KR19990006267A - Pulse power supply for electric dust collection and its protection method - Google Patents

Abstract

SUMMARY OF THE INVENTION An object of the present invention is to provide a Palth power supply device having the effects of suppressing surge voltage during sparking, overvoltage protection of a high voltage semiconductor switch, use of a low breakdown voltage semiconductor element, miniaturization of a switch, and cost reduction. , The high voltage semiconductor switch 3 connected to the first DC power supply 1, the first DC power supply 1, the reverse current feedback means 4 connected in anti-parallel to the high voltage semiconductor switch 3, and the resonance inductance 5. ), A pulse generating circuit composed of a resonant capacitor 6, and a second DC power supply 8, and a dust collecting chamber 7 connected to the second DC power supply 8, and the high voltage semiconductor switch 3 is turned on. In the pulse power supply which turns off the pulse generating circuit and adds the pulse output of the pulse generating circuit to the dust collecting chamber 7, the turn-on circuit 12 when sparking is applied to the control electrode of the high voltage semiconductor switch 3. Connected and sparks occurred in the dust collection chamber (7). At the time of sparking, the turn-on circuit 12 is operated and the high-voltage semiconductor is turned on to protect against overvoltage.

Description

Pulse power supply for electric dust collection and its protection method

Industrial use field

The present invention relates to a pulse power supply device for use in a pulse charged electrostatic precipitator and a method of protecting the same.

Problems to be solved by the prior art and the invention

Pulse-charged electrostatic precipitator utilizes series resonance between the capacitance of dust collection chamber and resonant inductance, and can improve the dust collection efficiency against the reverse cell action of high-resistance dust, and the resonance energy is recovered as a return current to the power supply. This has a nice feature.

7 is a view for explaining a conventional pulse power supply for electric dust collection. The normal current collecting voltage (hereinafter referred to as base voltage) Vb will be described as -40 kV and the pulse voltage Vp as -50 kV. In the figure, (1) is the first DC power supply, and +30 kV is applied to the pulse generating circuit. (2) a choke coil for current limitation, (3) a pulse generating switch formed by connecting a plurality of thyristors in series, for example, (4) a reverse current connected in reverse parallel to the switch (3) It is a feedback means, for example, it is formed of a diode connected in anti-parallel to each of the series-connected thyristors constituting the switch 3.

(5) is a resonant inductance (L) which is an element of the resonant circuit for determining the pulse waveform, (6) is a resonant capacitor for pulse coupling having a capacitance Cc, (7) a house having a discharge electrode and a dust collecting electrode As a matter of fact, a capacitance Cp is provided between the discharge electrode and the dust collecting electrode. The capacitance Cc is several times larger than the capacitance Cp, for example three times larger. Also, the dust collecting electrode on the anode side of the dust collecting chamber is ground. 8 is a second DC power supply for supplying the base voltage Vb, and a base voltage Vb of -40 kV is added to the dust collecting chamber 7. This constitutes a pulse generating circuit. Reference numeral 9 denotes a control circuit, which transmits a 12 times / s firing signal to the switch 3 in a 60 Hz region, for example, in a 60 Hz region in synchronization with a commercial power supply frequency in a normal operation state. Reference numeral 21 denotes a reverse voltage blocking diode for preventing the pulse voltage added to the dust collecting chamber 7 from being applied to the second DC power supply 8.

In the following description, the resonance inductance L is 2.4 mH, the capacitance Cc is 0.64 ㎌, the capacitance Cp is 0.2 ,, and the series circuit resonance frequency of the resonance inductance L and the capacitances Cc and Cp is 8.3 kHz, the resonance inductance L and the electrostatic The resonance frequency of the capacitor Cc is 4 kHz.

8 shows waveforms in a normal operating state. In this figure, Is is a current flowing through the switch 3 or the reverse current feedback means 4, and Ve is a pulse superimposed dust collecting voltage added to the dust collecting chamber 7, and the base voltage Vb and the pulse voltage at which the pulse generating circuit is generated. Sum of Vp

The operation in normal operation will be described.

