10 kv High Voltage Generator with LLC Resonant Circuit for Sterilizing Microbe Applications

Transcription

1 0 kv Hgh Voltage Generator wth LLC Resonant Crcut for Sterlzng Mcrobe Applcatons S.-Y. Tseng H.-C. Ln # Y.-D. Chang S.-T. Peng GreenPower Evoluton Appled Research Lab. (G-PEARL) Department of Electrcal Engneerng Chang Gung Unversty Kwe-Shan, Tao-Yuan, Tawan, R.O.C E-mal: sytseng@mal.cgu.edu.tw Tel: Fax: # Department of Electrcal Engneerng Natonal Chung Cheng Unversty ## S.-Y. Fan ## Lnear Motor Research Laboratory Department of Electrcal Engneerng Wufeng Insttute of Technology Mng-Hsung, Cha-Y, Tawan E-mal: syfan@mal.wfc.edu.cgu.tw TEL: FAX: Abstract-Ths paper proposes a hgh step-up voltage rato of full-brdge converter assocated wth LLC resonant crcut for sterlzng mcrobe applcatons. The proposed crcut structure adopts full-brdge converter to generate a hgh DC voltage, whle the LLC resonant crcut s used to recover the energy trapped n leakage nductance of transformer and to reach zero-voltage swtchng feature ncreasng converson effcency. Moreover, the LLC one can also avod generatng a large resonant current whch occurs n between the large leakage nductance and the large equvalent capactor of prmary wndng n transformer due to transformer wth a hgh turns rato. As compared wth a conventonal full-brdge converter wth hard-swtchng crcut or phase-shft control method, the proposed converter can reduce voltage and current stresses of swtches and ncrease converson effcency wth soft-swtchng features. Fnally, a prototype of hgh voltage generator under output voltage of 0 kv and maxmum output power of kw has been mplemented to prove the feasblty of the proposed hgh voltage generator. I. INTRODUCTION Due to the advanced development of semconductor technology, desgn and mplementaton of hgh output voltage generator become more faclty. It wll expand applcatons of pulsed electrc feld (PEF) technology, such as food sterlzaton, waste treatment, polluton control, and medcal dagnoss and treatment []-[0]. In partcular, when PEFs are used to sterlze mcrobes of lqud food, they only cause a lttle ncrease n temperature. As compared wth conventonal thermal processng, the PEF method can provde consumers wth safe and nutrtous food, and wth fresh qualty. It can replace or complement conventonal thermal processng methods. For food sterlzaton usng PEF processng, researchers have proposed varous processng waveforms, whch can be dvded nto two groups: wde pulse and narrow pulse. Snce effectveness of food sterlzaton usng wde pulses s hgher than that usng narrow pulses, wde pulses are usually used n a great deal of lqud food sterlzaton. In recent years, t s wdely used n frut juce and mlk sterlzaton. When a wde pulse wth hgh enough electrc ntensty s appled to the suspenson, as llustrated n Fg., and creates a voltage hgher then V across the cell membrane, t wll nduce rreversble pore changes and kll mcrobes wth a mechansm of rupturng cell membrane [9]-[0]. Ths process s called electroporaton and s llustrated n Fg., whch was dgested from [0]. Before PEFs are appled to cell, they wll create permeable pores over the membrane and water molecules wll flow nto the cell through the pores. If PEFs are contnuously across the cell membrane, they wll cause water nflux. When the repettve rate and pulse wdth are large enough, the cell membrane wll be ruptured and cytoplasm wll flow outsde the cell. Fnally, the cell s destructed. Suspenson Fg.. R S C S R S R S E feld Cell R C C m C n C n C m R n R C R C Intracelluar Membrane Outer Membrane E feld Nucleus R S C S R S Equvalent model of a cell nsdesuspenson. Intal State EF Exctaton Water Influx Membrane Rupture Legend: Electrc Feld Water Cytoplasm Fg.. Illustraton of electroporaton processng of a cell. R S Cell Destructon In PEF applcaton wth wde pulses, electrc ntensty vares from ten to tens of kv/cm, pulse wdth ranges