JP5066693B2 - Induction heating device with power control for each heating coil - Google Patents

Description

  The present invention relates to an induction heating apparatus that can supply desired high-frequency power to each of a plurality of heating coils with a single high-frequency inverter and a control device.

  When using multiple or large induction melting furnaces and induction heating devices, it was necessary to heat them simultaneously using multiple heating coils. Conventionally, in such a case, a high frequency power supply device is provided for each heating coil, and high frequency power is supplied to each heating coil.

  For this reason, there has been a problem that the high-frequency power supply facility becomes large and a plurality of expensive facilities must be provided.

  Moreover, the high frequency inverter used for the conventional induction heating apparatus is a current type inverter, and includes a forward converter, a DC reactor, an inverse converter, a power factor correction capacitor, and each thyristor constituting the forward converter and the inverse converter. The control circuit includes a control circuit that performs timing control for firing and protects the thyristor from overvoltage or overcurrent. However, these devices were connected to the output and there was one controllable heating coil.

  An example of a conventional induction heating apparatus is shown in FIG. Here, 1 is a power source, 12 is a transformer for a converter that adjusts a commercial power supply voltage to a predetermined voltage in order to obtain a target inverter output voltage, 2 is a forward converter composed of 21-26 thyristors, and 3 is a DC reactor. Reference numeral 4 denotes an inverse converter composed of 41-44 thyristors, 5 denotes a power factor correction capacitor, 6 denotes a heating coil, 8 denotes a DC voltage detection circuit, and 10 denotes a control circuit.

  That is, a plurality of the above induction heating apparatuses are used, and a plurality of or large melting furnaces are controlled to a predetermined desired temperature distribution.

  Therefore, as shown in Patent Document 1, an induction heating apparatus in which a single power source is connected to a plurality of induction coils via a switching circuit has been invented. According to the present invention, it is not necessary to use a plurality of induction heating apparatuses, and the problem of large-scale high-frequency power supply equipment and expensive equipment is solved.

  However, when controlling to a predetermined temperature distribution in Patent Literature 1, the period of power supplied to each induction coil via the switching circuit (that is, the duration or interval) is controlled by the control circuit.

  That is, the temperature distribution in the axial direction is controlled to a predetermined desired temperature distribution by changing the duration (duty cycle) to each of the coil sections by a predetermined method. (See paragraphs “0015”, “0018” and “0019” in Patent Document 1)

  Therefore, in the temperature distribution control system of Patent Document 1, the power duration (duty cycle) requires a relatively long time with respect to the inverter output voltage cycle time.

  For this reason, there has been a drawback that voltage fluctuations within each cycle time of the inverter output voltage cannot be dealt with. That is, there is a problem that precise voltage waveforms cannot be controlled. In particular, it is impossible to cope with proximity effects between induction coils to be dealt with within each cycle time, voltage fluctuations due to mutual induction, etc., and it is difficult to immediately cope with overvoltage and overcurrent.

JP-T-2002-529906 (2nd, 3rd page, Fig. 1)

  The present invention uses a single induction heating high-frequency inverter to automatically determine the high-frequency power required for each of the plurality of heating coils based on the transfer flow angle for each cycle of the inverter output voltage. Provided is an induction heating device capable of controlling power for each heating coil to which power can be supplied.

The induction heating device capable of controlling the power for each heating coil according to the present invention includes a forward converter that generates a DC voltage from an AC commercial power supply, a DC reactor that removes a ripple component of the generated DC voltage, and a load resonance frequency. An inverter having a single-phase inverter configuration that outputs a high-frequency voltage to the first heating coil, a power factor correction capacitor of the first heating coil, and each thyristor that constitutes each of the forward converter and the inverse converter. In the induction heating apparatus including at least a first control circuit that performs timing control for firing and protects the thyristor from overvoltage and overcurrent,
Based on the position of the first heating coil, a second heating coil or a plurality of second to n-th heating coil groups further disposed,
In the case of the second heating coil arrangement, a pair of thyristor switches connected in series to the second heating coil and connected in reverse parallel to limit the flow phase angle of the high-frequency voltage output to the heating coil;
In the case of arranging the plurality of second to nth heating coil groups, a plurality of anti-parallel connections that limit the flow phase angle of the high-frequency voltage for each heating coil in series with each heating coil. A pair of thyristor switches,
Both terminals of a series connection circuit of the second heating coil and thyristor switch pair or a plurality of terminals of each series connection circuit of the plurality of heating coils and a plurality of thyristor switch pairs are connected to the high-frequency voltage output terminal. An output lead-in line;
A forward pressure detection circuit that detects a forward pressure generated when any of the thyristors of the thyristor switch pair is turned off, and outputs a detection signal;
A second control circuit that controls the phase of each flow angle of the thyristor switch pair based on a detection signal from the forward pressure detection circuit, and can detect and protect overvoltage and overcurrent with respect to the thyristor elements. And
The flow phase angle to the second heating coil is limited on the basis of the output of the first heating coil and controlled to the required output, or for each of the second to nth heating coils. The flow phase angle is limited, and the output required for each heating coil is controlled.

