JP4729692B2 - Induction heating device for power harmonics - Google Patents

Description

  The present invention relates to a high frequency inverter induction heating apparatus using a load commutation type thyristor type inverter, wherein a harmonic component (especially 3 times and 6 times frequency) on the power source side which is a three-phase commercial power supply and an output frequency on the high frequency inverter side are A thyristor control voltage that causes a resonance phenomenon when approaching, resulting in a phenomenon in which the output voltage beats, and a negative voltage cannot be applied to the thyristor beyond the commutation margin time, so that a cycle that fails in commutation is not generated The present invention relates to an induction heating apparatus provided with application.

  Conventionally, the high-frequency inverter used in the induction heating apparatus is a current-type inverter, and its main circuit is composed of a forward converter, a DC reactor, and an inverse converter. These elements perform the following operations.

  The forward converter generates a DC voltage from a three-phase commercial power source. The DC reactor removes the ripple of the DC voltage generated by the forward converter and supplies power to the inverse converter.

  The inverse converter supplies high frequency power corresponding to the load resonance frequency to the heating coil. Since the reverse converter is a load commutation type thyristor inverter, a storage carrier in the thyristor is applied by applying a negative voltage to the thyristor that has been ignited until the commutation margin time defined by the thyristor element. The thyristor restores the insulation ability. In that case, the commutation reactive power is supplied from a power factor correction capacitor installed in the high-frequency rectifier unit.

  Conventionally, the inverter in the above configuration supplies power to the heating coil of the load via the forward converter and the reverse converter, so that the main circuit receives a DC charge from the commercial power source side by the operation of each converter. It always flows in, and the DC charge superimposed on the main circuit becomes maximum when the output frequency is 3 and 6 times the power frequency.

The following problems occur due to the superposition of DC charges on the main circuit.
(1) The output voltage detection transformer is dc-biased and is heated and burned.
(2) Since a negative voltage sufficient to commutate the inverse converter cannot be applied, the thyristor cannot recover the insulation capability, the next cycle is applied, and the commutation fails. In the worst case, the thyristor is damaged due to overcurrent.

  Patent Document 1 is an invention provided with a control circuit that automatically restarts when commutation fails and the thyristor inverter of the induction heating device abnormally stops as described above.

  However, in this invention, since the maximum value of the output voltage for each cycle of the inverter is not always detected, the control circuit cannot cope with the harmonic component of the three-phase commercial power supply.

JP-A-11-113268 (pages 2, 3 and 1)

In order to solve the above-described problems, it is an object of the present invention to provide a power harmonic corresponding induction heating apparatus that discharges a DC charge superimposed on a main circuit and performs stable main circuit operation.
Specifically, the output voltage of the inverter is always detected as a relationship of electrical angle (or phase angle) degrees, the maximum value from the “zero point” is stored every half cycle (180 degrees), and the difference is calculated. Provided is an induction heating apparatus for power supply harmonics, comprising means for adding to a control signal an addition that changes an ignition timing electrical angle or phase angle of a gate signal to a thyristor in the next cycle.

In order to solve the above-described problems, an induction heating apparatus for power harmonics according to the present invention eliminates a reverse converter that generates a DC voltage from a three-phase commercial power supply and a ripple of the DC voltage generated by the forward converter. A DC reactor that supplies power to the converter, a reverse converter having a single-phase inverter configuration that supplies high-frequency power corresponding to the load resonance frequency to the heating coil, and the delay power factor of the heating coil is improved in the forward direction, and In an induction heating apparatus comprising at least a power factor correction capacitor that supplies reactive power for commutation to an inverse converter,
A timing control for starting each thyristor constituting each of the forward converter and the reverse converter, and a control circuit unit for performing control to protect the thyristor from overvoltage or overcurrent;
The control circuit unit synchronizes with the inverter output voltage from the inverse converter, and generates a triangular wave PLL (Phase Locked Loop) signal for each half cycle (180 degrees) that alternately outputs positive and negative; and
When the triangular wave PLL signal value rises as the phase angle progresses, the next half cycle is alternately fired to the U-phase pair thyristor and V-phase pair thyristor of the inverse converter when the signal crosses the predetermined reference signal value K. An ignition control signal output means for sending a control signal to the gate electrode at the position angle;
The maximum value V1 of the inverter output voltage in half cycle by the U-phase pair thyristor of the inverse converter is detected and stored in the storage unit in the control circuit unit or the sample & hold circuit X1, and the half cycle by the next V-phase pair thyristor is detected. Inverter output voltage detection means that detects the highest value V2 of the inverter output voltage, stores it in the storage unit or the sample and hold circuit X2, and repeats sequentially,
The value of the inverter output voltages V1 and V2 of the storage unit or the sample and hold circuits X1 and X2 is compared every half cycle detection. If V1 <V2, the thyristor firing timing at that time is advanced, and V1> V2 If there is, an ignition timing changing means for delaying the ignition timing of the thyristor at that time is provided.

