JP4854567B2 - Induction heating method and induction heating apparatus - Google Patents

Description

  The present invention relates to an induction heating method and apparatus, and more particularly to a method and apparatus suitable for induction heating while conveying or stopping an object to be heated, such as a billet heater.

  In the heated object conveyance type induction heating device represented by the billet heater, the temperature of the heated object at the time of returning from the conveyance stop state due to inspection or failure of a processing device such as a hot forging press arranged in the subsequent stage Control is regarded as a problem, and various solutions have been proposed as shown in Patent Documents 1 to 3. Here, Patent Documents 1 and 2 show a technique for controlling heating of an object to be heated by a plurality of induction heating coils and a plurality of inverters corresponding to the induction heating coils. Patent Document 3 discloses a single induction heating coil. A technique for controlling the temperature of an object to be heated with an apparatus having a function has been proposed.

Such a difference in technology orientation can be distinguished from the viewpoint of placing importance on the cost for manufacturing the heating device and placing importance on the accuracy of the control temperature. That is, it can be said that an apparatus for controlling the temperature of an object to be heated by a single induction heating coil and a single inverter as disclosed in Patent Document 3 has an advantage in cost. However, it can be said that the techniques disclosed in Patent Documents 1 and 2 are superior in terms of accuracy of industrially heating and controlling an object to be heated. This is because as the number of divisions of the induction heating coil is increased, heating control can be performed such that the temperature rising pattern at the time of stop or low speed operation is closer to the temperature rising pattern at the time of steady operation.
JP-A-7-249478 Japanese Patent Laid-Open No. 10-144462 JP 2002-151246 A

  According to the induction heating apparatus as disclosed in Patent Documents 1 and 2, it is possible to shorten the return time from the temperature rising pattern during stoppage or low speed operation to the temperature rising pattern during steady operation. Conceivable. However, in the induction heating apparatus as disclosed in Patent Documents 1 and 2, when induction heating coils constituting each heating block are arranged close to each other, mutual induction occurs between the adjacent induction heating coils. Control can be difficult. In addition, when a gap is formed between adjacent induction heating coils so as not to be affected by mutual induction, the temperature of the object to be heated located between the coils is lowered. In order to avoid the influence of mutual induction, a method of taking the frequency of the current supplied to the induction heating coils arranged close to each other can be considered, but even in this case, the heating between the induction heating coils can be considered. Since the efficiency is reduced, the heated object located at the boundary between the two induction heating coils or a part of the heated object is discharged from the billet heater at a lower temperature than the preceding and following heated objects when the conveyance is stopped. There is a possibility that.

  Therefore, in the present invention, the temperature distribution control of the object to be heated at the time of stoppage or low-speed operation is performed with high accuracy, and the induction heating method capable of reducing the waste material further than before, and these are relatively inexpensive and compact. An object of the present invention is to provide an apparatus that can be realized.

In order to achieve the above object, an induction heating method according to the present invention includes an inverter provided corresponding to each of a plurality of induction heating coils arranged adjacent to each other, and heating between the plurality of induction heating coils. A heating method of an object to be heated by an induction heating device having a conveying means for conveying an object, wherein the inverter has a different power supply method to the induction heating coil according to the state of conveyance of the object to be heated by the conveying means. In the case where the object to be heated is regularly conveyed, the power is adjusted by controlling the current frequency while deviating the frequency of the current supplied to each induction heating coil arranged adjacently, When the conveyance of the object to be heated stops or becomes slower than the steady conveyance, the frequency of the current supplied to each induction heating coil is matched to be supplied to each induction heating coil. Adjusting the power by adjusting the duty ratio between one frequency while controlling the current waveform to be synchronized or maintaining a predetermined phase difference, and the temperature of the object to be heated is increased. To do.

  In addition, in the induction heating method having the above-described characteristics, the power adjustment of the inverter is performed in the heating region by each induction heating coil when the conveyance of the object to be heated is stopped or is slower than the steady conveyance. It is preferable to measure the temperature distribution of the object to be heated and compare the measured temperature of the object to be heated with the target temperature to increase or decrease the supply power.

