RU2663231C1 - Device of electric power supply of gas discharge systems - Google Patents

Abstract

FIELD: electrical engineering.SUBSTANCE: invention relates to electrical supply devices for gas discharge systems using a barrier discharge for plasma generation and can be used, in particular, for supplying ozonizers, plasma reactors designed for reactions of synthesis, condensation, polymerization, as well as medical devices and disinfection devices. Device can be used in any configuration of gas-discharge systems using a barrier discharge for plasma generation. Device comprises a primary oscillation circuit consisting of a series-connected semiconductor switch with an antiparallel diode, a storage capacitor and a primary winding of the transformer, a secondary oscillatory circuit consisting of a secondary winding of the transformer, with inductance series connected to the secondary circuit, a load in the form of a gas-discharge system and an interelectrode capacitance of the gas-discharge gap. Value of said inductance is selected in such a way that during one input pulse, which mainly forms damped oscillations in the primary circuit, oscillations of predominantly equal amplitude are formed in the secondary circuit, which provides multiple ignition of the discharge during the time of the specified input pulse and efficient transfer of energy from the primary storage device to the gas-discharge system.EFFECT: increasing the efficiency of low-temperature plasma generation in gas-discharge systems based on a barrier discharge.8 cl, 3 dwg

Description

The technical solution relates to devices for electric power supply of gas-discharge systems, which use a barrier discharge to generate plasma, and can be used, in particular, to power ozonizers, plasma reactors designed for synthesis, condensation, polymerization reactions, as well as medical devices and disinfection devices. The device can be used in any configuration of gas-discharge systems using a barrier discharge to generate plasma.

State of the art

A barrier discharge is now understood to mean a discharge arising in a gas under the action of a voltage applied to the electrodes, while at least one of the electrodes must be coated with a dielectric. Barrier discharge is a known and widespread type of discharge used on an industrial scale. Most often, this type of discharge is used in installations for producing ozone from oxygen and air, as well as in plasma reactors, for reactions of synthesis, condensation and polymerization [Samoilovich VG, Gibalov VI, Kozlov KV Physical chemistry of a barrier discharge. M .: Publishing house of Moscow State University, 1989. - 176 p.]. In addition, this type of discharge can be used in medical devices and disinfection devices.

The widespread use of this type of discharge determined the simplicity of its implementation, both in terms of design features and in terms of the parameters of its power sources. Typically, an alternating voltage is used to power this type of discharge in a wide frequency range, starting from industrial frequency and above, reaching tens of kilohertz.

The method of supplying gas-discharge systems based on barrier discharges in continuous mode has several disadvantages, one of which is the low active power at low frequencies. The active power in the barrier discharge is directly proportional to the product of the frequency of the supply voltage and the capacitance of the dielectric barriers. Thus, an increase in active power is usually accomplished by increasing the frequency of the supply voltage. But the creation of powerful power supplies with a switching frequency of tens and hundreds of kilohertz is a difficult technical task, since the working frequencies of powerful semiconductor devices (power transistors with insulated gates and thyristors do not exceed several tens of kilohertz). It should be noted that in high-frequency power supplies there are switching losses when switching power devices, which reduces their efficiency.

Despite the fact that developers are taking measures to reduce switching losses in high-frequency power supplies, they do not disappear completely when semiconductor devices operate at high frequencies. Also a drawback of such schemes is the lack of the possibility of returning (recovery) of energy unspent in the load.

Continuous operation of the device with high power leads to increased heat load on the electrodes of the discharge system. This necessitates the use of cooling systems. It is known that increasing the temperature of the electrodes adversely affects the efficiency of ozone production. To reduce the temperature of the electrodes, in addition to cooling, alternation of the ozonizer operation intervals with its cooling intervals is used under conditions that impede the use of the cooling system during its operation [Barrier electric ozonizer with temperature dynamics RU 42 818 U1 dated 08/25/2004].

Since the barrier discharge is a capacitive load, capacitive currents that do not participate in plasma formation constantly flow in its circuit in a continuous mode, additionally loading power supplies and resulting in Joule losses from heating of the conductors. When using gas-discharge systems with a large area of electrodes, their capacitance becomes significant, leading to large values of capacitive currents and losses, respectively.

