JPH0831559A - Induction heating apparatus - Google Patents

Abstract

PURPOSE:To provide an small article load detecting means which is economical, has simple structure, and scarcely generates strange sounds. CONSTITUTION:Voltage waveform generated from a resonance circuit 9 and waveform produced by filtering the voltage waveform is compared by a comparison means 22 and the rectangular waves sent out of the comparison means 22 are counted at the timing corresponding to zero cross points of a. c. voltage waveform and the counted number is compared with a standard value to judge whether there is load or not. In the case there is normal load, the high frequency is high and rectangular waves discontinuous near a zero cross point are sent out of the comparison means 22. In the case there is no load or a small article, high frequency is low and rectangular waves not discontinuous but continuous near a zero cross point are sent out of the comparison means 22. Consequently, whether it is a normal load or no load or a small article can be judged by comparing the counted value with the standard value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating device used in an electromagnetic cooker or the like, and more particularly to an induction heating device capable of detecting the presence or absence of its load.

[0002]

2. Description of the Related Art An electromagnetic cooker using an induction heating device is
As shown in FIG. 13, a rectifier circuit 2 and a smoothing capacitor 3 for converting an AC voltage from an AC power supply 1 into a DC voltage, an inverter circuit 6 for converting the DC voltage from the rectifier circuit 2 into a high frequency voltage, and the inverter. Resonant circuit 9 consisting of induction heating coil 7 and capacitor 8 connected to circuit 6
It consists of An eddy current is generated in a load such as a pan placed on the induction heating coil 7 by electromagnetic induction, and Joule heat based on the eddy current generates heat.

In this type of electromagnetic cooker, if a small load of a small metal object such as a spoon or a fork which is not a regular load such as a pan is erroneously placed, even a small object is heated in the same manner as a pan. When the small load is heated in this way, there is a risk of burns if touched without knowing it, which is dangerous. For this reason, in an electromagnetic cooker or the like, a means for detecting a small load is provided.

As a conventional means for detecting small articles, Japanese Patent Publication Sho 58
As disclosed in Japanese Laid-Open Patent Application No. 83539, it is detected that the input voltage is above a certain level near the time of zero crossing, or as shown in Japanese Laid-Open Patent Publication No. 4-332419, oscillation is interrupted immediately after energization to attenuate the frequency. There is something to detect.

[0005]

However, all of them are costly and complicated, and particularly in the latter case, there is a problem that an attenuation frequency passes through a human audible frequency range and a audible click sound is generated. It is an object of the present invention to solve the above problems, and an object thereof is to provide an induction heating device that is inexpensive and has a simple structure and does not generate abnormal noise.

[0006]

First, the basic principle of the present invention will be described. In the above-described induction heating device shown in FIG. 13, when the inverter circuit 6 is driven with a constant pulse width and the load size is changed, the induction heating coil 7
The energy release time from changes. That is, when the state with no load or the state with a small load is changed to the state with a load, as shown in FIG. 1, the energy emission time is shortened and the frequency of the voltage waveform (Vce waveform) of the resonance circuit 9 is increased. Therefore, the presence or absence of a load can be detected by counting the frequency of the voltage waveform of the resonance circuit 9.

In addition, when there is no load or a small load, the power factor deteriorates, and the discharge voltage of the smoothing capacitor 3 connected to the output side of the rectifier circuit 2 remains at the time corresponding to the zero cross point of the AC voltage. As a result, as shown in FIG.
A constant voltage is generated in the envelope waveform of the Vce waveform. Therefore, when the Vce envelope is cut at a constant level as shown by the alternate long and short dash line in FIG. 2 (A), when there is a load, the peak of the waveform is interrupted near the time point corresponding to the zero cross point of the AC voltage. The frequency decreases, but when there is no load or a small load, the waveform is continuous and the frequency increases. Therefore, the presence or absence of the load can be detected by counting the frequencies near the time point corresponding to the zero-cross point of the AC voltage.