In order to achieve the above object, an induction heating apparatus according to the present invention includes an inverter provided corresponding to each of a plurality of adjacent induction heating coils and a cover between the plurality of induction heating coils. An induction heating apparatus having a conveying means for conveying a heated object, wherein the inverter is configured to have a current frequency while causing the inverter to discontinue a frequency of a current supplied to the induction heating coil disposed adjacent to the inverter by a predetermined value or more . The frequency control or phase angle control for adjusting power by control and the phase of the current waveform supplied to each induction heating coil in a state where the frequency of the current supplied to each of the plurality of induction heating coils is synchronized, Or zone control control for adjusting the power by adjusting the duty ratio between one frequency while controlling to maintain a predetermined phase difference, and Is the power control unit to enable exchange control operation connection, the power control unit, said frequency control at the time of steady state operation based on the input signal for switching between the zone control control during maintenance operation, the Switching control operation is performed .

The transport speed in the induction heating apparatus of the above configuration, the the transport means, wherein to the power control unit detects the conveying speed of the object to be heated, and outputs a signal indicating the detected conveying speed Detection means is connected, and the power control unit is provided with determination means for setting a control mode between the frequency control and the zone control control based on the input signal indicating the conveyance speed. good.

  Furthermore, in the induction heating apparatus having the above-described configuration, it is desirable that the inverter is a half-bridge type, and that both are connected without providing a transformer between the inverter and the induction heating coil.

  According to the induction heating method and apparatus having the above-described features, the temperature distribution control of the object to be heated can be performed with high accuracy at the time of stoppage or low-speed operation, and the temperature unevenness on the object to be heated at the time of normal operation return There is no risk of occurrence. Further, a desired temperature increase gradient can be given to the object to be heated even when the conveyance is stopped by supplying arbitrary power to each induction heating coil. For this reason, it becomes possible to further reduce the amount of discarded material than in the past.

  In addition, the inverter is a half-bridge type, and by connecting both without providing a transformer between the inverter and the induction heating coil, the installation space can be reduced at a low cost while exhibiting the above effects. Induction heating apparatus that can be used.

Hereinafter, embodiments of the induction heating method and induction heating apparatus of the present invention will be described in detail with reference to the drawings.
First, a billet heater 100 will be described as an example of a product to which the induction heating apparatus 10 according to the present embodiment is applied with reference to FIG. The billet heater 100 has at least a heating furnace 110 for heating the billet 130 as an object to be heated, pinch rollers 120 and 122 for conveying the billet 130, and a skid rail (not shown) that defines a conveyance trajectory for the billet 130. .

  In the heating furnace 110, a plurality of (three in the embodiment shown in FIG. 1) induction heating coils 20 (20a, 20b, and 20c) that constitute the induction heating apparatus 10 according to the present embodiment as a heating source are arranged. ing. In the present embodiment, the induction heating coil 20 is a solenoid type, and the power supply unit 80 is connected to the induction heating coil 20. Moreover, it is preferable to provide a temperature measuring means (not shown) for measuring the temperature of the billet 130 in each heating region of each induction heating coil 20. This is because by controlling the temperature distribution of the billet 130 based on the measured temperature, highly accurate temperature control becomes possible.

  The power supply unit 80 includes a single or each inverter unit (inverter) 30 (30a, 30b, 30c) provided corresponding to each induction heating coil 20 and each inverter 30. A plurality of forward converters (converters) 40 provided corresponding to the inverters (the converter is single in the form shown in FIG. 1), and power for controlling the power supplied from each inverter 30 to each induction heating coil 20 And a control unit 50. The converter 40 is connected to a commercial power source (three-phase AC power source) 70, and a transformer (transformer) 60 is provided between the converter 40 and the three-phase AC power source 70.

  As shown in FIG. 2, the inverter 30 in the present embodiment is a so-called half-bridge series resonance inverter. The arms constituting the bridge include switching elements 36a1 and 36a2 (FIG. 2 representatively shows the configuration of the inverter 30a and the like connected to the induction heating coil 20a), and electrolytic capacitors 34a1 and 34a2 corresponding thereto. Is provided. Here, as the switching elements 36a1 and 36a2, an IGBT (Insulated Gate Bipolar Transistor), a MOSFET (Metal-Oxide Semiconductor Field Effect Transistor), an SIT (Static Induction Transistor), or the like can be employed. The inverter 30a having such a configuration can reduce the number of switching elements to ½ compared to a full-bridge type inverter, and can suppress the manufacturing cost. Further, by employing a half-bridge type inverter, the output voltage from the inverter 30a can be reduced to about ½ of the input voltage to the inverter 30a.