Also, as a disadvantage, the peak power in the discharge in the continuous mode cannot significantly exceed the average power.

It should be noted the difficulty of power adjustment in continuous mode. A change in the supply voltage level will lead to a change in the discharge burning mode, which may be undesirable in some cases.

Another class of devices for supplying gas-discharge systems based on a barrier discharge are pulsed systems with durations of single pulses of a few nanoseconds. Having a high power in the pulse, the disadvantage of these devices is the large duty cycle, that is, the ratio of the duration of the interval between pulses to the duration of the pulse itself. Because of this, the efficiency of gas treatment in the discharge gap is reduced, since it is subjected to processing insignificant of the total time. In addition, there are difficulties in constructing devices with a high output power on this principle, since, despite the high pulsed power, the energy, and hence the output power, is not large due to the short pulse duration. In addition, the formation of nanosecond pulses requires the use of gas arresters, specific solid-state switches, or magnetic compressors as switches. [Device for generating short high voltage pulses. RU 2 144 257 C1 dated February 18, 1998]. The use of arresters leads to a limited resource of the device due to the specifics of their operation, and the use of high-speed switches leads to an increase in the complexity of the entire device and a decrease in its efficiency due to the final efficiency of the switch itself [S.V. Korotkov et al. A device for plasma purification of air from organic pollutants using a nanosecond barrier discharge. Instruments and experimental equipment, 2012, No. 5, p. 99-102]. The use of magnetic compressors to reduce the duration of the generated pulses also reduces the efficiency of the device due to energy losses in the magnetic keys, especially in the nanosecond range. So, in a megavolt frequency SOS generator [Rukin S.N. at al. Megavolt repetitive SOS-based generator. Proc. of 13th IEEE Int. PulsedPower Conf, 2001, V. 2, p. 1272-1275.] The energy loss in the magnetic compressor of the device reached 50% of all losses. The pulse repetition rate in such devices does not exceed units of kilohertz.

There are devices that use pulses of damped harmonic oscillations to power gas-discharge systems with a barrier discharge. These devices are capable of repeatedly initiating a discharge in the gap, until the amplitude of the supply voltage is too small for its ignition due to its attenuation. One of such devices is presented in the description of the utility model [Ozone Generator RU 91 064 U1 of 10.22.2009], selected as a prototype. The circuit has low energy efficiency, since it uses only half of the energy of a capacitive storage device - capacitor C1. Only in the process of charging the capacitor does a part of the vibration energy enter the load. The discharge of a capacitive storage device charged to the voltage of the power source occurs through the key, and this energy does not enter the load, but dissipates (dissipates as thermal energy) in the key and conductors. The prototype circuit also lacks elements that limit the amount of current when the capacitor is discharged through the key, which can lead to the failure of the latter. Additionally, the energy efficiency of this solution is deteriorated by the inability to return the energy unexpended in the discharge to the primary circuit. The process of forming a pulse of damped oscillations begins with locking the key, while the energy accumulated in the inductance of the transformer will cause almost twice the voltage of the power source across the capacitance and key as a result of the resonant nature of the charge. This overvoltage imposes additional requirements on the key with respect to its maximum permissible operating voltage.

There are no elements allowing to form the shape (envelope) of the output pulse. The pulse shape will have a pronounced decaying character with the possibility of initiating a discharge only during the first periods of the output voltage.

Technical challenge

The technical problem is the efficient generation of low-temperature plasma in gas-discharge systems based on a barrier discharge.

The technical result is as follows:

• reducing the power consumption of the device as a whole and increasing its efficiency;

• due to the repeated ignition of the discharge in one pulse, an increase in the repetition rate of the discharge burning pulses;

• reduction of thermal loads on the electrodes of the discharge system, which allows us to refuse in some cases their cooling systems;

• providing a wide range of output power adjustment;

• ensuring the peak power level that is unattainable during continuous operation at a significantly lower average power, which may be relevant for various plasma-chemical reactions (while the circuit design features of the device do not limit the maximum value of peak power);

• high peak power allows you to work with discharge systems of a large area, efficiently charging significant interelectrode capacitances;

• increase, in contrast to pulsed nanosecond systems, the time of interaction between the plasma of a gas discharge and gas in the discharge gap;

• ensuring a long service life of the device, since it is made on solid-state elements and does not have parts with a known expense or wear (spark gap);

• reduction in the weight and size characteristics of the power source due to energy conversion at an increased frequency.

