JP2007026750A - Control method of induction heating apparatus, and induction heating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method of an induction heating apparatus capable of stably starting an inverter of the induction heating apparatus. <P>SOLUTION: The control method of the induction heating apparatus 10 including resonance type inverters 18 (18a, 18b) corresponded respectively to a plurality of induction heating coils 20 (20a, 20b), reduces an electric current input to the induction heating coils 20 at starting to be smaller than at rated operation. After synchronization control of the electric current input to the respective induction heating coils 20, or after a predetermined time passes as a time the synchronization control of the electric current is completed, the electric current is increased to a value at the rated operation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an operation technique of a zone control inverter that enables individual control of electric power supplied to a plurality of induction heating coils arranged close to each other for each zone.

  Regarding the operation of the heating device in which a plurality of induction heating coils are arranged close to each other, various technical developments have been made for the purpose of suppressing interference (mutual induction) between the induction heating coils. When the operation methods of the induction heating apparatus in which a plurality of induction heating coils are arranged close to each other are roughly classified, the following two methods can be given.

  The first technique is a technique used for general cooking utensils that do not require precise temperature control. For example, the technique disclosed in Patent Document 1 can be cited. The technique disclosed in Patent Document 1 is a technique for operating a device in which an inverter circuit is individually connected to each of a plurality of induction heating coils arranged close to each other. It relates to the technology of switching and driving. According to Patent Document 1, it is described that by adjusting the power supply switching timing for each inverter, it is possible to suppress fluctuations in the power supply voltage due to load fluctuations when switching power supply. Specifically, the zero cross of the power supply voltage is detected, and the inverter that supplies power is switched at the detection timing of the zero cross of the voltage.

The second technique is a technique suitable for a field that requires precise temperature control such as heat treatment of a semiconductor, and is also a technique that the applicant of the present application advances earnestly. As an example, a technique disclosed in Patent Document 2 can be cited. The technique disclosed in Patent Document 2 relates to a technique for simultaneously supplying power to inverters individually connected to a plurality of induction heating coils and simultaneously operating the plurality of induction heating coils. Specifically, the zero cross of the output current from each inverter connected to the series resonance circuit is detected, and the zero cross position of the output current from each inverter is compared with the rising position (zero cross position) of the reference pulse. The output current from each inverter is synchronized by adjusting the frequency of the output current so that the phase difference from the reference pulse individually calculated by comparison becomes 0 or approaches 0. In addition, after the output current of each inverter is synchronized, the current supplied to each induction heating coil is controlled by increasing / decreasing the output voltage of each inverter to achieve uniform temperature distribution of the object to be heated. is there.
JP 2004-22501 A JP 2004-146283 A

  It is considered that the operation of the heating device according to the technique disclosed in Patent Literature 1 can maintain a temperature distribution within a range that is acceptable as a technique used for a general-purpose electromagnetic cooker or the like. However, as a technique used in the semiconductor field that requires precise and high-speed temperature control, the possibility of causing fatal temperature unevenness cannot be denied.

  On the other hand, the technology disclosed in Patent Document 2 is a technology that has been studied with a view to the semiconductor field described above, and achieves necessary and sufficient uniform heating even when precise and high-speed temperature control is performed. be able to. However, in the present technology that performs complex power control compared to the technology disclosed in Patent Document 1, it is difficult to perform synchronous control of output current before shifting to stable operation, that is, immediately after starting the device. . That is, it is conceivable that the control of the output current from the inverter becomes unstable immediately after the device is activated due to the influence of mutual induction.

  Therefore, the applicant of the present application can realize safer, more accurate, and faster temperature control if each inverter can be stably started in a series resonance type induction heating apparatus that performs current synchronous control. Therefore, it is an object of the present invention to provide a control method capable of realizing these and an induction heating apparatus for carrying out the control method.

  In order to achieve the above object, a method for controlling an induction heating device according to the present invention is a method for controlling an induction heating device having a resonance type inverter corresponding to each of a plurality of heating coils. After the synchronous control of the current to be applied to each heating coil or after a predetermined time has elapsed as the time for completing the synchronous control of the current, the current is directed to the value during the rated operation. It is characterized by increasing.