  By such an action, the voltage difference between the voltage between the terminals in the induction heating coil 20a and the output voltage from the inverter 30a can be reduced, and the high-frequency transformer required for matching the current voltage is not required. Can be connected directly. The high-frequency transformer occupies a large area and is expensive in constructing the induction heating device, and thus the high-frequency transformer required between each induction heating coil 20 and each inverter 30 is unnecessary. This greatly contributes to the reduction of the manufacturing cost and installation space of the induction heating device.

で示すことができる共振コンデンサの一次側電圧、すなわちインバータ３０からの出力電圧に対する誘導加熱コイル２０の端子間電圧を下げることができる。これは、無効電力を補う必要性が低くなるからである。すなわち、Ｑ値の低下により無効電力分の電力を抑えることが可能となり、共振コンデンサ３２が無い場合、すなわち通常のインバータ（共振型でないインバータ）であっても供給電力を補うことが可能となるということである。なおこの場合、高周波帯においてもスイッチングによる電力損失の少ないＺＶＳ（Zero Voltage Switching）運転を行うことが望ましい。ここで、ＺＶＳ運転を行う場合には、隣接して配置する誘導加熱コイルをそれぞれ、加極性となるように配置し、電流が電圧に対して遅れ位相となるようにして運転すると良い。このように、高周波トランスに加えて共振コンデンサを排除することにより、誘導加熱装置の製造コスト、および設置スペースをさらに低減することが可能となる。このような構成のインバータでは、詳細を後述するコンバータから出力された直流電流を交流電流へと変換すると共に、誘導加熱コイルに供給する電力の電流調整と、電流周波数の調整・同期制御が成される。 Furthermore, if the resonance sharpness Q can be kept low by the material and size of the billet 130 and the frequency setting value of the output current from the inverter 30, the resonance capacitor 32 (32a, 32b, 32c) is not required. can do. The resonance capacitor 32 is required to compensate for the reactive power generated as the voltage between the terminals of the induction heating coil 20.

The voltage across the terminals of the induction heating coil 20 with respect to the primary side voltage of the resonance capacitor, that is, the output voltage from the inverter 30 can be reduced. This is because the necessity of supplementing reactive power is reduced. That is, it is possible to suppress the power corresponding to the reactive power by lowering the Q value, and it is possible to supplement the supplied power even if there is no resonant capacitor 32, that is, even if it is a normal inverter (non-resonant type inverter). That is. In this case, it is desirable to perform ZVS (Zero Voltage Switching) operation with little power loss due to switching even in a high frequency band. Here, when performing the ZVS operation, the induction heating coils arranged adjacent to each other may be arranged so as to have a positive polarity, and the operation may be performed so that the current is delayed in phase with respect to the voltage. Thus, by eliminating the resonant capacitor in addition to the high frequency transformer, it is possible to further reduce the manufacturing cost and installation space of the induction heating device. In the inverter having such a configuration, the direct current output from the converter, which will be described in detail later, is converted into an alternating current, and the current supplied to the induction heating coil is adjusted, and the current frequency is adjusted and synchronized. The

  Further, the converter 40 is a rectifier circuit in which a bridge circuit is configured by a thyristor, although details are not shown. The converter 40 having such a configuration converts the three-phase alternating current supplied from the three-phase alternating current power supply 70 into a direct current, and supplies the direct current to the inverter 30 having the above configuration. A filter including a smoothing capacitor 42 and an inductance 44 is disposed between the inverter 30 and the converter 40 having such a configuration.

Further, the power control unit 50 adjusts the frequency of the current supplied from each inverter 30 to each induction heating coil 20 and adjusts the current value supplied to each induction heating coil 20. The power control by the inverter 30 is performed by control of the current frequency in a constant voltage state or pulse width modulation (PWM) control in a constant voltage state .

The inverter 30 in the present embodiment is switched between power control methods when the billet heater 100 is in a steady operation and when it is stopped or operated at a low speed. Specifically, when the billet heater 100 is in a steady operation, that is, when the pinch rollers 120 and 122 are rotating at a steady speed, power control is performed by current frequency control (frequency control) , and the pinch roller 120 is controlled. , 122 is stopped or slowed down, the frequency of the output current from each inverter 30 is matched, the phase of the current waveform is synchronized, or a predetermined phase difference is maintained, or In the asymptotic state, power control is performed by PWM control. For this reason, the electric power control part 50 is comprised so that a predetermined | prescribed control signal may be output with respect to the inverter 30 so that it may correspond with the electric power control system set at the time of each driving | operation.