from several to hundreds of μs and repettve rate changes from 0. Hz to 00 Hz. To realze the above specfcatons, many PEF generators (PEFGs) adopt a hgh voltage generator (HVG) combned wth swtch sets wth hgh voltage ratngs (SSHVR) to generate pulse voltage waveforms, as shown n Fg. 3. Snce HVG must generate an extremely hgh output voltage ( 0 kv), t needs a converter wth a hgh step-up voltage rato. Moreover, the one wth hgh powerng capablty s also requred to acheve effectveness of lqud food sterlzaton. As mentoned above, a full-brdge converter assocated wth a transformer wth hgh turns rato s adopted, []-[3], as shown n Fg. 4(a). Due to transformer wth hgh turns rato, a /09/$ IEEE 64

2 large leakage nductance and a large equvalent capactance, whch s reflected from secondary wndng to prmary wndng of transformer, wll be nduced n the prmary wndng. As a result, a large resonant current s generated when swtches are wthn the turn-on transton nterval. To solve ths problem, a resonant crcut s ntroduced nto the full-brde converter [4]-[8], as shown n Fg. 4. Fg. 3. Block dagram of a wde pulse PEF generator for lqud food sterlzaton. Although full-brdge converter wth the resonant crcut can avod generatng a large resonant current, t requres a output nductor to generate dc voltage output, as shown n Fg. 4. When the output nductor s placed on output sde, t wll suffer a hgh voltage stress, resultng n a hgher cost for attanng hgh enough solaton and a larger volume. To resolve ths problem, full-brdge converter wth LLC resonant crcut s adopted. Moreover, the one can help swtches to operate at zero-voltage swtchng (ZVS) and ad secondary rectfer dodes to communcate wth zero-current swtchng (ZCS), as shown n Fg. 4(c). Wth ths crcut structure, the proposed HVG whch adopts LLC resonant crcut can avod a large resonant current, reduce weght, sze and volume, and ncrease converson effcency sgnfcantly. V M M M 3 M 4 C r L r L m (a) (c) Fg. 4. Schematc dagram of full-brdge converter (a) wth hard-swtchng crcut wth resonant crcut, and (c) wth LLC resonant crcut for generatng hgh output voltage. T r :N D 3 D 5 D4 D 6 C O R L I DC V DC II. ANALYSIS OF THE PROPOSED HVG In order to analyss of LLC resonant crcut, a sngle full-brdge converter wth one s shown n Fg. 4(c). Its equvalent crcut can be depcted n Fg. 5. where R ac s the equvalent load resstance of prmary sde n the transformer T r and V ab s appled to the LLC one. Accordng to equvalent crcut of LLC resonant crcut, the equvalent resstance R e(ac) can be determned as 8RL, () Re ( ac) = ( nπ ) where R L s load resstance and n s turns rato of transformer T r. To analyze the LLC resonant topology, the resonant frequency f r of C r and L r n seres s derved by f =. () r π LrCr Smlarly, the resonant frequency f r of C r and (L r + L m ) n seres s expressed as follows:. (3) f r = π ( L r + L m ) C r Addtonally, accordng to the Fourer theorem, the square wave, whch s appled to LLC resonant crcut, can be approxmated by the fundamental component V ab, and ts maxmum value V ab(max) can be derved by 4 V ab (max) = V, (4) π where V s nput voltage of full-brdge converter. Therefore, rms value of V ab can be determned as V ab V π ( rms ) =. (5) Accordng to analyss of LLC resonant crcut shown n Fg. 4(c), nput to output transfer rato M of full-brdge converter s derved by V M = nv DC slr + sc ( slm // Re( ac) ) + ( sl // R ) r m e( ac). (6) From (6), t can be seen that when the proposed converter s operated at dfferent loads, ts transfer rato M wll be vared. In order to attan a constant transfer rato M for generatng constant voltage output, the proposed one must regulate swtchng frequency. Thus, transfer rato M can be rewrtten as, (7) VDC M = nv L r LrCr ω s π ωs ωr + Q L m ω ωr 8 s ωr ωs where ω s (=πf s ) s the angular frequency of swtchng frequency f s, ω r (=πf r ) s that of frequency f r, ω r (=πf r ) s that of frequency f r and Q s qualty factor. In (7), qualty factor Q can be expressed by Q n r =. (8) R Lr C L /09/$ IEEE 64