The ignition timing changing means calculates a difference value V1−V2 = ΔV between the inverter output voltages V1 and V2 for each half cycle detection;
Means for adding the difference ΔV by a predetermined reference signal value K;
It comprises a change firing control signal output means for sending a control signal at the position angle when crossing the added reference signal value (K + ΔV) while the triangular wave PLL signal value is rising as the phase angle progresses. And

  According to the induction heating apparatus corresponding to the power supply harmonics of the present invention, the AC condition of the main circuit power supply is established by variably controlling the ignition of the inverter according to the DC charge generated by the power supply harmonics. That is, by discharging the DC charge superimposed on the main circuit every half cycle of the output voltage of the thyristor, the stable operation of the main circuit corresponding to the power harmonic can be performed.

  Embodiments of the induction heating apparatus for high frequency according to the present invention will be described with reference to the drawings. FIG. 1 is a view showing a configuration of an induction heating apparatus for power harmonics according to the present invention.

  In the figure, 1 is a three-phase commercial power source, 2 is a forward converter, which is composed of thyristors (21 to 26) and generates a DC voltage based on the three-phase commercial power source 1. Reference numeral 3 denotes a DC reactor, which removes a DC voltage ripple generated in the forward converter 2.

  The reverse converter 4 is composed of thyristors (41 to 44), and the direct current reactor 3 suppresses a sudden outflow of overcurrent when the reverse converter 4 or a load is broken.

  The inverter 4 has a single-phase inverter configuration, and supplies high-frequency power to the heating coil 6 according to the load frequency.

  A power factor improving capacitor 5 improves the delay power factor of the heating coil 6 in the forward direction, and supplies commutation reactive power to the thyristors (41 to 44) of the inverse converter 4.

  For example, when a metal material such as iron is put into the furnace, the heating coil 6 generates “eddy current” in the metal material in the furnace by being supplied with high-frequency power from an inverter having a reverse converter 4 configuration. The metal material is heated and melted by Joule heat generated by the current flowing between the metal materials.

  Reference numeral 7 denotes a control circuit unit that performs timing control for igniting the thyristors (21 to 26) and (41 to 44) of the forward converter 2 and the inverse converter 4, and detects whether the thyristor is overvoltage / overcurrent. Protect.

  In the induction heating apparatus having the above circuit configuration, resonance occurs when the frequency of the three-phase commercial power source 1 is 3 times and 6 times the frequency (eg, 50 Hz × 6 = 300 Hz at 50 Hz) and the output frequency on the high frequency side approach each other. A phenomenon occurs in which the high-frequency output voltage beats as shown in FIG.

  When this beat phenomenon becomes a trigger, PN voltage irregularities occur. The commutation margin time decreases and commutation failure occurs. FIG. 3 is a diagram showing a voltage waveform between P and N. When the DC charge is superimposed, the commutation margin time varies, and when the commutation margin time <the turn-off time, the worst commutation fails.

  As shown in FIG. 1, the PN voltage is set such that the anode side of the thyristors 41 and 42 of the inverter of the inverter 4 is the P terminal, the cathode side of the thyristors 43 and 44 is the N terminal, This is the voltage across the N terminals.

  The cause of the non-uniform PN voltage is that the residual voltage is superimposed on the main circuit of the inverter, so that the “voltage as a direct current component” is superimposed on the output voltage.

  The reverse converter 4 is commutated by supplying reactive power from the power factor adjusting capacitor 5, and the negative voltage period is on until the turn-off time Tq of the thyristors (41 to 44) used for the reverse converter 4. When applied to a thyristor that has been in the normal state, the thyristor discharges the storage carrier and recovers the insulation capability.

  However, as described above, when the DC voltage is superimposed on the output voltage, the zero point of the PN voltage of the main circuit fluctuates at a constant period, and a negative voltage longer than the commutation allowance time Tq inherent to the thyristor is applied. Failure to do so causes the thyristor to fail to commutate without recovering its insulating ability.

  In the normal induction heating apparatus, the ignition timing of the inverter is generated by synchronizing the main circuit voltage with a PLL (Phase Locked Loop) circuit in the control circuit unit 7 to generate a PLL signal triangular wave. The next inverter output voltage is output by a control signal that is set to generate a gate signal to the thyristor at the phase angle of the intersection with the reference signal. The state is shown in FIG. FIG. 4 is a diagram showing the inverter ignition timing (1).