このため、電圧×電流で示される電力も、変化させることができる。ここで一般に、電力損失の少ないＺＶＳ運転をする場合には、上述したように、電圧波形に対して電流波形が遅れ位相となるように制御される。また、周波数の使用帯域は、共振周波数よりも高い周波数帯を使用する（図３参照）。 The specific output timing of the control signal can be shown as follows. First, the output of the control signal during steady operation will be described. In the case of this embodiment, while adjusting the frequency of the supply current to the three induction heating coils 20 arranged in the heating furnace 110, the current value adjustment by frequency control is performed on each induction heating coil 20. . The current supplied to the induction heating coil 20 (current i flowing in the circuit ) can be obtained by changing the frequency even when the voltage V is constant as shown in Equations 2 and 3 and FIG. (See, for example, FIG. 7 as an equivalent circuit).

For this reason, the power indicated by voltage × current can also be changed. Here, in general, when ZVS operation with little power loss is performed, as described above, the current waveform is controlled to be in a delayed phase with respect to the voltage waveform. Further, the frequency band used is a frequency band higher than the resonance frequency (see FIG. 3).

  In the billet heater 100 according to the present embodiment, the frequency of the input current is 1.5 times or more different from the induction heating coil 20a located on the inlet side of the heating furnace 110 to the induction heating coil 20c located on the outlet side. By doing so, the influence of mutual induction between the induction heating coils arranged close to each other is avoided. The frequency change rate during power adjustment by frequency control is generally about 10% of the entire frequency. Further, it is desirable that the frequency of the current to be supplied be improved stepwise from the induction heating coil 20a on the inlet side to the induction heating coil 20c on the outlet side.

And the environment in the heating furnace 110 at the time of steady operation is various, such as an empty state, a state where the heated billet 130 is accommodated, a state where the cooled (unheated) billet 130 is accommodated, etc. Transition to a different state. Since the induction heating coil 20 is disposed so as to surround the billet 130, when the internal environment in the heating furnace 110 changes due to the flow of the billet 130, its impedance (particularly, the resistance component R and the inductance component L), and the natural resonance The frequency changes. In the operation by frequency control with respect to this change, the set current value can be secured by changing the frequency of the output current from each of the inverters 30a to 30c (see FIG. 4).
Here, the frequency is adjusted, for example, by switching the input of control signals to the two switching elements 36a1 and 36a2 provided in the inverter 30a.

  Next, the output of the control signal during stop or low speed operation will be described. Control of the inverter 30a during stop and low speed operation is more complicated than control of the inverter 30a during steady operation, and is performed in consideration of the frequency of the output current from the inverter 30a and the phase of the current waveform. Here, the current output from each inverter 30 to each induction heating coil 20 is detected via a current transformer (not shown), and based on this, the frequency of the output current, the phase difference of the current waveform, etc. are detected or calculated. It is configured to be. The phase difference of the current waveform is the difference between the zero crosses in each output current from the three inverters 30a, 30b, 30c, the difference between the zero cross in each output current and the zero cross in the reference waveform, and the average value of the zero cross in each output current. The calculation is based on the difference from the zero cross in each output current.

  The output timings of the control signals to the switching elements 36a1 and 36a2 are adjusted so that the frequencies of the output currents from the inverters 30 at the time of stop and low speed operation coincide with each other. When a phase difference occurs between the output currents detected as described above after performing such inverter control, this phase difference is made zero, a predetermined phase difference, or asymptotic thereto. As described above, the output timing of the control signal to the inverter 30 is adjusted. Specifically, when the phase of the current waveform is advanced, the control signal output switching timing should be instantaneously accelerated and the current frequency increased instantaneously. When the phase is delayed, the current frequency is instantaneously increased. Can be reduced.

  The current value supplied to the induction heating coil 20a is adjusted by measuring the temperature of the billet 130 measured by a temperature measuring means (not shown) arranged corresponding to each induction heating coil 20 and the temperature at the target temperature increase gradient. What is necessary is just to output the control signal for raising or lowering the current value by comparing the temperature of the means arrangement position. Specifically, the adjustment is made by adjusting the duty ratio by controlling the input time (on / off) of the output signal for each switching element 36a1, 36a2 that forms the half wavelength of the current waveform, that is, by adjusting the duty ratio per cycle. (See FIG. 5).

