil 6 (on-time increase flag) indicates that the operating frequency of the induction heating coil 6 is 20 kHz or less. This flag is common to a flag (on-time increase flag) for increasing or decreasing the on-time of the induction heating coil 6 when the frequency is within the range of 40 kHz. As a result, the programming of the control device 15 can be shared.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. For example, in the present embodiment, the lower limit of the operating frequency range of the switching element 5 is 22 kHz and the upper limit is 3 kHz.
Although it was set to 8 kHz, it is not limited to this.
The frequency may be set arbitrarily as long as it is in the range of more than kHz and less than 40 kHz.

[0027]

According to the electromagnetic induction heating control apparatus of the present invention, it is possible to control the high-frequency inverter within a desired operating frequency range regardless of the state of the load.

[Brief description of the drawings]

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

FIG. 2 is a waveform chart of each part of the above.

FIG. 3 is a flowchart showing an operation procedure of the control device.

FIG. 4 is a flowchart showing an operation procedure of the control device.

[Explanation of symbols]

 Reference Signs List 5 switching element (high-frequency inverter) 6 induction heating coil (induction heating means) 8 pot (load) 14 trigger timing detection means (detection means) 15 control device (control means)

Claims (1)

[Claims] 1. A high-frequency inverter, a detecting means for detecting an operating frequency of the high-frequency inverter, an induction heating means connected to the high-frequency inverter, and a load subjected to electromagnetic induction heating by a high-frequency magnetic field generated from the induction heating means And a control unit for controlling the high-frequency inverter so that the operating frequency of the high-frequency inverter is limited.