JP4605545B2 - Electromagnetic induction heating control device - Google Patents

Description

The present invention controls the pressurizing heat means, an electromagnetic induction heating control apparatus for electromagnetic induction heating of the load.

Electric The magnetic induction heating apparatus, the electromagnetic induction heating control system by changing the heating output from the electromagnetic induction heating unit according to determined control process proceeds pressurized heat is mounted. The electromagnetic induction heating control device is disclosed in Patent Document 1.

Further, in an electromagnetic induction heating device (for example, Patent Document 2) that heats a member to be heated by electromagnetic induction heating means, energization to the electromagnetic induction heating means is switched when a zero cross of a power source is detected.
Japanese Patent Laying-Open No. 2005-50725 JP 2004-22501 A

However, during the time of heating alternately heating member by electromagnetic induction heating means, for capturing the input current from the power source, so it took time to respond to changes in the input current, the heating of one of the heating element In addition, the other heating element is cooled, and it is difficult to make the temperature distribution uniform.

The present invention has been made in view of the above problems, and sequentially energized a plurality of heating means, and purpose is to provide an electromagnetic induction heating control apparatus capable of uniform temperature distribution of the heating element.

In the electromagnetic induction heating control apparatus according to the first aspect of the present invention, since the waveform indicating the change in current is taken into the control means without being smoothed, the change in the current can be detected at high speed, and a plurality of heating means can be detected in a short time. Can be sequentially energized.

According to claim 1 of the present invention to improve the response to the current, by energizing controlling a plurality of heating means in a predetermined time period of the cycle of the power supply, which can be made uniform temperature distribution of the heating member An electromagnetic induction heating control device can be provided.

  Hereinafter, preferred embodiments of an electromagnetic induction heating control apparatus according to the present invention will be described with reference to the accompanying drawings.

FIG. 3 shows a first embodiment of the present invention, in which 1 is an AC power source, 2 is a rectifying and smoothing circuit for rectifying and smoothing an AC power source voltage from a commercial power source 1 and converting it to DC input power. The rectifying / smoothing circuit 2 includes a diode bridge 2a, a choke coil 2c, and a smoothing capacitor 2b. One end of a parallel circuit of the induction heating coil 3 and the resonance capacitor 8 and one end of a parallel circuit of the induction heating coil 23 and the resonance capacitor 28 are connected to the output side of the rectifying and smoothing circuit 2. Switching elements 4 and 24 made of IGBT are connected to the other ends of these parallel circuits, respectively. Each series circuit of the switching elements 4 and 24 and the circuit in which the resonance capacitors 8 and 28 are connected in parallel to the induction heating coils 3 and 23 corresponds to an inverter circuit that converts the DC input power into high-frequency power. Then, the switching elements 4 and 28 are alternately switched by a pulse drive signal supplied to the gates of the switching elements 4 and 28, and the induction heating coil 3 and the resonance capacitor 8 or the induction heating coil 23 and the resonance capacitor 28 are switched. Is caused to cause a high-frequency current to flow through the induction heating coils 3 and 23.

  As power feedback control means for outputting the induction heating coil 3 with a desired set power, an input current detection means 7 for detecting an input current supplied from the commercial power source 1 to the inverter circuit, and the input current detection means 7 On the basis of the detection result obtained in the above, an induction heating control circuit 9 composed of, for example, a microcomputer for variably controlling the switching operation, that is, the on-time of the switching elements 4, 24 is provided. The input current detection means 7 includes a current transformer 1 inserted in a line connecting the commercial power source 1 and the diode bridge 2a, and a rectifier stack 31 as a rectifier that rectifies the detected current obtained on the secondary side of the current transformer 1. And a smoothing circuit including a resistor 32 and a smoothing capacitor 33 for smoothing the detected voltage after the rectification at the subsequent stage of the rectification stack 31. The microcomputer constituting the induction heating control circuit 9 periodically takes in the detected voltage after smoothing by the smoothing circuit from the A / D input port and performs induction heating control.

  Conventionally, after rectification by the rectification stack 31, the waveform is smoothed by hardware and the current A / D value is taken into the microcomputer and averaged, for example, 50 times every 1 ms. FIG. 4 shows the A / D input port voltage waveform of the induction heating control circuit 9 and corresponds to the power supply voltage waveform of the commercial power supply 1. As shown in the figure, in the present invention, the capacitance of the smoothing capacitor 33 as the smoothing means is made minute (for example, 0.1 μF) to such an extent that the waveform rectified by the rectifying stack 31 is not deformed. Then, the A / D conversion value of the detected current is taken into the induction heating control circuit 9 a plurality of times, for example, at a period of 1 ms, which is sufficiently shorter than a half period of the AC voltage waveform of the commercial power supply 1 (half period T in FIG. 4). The change of the input current from the commercial power source 1 is detected at high speed by performing the averaging process with software. Thereby, the induction heating coils 3 and 23 can be alternately switched and controlled at the zero-cross timing (timing when the input current becomes zero) of the half cycle of the commercial power source 1.

As described above, in the first embodiment, the input current detecting means 7 for detecting the input current supplied from the commercial power source 1 to the induction heating coils 3 and 23 as the heating means, and the change in the input current based on the change in the input current. An induction heating control device comprising an induction heating control circuit 9 as a heating control means for controlling a plurality of induction heating coils 3 and 23 for electromagnetically heating the heating member 5, wherein the input current detection means 7 The induction heating control circuit 9 includes a rectification stack 31 as a rectifier for rectifying current and a smoothing capacitor 33 having a capacity that does not deform the waveform after rectification by the rectification stack 31. In the meantime, the change of the input current is detected by taking in the current value of the input current from the input current detection means 7 a plurality of times.

