JP2014044867A - Method of controlling induction heating apparatus and induction heating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of controlling an induction heating apparatus by which a supply power can be stably supplied to an induction heating coil as a normal direction power by avoiding an overvoltage and an overcurrent of an inverter caused by influences of mutual induction.SOLUTION: There is provided an induction heating apparatus 10 in which inverters 20 (20a and 20b) by a single-phase bridge are respectively connected to circuits in each of which a resonance capacitor is connected in series to each of a plurality of induction heating coils 12 (12a and 12b) that are mutually induced, by each arm in which an IGBT 26 and a diode 28 are connected in antiparallel. The induction heating apparatus 10 has a power supply comprising smoothing capacitors 30 each connected in parallel to each inverter 20. In the inverters 20, frequencies of output currents Ifrom the respective power supplies are made be accorded with each other. The induction heating apparatus 10 includes minor loops 21 (21a and 21b) which directly control upstream voltage regulators 22 (22a and 22b) so that power supply currents Idc flowing into parallel circuits of the inverters 20 and the smoothing capacitors 30 are a predetermined value or more in a normal direction.

Description

  The present invention relates to an induction heating apparatus control method and apparatus, and more particularly to an induction heating apparatus in which mutual induction occurs between a plurality of induction heating coils that are stably operated in a positive power range. The present invention relates to a control method and apparatus for a heating apparatus.

  Conventionally, it has been known that induction heating is effective as means for rapid heating. However, since the heating method by induction heating uses electromagnetic induction, each of the heating coils (induction heating coils) each having an electric power control means (for example, an inverter) is arranged in close proximity and operated. Mutual induction occurs in the induction heating coil. When such a phenomenon occurs, the output voltage and output current from the inverter are greatly out of phase, making it difficult to control the output power, and generating reverse current due to overcurrent, resulting in damage to the equipment. Such an event may occur.

  In view of such a problem, a technique as disclosed in Patent Document 1 has been proposed. The technique disclosed in Patent Document 1 relates to an induction heating device having a plurality of induction heating coils arranged close to each other and a resonance type inverter connected to each of the induction heating coils. And in patent document 1, the frequency of all the inverters is made the same and it is made to drive | operate with the frequency which one inverter drive | operates with the phase nearest to a resonance point.

  However, the operation method as disclosed in the cited document 1 is the same as the control method in which the operation is performed without mutual induction between the induction heating coils. In other words, this is exactly the same as the phase control for ZVS operation of the voltage-type resonant inverter, and there is a problem that it cannot be applied (implemented) in a mutual induction environment.

  In order to operate in a mutual induction environment, it is necessary to consider that mutual induction provides regenerative power. The regenerative power is a case where the power factor = cos θ due to the voltage / current phase angle of the inverter becomes negative. Under a mutual induction environment, this power factor becomes “−”, reverse power is input to the inverter, the inverter becomes overvoltage and overcurrent, and may be damaged.

JP 2011-14331 A

  In order to prevent overvoltage and overcurrent of the inverter, the fluctuation of the output current is detected, and the detected current is fed back to an ACR (Automatic Current Regulator) to control the power supply current Idc input to the inverter. However, it is conceivable to take measures to prevent reverse current from occurring.

  Here, PID (Proportional Integral Derivative) control is used for ACR control by the detected current (command current). A time constant is set for PID control, and response speed is usually about 10 Hz in PID control used for induction heating.

  However, under the mutual induction environment, when the output state of the inverter connected to the adjacent induction heating coil changes suddenly, a sudden steep disturbance is received. This effect is particularly noticeable when the output current from the target inverter is small. For this reason, under a mutual induction environment, it is necessary to create an environment in which a high gain can be rapidly achieved (when the output current is targeted, the current gain can be increased). Such a change in power environment is faster than the response speed in the ACR, and cannot be dealt with by feedback control via the ACR.

  Therefore, the present invention provides an induction heating apparatus control method and apparatus that can stably supply power supplied to the induction heating coil as positive power while avoiding inverter overvoltage and overcurrent caused by mutual induction. For the purpose.