The second control circuit detects the inverter output voltage from a signal for controlling the voltage output from the single-phase inverter of the inverse converter of the first control circuit to the heating coil, and the second control circuit Means for generating a triangular wave synchronized with each positive and negative 180 degree cycle of the detection signal in a PLL (Phase Locked Loop) circuit built in
A reference signal value corresponding to the required electric energy is stored in advance for each heating coil arranged, and one of the phase angles at which the amplitude of the triangular wave PLL circuit signal matches the reference signal value in a positive 180 degree cycle. And igniting the other thyristor with a phase angle that coincides with a negative 180-degree cycle.

  A resonance circuit comprising at least a power factor correction capacitor connected in parallel to the first heating coil includes a thyristor switch circuit connected in series to the circuit, and when the apparatus is started, the thyristor is first connected. The switch circuit is turned on to form a resonance waveform.

  According to the present invention, by providing the same number of thyristor switches as the number of heating coils, a plurality of heating coils can be connected to one current type inverter. Furthermore, each thyristor switch can be controlled to supply a desired output for each heating coil.

  For this reason, the supply of high-frequency power having the same performance as the conventional one can be reduced in cost and greatly reduced in size.

  An embodiment of an induction heating apparatus capable of controlling power for each heating coil according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a first embodiment in which a second heating coil 62 to be added as necessary is arranged in the first heating coil 61, and the first heating is usually performed corresponding to the object to be heated. The arrangement position of the second heating coil is determined based on the position of the coil 61.

  1, reference numerals 1, 2 (21-26), 3, 4 (41-44), 5, 8, 10, and 12 have the same functions as those described in the background art in FIG. There is no explanation. Incidentally, 10 is referred to as a first control circuit.

  Reference numerals 71 and 77 denote thyristor switch pairs in which thyristors are connected in reverse parallel. This reverse parallel connection circuit is connected in series to the second heating coil, and limits the flow phase angle of the high-frequency voltage output from the inverse converter 4 to the heating coil 62 to generate electric power to be generated in the heating coil 62. Control.

  Reference numeral 9 denotes a forward pressure detection circuit that detects a forward pressure generated when any of the thyristors of the thyristor switch pair 71 and 72 is turned off, and outputs the detected signal.

  Reference numeral 11 denotes a second control circuit, which controls the phase of the flow angle for each thyristor of the thyristor switch pair 71 and 72 on the basis of the detection signal from the forward pressure detection circuit 9, while overvoltage to the thyristor elements. , Overcurrent is detected, and protection processing (at least warning display, etc.) is performed.

  Reference numeral 13 denotes a starting circuit. The starter circuit 13 is a load commutation type and a current type inverter because the inverter 4 is composed of a load commutation type, and therefore a parallel resonance composed of a power factor correction capacitor 5, a heating coil 61 and a material heated in the heating coil. Since the circuit does not have a resonance waveform at the start-up, the start-up circuit 13 is turned on to induce the resonance waveform of the load resonance circuit.

  The thyristors 41 to 44 of the inverse converter are single-phase inverters, and a pair of thyristors 41 and 44 (hereinafter referred to as U phase) and a pair of thyristors 42 and 43 (hereinafter referred to as V phase) for the inverse converter are alternately arranged. It operates by repeating ON / OFF.

