JP2002124368A - Control method of induction heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method that can change the heating power over a wide range by reducing the electromagnetic noise in the induction heating device, in which inverters that supply high-frequency power individually, to each of the plural sets of resonance load circuits, are installed in the same case. SOLUTION: Power factor for the high-frequency power that is outputted by the inverter main circuits 51, 52 is made capable of operating in both the directions of gain or loss, and by this operation the frequency of the high-frequency power is made lie within a prescribed range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an induction heating apparatus comprising a plurality of sets of a resonance load circuit and an inverter for supplying high-frequency power to the resonance load circuit, which are installed close to each other.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional example of this type of induction heating apparatus in which two inverters are arranged in the same housing and each of the inverters is supplied to a high frequency power supply of an electromagnetic cooker. Reference numeral 1 denotes a single-phase AC power supply such as a commercial power supply, 2 denotes an induction heating device fed from the AC power supply 1, and 3 and 4 denote pots each of which is induction-heated by the induction heating device 2.

A rectifier circuit 21 as one inverter, a filter capacitor 22, an IG
An inverter main circuit 23 having an antiparallel circuit of a BT and a diode as an upper and lower arm, a heating coil 24 forming one resonance load circuit, resonance capacitors 25 and 26, a rectifier circuit 31 serving as the other inverter, and a filter capacitor 3
2, an inverter main circuit 33 having an antiparallel circuit of an IGBT and a diode as an upper and lower arm, a heating coil 34 forming the other resonance load circuit, and resonance capacitors 35 and 36. The filter capacitors 22 and 32 are provided for the purpose of lowering the high-frequency impedance of the rectifier circuits 21 and 31, respectively.

A conventional control method of the induction heating apparatus shown in FIG. 4 will be described below with reference to a characteristic diagram of an operation trajectory shown in FIG.

FIG. 5 shows a heating coil (reference numeral 24 or 3).
4) and a resonance capacitor (reference numeral 25, 26 or 35,
36) is a characteristic diagram showing a relationship between the frequency of the high-frequency power supplied to the resonant load circuit composed of 36) and a pot (reference numeral 3 or 4) and the active power injected into the load circuit.
Assuming that the characteristic on the right side of the drawing is the pan 3 side and the characteristic on the left side of the drawing is the pan 4 side, the frequency of the peak point in each characteristic is the resonance frequency of each resonance load circuit, and the frequency of the high-frequency power output from each inverter. When the frequency is higher than the resonance frequency, the power factor of the high-frequency power is in a lag region, and when the frequency is lower, the power factor is in a leading region.

In the conventional control method of the induction heating apparatus shown in FIG. 4, by changing the frequency of the high frequency power output from each inverter in the delay region,
The active power component injected into the resonance load circuit, that is,
Adjusting the heating power to the pot 3 or 4 to a desired value has been performed.

[0007]

According to the above-described conventional method for controlling an induction heating device, the pots 3 and 4 having different resonance frequencies are used.
Are placed close to each other and heated at the same time, the pan 3 or the pan 4 is heated with the high-frequency power of the frequency indicated by the triangle or the circle indicated in FIG.
The heating power reaches the rated value, but the difference in frequency at this time, or the difference in the frequency of the high-frequency power output from each inverter during simultaneous heating of the pot 3 and the pot 4, generates an electromagnetic sound, In particular, when the difference is several kHz, the electromagnetic sound sometimes gives discomfort to the surrounding people.

As a measure to alleviate this discomfort, while heating the pots 3 and 4 at the same time when the respective heating powers are equal to or more than a predetermined value, the difference between the frequencies of the high-frequency powers output from the respective inverters is determined. For example, it is effective to set the frequency to 1 kHz or less, but in the conventional control method in which the power factor of the high-frequency power output from the inverter is operated only in the delay region, the difference between the frequencies of the high-frequency powers output from the respective inverters is reduced. If the frequency is set to 1 kHz or less, the desired heating power cannot be obtained depending on the type of the pan, and as a result, there is a problem that the cooking time of at least one of the pans becomes extremely long.

An object of the present invention is to solve the above-mentioned problems and to provide an induction heating apparatus capable of obtaining desired heating power for each pot while keeping the frequency of high-frequency power output from each inverter within a predetermined range. It is to provide a control method.

[0010]

According to a first aspect of the present invention, there is provided an induction heating apparatus comprising a plurality of sets of a resonance load circuit and an inverter for supplying high-frequency power to the resonance load circuit, which are installed close to each other. Of the high-frequency powers, the active power component of which is equal to or more than the lower limit value is at least 2
When a set is present, the power factor of the high-frequency power is controlled so as to be within a predetermined range so that the frequency of the high-frequency power output from these inverters is within a predetermined range. The control method is performed.

According to a second aspect of the present invention, in the induction heating apparatus, when there are at least two sets of inverters whose active power component is equal to or more than a lower limit value among the respective high-frequency powers, the frequency of the high-frequency power output from these inverters So as to be within a predetermined range, while controlling the power factor of the high-frequency power over both the leading and lagging regions, and the frequency of the high-frequency power at which the active power components of the respective high-frequency powers are substantially equal. When a smaller active power component is supplied, a control method characterized by mutually controlling such a frequency is maintained.