The present invention is based on the above-mentioned basic principle, and as described in claim 1, a rectifier circuit for converting an AC voltage into a DC voltage, and a DC voltage from the rectifier circuit for converting to a high frequency voltage. In an induction heating device including an inverter circuit and a resonance circuit composed of an induction heating coil and a capacitor connected to the inverter circuit, a rectangular wave is obtained by comparing a voltage waveform generated from the resonance circuit with a waveform obtained by smoothing the voltage waveform. Comparing means for outputting a rectangular wave output from the comparing means, a counting means for counting within a predetermined time at a time point corresponding to the zero cross point of the AC voltage waveform, and a count value counted by the counting means. A determination unit that determines the presence or absence of a load by comparing with a predetermined reference value, and a control unit that controls the inverter circuit based on the determination result by the determination unit. It is characterized in that the.

In such a configuration, when the voltage waveform of the resonance circuit and the waveform obtained by smoothing the resonance circuit are compared by the comparison means, when there is a normal load, a rectangular wave with a high frequency and a break near the zero cross point is obtained. Is output. In the case of no load or a small object, a rectangular wave having a low frequency and having no interruption in the vicinity of the zero-cross point is output. Therefore, when the frequency of the rectangular wave counted by the counting means, that is, the count value, is compared with the reference value by the determination means at the time point corresponding to the zero-cross point, it is determined whether the load is normal load, no load, or a small item.

As a preferred embodiment, as described in claim 2, the counting means sets the rectangular wave output from the comparing means to a predetermined time after a certain time has elapsed from the time corresponding to the plurality of zero-cross points. You may make it count in time. According to this, when the count value is less than the reference value, the frequency is low and it is determined that there is no load or small items,
If the count value is greater than the reference value, the frequency is high and it is determined that there is a load.

As another preferred embodiment, as described in claim 3, the counting means outputs the rectangular wave output from the comparing means within a predetermined time before and after a time point corresponding to a plurality of zero-cross points. You may make it count with. According to this, when the count value is less than the reference value, it is judged that there is a load because the pulse is interrupted near the zero cross point and the frequency is low, and when the count value is more than the reference value, the pulse is detected near the zero cross point. Since the frequency is high continuously, it is judged that there is no load or small items.

[0012]

Next, an embodiment of the present invention will be described with reference to the accompanying drawings. The first embodiment described below is based on the principle shown in FIG. 1, and the second embodiment is based on the principle shown in FIG. (1) First Embodiment FIG. 3 is an electric circuit diagram of the induction heating device according to the present invention.
A rectifier circuit 2 is connected to the AC power supply 1, a smoothing capacitor 3 is connected to the output side of the rectifier circuit 2, and a diode 5 connected between a transistor (IGBT) 4 and a collector-emitter of the transistor 4. An inverter circuit 6 composed of and is connected. A resonant circuit 9 including an induction heating coil 7 and a capacitor 8 connected in parallel to the induction heating coil 7 is connected in series to the transistor 4 of the inverter circuit 6. A control circuit 10 for controlling a drive pulse to the base is connected to the base of the transistor 4.

A resistor 1 connected in parallel with the AC power source 1.
The AC voltage extracted from between 1 and 12 is applied to the zero-cross detection circuit 13, and the zero-cross signal detected here is input to the input port of the microcomputer 14. Further, the high frequency voltage (Vc) drawn from between the resistors 15 and 16 connected to the resonance circuit 9
e) is a diode 17, a resistor 18, a smoothing capacitor 1
It is input to the reference input terminal (minus) of the comparator 22 via the smoothing circuit 21 composed of 9 and the resistor 20, and to the comparison input terminal (plus) of the comparator 22 via the diode 23 and the resistors 24 and 25. It has been entered. It should be noted that the diodes 26 and 27 are for protecting the overvoltage of the comparator input, and the diode 23 is for level matching and are not always necessary.

The output signal of the comparator 22 is input to the input port of the microcomputer 14. The microcomputer 14 uses the zero-cross signal from the zero-cross detection circuit 13 and the comparator 22.
By receiving a rectangular wave (hereinafter referred to as a pulse) from the control circuit 10 and executing a predetermined program to output a control signal to the control circuit 10, the transistor 4 is driven through the control circuit 10 to heat the load. In addition to performing control, presence / absence of load or small object detection is performed.