  The control circuit unit 7 constantly detects the inverter output voltage, stores the first detection voltage V1 in the sample-and-hold circuit or the storage unit in the control circuit unit 7, and similarly samples the next detection voltage V2. Store in the hold circuit or storage unit.

  Here, if V1 <V2, the control circuit unit 7 advances the current thyristor ignition timing, and conversely if V1> V2, the control circuit unit 7 delays the thyristor ignition timing.

  Next, the ignition timing is set by the program means in the control circuit unit 7 as follows.

  The program means reads V1 and V2 from the stored memory, calculates a difference ΔV between V1 and V2, and outputs a control signal corrected by adding the difference value to the predetermined reference signal.

  The state is shown in FIG. FIG. 5 is a diagram showing the ignition timing (2) of the inverter according to the present invention. In FIG. 5, the inverter output voltage is detected with respect to the zero point (indicated by a broken line), and stored V1, V2, a PLL signal synchronized with the output voltage, a reference signal for comparison with the PLL signal, and generated by a comparison operation. Shows the gate signal.

  Since V2 is detected in the next half cycle and V1 <V2, the timing of the gate signal (ignition timing) is set so that the current reference signal is lowered, that is, the crossover with the PLL signal occurs earlier than when correction is not performed. To be quick.

  As shown in the PN voltage waveform of FIG. 6, the ignition timing is advanced so that the commutation margin time in the half cycle of V2 is not short, and no commutation failure occurs.

  As described above, by changing the gate timing of the inverter, the AC condition (positive = negative) of the output current is made the same as shown in FIG. It prevents current failure and DC magnetism of the inverter output voltage detection transformer (VT).

  This method can discharge the residual charge superimposed on the main circuit regardless of the matching method (HMT method, capacitor voltage doubler method) between the inverter and the heating coil.

It is a figure which shows the structure of the power supply harmonic corresponding | compatible induction heating apparatus of this invention. It is a figure which shows the beat phenomenon of an output voltage. It is a figure which shows a PN voltage waveform. It is a figure which shows the ignition timing (1) of an inverter. It is a figure which shows the ignition timing (2) of the inverter of this invention. It is a figure which shows the alternating current conditions of a power supply.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Three-phase commercial power source 2 Forward converter 3 DC reactor 4 Reverse converter 5 Power factor improvement capacitor 6 Heating coil 7 Control circuit part

Claims (2)

A forward converter that generates a DC voltage from a three-phase commercial power supply, a DC reactor that removes the ripple of the DC voltage generated by the forward converter and supplies power to the inverter, and high-frequency power corresponding to the load resonance frequency An inverter having a single-phase inverter configuration to be supplied to the heating coil, and a power factor improving capacitor for improving the delay power factor of the heating coil in the forward direction and supplying the reactive power for commutation to the inverter. In the induction heating apparatus provided,
A timing control for starting each thyristor constituting each of the forward converter and the reverse converter, and a control circuit unit for performing control to protect the thyristor from overvoltage or overcurrent;
The control circuit unit synchronizes with the inverter output voltage from the inverse converter, and generates a triangular wave PLL (Phase Locked Loop) signal for each half cycle (180 degrees) that alternately outputs positive and negative; and
When the triangular wave PLL signal value rises as the phase angle progresses, the next half cycle is alternately fired to the U-phase pair thyristor and V-phase pair thyristor of the inverse converter when the signal crosses the predetermined reference signal value K. An ignition control signal output means for sending a control signal to the gate electrode at the position angle;
The maximum value V1 of the inverter output voltage in half cycle by the U-phase pair thyristor of the inverse converter is detected and stored in the storage unit in the control circuit unit or the sample & hold circuit X1, and the half cycle by the next V-phase pair thyristor is detected. Inverter output voltage detection means that detects the highest value V2 of the inverter output voltage, stores it in the storage unit or the sample and hold circuit X2, and repeats sequentially,
The value of the inverter output voltages V1 and V2 of the storage unit or the sample and hold circuits X1 and X2 is compared every half cycle detection. If V1 <V2, the thyristor firing timing at that time is advanced, and V1> V2 If there exists, the power source harmonic corresponding | compatible induction heating apparatus provided with the ignition timing change means which delays the ignition timing of the thyristor at that time. The ignition timing changing means calculates a difference value V1−V2 = ΔV between inverter output voltages V1 and V2 for each half cycle detection;
Means for adding the difference value ΔV to the predetermined reference signal value K;
It comprises a change firing control signal output means for sending a control signal at the position angle when crossing the added reference signal value (K + ΔV) while the triangular wave PLL signal value is rising as the phase angle progresses. The induction heating apparatus for power supply harmonics according to claim 1.

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