In the dust collecting chamber 7, a voltage of Vb = -40 kV is added from the second DC power supply 8, and the resonant capacitor 6 is charged up to 70 kV with the polarity shown. When the firing signal IGO is sent from the control circuit 9 to the switch 3 at time tO, the switch 3 is turned on. In the period T1, the resonance inductance 5 and the switch 3 are turned off in the resonance capacitor 6. The resonant current Is = I1 of the sinusoidal half-wave shape in the forward direction flows through the capacitance Cp of the dust collecting chamber 7, and the pulse generating circuit generates the pulse voltage Vp. The pulse voltage Vp is 50 kV, which is almost twice the voltage of the first DC power supply because the capacitance C c is larger than the capacitance C p, and the total pulse voltage is -90 kV. It is strictly determined by the ratio of the capacitances Cc and Cp. The period T1 is 60 Hz because the resonance frequency is 8.3 kHz.

Next, when the dust collection voltage Ve exceeds the peak voltage (-90 kV), the capacitor Cc and Cp are subjected to the reverse current feedback means 4 and the resonance inductance 5 in the period T2 (60 kV) to the resonance capacitor 6 in the period T2 (60 kV). The resonant current IS = I2 in the sinusoidal half wave shape in the negative direction flows, and the resonant energy is recovered to the resonant capacitor 6 as a feedback current. When the switch 3 is composed of a thyristor, a thyristor element having a turn-off time characteristic of less than 60 ms is selected. For example, if a turn-off time characteristic of 20 ms is selected, a reverse bias of 20 ms or more is added to the reverse current period T2. Restores forward blocking ability, ie, turns off.

Next, after the sine half-wave resonant current Is = I2 does not flow, and the collection period Ve becomes the base voltage, the waiting period T3 (8.2 ms when the firing pulse is 120 pulses / s) passes, and the control circuit 9 switches the switch 3 again. A call signal is transmitted to the switch 3, the switch 3 is turned on to generate a pulse, and the following operation is repeated.

In this way, the pulse collection dust collection voltage Ve of -40 kV--90 kV is added to the normal dust collection chamber 7, and the switch 3 and the reverse current return means 4 are connected to the 1st DC power supply 1 immediately after completion | finish of a return current. The turn-off surge voltage, about 45 kV, is added to switch the voltage of +30 kV.

Next, the case where a spark generate | occur | produced in the dust collecting chamber 7 is demonstrated.

Sparks are largely classified into two types by the state of turn-off of the thyristor. The first mode is a simple mode, when the thyristor is completely on or off, for example, a pulse of the pulseless base voltage period T3. The second mode is a spark just after the start of turn-off, when the thyristor is in an unstable state, that is, when the reverse current I2 starts to flow.

First, the first mode will be described. At this time, since a voltage of +30 kV is added at the first DC power supply 1 and -40 kV at the second DC power supply 8, respectively, a voltage of 70 kV is charged between the resonant capacitors 6 with the polarity shown. When a spark occurs in the dust collecting chamber 7, the dust collecting chamber 7 is turned on, and a resonant capacitor voltage of 70 kV and a surge voltage are applied to the switch 3, so that a voltage of about 100 kV is added and is usually the highest voltage.

When referring to the number of thyristors in series, if you use a 700V thyristors with a breakdown voltage of 800V and use them at 700V, a voltage of 45kV is normally added, so 45kV / 700V = 65 or more thyristors can be connected in series.

When the spark of the first mode occurs in the dust collecting chamber 7, as described above, since a surge voltage of about 100 kV is added to the switch 3, 100 kV / 700 V = 143 (pieces) means that a plurality of thyristors are not connected in series. Can not be done. That is, two or more thyristors must be connected in series to the required number of 65 normal operations. However, even if the number of series is increased, it cannot cope with the unstable state of the thyristor, that is, the spark of the second mode immediately after the start of the turn-off period.

Next, the spark of the second mode will be described. As shown in Fig. 9, the spark is generated in the second half of the pulse period and after the start of the reverse current period, around 20 ms of the turn-off characteristic of the thyristor element. At this time, the turn-off of 143 series thyristors is mixed with the thyristor turned off by the characteristic dispersion of an element, and the thyristor which is not turned off yet is mixed. In the worst case, when one is turned off with 142 on, the overvoltage at the time of spark is destroyed by the overvoltage with respect to the turned off one. That is, thyristors cannot be protected from overvoltage only by the countermeasures for increasing the number of series of thyristors.

