JP2006278097A - Induction heating method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating method stabilizing control of an output current from an inverter by setting the output voltage of the inverter by considering a voltage induced in a circuit by an interference magnetic field generated in a heating object. <P>SOLUTION: This induction method is used for induction-heating a heating object by an induction heating device equipped with a power supply part in which a series resonant circuit is composed for each of a plurality of induction heating coils arranged adjacently to one another, frequencies and currents thereof are synchronized with one another and power is allowed to be individually controlled. The frequency of the output current is set or controlled to a value that makes impedance calculated from inductance and capacitance set for each individual circuit inductive. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an induction heating method and an induction heating apparatus, and more particularly to an induction heating method and an induction heating apparatus in a high magnetic coupling induction heating apparatus that heats an object to be heated by arranging a plurality of induction heating coils close to each other.

  As a problem when heating an object to be heated using a plurality of induction heating coils arranged close to each other, heating the object to be heated uniformly or controlling the heating with high accuracy is cited. As a factor that hinders the solution of this problem, a mutual induction voltage generated between induction heating coils arranged close to each other is known.

  Examples of a method for suppressing the influence of mutual induction between induction heating coils in an induction heating device with high magnetic coupling and a device corresponding to the method include those disclosed in Patent Documents 1 to 3. .

  In Patent Document 1, the frequency of current input to the induction heating coils arranged close to each other is changed, and the arrangement direction (for example, the winding direction) of the coils is opposite to that of the adjacent coils, thereby causing mutual induction generated in the coils. It is disclosed to cancel the voltage. However, Patent Document 1 does not consider the size of the coil. For this reason, it is considered that the mutual induction voltage cannot be completely canceled out when it is actually applied to an induction heating device with high magnetic coupling. Further, when canceling the mutual induction voltage generated in the coil, the magnetic field for heating the object to be heated is also canceled, and it may be difficult to heat the object to be heated.

Patent Documents 2 and 3 disclose that the effects of mutual induction are eliminated by switching power supplied to a plurality of induction heating coils in a time-sharing manner. According to such a technique, the operating coil is not affected by mutual induction. However, a mutual induction voltage is still generated in the coil that is not operating. In addition, since the objects to be heated cannot be heated at the same time, heating unevenness occurs in the objects to be heated.
Japanese Patent Laid-Open No. 10-27681 JP 2000-243544 A Japanese Patent Laid-Open No. 2004-220928

  In addition to what is disclosed in Patent Documents 1 to 3, many techniques for suppressing and eliminating the influence of mutual induction generated between coils have been proposed. However, neither technique can completely suppress the influence of mutual induction in a high magnetic coupling induction heating apparatus.

Under such circumstances, the following has been elucidated by the applicant's research.
In an induction heating device with high magnetic coupling that controls a plurality of induction heating coils, the magnetic lines of force generated from each coil also affect the heating region (zone) of an object to be heated (work) in another coil. For this reason, a phenomenon occurs in which the induced electromotive force generated in the work upon receiving the magnetic field lines of one coil affects the other coils as a mutual induction voltage.

  Here, a voltage component generated in the circuit by an induced electromotive force that interferes with a heating zone corresponding to another heating coil in the workpiece and promotes heating of the workpiece (a voltage component induced in the circuit by an interference magnetic field generated in the workpiece) ) Is defined as the mutual induction voltage due to the mutual induction of the effective part (the mutual induction voltage of the effective part). The mutual induction voltage between the coils not involved in the heating of the workpiece is defined as the mutual induction voltage for the ineffective portion.

  According to the above theory, inductive heating coils arranged adjacent to each other generate a mutual induction voltage due to the mutual induction in addition to the mutual induction voltage due to the mutual induction. For this reason, the conventional control method for suppressing the mutual induction voltage for the ineffective portion cannot suppress the mutual induction voltage generated in the coil due to the unexpected mutual induction for the effective portion, and the output current from the inverter cannot be controlled. It becomes unstable.

  Therefore, an object of the present invention is to set the output voltage of the inverter in consideration of the mutual induction voltage generated by the mutual induction of the effective amount, stabilize the control of the output current from the inverter, and improve the control performance. .