  Since the thyristors 41 to 44 of the inverse converter are thyristor inverters, for example, when the U phase is turned off and the V phase is turned on (hereinafter referred to as commutation), the predetermined reactive power is supplied to the thyristors 41 and 44 that are turned off. As a result, the storage carrier in the thyristor that has been turned on so far is discharged to restore the insulation ability to withstand the next V-phase forward pressure.

  The commutation reactive power is supplied from the power factor correction capacitor 5 and is commutated, and a negative voltage (hereinafter referred to as γ) longer than the turn-off time Tq of the thyristor used for the thyristors 41 to 44 of the reverse converter is turned on until now. By applying to the thyristor that has been in the state, the thyristor discharges the storage carrier and restores the insulation capability.

  Next, the operations of the thyristor switch pair 71, 72, the forward pressure detection circuit 9, and the second control circuit 11 will be described in detail with reference to FIG.

  The second control circuit 11 includes at least the following two means.

  One of the means detects the inverter output voltage from a signal for controlling the voltage output to the heating coil from the single-phase inverter of the inverter 4 by the first control circuit, and incorporates the inverter output voltage in the second control circuit. A PLL (Phase Locked Loop) control circuit is a means for generating a triangular wave that is synchronized every 180 degrees (half cycle) of the detected signal.

  The following means stores in advance a reference signal value corresponding to the required electric energy in the arranged second heating coil 62, and (1) the amplitude of the triangular wave PLL circuit signal in a positive 180 degree cycle. One thyristor is fired at a phase angle that matches the reference signal value, and the other thyristor is fired at a phase angle that coincides in a negative 180 degree cycle as in (2).

  Note that the PLL control circuit is a known circuit, and includes a binarization circuit that converts a sinusoidal inverter output voltage into a rectangular wave, and a phase comparator that compares the phase of the rectangular wave with the output waveform of the PLL control circuit. A loop filter that converts a digital signal that is an output of the phase comparator into an analog signal that can be recognized by a VCO (voltage controlled oscillator) at a subsequent stage, a VCO that varies an oscillation frequency according to the input voltage, and a VCO output that has the phase And a frequency divider that divides the frequency into frequencies that can be recognized by the comparator.

  FIG. 3 is an explanatory diagram of the ignition timing of the thyristor switch pair 71 and 72 as described above. A sine wave of the inverter output voltage from the inverse converter 4 to the first heating coil 61 is shown in the upper part of FIG.

  The PLL signal indicates the above-described triangular wave PLL circuit signal, and indicates a PLL signal voltage generated by a circuit built in the second control circuit 11.

  On the other hand, the reference signal indicated by a broken line indicates a desired amount of power for the second heating coil 62, and the intersection with the PLL signal is controlled to an applied voltage corresponding to the power at the pair of thyristor switches 71 and 72. The gate signals 1 and 2 to the thyristors 71 and 72 are shown. That is, the electric power is controlled by the phase flow angle.

  Gate signal 1 fires thyristor 71 when the inverter output voltage is positive 180 degrees half cycle, and gate signal 2 fires thyristor 72 when the inverter output voltage is negative 180 degrees half cycle.

  That is, the gate signal is generated at the phase angle when the reference signal voltage matches the triangular-wave PLL circuit signal voltage.

  That is, the reference signal is a signal for firing the thyristor switch pair at an arbitrary electrical phase angle.

  Thereby, arbitrarily variable power can be simultaneously supplied to a plurality of heating coils based on the high-frequency power synchronized with the inverter output frequency.

  FIG. 2 shows a second embodiment of the induction heating apparatus of the present invention in which a plurality of second to nth heating coils are arranged based on the first heating coil.

  Here, 62... 69 indicate second... Nth heating coils. A thyristor switch pair 71 and 72 is connected in series to each of the second to n-th heating coils 62 to 69, and both ends of the series circuit are generated by the inverter 4. Corresponding to the load resonance frequency, the high frequency voltage output terminal connected to the first heating coil 61 is connected to an output lead line.

  Further, each of the thyristor switch pairs 71 and 72 connected in series to each of the second to nth heating coils has a forward pressure generated when the forward pressure detection circuit 9 is turned off. The detection signal line is connected to the second control circuit 11 for each thyristor switch pair, and the detection signal is input.