3 When rato α (=L m / L r ) and frequency gan γ (=f s / f r ) are defned, transfer rato M can be further rewrtten as VDC M = nv + α αγ 4 π + Q 64 γ γ. (9) Accordng to (7), the DC characterstc of the LLC resonant converter can be llustrated n Fg. 6. From Fg. 6, t can be observed that operatonal regons of LLC resonant crcut can be dvded nto three regons: regon I, regon II and regon III. Accordng to dfferent operaton regon, the proposed converter has dfferent operatonal features. In the followng, features of each operatonal regon are brefly descrbed. Fg. 5. Equvalent crcut of LLC resonant crcut. Fg. 6. Plots of characterstc of the LLC resonant converter. A. Regon I (f s < f r ) When f s < f r, operatonal regon of LLC resonant converter s on the rght hand sde of frequency f r, operatonal prncple of the proposed converter s smlar to tradtonal seres resonant converter. Therefore, t can reach ZVS feature. In ths operatonal regon, resonant components L r and C r act as seres resonant, whle L m s clamped by output voltage and does not partcpate n the resonant process. As a result, output dodes can not be operated wth ZCS, resultng n voltage spke across output dodes. B. Regon II (f r < f s < f r ) When f r < f s < f r, operatonal regon of the proposed one s on between frequency f r and f r. The converter can be operated at a hgher gan and wth ZVS feature. Addtonally, the proposed one can operated n two dfferent resonant perods. When swtches are communcated, resonant nductor L r and capactor C r wll start to resonate. The resonant perod enters the frst resonant perod. Wthn ths tme perod, nductor L m s clamped to output voltage and s lnearly ncreased. When resonant current Lr s equal to current Lm, the second resonant wll occur, whch s the resonant between C r and L m n seres wth L r. Ths resonant perod wll last tll the prmary swtches have been turned on agan. Durng the second resonant tme perod, the current of secondary sde n transformer remans zero. As a result, secondary output dodes are operated wth ZCS. C. Regon III (f s < f r ) When f s < f r, operatonal regon of the proposed one s on the left hand sde of f r. The proposed converter s operated wth ZCS. It s not sutable for power MOSFET applcatons. As mentoned above, the proposed converter s desgned n regon II to ncrease converson effcency. III. OPERATIONAL PRINCIPLE OF THE PROPOSED PVG In the lqud food sterlzaton system, the PEFG shown n Fg. 7 conssts of two crcuts: a hgh voltage generator (HVG) and a swtch set wth hgh voltage ratngs (SSHVR). They can process power from nput voltage V ac to treatment chamber (TC) for sterlzng mcrobes. The HVG adopts two full-brdge converters connected n parallel to generate a hgh dc-lnk voltage V DC, and ts soft-swtchng features whch nclude ZVS n swtches and ZVS n output dodes are acheved wth LLC resonant technology. The SSHVR s composed of four sets of hgh-voltage swtch, n whch each of the hgh-voltage swtches s formed wth 5 MOSFETs n seres, to chop a DC voltage to pulse voltage. Fg. 4(c) shows schematc dagram of sngle full-brdge converter wth LLC resonant crcut. Accordng to operatonal prncple of the proposed one, ts operatonal modes can be dvded nto 6 modes over one swtchng cycle, as shown n Fg. 8, whle ts key waveforms are shown n Fg. 9. In the followng, each operatonal mode s descrbed brefly. Fg. 7. Schematc dagram of a complete PEF generator /09/$ IEEE 643

