M. A. Elgenedy 1, A. M. Massoud 2, D. Holliday 1, S. Ahmed 3 and B.Williams 1 1. University of Strathclyde, Glasgow, UK. 2

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1 owvoltage DC Input, HighVoltage Pulse Geneato Using NanoCystalline Tansfome and Sequentially Chaged MMC Submodules, fo Wate Teatment Applications M. A. Elgenedy 1, A. M. Massoud 2, D. Holliday 1, S. Ahmed 3 and B.Williams 1 1 Univesity of Stathclyde, Glasgow, UK. 2 Qata Univesity, Doha, Qata. 3 Texas A&M Univesity at Qata, Doha, Qata. mohamed.elgenedy@stath.ac.uk Abstact This pape poposes a new highvoltage Pulse Geneato (PG), fed fom low voltage dc supply. This input supply voltage is utilized to chage two ams of N seiesconnected modula multilevel convete submodule capacitos sequentially though a esistiveinductive banch, such that each am is chaged to N. With a stepup nanocystalline tansfome of n tuns atio, the poposed PG is able to geneate bipola ectangula pulses of peak ±nn, at high epetition ates. Howeve, equal voltagesecond aea of consecutive pulse pai polaities should be assued to avoid tansfome satuation. Not only symmetical pulses can be geneated, but also asymmetical pulses with equal voltagesecond aeas ae possible. The poposed topology is tested via simulations and a scaleddown expeimentation, which establish the viability of the topology fo wate teatment applications. Keywods Pulse geneato; Modula Multilevel Convete (MMC); nanocystalline tansfome; bipola pulses; ectangula pulsewavefom I. INTRODUCTION The disinfection pocess in wate teatment is a cucial step befoe piping the wate to homes and businesses. Usually, it takes place afte filtation, whee a disinfectant (fo example chloine, and chloamine) is added to the wate. The disinfection pocess aims to kill any emaining paasites, bacteia, and viuses to potect the wate fom gems befoe its piping [1]. Altenatively, disinfection can be successfully achieved by applying lethal electopoation to the wate unde teatment [2]. Geneally, electopoation is the pocess of applying High Voltage (HV) pulses, a Pulsed Electic Field (PEF), acoss a biological cell membane. If the electic field is highe than the citical field that the cell membane can withstand, the cell dies and the electopoation is lethal. Othewise, the electopoation is nonlethal [2]. ethal electopoation is utilized in seveal applications, such as wate teatment, ai pollution contol, food steilization and tissues ablation in medical applications [3]. In contast, nonlethal electopoation is utilized, fo example, in biofouling in industial applications and potein insetion in medical applications [3]. This wok was suppoted by a National Pioities Reseach Pogam (NPRP) gant NPRP (723297) fom the Qata National Reseach Fund (QNRF). HV Pulse Geneatos (PGs) have been utilized in electopoation applications. They vay fom classical geneatos, such as Max geneato and pulse foming netwoks, to moden powe electonicsbased geneatos [2]. Geneally, classical PGs geneate HV pulses with limited flexibility and low epetition ates. Howeve, employing powe electonic switches with thei late developments (such as high voltage withstand and high switching fequency opeation) has led the emegence of new HV PG topologies. Modula Multilevel Convete (MMC) SubModules (SMs) ae utilized in moden PGs to affod edundancy, scalability and modulaity [4][8]. Usually, MMCbased PG topologies ae fed fom a HVDC input (V dc ), as in HVDC tansmission applications, and the novelty of these emeged MMC PG topologies focused on the concept of geneating the HV pulses with flexible pulse shapes, whilst assuing individual voltage balance of each SM capacito with educed (o no) capacito voltage measuements [4][6]. Accodingly, the maximum peak voltage of the geneated pulses is ±V dc, if fou MMC ams