  In this way, since the waveform indicating the change in the input current is taken into the induction heating control circuit 9 without being smoothed, the change in the input current can be detected at high speed, and the plurality of induction heating coils 3, 23 can be detected in a short time. Can be sequentially energized. Therefore, an electromagnetic wave capable of improving the responsiveness to the input current and making the temperature distribution of the member to be heated 5 uniform by controlling energization of the plurality of induction heating coils 3 and 23 in a half cycle of the commercial power source 1. An induction heating control device can be provided.

FIG. 5 shows a second embodiment of the present invention, in which the commercial power source 1 supplies AC power to the induction heating coils 3 and 23. 50 is an inverter circuit as a switching means provided with a switching element for driving the induction heating coil 3, detects a high frequency current supplied to the induction heating coil 3, and sends a current detection signal 52 to the induction heating control circuit 9. Output. On the other hand, 60 is an inverter circuit as a switching means provided with a switching element for driving the induction heating coil 23, detects a high-frequency current supplied to the induction heating coil 23, and sends a current detection signal to the induction heating control circuit 9. 62 is output. The induction heating control circuit 9 receives output setting signals 53 and 63 for determining the heating output of the induction heating coils 3 and 23, respectively, and current detection signals 52 and 62 as feedback signals input from the inverter circuits 50 and 60, respectively. Accordingly, the PWM signals 51 and 61 that are PWM-controlled are configured as the inverter circuits 50 and 60 so that the heating outputs of the induction heating coils 3 and 23 become the outputs determined by the output setting signals 53 and 63, respectively. The heating output is input to each switching element and the heating output is feedback-controlled.

  When the induction heating coils 3 and 23 are simultaneously oscillated, if the difference between the oscillation frequencies of the respective switching elements constituting the inverter circuits 50 and 60 is less than the audible sound range (for example, less than 20 KHz), the frequency causes the coil and the heated object to change. It may vibrate and hear annoying sounds. Therefore, it is necessary to control each oscillation frequency so that the difference between the frequencies of the PWM signals 51 and 61 is more than the audible range (20 KHz or more in the above example). In the third embodiment, as shown in the timing chart of FIG. 6, the frequency of the PWM signal 51 is 25 KHz and the frequency of the PWM signal 61 is 45 KHz, so the difference is 45 KHz−25 KHz = 20 KHz, Satisfies. If the output setting signals 53 and 63 are the same setting value, the tuning is performed so that the frequency difference between the PWM signals 51 and 61 is 20 KHz or more and the same output (watt) can be obtained from both electromagnetic induction heating coils. To do. That is, the pulse conduction widths of the PWM signals 51 and 61 are fixed, and only the cycle (frequency) is changed so that the difference between the frequencies is 20 KHz or more and the total pulse conduction width per unit time is the same. For example, in FIG. 6, when the single pulse conduction width of the PWM signal 51 is 10 μs and the single pulse conduction width of the PWM signal 61 is 5 μs, the PWM signal 61 is output during one pulse of the PWM signal 51 (one cycle). What is necessary is just to change a frequency so that two pulses may be output. In addition, the above control method can be used also for cooking appliances, such as a rice cooker provided with the lid heating means by electromagnetic induction heating, and the pot heating means.

As described above, in the second embodiment, the electromagnetic induction heating for controlling the induction heating coil 3 as the first induction heating means for heating the inner pot by the alternating magnetic field and the induction heating coil 23 as the second induction heating means. In the control device, the pulse frequency of the switching element constituting the inverter circuit 50 as the switching means for energizing the induction heating coil 3 and the pulse frequency of the switching element constituting the inverter circuit 60 as the switching means for energizing the induction heating coil 23 Is configured to perform switching operation at a distance greater than the audible range.

  In this way, since the switching operation can be performed so that the difference in pulse frequency between the two inverter circuits 50 and 60 does not fall below the audible range, the two induction heating coils 3 and 23 are driven simultaneously. However, no annoying audible noise associated with the vibration of the coil or heated object is generated.

  The present invention is not limited to the above embodiments, and can be modified without departing from the spirit of the present invention.

It is a circuit diagram showing a configuration of an electromagnetic induction heating apparatus equipped with an electromagnetic induction heating controller definitive to the onset bright. It is a flowchart which shows the control data storage process of an electromagnetic induction heating control apparatus same as the above. It is a circuit diagram which shows the structure of the electromagnetic induction heating apparatus carrying the electromagnetic induction heating control apparatus in 1st Example of this invention. It is a wave form diagram which shows the A / D input port voltage of an electromagnetic induction heating control apparatus same as the above. It is a block diagram which shows the structure of the electromagnetic induction heating apparatus carrying the electromagnetic induction heating control apparatus in 2nd Example of this invention. It is a timing diagram which shows the control signal of an electromagnetic induction heating control apparatus same as the above.

1 Commercial power supply
3 Induction heating coil (heating means)
5 Heated member 7 Input current detection means (current detection means)
9 Induction heating control circuit (heating control means)
23 Induction heating coil (heating means)
31 Rectifier stack (rectifier)
33 Smoothing capacitor (smoothing means)

Claims (1)

Induction comprising a plurality of heating means for electromagnetically heating a member to be heated, a current detection means for detecting an input current supplied from a power source to the plurality of heating means, and a control means for controlling the plurality of heating means In the heating control device, the current detection unit includes a rectifier that rectifies the current and a smoothing unit having a capacity that does not deform the waveform after rectification, and the control unit includes a half of the waveform of the power supply. the current value of the current from said current detecting means at a shorter period periodic viewed multiple times up write, electromagnetic induction heating, characterized in that by averaging process is one that is configured to detect a change in the current Control device.

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