In order to solve the said subject, the invention of Claim 1 WHEREIN: The high voltage semiconductor switch with which a 1st DC power supply was connected to the 1st DC power supply, the reverse current feedback means connected in reverse parallel to this high voltage semiconductor switch, and a resonance inductance. And a generation circuit formed of a resonant capacitor, a second DC power supply and a dust collection chamber connected thereto, and turning on and off the high voltage semiconductor switch to generate pulses in the pulse generation circuit. A pulse power supply for electric dust collection that adds a pulse output to the dust chamber, wherein a spark turn-on circuit is added to a control electrode of a semiconductor element constituting the high voltage semiconductor switch in addition to a control circuit for controlling periodic on / off of the semiconductor element. Is connected, and the spark-on turn-on circuit is operated at the overvoltage caused by the spark in the dust collecting chamber. Is turned on, and is continuously turned on through the resonance inductance and the series resonance current by the resonant capacitor until the main electrode voltage of the semiconductor element after its reverse current period becomes less than or equal to the operating voltage of the turn-on circuit during sparking. It is to provide a pulse power supply for electric dust collection, characterized in that to protect from overvoltage.

In order to solve the said subject, the invention of Claim 2 connected the capacitor | condenser for compensating transient characteristics large enough than the earth-distribution capacitance of these semiconductor elements to each semiconductor element connected in series, The claim 1 characterized by the above-mentioned. It is to provide a pulse power supply for electric dust collection.

In order to solve the said subject, the invention of Claim 3 connected the energy consumption resistor of the series resonant capacitor at the time of spark in series with a high voltage semiconductor switch, The electric dust collection pulse of Claim 2 characterized by the above-mentioned. It is to provide a power supply.

According to the invention of claim 4, in order to solve the above problems, a spark turn-on circuit is constituted by a trigger element, and a voltage added to the thyristor using a thyristor as a semiconductor element is used to reduce the breakdown voltage of the two-terminal trigger element. The present invention provides a pulse power supply for electric dust collection according to claim 1, wherein the thyristor is fired through the gate current when exceeded.

In order to solve the said subject, the invention of Claim 5 connected the series circuit of a diode and a resistor in parallel with a resonance capacitor, The pulse power supply for electric dust collection as described in any one of Claims 1-4 characterized by the above-mentioned. To provide a device.

In order to solve the said subject, the invention of Claim 6 has the 1st DC power supply, the high voltage semiconductor switch connected to the 1st DC power supply, the reverse current feedback means connected in anti-parallel to the said high voltage semiconductor switch, and resonance. A high voltage semiconductor switch having an inductance, a pulse generating circuit formed of a resonant capacitor, a control circuit for controlling periodic on / off of the high voltage semiconductor switch, a second DC power supply and a dust collecting chamber connected thereto, A method of protecting an electrical dust collection pulse power supply that generates a pulse in a pulse generating circuit and adds a pulse output of the pulse generating circuit to a dust collecting chamber, wherein the surge voltage generated during sparking is a high voltage semiconductor switch during normal pulse operation. The high voltage semiconductor switch is turned on when it is going to rise above the set voltage set higher than the voltage added to the above. It is to provide a method for protecting an electric dust collection pulse power supply, characterized in that the high voltage semiconductor switch is protected from overvoltage.

BRIEF DESCRIPTION OF THE DRAWINGS The figure for demonstrating 1st Embodiment of this invention.

2 is a diagram showing a concrete example of the switch portion of the embodiment of the present invention.

3 is a diagram for explaining the operation of the first embodiment of the present invention;

4 is a diagram for explaining a second embodiment of the present invention.

5 is a diagram for explaining the operation of the second embodiment of the present invention;

6 is a view for explaining a third embodiment of the present invention.

7 is a view for explaining a form of a conventional pulse power supply.

8 is a waveform diagram for explaining the operation in the normal operation state of a conventional pulse power supply.

9 is a waveform diagram illustrating a spark state of a conventional pulse power supply.

