RU2647662C1 - Generator of impulses of damped vibrations of limited duration - Google Patents

Abstract

FIELD: instrument engineering.

SUBSTANCE: invention relates to devices for generating impulses of damped oscillations and can be used, in particular, in devices designed to ignite gas discharges in order to excite low-temperature plasma. Essence of solution is pulse generator based on quarter-bridge converter, which includes power supply, antiparallel diode, current sensors, semiconductor switch, connected in series to oscillatory circuit with capacitive storage and primary winding of transformer and intended to generate impulses of damped oscillations in load of transformer winding, characterized in that it comprises control circuit for monitoring voltage on storage capacitor and turning on of switch when reaching certain level of this voltage, and also disabling switch via signals from current sensors at fixed time interval at the moment of current flowing through it, when current flows through diode parallel to switch.

EFFECT: technical result consists in reducing power consumption of device and reducing power consumption from power source.

6 cl, 3 dwg

Description

The invention relates to a device for generating pulses of damped oscillations and can be applied, in particular, in devices designed to ignite gas discharges with the aim of exciting low-temperature plasma.

State of the art

There are devices for receiving pulses of damped harmonic oscillations. The intermittent oscillations obtained with their help are damped in nature, which is of no fundamental importance for a number of applications (induction heating, excitation of low-temperature plasma, etc.) (V. Mastyaev. Pulse thyratron generators for induction heating. - M.: Energy, 1978 , 96 p.).

RF patent No. 2523163 describes a solid-state high-frequency generator with a shock excitation circuit (Solid state high-frequency generator with a shock excitation circuit. RF patent No. 2523163, 2014). The device allowed to generate pulses of damped oscillations at the output with an oscillation frequency reaching units of megahertz. The device was used to ignite gas discharges to excite low-temperature plasma (AV Ponomarev et al. High-frequency generator based on pulsed excitation of the oscillating circuit for biological decontamination. Pulsed Power Conference (PPC), 2013 19th IEEE, p. 1–5, 2013.doi: 10.1109 / PPC.2013.6627495).

It was shown in the work that upon excitation of a low-temperature plasma by pulses of damped harmonic oscillations, the discharge current flowed only in the first periods of the supply voltage. Due to the attenuation of the voltage amplitude over time, its value became insufficient to ignite the discharge in subsequent periods of oscillation. Thus, part of the pulse energy wasted uselessly, dissipating as heat in the conductors. This led to increased consumption by the device of energy not entering the load, and excessive heat generation in the circuit elements.

One of the solutions to the problem of increasing the efficiency of a damped oscillation pulse generator is described in JPS5862924 from 1983 (Powerful damped oscillation pulse generator). In the work, damped oscillations in the load circuit were stored as residual energy in an additional capacitive storage. After a complete cessation of oscillations, the stored energy was returned to the power source using an additional recovery circuit, increasing the efficiency of the device.

The disadvantage of this solution is the prolonged presence of oscillations in the power circuit until they are completely damped and the associated thermal losses in the conductors. In addition, this solution complicates the circuit solution by introducing additional elements of the energy recovery circuit.

The closest in technical essence and the achieved positive effect to the claimed device is selected as a prototype "Generator of excitation of oscillations" described in US patent No. 4837525 from 1989 (Transient waveform generator). The device is a quarter-bridge converter in which high-frequency oscillations in the circuit occur after the capacitive storage is switched by a thyristor with a diode installed parallel to it. The device generates pulses of damped oscillations with a frequency of about 1 MHz. The use of a partially controlled switch, namely a thyristor, does not allow limiting the duration of the generated pulses of damped oscillations by locking it with an external control signal. The inability to lock the thyristor eliminates the repeated supply of a supply voltage to it until the current flowing through it is completely stopped and its electrical strength is restored. This circumstance limits the repetition rate of pulses generated by the device.

Technical challenge

The technical task of this invention is the task of increasing the efficiency of low-temperature plasma initiating devices when igniting gas discharges by pulses of damped oscillations and increasing the maximum frequency of their repetition.

The technical result coincides with the technical task and is achieved by forcibly limiting the pulse duration at the moment of termination of energy input to the load. Obtaining such (limited in duration) pulses makes it possible to save part of the pulse energy not consumed by the load, which in turn allows reducing the power consumption from the power source. This leads to lower power consumption of the device and increase its efficiency. An additional advantage of reducing the pulse duration is the possibility of increasing the frequency of their repetition.