According to such a control method, the voltage value output from each inverter also becomes a small value by keeping the value of the output current small in the state before current synchronization immediately after startup. Therefore, even when the output voltage increases or decreases due to the influence of mutual induction, etc., it is possible to prevent a sudden change in the current input into the circuit and to stabilize the operation at the time of starting the induction heating device. Can do.
Moreover, in the control method of the induction heating apparatus as described above, the frequency of the current input to the heating coil at the time of startup is preferably set higher than the frequency during rated operation.

According to such a control method, in addition to the effect of the above control method, the width of the phase difference of the output current from each inverter at the time of start-up can be reduced, and a state in which pseudo synchronous control is performed is achieved. Can do. In addition, even when current synchronous control is actually performed, synchronization can be achieved in a short time, and the time until reaching the rated operation can be shortened, thereby improving safety. Further, since the frequency of the output current is lowered after the rated operation, the load applied to the inverter can be suppressed and the energy loss is small.
Moreover, in the control method of the induction heating apparatus as described above, it is preferable to operate by setting the voltage value or voltage value ratio of each inverter at the time of start-up and the voltage phase difference between the inverters.

According to such a control method, it is possible to realize a desired operation state at the time of start-up by the voltage value or voltage value ratio set for each inverter and the voltage phase difference between the inverters.
Furthermore, in the control method of the induction heating apparatus as described above, it is desirable that the voltage value or voltage value ratio during rated operation and the voltage phase difference between the inverters are set values at startup.
According to such a control method, the voltage balance in the rated operation can be realized before the synchronous control of the output current is performed, so that the operation state at the start can be stabilized.

An induction heating apparatus for achieving the above object, the induction heating apparatus for performing the control method described above performs current synchronous control by detecting a zero cross of a current corresponding to each of a plurality of heating coils. An induction heating apparatus including a resonance type inverter that enables the inverter to include a setting means for setting a current value, a current frequency, a voltage value or a voltage value ratio of each inverter at startup, and a voltage phase difference between the inverters It is characterized by that.
If it is an induction heating apparatus which has such a characteristic, the control method of the said induction heating apparatus can be implemented.

  According to the control method of the induction heating apparatus as described above, it is possible to stably perform the operation immediately after starting the induction heating apparatus. Moreover, according to the induction heating apparatus of the said structure, the said control method can be implemented.

  Hereinafter, embodiments of the control method for an induction heating apparatus and the induction heating apparatus according to the present invention will be described with reference to the drawings. The following embodiments 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 10 according to the present invention.
The schematic configuration of the induction heating apparatus 10 in the present embodiment includes a plurality of induction heating coils (heating coils) 20 (20a, 20b) for heating an object to be heated (not shown), and current / current to each of the induction heating coils 20. And a power supply unit for supplying voltage.

  The plurality of induction heating coils 20 are arranged close to each other, and in order to enable uniform heating of an object to be heated, a mutual induction voltage generated in each induction heating coil 20 is suppressed by a power supply unit described later, It is possible to control the electric power supplied to the induction heating coil 20. In FIG. 1, internal resistors 24 (24a, 24b) relating to the circuit are schematically shown.

  The power supply unit includes a voltage adjustment circuit and an inverter 18 (18a, 18b) which is a current adjustment circuit 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 12 serving as a power source for the entire apparatus, a converter (forward converter) 14 that converts an output current from the three-phase AC power source 12 into a DC current, and an output. Any combination with the chopper circuit 16 (16a, 16b) for controlling the voltage of the current to be generated may be used. The inverter 18 is an inverse converter that controls the frequency of the output current to the induction heating coil 20 and converts the current converted to direct current by the converter 14 into alternating current and outputs the alternating current. Note that the voltage regulating circuit defined here may have other configurations. In addition, the voltage adjustment circuit includes smoothing capacitors 30 and 34 and a coil 32 to stabilize the power supplied to the inverter 18.