* Explanation of symbols for the main parts of the drawings

DESCRIPTION OF SYMBOLS 1st DC power supply, 2nd choke coil, 3 high voltage semiconductor switch, 31-2n thyristor, 4 reverse current feedback means, 41-4n diode, 5 resonant inductance, 6 resonant capacitor, 7 house Truth, 8: second DC power supply, 9: control circuit, 101-10n: current transformer, 111-11n: diode, 12: spark-on turn-on circuit, 13, 131-13n: 2-terminal trigger element, 15: resistor, 14, 141 to 14n: resistor, 16: capacitor for improving transient characteristics, 17: resonant capacitor, 18: pulse transformer, 21, 23: diode, 22, 24: resistor

(Example)

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure for demonstrating 1st Embodiment of this invention, and the code | symbol same as the code | symbol shown in FIG. 7 represents the same element. The basic concept of the present invention is that when the surge voltage generated during sparking is about to rise above a predetermined voltage set higher than the voltage applied to the switch 3 in normal operation, the switch is turned on to protect against overvoltage and to resonate. The energy of the capacitor is consumed in the circuit. The circuit which acts is the spark-on turn-on circuit 12 and is connected between the anode of the switch 3 and the gate. Reference numeral 22 is a resistor for consuming energy of the resonant capacitor.

It is a specific example of the switch part explaining 1st embodiment of this invention. The switch 3 is configured by connecting a plurality of thyristors 31 to 3n in series, and the reverse current feedback means 4 reverses the thyristors 31 to 3n and the same number of diodes 41 to 4n with the respective thyristors. It is configured by connecting. The firing of the thyristors 31 to 3n is performed in the control circuit 9 via the current transformers 101 to 10n and the countercurrent blocking diodes 111 to 11n. 121 to 12n are operational stability resistors connected between the thyristor gate and the cathode.

The spark-on turn-on circuit 12 is a series of two-terminal trigger elements 131 to 13n and resistors 141 to 14n between the anode and the gate of each of the plurality of series connected thyristors 31 to 3n constituting the switch 3. It is formed by connecting a connection circuit. When a voltage equal to or greater than a predetermined value is applied between the anodes and the cathodes of the thyristors 31 to 3n, the two-terminal trigger elements 131 to 13n yield to a conductive state, and current flows through the gates of the respective thyristors. In Example, the breakdown voltage of 690V was taken. The resistors 141 to 14n are omitted if the two-terminal trigger elements 131 to 13n have high surge current resistance. Reference numerals 151 to 15n denote voltage balance resistors connected to the respective thyristors together, and 161 to 16n denote capacitors for improving transient characteristics.

Since a delay time occurs between the two-terminal trigger elements 131 to 13n until the switch 3 is turned on, the voltage added to the switch 3 becomes higher than the breakdown voltage of the two-terminal trigger element. If the time until turn-on is long, the high speed turn-on of the switch 3 is necessary because the spark voltage may exceed the breakdown voltage of the switch until the switch 3 is turned on, but the turn-on time of the switch depends on the gate current. Therefore, it is preferable to perform high-speed turn-on by selecting the series resistor 14 to 0 or a minimum value and making the gate current larger than the normal value.

In the experiment, when the two-terminal trigger elements 131 to 13n break down to 690V, a gate current of about 1A flows to drive the gate of the switch 3, and the switch 3 is turned on with a thyristor turn-on delay time of 700 ns. At this time, the voltage between the anode and the cathode of the thyristors 31 to 3n rises to 740V and falls below 800V of the thyristor. Since the breakdown voltage of the two-terminal trigger element is 690 V, the number of series of the thyristors 31 to 3 n requires 45 kV / 690 V = 65 or more in order not to break down to the normal 45 kV voltage.

However, because the breakdown voltage decreases for the reasons described below, the number of re-ignition during sparking increases, switching loss increases, and the thyristor junction temperature may be higher than the standard value. The breakdown voltage was set to 100 and about 69 kV.

In this case, firing by the turn-on circuit 12 during sparking is not performed until a voltage of 69 kV is added to the switch 3. In other words, since the surge voltage of 45 kV is added to the switch 3 during normal operation, only the normal firing signal from the control circuit 9 is applied to perform the normal operation. When spark occurs in the dust collecting chamber 7 during the pulse operation and a voltage of 69 kV or more is added to the switch 3, during turn-on, the turn-on circuit 12 breaks down and causes the gate current to flow to the gate of the thyristor, thereby controlling the control circuit 9 The call is not performed by).

When spark occurs in the dust collecting chamber 7, the switch 3 has 70 kV + , A surge voltage of about 100 kV is added. Here, by setting the set voltage of the spark turn-on circuit 12 to be lower than the additional voltage, the turn-on circuit 12 breaks while the surge voltage caused by the spark is higher than the set voltage, and the switch 3 is turned off. By repeatedly turning on and on, the energy of the resonant capacitor 6 is attenuated by the power loss of the circuit components, in particular the resistor 22. Thereafter, the firing ends when the voltage added to the switch 3 becomes lower than the set voltage of the turn-on circuit 12 when sparking.