  In order to achieve the above object, a method of controlling an induction heating apparatus according to the present invention includes a transistor and a diode connected in reverse parallel to a circuit in which a resonance capacitor is connected in series with each of a plurality of induction heating coils that are mutually induced. A method of controlling an induction heating apparatus having a power supply including a smoothing capacitor connected in parallel to a reverse conversion unit by a single-phase bridge in an arm, and connected to the reverse conversion unit in parallel. And a voltage regulator disposed upstream of the inverse converter so that a direct current flowing into a parallel circuit of the inverse converter and the smoothing capacitor is equal to or greater than a predetermined value in the forward direction. It is characterized by controlling.

  In order to achieve the above object, an induction heating apparatus according to the present invention includes an arm in which a transistor and a diode are connected in reverse parallel to a circuit in which a resonance capacitor is connected in series with each of a plurality of induction heating coils that are mutually induced. In the induction heating apparatus having a power source including a smoothing capacitor connected in parallel to each of the inverse conversion units by a single-phase bridge in the inverse conversion unit, the frequency of the output current from each power source is And a means for controlling a voltage regulator arranged upstream of the inverse converter so that the direct current flowing into the parallel circuit of the inverse converter and the smoothing capacitor is equal to or greater than a predetermined value in the forward direction. It is characterized by that.

  Further, the means for controlling the voltage regulator in the induction heating apparatus configured as described above, the direct current flowing into the parallel circuit of the inverse converter and the smoothing capacitor, and the voltage of the direct current flowing through the parallel circuit. It is desirable to control the voltage regulator so that the equivalent resistance value based on it is less than or equal to a predetermined value.

  Moreover, in the induction heating device configured as described above, in the inverse conversion unit, the phase difference between the output voltage and the output current of the inverse conversion unit, or a delay time corresponding to the phase difference is a predetermined value or more, The frequency of the output current may be controlled.

  Further, in the induction heating apparatus configured as described above, the phase difference between the output voltage and the output current of the inverse conversion unit, the position of the gate pulse input to the transistor of the inverse conversion unit, and the output from the inverse conversion unit It can also be obtained from the relationship of the delay time of the rise of the current waveform.

  According to the control method of the induction heating apparatus having the above-described characteristics, it is possible to stably operate with the positive power for the output power from each power source. Thereby, damage of the apparatus resulting from generation | occurrence | production of reverse power can be prevented.

It is a block diagram which shows the structure of the induction heating apparatus which concerns on 1st Embodiment. It is a figure which shows the mode of increase / decrease in a direct current and a DC voltage, and the increase / decrease in the phase angle between the output voltage and output current from an inverter. It is a figure which shows the relationship between the gate pulse with respect to an inverter, and the phase angle of an output voltage and an output current. It is a block diagram which shows the structure of the induction heating apparatus which concerns on 2nd Embodiment. It is a block diagram which shows the structure of the induction heating apparatus which concerns on 3rd Embodiment. It is a block diagram which shows the structure of the induction heating apparatus which concerns on 4th Embodiment.

  Hereinafter, embodiments of the control method for an induction heating apparatus and the apparatus according to the present invention will be described in detail with reference to the drawings. First, the induction heating apparatus according to the first embodiment will be described with reference to FIG.

  The induction heating apparatus 10 is configured based on an induction heating coil 12 (12a, 12b), an inverter 20 (20a, 20b), and an ACR 24 (24a, 14b).

  The induction heating coil 12 is a coil for generating a magnetic flux for heating the induction heating member. In the present embodiment, a plurality (two in the example shown in FIG. 1) of induction heating coils 12a and 12b are arranged close to each other. Here, the close arrangement refers to a distance that is at least affected by mutual induction (M) when power is supplied to a plurality (two in the present embodiment) of induction heating coils 12a and 12b. This is the distance that is mutually induced in the driving state.

  In this embodiment, the inverter 20 is individually connected to each of the plurality of induction heating coils 12a and 12b. The inverter 20 is an inverse converter that supplies electric power supplied as a direct current to the induction heating coil 12 as an alternating current having a predetermined frequency. For this reason, it becomes possible to perform electric power control with respect to each induction heating coil 12a, 12b separately by connecting to each of the some induction heating coil 12a, 12b. In addition, when supplying electric power to each of the induction heating coils 12a and 12b, the frequency of the supplied current is made to match.

  In the present embodiment, a voltage type inverter is adopted as the inverter 20, and a series resonance circuit is configured with the induction heating coil 12 described above. The specific configuration of the inverter 20 is as follows. That is, a single-phase full-bridge inverter is configured. As the switching element, a transistor (IGBT 26 or the like) is employed, and an arm is configured by connecting diodes 28 in antiparallel in order to commutate the load current. A smoothing capacitor 30 for smoothing the DC voltage is provided in the previous stage (upstream side) of the bridge circuit.

