JP2015035361A - Induction heating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating apparatus that has a plurality of heating coils approximated to each other with respect to a heated member and respectively corresponding resonance type power supplies and that enables high power factor operation by reducing variation in displacement of a phase angle of each resonance type power supply even at frequency control.SOLUTION: An induction heating apparatus is configured so that respective induction heating coil power supplies are synchronized with each other, resonance sharpness (=an inductive reactance/an equivalent resistance) of the induction heating coils becomes substantially the same at all coils after execution of reduction in mutual induction between respective zones by a reverse coupling inductance for reducing mutual induction between coils, and phases of self-resonance circuits each configured by a resonance capacitor become substantially the same at all coils. When an output phase of each power supply is changed by a change in the equivalent resistance accompanying heating of the heated object, a high power factor operation is performed by controlling so that each power supply output is within a predetermined phase angle range, by common frequency control.

Description

  The present invention relates to an apparatus for heating a member to be heated by induction heating, and more particularly to an induction heating apparatus suitable for heating a heating target zone corresponding to each heating coil after arranging a plurality of heating coils close to each other.

  Conventionally, it has been known that induction heating is effective as means for rapid heating. In an induction heating apparatus that employs one heating coil for a member to be heated, induction reactance and equivalent due to changes in the state of the member to be heated (for example, changes that occur when the member to be heated is heated from room temperature to high temperature) The phase angle is controlled so that the maximum power factor and ZVS (Zero Voltage Switching) can be secured by controlling the frequency with respect to the output phase change of the resonance type power supply caused by the change in resistance.

  However, in the induction heating apparatus having such a configuration, the temperature distribution of the heated member is likely to vary, and it is difficult to cope with the heated member that requires uniform temperature control. For this reason, the structure which arrange | positions the heating coil divided | segmented into plurality with respect to one to-be-heated member, and provides a resonance type power supply for each heating coil was proposed. However, in this case, there is a problem in that the influence of mutual induction occurs between the heating coils arranged close to each other, and it becomes impossible to control the power supplied to each heating coil. With respect to such a problem, in Patent Document 1, the frequency of the current supplied to each heating coil is made the same, and the phase of the current supplied to each heating coil is synchronized to avoid the influence of mutual induction. The control is realized.

  However, in such a configuration, it is necessary to make the frequency of the output current from each resonance type power supply the same, so frequency control cannot be performed for each resonance type power supply. For this reason, when the frequency control is performed according to the state change of the heated member, the phase angle between the output current and the output voltage is greatly changed, and the power factor is lowered to generate a predetermined output. There is a case where a resonance type power supply disappears or a switching loss increases due to hard switching at a high frequency.

  In response to the deterioration of the power factor, instead of increasing the converter capacity of the inverter, as disclosed in Patent Document 2, between the heating coil and the resonance type power source, the mutual generated between the heating coils. It has been proposed to reduce the output phase angle and improve the power factor by providing an inductance (reverse coupling inductance) that causes mutual induction of induction and reverse polarity.

  Patent Document 3 discloses a technique for adjusting the output phase angle of a plurality of resonant power sources by frequency control.

JP 2005-529475 A JP 2004-259665 A JP 2011-14331 A

  If the technique disclosed in Patent Document 2 is applied to the technique disclosed in Patent Document 1, it is considered that the influence of mutual induction can be reduced. However, the problem based on the frequency adjustment of the resonance type power supply with respect to the state change of the heated member cannot be dealt with.

  In addition, the technique disclosed in Patent Document 3 is simply a resonance in which the output phase angle of the resonant power source connected to all the heating coils can perform the most efficient operation for a given frequency. It is made to operate according to the frequency of the mold power supply, and the output from the reference resonance power supply is matched with the output from the other resonance power supply, thereby suppressing output variations. For this reason, high-efficiency operation cannot be performed, and when the output phase angle becomes too large, it is described that the operation is stopped, and no solution has been taken.