Decision

To solve this problem, a device for electric power supply of gas-discharge systems, including

a. primary oscillating circuit, consisting of a series-connected semiconductor switch with an antiparallel diode, storage capacitance and the primary winding of the transformer,

b. a secondary oscillatory circuit, consisting of a secondary winding of a transformer, with an inductance, a load in the form of a gas discharge system and an interelectrode capacitance of a gas discharge gap, sequentially connected to the secondary circuit, while the value of the indicated inductance is selected so that during one input pulse, which forms mainly damped oscillations in primary circuit, in the secondary circuit oscillations are formed predominantly of the same amplitude, which provides multiple ignition discharge time for said input pulse and efficient energy transfer from the primary storage device to a discharge system.

The value of the indicated inductance L1 in the secondary circuit is selected empirically from the interval 0.9Lcalc to 1.1Lcalc, where Lcalc is calculated by the formula

,

,

where Lperv is the inductance of the primary circuit; Srs - the total capacity of the discharge system; L second is the inductance of the secondary circuit, C1 is the capacity of the primary circuit (primary storage).

Moreover, in the tested device L1 lies in the range from 4.8L second to 5.6L second.

The output pulse includes several periods of harmonic oscillations, for example, four as in the experiment. At the same time, during one input pulse, a multiple ignition of a discharge occurs in a gas discharge system (at least seven times in the configuration used).

As a result of repeated ignition of the discharge in one pulse, the interaction time of the plasma of the gas discharge and gas in the discharge gap increases to 10 μs or more in one pulse.

In the implemented device, the peak power in the pulse of the system is of the order of 30 kW or more, which allows efficient charging of interelectrode capacitances, while the frequency of harmonic oscillations is hundreds of kilohertz (over 100 kHz).

Description of drawings

In FIG. 1 shows an electrical diagram of the proposed device. The following notation is introduced: 1 - power supply and a control circuit for a pulse generator of damped oscillations, 2 - commutator, 3 - diode D1, 4 - primary drive C1, 5 - transformer, 6 - additional inductance L1, 7 - load (gas discharge gap), 8 , 9 - sensors of load currents and primary circuit, respectively.

In FIG. 2 shows the structure of the barrier discharge and its equivalent circuit in the absence (Fig. 2a) and the presence of a discharge (Fig. 2b) in the discharge gap. The following notation is introduced: 10 is the capacitance of the dielectric barrier Sb, 11 is the capacitance of the discharge gap Срп, 12 is the equivalent corresponding to the burning voltage of the discharge Uр, 13 is the equivalent corresponding to the energy loss in the discharge Rр.

In FIG. 3 shows the voltage curves Uc on the primary storage device C1, the current in the primary circuit Iperv and the output voltage and current Uoutput and Iout, respectively.

Detailed description

A device is proposed that would be free from the disadvantages of both pulsed and continuously operating devices for supplying gas-discharge systems based on a barrier discharge and would have their advantages. It is proposed to use power sources with an output voltage in the form of harmonic oscillation pulses to power such devices. Having high power, as in the case of monopulse systems, this form of supply voltage allows you to repeatedly initiate a discharge in the gap in one pulse. This leads to an increase in the effective frequency of the device, which will be equal to the product of the pulse repetition rate by the number of discharge initiation events per pulse.

The discharge burning time in this case is significantly higher than in short-pulse systems, which leads to an increase in the interaction time of the gas-discharge plasma and gas in the discharge gap.

Due to the possibility of regulation over a wide range of the pulse repetition period, it becomes possible to change the average power in the discharge also over a wide range. This allows you to reduce the thermal load on the electrodes of the discharge system while maintaining high pulse power. Reducing the thermal load on the electrodes allows you to abandon the cooling systems that are required for powerful continuous installations.

Since the barrier discharge is a capacitive load, the recharge current of the dielectric capacitance and the discharge gap is constantly present in continuous systems. The flow of capacitive currents leads to additional heating of the conductors, reducing the efficiency of the system. In a pulsed device, capacitive current flows only during a pulse, which reduces losses from capacitive currents in conductors.

