JP4887510B2 - Induction heating device with commutation failure detection. - Google Patents

Description

  The present invention relates to a high frequency inverter induction heating apparatus using a load commutation type thyristor type inverter, and a thyristor is caused by an overcurrent flowing in a short circuit state without recovering an insulation capacity due to a commutation failure due to a shortage of commutation margin angle. The present invention relates to an inductive heating apparatus with commutation failure detection that can detect the commutation failure at a high speed and can deal with it in order to prevent damage and permanent failure.

  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 commutated thyristor inverter, the storage carrier in the thyristor is removed by applying a negative voltage to the thyristor that has been ignited until the turn-off time specified by the thyristor element. Thus, the thyristor restores the insulation capability. In that case, the commutation reactive power is supplied from a power factor correction capacitor installed in the high-frequency matching unit.

  Conventionally, the commutation failure detection due to the shortage of the commutation margin time of the inverter in the above configuration is performed as follows. That is, when the inverter reverse converter of the conventional inverter fails to commutate, the thyristor that has failed commutation is short-circuited, causing unnecessary overcurrent, and the difference between the input current and the output current is 20% or less. The commutation failure was detected.

  However, since the forward converter and the reverse converter are connected via a DC reactor, even if the reverse converter fails in commutation, sudden transient fluctuations in current cannot be made, and protection processing is performed after the commutation fails. When an excessive current continues to flow through the failed thyristor until it enters the thyristor, the thyristor is often damaged, resulting in a permanent failure.

  Patent Document 1 is an invention relating to a control circuit that automatically restarts a high-frequency power supply device or induction heating device having a thyristor inverter of an inverse converter when the thyristor inverter is abnormal and stops.

  The invention of Patent Document 1 includes a control circuit including a commutation failure detection circuit, a gate pulse phase control circuit, and a correction amount control circuit that sets a gate pulse position to a correction value of a commutation margin angle. The system is restarted by a gate pulse.

  However, since it takes time until the abnormality is detected, the thyristor often breaks down due to an overcurrent before restarting.

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

  In order to solve the above-mentioned problems, it is an object of the present invention to prevent failure of a thyristor by detecting a commutation failure of a thyristor type inverter at high speed.

  Specifically, the forward pressure by the DC voltage detection circuit installed between the forward converter and the reverse converter and the forward pressure (presence / absence) at the timing of a predetermined electrical angle or phase angle generated by the PLL control circuit in the control circuit And a means for detecting a commutation failure with normal pressure (with).

In order to solve the above problems, an inductive heating apparatus with commutation failure detection according to the present invention removes a forward 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 inverter, an inverter of a current type single-phase inverter 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. In addition, in an induction heating apparatus comprising at least a power factor correction capacitor for supplying reactive power for commutation to the inverse converter, a DC circuit P for connecting the DC reactor and the inverse converter, and a zero point circuit N And a timing control for starting each thyristor constituting each of the forward converter and the reverse converter, and an overvoltage or overcurrent. Further comprising a control circuit section for performing control to protect al the thyristor, wherein the control circuit unit takes the inverter output voltage and synchronizing said inverter generates, each half cycle of outputting alternately positive and negative (180 ° ), And a PLL circuit that generates a triangular wave PLL (Place Locked Loop) signal, and a U-phase pair to the inverse converter when crossing to a predetermined reference signal value K while the triangular wave PLL signal value increases as the phase angle progresses A firing control signal output means for sending a control signal at the crossed phase angle to the gate electrode so as to alternately fire the next half cycle to the thyristor and the V-phase pair thyristor; and the PN DC voltage detection circuit section but the read voltage waveform data between P-N as a function of the phase angle the every half cycle (180 degrees), the between half cycle, the positive voltage period positive Pas A forward pressure detection signal A receiving means for receiving a forward pressure detection signal A output as a pulse voltage waveform; an inversion means for inverting the forward pressure detection signal A to generate an inverted forward pressure detection signal B; and the PLL circuit An angle generating means for generating an angle detection signal C having a predetermined angular width at a predetermined phase angle within a quarter cycle (90 degrees) of a half of the half cycle from the generated triangular wave PLL signal; wherein the inverted order pressure detection signal B to generate a commutation failure detection signal D from the logical product of the angle detection signal C, the commutation failure detection signal D is equal in the on state, determines that commutation failure, the result And a commutation failure determination means for outputting or displaying the above.