fom an Hbidge as in [6], o ± 1 2 V dc if two MMC ams ae utilized as in [4][5]. Sequential chaging of the individual seiesconnected Half Bidge (HB)MMC SM capacitos though esistos fom a ow Voltage dc (VDC) supply is poposed in [7] to geneate unipola ectangula pulses. In [8] the sequential topology of [7] is modified by using fullbidge SMs to geneate bipola pulses. This pape poposes a new PG topology fed fom VDC supply and geneates HV bipola ectangula pulses. The poposed PG is fomed of two paallel phaselegs, one leg is esponsible of positive pulse geneation while the othe leg geneates a negative pulse polaity. Each phaseleg contains two ams, the uppe am is fomed of seies connected HBMMC SMs, while the lowe am is fomed of seiesconnected evese blocking switches. The SM capacitos ae chaged sequentially fom the VDC supply though a esistiveinductive () banch such that the input chaging cuent has a slightly unde damped esponse which allows apid sequential chaging of the SM capacitos. The sequentiallychaged SMcapacitos ae inseted simultaneously duing pulse geneation, hence the peak pulse voltage is ±N. The fomed bipola pulses ae applied

2 acoss the load though a stepup nanocystalline coe based tansfome with n tuns atio. Accodingly, the geneated pulses have a peak voltage of ±nn as a esult of the double magnification. The validity of the poposed topology is assessed via Matlab/Simulink simulations and scaleddown expeimentation. The obtained esults validate the poposed topology fo wate teatment applications. The poposed PG topology is intoduced in section II, along with its opeation pinciple. Simulation and expeimental esults ae pesent in sections III and IV, espectively. Finally, section V outlines the conclusions. II. PROPOSED TOPOOGY PRINCIPE OF OPERATION Positive pulse geneation via Am1 SMs The SMs of Am1 ae chaged sequentially and the load is subjected to Null Voltage (NV) Negative pulse geneation via Am2 SMs The SMs of Am2 ae chaged sequentially and the load is subjected to Null Voltage (NV) The poposed PG topology is shown in Fig. 1. The uppe ams, Am1 and Am2, ae fomed of N seiesconnected HB MMC SMs which ae chaged sequentially fom the VDC supply though an banch via evese blocking switches S 1 and S 2 espectively. Duing chaging of a paticula am SM capacitos, the othe am SMs ae idled. The SM capacitos of the chaging am ae chaged sequentially by bypassing the othe seies SMs in the am while inseting the chaging SM capacito. The opeating sequence of the topology to geneate bipola ectangula pulses, shown in Fig. 2, is illustated in Table I. The pulse geneation is fomed of fou stages, consecutively, the positive pulse, the positive SM capacitos chaging, the negative pulse, and the negative SM capacitos chaging. The fomed voltage pulse (V t ) acoss the pimay winding of the tansfome is stepped up by tansfome tuns atio n befoe being applied acoss the load. Hence, the geneated voltage pulse (V ) is magnified by the numbe of N sequentially chaged SMs as well as the tansfome tuns atio n yielding to a voltage pulse of peak ±nn acoss the load. By vaying the numbe of MMC cells incicuit, up to N cells, output pulse shaping is possible. Revese blocking semiconducto switches ae equied fo S 1 and S 2 which can compise an IGBT in seies with a diode, as shown in Fig. 1. This is because duing pulse geneation, S 1 and S 2 ams ae and a evese voltage of (N 1) is applied acoss them. The ating of the IGBT switch is, and since an VDC input souce is used, a single IGBT should be sufficient. Additionally, Zeo Voltage Switching (ZVS) is assued duing IGBT tun ON/, thus, seies connection of IGBTs (if equied) o the diode(s) should not pesent a shaing issue. The nanocystalline coe mateial is pefeed (ove feite) fo highfequency opeation due to its high coe