  Therefore, in the present invention, in an induction heating apparatus having a plurality of heating coils close to each other and a resonance type power supply corresponding to each member to be heated, the displacement of the output phase angle of each resonance type power supply also during frequency control It is an object of the present invention to provide an induction heating device that enables high power factor operation by reducing the variation of.

  In order to achieve the above object, an induction heating apparatus according to the present invention includes a member to be heated, a plurality of heating coils arranged in close proximity to each other, and each heating coil individually connected, and synchronous control of each current value and current waveform. In the induction heating apparatus having a resonance type power source capable of performing the above, the ratio of the inductive reactance and the equivalent resistance of the resonance circuit composed of each heating coil, the heated member, and the resonance capacitor is matched or approximated. .

  In addition, the induction heating apparatus having the above-described characteristics has the same or approximate ratio of the inductive reactance and the equivalent resistance. The heating area of the heated member to be heated in each heating coil, and each heating It is good to make it by making the geometric relationship with a coil the same.

  In addition, in the induction heating apparatus having the above-described characteristics, it is desirable that the phase of the resonance circuit formed by each of the heating coils, the heated member, and the resonance capacitor is the same in all the self-resonance circuits.

  The induction heating apparatus having the above-described characteristics may be provided with a reverse coupling inductance for reducing mutual induction between the heating coils.

  Furthermore, the induction heating apparatus having the above-described characteristics may include control means for commonly controlling the frequency so that the phase angle between the output voltage and the output current of each of the resonance type power supplies falls within a predetermined range. desirable.

  According to the induction heating device having the characteristics as described above, in the induction heating device having a plurality of heating coils close to each other and the resonance type power supply corresponding to each member to be heated, It is possible to reduce the variation in the displacement of the output phase angle of the resonance type power supply and enable high power factor operation.

It is a graph which shows the relationship between the frequency change and phase change in the self-resonance circuit from which resonance sharpness differs. It is a figure for demonstrating briefly the induction heating apparatus which concerns on embodiment, (A) is front sectional drawing, (B) is a side view. BRIEF DESCRIPTION OF THE DRAWINGS It is the induction heating apparatus relevant to embodiment, Comprising: It is a figure explaining the case where the length of a to-be-heated member is shortened with respect to a heating coil, (A) is front sectional drawing, (B) is a side view. is there. It is a figure for demonstrating the structure of the induction heating apparatus which concerns on embodiment, (A) is front sectional drawing, (B) is a side view. It is an equivalent circuit diagram which shows the structure of the induction heating apparatus which concerns on embodiment. It is an equivalent circuit diagram which shows a structure in the case of providing a reverse coupling inductance between self-resonant circuits provided with the heating coil arrange | positioned adjacently. It is a figure which shows the relationship between the voltage waveform and current waveform in two self-resonance circuits which are implementing ZVS control, performing current synchronous control. In two self-resonant circuits that perform ZVS control while performing current synchronous control, the voltage waveform and current waveform when the frequency of the output current is changed after matching the Q values in the two self-resonant circuits It is a figure which shows the relationship. In two self-resonant circuits performing ZVS control while performing current synchronous control, voltage waveforms and current waveforms when the frequency of the output current is changed when the Q values in the two self-resonant circuits are separated It is a figure which shows the relationship.

  Hereinafter, embodiments of the induction heating apparatus and the induction heating method of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, even if two self-resonant circuits performing current synchronous control under a mutual induction environment, if the resonance sharpness Q (hereinafter referred to as Q value) is different, the operating frequency (output current) Difference in the output phase angle with respect to the frequency). Specifically, the amount of change in the output phase angle with respect to the change in operating frequency is higher in a circuit having a high Q value (a circuit indicated by Q = 10) than in a circuit having a low Q value (a circuit indicated by Q = 5). It can be read that it is large.