The resistance value of the energy consumption resistor 22 is a value that can be practically ignored for the loss of the normal current, and consumes energy due to a large amount of current during sparking, and can limit the number of calls. Ohm. In addition, the resistor 22 may be omitted, and energy may be consumed by the loss of components such as thyristors, diodes, resonant inductances, and the like.

3 shows waveforms of respective parts in the first spark mode. In the figure, IS is the current flowing through the switch 3 or the reverse current return means 4, VBK is the breakdown voltage of the spark-on turn-on circuit 12, VAK is the anode-cathode voltage of the switch 3, IG is The gate current Ve of the switch 3 is a pulse superimposition voltage added to the dust collecting chamber 7 and is the sum of the base voltage Vp and the pulse voltage Vp generated by the pulse generating circuit.

First, at time t0, when the firing signal IG0 is transmitted from the control circuit 9 to the switch 3, the switch 3 is turned on, and the sinusoidal half-wave resonant current IS = I1 flows in the switch 3. The pulse generating circuit generates the pulse voltage VP. Since the pulse voltage VP is a negative characteristic, it increases in a negative direction.

When the pulse voltage VP exceeds the peak voltage (-90 kV), the sinusoidal half-wave resonant current IS = I2 flows to the reverse current feedback means 4, and the switch 3 reverses the bias during the reverse current period. Is turned off.

Next, the spark occurring in the first mode, that is, the spark occurring when the thyristor of the switch 3 is completely turned on or off will be described. In the example shown in FIG. 3, the spark generate | occur | produces in the dust collecting chamber 7 in the state in which all the thyristors of the switch 3 are completely turned off at the time when a return current is almost complete. The surge voltage VAK1 that rises toward about 100 kV is applied to the switch 3. When the spark voltage VAK1 exceeds the breakdown voltage VBK at time t1, the gate current IG1 flows through the turn-on circuit 12 at the gate to the gate of the switch 3, and the switch 3 is fired. By setting the breakdown voltage to 69 kV lower than the surge voltage, the switch 3 is fired at the time of sparking to protect it from overvoltage, and a resonant inductance and a series resonant current by the resonant capacitor flow. The series resonance current shortens the capacitance of the dust collector so that the resonance frequency decreases to about 4 kHz, and the reverse current period increases to 123 kHz.

The thyristor is turned off in the reverse current period of the resonance current, and the overvoltage VAK2 is applied again immediately after the reverse current. When this voltage is 69 kV or more, the gate current IG2 flows through the spark-turn-on circuit 12 to the gate of the switch 3, and the switch 3 is turned on for the second time.

When a resonant current flows through the switch 3 and the reverse current feedback means 4 by the voltage VAK2, and when the voltage VAK3 exceeding the breakdown voltage VBK is applied to the switch 3 again at time t3, the spark-on turn-on circuit 12 The gate current IG3 flows through the gate of the switch 3 through), and the switch 3 is turned on three times by performing a third firing.

By repeating the ON by the spark-on turn-on circuit 12 in this manner, the energy of the spark is attenuated by the resistor 22, the thyristor switch 3, the diode, the wiring resistance, and the like, and the re-overvoltage immediately after the reverse current falls. Therefore, after the resonant current flows through the switch 3 and the reverse current feedback means 4 by VAK3, at time t4, if the maximum voltage VAK4 applied to the switch 3 does not reach the breakdown voltage VBK, it is turned on during sparking. The circuit 12 does not call the switch 3 again, and the firing of the series of switches 3 ends.

Next, the operation in the second spark mode will be described. Spark the thyristor in an unstable state, i.e. immediately after the turn off period begins. As shown in Fig. 9, a spark occurs in the second half of the pulse period and after the start of the reverse current period, before and after the turn-off characteristic of the device is about 20 ms. At this time, the turn-off of the 100 series thyristors is mixed with the thyristor and the thyristor turned off by the dispersion | distribution of a device characteristic.