High pulse power allows you to effectively recharge the interelectrode capacitance of large magnitude. This opens up the possibility of using this technical solution to create powerful industrial plants with a large area of electrodes of a gas discharge system. It should be noted that the circuitry features of the proposed device do not limit the maximum achievable value of the average and peak power. The proposed method for generating pulses of harmonic oscillations is economical, does not require the use of gas arresters, semiconductor voltage sharpeners and magnetic compressors. In case of incomplete consumption by the load of energy stored in the power source, part of it, with the exception of losses, is returned after the end of the pulse to the power source (recovered). This leads to lower power consumption of the device as a whole, increasing its efficiency.

The increased frequency of harmonic oscillations in the pulse, capable of reaching hundreds of kilohertz, allows you to create small-sized power supplies with reduced material consumption of different power and the required output voltage level.

A distinctive feature of this technical solution from the prototype is that in the power supply in this embodiment, to obtain pulses of harmonic oscillations, the discharge of the storage capacitor is used, and not its charge. This eliminates the need to uselessly discharge the storage capacity, charged to maximum voltage, through the key. In our case, the discharge current of the storage capacitance through the key is limited by the transformer inductance from the side of the primary winding. Moreover, most of the accumulated energy in the capacitive storage when it is discharged enters the load. The rest of the energy at the time of the end of the pulse is returned to the capacitive storage, which helps to increase the efficiency of the device compared to the prototype. A voltage with an amplitude not exceeding the voltage of the power source is applied to the key in the proposed embodiment. In addition, additional elements (inductance L1) are introduced into the supply circuit of the gas-discharge system, which make it possible to set the optimal pulse shape of the output voltage also in order to achieve the most efficient generation of the barrier discharge plasma. This solution allows you to generate a pulse of the required duration on the load. The duration of this pulse is selected from the condition of effective multiple generation of plasma in the discharge during the entire pulse.

The electrical circuit of the proposed device is shown in FIG. 1. The device consists of a power source and control circuit (1), a solid state switch with full control (2), diode D1 (3), capacitive storage C1 (4), transformer (5), additional inductance L1 (6), load ( gas-discharge system) (7), load current sensors Iout and primary circuit Iper (8, 9), respectively.

The power source charges the capacitive storage to the desired voltage value Uc. The control circuit generates control signals for the switch, turning it on and off. The switch together with the capacitive storage and the primary winding of the transformer form an oscillatory circuit. The occurrence of amplitude-damped oscillations in the circuit occurs after the switch is turned on when there is energy in the capacitive storage C1. The vibration energy from the primary circuit through the transformer enters the load. The load is included in the secondary circuit of the transformer. The transformer is used to coordinate the impedance of the device with the impedance of various loads in order to transfer energy to them as efficiently as possible. The oscillation frequency in the primary circuit is determined by the value of the storage capacity and the inductance of the transformer on the side of the primary winding. The oscillation frequency in the secondary circuit is determined by the inductance of the transformer on the side of the secondary winding, the additional inductance L1 and the capacity of the discharge system. The capacity of the discharge system consists of series-connected capacitances of the dielectric barrier Sb and the capacitance of the discharge gap Srp (Fig. 2).

In the proposed device, similar to how it is done in Tesla transformers, the approximate equality of the oscillation frequencies of the primary and secondary circuits is provided. The adjustment of the oscillation frequency in the secondary circuit is carried out by changing the value of the additional inductance L1.

In this case, the frequencies of the primary and secondary circuits will be determined as:

.

.

The shape of the pulse (envelope corresponding to a change in the amplitude of high-frequency harmonic oscillations) is determined by both the values of the elements used in the device and the magnitude of the magnetic coupling between the primary and secondary windings of the transformer. This value depends on the parameters and design of the transformer, and is decisive for the magnitude of the rate of energy escape from the primary circuit to the load. By changing the magnitude of the magnetic coupling and the value of the additional inductance L1, it is possible to achieve a different shape of the envelope of the output pulses. Optimization of the parameters and design of the transformer was carried out in order to achieve multiple initiation of a barrier discharge during a pulse of a given duration and the most efficient transfer of energy from the primary storage device to the gas discharge system.