  A power source (not shown) is connected to the upstream side of the inverter 20 via a voltage regulator 22 (22a, 22b). The voltage regulator 22 may be a chopper circuit or a forward converter, for example. When a chopper circuit is used as the voltage regulator 22, the voltage duty ratio is changed by chopping the constant DC voltage output from the forward converter 32, and the voltage input to the inverter 20 is changed. It becomes. On the other hand, when voltage control is performed using a forward converter, a method is adopted in which a voltage change corresponding to a frequency determined by the inverter 20 is obtained by a thyristor constituting the forward converter.

  In the induction heating apparatus 10 having such a basic configuration, the phase difference θ between the output current and the output voltage in the zone where the output current is reduced (the induction heating coil 12 set for each heating region) is increased. In such a state, if the current supplied to the target zone is made smaller, the phase angle of the current with respect to the voltage may be a delayed phase of −90 °. In such a state, the output power from the inverter 20 is zero, and the power supply current is also zero. For this reason, when the output current is further reduced, the phase angle of the output current with respect to the output voltage is delayed from −90 °, cos θiv = “− (minus)”, and reverse power is generated.

  For this reason, normally, an output current from the inverter 20 is detected, input to the ACR, and a signal for changing the duty ratio is output to the voltage regulator 22 so that the current value maintains a predetermined value. It is said.

  However, when the current value changes due to a steep disturbance (influence of mutual induction), there is a limit in response speed in current adjustment (current control by voltage adjustment) via ACR, which may be difficult to cope with. .

  Therefore, in the present embodiment, the minor loop 21 (21a, 21b) is configured as an example of means for detecting the power supply current Idc on the upstream side of the inverter 20 and controlling the voltage regulator 22 without going through the ACR. .

  The minor loop 21 includes a current detector 23 using a current transformer provided between the voltage regulator 22 and the smoothing capacitor 30, and a comparator 25. The comparator 25 includes a voltage regulator 22 so that an equivalent resistance value obtained from the power source current (DC current) detected by the current detector 23 and the DC voltage is equal to or less than a predetermined value (predetermined value). This is an element that outputs a signal for changing the duty ratio.

An increase in reactive power can be cited as a factor that increases the phase angle θ between current and voltage. That is, when the substantial output voltage with respect to the output voltage V _iv1 of the inverter decreases due to the increase of the mutual induction voltage, the output current also decreases and the active power decreases. In general, these factors are considered that the power factor deteriorates, that is, the equivalent resistance (DC resistance) in the parallel circuit constituted by the IGBT 26 of the inverter 20 and the smoothing capacitor 30 increases, and the output current I _iv1 decreases. It is done. However, in a mutual induction environment, it can be replaced with a substantial decrease in output voltage due to an increase in the mutual induction voltage Vm21. That is, when the values of the output current V _IV1 from the inverter 20a and the mutual induction voltage Vm21 are equal, the substantial output power is zero. The output current is also zero, and the power supply current Idc1 is inevitably zero, and the ratio of Idc1 to the power supply voltage Vdc1 is rapidly reduced. The DC resistance R1 can be obtained as Vdc1 / Idc1 = R1 from the DC voltage Vdc1 and the DC current Idc1 input to the inverter 20a. That is, when the ratio of Idc1 to Vdc1 decreases due to the influence of the mutual induction voltage Vm21, the DC resistance R1 increases, and when the ratio of Idc1 to Vdc1 increases, the DC resistance R1 decreases. be able to. Here, as shown in FIGS. 2A and 2B, Idc1 relatively increases as Vdc1 increases, and decreases the value of DC resistance R1. 2, FIG. 2 (A) is a diagram showing waveforms of the output voltage V _iv1 and the output current I _iv1 when the DC voltage Vdc1 and the DC current Idc1 are equal to or higher than predetermined values, and FIG. It is a figure which shows the _mode of _Viv1 , _Iiv1 when Vdc1, Idc1 falls.