Decision

To solve this problem, a pulse generator based on a quarter-bridge converter is proposed, which includes a power supply, a semiconductor switch, an antiparallel diode, current sensors connected in series to an oscillatory circuit with a capacitive storage and transformer primary winding and designed to generate damped oscillation pulses in a load connected to the circuit the secondary winding of the transformer, characterized in that it contains a control circuit that provides voltage control on mkostnom drive switch and switch when reaching a certain level of voltage, and also by signals from current sensing switch off after a fixed time interval at the time of no current flowing therethrough when a current flows through the parallel diode switch.

As a switch with an antiparallel diode, a device with full control can be used to interrupt oscillations in the circuit at a certain point in time after their occurrence. In turn, as a device with full control can be used a bipolar transistor with an insulated gate (IGBT transistor) or a MOSFET transistor.

An array of series-connected switches can be used to increase the operating voltage. And to increase the operating current, an array of parallel or mixed connected switches can be used.

Description of drawings

In FIG. 1 shows an electrical diagram of the proposed device. The following notation is introduced: 1 - power supply, 2 - control circuit, 3 - switch, 4 - antiparallel diode, 5 - capacitive storage, 6 - transformer, 7 - load, 8, 9 - primary current and load current sensors, respectively.

In FIG. 2 shows the current curves in the primary circuit I1 and the voltage across the capacitive storage Uc. FIG. 2a: the formation of pulses of a damped oscillation limited in duration. FIG. 2b: the formation of pulses of damped oscillations without limiting their duration.

Detailed description

A distinctive feature of this technical solution from the prototype is that the device with full control is used as the primary switch - in our case, an insulated gate bipolar transistor (IGBT transistor). Having the ability to turn it on and off with an external control signal allows him to interrupt the oscillations in the primary circuit at the right time or at the moment the load ceases to consume energy. In this case, part of the pulse energy not consumed by the load remains in the capacity of the primary circuit storage device. The amount of this residual energy decreases the energy supplied to the drive from the power source to form a subsequent pulse. This is what leads to lower power consumption of the device and increase its efficiency.

Reducing the duration of the pulse itself allows you to increase the maximum frequency of their repetition.

The switch is turned on and off by the control system. In order to avoid overvoltage on the switch in the event of a current interruption in the primary circuit, shutdown is performed only when there is no current flowing through the switch. The switch is turned off when the current flows through a diode parallel to the transistor. Thus, only an integer number of periods of damped oscillations is formed.

A device for generating pulses of damped harmonic oscillations of limited duration is proposed. The electrical circuit of the proposed device is shown in FIG. one.

The device is a quarter-bridge converter of direct voltage to alternating - pulse. The device consists of a power source (1), a control circuit (2), a switch (3), an antiparallel diode (4), a capacitive storage device (5), a transformer (6), a load (7), current sensors (8, 9). The power source charges the capacitive storage to the desired voltage value. The control circuit monitors the value of this voltage Uc and, when it reaches a certain level, stops the charging process of the capacitive storage by turning off the power source.

The control circuit also generates control signals of the switch, translating it into open or closed state at certain points in time. To determine these points in time, the control circuit can receive signals from current sensors of the primary circuit I1 or current in the load circuit I2.

The switch together with the diode, capacitive storage and the primary winding of the transformer form a primary oscillatory circuit. Any types of devices with full control that satisfy their electrical parameters and speed can be used as a switch. The switch may consist of a single device or be composite. To increase its operating voltage, a series connection of devices can be used. An increase in the operating current is possible with their parallel or mixed - parallel-serial connection. It is possible to use switches with an antiparallel diode already built into the device (MOSFET, IGBT transistors), which allows you to exclude an additional separate diode from the 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. The oscillation frequency is determined by the value of the storage capacity and inductance of the transformer and can reach hundreds of kilohertz. The limiting oscillation frequency is determined by the speed of the switch and the control system. 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 rate of energy escape from the primary circuit to the load is determined by the magnitude of the magnetic coupling between the primary and secondary windings. This value is determined by the parameters and design of the transformer.

The process of generating a pulse of damped oscillations begins from the moment the charging by the power source of the capacitive storage starts to the desired voltage value (time t1, Fig. 2a, b). When this value is reached at time t2, the control circuit turns off the power source and sends a signal to turn on the switch. 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 ∆E due to the energy transferred to the load, as well as the energy of losses. The energy of losses consists of resistive losses and losses in the core of the transformer, if used. In the absence of a device to stop oscillations in the circuit, the energy in the primary circuit decreases until the oscillation processes cease (Fig. 2b).