  For this reason, in the induction heating apparatus performing current synchronous control, when performing frequency control, it can be understood that it is desirable to align the Q values in the respective self-resonant circuits. Hereinafter, the reason why the output phase angle changes due to the difference in the Q value in each self-resonant circuit and the means for aligning the Q value in each self-resonant circuit will be described.

  First, in two induction heating circuits in a mutual induction state as shown in FIG. 5, output voltages Viv1 and Viv2 from the respective inverters INV1 and INV2 required to obtain power for heating the object to be heated. Is a combination of self-resonant circuit voltages (Vs1, Vs2) and mutual induction voltages (Vm21, Vm12), as shown in equations 1 and 2, respectively. Here, the self-resonant circuit refers to a circuit including a heating coil, a resonant capacitor, a wiring path, and the like.

In the circuit configured as described above, the operating state of the inverter in the mutual induction environment is
... Formula 1
Can be shown. In addition, Formula 1 shows the operation state in the inverter INV1. In Equation 1, θiv1 represents a phase difference between the output voltage Viv1 of the inverter INV1 and a reference position (reference signal). Θi1 and θi2 are the phase differences between the inverter currents Iiv1 and Iiv2 and the reference signal, and θs1 is the phase angle of the combined voltages Vs1 and Vs2 of the self-resonant circuit with respect to the inverter currents Iiv1 and I2iv. Furthermore, θm is a phase angle of the mutual induction voltages Vm21 and Vm12 with respect to the inverter currents Iiv1 and Iiv2.

In Equation 1, when the currents between adjacent heating coils are synchronized, θi1 = θi2 = 0.
... Formula 2
Can guide you.

In the induction heating apparatus shown by an equivalent circuit as shown in FIG. 5, the impedance Zs1 of a specific self-resonant circuit and the mutual induction impedance Zm for the specific self-resonant circuit are respectively
... Formula 3
... Formula 4
Can be shown.

Here, when the coupling coefficient k in Expression 4 is small, the value of Zm is extremely smaller than the value of Zs1 (Zm << Zs1). Therefore, assuming that Zm≈0, Equation 2 is
... Formula 5
Can be expressed as follows.

Here, θs1 and θs2 are
... Formula 6
... Formula 7
It is expressed. Expressing this using the resonance sharpness Q, from the relationship of XL1 = Q1 × R1 × (F / F ₀ ) and XC1 = Q1 × R1 / (F / F ₀ ),
... Formula 8
... Formula 9
Will hold. In Equations 6 and 7, F ₀ is a frequency at the natural resonance point, and F is a specific frequency when synchronizing the phase angle of the current in each self-resonant circuit in the output current Iiv of the inverter. Q1 and Q2 are resonance sharpnesses, respectively.

  It can also be read that the values of θs1 and θs2 are different when the resonance sharpness Q1 and Q2 are different. Therefore, the output phase angles θiv1 and θiv2 of the inverter are greatly affected by changes in θs1 and θs2. Therefore, when the frequency F changes when the Q values are different, it can be said that θiv1 and θiv2 also change greatly.

Next, means for aligning the Q values in each self-resonant circuit will be described. In order to adjust the Q value of each self-resonant circuit from the general formula represented by Q = ω ₀ L / R, the reactance value ω ₀ L (induction of the resonance circuit including each heating coil, a heated member, and a resonance capacitor is used. And the equivalent resistance value R of the circuit may be adjusted. Then, the Q values in the respective resonance circuits can be made uniform (matched) by matching or approximating the ratio between the two. Here, the reactance value ω ₀ L changes according to the length of the heating coil, and increases as the heating coil becomes longer. The reactance value ω ₀ L also changes depending on the ratio of the heated member heated by the heating coil. Specifically, ω ₀ L is maximized when there is no member to be heated that is heated by the heating coil, that is, when the magnetic flux generated around the heating coil is generated without stagnation. On the other hand, when there is a member to be heated by the heating coil, the magnetic flux generated around the heating coil is linked to the member to be heated, and an eddy current is generated inside the heated member to try to cancel the flux linkage To do. Since the magnetic flux generated around the eddy current becomes a magnetic flux in the opposite direction to the magnetic flux generated around the heating coil, cancellation occurs between the two and the reactance value ω ₀ L decreases.