The presence / absence of a load or the detection of small items in the induction heating apparatus having the above circuit configuration will be described below with reference to the flow charts shown in FIGS. FIG. 4 shows a main routine, in which the operation of the 2-second timer clocked by the interrupt program of the timer interrupt 1 is soft-started in step 101, the timer interrupt 1 and the external interrupt 2 are enabled in step 102, and the step At 103, key input processing such as an on / off key and other processing are performed.

FIG. 5 shows a flow of the interrupt program of the timer interrupt 1. Here, in step 201, 2 is executed.
It is determined whether or not the time counted by the second timer has passed 2 seconds from the start-up time. If 2 seconds have not passed, the system waits, if it has passed, the nabe flag 1 is set in step 202, and the total register is set in step 203. Reset, step 20
At 4, the 4 counter is reset. In addition, nabe flag 1
Is a flag indicating that the small object detection can be started 2 seconds after the activation. Further, the total register is the total of the count values of the pulses output from the comparator 22, and the 4 counter is a counter that is incremented by 1 every time the counting of the four counting areas is completed.

FIG. 6 shows a flow of an interrupt program of the external interrupt 2. Here, in step 301, it is judged based on the zero cross signal from the zero cross detection circuit 13 whether or not there is a zero cross. If there is a zero cross, it is determined in step 302 whether or not the nabe flag 1 is set (H). If it is H, the nabe flag 2 is set in step 303. Here, the pan flag 2 is a flag indicating that the counting operation is in progress.

Next, in step 304, the operation of the 4.6 ms timer clocked by the interrupt program of timer interrupt 2 is soft-started, the count register is reset in step 305, and after waiting 1 ms in step 307, in step 306. External interrupt 1 and timer interrupt 2 are enabled.

The external interrupt 1 and the timer interrupt 2 will be described below. As shown in FIG. 7, the external interrupt 1 determines in step 401 whether the pulse from the comparator 22 has a count waveform, that is, whether the waveform has a falling edge. 1 is added to the count register to make this a count register.
The timer interrupt 2 is step 5 as shown in FIG.
At 01, it is judged by the 4.6 ms timer whether 4.6 ms has elapsed from the zero cross time point, and if it has passed, the nabe flag 2 is reset at step 502.

External Interrupt 2 Routine Step 30
Returning to step 6, as described above, here, the external interrupt 1
And the interrupt of timer interrupt 2 is enabled. Therefore, every time the count waveform is reached, the count register is added to interrupt this routine, and when 4.6 ms elapses from the zero-cross point, the nabe flag 2 is reset and the routine is interrupted.

When the timer interrupt 2 is interrupted, the pan flag 2 is reset.
In step 8, it is determined that the flag 2 is L, and step 30
9, the interrupts of the external interrupt 1 and the timer interrupt 2 are prohibited here. Then, at step 310, 1 is added to the 4 counter, at step 311 the count register is added to the total register to make it the total register, and then at step 312, it is judged whether or not the 4 counter is 4.

If the counter is not 4 in the judgment in step 312, the process returns to step 301, the counting from the next zero crossing point is restarted, and the process is repeated until the 4 counter becomes 4. If the counter is 4 in the determination in step 312, the counting in all the counting areas is completed, and therefore the process proceeds to step 313, in which it is determined whether the total registration exceeds a predetermined reference value. This reference value is 0DDH (hexadecimal number) in this embodiment.

If the total register is less than the reference value, the IH operation, that is, the induction heating operation is stopped by considering it as a pancake or a small item. If the total registration is more than the reference value, the induction heating operation is started by considering it as Nabeari. In step 316, the pan flag 2 is reset and the process ends.

According to the induction heating apparatus of this embodiment, the zero cross point of the voltage waveform of the AC power supply 1 shown in FIG.
The zero-cross signal detected by the zero-cross detection circuit 13 and indicated by (B) in FIG.
4 is input. The AC voltage is rectified and smoothed by the rectifier circuit 2 and the smoothing capacitor 3, and is converted by the transistor 4 of the inverter circuit 6 into the high frequency voltage Vce shown by (C) in the figure. Then, the high frequency voltage is applied to the resonance circuit 9 to heat the load.