It should be noted that the formation of harmonic oscillations by the proposed method is much more efficient compared to the use of high-frequency generators operating in a continuous mode. In continuous mode, the formation of harmonic oscillations requires switching the switch at the frequency of these oscillations. Switching the device with a high frequency leads to the appearance of switching losses and a decrease in the efficiency of the device. In our case, the unlocking of the switch occurs once, after which it remains in the open state until the end of the generated pulse. The device is locked when there is no current flowing through it. As a result of this, switching losses in the switch are practically absent. This allows you to generate harmonic oscillations of high frequency, including exceeding the maximum operating frequency of the switch used. In addition, operation in pulsed mode allows the generation of pulses with high peak power, unattainable when operating in continuous mode. In this case, the average power will depend on the duty cycle. Duty rate determines the ratio of the peak power of a pulse installation to its average power.

In the proposed device, the moment of termination of the oscillatory processes (time t3, Fig. 2a, b) in the primary circuit can be carried out according to a number of events or conditions. When these events or conditions occur, the control system generates a switch off signal. The switch is locked, and the energy unspent by this moment is returned through the antiparallel diode to the capacitive storage. It is by this value that the selection of energy from the power source for the formation of a subsequent pulse will decrease. The value of this energy determines the value of the residual voltage on the drive ∆U. From this non-zero voltage value, the capacitive storage will be charged to the required value for the formation of a subsequent pulse.

Switching off the switch by the control system can be performed according to the following conditions or events. The moment of switch off time can be set; the oscillation periods can be calculated using the primary circuit current sensor and the switch is turned off at a given oscillation number; the load current can be detected by the sensor and shutdown will occur upon its termination. All these conditions and events are united by the fact that the switch always turns off when there is no voltage on it and no current flowing through it, which reduces switching losses and prevents overvoltage on it.

The curves shown in FIG. 2a, b, demonstrate the advantages of the proposed solution. When using a gas spark discharge as a load between two electrodes, the following results were obtained to demonstrate the operation of the device. Considering that the energy in the capacitive storage is proportional to the square of the voltage on it and that the maximum voltage on the storage is 1000 V, we can conclude that in the circuit without limiting the pulse duration (Fig. 2b), the energy returned to the primary circuit was 4% (∆U = 200 V). Moreover, in the circuit with a limited pulse duration (Fig. 2a), the value of the energy returned to the circuit exceeded this value by 6 times and reached 25% (∆U = 500 V). This means that if the pulse duration is limited during operation, the device will consume 21% less energy from the primary power source than without it. The comparison of the curves obtained by reducing the oscillation period T from 250 to 125 μs shows that the maximum pulse repetition rate while limiting their duration can be increased by almost 2 times (from 4 to 8 kHz). These data are obtained when using a spark discharge as a load and can vary when using other types of discharges and other values of circuit elements.

A spark discharge is the simplest implementation of a discharge type, and was used only to demonstrate the operability of the circuit. The solution can be applied to many types of gas discharges. The voltage of 1000 V used in the work is also just an example of implementation. When implementing this solution, various voltages can be used both above and below this value. But the principle of operation of the circuit will not change from this. To increase its value above the operating voltage of a single switch, a serial connection of devices can be used. Therefore, the operating voltage in the circuit is not determining the principle of its operation. By analogy, the value of the operating frequency is not a determining factor in the implementation of the solution. The meanings given in the description are only an example of implementation, while the scope of legal claims is determined solely by the patent formula.

Claims (6)

1. A pulse generator based on a quarter-bridge converter, including a power supply, an antiparallel diode, current sensors, a semiconductor switch, connected in series to an oscillating circuit with a capacitive storage and the primary winding of the transformer and designed to generate pulses of damped oscillations in the load connected to the secondary circuit of the transformer , characterized in that it contains a control circuit that provides voltage control on the capacitive storage and switching on the switch when a certain level of voltage, and also by signals from current sensing switch off after a fixed time interval at the time of no current flowing therethrough when a current flows through the parallel diode switch. 2. The generator according to claim 1, characterized in that a device with full control is used as a switch with an antiparallel diode, which allows interrupting oscillations in the circuit at a certain point in time after their occurrence. 3. The generator according to claim 2, characterized in that the device with full control uses a bipolar transistor with an insulated gate (IGBT transistor). 4. The generator according to claim 2, characterized in that a MOSFET transistor is used as a device with full control. 5. The generator according to paragraphs. 3, 4, characterized in that to increase the operating voltage using an array of series-connected switches. 6. The generator according to paragraphs. 3, 4, characterized in that to increase the operating current, an array of parallel or mixed connected switches is used.

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