  In addition, in the induction heating apparatus 10 as in the present embodiment, the phase difference of the current zero cross is based on the frequency of the output current from the inverter 30c that supplies power to the induction heating coil 20c disposed at the position that becomes the high temperature portion. To control. This is because the radiant heat from the billet 130 which is the object to be heated is large in the high temperature portion where the induction heating coil 20c is arranged. In places where the radiant heat from the object to be heated is large, the energy required to maintain the heating temperature is also large, and thus the output power from the inverter 30c is also large. On the other hand, the radiant heat in the portion where the induction heating coils 20a and 20b are arranged is small, and the energy required for temperature rise is shared with the energy from other induction heating coils. The power consumption of the inverters 30a and 30b connected to the coils 20a and 20b is extremely small. Therefore, it is possible to easily perform power adjustment by PWM control by determining the frequency with reference to the inverter 30c having the largest power consumption. In FIG. 5, the current value is determined by changing the width of a single pulse. However, when the distortion generated in the current waveform becomes large, such as when the current falls sharply, the distortion is reduced. In order to make it dull, as shown in FIG. 6, the current value may be determined by controlling the width of a plurality of pulses, and a waveform may be formed.

  A drive motor (not shown) and a control means (not shown) for controlling the drive motor are connected to the pinch rollers 120 and 122. The drive motor 50 and the power control unit 50 of the power supply unit 80 are connected to the pinch rollers 120 and 122. Is intended to work as described above. For example, the control means for controlling the drive motor includes speed detection means for detecting the rotational speed of the pinch rollers 120 and 122, that is, the conveying speed of the billet 130, and the power connected to the inverter 30 using this detected speed as a signal. A means for outputting to the control unit 50 may be provided. Then, the power control unit 50 may be provided with a determination unit that performs selection switching of a control mode between a frequency control described later and a zone control control described later based on the input speed signal.

  Here, the frequency control in the state where the frequency of the output current from each inverter 30 is deviated (hereinafter simply referred to as frequency control) and the output current from each inverter 30 are matched, and the current value is synchronized with the current. Each of the adjustment controls (hereinafter referred to as zone control control) has the following characteristics.

  First, frequency control is characterized by low apparent power because there is no mutual induction effect. In addition, since frequency control is not affected by mutual induction between adjacent induction heating coils 20, magnetic field interference at the boundary of the heating region is also small, so that a low temperature portion is generated at the boundary portion of the induction heating coil 20. is there.

  Next, since the zone control control is performed while suppressing the mutual induction voltage generated in the induction heating coil 20 by mutual induction, the apparent power is higher than the operation by frequency control, while the induction heating coil 20 There is a feature that it is possible to prevent generation of a low temperature portion in the boundary portion.

で表すことができる。ここで、電圧の実効値、すなわちインバータからの出力電圧Ｖ_ＩＶについて検討するため、図７に２ゾーンの誘導加熱装置に関する等価回路を示す。 Hereinafter, the reason why the above characteristics occur will be described with reference to FIGS.
First, regarding apparent power,

Can be expressed as Here, in order to examine the effective value of the voltage, that is, the output voltage V _IV from the inverter, FIG. 7 shows an equivalent circuit relating to a two-zone induction heating apparatus.

In FIG. 7, IV ₁ indicates an inverter of zone 1, i ₁ is a current flowing through zone 1, R ₁ is a resistance of zone 1 circuit, L ₁ is an inductance of zone 1, C ₁ is a capacitance of zone 1, and Vm ₂₁ Indicates a mutual induction voltage generated by mutual induction from zone 2 to zone 1. In addition, IV ₂ , i ₂ , R ₂ , L ₂ , C ₂ and Vm ₁₂ represent each element of zone 2. In an equivalent circuit having such a configuration, the output voltage from the inverter IV _{1 in} zone 1 can be represented by V _IV1 , the resistance voltage is i ₁ · R ₁ , the inductance voltage is i ₁ · jωL ₁ , and the capacitance The resistance can be indicated by i ₁ · (−j · (1 / ωC ₁ )), respectively.

When _VIV1 is represented by a vector, when the real number component is taken on the horizontal axis and the imaginary number component is taken on the vertical axis, it can be shown as in FIG. Here, when frequency control is performed, the mutual induction voltage indicated by Vm ₂₁ does not occur, so the vector for V _IV1 can be shown as shown in FIG. Since smaller than θ0 is θ1 as can be read from FIG. 8, the inverter output voltage V _IV1 in the case of performing the frequency control is smaller than the output voltage V _IV1 of the inverter in case of performing zone control control It can be said.