  Control of the output current of the inverter is considered to be achieved by controlling the output voltage of the inverter so as to secure a voltage for obtaining a current to be turned on for the resonant element (circuit) in the circuit including the induction heating coil. It is done. In other words, the output voltage of the inverter is necessary to obtain the mutual induction voltage generated in the circuit by the mutual induction of the ineffective part, the mutual induction voltage generated in the circuit by the effective part of the mutual induction voltage, and the current input to the resonant element. It is sufficient that the value is equal to the sum of the voltage and.

  Therefore, in the induction heating method according to the present invention for achieving the above object, a series resonance circuit is configured for each of a plurality of induction heating coils arranged close to each other, and each frequency and current are synchronized and individually controlled in power. This is a method of induction heating of an object to be heated by an induction heating device equipped with a power supply unit, and the impedance calculated from the inductance and capacitance set for each circuit is output to an inductive value. It is characterized by setting or controlling the frequency of the current.

  With such an induction heating method, the output voltage from the power supply unit is always higher than the mutual induction voltage generated in the circuit. Therefore, there is no possibility that current cannot be supplied to the induction heating coil, and the induction heating device can be stably operated.

  Further, when controlling the output voltage from the power supply unit, a control equivalent value for the mutual induction voltage generated in the circuit is calculated from the current value, resistance value and interference coefficient of the circuit, and the output voltage of the output voltage is calculated as a feedforward control value. It is preferable to control so that the output voltage from the power supply unit is higher than the mutual induction voltage, reflecting the control calculation.

  According to such an induction heating method, the output voltage from the power supply unit can be set based on the feedforward control with respect to the varying mutual induction voltage. For this reason, the voltage value calculated from the impedance and the set value of the output current can be accurately ensured as the output voltage from the power supply unit. Therefore, the set output current can be output stably.

In the induction heating method as described above, it is desirable to set the impedance of the resonance circuit so that the output voltage from the power supply unit becomes a value that can obtain a desired resolution with respect to the output current. .
By such a method, the output current is hardly affected by the fluctuation of the mutual induction voltage.

  In order to achieve the above object, an induction heating apparatus according to the present invention includes a plurality of induction heating coils arranged close to each other, a series resonance circuit configured for each induction heating coil, and a frequency / current for each series resonance circuit. And an induction heating device for inductively heating an object to be heated, and based on inductance and capacitance set for each circuit. Control means for calculating a frequency at which the impedance of the resonance circuit becomes inductive and outputting the frequency as a control value for the frequency of the output current to an inverter provided in the power supply unit is provided.

  Further, in the induction heating apparatus having the above characteristics, a voltage adjustment circuit is provided on an input side of the inverter in the power supply unit, and a current adjusted in voltage via the voltage adjustment circuit is input to the inverter. The inverter is configured to adjust the frequency of the input current and output it, and the control means calculates a control equivalent value for the mutual induction voltage generated in the circuit from the current value of the circuit, the resistance value, and the interference coefficient. The feed forward control value may be reflected in the output voltage control calculation, and the value calculated by the calculation may be applied to the voltage adjustment circuit as the voltage control value.

Furthermore, in the induction heating apparatus having the above configuration, the control means calculates an impedance at which the output voltage from the inverter can obtain a desired resolution with respect to the output current, and the output current is calculated based on the impedance. It is desirable that the frequency be calculated.
According to the apparatus of the said structure, the said induction heating method can be implemented and there can exist an effect by the said induction heating method.

  Hereinafter, embodiments of the induction heating method and the induction heating apparatus of the present invention will be described with reference to the drawings. The following embodiments and examples are some embodiments and examples according to the present invention, and the present invention is not limited only to the following embodiments.

FIG. 1 shows a schematic block diagram of an induction heating apparatus according to the present invention. 1A is a plan view, and FIG. 1B is a side cross-sectional view.
The schematic configuration of the induction heating device in the present embodiment includes an object to be heated (work) 10 and induction heating coils 12, 14, 16, 18, which are provided on the lower surface side of the work 10 and heat the work 10. 20 and 22 and a power supply unit for supplying current and voltage to each induction heating coil.

  The workpiece 10 is made of a conductive material. In the present embodiment, the workpiece 10 is a circular plate-like body as shown in FIG. In order to increase the heating efficiency, it is desirable for such a workpiece 10 to employ a material having a high specific resistance per volume.