  The induction heating device with commutation failure detection of the present invention has the following effects. That is, the “angle detection signal” can be set at an arbitrary position of the electrical angle, that is, the phase angle for each positive and negative cycle of the inverter output voltage (for every 180 degrees of the electrical angle). ”Is set to 90 degrees before the electrical angle of each cycle for a certain period, the thyristor that fails in commutation is stopped before the maximum forward pressure of the next phase is applied, and the thyristor is protected from damage. Can enter and stop operation.

  An embodiment of the induction heating device with commutation failure detection according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of an induction heating device with commutation failure detection.

  In FIG. 1, reference numeral 1 denotes a three-phase commercial power source, and 2 denotes a forward converter, which includes 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 ripple component of the DC voltage 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 DC voltage detection circuit unit that detects a PN voltage applied to a DC voltage rectified via the DC reactor 3 between both ends PN of the inverter 4 (see FIG. 1). .

  Reference numeral 8 denotes a control circuit unit which protects the thyristor and the like from timing control for firing the thyristors of the forward converter 2 and the reverse converter 4 and overvoltage / overcurrent.

  The inverse converter 4 is a single-phase inverter, and the high-frequency power is generated by alternately turning on and off the pair of thyristors 41 and 44 (U-phase pair) and the pair of 42 and 43 (V-phase pair) at a predetermined frequency. Output.

  Since the above inverter 4 has a thyristor inverter configuration, for example, in the case of commutation in which the U-phase pair is turned off and the V-phase pair is turned on, the predetermined reactive power is supplied to the thyristors (41, 44). Thus, by discharging the storage carrier in the thyristor that has been turned on so far, the insulation ability to withstand the forward pressure of the next V-phase pair is recovered.

  The reactive power for commutation is supplied from the power factor improving capacitor 5 and commutated, and the negative voltage application period electrical angle γ equal to or longer than the turn-off time Tq of each thyristor used in the inverter 4 is used so far. When applied to the thyristor that is in the on state, the thyristor discharges the storage carrier and restores the insulation capability.

  If the negative voltage application time corresponding to the electrical angle γ is longer than the turn-off time Tq, the normal operation can be performed. However, if the turn-off time Tq is shorter, the thyristor cannot recover the insulation capability, and then turns on. The commutation fails without being able to withstand the forward pressure of the U-phase pair or V-phase pair.

  FIG. 2 is a diagram illustrating timings at which the thyristors (41 to 44) operated as single-phase inverters of the inverter 4 are fired.

  The control circuit unit 8 is provided with a phase locked loop (PLL) circuit, which generates a triangular wave PLL signal in synchronization with the main circuit voltage. When the PLL signal reaches a predetermined reference signal, a gate signal, that is, a control signal is output to a U-phase pair or V-phase pair thyristor. Their timing is shown in FIG.

  As shown in FIG. 2, the PLL circuit generates an angle signal of 180 degrees in electrical angle every positive and negative half cycles in synchronization with the inverter output voltage.

  FIG. 3 is a diagram showing the commutation failure detection timing for each thyristor in the inverter 4 that performs the operation of the single-phase inverter shown in FIG.

First, the DC voltage detection circuit unit 7 takes in the voltage waveform between PN of the inverse converter 4 shown in FIG. The PN voltage waveform is as shown in FIG. In the figure, u is a commutation overlap angle, which is an angle expressed by a phase angle from when a reverse voltage is applied until it becomes zero potential.