In the worst case, when one is turned off with 99 turned on, the overvoltage at the time of the spark is related to the turned off one, but the one is turned on at a voltage of VBK or higher due to the presence of the turn-on circuit 12 at the time of spark, A series resonant current flows. Since the reverse current period of the series resonant current during sparking is 120 mA or more, the entire thyristor is completely turned off, and after this reverse current period has elapsed, an overvoltage is applied, and if it is above the breakdown voltage VBK, it is fired. This operation is the same as that of the first spark mode described above, and when the maximum voltage VAK4 applied to the switch 3 does not reach the breakdown voltage VBK, the switch 3 is not fired again, and the series of switches 3 The call is over.

When the surge voltage generated at such a spark reaches the set value, the switch 3 is turned on by the firing action of the turn-on circuit 12 at the time of the spark, so that the switch 3 does not have to withstand the overvoltage during the spark. The number of series of thyristors can be greatly reduced.

Next, the action of the transient characteristic improvement capacitors 161 to 16n will be described. The direct voltage sharing of the thyristors connected in series is all performed by the parallel resistors 151-15n of the same value. Since the base voltage or the pulse voltage at the time of normal operation is not so rapid, share the same. However, the overvoltage at the time of spark is sudden, as shown in FIG. 3, and voltage sharing by parallel resistance cannot be expected. This is because a large number of thyristors have a distributed capacitance CS to earth, and the higher the voltage, the greater the transient voltage sharing.

As a result, the thyristor on the high voltage side first fires, and the thyristor on the low voltage side sequentially fires, and thus, the problem of not reaching a predetermined breakdown voltage, or, in the worst case, is caused by an excessively high voltage rising rate of the thyristor or diode on the low voltage side. Due to the turn-on time delay of the thyristors, the firing does not reach, and the thyristor or diode on the low voltage side is destroyed due to overvoltage. Therefore, it is preferable to connect the transient characteristics improvement capacitors 161 to 16n which are sufficiently larger than the land distribution capacitance to the thyristor. In the experiment, stable operation can be achieved by selecting 500 kW of parallel resistance (151 to 15n) and 30 kW of transient improvement capacitor (161 to 16n) for a earth distribution capacity of 1.4 pF per 100 series thyristors. have.

4 shows another embodiment of the present invention, and the same reference numerals as those shown in FIG. 1 denote the corresponding elements. In this embodiment, a means is provided in which the energy of the resonant capacitor 6 during sparking is quickly consumed to reduce the number of resonant cycles, but not be lost in normal pulse operation.

This means uses the inverting voltage when the charging voltage of the resonant capacitor 6 is not reversed during normal pulse operation but is sparked, and the series connection circuit between the high voltage diode 23 and the resistor 24 is connected to the resonant capacitor 6. ) In parallel. The polarity of the high voltage diode 23 is a direction for blocking the charging voltage of the resonant capacitor 6.

According to the above configuration, the reverse voltage is always applied to the high voltage diode 23 during normal pulse operation, does not conduct, and does not affect the circuit operation. When a spark occurs and the switch 3 turns on due to the overvoltage and the voltage of the resonant capacitor 6 starts to invert, the high voltage diode 23 conducts and consumes energy in the resistor 24. By appropriately selecting the value of the resistor 24, it is possible to change the resonance current from non-vibration to attenuating vibration. FIG. 5 shows the current waveform IS and the additional voltage VAK of the switch 3 in which the resonance current is limited to one cycle by appropriately selecting the value of the resistor 24. The thermal stress of the thyristor switch 3 can be greatly reduced. Can be.

In the above-described embodiment, the thyristor switch is provided in the high voltage circuit. However, by using a boosting means such as a pulse transformer, the thyristor switch can be installed in the low voltage side. Fig. 6 is a diagram for explaining such a third embodiment of the present invention. In the figure, the same symbol as that shown in FIG. 1 is assumed to represent the same element. In this circuit, the capacitor 17 functions as the first resonant capacitor, and the capacitor 16 functions as the second resonant capacitor and the pulse coupling function. In addition, (18) is a boost pulse transformer, and the turns ratio of a primary side and a secondary side is 1:20, for example.

The first resonant capacitor 17 is charged with -1.5 kW from the first DC power supply and the second resonant capacitor 6 with -40 kW from the second DC power supply 8, respectively, with the polarity shown. In this circuit, the series resonant circuit is composed of the resonance inductance 5 and the capacitance of the dust collecting chamber 7 and the first and second resonant capacitors 17 and 6. It is common to make the first resonant capacitor 17 equal to several times the second resonant capacitor 6.