  The induction heating coils 12, 14, 16, 18, 20, and 22 are arranged close to each other in an annular shape (C-type) so as to be concentric, and will be described later to enable uniform heating of the workpiece 10. The power supply unit suppresses the mutual induction voltage generated in each induction heating coil due to the influence of the mutual induction, and the input power to each induction heating coil 12, 14, 16, 18, 20, 22 is set to be controllable. Yes.

  The power supply unit includes a voltage adjustment circuit and an inverter 32 (32a to 32f) to which a current adjusted by the voltage adjustment circuit is input. Here, the voltage adjustment circuit is, for example, a three-phase AC power source 24 that is a power source for the entire apparatus, a converter (forward converter) 26 that converts an output current from the three-phase AC power source 24 into a DC current, and an output. It means the chopper circuit 30 (30a-30f) that controls the voltage of the current to be generated. The inverter 32 is an inverse converter that controls the frequency of the output current to the induction heating coils 12 to 22 and converts the current converted into direct current by the converter 26 into alternating current and outputs the alternating current. Note that the voltage regulating circuit defined here may have other configurations.

  In the case of the induction heating apparatus of this embodiment, the inverter 32 is a series resonance type inverter, and a capacitor (capacitor) 42 is connected between the induction heating coil and the inverter 32 in series with the induction heating coil. . In addition, a transformer 38 is provided in parallel with the induction heating coil between the induction heating coil and the inverter 32, and a current transformer 36 is provided in series with the induction heating coil. The output voltage and output current can be detected. Note that the output voltage and output current from the inverter 32 detected by the transformer 38 and the current transformer 36 are fed back to a control unit 34 (34a to 34f) described later.

  The control unit 34 includes a drive control unit (not shown) that controls the drive of the inverter 32 and the chopper circuit 30, and a phase control unit that adjusts the phase of the load current (output current) that flows in the induction heating coils arranged in proximity. (Not shown) and a calculation unit (not shown) for calculating a control value based on various signals. The control unit 34 receives a current waveform supplied from the reference signal generator 28 to the induction heating coils 12 to 22, and sends a control signal to each inverter 32 and each chopper circuit 30 based on this.

  As will be described in detail later, the control unit 34 of the present embodiment calculates a frequency value at which the impedance obtained from the inductance in the circuit including the induction heating coil and the capacitance for series resonance becomes inductive, and this is calculated. It is output as a frequency control value for the inverter 32. By performing such control, the output voltage from the inverter becomes higher than the mutual induction voltage generated in the circuit, so that the operation of the induction heating apparatus is stabilized.

  Further, the control unit 34 of the present embodiment obtains a PWM (Pulse Width Modulation) control rate by PID (Proportional Integral Derivative) control considering FF (feed forward) control, and gives this as a control value of the chopper circuit 30. Thus, the output voltage from the inverter 32 is controlled. By performing such control, the control performance of the output voltage from the inverter 32 is significantly improved.

In the induction heating apparatus configured as described above, the influence of mutual induction is achieved by detecting the output current / voltage from the inverter 32, detecting the current phase difference, correcting the current phase difference, and the output current / voltage at high speed. It is possible to control the induction heating coil arranged in close proximity while suppressing the above.
The detailed circuit configuration and current control are based on a known technique (for example, JP-A-2003-17426) and a control theory described later.

  In controlling the induction heating apparatus having the above-described configuration, the mutual induction voltage generated in each circuit including the induction heating coil is the mutual induction of the ineffective portion as described in the section of the problem to be solved by the invention. And a mutual induction voltage (effective mutual induction voltage) generated by the effective mutual induction. Hereinafter, an induction heating method for stably controlling the output current from the inverter 32 in consideration of these mutual induction voltages and an induction heating method for improving the control performance of the inverter will be described.

Hereinafter, in order to simplify the description, an induction heating method in the case of performing induction heating of a workpiece in two zones will be described with reference to FIG.
In order to pass the set current (desired current) I ₁ to the circuit connected to the inverter IV ₁ , the inductance (L ₁ + Ls ₁ ) in the circuit including the induction heating coil L ₁ and the capacitance C _{1 of} the capacitor are used. it is necessary to ensure the voltage Vz of the load against the configured resonance element as an output voltage from the inverter IV _1.