  In the case of the induction heating device 10 of the present embodiment, the inverter 18 is a series resonance type inverter, and a capacitor (capacitor) 22 (22a) is connected in series with the induction heating coil 20 between the induction heating coil 20 and the inverter 18. , 22b). A transformer 26 (26a, 26b) is provided between the induction heating coil 20 and the inverter 18 in parallel with the induction heating coil 20, and a current transformer 28 (28a, 28b) is provided so that the current and voltage (output voltage and output current from the inverter 20) input to the induction heating coil 20 can be detected. The voltage and current detected by the transformer 26 and the current transformer 28 are input to the control unit 50 described later.

  A signal is sent to the control unit 50 to the inverter 18 and the chopper circuit 16 to detect the phase angle of the load controller (output current) flowing in the drive control unit 56 for controlling the drive and the induction heating coil 20 arranged in proximity. A phase difference detector 52, a power detector 54 for detecting a current / voltage flowing through the induction heating coil 20, and a current frequency correction value and a supply voltage control value are calculated based on the detected information of various signals. , A calculation unit 58 for outputting the calculated value to the drive control unit 56 is provided.

  In addition, in the induction heating apparatus 10 of the present embodiment, the control unit 50 includes setting means (not shown), and is controlled by the current value, current frequency, and chopper circuit 16 output from the inverter 18 at the time of startup and output from the inverter 18. The voltage value or voltage value ratio (voltage level ratio) of the voltage, the voltage phase difference (pulse position), etc. in each inverter 18 can be set. One specific example of the setting means is a storage unit 60 as shown in FIG. The storage unit 60, for example, the current output from the inverter 18, the pulse position of the voltage controlled by the chopper circuit 16, the level ratio, the value of the output current set at startup, and the value of the frequency of the output current set at startup. It is possible to memorize the value of the output current that is used as a guide during rated operation, the frequency of the output current that is used as a guide during rated operation, and reflect the stored data in the control value or correction value calculated by the calculation unit 58. Can do.

In the induction heating apparatus 10 having the above-described configuration, the influence of mutual induction can be avoided by performing the following control during rated operation. First, the phase difference detection unit 52 acquires waveform information I ₁ and I ₂ of the current (output current from the inverter 18) flowing through each induction heating coil 20 via the current transformer 28 provided in each zone ( (See FIG. 2). Based on the acquired information, the zero cross of the current flowing through each induction heating coil 20 is detected, and the position of this zero cross is compared with the reference waveform, for example, the position of the zero cross in the waveform I ₁ of the current flowing through the induction heating coil 20a. Then, the phase difference θ ₁ which is a deviation amount is derived. Based on the phase difference θ ₁ , the calculation unit 58 calculates a correction value for matching the zero cross of the output current I ₂ of the corresponding inverter 18 b with the zero cross of the reference output current I ₁ . Correction of the position of the zero cross in the current waveform can be performed by temporarily changing the frequency of the output current. Therefore, the calculation unit 58 calculates a frequency for correcting the zero-cross position of the output current of each inverter 18 and outputs this to the drive control unit 56 as a correction value. The drive control unit 56 controls each inverter 18 so as to output a current at a frequency given as a correction value. By repeating this control, the output current from each inverter 18 is synchronized within a certain range, and the voltage value determined for supplying a prescribed current to each induction heating coil 20 is stabilized. . And the electric current thrown into each induction heating coil 20 can be stabilized with stabilization of a voltage value. The power detection unit 54 corrects the difference between the voltage and current values supplied to the induction heating coil 20 and the voltage and current values that are the control values. Thus, the voltage and current actually supplied to the induction heating coil 20 are acquired through the control unit 58, fed back to the calculation unit 58, and a correction value is given to the drive control unit 56. Note that the current subjected to the synchronous control is controlled so as to be in a delayed phase with respect to the voltage in order to prevent power loss.

  As can be understood from the above, during rated operation in the present invention, the control is performed to synchronize the phase of the current output from each inverter 18 to the corresponding induction heating coil 20, and output in a state in which synchronous control is performed. It means a state in which the voltage is controlled and the value of the current output to the induction heating coil is controlled.

