RU2214040C2 - Pulse modulator for feeding capacitance load - Google Patents

Abstract

FIELD: switch-mode power supplies for dust precipitators. SUBSTANCE: pulse modulator feeding load 8 has power supplies 11-14 with partial-discharge storage capacitor operating into capacitance load, series-connected controlled switches 1, 2 having flat and drooping turn-on characteristics, respectively, and control system 15 with control circuits 17, 16. Anode of controlled switch 1 is connected to plus terminal of power supply and cathode of controlled switch 2, to its minus terminal and to second terminal of load 8; modulator also has regenerative switch 25 connected in parallel opposition to controlled switch 2. Starting lead of inductance coil 35 incorporated in LC discharge circuit is connected to anode of controlled switch 2, first plate of coupling capacitor 5, to finishing lead of inductance coil 35, and second plate of this capacitor is connected to load 8. Resistor 9 is inserted between anode and control electrode of controlled switch 1. Load 8 is shorted out by diode 6. EFFECT: enhanced modulator efficiency under normal and abnormal conditions. 6 cl, 8 dwg

Description

 The invention relates to switching power supplies (for example, modulators) operating on a capacitive load with a partial discharge of the capacitive storage and is intended to power electrostatic precipitators or other devices having a large fraction of the capacitive component in the load, especially when the breakdown in the load is standard, as well as in those cases when the load is constantly present high voltage (stand) from any external source of high voltage, and the pulse is superimposed on it.

 An analysis of the known electrical circuits of modulators showed that due to a large voltage drop across the switch, it is difficult to obtain high voltage pulses at a capacitive load, for example an electrostatic precipitator, with an electric capacity of 0.15 μF or more, with a pulse duration of 20 ... 60 μs, and a pulse voltage of 20 kV, voltage “stand” more than 20 kV, repetition rate up to 1 kHz, with a service life of at least 1000 hours

 A known source of high voltage for an electric dust collector, made using an uncontrolled arrester, which does not allow long-term operation of the device with a relatively high frequency. Regular breakdowns in the dust collector can lead to a periodic malfunction of the source [1].

 The source generates pulses of a random shape, which can arbitrarily change when the parameters of the medium in the electrostatic precipitator change, and has a relatively short lifetime of the arrester (at a high repetition rate). The service life of the discharge is the long service life of the arrester (at a high repetition rate). The service life of the arrester, as a rule, is estimated not by the operating hours, but by the number of operations. The circuit is not sufficiently protected from electrical breakdowns of the dust collector, has a low efficiency and large losses during regular breakdowns of the capacitive load.

 Also known are pulse modulators containing a DC power source and two series-connected modulator lamps [2, 3, 4]. Such modulators are able to provide stable operation, however, modulator lamps are not able to pass currents of hundreds of amperes per microsecond. The disadvantages of these modulators include low efficiency in the formation of fronts, as well as a relatively large voltage drop on an open device and gentle fronts of a relatively large magnitude when operating on a capacitive load.

 As a prototype, a pulsed modulator [4] was selected, containing a voltage source supplying two series-connected modulator lamps shunted by diodes, the first of which is connected to the positive bus of the power supply by the anode, by the cathode through the inductance and capacitance to the first load input, and the second load input is connected with a common bus, the second lamp is connected anode to the cathode of the first lamp, and the cathode to the common bus, the first diode is connected by the cathode to the anode, and the anode to the cathode of the first modulator lamp, and the second diode is connected it is connected with the cathode to the anode and the anode to the cathode of the second modulator lamp, the second power supply of positive polarity is connected through the inductance to the load, the second negative polarity terminal of both power supplies is connected to a common bus, the control pulse generators are connected to the control electrodes of the modulator lamps.

 The aim of the present invention is to increase the efficiency of the modulator both in the normal mode of operation when converting direct voltage to pulse, and for any kind of abnormal breakdowns in the load, as well as increasing the efficiency of the electrostatic filter (dust collector) in general and reducing the cost of dust cleaning.

 This is achieved due to extremely small losses in the formation of fronts, a small direct voltage drop, recovery of electrical energy during the formation of each pulse and during breakdowns in the load, high stability of the parameters of the electrical pulses in the load, regardless of changes in the parameters of the medium in the electrostatic precipitator (capacitive load).