pemeability, hence high magnetizing inductance, high flux density, and nea squae hysteesis loop [9]. The educed tansfome volume, due to highfequency opeation, enhances the modulaity of the poposed topology. Bipola ectangula voltage pulses ae advantageous ove unipola ectangula pulses in tems of applying mechanical stesses to the sample unde teatment in addition to electical stesses [1]. Using a tansfome in the poposed PG suppots bipola voltage pulse geneation, howeve, two aspects should be consideed namely: the leakage inductance of the tansfome and the voltagesecond balance. SM 1 Fig. 1. Poposed PG topology. V tpp i SM V pp t pc SM 2 SM N Am 1 NanoCystalline Tansfome V t 1:n Am 2 SM 1 SM 2 SM N S 1 S 2 T m ON C c T x Fig. 2. Geneated bipola ectangula voltage pulse acoss the tansfome pimay. ON T x R V T m SM Switching States T s t np A V AB B State Bypassed Inseted Idled t nc I II III IV t V np

3 TABE I SEQUENCE OF OPERATION AND CIRCUIT CONFIGURATION DURING THE GENERATION OF A COMPETE BIPOAR PUSE CYCE Positive Pulse Positive am SMs chaging Negative Pulse Negative am SMs chaging Cicuit configuation I v t C c /N Am1 Am2 N II Vs Tx Cc Am1 Am2 Tm v t III v t Am1 C c /N Am2 N IV Am1 Vs Tx Cc v t Am2 Tm Sequence of opeation S 1 and S 2 switches ae. Am2 SMs ae bypassed to povide a path fo Am1 dischaging SM capacitos. A Positive pulse of voltage peak V pp is fomed acoss the tansfome pimay fo a duation of t pp. S 1 is ON (while chaging SM capacitos of Am1) and S 2 is. Am1 SM capacitos ae inseted sequentially to echage Am1 SM capacitos, each to. All Am2 SMs ae idle *. To chage SMs of Am1, the fist chaging SM is inseted, then S 1 is tuned ON (hence, it has ZVS). Afte chaging the last SM, S 1 is tuned safely since the chaging cuent is zeo. Duing Am1 SMs chaging duation t pc the tansfome pimay voltage is nullified. S 1 and S 2 switches ae. Am1 SMs ae bypassed to povide a path fo Am2 dischaging SM capacitos. Negative pulse V np is fomed acoss the tansfome pimay fo a duation of t np. * The idled ams eventually act as an open cicuit since no cuent passes, as epesented in the cicuits outline. S 1 is and S 2 is ON (while chaging SM capacitos of Am2). Am2 SM capacitos ae inseted sequentially to echage the individual Am2 SM capacitos to. All Am1 SMs ae idle *. To allow chaging the SMs of Am2, the fist chaging SM is inseted, then S 2 is tuned ON (hence, it has ZVS). Afte chaging the last SM, S 2 tuns safely since the chaging cuent is zeo. Duing the Am2 SMs chaging duation t nc the tansfome pimay voltage is nullified. The tansfome leakage inductance limits the geneated duation of the pulses, thus, the leakage should be measued in ode to detemine the allowable pulse duation ange. Voltagesecond balance is assued fo symmetical bipola pulses, howeve, asymmetical pulses must maintain the voltagesecond balance (othewise, the tansfome coe will accumulate flux and satuate). Thus, the following equation should be applied to detemine the suitable pulse polaity magnitude and duation while assuing tansfome voltagesecond balance V pp t pp = V np t np (1) whee, V pp and V np ae the peak of the positive and negative pulse polaities while t pp and t np ae the coesponding pulse polaity duations, espectively (assuming ectangula pulses). Effectively, the geneated pulses should be in the kilovolt magnitude ange (11 kv) with pulse duations between nanoseconds and milliseconds [1]; geneally deceasing in duation as voltage inceases. The wate sample unde teatment is modelled as an R load when consideing pulse duations of micoseconds and above [11]. III. SIMUATION RESUTS The chaging of the individual SM capacitos though the banch is based on a slightly undedamped esponse of the C c cicuit, hence, the SM capacitos have fast chaging. Thus, the selection of C c values is