  In the present invention, when controlling the induction heating device 10, the control method as described below is proposed in order to stably operate the induction heating device 10 at the time of startup, particularly focusing on the control at the time of startup (immediately after the startup).

  The outline of the first control method is that the value of the output current (current flowing through the induction heating coil 20) from the inverter 18 at startup is made smaller than the value of the output current during rated operation. Then, synchronous control of the output current from each inverter is performed in the small current operation, and then the value of the output current from the inverter 18 is brought close to the value of the output current during the rated operation.

The value of the output current at the time of start-up may be a very small value that can detect a zero crossing of the current frequency. Here, since noise is generated in the output current from the inverter 18 due to the influence of mutual induction, etc., it is necessary to prevent the device from misidentifying the zero cross due to the influence of the noise. In the present embodiment, in order to prevent malfunction of the apparatus, a threshold for detecting a zero cross is provided, and a position where the current exceeds the value is determined as a zero cross position. Therefore, the output currents I ₁ st and I ₂ st at the start can exceed the threshold value for the current value 0A, and the phase difference Δθ ₂ from the actual zero cross position to the threshold value can be within a predetermined range. It is desirable to have a small value.

Note that Δθ ₂ , which is an error when detecting a zero cross, has a larger value than the phase difference Δθ ₁ , which is an error during rated operation, because there is a difference in the rising angle of the pulse due to the influence of the current value. However, if the values of the output currents I ₁ st and I ₂ st at startup are about 5% of the values of the output currents I ₁ and I ₂ at rated operation, it is sufficient for current synchronization. It is considered that the zero cross position can be obtained with high accuracy. That is, the synchronization control referred to in the present invention includes not only complete synchronization but also control for achieving synchronization within a predetermined threshold range.

  By reducing the value of the output current in the state before current synchronization immediately after startup, the voltage value in each inverter 18 also becomes a small value. Therefore, even when the output voltage increases or decreases due to the influence of mutual induction or the like, it is possible to prevent a sudden change in the current input into the circuit and to stabilize the operation at the time of starting the induction heating apparatus 10. be able to.

  Next, the second control method will be described. The outline of the second control method is that, in addition to the above control method, the frequency value of the output current from the inverter 18 at startup is set higher than the frequency of the output current during rated operation. Then, synchronous control of the output current from each inverter 18 is performed during high-frequency operation, and then the frequency value of the output current from the inverter 18 is brought close to the frequency value of the output current during rated operation. . By performing such control, the width of the phase difference of the output current from each inverter 18 at the time of start-up is reduced, and a state in which pseudo synchronous control is performed can be achieved. In addition, even when current synchronous control is actually performed, it can be executed in a short time, and the time to reach stable operation can be shortened and safety can be improved. Further, since the frequency of the output current is lowered and the operation is shifted to the rated operation after the stable operation, the load applied to the inverter 18 can be suppressed and the energy loss is small. Naturally, the effect of the first control method described above can also be achieved.

と表すことができる。ここで、数式１は、

と表すことができ、Ｌはコイル容量（インダクタンス）、Ｃはコンデンサ容量（リアクタンス）、ωは角周波数、ｆは周波数を示すため、Ｒ、Ｌ、Ｃの値が既知であれば、周波数ｆの設定値を向上させるほど数式１におけるＸの値は大きくなり、

を成立させることができる。また、誘導加熱コイル２０を流れる電流の電圧に対する位相差θ_０は、

と表すことができ、Ｘ／Ｒは、

と表すことができるため、数式３におけるＲと｜Ｘ_Ｌ−Ｘ_Ｃ｜との差が大きくなればなるほど、各誘導加熱コイル２０を流れる電流の電圧に対する位相差は９０°に近づくこととなり、各インバータ１８間における電圧に対する位相差のバラツキは少なくなる。よって、上述したように、周波数を高めることにより誘導加熱コイル２０に投入される電流の擬似的な同期制御が可能となり、起動直後の安定運転を実現することができる。すなわち、各誘導加熱コイル２０を備える回路の回路定数が異なる非対称負荷の誘導加熱装置であっても、起動を安定させることができるのである。 The standard value of the current frequency setting at startup is as follows. The frequency is set so that the reactance component of the impedance of the resonance element constituting the heating unit, that is, the induction heating coil 20 and the capacitor 22, has a sufficiently larger value than the resistance component (internal resistance 24) of the circuit. If the impedance of the resonant element is Z, the reactance component is X, and the resistance component (internal resistance) is R,