For example, as an example of a heating device configuration for matching the Q values, as shown in FIG. 2, four heating coils 12 (12 a to 12 d) formed in a solenoid shape are arranged adjacent to each other in the axial direction. An example is a configuration in which the member to be heated 30 is arranged in the formed surrounding space. In FIG. 2, FIG. 2A is a front cross-sectional view showing the configuration of the induction heating apparatus, and FIG. 2B is a side view. In order to match the Q values in the apparatus having such a basic configuration, first, the distance d1 between the heating coil 12 and the heated member 30 is set equal. And the to-be-heated member heated by the heating zone (the 1st zone to the 4th zone) by the four heating coils 12a-12d is equal to the axial direction length of the heating coil 12, and the to-be-heated member 30 axial direction length. By equalizing the ratio of 30, the reactance value ω ₀ L and the equivalent resistance value R of the self-resonant circuits constituting the plurality of heating zones are equalized, and the resonance sharpness Q is approximated. Each self-resonant circuit having each heating coil 12 as a component may be provided with an inverter 20 (20a to 20d) that can individually supply a high-frequency current to each heating coil 12.

On the other hand, as shown in FIG. 3, the four heating coils 12 formed in a solenoid shape are arranged adjacent to each other in the axial direction, and the heated member 30 is arranged in the surrounding space formed by the heating coils 12. Even if the length in the axial direction of the heated member 30 is shorter than the length in the axial direction of the heating coil 12, the heating target is heated by the heating coils 12a and 12d corresponding to both ends in the longitudinal direction (first zone and fourth zone). The ratio of the heated member 30 to be heated is smaller than that of the heated member 30 to be heated by the heating coils 12b and 12c in the center (second zone and third zone). For this reason, the reactance value ω ₀ L in the self-resonant circuit constituting the first zone and the fourth zone is larger than that in the device configuration shown in FIG. Therefore, the value of the resonance sharpness Q is also increased. In FIG. 3, FIG. 3 (A) is a front sectional view showing the structure of the induction heating apparatus, and FIG. 3 (B) is a side view.

The equivalent resistance value R also varies depending on the length of the heating coil, the distance between the heating coil and the member to be heated, the length of the member to be heated in the heating target region, and the like.
For example, in two self-resonant circuits configured as the equivalent circuit shown in FIG. 5, when current synchronous control is performed at an arbitrary output frequency, current and voltage waveforms are as shown in FIG. Become. Here, when the Q values in the two self-resonant circuits are aligned, the output voltages Viv1 and Viv2 in the two self-resonant circuits are increased even when the frequency of the output current from the inverters INV1 and INV2 is increased. As shown in FIG. 8, the phase angles θiv1 and θiv2 between the reference position and the reference position are almost the same as those in the current synchronous control at an arbitrary output frequency shown in FIG. 7, and the phase difference between θiv1 and θiv2 is also small. For this reason, the fluctuation of the power factor between the respective self-resonant circuits that occurs when the output frequency of the output currents Iiv1 and Iiv2 is changed is approximated, and it is possible to select the frequency at which the induction heating apparatus as a whole becomes highly efficient operation. It becomes possible.

  On the other hand, if there is a difference between the Q values in the two self-resonant circuits, the output frequencies of the output currents Iiv1 and Iiv2 are increased, and when current synchronization control is performed in this state, as shown in FIG. There will be a large difference in the phase difference between the output voltages Viv1, Viv2 and the reference value between the self-resonant circuits. For this reason, in the example shown in FIG. 9, the phase difference θs1 between the output voltage Viv1 and the output current Iiv1 in the self-resonant circuit having a large Q value is the level of the output voltage Viv2 and the output current Iiv2 in the self-resonant circuit having a small Q value. It becomes extremely larger than the phase difference θs2. For this reason, during current synchronous control, if the power factor in the self-resonant circuit having a small Q value is operated at a frequency that favorably maintains the power factor, the power factor in the self-resonant circuit having a large Q value becomes low. Although not shown, when operating at a frequency that maintains a good power factor in a self-resonant circuit having a large Q value, in the self-resonant circuit having a small Q value, the current advances in phase with respect to the voltage, and ZVS control is performed. There is a risk that it will not be possible.

