A control and pulse discharge current limiting system integrated into an AC/DC converter and pulse modulator of a high voltage pulse generator have been developed. The peculiarity of such system\textquotesingle s operation is the stabilization of the power supplied to the discharge and the correction of the width of output electric pulses towards decrease upon reaching the specified pulsed current amplitude value. The system enables the pulse generator to work in the modes close to the ``short circuited load'' mode. In this case the driving module of a composite IGBT key performs the correction of the working pulse width and blocks the pulse generator operation if needed. The suggested circuit design solutions allow using the generator in a wide range of electric plasma-forming parameters' modes and working with various types of vacuum gas discharge systems

Bordusau, S. V.

Budzko, G. P.

Godun, D. V.

English

CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)

doi:10.14311/ppt.2019.1.7Plasma Physics and Technology 6(1):7–9, 2019 © Department of Physics, FEE CTU in Prague, 2019OUTPUT CURRENT CONTROL SYSTEM OF A HIGH VOLTAGEELECTRIC PULSE GENERATOR FOR PLASMA EXCITATIOND.V. Godun∗, S.V. Bordusau, G.P. BudzkoBelarusian State University of Informatics and Radioelectronics, P. Brovki 6, 220013, Minsk, Belarus∗ godundv@mail.ruAbstract. A control and pulse discharge current limiting system integrated into an AC/DC converterand pulse modulator of a high voltage pulse generator have been developed. The peculiarity of suchsystem's operation is the stabilization of the power supplied to the discharge and the correction of thewidth of output electric pulses towards decrease upon reaching the specified pulsed current amplitudevalue. The system enables the pulse generator to work in the modes close to the “short circuited load”mode. In this case the driving module of a composite IGBT key performs the correction of the workingpulse width and blocks the pulse generator operation if needed. The suggested circuit design solutionsallow using the generator in a wide range of electric plasma-forming parameters' modes and workingwith various types of vacuum gas discharge systems.Keywords: output current, control, electric pulses, plasma load.1. IntroductionIt is known that for working with plasma load inorder to protect a generator of electric pulses from theavalanche current flowing through the open crossoverof the power IGBT key, it is necessary to provide highspeed electronic protection system [1, 2]. It is due tothe fact that unstable plasma load may lead to thechange of its electric characteristics (as well as becauseof spontaneous transition into another kind of gasdischarge). The speed and the value of the growingcurrent, flowing across the power key, are directlydetermined by the conductivity and volume of theformed discharge zone. The stability of output electricpulse generator characteristics can be achieved withthe specific circuit solutions and a modern componentbase.The most important factor influencing the effectiveoperation of a power pulse generator is the right choiceof the key IGBT transistor. The key block musthave the necessary frequency properties enabling itto perform commutation of the load at the specifiedfrequencies, provided the rate of power pulses risecorresponds to the required. Non-compliance of thefrequency properties of the selected key can cause abreakdown of a transistor, distortion of the powerpulse fronts, the emergence of inflowing currents andthe increase of the formed plasma discharge reactivity[3].The most perspective concept of designing a powerkey for a universal pulse plasma discharge systems isthe use of high speed discrete keys with sequentialswitching [4]. Such circuit solution allows to get therequired steepness of the formed pulses fronts at fre-quencies up to 60 kHz while switching pulses currentsup to 80 A.Because of the peculiarities of a pulse generatorapplication for synthesizing an unstable plasma, it isdesirable to embed a system of pulse current controlinto an output generator circuit. Such system shouldprovide the required time for safety shutdown andprovide the function of a controlled turn off threshold.To reduce the number of false protection block's trig-gering, the preliminary amplifier should be based ona separate low noise operational amplifier and providethe selection of the desired signal with the help ofpassive filtering elements.2. Main partIn reference source [5] some circuit solutions of design-ing a powerful high voltage electric pulse generatorwith the functions of stabilizing the current dischargeas well as the voltage at a discharge gap are presented.In the designed high voltage pulse generator, to pro-vide a breakdown of gas discharge medium at differentwork pressure, control and a mode of stabilizing thevoltage amplitude applied to the gas discharge gap areprovided. The availability of such option in the pulsegenerator allows to control the amplitude of pulses inthe interval from -600 to -1200 V with the function oflimiting the current in the load circuit. It allows toabandon the additional high voltage igniting devices.It makes the cost of a generator significantly lower,simplifies the construction and improves its operationreliability. The availability of an output pulse voltagecontrol makes it possible to use the pulse generatorfor different discharge systems.The discharge current stabilization mode is requiredto move smoothly through the voltage-current char-acteristic of the pulse discharge. It is also necessaryto take care of limiting the pulse power consumedby the non-stationary plasma discharge. After thegas breakdown the pulse generator allows to work indifferent stationary modes, even close to the mode7D.V. Godun, S.V. Bordusau, G.P. Budzko Plasma Physics and TechnologyFigure 1. Structural diagram of a driver device with the function of pulse discharge current limitingof forming an arc discharge. The implemented cir-cuit design solutions provide a decreased probabilityof damaging the processed samples due to the for-mation of a great number of micro-arcs in a limitedvolume [6]. The mentioned effect can be eliminatedby increasing the off-duty factor of power pulses bothmanually and automatically. Note, the system, in thiscase, increases the amplitude value of current pulsesand this, in practice, ensures maintaining constantlevel of the pulse power applied to the discharge. Theimplementation