It can be expressed as. Here, Equation 1 is

L is a coil capacity (inductance), C is a capacitor capacity (reactance), ω is an angular frequency, and f is a frequency. Therefore, if the values of R, L, and C are known, the frequency f As the set value is improved, the value of X in Equation 1 increases.

Can be established. The phase difference θ _{0 with} respect to the voltage of the current flowing through the induction heating coil 20 is

X / R can be expressed as

Therefore, as the difference between R and | X _L −X _C | in Equation 3 increases, the phase difference with respect to the voltage of the current flowing through each induction heating coil 20 approaches 90 °. The variation in the phase difference with respect to the voltage between the inverters 18 is reduced. Therefore, as described above, by increasing the frequency, pseudo synchronous control of the current input to the induction heating coil 20 becomes possible, and stable operation immediately after startup can be realized. In other words, even an induction heating device with an asymmetric load having different circuit constants of the circuit including each induction heating coil 20 can stabilize the start-up.

The output voltage V during the control process carried out, the output current I, the shift trend change trend of the current frequency f _i shown in FIG. Each detailed numerical value changes variously depending on an arbitrary setting, and thus only the tendency is shown in the drawing.
The output voltage V slightly rises from the value set at startup to the current synchronization period. This is a voltage adjustment performed to adjust the output current to a state in which synchronous control is possible. Thereafter, a substantially constant value is maintained in the current synchronization period, and increases with an increase in the value of the output current in the transition period, leading to a rated operation and maintaining a stable state at a high voltage.

  The output current I rises to a current value that can be synchronously controlled from the time of startup to the current synchronization period. In the current synchronization period, synchronization control is performed while maintaining a substantially constant current. During the transition period, the voltage rapidly increases with the voltage value while maintaining the synchronous control toward the current value for performing the rated operation. After reaching the rated operation, in order to secure a current value required to uniformly heat the object to be heated, a state in which there is no sudden change in the current value is maintained.

Frequency f _i in the control process, to be set high at startup ends the current synchronization period, there is no abrupt changes up to the transition period. In the current synchronization period, although the frequency is temporarily adjusted for the purpose of current synchronization control between the inverters, the reference frequency does not change. In the transition period, in order to reduce the load on the inverter, the current frequency is lowered toward the frequency during rated operation. Naturally, since the current synchronous control is executed during the rated operation period, there is no rapid change.

  As can be seen from FIG. 3, according to the present control method, it is understood that the current synchronization control has already been completed during the transition period, and stable operation has been achieved. Even during the period from the start to the current synchronization period, that is, during the start-up operation, as described in the first control method, since the output current value is reduced, the current value changes rapidly. It can be said that the state does not occur, that is, a stable state. Furthermore, by setting the frequency of the output current at the time of startup high, a stable state in the startup operation can be ensured. Furthermore, by setting the frequency of the output current at start-up high, it is possible to shorten the start-up operation period from the start-up to the transition period, which leads to stable operation at an early stage. it can.

  Next, the third control method will be described. The outline of the third control method is that the pulse position of the output voltage (voltage controlled by the chopper circuit 16) and the voltage ratio from each inverter 18 during rated operation are acquired in advance, and the pulse position of the acquired output voltage is obtained. And the voltage level ratio are set as the pulse position and voltage level ratio of the output voltage from the inverter 18 at the start-up, and then the first or second control method is performed (see FIG. 4). ).

