Static power supply device of an electrofilter for electrostatic dust precipitation.

The invention relates to a method and a static power supply device with electric current an electrofilter having two electrodes, one connected to the positive polarity and the other to the negative polarity of the power supply for generating an electric field electrification of the particles flowing between the electrodes, wherein the high DC voltage of a predetermined duration pulses applied to said electrodes are produced by a static converter, in a high step-up transformer and rectified in a rectifier.

A known device of the kind mentioned comprises a thyristor dimmer feeding under a zero variable voltage to the nominal value and a frequency corresponding to that of the network, the primary of the step-up transformer by varying the opening angle of the thyristor controlled. an analog controller. It detects the occurrence of each spark at Inter, and develops the electrostatic ieur'de adjustable steering set, called rate against reaction, and applied to a control amplifier. The high voltage tracks changes in the breakdown voltage by presenting a rate sawtooth. If the discharge voltage is reduced by the regulator of a small percentage, then crolt again to the breakdown voltage. The current injected into the electrostatic precipitator is not stable because it follows the variations of the voltage in sawtooth. The efficiency of the dust depends mainly on the average value of the high voltage DC and this known device does not allow at- dye maximum efficiency.

The invention aims to overcome this disadvantage and achieve a simple diet ensuring optimal operation of the ESP.

The supply method according to the invention is characterized in that said high DC voltage pulses are generated by an inverter to provide a peak voltage less than the breakdown voltage of the electrostatic precipitator, the duration of each pulse being less than the time forming a spark in éleotrofiltre and the average value of the high voltage DC injected into the electrostatic precipitator is adjusted by a regulating circuit by varying the frequency F of the pulses and / or the supply voltage of the inverter to maintain optimum average value of said high voltage current corresponding to a high DC voltage between said electrodes substantially constant.

The duration of each injected current pulse is significantly reduced and preferably less than 0.5 milliseconds while the pulse frequency is increased, for example between 500 and 2000 Hz to obtain an important current injected into the electrostatic precipitator. The pulse peak voltage is maintained at a value lower than the breakdown voltage of the electrostatic precipitator to prevent any priming.

For each filter is sought by calculation and / or testing the optimal value of the average injected current and a control device maintientcette constant value during normal operation of filtreo The regulation of injected average current is achieved by varying the pulse frequency and / or variation of the supply voltage of the inverter. These parameters can be varied simultaneously with the pulse duration.

Increasing the frequency of the pulses associated with the discharge time inherent in the electrostatic precipitator, allows a reduction of the high ripple voltage applied to the filter, the average value may be compared with the breakdown voltage of the filter without the peak value exceeds the breakdown voltage.

The device of the invention does not cause any disruption of the supply network by the current form factor upstream of the rectifier transformer group.

It should be noted that the electrostatic power by high frequency pulses have already been proposed (US Patent 3,984,215 and 3,641,740) in order to exceed the breakdown voltage for a short time without causing a boot. These known power supplies carry a different power principle.

The feeding device according to the invention advantageously comprises an inverter oscillating blocking circuit arranged in series in the inverter load circuit, and setting the duration and the peak intensity I_Max of each current pulse. The primary winding of the step-up transformer provides the inductance of the oscillating circuit.

According to a development of the invention, the circuit controller .tion of the average value of high voltage current comprises a deviation detector of this average value to a reference value and a digital-analog converter which supplies pulses of control to the ignition circuit of the thyristors of the inverter according to the difference signal for varying the frequency of high voltage pulses.

According to an alternative embodiment, the deviation detector of the average value circuit for regulating the high voltage acts on the DC voltage of the inverter power supply, in particular by varying the ignition of the thyristors of a thyristor rectifier feeding the inverter.

According to another embodiment, the inverter from the forced switching type is controlled by said regulation of the mean value of the high voltage circuit for varying the duration and frequency of the high voltage pulses in accordance with said average value by changing the ignition time blocking thyristor and the main thyristor.

The invention is of course not limited to a particular type of inverter and power device may comprise conventional security such as an arc detector at interrupting the supply of unwanted boot.

Other advantages and features will become more clear from the following discussion in various embodiments of the invention, given as non-limiting examples and represented in the accompanying drawings, wherein:<ul><li>Figure 1 is a circuit diagram of a static supply of an electrostatic filter according to the invention;</li><li>2a and 2b show the curves representing the voltage U applied to the electrostatic precipitator, and .courant 1 injected as a function of time;</li><li>3 shows a block diagram of the frequency regulator according to Figure 1;</li><li>Figure 4 is an electrical diagram of an alternative embodiment of a power supply according to the invention;</li><li>Figures 5 and 6 show block diagrams of the control oscillator respectively of the switching circuit of the inverter, and the current controller according to Figure 4;</li><li>Figures 7 and 8 show two other eating embodiments of the invention.</li></ul>

The same reference numerals in the various figures the same elements or similar elements.