  As in the case of the first embodiment, the second control circuit 11 is based on the detection signals from the thyristor switch pairs 71 and 72 via the barometric pressure detection circuit 9, and each of the thyristor switch pairs 71 and 72. Phase control of the flow angle for each thyristor is performed, and overvoltage and overcurrent are detected for each thyristor to perform protection processing.

  In the second control circuit 11, the two means described above are also applied to a plurality of heating coils and thyristor switch pairs in the same manner as in the first embodiment.

  One of the means is a means for generating a triangular wave having a period every 180 degrees (half cycle) of the inverter output voltage as described above.

  The following means stores in advance a reference signal voltage corresponding to the amount of power required for each of the second to n-th heating coils 62 to 69 arranged, and the triangular wave of each thyristor switch pair is stored. Each thyristor is ignited at the phase angle of each positive and negative cycle in which the amplitude voltage of the PLL circuit signal matches the reference signal voltage.

  FIG. 4 shows an example of firing timing of a plurality of thyristor switch pairs. In this embodiment, (a) the output voltage of the thyristor switch pair 1 is compared with (b) the output voltage of the thyristor switch pair 2.

  The case where there are the Pth and Qth heating coils respectively connected in series to the thyristor switch pairs of (a) and (b) arranged in addition to the first heating coil 61 of the induction heating device is shown.

  Since the first heating coil 61 does not have a thyristor switch pair, the entire phase angle of the inverter output voltage is naturally distributed and applied to the first heating coil, but the circulating phase is applied to the Pth heating coil as shown in FIG. The angle is partially limited, and the Pth heating coil is less than the output power of the first heating coil 61 by the thyristor switch pair 1.

  On the other hand, as shown in FIG. 4 (b), the Q-th heating coil is limited to a narrower phase angle than the case of (a) by the thyristor switch pair 2, and becomes smaller than the output voltage of (a).

  Here, the flow phase angle in the case of (a) depends on the gate signal 1A in the positive cycle of the thyristor switch pair 1 and the gate signal 1B in the negative cycle.

  On the other hand, the flow phase angle in the case of (b) depends on the gate signal 2A in the positive cycle of the thyristor switch pair 2 and the gate signal 2B in the negative cycle.

  4 (a) and 4 (b), the phase angle of the generation position of the gate signal 1 is smaller than the phase angle of the generation position of the gate signal 2, and in FIG. 4 (a) is the center of the positive or negative cycle. Near (maximum voltage).

  As described above, the phase position of the gate signal is determined by the respective reference signal voltages as described in FIG.

  That is, the closer the reference signal voltage is to ½ of the maximum voltage of the triangular wave, the higher the output from the heating coil, and the closer to the maximum voltage of the triangular wave, the smaller the output from the heating coil.

  In addition, about the arrangement position of a plurality of heating coils, it is related with the form, structure, etc. of the heating object of an induction heating device, and the output for every heating coil is related to the temperature distribution with respect to the heating object required as a whole. To be determined.

The operation of the apparatus will be described in further detail below.
The thyristor switch pair 71 and 72 operate in conjunction with an inverter that operates in synchronization with a parallel resonance waveform generated from the power factor improving capacitor 5, the heating coil 61, and the material heated in the heating coil. Since there is no resonance waveform in the load resonance circuit, the thyristor switch pair 71 and 72 cannot be activated independently.

  For this reason, it is necessary to start the thyristor switch pair 71 and 72 next after the inverter is started and the resonance waveform of the load resonance circuit of the heating coil 61 directly connected to the inverter is stabilized.

  The output power of the thyristor switch pair 71 and 72 is synchronized with the output voltage of the thyristors 41 to 44 of the inverse converter by the PLL control circuit in the second control circuit 11, and is 180 in electrical angle every positive and negative half cycle. The thyristor used for the thyristor switch pair 71 and 72 is ignited at a predetermined electrical angle by the triangular wave signal generated as the angle signal and the reference signal for determining the power supplied to the heating coil 62. The phase is controlled as follows.

  The thyristor switch pair 71 and 72 alternate with the thyristor switch 71 when the output of the thyristors 41 to 44 of the reverse converter is positive in the half cycle, and with the thyristor switch 72 when the output of the thyristors 41 to 44 of the reverse converter is negative. Is turned on to supply power to the heating coil 62.

  The output power of the thyristor switch pair 71 and 72 is distributed from the high frequency power output from the inverter by output voltage control, and the output voltage control of the thyristor pair 71 and 72 can be performed with a setting lower than the inverter output voltage.