 For this, a third (recovery) switch is introduced into the pulse modulator containing a direct current power source with an energy storage device and two series-connected managed switches, the anode of the first of which is connected to the positive terminal of the power source, and the cathode of the second - with the first terminal of the capacitive load an anode and cathode, which can be either controlled or uncontrolled (for example, a pulsed high-current diode), and a series discharge LC circuit, the inductor of which is free to the end is connected to the anode of the second managed switch, and the free end of the capacitor of the LC circuit is connected to the second terminal of the load. The circuit of the third (recuperation) switch is connected counter-parallel to the circuit of the second managed switch, the anode to the cathode, and the cathode to the anode. A resistor is connected between the anode and the control electrode of the first switch. At the same time, a device with a rigid switching characteristic (for example, an electron beam valve or a high voltage transistor) was used as the first controlled switch, from which large pulsed currents are not required, and only a very small direct voltage drop at low currents and tight controllability are required. As a second controlled switch, a device with a soft switching characteristic, for example, a pulsed hydrogen thyratron or a pulsed frequency thyristor, having an extremely small forward voltage drop and large permissible pulsed currents / cm, was used. Handbook of Radar edited by Skolnik. New York, 1970 - translation from English under the general editorship of K.N. Trofimova, Volume 3. Radar devices and systems - Moscow: Sov. Radio, 1978, 528 pp. /. The control circuit of the first switch is made in the form of a pulse shaper of locking polarity, and the control circuit of the second and third switches is in the form of a pulse shaper of unlocked polarity. Moreover, a timer is introduced into the control circuit of the third switch. To increase the efficiency of the electrostatic precipitator, a variant of the circuit with two inductors of the discharge LC circuit is proposed, one of which is included in the anode circuit of the second managed switch, and the second in the anode circuit of the third switch. In the event that the voltage on the electrostatic precipitator has any negative constant value of the "stand", i.e. a voltage source is connected in parallel with the capacitive load, a recovery diode is connected to the modulator, connected in parallel with the first controlled switch, the anode to the cathode, the cathode to the anode. The proposed pulse modulator can be called resonant, since in this modulator the load capacitance is part of a high-quality oscillatory circuit. The modulator generates a bell-shaped pulse, consisting of the duration of the front and the slice. The processes of front and slice formation are resonant with almost complete recovery of all the electricity not consumed in the load capacitance back to the coupling capacitor of the LC circuit through the third switch. In turn, a diode mounted parallel to the first switch ensures the recovery of the electrical energy of the coupling capacitor into the storage capacitor of the power source during regular (or non-standard) breakdowns in the electrostatic precipitator (if the voltage on the electrostatic precipitator has any negative constant value of the "stand"). In this case, the voltage at the coupling capacitor is equal to the sum of the voltages of the modulator power supply and the voltage of the "stand". The inductor in the anode circuit of the first switch provides the formation of a charging current pulse of the coupling capacitor of the LC circuit. The main losses of electricity occur in the charge-discharge branches of the resonant power oscillatory circuit of the second and third switches. Losses in the electrostatic precipitator are negligible.

 The control system of the switches contains a control pulse generator connected to the control input of the first and second switches, for example, through isolation pulse transformers. The control system generates two synchronously starting rectangular control pulses, the first of a short duration (unit μs) of unlocked polarity to the second switch (for example, a power hydrogen thyratron), and the second of much longer duration (tens, hundreds of μs) of locking polarity to the first switch (for example , electron beam lamp type ELV). The inclusion of the second switch through the inductance forms a pulse front at the load, and the inclusion of the third switch through the same inductance ensures the formation of a slice. The first switch during the formation of the pulse is closed, and opens only during pauses between pulses, provides the restoration and retention of the potential of the coupling capacitor at a potential extremely close to the potential of the power source.