となるように制御する必要がある。 When current is simultaneously supplied to the circuits connected to the inverters IV1 and IV2, an ineffective mutual induction voltage Vm and an effective mutual induction voltage Vr are generated in each circuit as shown in FIG. To do. Therefore, in order to load the voltage Vz to the resonant element, the output voltage Viv of the inverter is

It is necessary to control so that

ここで、Ｖｒ_１１とは、当該回路の電流によって誘起される電圧（有効分の電圧）を示し、Ｖｒ_２１とは有効分の相互誘導の影響により誘起される相互誘導電圧（有効分の相互誘導電圧）を示し、Ｖｒ_１はその和を示す。また、ｋは無効分の相互誘導の結合係数であり、αは有効分の結合係数である。また、Ｒｗはワークの等価抵抗を示す。 An ineffective mutual induction voltage Vm ₂₁ and an effective mutual induction voltage Vr ₂₁ that interfere with the circuit connected to the inverter IV ₁ can be expressed as Equation 2.

Here, Vr ₁₁ indicates a voltage (effective voltage) induced by the current of the circuit, and Vr ₂₁ indicates a mutual induction voltage (effective mutual induction) induced by the mutual induction effect. Voltage), and Vr ₁ indicates the sum. Further, k is a mutual induction coupling coefficient for ineffective parts, and α is a coupling coefficient for effective parts. Rw represents the equivalent resistance of the workpiece.

と表すことができる。すなわち、共振素子のインピーダンスＺが定まれば、回路に対して所望する電流値Ｉを供給するために必要とする電圧Ｖｚが求まる。ここで、共振素子を構成するインダクタンスＬに係るインピーダンスＺ_Ｌと、キャパシタンスＣに係るインピーダンスＺ_Ｃはそれぞれ、

と表すことができる。よって回路内の共振素子（共振回路）のインピーダンスＺは、

となる。ここで、ｊは虚数を表し、Ｌ、Ｃはそれぞれ定数であるから、Ｚを定めるには周波数ωを制御すれば良いこととなる。 Further, since the voltage Vz desired for the resonant element is the impedance Z of the resonant element × current value I input to the circuit, Equation 1 is

It can be expressed as. That is, when the impedance Z of the resonant element is determined, the voltage Vz necessary for supplying the desired current value I to the circuit can be obtained. Here, the impedance Z _L related to the inductance L constituting the resonant element and the impedance Z _C related to the capacitance _C are respectively

It can be expressed as. Therefore, the impedance Z of the resonant element (resonant circuit) in the circuit is

It becomes. Here, j represents an imaginary number, and L and C are constants. Therefore, in order to determine Z, the frequency ω may be controlled.

となる。この場合、Ｖｉｖ_１は相互誘導電圧の総和（Ｖｍ_２１+Ｖｒ_２１）よりも必ず高い値となる。一方、インピーダンスＺが容量性となった場合のインバータＩＶ_１からの出力電圧Ｖｉｖ_１の設定値を表すと、

となる。この場合、インバータＩＶ_１からの出力電圧Ｖｉｖ_１の設定値は相互誘導電圧の総和（Ｖｍ_２１+Ｖｒ_２１）よりも低い値となってしまう（図３参照）。こうした場合、電流がインバータ側に逆流し、装置の故障原因となることがある。したがって、インバータＩＶ_１は、出力電流の周波数を定めるにあたり、インピーダンスＺ_１が誘導性となるように設定、又は制御する必要がある。また、インピーダンスＺ_１が誘導性となるように設定、又は制御することにより、インバータからの出力電圧が回路内に発生する相互誘導電圧の総和よりも高い値となるため、誘導加熱装置の運転が安定する。 Here, it is considered that the impedance Z is inductive (plus) and capacitive (minus). When the impedance Z is inductive, the set value when calculating the output voltage Viv ₁ from the inverter IV ₁ In the above Equation 2,

It becomes. In this case, Viv ₁ is always higher than the sum of the mutual induction voltages (Vm ₂₁ + Vr ₂₁ ). On the other hand, when the set value of the output voltage Viv ₁ from the inverter IV ₁ when the impedance Z becomes capacitive,

It becomes. In this case, the set value of the output voltage Viv ₁ from the inverter IV ₁ becomes a value lower than the sum of the mutual induction voltage _{(Vm 21} + _{Vr 21)} (see FIG. 3). In such a case, the current flows backward to the inverter side, which may cause a failure of the device. Therefore, the inverter IV ₁ needs to be set or controlled so that the impedance Z ₁ is inductive when determining the frequency of the output current. Further, set as the impedance Z ₁ is inducible, or by controlling, the output voltage from the inverter is higher than the sum of the mutual induction voltage generated in the circuit, the operation of the induction heating device Stabilize.