  Therefore, even if the reference signal for the thyristor switch pair 71 and 72 is set to power or voltage higher than the inverter output, the thyristor switch pair 71 and 72 cannot output.

  Thus, if the total output power of the thyristor switch is less than the inverter output power and each output voltage of the thyristor switch is less than the inverter output voltage, a plurality of thyristor switches are synchronized with the inverter output frequency. Power can be supplied to the heating coil.

It is a 1st Example of an induction heating apparatus. (When the second heating coil is further provided) It is a 2nd Example of an induction heating apparatus. (When a plurality of second to nth heating coils are further provided) It is an ignition timing example of a thyristor switch pair. It is a firing timing example of a plurality of thyristor switch pairs. It is a block diagram of the conventional induction heating apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Three-phase alternating current commercial power supply 2 Forward converter 3 DC reactor 4 Inverter 5 Power factor improvement capacitor 6 Heating coil 21-26, 41-44 Thyristor 61, 62, ... 69 1st-nth heating coil 71・ 72 thyristor switch pair (reverse parallel connection circuit)
DESCRIPTION OF SYMBOLS 8 DC voltage detection circuit 9 Forward pressure detection circuit 10 1st control circuit 11 2nd control circuit 12 Transformer for converters 13 Start-up circuit

Claims (3)

A forward converter that generates a DC voltage from an AC commercial power supply, a DC reactor that removes a ripple component of the generated DC voltage, and a single-phase inverter configuration that outputs a high-frequency voltage corresponding to the load resonance frequency to the first heating coil Inverter, the power factor improving capacitor of the first heating coil, and each thyristor constituting each of the forward converter and the reverse converter are controlled in timing, and the thyristor is detected from overvoltage and overcurrent. In an induction heating apparatus comprising at least a first control circuit for protecting
Based on the position of the first heating coil, a second heating coil or a plurality of second to n-th heating coil groups further disposed,
In the case of the second heating coil arrangement, a pair of thyristor switches connected in series to the second heating coil and connected in reverse parallel to limit the flow phase angle of the high-frequency voltage output to the heating coil;
In the case of arranging the plurality of second to nth heating coil groups, a plurality of anti-parallel connections that limit the flow phase angle of the high-frequency voltage for each heating coil in series with each heating coil. A pair of thyristor switches,
Both terminals of a series connection circuit of the second heating coil and thyristor switch pair or a plurality of terminals of each series connection circuit of the plurality of heating coils and a plurality of thyristor switch pairs are connected to the high-frequency voltage output terminal. An output lead-in line;
A forward pressure detection circuit that detects a forward pressure generated when any of the thyristors of the thyristor switch pair is turned off, and outputs a detection signal;
A second control circuit that controls the phase of each flow angle of the thyristor switch pair based on a detection signal from the forward pressure detection circuit, and can detect and protect overvoltage and overcurrent with respect to the thyristor elements. And
The flow phase angle to the second heating coil is limited on the basis of the output of the first heating coil and controlled to the required output, or for each of the second to nth heating coils. An induction heating apparatus capable of controlling electric power for each heating coil, wherein the flow phase angle is limited and controlled to an output required for each heating coil. The second control circuit detects the inverter output voltage from a signal for controlling the voltage output from the single-phase inverter of the inverse converter by the first control circuit to the heating coil, and is incorporated in the second control circuit. Means for generating a triangular wave synchronized with each positive and negative 180 degree cycle of the detected signal in a PLL (Phase Locked Loop) circuit,
A reference signal value corresponding to the required electric energy is stored in advance for each heating coil arranged, and one of the phase angles at which the amplitude of the triangular wave PLL circuit signal matches the reference signal value in a positive 180 degree cycle. And a means for igniting the other thyristor with a phase angle that coincides with a negative 180-degree cycle, the power control being possible for each heating coil. Induction heating device. A resonance circuit comprising at least a power factor correction capacitor connected in parallel to the first heating coil includes a thyristor switch circuit connected in series to the circuit, and when the apparatus is started, the thyristor switch circuit is first provided. 2. An induction heating apparatus capable of controlling power for each heating coil according to claim 1, wherein a resonance waveform is formed by turning ON the power.

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