 To illustrate the essence of the invention, Fig. 1 shows a power circuit diagram of a pulse modulator with an uncontrolled recovery switch and one coil of an LC circuit; figure 2 is a structural diagram of a control system for this circuit; figure 3 is a sequence diagram explaining the operation of the modulator; in FIG. 4 is a power circuit of an embodiment of a modulator with a controlled recovery switch; figure 5 is a structural diagram of a control system for this option; figure 6 is a sequence diagram explaining the operation of the circuit with a managed recovery switch; Fig.7 is a power diagram of a variant of a modulator with a controlled recovery switch that allows you to generate pulses with different lengths of the front and cut; on Fig - a variant of the construction of the modulator using the included on the anode recovery switch based on a managed switch.

 The power circuit of the pulse modulator (Fig. 1) contains a switch 1 connected by a cathode to the anode of switch 2, a recovery switch 3 is connected in parallel to switch 2. The beginning of the inductor 4 is connected to the connection point of the switch cathode 1, switch cathode 3 and switch anode 2, to the end which is connected to the first lining of the coupling capacitor 5, the second lining of which is connected to the cathode of the load shunt rectifier 6 (or to the negative pole of the power rectifier of the unipolar standard power supply 7, e if there is one) to the capacitive load 8. A resistor 9 is connected between the anode and the grid of switch 1, and a recovery diode 10 is connected between the anode and cathode of the same switch. The diode is connected by the cathode to the anode and the anode to the switch cathode 1. Next, the anode connection point the switch 1, the resistor 9 and the cathode of the diode 10 is connected to the beginning of the inductor 11, the end of which is connected to the first plate of the power capacitor 12 and to the cathodes of the rectifier diodes 13. The second plate of the capacitor 12 and the anodes of the diodes 13 are grounded, and a high voltage is connected to the rectifier 13 AC power supply 14.

 The control system 15 is connected to the control electrode of the switch 2 through a high-voltage isolation pulse transformer 16, and to the control electrode of the switch 1 through the isolation pulse transformer 17 with an isolation capacitor 18.

 The control system 15 (Fig. 2) consists of a master oscillator 19 (for example, on a chip 1006ВИ1), a pulse transformer 20 (for example, IT007), a power frequency pulse thyristor 21 (for example, ТЧИ-100), a timer 22 (for example, on a chip 1006VI1), a charging transistor 23 (for example, КТ828А), a direct current power supply 24 (for example, for +500 V for power elements and +15 V for microcircuits), two capacitors 25, 26 with antiphonance forming chains 27, 28, two step-up pulse transformers 16 and 17.

 The power circuit of the modulator operates as follows. The energy storage device of the power source 12 is charged from the high voltage source 14 through the high-voltage diode assembly 13. The coupling capacitor 5 is charged through the inductor 11, the switch 1 (open through the resistor 9), the inductor 4, the rectifier diodes 6 to a voltage equal to the voltage on the power capacitor 12. The voltage applied to the switch 2 in the forward direction and the switch 3 in the opposite direction also becomes equal to the supply voltage, and the voltage on the switch 1 approaches zero. At the above potentials, the pulse modulator is in its original state.

 The control system 15 sets the pulse repetition frequency of the modulator by unlocking the switch 2 (Fig. 3 c) and simultaneously locking the switch 1 (Fig. 3 g), the coupling capacitor 5 is connected in parallel to the load capacitance 8 through the inductor 4, and the voltage at the load 8 increases rapidly to a voltage level equal to or slightly higher than the voltage across the capacitor 5, and is set (Fig. 3 d) - the front is formed. This is due to the resonant mode of recharging the capacitors of the coupling capacitors 5 and the electrostatic precipitator 8 through the inductor 4.

 The electric capacity of the capacitor 5 with respect to the capacity of the electrostatic precipitator 8 is selected as much as possible, but from structural considerations it is taken only 3 ... 4 times more.

 At the same time, the control system 15 provides a locked state of the switch 1 during the entire time of pulse formation at the load 8 plus some additional time necessary to restore the non-conductive state of the switch 2 (Fig. 3 g).

 During the formation of the front, the voltage is reversed at switches 3 and 2. The reverse potential that has arisen forcibly locks the switch 2 and unlocks the switch 3, ensuring that the reverse current flows through the inductor 4, capacitance 5 and 8. A pulse cutoff occurs at load 8. The voltage at load 8 decreases rapidly, and the voltage at the coupling capacitor 5 is restored almost to its original value (voltage loss is associated with active losses during the passage of current through all of the above elements to oscillatory circuit). The slice has formed.