of the stabilization mode of the dis-charge pulse current allows a significant reduction inthe pulse current growth rate through the power keywhen operating in non-stationary modes. This is oneof the most important advantages of the system understudy.An additional barrier of protecting power semicon-ductor devices from admissible pulse current excessis an integrated protection system built in a drivermodule.A structural diagram of the designed driver modulewith the function of pulse current limiting is shownin Fig.1.As it has been mentioned above, a composite pulsekey on the discrete IGBT transistors connected inseries is the most preferable variant of designing apulse modulator. Because of a standard constructionof the pulse modulator to control the upper key at VTItransistor, let's analyze the functioning of the lowerkey based on the VT2 transistor with its functionalpeculiarities.The generator forms one channel of program-controlled pulses that get simultaneously through theoptical converters block to the driver module of theupper key and through the logical circuit to the drivermodule of the lower key. The driver forms the signalscontrolling the VT1 transistor. In a normal mode ofsystem operation, the two keys must open in-phase.The logical circuit is implemented for converting sig-nals into the required type according to the developedoperation algorithm. After processing in the block oflogical conversion, the pulses get to the input of thelower key driver module. The lower IGBT transistoris controlled in the same way as the upper key. In thepresented structural diagram, the formed plasma non-stationary discharge is indicated as RL. The voltagecontrolled AC/DC converter with the function of sta-bilizing the output power through RL, the compositekey and the current sensor is connected to the ground.The signal, proportional to the value of the flowingcurrent, is taken from the sensor RS and is passed tothe low noise amplifier with a controlled amplificationcoefficient. The use of passive correction circuits inthe scheme of a low-noise amplifier of provides thefiltration and conversion of the signal which subse-quently is passed to the input of the current controlof lower key driver module. The driver's micro circuitat this input differentiates two modes – overload andshort circuit mode. All pulse current control systemsare included into driver's microcircuit. According tothe technical characteristics of the driver's microcir-cuit the time of the safety shutdown does not exceed3 microseconds. This has been proved by practicalexperiments. When in an overload mode, the drivermakes the lower key control pulse narrower, thus, lim-iting the average value of the pulse current flowingthrough the composite transistor. In the short circuitmode, the driver module blocks the operation of thelower IGBT transistor, forms an error signal which ispassed to the trigger circuit and, further, a blockingsignal of module operation is formed. The withdrawalof the system from this state is possible on an user'sexternal signal, using the reset block included in thesystem.8vol. 6 no. 1/2019 Output Current Control System of a High Voltage Pulse GeneratorFigure 2. Oscillograms of current pulses and voltage at plasma load at f=5 kHz; 1- signal from current pulse; 2- pulsevoltage signalThe presented device has been implemented andtested as part of the high voltage pulse generator.The examples of the developed generator's outputparameters control system while working with a non-stationary plasma load for the output pulses' fre-quency f=5 kHz are given in Fig.2.Fig.2a shows the pulse current and voltage oscillo-grams at plasma load. Fig.2b shows the change ofcurrent and voltage pulses when the consumed powerof the discharge increases. Fig.2c shows the oscillog-aram of current and voltage pulses when the pulsepower supply source works in the mode of dischargecurrent stabilization close to the short circuit mode.One can see that when the generator works for plasmaload using the function of stabilization of the powerapplied to the discharge, it is possible to maintaindifferent current and voltage modes in the load, i.e.to move along the voltage-current characteristic of thedischarge.3. ConclusionA system for the output current control of a high-voltage electric pulse generator has been developedand tested with the formation of a non-stationaryplasma discharge. It has been experimentally estab-lished that the reaction time of the system to theexcess of pulse value of the current flowing throughthe non-stationary discharge does not exceed 3 mi-croseconds. Taking into account that the system al-ready includes the circuit of current negative feedbackwhich provides the stabilization of AC/DC converter'soutput power, the rate of current growth in the loadcircuit in emergency situations significantly decreasesand the reaction time of the system is sufficient toprotect the key IGBT transistors from overloading.AcknowledgementsThis research has been supported by Belarusian State Pro-gram of Scientific Research “Science of physical materials,new materials and technologies”, assignment 3.5.02References[1] C. Yong-Nong and K. Chih-Ming. Design of plasmagenerator driven by high-frequency high-voltage powersupply. Journal of Applied Research and Technology,11(2):225–234, 2013.doi:10.4028/www.scientific.net/amm.284-287.1136. doi:10.4028/www.scientific.net/AMM.284-287.1136.[2] J. E. Harry. Introduction to Plasma Technology:Science, Engineering, and Applications. Wiley-VCH,2010.[3] A. Polishchuk. Selection of key transistors for hard-switching converters. Power Electronics, (2):22–25, 2004.[4] A. Wintrich, U. Nicolai, W. Tursky, and R. T. Problemsof parallel and serial igbt connection. part 2. sequentialwork of the igbt. Power Electronics, (5):34–40, 2013.[5] D. Godun, S. Bordusov, and A. Dostanko. Thesoftware-controlled generator of high-voltage impulsesfor plasma technological application. Acta Technica,(56):332–337, 2011.[6] D. Godun, S. Bordusov, and A. Dostanko. Systems ofelectronic overcurrent protection in pulse powergenerator operating on plasma load. Acta Polytechnica,53(2):152–154, 2013.9

Output Current Control System of a High Voltage Electric Pulse Generator for Plasma Excitation

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Output Current Control System of a High Voltage Electric Pulse Generator for Plasma Excitation

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