JP6054103B2 - Induction heating apparatus control method - Google Patents

Description

  The present invention relates to a method for controlling an induction heating device, and more particularly to induction heating feeding suitable for a case where an induction heating device in which mutual induction occurs between a plurality of induction heating coils is stably operated in a positive power range. It relates to a control method.

  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.

JP 2011-14331 A

  The operation method is the same as the control method in which the operation is performed without mutual induction between the induction heating coils. That is, it is exactly the same as the ZVS operation phase control of the voltage-type resonant inverter, and 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 the mutual induction environment, this power factor becomes “−”, and reverse power is input to the inverter, resulting in inverter overvoltage and overcurrent.

  An object of the present invention is to provide a control method for an induction heating apparatus that can stably supply power supplied to an induction heating coil as positive direction power while avoiding inverter overvoltage and overcurrent caused by mutual induction.

In order to achieve the above object, an induction heating apparatus control method according to the present invention provides an induction heating apparatus having a power supply for supplying power to each of a plurality of mutually induction induction coils. In addition, the phase angle θ of the polarity change point of the output current and the output voltage is obtained, and it is determined whether or not the phase angle θ is within the range of 0 ° ≧ θ ≧ −90 °, and the phase angle θ is within the range. If not, a control method for the induction heating device, wherein the control is performed so as to increase the power supply current or the power supply voltage.

In the control method of the induction heating device having the features as described above, while at the same the operating frequency of the output current, the output power factor is as Yasu increasing the supply current or the supply voltage when decreased Also good.

Moreover, in the control method of the induction heating apparatus having the above-described characteristics, the increase of the power supply current or the power supply voltage may be performed by controlling the frequency of the output current in a direction away from the resonance point. .

  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 for implementing the control method which concerns on 1st Embodiment. It is a block diagram for demonstrating the structure of the voltage type inverter employ | adopted with the induction heating apparatus shown in FIG. It is a figure for demonstrating the range of a phase angle. 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 block diagram for demonstrating the structure of the current type inverter employ | adopted with the induction heating apparatus for implementing the control method which concerns on embodiment relevant to this invention . 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.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments according to a method for controlling an induction heating apparatus of the present invention will be described in detail with reference to the drawings. First, with reference to FIG. 1, the induction heating apparatus for implementing the control method which concerns on 1st Embodiment is demonstrated.

  The induction heating apparatus 10 used in this embodiment includes an induction heating coil 12 (12a, 12b), an inverter 20 (20a, 20b), waveform detection means 14 (14a, 14b), 16 (16a, 16b), and a phase angle determination means. 18 (18a, 18b) and voltage control means 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 affected at least by mutual induction when power is supplied to a plurality of (two in this embodiment) induction heating coils 12a and 12b, that is, in an operating state. This is the distance that leads to mutual guidance.

  In this embodiment, the inverter 20 is individually connected to each of the plurality of induction heating coils 12a and 12b. The inverter 20 supplies an alternating current having a predetermined frequency to the induction heating coil 12. 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, as shown in FIG. 2, a single-phase full-bridge inverter is configured. As the switching element, an IGBT 26 is employed, and a diode 28 is connected in antiparallel in order to commutate the load current. A smoothing capacitor 30 for smoothing the DC voltage is provided in the previous stage of the bridge circuit.

  A power source 32 is connected to the upstream side of the inverter 20 via a voltage converter 22 (22a, 22b). The voltage converter 22 may be a chopper circuit or a forward converter, for example. When the chopper circuit is used, the voltage input to the inverter 20 is changed by chopping the constant DC voltage output from the forward converter. 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.

  The waveform detection means 14 and 16 are means for detecting the current value, the voltage value, and the current and voltage waveforms output from each inverter 20. The waveform detection means 14 and 16 may be an oscilloscope or the like. In the present embodiment, a waveform detection unit 16 that detects a current waveform is provided in series with the induction heating coil 12, and a waveform detection unit 14 that detects a voltage waveform is provided in parallel with the induction heating coil 12. Yes. The waveform data detected by the waveform detection means 14 and 16 is output to the phase angle determination means 18 described later in detail. In addition, the current value and the voltage value are output to the voltage converter 22.

  The phase angle determination means 18 detects the phase difference (phase angle: power supply output phase θ) between the polarity change points of the current and voltage by comparing the current and voltage waveforms output from the inverters 20. This is means for determining whether or not the angle θ is within the range of the appropriate value. Therefore, the phase angle determination means 18 first measures the polarity change point in the waveform of the current and voltage output from each inverter 20, and obtains the phase angle θ of the measured current and voltage polarity change point. Here, the phase angle θ is shown as a phase difference of current with respect to voltage. That is, when the current has a lagging phase with respect to the voltage, it is indicated by a minus (-), and when the current has a leading phase, it is indicated by a plus (+).

  After the phase angle θ of the current and voltage is detected, it is determined whether or not the detected phase angle θ is within the phase angle range for stable operation of the inverter 20. The determination is performed by comparing each of the predetermined phase angle upper limit value and the phase angle lower limit value with the detected phase angle θ.