が成り立てば良い。この式を周波数ωについて解くと、

となる。すなわち、数式９が成り立つようにインバータの出力周波数ωを定めることにより、インピーダンスＺ_１を誘導性とすることができる。そして、周波数ωを設定、又は制御して所望のインピーダンスＺ_１を定めることにより、共振回路への投入電流Ｉ_１に対する電圧値Ｖｚが定まる。これにより、インバータの出力電圧Ｖｉｖ_１が求まるため、電源部はインバータの出力電圧がＶｉｖ_１となるようにチョッパ回路３０にて出力電圧の制御を行うことにより、インバータ３２からの出力電流Ｉ_１を安定させることが可能となる。 Here, in order to make the impedance Z ₁ inductive,

Should be established. Solving this equation for frequency ω

It becomes. In other words, the impedance Z ₁ can be made inductive by determining the output frequency ω of the inverter so that Equation 9 is satisfied. Then, by setting or controlling the frequency ω to determine the desired impedance Z ₁ , the voltage value Vz with respect to the input current I ₁ to the resonance circuit is determined. As a result, since the output voltage Viv ₁ of the inverter is obtained, the power supply unit controls the output voltage by the chopper circuit 30 so that the output voltage of the inverter becomes Viv ₁ , thereby obtaining the output current I ₁ from the inverter 32. It becomes possible to stabilize.

In order to stably output the input voltage Viv ₁ for stably controlling the input current I ₁ to the circuit calculated as described above, the control unit 34 performs PID considering FF (feed forward) control. By determining a PWM (Pulse Width Modulation) control rate by (Proportional Integral Derivative) control and giving this as a control value of the chopper circuit 30, the output voltage Viv ₁ from the inverter 32 is controlled (see FIG. 4).

となる。ここで、Ｖ_ＤＣ１はコンバータ２６から出力される直流電流の電圧を示す。また、ＰＷＭ制御率とは、チョッパ回路のＯＮ／ＯＦＦ周期：ＴにおけるＯＮ時間：ｔの割合（ｔ／Ｔ）のことをいう。すなわち、コンバータ２６からの出力電圧Ｖ_ＤＣ１をチョッパ回路に入力し、チョッパ回路にてＰＷＭ制御率に従った出力制御を行うことで、インバータからの出力電圧がＶｉｖ_１となるように制御するのである。したがって、ＰＷＭ制御率の精度によりインバータ３２からの出力電圧Ｖｉｖ_１の制御精度が変わることとなる。 In this case, the output voltage Viv ₁ from the inverter is

It becomes. Here, V _DC1 indicates the voltage of the direct current output from the converter 26. Further, the PWM control rate refers to the ratio (t / T) of the ON time: t in the ON / OFF cycle: T of the chopper circuit. That is, the output voltage V _DC1 from the converter 26 is input to the chopper circuit, and output control according to the PWM control rate is performed by the chopper circuit so that the output voltage from the inverter becomes Viv _1. . Therefore, the control accuracy of the output voltage Viv ₁ from the inverter 32 varies depending on the accuracy of the PWM control rate.

In this embodiment, the PWM control rate is calculated by the following method. For example, a PWM control rate at a certain time n: PWM _n can be expressed as Equation 11.

Here, FFcr _n−1 and FFcr _n are PWM control equivalent values (cr: contain reading) given to the feedforward voltage (FF), respectively. I _set is a target (set) value of the current to be input to the circuit, and I _1n is a current value to be input to the circuit at a certain time n. Note that k _i and k _p represent an integral gain and a proportional gain, respectively.

The voltage acquired as the feed forward voltage (FF) in Formula 11 is the sum of the mutual induction voltage for the ineffective portion and the mutual induction voltage for the effective portion. Accordingly, the feedforward voltage FF _n at a certain time n can be expressed as follows.