 Further, after some time, determined by the closing time of the controlled switch 2, the locking voltage is removed from the switch 1 and the voltage on the capacitor 5 is quickly restored to its original value due to the flow of current from the capacitor 12 through the inductor 11, switch 1, inductor 4, diode assembly 6.

 In turn, the potential of the capacitor 12 is restored due to the AC power source 14 through the diode assembly 13 (it is permissible to have a constant voltage source instead of the AC source 14 and the diode assembly 13).

 The pulse duration and the rate of change of voltage on the capacitance of the electrostatic precipitator 8 is determined by the value of the resulting capacitance of the capacitances 5 and 8 connected in series and the inductance of the inductor 4.

 In the electrostatic precipitator 8, in the presence of the voltage of the “stand” from the source 7, the voltage on the coupling capacitor 5 is equal to the sum of the voltages of the stand and the power of the modulator. For any type of breakdown of the electrostatic precipitator 8, its capacitance is short-circuited and a rapidly increasing voltage is applied to the switch 2 and the recovery diode 10 in the forward direction with the rate of breakdown development. As soon as it exceeds the voltage on the capacitor 12, the diode 10 will open and through it and the inductor 11 will flow "reverse" current from the capacitor 5 to the capacitor 12 (Fig.3 g). As a result, there is a rapid voltage equalization between the power capacitor (large capacity) and the coupling capacitor - (small capacity). The resulting voltage at the capacitance 12 slightly increases inversely with the ratio of the capacitances 12 and 5. Further, this potential is used in the formation of pulses at the load 8, as a result of which the first pulses after the breakdown are slightly larger in amplitude than previously generated. However, the resulting voltage at load 8 after breakdown is lower than the previous one, but higher than if there were no breakdown. Faster voltage recovery at load 8 contributes to an increase in the efficiency of the electrostatic precipitator.

 In practice, when the electric load capacitance of the electrostatic precipitator 8 is 0.15 μF, the capacitance of the coupling capacitor 5 is about 0.4 μF, the capacitance of the capacitor 12 of the modulator power supply is about 1.0 μF.

 The control system 15 (Fig. 2) operates as follows. In the initial state, the thyristor 21 and the transistor 23 are closed. When the thyristor 21 is locked with the first pulse received, the transistor 23 opens and charges the storage capacitors 25, 26 from the power source 24 through the inductances of the forming lines 27, 28 and the primary windings of the pulse transformers 16, 17, and closes. Under these conditions, the control system is in its original state.

 The pulse repetition frequency of the modulator is set from the generator 19 (Fig.3 a). The thyristor 21 opens and the storage capacitors 25 and 26 are discharged to the primary windings of the transformers 16, 17 through the anti-resonance forming lines 27, 28. At the same time, the timer 22 is activated and with a time delay equal to the sum of the pulse formation time and the thyristor closing time, it gives a pulse to open the transistor 23 (Fig.3 b). The duration of this pulse is determined by the duration of the voltage recovery time at the capacitors 25, 26. Opening, the transistor 23 restores the potentials of the capacitors 25, 26 to its original value, and the control system is again in its original state.

 The duration of the pulse locking the switch 1 is much longer than the duration of the pulse unlocking the switch 2. The difference in the durations of the pulses received from the control system is obtained due to the difference in the electric capacitance of the capacitors 25 and 26 and the parameters of the anti-resonance circuits 27, 28. The larger the capacity, the longer duration.

 If for more efficient operation of the electrostatic precipitator it is necessary to increase the pulse duration and change it from a bell-shaped to a rectangular shape, then instead of a diode uncontrolled switch 3, a controlled switch 25 is installed in the power circuit (for example, the same hydrogen thyratron as in switch 2) (Fig. 4), and an additional timer 27, an isolation pulse transformer 28, a 2nd frequency thyristor 29, a charging diode 30, a capacitor 31, a forming line 32, an isolation transformer 33, is introduced into the control system (Fig. 5).

 The principle of operation of a variant of a modulator with a controlled recovery switch (Fig. 4) differs from that previously considered (Fig. 1) in that when applying a reverse voltage after the formation of the pulse front, the reverse voltage switch 25 does not turn on immediately (like diode switch 4), but the time delay from the timer 27 of the control system 34 (figure 5). Further, the power circuit and control system work similarly to those discussed above, but with some changes presented on the sequence diagram (Fig.6).