  When the voltage and current phase angles θ are shown in four quadrants as shown in FIG. 3, in the voltage type inverter 20, when the phase angle θ is within the fourth quadrant, ZVS (Zero Volt Switching). Is maintained, and a stable operation with a positive power factor is possible.

  When the phase angle θ falls within the range of the first quadrant and the second quadrant, the current advances with respect to the voltage, and ZVS cannot be maintained. For this reason, when current flows through the diode 28, the IGBT 26 is switched on, a recovery current flows through the diode 28, and the power loss of the IGBT 26 increases. Further, when the phase angle θ falls within the range of the third quadrant, ZVS can be maintained, but since the power factor is in a negative direction, when the power source cannot be regenerated, the voltage converter 22 It becomes necessary to set the output voltage excessively.

For this reason, in this embodiment, the phase angle upper limit value and the phase angle lower limit value are determined within the range of 0 ° ≧ θ> −90 ° at the phase angle θ.
As a result of comparison, if the detected phase angle θ is not within the range of the phase angle upper limit value to the phase angle lower limit value, the current and voltage phase angles θ should be within the range of the phase angle upper limit value and the phase angle lower limit value. Control to return.

In a mutual induction environment, 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 and the smoothing capacitor 30 of the inverter 20 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.

For this reason, in the present embodiment, when the phase angle θ is not within the range between the upper limit value and the lower limit value of the phase angle, the voltage control unit 24a is controlled so as to increase Vdc1. As shown in FIGS. 4A and 4B, Idc1 relatively increases as Vdc1 increases, and increases the active power component. For this reason, the phase angle θ can be returned within a predetermined range. 4A 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. is a diagram showing a state of a _{V IV1, I IV1} when the Vdc1, Idc1 is lowered.

Further, since the phase difference (phase angle θ) between the voltage and the current changes depending on the circuit resistance, it can be expressed as Equation 1 using impedance.
... (Formula 1)
Xs is a reactance component of impedance, and Rs is a resistance value. Vm21sin θm is an ineffective component of the mutual induction voltage, and Vm21 cos θm is an effective component of the mutual induction voltage. Here, θm is a phase angle between the mutual induction voltage and the mutual induction current. And if Xs is shown using L (inductance) and C (capacitance), it can be shown like Formula 2.
... (Formula 2)
Here, ω is an angular frequency of alternating current, and ω = 2πf.

Therefore, when the frequency f of the output current from the inverter 20 becomes large, also the phase angle theta increases, when the frequency f of the output current I _IV is reduced is reduced even phase angle theta.

Therefore, when the phase angle θ exceeds the phase angle upper limit value, the frequency adjustment signal outputs a signal indicating that the frequency f of the output current I _IV is smaller than the resonance frequency. On the other hand, when the phase angle θ exceeds the phase angle lower limit value, a signal indicating that the frequency f of the output current I _IV is larger than the resonance frequency is output. That is, in the present embodiment, when the phase angle θ approaches −90 °, the power factor of the output power represented by cos θ decreases. For this reason, when the phase angle θ approaches −90 °, control is performed so that the frequency of the output current is separated in a direction larger than the resonance point (resonance frequency), and the value of the phase angle θ is increased.

After performing such control, by controlling the output voltage V _IV from the inverter 20 as described above, the phase angle θ can be maintained in the range of 0 ° ≧ θ> −90 °. ZVS control can be performed stably.

Next, as an embodiment related to the present invention, a control method related to an induction heating apparatus employing a current type inverter as an inverter will be described with reference to FIG. Therefore, FIG. 1 which shows the structure of the induction heating apparatus used by description of 1st Embodiment shall be used about structures other than the structure of inverter 21 (21a, 21b). The inverter 21 according to the present embodiment has a configuration in which a diode 28 is connected in antiparallel to an IGBT 26 serving as a switching element, and a diode 27 is connected in series. This is because reverse pressure is prevented by the diode 28 connected in reverse, and reverse current is blocked by the diode 27 connected in series. In the inverter 21 according to the present embodiment, a DC reactor 29 for smoothing a DC current is connected in series with the voltage converter 22. And the inverter 21 which concerns on this embodiment comprises the parallel resonance circuit between the induction heating coils 12. FIG.

In the induction heating apparatus according to the present embodiment, in order to perform power running operation in the inverter 21, ZCS (Zero Current Switching) is possible in the relationship of the phase angle θ between the output voltage V _IV and the output current I _IV from the inverter. It is set as the structure which drive | operates within the range of the 1st quadrant which becomes. Therefore, the relationship between the output voltage V _IV of the inverter 21 and the output current I _IV in the induction heating device of the present embodiment is controlled so that the output current I _IV is in a leading phase with respect to the output voltage V _IV . The phase angle lower limit value and the phase angle upper limit value of the phase angle θ are determined in the range of 0 ° ≦ θ <90 °.