On the other hand, Vce drawn from the resonance circuit 9
The voltage waveform is smoothed by the smoothing circuit 21 and has a smooth waveform as shown by (D) in FIG. Then, the smoothed waveform and the Vce high frequency voltage are compared by the comparator 22, and the pulse indicated by (E) in the figure is input to the microcomputer 14 from the comparator 22. In addition, in FIG.
It is shown as the load changed from Nabeari to Navenashi at time P. That is, after the time point P, V
The frequency of ce decreases and the residual voltage occurs at the zero cross point.

By executing the program of the microcomputer shown in the above-mentioned flow chart, at the time S as shown by (F) in FIG. 9, when 2 seconds have elapsed after the start-up, as shown in (G), the nabe flag 1 Stands, and small object detection is started. That is, as shown in (H), the nabe flag 2 is set at each time point corresponding to the zero-cross point of the AC waveform, and the nabe flag 2 is lowered after a predetermined time (4.6 ms) has elapsed. Then, as shown in (I),
Predetermined time (1 ms) since the nabe flag 2 was set
After waiting, the pulses from the comparator 22 are counted until the nabe flag 2 is cleared. The nabe flag 2 is set up four times in total, and the pulse is counted and summed up every time.

Count value of total pulse (total register)
Is compared with a predetermined reference value, and if it is larger than the reference value, it is judged to be a normal load, and if it is smaller than the reference value, it is judged to be no load or a small item. In FIG. 9, although it is not active at the time point P, in this case, since the pulse frequency decreases thereafter, the pulse frequency becomes less than the reference value, so it is determined that there is no load or a small item.

FIG. 11 shows an iron pot with a diameter of 250 mm and a diameter of 110.
The results of counting four times in each of the mm iron pan, small items, and no load (no pan) are shown. According to this, the normal load and the abnormal load are distributed on both sides of the determination reference value (0DDH), which shows that a small object or a no-load state can be reliably detected.

(2) Second Embodiment The electric circuit of the induction heating apparatus according to the second embodiment is exactly the same as that of the first embodiment shown in FIG. 3, and the program executed by the microcomputer is as shown in FIG. The 4.6 ms timer in step 304 of the flowchart shown in FIG. 6 is a 1.2 ms timer, the waiting time in step 307 is 0, and the reference value in step 313 is 0B.
DH (hexadecimal number), the direction of determination is opposite, and step 501 of the flowchart shown in FIG.
Since the flow is exactly the same except that the elapsed time in 1.2 is 1.2 ms, duplicated illustration of the electric circuit diagram and the flow chart of the second embodiment will be omitted.

Also in this embodiment, the program of the microcomputer shown in the above-mentioned flow chart is executed, and as shown in (F) of FIG. As shown by, the pan flag 1 is raised and the small object detection is started. That is, as shown in (H), the nabe flag 2 is set at each time point corresponding to the zero-cross point of the AC waveform, and the nabe flag 2 is lowered after a predetermined time (1.2 ms) has elapsed.
Then, as shown in (I), the pulse from the comparator 22 is counted while the pan flag 2 is set. The nabe flag 2 is set up four times in total, and the pulse is counted and summed up every time.

Count value of total number of pulses (total register)
Is compared with a predetermined reference value, and if there is more than the reference value, it is determined that there is no load or small items, and if it is less than the reference value, it is the normal load. In FIG. 10, there is no pulse in the vicinity of the zero cross until the time point P, but after the time point P, there is nothing. In this case, as a result of the existence of the pulse near the zero-cross point, the count value of the pulse becomes larger than the reference value, so that it is determined that there is no load or a small item.

FIG. 12 shows the results of counting 10 times in each of the four types of load conditions, as in FIG. 11 of the first embodiment. Even in this case, the judgment reference value (0BD
It can be seen that the normal load and the abnormal load are distributed on both sides of (H), and small objects and no-load conditions can be reliably detected.