The formation of a pulse of damped oscillations in the primary circuit begins with achieving the required voltage level on the primary capacitive storage and applying a switch on signal. In the primary oscillatory circuit, consisting of a switch, a capacitive storage device and the primary winding of the transformer, damped harmonic oscillations occur. The energy of each subsequent half-cycle of oscillations is less than the previous one by the amount of energy ΔE due to the sum of the energy transferred to the load and the energy of losses. The energy of losses consists of resistive losses and losses in the core of the transformer, if used.

The advantage of the proposed solution is the ability to return (recovery) of energy unspent in the load. After disconnecting at the right moment of the switch, the energy unspent by this moment through the diode D1 is returned to the primary capacitive storage C1. The value of this energy determines the value of the residual voltage on the drive Uost. It is by this value that the selection of energy from the power source for the formation of a subsequent pulse will decrease. This leads to lower power consumption of the device as a whole, increasing its efficiency.

The voltage on the secondary side of the transformer is also a pulse formed by several periods of harmonic oscillations. By selecting the parameters of the device elements in the load circuit, it is possible to form several voltage periods with amplitudes without a pronounced attenuation in time. This allows you to repeatedly initiate a barrier discharge during the pulse. So, from the presented current and voltage curves, we can conclude that the discharge in the device under study was ignited for one pulse at least seven times. The effective frequency of its ignition increases by the same amount compared to the pulse repetition rate. Thus, at pulse repetition frequencies of units of kilohertz, as in the case of monopulse systems, the discharge ignition frequency in our case will reach tens of kilohertz. The number of acts of initiation of a discharge per pulse can have different values - both greater and less than that obtained in this particular case. It is determined by the energy reserve in the capacitive storage C1, the parameters used in the device elements and the properties of the gas discharge system.

The device allows the formation of high power pulses. So, the power of the first half-cycle of oscillations in the primary circuit in this particular device is more than 30 kW. A continuous installation of such power would be distinguished by impressive weight and size indicators and the indispensable presence of a cooling system. Despite the high peak power of the oscillations during the pulse, the average power of the proposed device can be controlled by changing the pulse repetition rate (change in duty cycle) over a wide range. The maximum peak power of the proposed method for generating pulses is not limited by the values given on the curves and can reach a megawatt power level.

Current and voltage curves were obtained using an HP54542A oscilloscope with an operating frequency of up to 500 MHz, current transformers were used Stangenes 0.5-0.1 current transformers with a rise time of 10 ns, the output voltage was measured with a Tektronix P6015 high-voltage probe, and an HP high-voltage probe was used to measure the voltage on the primary drive -9258.

Claims (11)

1. A device for electric power supply of gas-discharge systems, including but. primary oscillating circuit, consisting of a series-connected semiconductor switch with an antiparallel diode, storage capacitance and the primary winding of the transformer, b. a secondary oscillating circuit, consisting of a secondary winding of a transformer, with inductance in series, a load in the form of a gas discharge system and an interelectrode capacitance of a gas discharge gap, sequentially connected to the secondary circuit, the magnitude of the indicated inductance is selected in such a way that during one input pulse, which forms predominantly damped oscillations in the primary circuit, oscillations of predominantly the same amplitude are formed in the secondary circuit, which ensures multiple discharge ignition during the time of the specified input pulse and efficient energy transfer from the primary drive into the gas discharge system. 2. The device according to claim 1, characterized in that the value of the indicated inductance L1 in the secondary circuit is selected empirically from the interval 0.9Lcalc to 1.1Lcalc, where Lcalc is calculated by the formula

. 3. The device according to claim 2, characterized in that the magnitude of the inductance L1 in the secondary circuit is in the range from 4.8L second to 5.6L second. 4. The device according to p. 3, characterized in that the output pulse includes several periods of harmonic oscillations. 5. The device according to claim 4, characterized in that the output pulse includes four periods or more of harmonic oscillations. 6. The device according to p. 5, characterized in that during one input pulse there is at least 7 discharge ignitions in the gas discharge system. 7. The device according to claim 6, characterized in that as a result of multiple ignition of the discharge in one pulse, the interaction time of the plasma of the gas discharge and gas in the discharge gap increases to 10 μs or more in one pulse. 8. The device according to claim 7, characterized in that the pulse power for charging the interelectrode capacitance of the discharge system is of the order of 30 kW or more, the frequency of harmonic oscillations is 100 kHz or more.

Images