In Figure 1, the feeding device 10 with an electrostatic high voltage electrostatic precipitator 12 includes a single-phase line-commutated inverter, formed by four thyristors 14, 16, 18, 20 connected in bridge. The DC voltage E applied to the input terminals 22, 24 of the inverter 12 is obtained by rectifying the three-phase supply voltage of the AC network RST in a static rectifier 26 followed by a filter in a filter 28 continuous inductor 30 and capacitor 34. the coil 30 is connected in series in a power supply conductor 32 connecting the rectifier 26 to the terminal 22 of the inverter. The capacitor 34 of the smoothing circuit is connected in parallel to input terminals 22, 24 of the inverter 12 carried respectively to the positive and negative potential of the source E. The output terminals 36, 38 of the inverter bridge 12 are connected by two connecting conductors 40, 42 to the primary winding 44 of a low voltage step-up transformer 46. a capacitor 48 of a predetermined value C is inserted in series in the conductor 40 and form an oscillating circuit as LC with 'self-inductance L of the transformer 46. the secondary winding 50 of the high voltage transformer 46 is associated with a high voltage rectifier 52 connected to the electrostatic precipitator 10 for removing dust.

The supply device is equipped with a regulation and control system, designated by the general reference 54. The control system 54 is controlled by the average value of the high voltage DC current detected by a shunt 58 inserted between the electrostatic 10 and the secondary winding 50. This average value can also be measured by a current transformer 60 (shown dotted) ensuring the capture of the primary current of the transformer 46. the measure of said mean value is applied to the input of a frequency controller 56 whose output is connected by a conductor 62 to a switching circuit 64 which develops the control pulses ignition of the thyristors 14, 16, 18, 20 of the inverter 12 to LC resonant circuit .

Referring to Figure 3, it is seen that the frequency controller 56 is formed by a comparator 66 associated with an amplifier 68, which drives a digital to analog converter 70 type voltage / frequency. The comparator 66 outputs an error signal or deviation from an against current intensity measured reaction 1 compared to a reference current 1.

The regulation and control system 54 is equipped on the other hand an arc detector 72 connected to the switching circuit 64 to ensure the blocking of the control pulses and the extinction of the thyristors of the inverter 12 during the possible occurrence of an arc inside the electrostatic precipitator 10. This detection is carried out in a manner well known from the secondary voltage imposed by a potentiometric divider 74 and the secondary current transformer 1 46.

The operation of the control 54 of the inverter 12 to the LC oscillating circuit system is based on the principle of control of the rectified current injected into the electrostatic precipitator 10:<ul><li>The thyristors 14, 20; 16, 18 of the single-phase inverter 12 are alternately switched by the control pulses of the switching circuit 64 to apply the voltage + E, -E and the LC series resonant circuit formed by the capacitor 48 and the self-induction the primary winding 44. the natural oscillation of the LC circuit causes blockage lighted thyristors 14, 20; 16, 18 after a predetermined time Z and τ duration pulse is higher in the step-up transformer 46. The high voltage current pulse from the secondary 50 of the boost converter 46 is redresséedans the rectifier 52 and applied to the electrodes of the electrostatic precipitator 10. the frequency F of repeated current pulses injected into the electrostatic filter is controlled by the frequency regulator 56 based on the average high voltage measured by the shunt 58, so as to maintain the constant average current.</li></ul>

The length Z and the peak intensity I_max of each current pulse are determined by the LC oscillating circuit, in particular by the choice of the capacitance of capacitor C 48 and the inductance L of the transformer 46. The Z duration is less than 0.5 milliseconds and the frequency of the pulses is between 500 and 2000 Hz. The peak intensity I_Max is chosen so that the peak voltage remains below the breakdown voltage of the electrostatic precipitator.

It is seen from the curves representing the voltage U at the terminals of the electrostatic filter (Fig. 2a) and the current injected 1 (Fig. 2b) that the voltage U remains substantially constant and less than the breakdown voltage.

The low AV voltage ripple results from the discharge time of the electrostatic precipitator 10 between two successive current pulses and high pulse frequency F.

The low ζ duration (less than 0.5 millisecond) pulses decreases boot risks between the electrodes of the electrostatic precipitator 10.

Power over static inverter 12 according to the invention can improve the efficiency of existing facilities. It is then connected in parallel across the electrostatic precipitator with traditional food comprising such a Thyristor.

In the alternative embodiment illustrated by Figure 4, the inverter 12 LC oscillating circuit is powered by a variable DC voltage E delivered by a rectifier 100 static thyristor three-phase bridge, which rectifies the three-phase supply voltage of the AC network RST. The filter 28 is interposed between the rectifier 100 and the inverter 12 for smoothing the rectified voltage E applied to the input terminals 22, 24 of the inverter 12 carried respectively to the positive and negative potentials.