When the small object detecting operation of the second embodiment is executed when the IH heating operation is stopped, when the small object detecting operation and the IH operation are started at the same time, the charge of the capacitor 3 near the zero cross for the first time is performed. Since the voltage is high and the interruption of the pulse near the first zero cross cannot be obtained accurately, only the IH operation is started from one cycle before the zero cross (hereinafter referred to as the pre-placed IH operation) and the small object detection operation is started. Good.

Further, in the small object detecting operation of the second embodiment, it is necessary to perform the IH operation in the maximum output state in order to make the cycle of the pulse waveform (E) as long as possible in order to save the processing time of the microcomputer. Yes, but I
If the H operation is suddenly performed in the maximum output state, it causes a sound generation. Therefore, it is preferable to perform the pre-position IH operation in the minimum output state.

[0035]

As is apparent from the above description, according to the present invention, the operation is not interrupted for detecting the presence / absence of a load as in the conventional case, and therefore no detection sound is generated. Further, since the presence / absence of a load and the detection of small objects are processed by software, the circuit configuration is simple and the cost is low.

[Brief description of drawings]

FIG. 1A is a view for explaining the first principle of the present invention.
It is a figure which shows the change of a drive pulse and the change of (B) Vce waveform, respectively.

FIG. 2 (A) for explaining the second principle of the present invention.
Envelope near zero cross, (B) Counting time,
(C) It is a figure which shows a counting pulse.

FIG. 3 is an electric circuit diagram of the induction heating device of the present invention.

FIG. 4 is a flowchart of a main routine of a small object detection operation by a microcomputer.

FIG. 5 is a flowchart of timer interrupt 1.

FIG. 6 is a flowchart of external interrupt 2.

FIG. 7 is a flowchart of external interrupt 1.

FIG. 8 is a flowchart of timer interrupt 2.

9 (A) AC waveform in the first embodiment, (B)
Zero cross signal, (C) Vce envelope, (D) smooth waveform, (E) pulse waveform, (F) 2s timer, (G)
3 is a time chart of a pan flag 1, (H) pan flag 2, and (I) counting pulse.

FIG. 10 (A) AC waveform in the second embodiment,
(B) Zero cross signal, (C) Vce envelope,
(D) Smooth waveform, (E) Pulse waveform, (F) 2s timer, (G) Pan flag 1, (H) Pan flag 2, (I)
It is a time chart of a counting pulse.

FIG. 11 is a diagram showing a counting result of the first embodiment.

FIG. 12 is a diagram showing a counting result of the second embodiment.

FIG. 13 is a general circuit diagram of the induction heating device.

[Explanation of symbols]

1 ... AC power supply, 2 ... rectifier circuit, 6 ... inverter circuit, 7
... induction heating coil, 8 ... capacitor, 9 ... resonance circuit, 1
4. Microcomputer (counting, judgment, control means),
21 ... Smoothing circuit, 22 ... Comparator.

Claims (3)

[Claims] 1. A resonance circuit including a rectifier circuit for converting an AC voltage into a DC voltage, an inverter circuit for converting a DC voltage from the rectifier circuit into a high frequency voltage, and an induction heating coil and a capacitor connected to the inverter circuit. In an induction heating device including: a comparison unit configured to compare a voltage waveform generated from the resonance circuit with a waveform obtained by smoothing the waveform to output a rectangular wave; and a rectangular wave output from the comparison unit to the AC Counting means for counting within a predetermined time at a time point corresponding to the zero-cross point of the voltage waveform; judging means for judging the presence or absence of a load by comparing a count value counted by the counting means with a predetermined reference value; An induction heating circuit comprising: a control unit that controls the inverter circuit based on a determination result of the determination unit. 2. The counting means counts the rectangular wave output from the comparing means within a predetermined time from the time when a certain time has elapsed from the time corresponding to a plurality of zero-cross points. Induction heating device according to. 3. The counting means counts the rectangular wave output from the comparing means within a predetermined time before and after a time point corresponding to a plurality of zero-cross points.
Induction heating device according to.