  Moreover, in the said embodiment, in order to simplify and demonstrate the relationship between Q value, the heating coil 12, and the to-be-heated member 30, the to-be-heated member 30 is shown like a cylindrical material, but actually the heating apparatus 10 is shown. 4, a susceptor (graphite) as the member to be heated 30 is preferably arranged on the inner peripheral side of the heating coil 12 as shown in FIG. The susceptor has a cylindrical shape along the surrounding shape of the heating coil 12, and is configured to accommodate a member to be processed 40 for heat treatment inside the cylinder. In FIG. 4, FIG. 4A is a cross-sectional view illustrating a front configuration of the induction heating apparatus, and FIG. 4B is a side view.

  In such a configuration, the member heated by the heating coil 12 is a susceptor that is the heated member 30. Therefore, the length of each heating coil 12 in the longitudinal direction, the length of each heating coil 12 in the longitudinal direction of the susceptor to be heated, and the distance d1 between each heating coil 12 and the susceptor are combined, and each heating coil 12 is provided. The Q values between the self-resonant circuits are made uniform. And the to-be-processed member 40 is arrange | positioned so that both ends may be located inside a susceptor edge part by making the longitudinal direction length shorter than the heating coil 12 and a susceptor, and making the longitudinal direction center position of a susceptor a base point It is desirable to perform heat treatment.

  This is because by performing the heat treatment after having such an arrangement configuration, it is possible to uniformly heat the entire processing target member 40 in consideration of heat radiation from the end of the processing target member 40.

  Moreover, in the said embodiment, when the coupling coefficient k between the heating coils arrange | positioned adjacently is small, it can be considered that Zm ≒ 0, and it demonstrated that Numerical formula 5 was formed. However, even if the coupling coefficient k is relatively large, as shown in FIG. 6, by providing the reverse coupling inductance Ls1 between the self-resonant circuits, Zm can be kept small. Can be established. In the present embodiment, the reverse coupling inductance is a coil that generates a mutual induction power having a polarity opposite to that of the mutual induction power generated between the heating coils.

DESCRIPTION OF SYMBOLS 10 ......... Induction heating apparatus, 12 (12a-12d) ......... Heating coil, 20 (20a-20d) ......... Inverter, 30 ......... Heating member, 40 ... Processing member.

Claims (5)

In an induction heating apparatus including a member to be heated, a plurality of heating coils arranged in close proximity to each other, and a resonance type power source that is individually connected to each heating coil and capable of synchronous control of each current value and current waveform,
An induction heating apparatus characterized in that a ratio of an inductive reactance and an equivalent resistance of a resonance circuit including each of the heating coils, the heated member, and a resonance capacitor is matched or approximated.   The coincidence or approximation of the ratio between the inductive reactance and the equivalent resistance is achieved by making the heating region of the heated member to be heated in each heating coil the same geometrical relationship between each heating coil. The induction heating apparatus according to claim 1.   The induction heating apparatus according to claim 1 or 2, wherein the phase of a resonance circuit formed by each of the heating coils, the member to be heated, and the resonance capacitor is the same in all self-resonance circuits.   The induction heating apparatus according to any one of claims 1 to 3, wherein a reverse coupling inductance is provided to reduce mutual induction between the heating coils. 5. The control unit according to claim 1, further comprising a control unit configured to commonly control a frequency so that a phase angle between an output voltage and an output current of each of the resonance type power supplies falls within a predetermined range. Induction heating device.