Since the apparent power is obtained by Equation 2, it can be said that when the effective value (current value) of both currents is the same, the apparent power is smaller in the operation by frequency control.

ここで、αについて０．５を代入した場合、ベクトル和では約０．７となるのに対し、スカラー和では１とすることができる。このことより、ゾーンコントロール制御による運転では、周波数制御による運転よりも誘導加熱コイルの境界部分での加熱効率が良いということができる。なお、誘導加熱コイルと磁界との関係を模式的に示すと図９のようになる。ここで、図９（Ａ）は誘導加熱コイルとビレット、および磁界の関係を示すブロック図であり、図９（Ｂ）はビレットの長手方向における磁界の強さを示すグラフである。 On the other hand, the strength of the magnetic field with respect to the object to be heated at the boundary portion of the induction heating coil can be expressed by a vector sum (Formula 5) in the case of frequency control, and by a scalar sum (Formula 6) in the case of zone control control. be able to. Α represents the ratio of the strength of the magnetic field from the induction heating coils arranged adjacent to each other.

Here, when 0.5 is substituted for α, the vector sum is about 0.7, whereas the scalar sum can be 1. From this, it can be said that the operation by the zone control control has better heating efficiency at the boundary portion of the induction heating coil than the operation by the frequency control. The relationship between the induction heating coil and the magnetic field is schematically shown in FIG. Here, FIG. 9A is a block diagram showing the relationship between the induction heating coil, billet, and magnetic field, and FIG. 9B is a graph showing the strength of the magnetic field in the longitudinal direction of the billet.

  And in the billet heater 100, the heating control at the time of stop or low speed can be operated with lower electric power than in the steady operation. Further, in the billet heater 100, the amount of movement of the billet 130, which is the object to be heated, is large during steady operation, so there is no significant temperature drop at the boundary between the induction heating coils 20, and it can be almost ignored.

  For this reason, the temperature reduction in the boundary part of the induction heating coil 20 can be avoided by performing the operation by the frequency control during the steady operation, and the apparent power can be kept low. Further, at the time of stopping, the electric power required during the so-called heat retention operation that keeps the billet heat pattern the same as during the steady operation may be about 1/10 or less of that during the steady operation. For this reason, the temperature distribution in the boundary part of the induction heating coil 20 can be kept good by performing the operation by the zone control control at the time of the stop or the low speed operation, and the low power operation can be achieved. Therefore, even when zone control control is performed, the apparent power can be kept low. Therefore, about the inverter 30 used for the induction heating apparatus 10, the heating accuracy of the billet 130 which is the object to be heated can be kept high while using the inverter 30 having a small apparent power capacity.

  In the above embodiment, the induction heating coil is a solenoid type. However, when the object to be heated is a flat plate or the like, the object to be heated is moved upward, downward, or both by an induction heating coil arranged in a spiral shape. Induction heating may be used. Further, although the inverter in the embodiment is a half-bridge type, the inverter may be a full-bridge type for the purpose of reducing the apparent power of the entire operation by switching the power control method. In this case, it is desirable to arrange a high frequency transformer between the induction heating coil and the output of the inverter.

  When the induction heating device according to the above embodiment is applied to a billet heater, as shown in FIG. 10, an induction heating coil and a power supply unit (inverters 30d to 30f and resonance capacitors 32d to 32f) are added. The heating coils 20d to 20f for the test striking material 140 can also be used.

  The trial striking material 140 has a different length for each member and is heated in a stopped state, so that temperature unevenness in the longitudinal direction may occur. On the other hand, if the current control by the zone control control described above is performed, the induction heating coil for supplying power can be arbitrarily selected, and the power supplied to the induction heating coil located at the end of the test hit material 140 can be selected. It can be raised arbitrarily. For this reason, heating without unevenness can be performed regardless of the size and length of the test hit material 140. Further, since the test hit material 140 is heated in a stopped state, the temperature raising time to the specified temperature can be made relatively long. Therefore, even when zone control control is performed, the apparent power can be kept low.