  Fork γ is a commutation margin angle in which the time from when the reverse voltage is applied until the voltage returns to 0 is expressed by a phase angle.

  The direct-current voltage detection circuit 7 further outputs a positive voltage period, that is, a positive pulse voltage as a forward pressure detection signal (A) from the data value of the acquired PN voltage waveform.

  The control circuit unit 8 receives the forward pressure detection signal (A) from the DC voltage detection circuit unit 7 and generates a forward pressure detection signal (B) obtained by inverting the detected voltage. Further, an angle detection signal (C) at a predetermined phase angle is generated using a triangular wave PLL signal.

  The control circuit unit 8 calculates a logical product of the forward pressure detection signal (B) automatically generated therein and the angle detection signal (C), and further calculates the logical product of the commutation failure detection signal (D). If it is in the on state, it is determined that there is a commutation failure in the half cycle in which the on state is detected.

  FIG. 3 is a diagram illustrating commutation failure detection timing. FIG. 3 shows an example of commutation failure as follows. That is, in the third half cycle, the commutation margin angle γ is small, the negative potential application period is narrow, ignition is not performed, the voltage waveform between PN does not rise to zero potential, and therefore the forward pressure detection signal (A) Is 0, and the barometric pressure detection signal (B) is 1, and the commutation failure detection signal (D) is 1 from the logical product at the phase angle of the angle detection signal (C), that is, the ON state.

  That is, the present invention has a feature that it is detected in a quarter cycle in which commutation fails immediately.

  Note that the position of the phase angle of the angle detection signal in FIG. 3 can be arbitrarily set. Therefore, the angle detection signal is set to a period of a certain width before the electrical angle of 90 degrees (before the maximum voltage value in the half cycle of 180 degrees), so that the thyristor that has failed to commutate becomes the maximum of the next phase. It can be stopped before the forward pressure is applied, and the protection operation can be started and stopped without the thyristor being damaged. That is, the thyristor can be reliably prevented from being damaged.

It is a figure which shows the structure of the induction heating apparatus with a commutation failure detection of this invention. It is a figure which shows the ignition timing of the inverter of this invention. It is a figure which shows the commutation failure detection timing of this invention.

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 DC voltage detection circuit part 8 Control circuit part

Claims (1)

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 inverse converter having a current type single-phase inverter configuration to be supplied to the heating coil, a power factor improving capacitor for improving the delay power factor of the heating coil in the forward direction and supplying reactive power for commutation to the inverse converter; In an induction heating apparatus comprising at least
A DC circuit P for connecting the DC reactor and the inverse converter, a P-N DC voltage detection circuit unit for a potential difference of the zero point circuit N, and
A control circuit unit that performs timing control for starting each thyristor that constitutes each of the forward converter and the reverse converter, and that performs control to protect the thyristor from overvoltage or overcurrent, and
The control circuit unit synchronizes with the inverter output voltage generated by the inverse converter, and generates a triangular wave PLL (Place 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 to the inverse converter when crossing to the predetermined reference signal value K. Firing control signal output means for sending a control signal to the gate electrode at the crossed phase angle;
The inter-P-N DC voltage detection circuit portion, the read voltage waveform data between P-N as a function of the phase angle the every half cycle (180 degrees), the between half cycle, the positive voltage period positive pulse A forward pressure detection signal A receiving means for receiving the forward pressure detection signal A output as a voltage waveform;
Inverting means for inverting the barometric pressure detection signal A to generate an inverted barometric pressure detection signal B;
An angle for generating an angle detection signal C having a predetermined angular width at a predetermined phase angle within a quarter cycle (90 degrees) of the half cycle of the triangular wave PLL signal generated by the PLL circuit. Generating means;
Wherein the inverted order pressure detection signal B to generate a commutation failure detection signal D from the logical product of the angle detection signal C, the commutation failure detection signal D is equal in the on state, determines that commutation failure, the result An induction heating apparatus with commutation failure detection, comprising: commutation failure determination means for outputting or displaying the commutation failure.

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