The regulating device 54 comprises an oscillator 102 connected to the shunt 58 or the transformer 60 and applying to the switching circuit 64 of fixed frequency pulses. The oscillator 102 is for example composed of a transition detector 104 of current zero 1 and an auxiliary pulse generator 106 connected to the inputs of a logic gate 108 whose output is connected to the switching circuit 64 the driver 62 (fig. 5). The detector 104 of current zero-crossing slaves the pulse generator 106 so that a control pulse can succeed another in the output of the logic gate 108 after the zero crossing of the current, which originated with that pulse. The fixed oscillator 102 frequency of pulses at a predetermined optimum value.

Regulating the average value of the high voltage current injected into the electrostatic precipitator 10 is effected by variation of the DC voltage E applied to the inverter 12 in the following manner:<ul><li>The control electrodes of the thyristors of the rectifier 100 are connected to an ignition circuit 110 connected by a conductor 116 to a current controller 112. The input thereof is connected by a conductor 114 is the shunt 58, is the transformer intensity 60.</li></ul>

Referring to Figure 6, we see that the current regulator 112 is formed by a comparator 118, which develops an error voltage from a reaction against the intensity of the medium high voltage current compared with a current I set I_C. The error voltage is applied to an amplifier 120 and converted into pulses by an adjustable converter 122. These pulses synchronized with the RST supply network are transmitted to the control electrodes of the thyristor rectifier bridge 100 by the ignition circuit 110 and determine the value of the voltage E of the inverter power supply 12.

The arc detector 72 cooperates with the comparator 118 of the current controller 112 to cause if triggered a decrease in the voltage E input of the inverter 12.

The oscillator 102 of fixed frequency may be replaced by the controller 56 according to Figure 1. The average current setting injected into the electrostatic filter 10 then results from the variation of the frequency F of the current pulses and the variation in supply voltage E of the inverter 12. in this case the controller 112 may be replaced by a regulator of the rate of discharge.

Figure 7 shows another alternative embodiment, inverter 140 forced commutation. The inverter 140 includes main thyristors 142, 144; 146, 148 connected in series in pairs respectively in the two arms 150, 152 in parallel to the inverter, each arm being powered by the DC voltage E delivered by the rectifier bridge 26. The main thyristors 142-148 are alternately turned on -by control pulses supplied by a first ignition circuit 154, so as to apply the voltage + E and -E to the primary group 44 of transformer 46, rectifier 52. the AC voltage at the output of the inverter 140 and from switching, either the positive pole or the negative pole of the DC voltage E with the outlet. Each arm 150, 152 of the inverter 140 has two turn-off thyristors 156, 158; 160, 162 associated with a quenching circuit 164, 166 comprising an inductor 168 in series with a capacitor 170. The off thyristors 156 to 162 are alternately turned on by control pulses generated by a second ignition circuit 172 for cause the extinction of the respective thyristors 142 and 148 and stopping the current in the primary 44 of the transformer 46. the extinction takes place in a manner well known specialists in the discharge of the capacitor 170 of the quenching circuit 164 , 166 in the opposite direction of the main thyristor to defuse. The primary voltage applied to the rectangular wave 44 of transformer 46 generates current pulses rectified by the high voltage rectifier 52 before being injected into the electrostatic precipitator 10.

A frequency controller 174, controlled either by the rectified secondary current flowing in the electrostatic filter 10, or by the primary current of the winding 44 of transformer 46 is connected by two conductors 177, 178 connecting the first and second circuits respectively ignition 154, 172. the duréeZ and the frequency F of repetition of the current pulses injected into the electrostatic precipitator 10 is controlled by the frequency controller 174, which controls the average current injected at a predetermined value.

An arc detector 176 causes if triggered interrupt the current injected into the electrostatic precipitator by the ignition off thyristors 156 to 162 causing the blocking of main thyristors 142-148 correspondents.

-The Bridge rectifier 26 to the inverter power diodes 140 forced commutation may of course be replaced by a thyristor rectifier bridge of the type shown in Figure 4 and controlled in the manner described above.

Figure 8, similar to Figure 4, illustrates an alternative embodiment of the inverter. The capacitive filter element 28 consists of two capacitors 182, 184 connected in series and connected to the input terminals 22, 24 of the inverter 180 commutated. The inverter 180 includes two thyristors 186, 188.dont ignition electrodes are connected to switching circuit 64. The output terminals 36, 38 of the inverter are connected to the primary 44 consists of two windings 194, 196 wound such that the winding beginnings are connected to terminals 36, 38 while the winding ends are connected together to a terminal 190. This terminal 190 is connected to the midpoint 132 of the capacitors 182, 184 by a capacitor of oscillation 48. Each winding 194, 196 and forms with capacitor 48 an oscillating blocking circuit. The operation of the feeder is of course identical.