The pulse position of the output voltage (phase difference Δθ ₃ ) and the voltage level ratio (V _L1 : V _L2 ) are normally automatically adjusted to maintain the output current synchronization after the output current synchronization control. It is what is said. Therefore, the pulse position of the output voltage and the voltage level ratio are input to the calculation unit 58 as values at the time of start-up and reflected as control values to the drive control unit 56. A voltage balance during operation can be realized. For this reason, the current output from the inverter 18 at the time of startup does not show an abnormal value, and the operation state immediately after startup can be stabilized. Moreover, each said effect can be show | played by implementing the 1st, 2nd control method mentioned above after performing the said control.

Specifically, in the induction heating apparatus 10 in the rated operation state, the waveform of the output current is synchronized between the zones, and the pulse position and voltage level of the output voltage are slightly shifted. For example, as shown in FIG. A waveform like this can be seen.
In the present embodiment, the waveform (pulse position, voltage level ratio) of the output voltage shown in FIG. 4 is acquired and calculated from a prior experiment or experience, and this is set and stored in the storage unit of the control unit 50 referred to in the present embodiment. Enter 60. The input information is input as a control value to the drive control unit 56 via the calculation unit 58 and is reflected in the pulse position and voltage level ratio of the output voltage at the time of startup.

  In the present embodiment, the current and voltage pulse positions for controlling the induction heating device 10, the level ratio, the value of the output current set at startup, the value of the frequency of the output current set at startup, and the output used as a guide during rated operation Although it has been described that control is performed by storing the current value, the frequency of the output current as a guide during rated operation, and the like in the storage unit 60 provided in the control unit 50, these pieces of information are sequentially controlled by an operator who operates the induction heating apparatus. Even if it is a case where it inputs and it is a case where it inputs via another setting means, it will not change in implementing the control method of the induction heating apparatus which concerns on this invention.

Moreover, although the induction heating apparatus shown in the embodiment includes two induction heating coils, it may naturally include a plurality of induction heating coils.
Further, in the above embodiment, it is described that the synchronous control of the current at the start is surely performed and the operation is stabilized and then the operation is shifted to the rated operation. However, the synchronous control is performed according to the conditions set at the start. It is also possible to measure or calculate the time predicted until the start of the operation, consider that synchronous control has been performed with this time, and perform control to shift to rated operation.

It is a block diagram which shows the structure of the induction heating apparatus of this invention. It is a figure which shows the example of the current waveform at the time of rated operation, and the example of the current waveform at the time of starting. It is a figure which shows the transition tendency of an output voltage, an output current, and a current frequency. It is a figure which shows the example of a voltage waveform and a current waveform.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ......... Induction heating apparatus, 12 ......... Three-phase alternating current power supply, 14 ......... Converter, 16 (16a, 16b) ...... Chopper circuit, 18 (18a, 18b) ......... Inverter, 20 (20a, 20b) ..... induction heating coil, 22 (22a, 22b) ..... capacitor, 24 (24a, 24b) ..... internal resistance, 26 (26a, 26b) ..... transformer, 28 (28a, 28b) ……… Current transformer, 50 ……… Control unit.

Claims (5)

In a control method of an induction heating apparatus having a resonance type inverter corresponding to each of a plurality of heating coils,
The current input to the heating coil at startup is smaller than that during rated operation,
Induction heating, characterized in that the current is increased toward the value during rated operation after the synchronous control of the current supplied to each heating coil or after a predetermined time has elapsed as the time for completing the synchronous control of the current Control method of the device.   The method for controlling an induction heating apparatus according to claim 1, wherein the frequency of the current input to the heating coil at the time of startup is set higher than the frequency during rated operation.   The method of controlling an induction heating apparatus according to claim 1 or 2, wherein the inverter is operated by setting a voltage value or a voltage value ratio of each inverter at startup and a voltage phase difference between the inverters.   4. The induction heating apparatus control method according to claim 3, wherein the voltage value or voltage value ratio during rated operation and the voltage phase difference between the inverters are set values at startup. An induction heating apparatus including a resonance type inverter capable of performing current synchronous control by detecting a zero cross of a current corresponding to each of a plurality of heating coils,
An induction heating apparatus comprising setting means for setting a current value, a current frequency, a voltage value or a voltage value ratio of each inverter at startup, and a voltage phase difference between the inverters.

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