As described above, when calculating the ON time control rate (PWM control rate) in the ON / OFF control of the chopper circuit 30 that controls the inverter voltage Viv ₁ , By giving a control value corresponding to the sum total voltage as a feedforward value, stable control of the output voltage Viv ₁ of the inverter becomes possible. What should be noted here is that the control value given as the feedforward value includes the control equivalent value for the effective mutual induction voltage. As described above, the control value of the control system is remarkably improved by reflecting the fluctuation value (control equivalent value for the effective mutual guidance) that has not been considered in the past as a feedforward value in the calculation.

Further, in the induction heating method and apparatus according to this embodiment, FIG. 5 (A), the by increasing the value of the impedance Z ₁ (B), the change in Viv ₁ to variations of input current I ₁ growing. In other words, the change of the input current I ₁ with respect to the fluctuation of Viv ₁ is small.

That is, the resolution of the output current I ₁ by the output voltage Viv ₁ from the inverter 32 can be improved by improving the set value of the impedance Z ₁ . Further, even if the sum of the mutual induction voltages fluctuates due to the influence of the mutual induction and the input voltage Vz to the resonance circuit fluctuates, the influence on the output current I ₁ from the inverter 32 is reduced. Heating control is stable.

It is a figure which shows schematic structure in the induction heating apparatus of this invention. It is a block diagram which shows the relationship of the mutual induction in 2 zones. It is a figure which shows the change of the output voltage by the difference in impedance. It is a block diagram of the power supply part and control unit in an induction heating apparatus. It is a figure which shows the relationship between the change of the output voltage from an inverter, and the change of an impedance.

Explanation of symbols

  10 ......... Substance to be heated (workpiece) 12, 14, 16, 18, 20, 22 ......... Induction heating coil, 24 ......... Three-phase AC power supply, 26 ......... Forward converter (converter), 28 Reference signal generator, 30 (30a to 30f) ... Chopper circuit, 32 (32a to 32f) ... Inverter (inverter), 34 (34a to 34f) ... Control unit.

Claims (6)

A series resonance circuit is configured for each of a plurality of induction heating coils arranged close to each other, and an object to be heated is induced by an induction heating device having a power supply unit that can synchronize each frequency and current and individually control power. A method of induction heating,
An induction heating method, wherein the frequency of an output current is set or controlled to a value at which an impedance calculated from an inductance and a capacitance set for each circuit is inductive. When controlling the output voltage from the power supply unit,
The control equivalent value for the mutual induction voltage generated in the circuit is calculated from the current value and resistance value of the circuit and the interference coefficient,
Reflected in the control calculation of the output voltage as a feedforward control value,
The induction heating method according to claim 1, wherein the output voltage from the power supply unit is controlled to be higher than the mutual induction voltage.   The impedance of the resonance circuit is set so that an output voltage from the power supply unit becomes a value that can obtain a desired resolution with respect to an output current. Induction heating method. A plurality of induction heating coils arranged close to each other, a series resonance circuit configured for each induction heating coil, and a power supply unit that can synchronize frequency and current for each series resonance circuit and individually control power And an induction heating device for induction heating an object to be heated,
Control that calculates the frequency at which the impedance of the resonant circuit becomes inductive based on the inductance and capacitance set for each circuit, and outputs the frequency to the inverter provided in the power supply unit as a control value for the frequency of the output current An induction heating apparatus comprising means. A voltage adjustment circuit is provided on the input side of the inverter in the power supply unit, and the current that has been subjected to voltage adjustment is input to the inverter through the voltage adjustment circuit, and the inverter adjusts the frequency of the input current. It is configured to output,
The control means calculates a control equivalent value for the mutual induction voltage generated in the circuit from the current value, resistance value, and interference coefficient of the circuit, reflects it in the control calculation of the output voltage as a feedforward control value, and calculates by the calculation The induction heating apparatus according to claim 4, wherein the measured value is provided to the voltage adjustment circuit as a voltage control value.   The control means is configured to calculate an impedance at which the output voltage from the inverter can obtain a desired resolution with respect to the output current, and to calculate the frequency of the output current based on the impedance. The induction heating device according to claim 4 or 5.

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