Further, a third invention is the control method of the induction heating apparatus according to the second invention, wherein, when the active power component of each high-frequency power is smaller than the lower limit, the control method is performed at the lower limit. It is characterized in that control is performed to change the frequency of the high-frequency power output from each inverter from the frequency of the high-frequency power.

The present invention has been made by paying attention to the following.

That is, when the power factor of the high-frequency power output from the inverter is in the advanced region, as is well known, a diode connected in anti-parallel to the self-extinguishing element constituting the main circuit of the inverter has a relatively large value. A reverse recovery current flows during the reverse recovery period.

Therefore, by using an inverter using a diode that allows the reverse recovery current, the inverter can operate over a region where the power factor of the output high-frequency power is advanced or delayed. By doing so, the frequency of the high-frequency power output from each inverter is within a predetermined range, while reducing the aforementioned electromagnetic noise,
Desired heating power can be supplied to the pan.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing an embodiment of the present invention in which two inverters are arranged in the same housing and each of the inverters is supplied to a high-frequency power supply of an electromagnetic cooker. The components having the same functions as those of the conventional configuration shown in FIG. 4 are denoted by the same reference numerals.

That is, the point that the circuit configuration of the induction heating apparatus 5 shown in FIG. 1 is different from the circuit configuration shown in FIG. 4 is that the inverter main circuits 51 and 33 are replaced with the inverter main circuits 51 and 33.
52.

As the diodes connected in reverse parallel to the IGBTs constituting the inverter main circuits 51 and 52, a diode having a rating that allows the above-described reverse recovery current, a first recovery diode that can reduce the reverse recovery current, and the like are selected. ing. As a result, the heating coil (reference numeral 2)
4 or 34), a resonance capacitor (reference number 25, 26 or 35, 36), and a pan (reference number 3 or 4). , And high-frequency power having a frequency ranging from the inverter main circuits 51 and 52 can be supplied.

A control method according to a first embodiment of the present invention in the induction heating apparatus shown in FIG. 1 will be described below with reference to a characteristic diagram of an operation trajectory shown in FIG.

FIG. 2 shows the induction heating device 5 shown in FIG. 1 in which a heating coil (reference numeral 24 or 34), a resonance capacitor (reference numeral 25, 26 or 35, 36) and a pot (reference numeral 3 or 4). FIG. 5 is a characteristic diagram of an operation trajectory showing a relationship between the frequency of high-frequency power supplied to the resonant load circuit and the active power injected into the load circuit, and is similar to the characteristic diagram shown in FIG. The characteristic on the right side of the paper is the pot 3 side,
The characteristic on the left side of the drawing is the pot 4 side.

That is, in the control method according to the first embodiment of the present invention, in order to keep the frequency of the high-frequency power output from each of the inverter main circuits 51 and 52 within a predetermined range, both inverters operate in the delay region. If the frequency is less than the predetermined range, for example, 1 kHz, the operation is continued as it is, and if the frequency exceeds the predetermined range, for example, by the same applicant, As described in Japanese Patent Application No. 127327/2000, the frequency when a predetermined heating power is supplied to both pans while the pans 3 and 4 are placed, and the voltage and current of the high-frequency power at this time According to the characteristics shown in FIG. 2, the inverter on the pot 3 operates in the above-mentioned advance region, and the inverter on the pan 4 operates in the above-described delay region. At this time, the inverter main circuits 51 and 52
PWM (pulse width modulation) control and PFM for each
(Pulse frequency modulation) control, the pulse train signal obtained by the PWM control or the PFM control of the combined result is further thinned out, and the inverter main circuit 51,
52, the active power component injected into the resonance load circuit, that is, the heating power to the pan 3 or the pan 4 also passes through the operation locus of the thick solid line shown in FIG. Can be

As a result, the heating power to the pan 3 or the pan 4 reaches the rated value with the high-frequency power of the frequency indicated by the triangle mark or the circle mark shown in FIG. 2, but the difference in the frequency at this time is also small. Can be

In the induction heating apparatus shown in FIG. 1, when only one of the pot 3 and the pot 4 is in the heating state, the above-mentioned electromagnetic sound is not generated. May be operated in the above-mentioned delay region, and the level for detecting the heating state (the lower limit shown in FIG. 2) is preferably 5 to 10% of the rated value of the heating power. For this detection, the inverter main circuit 51,
What is necessary is just to monitor the input power to each 52, the set value of the heating power commanded to this induction heating device, and the like.

A control method according to a second embodiment of the present invention in the induction heating apparatus shown in FIG. 1 will be described below with reference to a characteristic diagram of an operation trajectory shown in FIG.

FIG. 3 shows the characteristics of the induction heating device 5 shown in FIG. 1 in the same manner as the characteristic diagram shown in FIG. I do.