In addition, the adjustment method of phase angle (theta) is the same as that of the induction heating apparatus 10 which concerns on 1st Embodiment mentioned above. That is, the waveforms of the output voltage V _IV and the output current I _IV from the inverter 21 are detected by the waveform detection means 14 and 16. The detected waveform is input to the phase angle determination means 18, and after determining the phase angle θ of the current with respect to the voltage, it is determined whether or not the phase angle θ is within an appropriate value range. As a result of the determination, if the phase angle θ is not between the predetermined phase angle lower limit value and the phase angle upper limit value, a phase angle adjustment signal is output to the inverter 21. In the present embodiment, the operation is performed after the frequencies of the currents output from the respective inverters 21 are matched with each other.

Also in this embodiment, 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 value of the substantial output current I _IV1 with respect to the output voltage V _IV1 of the inverter decreases due to the increase of the mutual induction voltage, the same effect as the increase in circuit resistance occurs, and the active power decreases.

That is, in this embodiment employing the parallel resonance type inverter 21, the output current I _IV1 from the inverter 21a is the current Ic1 that passes through the resonance capacitor and the current I11 that passes through the induction heating coil 12a. It becomes a composite value. Here, if the mutual induction voltage Vm21 occurs, minute voltage of the current Il1 passing through the induction heating coil 12a is a value obtained by subtracting the mutual induction voltage Vm21 from the inverter output voltage _{V IV1 (V IV1} -Vm21) Therefore, when the values of V _IV1 and Vm21 are equal, the current supplied to the induction heating coil 12a becomes zero. That is, the effective power becomes zero. Such a situation is a state in which the phase difference (phase angle θ) between the output current and the output voltage is 90 °.

On the other hand, in order to increase the active power, that is, to reduce the phase angle θ, the inverter output voltage V _IV1 is increased so that a desired current value is supplied to the induction heating coil 12a. _{It is} sufficient to keep _IV1 > Vm21.

Since the output current I _IV1 from the inverter 21a is represented by Ic1 + Il1, it fluctuates due to the change in Il1. Therefore, in accordance with the change (decrease) in I _IV1 , the voltage control means is configured to change (increase) the power supply current Idc1 that determines the output voltage of the inverter 21a and change (increase) the power supply voltage Vdc1 (= V _IV1 ). What is necessary is just to control 24a.

An increase in the advance degree of the phase angle θ can be determined based on the gate pulse of the IGBT 26 input to the inverter 21. As shown in FIG. 6, although there is a difference in the dead time (dt) required as the commutation overlap angle between the gate pulse and the waveform of the output current, the rise of the waveform is linked. Yes. Therefore, the advance degree 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 voltage V _IV1 .

  That is, when the time from the rise of the gate pulse to the switching of the output voltage VIV1 is short as shown in FIG. 6 (A), it is determined that the normal operation is performed, and the switching is performed as shown in FIG. 6 (B). It can be determined that the current advance angle θ with respect to the voltage has increased. The correlation between the advance angle and the elapsed time until switching may be examined in advance. Even when the degree of advance is detected in this way, it is possible to maintain the operation with the positive power by increasing Idc1 and increasing Vdc1.

Further, when the phase angle θ between the output current from the inverter 21 and the output voltage falls below the lower limit of the phase angle, a signal for improving the frequency of the output current I _IV may be output. On the other hand, when the phase angle θ exceeds the upper limit value of the phase angle, it is preferable to output a signal for decreasing the frequency. Particularly in this embodiment, when the phase angle θ increases, the power factor indicated by cos θ deteriorates. For this reason, when the phase angle θ approaches + 90 °, control is performed so that the frequency of the output current is separated from the resonance point (resonance frequency). By performing such control, it is possible to maintain the leading phase of the current with respect to the voltage, and it is possible to stably perform the ZCS operation.
It is effective to perform voltage control as described above after performing such frequency control.

DESCRIPTION OF SYMBOLS 10 ......... Induction heating apparatus, 12 (12a, 12b) ......... Induction heating coil, 14 (14a, 14b) ......... Waveform detection means, 16 (16a, 16b) ......... Waveform detection means, 18 (18a) 18b)... Phase angle determination means, 20 (20a, 20b) ......... Inverter, 22 (22a, 22b) ... Voltage converter, 24 (24a, 24b) ... Voltage control means, 26 ... ... IGBT, 28 ... ... Diode, 30 ... ... Smoothing capacitor, 32 ... ... Power supply.

Claims (3)

In an induction heating apparatus provided with a power source for supplying power to each of a plurality of induction heating coils that are mutually induced,
While making the operating frequency of the output current the same, obtain the phase angle θ of the polarity change point of the output current and output voltage ,
Determining whether the phase angle θ is in the range of 0 ° ≧ θ ≧ −90 °;
A control method for an induction heating apparatus, wherein control is performed to increase a power supply current or a power supply voltage when the phase angle θ is not within the range . The method of the induction heating apparatus according to claim 1, wherein while the same operation frequency of the output current, output power factor and controls to increase the power supply current or the supply voltage when decreased . The method for controlling the induction heating apparatus according to claim 1 or 2, wherein the increase in the power supply current or the power supply voltage is performed by controlling the frequency of the output current in a direction away from a resonance point.