made such that the capacito voltage has a smalle dop [11] while the input chaging cuent has an undedamped esponse, that is C c < 4 2. Accodingly, the SM capacito size is calculated fom [11], C c = 2Nt pl (1 β 2 )R whee β is the pecentage emaining voltage on the SM capacito afte pulse geneation and t pl is the longest pulse polaity duation (i.e. the longest among t pp and t np ). While the chaging cuent is expessed as i(t) = (2) β ( e 2 t sin C c 4 ) C c 4 2 t (3) Afte echaging the SM capacito, the chaging cuent is educed to zeo, i(t c ) =, solving (3) fo the chaging time t c yields t c = π 1 C c (4)

4 The SM chaging time, t c, is the contol vaiable to detemine the maximum possible epetition time povided by the PG, whee T s = 2Nt c t pp t np (5) Voltage, kv Pimay voltage oad voltage TABE II SIMUATION AND EXPERIMENTA SPECIFICATIONS Paamete Simulation Expeimental VDC input voltage 5 V 3 V Input inductance.1ω and 2µH.5Ω and 5µH Numbe of SMs/am N 5 3 Tansfome tuns atio n 4 3 oad esistance R 2 kω 1 kω SM capacitance C c 1 µf 15 µf SM chaging time t c 14 µs 3 µs Pecent emaining voltage β > Voltage, V Voltage, V Cuent, A (a) (b) (c) 5 (d) Fig. 3. Geneation of 1 kv peak, 1µs bipola pulses. (a) Voltage pulses acoss the tansfome pimay and the load. (b) Five SM capacito voltages of the negative pulse, Am1. (c) Five SM capacito voltages of the positive pulse, Am2. (d) Input chaging cuent of the SM capacitos. Voltage, kv 5 1 Voltage, kv (a) cycles (b) Fig. 4. Geneation of diffeent bipola pulse shapes whilst ensuing the tansfome voltagesecond balance constaint. (a) Combined nullload voltage duation bipola pulses of 1µs pulse duations and 1 kv peak. (b) Asymmetic bipola pulses of 1µs positivepulse duation and 4 kv peak and 5µs negativepulse duation with 8 kv peak. Matlab/Simulink simulations ae used to validate the poposed topology, with the specifications given in Table II. Bipola ectangula pulses with positive and negative duations of 1µs, voltage pulse peak of 1kV and epetition ate of 5 khz ae shown in Fig. 3a. In Fig. 3a, the pimay voltage of the tansfome is 2.5kV, which is the sum of the sequentially chaged five SM capacitos, while the voltage acoss the load is 1kV, since the tansfome has n = 4. The capacito voltages of Am1 and Am2 ae shown in Figs. 3b and 3c, espectively, whee each capacito fluctuates aound 5 V, with a voltage ipple lesse than 5%.

The flexibility of the poposed PG is exploed by geneating asymmetical bipola pulses and combined nullload voltage duations pulses as in Fig.

5 The cuent flows fom the VDC supply to chage the individual SM capacitos duing the chaging peiod is shown in Fig. 3d. It can be seen that the cuent dops to zeo afte the SM capacito echaged to 5 V with chaging time of 14µs. The flexibility of the poposed PG is exploed by geneating asymmetical bipola pulses and combined nullload voltage duations pulses as in Fig. 4. Fig. 4a shows asymmetic bipola pulse with a positive polaity peak of 4 kv and 1µs duation, while the negative pulse polaity has an 8 kv peak and 5µs duation. Moeove, combining the nullload voltage duations is exploed in Fig. 4b with 1µs pulse duations and 1 kv peak voltage. Zoomed view Pimay voltage Seconday voltage Time: 5 µs/div. Voltage: 1 V/div. Time: 5 µs/div. Voltage: 4 V/div. (a) (b) Time: 5 µs/div. Voltage: 4 V/div. Time: 25 µs/div. Voltage: 1 V/div. (c) (d) Time: 5 µs/div. Cuent: 1 ma/div. (e) Fig. 5. Scaleddown expeimental esults of the poposed topology. (a) Pimay and seconday voltage pulses of noncombined nullload voltage duations bipola pulses. (b) Pimay voltage pulses of noncombined nullload voltage duations bipola pulses. (c) Pimay voltage pulses of combined nullload voltage duations bipola pulses. (d) Thee individual SM capacitos voltage of Am2. (e) Input chaging cuent.