The operation in normal operation will be described. A voltage of VB = −40 kV is added to the dust collecting electrode 7 in the second DC power supply 8. When a firing signal is transmitted from the control circuit 9 to the switch 3, the switch 3 is turned on, and in the resonant capacitor 17, the primary winding of the pulse transformer 18, the resonance inductance 5, and the switch ( Resonant current i flows through 3) and generates a voltage in the secondary winding of the pulse transformer. This voltage is superimposed on the charging voltage of the resonant capacitor 6 and a pulse voltage is added to the dust collecting electrode 7.

Next, in the electrostatic capacitance of the dust collecting electrode 7, the resonant current reverse to the resonant current i flows through the secondary winding of the pulse transformer 18, and the resonant energy is recovered to the resonant capacitor 6 as a return current. In the primary winding of the pulse transformer 18, the reverse current flows through the reverse current feedback means 4 and the resonance inductance 5, and the resonance energy is recovered to the first resonant capacitor 17 as the feedback current. The switch 3 is turned off because a reverse bias is added to this reverse current period.

Next, after the elapse of the waiting period in which the resonant current does not flow, and the pulse voltage added to the dust collecting electrode becomes a constant voltage of -40 kV, the firing signal is transmitted from the control circuit 9 to the switch 3 again to switch ( 3) turns on. The same operation is repeated below.

In this way, in normal operation, a control signal 9 is added to the switch 3, for example, a 120 times / s firing signal is added, and the switch 3 is turned on, and the dust collecting electrode 7 is -40 kV. A pulse voltage of ˜−70 Hz is applied, and a voltage of 1.5 Hz is applied to the switch 3.

Next, the case where the spark generate | occur | produced in the dust collection electrode 7 is demonstrated. When a spark arises in the dust collection electrode 7, the dust collection electrode 7 will conduct and the switch 3 will be 1.5 mA + The surge voltage is added, but when a constant value, for example, 1.6 kV or more is applied between the anode and the cathode of the switch 3, the two-terminal trigger element 13 is brought into a conductive state. Therefore, the gate current flows through the two-terminal trigger element 13 and the resistor 14 to drive the gate of the switch 3 and turn on the switch. In this way, during sparking, the sparking is turned on by the spark-on turn-on circuit 12 not by the control circuit 9, and as a result, a voltage of 1.6 mA or more is not applied to the switch 3.

The series resonance at the time of sparking by this firing is performed by the 1st and 2nd resonance capacitors 17 and 6 and the resonance inductance 5, and when the voltage of the 1st resonance capacitor 17 becomes inverse to the polarity shown in figure, , Energy is consumed in the resistor 24. By appropriately selecting the resistance value of the resistor 24, this single firing consumes enough energy in the resistor 24, and the voltage added to the switch 3 is greater than the set voltage of the turn-on circuit 12 during sparking. Can be lowered. In this case, since the thyristor switch 3 is not fired or conducted again and again, the power loss of the thyristor switch 3 can be reduced.

However, if the energy of the spark cannot be absorbed in the circuit by one magnetic firing, this magnetic firing is repeated. By repeating the magnetic firing, the energy of the spark is attenuated, and the magnetic firing is terminated when the voltage added to the switch 3 becomes lower than the set voltage of the spark-on turn-on circuit 12.

When the turn-on circuit 12 is not connected between the anode and the gate of the switch 3 at the time of sparking, a voltage (approximately 3 mA) twice that of normal operation as a surge voltage at the time of sparking is applied to the switch 3. However, by connecting the turn-on circuit during the spark between the anode of the switch 3 and the gate, a surge voltage of 1.6 kΩ which is close to the voltage (1.5 kΩ) applied to the switch 3 during normal operation even during sparking is applied to the switch 3. Since it is only added to, it is possible to use a switch 3 having a lower internal pressure.

As described above, in the third embodiment using the pulse transformer 18, since the overvoltage is added to the switch 3 at the time of sparking, a switch having a breakdown voltage guessing the surge voltage must be selected. By adding the circuit 12, it is possible to use a low breakdown voltage switch and to reduce the cost since only the voltage at the time of normal operation is considered.

In the above embodiment, the series connection circuit of the diode 23 and the resistor 24 is provided in parallel with the first resonant capacitor 17. However, as shown by a dotted line, the series connection circuit is connected to the second resonant capacitor ( 6) may be provided in parallel, and the same effect can be obtained even if both are connected in parallel.