  Further, since inverters 30a to 30f are arranged in parallel to converter 40, inverters 30d to 30f connected to induction heating coils 20d to 20f for test hitting material 140, and inductions arranged in the billet heater main body. You may make it arrange | position the switch which is not illustrated between the inverters 30a-30c connected to the heating coils 20a-20c. By setting it as such a structure, when not heating the test hit material 140, supply of the electric power with respect to the inverters 30d-30f connected to the induction heating coils 20d-20f is interrupted | blocked, and suppression of power consumption can be aimed at. This is because it becomes possible.

  Further, in the above-described embodiment, the details of performing power adjustment by frequency control in a state where the frequencies of output currents from the inverters 30a to 30c are deviated as a power control method during steady operation. However, as a steady-state power control method, instead of frequency control, power adjustment may be performed by phase angle control of the voltage waveform and the current waveform in a state where the frequencies are separated. By changing the phase angle of the output voltage waveform and the output current waveform from the inverter (changing each other's pulse position), the inverter operating frequency can be changed and the output current value adjusted. Because it can.

It is a figure which shows the billet heater to which the induction heating apparatus which concerns on embodiment is applied. It is a figure which shows the structure of an electric power supply unit. It is a figure which shows the relationship between the frequency and electric current at the time of PFM control. It is a figure which shows the example of the electric current adjustment by PFM control. It is a figure which shows the example of the current adjustment by PWM control. It is a figure which shows the example of the PWM control by multiple pulse control. It is an equivalent circuit diagram of two induction heating coil units arrange | positioned adjacently. It is a figure which shows the difference of the consumption voltage by zone control control, and the consumption voltage by frequency modulation control. It is a figure which shows the relationship between an induction heating coil, a billet, and a magnetic field. It is a figure explaining the application example of the induction heating apparatus which concerns on embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ......... Induction heating apparatus, 20 (20a-20f) ......... Induction heating coil, 30 (30a-30f) ......... Inverter, 32 (32a-32f) ......... Resonance capacitor, 40 ......... Converter, 50... Power control unit 60... Transformer 70.

Claims (5)

An object to be heated by an induction heating apparatus having an inverter provided corresponding to each of a plurality of induction heating coils arranged adjacent to each other and a conveying means for conveying the object to be heated between the plurality of induction heating coils. Heating method,
The inverter varies the power supply method for the induction heating coil according to the state of conveyance of the object to be heated by the conveying means,
When the object to be heated is being transported constantly, the power is adjusted by controlling the current frequency while deviating the frequency of the current supplied to each induction heating coil arranged adjacently,
When conveyance of the object to be heated is stopped or slower than steady conveyance, the frequency of the current supplied to each induction heating coil is matched, and the current waveform supplied to each induction heating coil is synchronized, or While controlling to maintain a predetermined phase difference, the duty ratio between one frequency is adjusted to adjust the power,
An induction heating method, wherein the object to be heated is heated. The power adjustment of the inverter when the conveyance of the heated object is stopped or at a lower speed than the steady conveyance is to measure the temperature distribution of the heated object positioned in the heating region by each induction heating coil,
Compare the measured temperature of the object to be heated with the target temperature,
The induction heating method according to claim 1, wherein an increase or decrease in supplied power is attempted. An induction heating apparatus having an inverter provided corresponding to each of a plurality of induction heating coils arranged adjacent to each other, and a conveying means for conveying an object to be heated between the plurality of induction heating coils,
The inverter includes a frequency control that performs power adjustment by controlling a current frequency while separating a frequency of a current supplied to the induction heating coils arranged adjacent to each other by a predetermined value or more, and a plurality of the induction heating coils. Adjusting the duty ratio between one frequency while controlling the phase of the current waveform supplied to each induction heating coil to be synchronized or maintaining a predetermined phase difference in a state where the frequency of the current supplied to each of them is matched. A power control unit that enables a switching control operation between the zone control control that adjusts the power and
The said electric power control part performs the said switching control driving | operation based on the input of the signal which switches the said frequency control at the time of steady operation, and the said zone control control at the time of a heat retention driving | operation . Wherein the conveying means, the relative to the power control unit detects the conveying speed of the object to be heated, conveying speed detecting means for outputting a signal indicating the detected conveying speed is connected,
4. The power control unit is provided with determination means for setting a control mode between the frequency control and the zone control control based on the input signal indicating the transport speed. The induction heating device described in 1.   The induction heating apparatus according to claim 3 or 4, wherein the inverter is a half-bridge type, and both are connected without providing a transformer between the inverter and the induction heating coil.

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