 If, to further increase the efficiency of the electrostatic precipitator, different front and cut lengths are required, then the problem is solved by introducing instead of one or two chokes: the first 35, included in the anode circuit of the second managed switch 2 and forming the duration of the front, and the second 36, included in the anode circuit recovery switch 25 and forming the duration of the slice (Fig.7). The previously reviewed sequence diagram (Fig.6 g) shows separately the duration of the front and cut determined by the chokes 35, 36, respectively.

 Instead of a high-current high-voltage high-frequency diode used as a recovery switch 3, it is possible to use a high-current hydrogen thyratron having a very small forward voltage drop. To do this, you can use the circuit with the anode launch of a managed switch (for example, the thyratron TGI2500 / 35) (Fig. 8). For this, a resistor 37, a diode 38, a resistor 39, a capacitor 40 are used.

 The scheme works as follows. When a negative voltage appears on the cathode of the switch 25, the capacitor 40 is charged through the resistor 37 and the diode 38 to an amplitude equal to the turn-on voltage of the switch 25. When the voltage reaches the ignition voltage on the control electrode of the switch 25, the switch is turned on and with the help of the capacitor 40, a regular current is generated by a control electrode for reliable inclusion of the switch 25 (thyratron) with the standard duration of the control pulse. The inclusion of the switch 25 forms a slice of the pulse of the modulator. The resistor 39 ensures equal potentials of the control electrode and the cathode of the switch 25 during pauses between pulses.

Sources of information
1. Japan patent 2-3395, 02.03.83.

 2. US patent 3435378, CL. 332-41, 03/25/1969.

 3. A.S. 932610, BI 20, 05.05.82.

 4. Artym A.D., Bakhmutsky A.E., Kozin E.V., Kondratiev M.V., Nikolaev V.V., Pustovoitovsky A.S., Sadykov E.K., Sokolov E.P. Improving the efficiency of powerful radio transmitting devices; under the editorship of HELL. Artymova. - M .: Radio and communications, 1987. - 176 p .: ill.

Claims (6)

 1. A pulse modulator for powering a capacitive load, comprising a DC power source with an energy storage device, serially connected first and second managed switches and a control system with a master pulse generator, including control loops of the first and second managed switches, the anode of the first managed switch being connected to the positive output of the DC power source, the cathode of the second managed switch is connected to the negative output of the pit source DC and the second output of the capacitive load, as well as a recovery switch connected counter-parallel to the second managed switch, a series LC discharge circuit, the beginning of the inductor of which is connected to the anode of the second managed switch, the first lining of the coupling capacitor is connected to the end of the inductor, the second the lining of which is connected to a capacitive load, characterized in that a resistor is connected between the anode and the control electrode of the first controlled switch, e Bone load shunted diodes, the cathode of which is connected to the second terminal of the capacitive load, wherein, as a first controlled switch device used with a rigid characteristic inclusion, and as a second controlled switch device used with soft switching characteristic.  2. The pulse modulator according to claim 1, characterized in that the cathode of the first managed switch is connected to the anode of the second managed switch.  3. The pulse modulator according to claim 1, characterized in that an inductance coil is included in the anode circuit of the recovery switch, forming a pulse cutoff duration, while an inductance coil of a series discharge LC circuit is included in the anode circuit of the second controlled switch and forms a pulse front duration.  4. The pulse modulator according to claim 1, or 2, or 3, characterized in that the recovery switch is made controllable, while the control circuit of the recovery switch containing a timer is introduced into the control system.  5. The pulse modulator according to claim 3, characterized in that the recovery switch is made controllable, a resistor and a capacitor are connected in parallel between the cathode and the controlled electrode, and a serial circuit of a diode and a resistor is introduced between the control electrode of the recovery switch and the cathode of the second controlled switch.  6. The pulse modulator according to claim 1, or 2, or 3, or 4, or 5, characterized in that a recovery diode is inserted, connected in parallel with the first controlled switch, the anode to the cathode, and the cathode to the anode.

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