In the above embodiment, any one of a series of thyristors connected in series is used as the high voltage semiconductor switch. However, in the present invention, since overvoltage protection can be reliably used, other power semiconductor devices such as MOSFET or IGBT can be used to open and close the flow of power. Can be. In this case, the spark-on turn-on circuit operates at an overvoltage caused by the generation of sparks and has a function of keeping the power semiconductor element on for about a predetermined period, preferably for a period corresponding to a positive half cycle of almost one resonance period. Also good. Such a function can be easily configured by using a combination of a driving IC for generating a drive signal having a constant pulse width and an overvoltage detection circuit, which are generally known, and thus a detailed description thereof will be omitted.

As described above, in the present invention, when the surge voltage generated during sparking is about to rise above a predetermined voltage set higher than the voltage added to the normal high voltage semiconductor switch, the high voltage semiconductor switch is turned on so that the switch is turned on. It can protect against overvoltage.

In addition, the present invention connects a spark-on turn-on circuit of a very simple configuration with a breakdown element such as a two-terminal thyristor which breaks down to a predetermined voltage smaller than the maximum spark voltage to the control pole of the thyristor switch to be protected from the spark voltage. Since the energy of the resonant capacitor in the circuit is consumed in the circuit, it is possible to reliably protect each of the series-connected thyristors from overvoltage during sparking with a simple circuit configuration even when the thyristor is in a stable state as well as in an unstable state. The number of series connections can be reduced, and the size of the switch can be reduced, and the cost can be reduced.

Claims (6)

A pulse generator circuit formed of a first DC power supply, a high voltage semiconductor switch connected to the first DC power supply, a reverse current feedback means connected in anti-parallel to the high voltage semiconductor switch, a resonance inductance, and a resonance capacitor; And a dust collecting chamber connected thereto, wherein the high voltage semiconductor switch is turned on and off to generate pulses in the pulse generating circuit and to apply a pulse output of the pulse generating circuit to the dust collecting chamber. To A spark turn-on circuit is connected to a control electrode of a semiconductor element constituting a high-voltage semiconductor switch in addition to a control circuit for controlling periodic on / off of the semiconductor element, and the spark turn-on circuit is connected with an overvoltage caused by a spark in the dust chamber. Operate to turn on the semiconductor element, to flow a series resonant current by the resonance inductance and the resonant capacitor, and to continue turning on until the main electrode voltage of the semiconductor element after its reverse current period becomes below the operating voltage of the turn-on circuit during sparking. The overvoltage protection of the high voltage semiconductor switch is performed. 2. The pulse power supply for electric dust collection according to claim 1, wherein a capacitor for transient characteristic compensation, which is sufficiently larger than the land distribution capacitance of the semiconductor element, is connected in parallel to each of the semiconductor elements connected in series. The electric power collector pulse power supply device according to claim 1 or 2, wherein an energy consumption resistor of said series resonant capacitor is connected in series with said high voltage semiconductor switch. The spark-turn turn-on circuit is composed of a two-terminal trigger element, a thyristor is used as the semiconductor element, and a voltage applied to the thyristor is applied to the two-terminal trigger element. A pulse power supply for electric dust collection, characterized in that the thyristors are fired by flowing a gate current when the breakdown voltage is exceeded. The pulse power supply for electric dust collection according to any one of claims 1 to 4, wherein a series circuit of a diode and a resistor is connected in parallel with the resonance capacitor. A pulse generating circuit formed of a first DC power supply, a high voltage semiconductor switch connected to the first DC power supply, a reverse current feedback means connected in anti-parallel to the high voltage semiconductor switch, a resonance inductance, a resonance capacitor, and a period of the high voltage semiconductor switch A control circuit for controlling an on-off, a second DC power supply, and a dust collecting chamber connected thereto, and turning on and off the high voltage semiconductor switch to generate pulses in the pulse generating circuit, In the protection method of the electric power collector pulse power supply which applies the pulse output of the said dust collection chamber, When the surge voltage generated during sparking is about to rise above a set voltage set higher than the voltage applied to the high voltage semiconductor switch in the normal pulse operation, turning on the high voltage semiconductor switch to protect the high voltage semiconductor switch from overvoltage. A method for protecting an electric dust collector pulse power supply, characterized in that.