That is, in the control method according to the second embodiment of the present invention, similarly to the characteristic diagram of FIG. Will be operated in the delay region. At this time, by using both PWM (pulse width modulation) control and PFM (pulse frequency modulation) control for each of the inverter main circuits 51 and 52, the frequency of the high-frequency power output from each of the inverter main circuits 51 and 52 can be reduced. It can be within a predetermined range, and at the same time, the active power component injected into the resonance load circuit, that is, the heating power to the pot 3 or the pot 4 can be set to a desired value.

As a result, in the heating power from the frequency indicated by the triangle mark or the point indicated by the circle shown in FIG. 3 to the point A shown in FIG. 3 (the point at which both frequencies become substantially equal), the characteristic shown in FIG. The operation is the same as that shown in the drawing, except that from the point A to the point B (the lower limit point) shown in FIG.
PWM control is performed so that the operation locus of the high-frequency power output from the power supply 1 or 52 is fixed, and the pulse train signal obtained by the PWM control is further decimated to obtain the inverter main circuit 51. Or, by operating 52, the difference in frequency at this time can be made substantially zero while the heating power to the pan 3 or the pan 4 is set to a desired value.

Here, when at least one of the heating powers is set below the point B (point of the lower limit value) from the state of operating at the frequency between the points A and B, If PWM control is to be performed with the heating power at the frequency between the points A and B, the ON period of the IGBTs constituting the inverter main circuits 51 and 52 becomes shorter. The operation of the inverter main circuits 51 and 52 may become unstable due to a delay in the control operation or the like.
While ensuring the ON period of the IGBT at the point,
The operation is shifted to the PFM control as indicated by the operation locus indicated by the bold broken line below the point. Here, the motion trajectory by the PFM control that is higher than the frequency at the point B corresponds to the pan 4, and the motion trajectory by the PFM control that is lower than the frequency corresponds to the pan 3. As a result, a sudden change in the frequency of the high-frequency power when passing the lower limit is avoided.

In the operation trajectory shown in FIG. 3, different frequencies are used in the range from the frequency at the rated power (the frequency of the point marked with ◇ <the frequency of the point marked with ○) to the point A. But depending on the type of pot,
In some cases, the condition of “frequency at the leading power factor operation side at rated heating power <frequency at lagging power factor operation side at rated heating power” may be satisfied. When this condition is satisfied, each heating power is at the rated power But the inverter main circuits 51 and 5
It is possible to set the operation trajectory at the time of the point B or more to make the frequency of the high-frequency power output from the point 2 substantially equal,
As a result, the aforementioned electromagnetic noise can be further reduced.

[0030]

According to the control method of the induction heating apparatus of the present invention, it is possible to obtain desired heating power for each pot while keeping the frequency of the high-frequency power output from each inverter within a predetermined range. it can. As a result, it is possible to provide an electromagnetic cooker suitable for heating a plurality of pots placed close to each other simultaneously.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an induction heating device showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating an operation trajectory according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram illustrating an operation trajectory according to a second embodiment of the present invention.

FIG. 4 is a circuit configuration diagram of an induction heating device showing a conventional example.

FIG. 5 is a characteristic diagram illustrating an operation locus of FIG. 5;

[Explanation of symbols]

1: AC power supply, 2, 5: induction heating device, 3, 4: pan, 2
1, 31 ... rectifier circuit, 22, 32 ... capacitor, 23,
33, 51, 52 ... inverter main circuit, 24, 34 ... heating coil, 25, 26, 35, 36 ... resonance capacitor.

 ──────────────────────────────────────────────────の Continued on the front page F term (reference) 3K051 AA02 AA07 AB05 AC09 AC12 AC18 AC54 AD23 AD39 BD02 CD22 3K059 AA02 AA07 AB04 AC09 AC12 AC18 AC54 AD23 AD39 BD02 CD22

Claims (3)

[Claims] 1. An induction heating apparatus comprising a plurality of sets of a resonance load circuit and an inverter for supplying high-frequency power to the resonance load circuit, and these are installed in close proximity to each other. When there are at least two sets of inverters having the lower limit or more, the power factor of the high-frequency power over both the leading and lag ranges is set so that the frequency of the high-frequency power output from these inverters falls within a predetermined range. A method for controlling an induction heating device, characterized by controlling each other. 2. An induction heating apparatus comprising a plurality of sets of a resonance load circuit and an inverter for supplying high-frequency power to the resonance load circuit, wherein the active power component of each high-frequency power is When there are at least two sets of inverters having the lower limit or more, the power factor of the high-frequency power over both the leading and lag ranges is set so that the frequency of the high-frequency power output from these inverters falls within a predetermined range. Induction heating characterized by controlling each other and, when supplying a smaller active power component at the frequency of the high-frequency power at which the active power components of the respective high-frequency powers are substantially equal to each other, maintaining this frequency. How to control the device. 3. The method of controlling an induction heating device according to claim 2, wherein, when the effective power component of each of the high-frequency powers is less than the lower limit, the frequency of the high-frequency power at the lower limit Controlling the frequency of the high-frequency power output from each inverter to each other.