In the present embodiment, the phase angle θ is increased when the value of the DC resistance R1 reaches the threshold value (R _MAX ) on the basis of the rated value (R _Rat ) of the DC resistance predetermined as the circuit resistance. Judgment and control to increase Vdc1 are performed. Here, R _MAX may be about 50 times R _Rat , that is, R _MAX ≈50 × R _Rat , as an example. Then, the value of Vdc1 / Idc1 is detected, and when this value reaches R _MAX , control is performed so that the comparator outputs a pulse signal for increasing the duty ratio of the chopper so as to increase Vdc1. Make it. As a result, the ratio of Idc1 increases, the DC resistance R1 decreases, the absolute value of the phase angle θ decreases, and the output power factor can be stabilized in the positive direction. Further, according to such control, there is no possibility that the output voltage V _IV1 from the inverter 20a becomes smaller than V _m , and the output current I _iv1 can be maintained at a predetermined value. For this reason, there is no possibility that Idc1 flows backward. Therefore, there is no possibility that Vdc1 / Idc1 becomes minus (−).

  In addition, by adopting such a control format, it is possible to realize a faster response speed than the power supply current Idc control based on the output current via the ACR, and a steep current change due to the influence of mutual induction. Can also be supported.

In the above description, the problem in the case where the phase difference between the output current I _iv1 and the output voltage V _iv1 is 90 ° or more has been described. However, when performing such control, the phase difference between the output current _{I iv1} for the output voltage _{V iv1} (absolute value of the phase angle theta) is the case close to 0, or the output current _{I iv1} to the output voltage _{V iv1} On the other hand, when the lead phase is reached, the following problem occurs. That is, ZVS (Zero Volt Switching) control becomes difficult, and power control itself in the inverter 20a becomes difficult.

Therefore, in the present embodiment, the output current I _iv is detected by the current detector 16 (16a, 16b), the output voltage is detected by a voltage detector (not shown), and the output voltage V _iv and the output current I from the inverter 20 are detected. The frequency (operating frequency) of the output current I _iv is controlled so that the phase difference from _iv (absolute value of the phase angle θ) or the delay time corresponding to the phase difference is equal to or greater than a predetermined value. ing.

Here, the phase difference between the output voltage V _iv from the inverter 20 and the output current I _iv is the value of the IGBT 26 input to the inverter 20 instead of directly detecting the output current I _iv and the output voltage V _iv . It can also be determined based on the gate pulse. As shown in FIG. 3, there is a difference in the dead time (dt) required as the commutation overlap angle between the gate pulse and the output voltage waveform, but the rise of the waveform is linked. Yes. Therefore, the degree of delay of the phase angle θ can also be determined based on the elapsed time from the rise of the gate pulses A and B to the switching of the output current I _iv1 .

That is, when the elapsed time from the rise of the gate pulse to the switching of the output current I _iv1 is short as shown in FIG. 3A, it is determined that the normal operation is performed, and as shown in FIG. When the elapsed time until switching becomes longer, it can be determined that the current delay angle | θ | The correlation between the delay angle and the elapsed time until switching may be examined in advance.

  Next, 2nd Embodiment which concerns on the induction heating apparatus of this invention is described with reference to FIG. Most configurations of the induction heating device according to the present embodiment are the same as the configurations of the induction heating device 10 according to the first embodiment described above. Therefore, portions having the same configuration are denoted by the same reference numerals in the drawings, and detailed description thereof is omitted.

  The minor loop 21 is different from the induction heating device 10a according to the present embodiment and the induction heating device 10 according to the first embodiment. Specifically, in the induction heating apparatus 10 according to the first embodiment, the minor loop 21 includes a direct current from between the chopper that is the voltage regulator 22 and the smoothing capacitor 30 that is disposed in the previous stage of the inverter 20. Idc was detected (second-order chopper method). On the other hand, in the present embodiment, the DC current Idc is detected from the front stage of the chopper that is the voltage regulator 22, that is, the primary side of the chopper, and the duty ratio of the chopper is controlled based on this detection (the chopper primary ratio). method).

  Even if it is a case where it is set as such a structure, control similar to the induction heating apparatus 10 which concerns on 1st Embodiment mentioned above will be attained, and the same effect can be exhibited. In addition, about another structure, an effect | action, and an effect, it is the same as that of the induction heating apparatus 10 which concerns on 1st Embodiment mentioned above.

  Next, a third embodiment according to the induction heating apparatus of the present invention will be described with reference to FIG. The induction heating device 10b according to this embodiment is almost the same in configuration as the induction heating devices 10 and 10a according to the first and second embodiments described above. Therefore, portions having the same configuration are denoted by the same reference numerals in the drawings, and detailed description thereof is omitted.