6 IV. EXPERIMENTA RESUTS Although tansfome leakage inductance is ignoed in the simulations, its effect is seen in the expeimental validation. To minimize tansfome leakage inductance, the pimay tuns ae wound ove the seconday windings. Its expeimentallydeduced value fom the seconday side leakage inductance l, which will be connected acoss the load, is 3.56 μh. Accodingly, fo load esistance of 1 kω, the geneated pulse will equie t = l R = 3.56 ns fo each polaity to each the equied peak value. Thus, fo pope opeation, the pulse polaity duation time should be lage than t. Consequently, micosecond pulse duations can be geneated safely, which ae tageted in this pape. The pimay and seconday voltages of bipola pulses with pulse polaity duation of 1μs and epetition time of 4μs, ae shown in Fig. 5a. The voltagepeak of the geneated pulses acoss the load is 3 V, since the tansfome tuns atio is 3 and the pimay voltage is 1V, as in Fig. 5a. The pimay voltage of bipola pulses with noncombined as well as combined nullload voltage duations and a peak voltage of 9V, ae shown in Figs. 5b and 5c, espectively. Accodingly, each of the thee individual SM capacito voltages in the two MMC ams fluctuate aound 33V as shown fo Am2 SMcapacitos in Fig. 5d. Finally, the chaging input cuent is shown in Fig. 5e fo the pulses in Fig. 5a. V. CONCUSION This pape pesented a new PG topology to geneate HV bipola pulses fo disinfection in wate teatment applications. The poposed PG is based on HBMMC SMs which povide modulaity and scalability of the topology. The individual SM capacitos ae chaged sequentially though evese blocking semiconducto switches and an banch fom a VDC input supply. The selection of the banch is such that, duing the sequential chaging of the SM capacitos, the chaging cuent has an undedamped esponse, theefoe the capacitos chage fast. A stepup nanocystalline coe based tansfome, with low leakage inductance, is connected acoss the load fo pulsevoltage magnification. The poposed topology was assessed via simulations and scaleddown expeimentation, which established the viability of the topology fo wate teatment application. ACKNOWEDGMENT This wok was suppoted by the Qata National Reseach Fund (a membe of the Qata Foundation) unde NPRP Gant ( ). The statements made heein ae solely the esponsibility of the authos. REFERENCES [1] Wate Teatment Manual: Disinfection, Office of Envionmental Enfocement, Envionmental Potection Agency EPA, Wexfod, Ieland, 211. [2] H. Bluhm, Pulsed powe system: Pinciples and applications: Belin: Spinge, 26. [3] J. Raso and V. Heinz, Pulsed electic fields technology fo the food industy: Fundamentals and applications: New Yok ; ondon : Spinge, 26. [4]. amy Rocha, J. F. Silva, and. M. Redondo, "Multilevel highvoltage pulse geneation based on a new modula solidstate switch," IEEE Tans. Plasma Sci., vol. 42, pp , Oct [5] A. A. Elseougi, A. M. Massoud, and S. Ahmed, "Modula multilevel convetebased bipola highvoltage pulse geneato with sensoless capacito voltage balancing technique," IEEE Tans. Plasma Sci., vol. 44, pp , 216. [6] M. A. Elgenedy, A. Dawish, S. Ahmed, and B. W. Williams, "A modula multilevelbased highvoltage pulse geneato fo wate disinfection applications," IEEE Tans. Plasma Sci., vol. 44, pp , 216. [7] A. A. Elseougi, A. M. Massoud, and S. Ahmed, A modula highvoltage pulsegeneato with sequential chaging fo wate teatment applications," IEEE Tans. Ind. Electon., vol. 63, pp , 216. [8] A. A. Elseougi, I. Abdelsalam, A. M. Massoud, and S. Ahmed, A fullbidge submodulebased modula unipola/bipola highvoltage pulse geneato with sequential chaging of capacitos, IEEE Tans. Plasma Sci., vol. PP, pp. 19, 216. [9] B. W. Williams, Powe Electonics: Devices, Dives, Applications, and Passive Components. ondon, U.K.: Macmillan, [1] K. H. Schoenbach, S. Katsuki, R. H. Stak, E. S. Buesche, and S. J. Beebe, "Bioelecticsnew applications fo pulsed powe technology," IEEE Tans. Plasma Sci., vol. 3, pp. 2933, 22. [11] M. A. Elgenedy, A. Dawish, S. Ahmed, and B. W. Williams, "A tansition am modula multilevel univesal pulsewavefom geneato fo electopoation applications," IEEE Tans. Powe Electon., vol. PP, no. 99, pp. 11, 217.

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