  The characteristic configuration of the induction heating device 10b according to the present embodiment is that the chopper disposed as the voltage regulator 22 in the induction heating devices 10 and 10a according to the first and second embodiments is eliminated and output by the inverter 20. It is the point which was set as the structure which controls both the voltage and frequency of an electric current. That is, in the present embodiment, a PWM (Pulse Width Modulation) control type inverter 20 is employed, the input direct current is divided into pulses, and according to the frequency of the output current determined by the gate pulse input to the IGBT 26. By changing the flow rate (duty ratio), the average voltage is used as the output voltage.

For this reason, in this embodiment, the power supply current Idc is detected before the smoothing capacitor 30 connected in parallel to the inverter 20, and the duty ratio command value obtained through the comparator 25 is directly input to the inverter. It becomes. In the inverter, the voltage (output voltage V _iv1 ) of the output current I _iv1 is determined according to the input duty ratio.

  Even in the induction heating device 10b having such a configuration, the supply power to the induction heating coil 12 is stably set as the positive direction power, similarly to the induction heating devices 10 and 10a according to the first and second embodiments. Can be supplied. Other constituent actions and the like are the same as those of the induction heating devices 10 and 10a according to the first and second embodiments.

  Next, 4th Embodiment which concerns on the induction heating apparatus of this invention is described with reference to FIG. The induction heating device 10c according to the present embodiment has almost the same configuration as the induction heating device 10b according to the third embodiment described above. Therefore, portions having the same configuration are denoted by the same reference numerals in the drawings, and detailed description thereof is omitted.

  A characteristic configuration of the induction heating apparatus according to the present embodiment is that a half-bridge inverter is employed as the inverter 20. This is because even with such a configuration, the same effects as those of the induction heating device 10b according to the third embodiment described above can be exhibited. Further, by adopting the half-bridge inverter, switching loss can be reduced.

10 ......... Induction heating device, 12 (12a, 12b) ......... Induction heating coil, 16 (16a, 16b) ...... Current detector, 20 (20a, 20b) ......... Inverter, 22 (22a, 22b) ) ... Voltage regulator, 24 (24a, 24b) ... ACR, 26 ... IGBT, 28 ... Diode, 30 ... Smoothing capacitor, 32 ... Forward converter.

Claims (5)

Connect a reverse conversion unit using a single-phase bridge to the circuit in which a resonant capacitor is connected in series with each of a plurality of induction heating coils that are mutually inducted, and an arm in which a transistor and a diode are connected in reverse parallel. A method for controlling an induction heating apparatus having a power supply with smoothing capacitors connected in parallel,
In the inverse converter, the frequency of the output current from each power supply is matched,
Induction heating characterized by controlling a voltage regulator arranged upstream of the inverse converter so that a direct current flowing into a parallel circuit of the inverse converter and the smoothing capacitor becomes a predetermined value or more in the forward direction. Control method of the device. Connect a reverse conversion unit using a single-phase bridge to the circuit in which a resonant capacitor is connected in series with each of a plurality of induction heating coils that are mutually inducted, and an arm in which a transistor and a diode are connected in reverse parallel. In an induction heating apparatus having a power supply with smoothing capacitors connected in parallel,
In the inverse converter, the frequency of the output current from each power supply is matched,
And a means for controlling a voltage regulator disposed upstream of the inverse converter so that a direct current flowing into a parallel circuit of the inverse converter and the smoothing capacitor becomes a predetermined value or more in a positive direction. Induction heating device.   In the means for controlling the voltage regulator, an equivalent resistance value based on a direct current flowing into a parallel circuit of the inverse converter and the smoothing capacitor and a voltage of the direct current flowing through the parallel circuit is set to a predetermined value or less. The induction heating apparatus according to claim 2, wherein the voltage regulator is controlled.   The inverse conversion unit controls the frequency of the output current so that the phase difference between the output voltage and the output current of the inverse conversion unit, or a delay time corresponding to the phase difference becomes a predetermined value or more. The induction heating apparatus according to claim 2.   The phase difference between the output voltage and output current of the inverse converter is obtained from the relationship between the gate pulse position input to the transistor of the inverse converter and the delay time of the rise of the waveform of the output current from the inverse converter. The induction heating device according to any one of claims 2 to 4, wherein

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