4 (a) Fg. 9. Key waveforms of full-brdge converter wth LLC resonant crcut over one swtchng cycle. V M M 3 I DS3 D M CM D M3 CM3 M D MC M I DS C r r M 4 D M4C M4 L r m L m (c) (d) (e) (f) Fg. 8. Equvalent crcut of full-brdge converter wth LLC resonant crcut operated n regon II for each operatonal mode over one swtchng cycle. T r :N D D 3 D D 4 I D I C C O I DC R L V DC Mode [Fg. 8(a); t 0 t < t 0 ]: Before t 0, swtches M and M 3 are n the on state, whle M and M 4 are n the off state. Wthn ths tme nterval, magnetzng nductor L m, leakage nductor L r and capactor C r form a resonant network and they are n the resonant state. In addton, output dodes D ~ D 4 are n reversely bas, and the energy stored n output capactor C O s suppled to load R L. When t = t 0, swtches M and M 3 are turned off. Resonant nductor L r, capactor C r and parastc capactors C M ~ C M4 connect n seres and they wll start to resonate. Wthn ths tme nterval, snce resonant current Lr s greater than Lm, current of secondary sde of transformer s not equal to zero. Therefore, dodes D and D 4 are forced to forwardly conduct. As a result, magnetzng nductor of secondary sde s clamped to output voltage V DC. The current Lm of prmary sde lnearly ncreases. Addtonally, resonant current Lr ncreases wth the resonant mode. Snce resonant current Lr ncreases, voltages across body dodes C M and C M4 are released from V to 0. Those across C M and C M3 are charged from 0 to V. Mode [Fg. 8; t t < t ]: At t, snce energes stored n C M and C M4 are dscharged to 0, body dodes D M and D M4 are n forwardly bas. At the moment, swtches M and M 4 are turned on. They are operated wth ZVS at turn-on transton. Moreover, resonant nductor L r and capactor C r form a resonant network and they wll start to resonate. Therefore, resonant current Lr ncreases wth the resonant manner. Wthn ths tme nterval, dodes D and D 4 stll keep n the forwardly bas state. Thus, current Lm also ncreases wth the lnear manner. Addtonally, energes are transferred from nput voltage V to load through transformer and dodes D and D 4. Mode 3 [Fg. 8(c); t t < t 3 ]: When t = t, resonant current Lr s equal to current Lm. At the moment, current of secondary sde n transformer decreases to 0. As a result, dodes D and D 4 are reversely based. Resonant nductor L r, magnetzng nductor L m and capactor C r form a resonant network and they wll begn to resonate. Durng ths tme nterval, currents Lr and Lm decrease wth the resonant manner. Addtonally, energy stored n output capactor C O supples power to load /09/$ IEEE 644

5 Mode 4 [Fg. 8(d); t 3 t < t 4 ]: When t = t 3, swtches M and M 4 are turned off. Resonant nductor L r, capactor C r and parastc capactors C M ~ C M4 form a resonant network and they wll start to resonate. Snce resonant current Lr s greater than Lm, current of secondary sde s not equal to 0. As a result, dodes D and D 3 are n forwardly bas and secondary wndng s clamped to output voltage V DC. Therefore, current Lm lnearly decreases. Moreover, resonant current Lr ncreases wth the resonant mode. Snce resonant current Lr ncreases, voltages across C M and C M3 are dscharged from V to 0, whle those across C M and C M4 are charged from 0 to V. Mode 5 [Fg. 8(e); t 4 t < t 5 ]: When t = t 4, voltages across C M and C M3 are clamped to 0 and body dodes D M and D M3 are n forwardly bas. At the same tme, swtches M and M 3 are turned on. Thus, swtches M and M 3 are operated wth ZVS at turn-on transton. In addton, resonant nductor L r and capactor C r form a resonant network and they wll start to resonate. Therefore, resonant current Lr ncreases wth the resonant manner. Durng ths tme nterval, dodes D and D 3 are stll n forwardly bas. Thus, current Lm lnearly ncreases. Moreover, energes are transferred from nput voltage V to load through transformer and dodes D and D 3. Mode 6 [Fg. 7(f); t 5 t < t 6 ]: At t 5, resonant current Lr s equal to current Lm. As a result, current of secondary sde decreases to 0 and dodes D and D 3 are reversely based. Therefore, D and D 3 can reach ZCS feature. Wthn ths tme nterval, resonant nductor L r, magnetzng nductor L m and capactor C r form a resonant network and they wll keep n the resonant state. Therefore, currents Lr and Lm decrease wth the resonant manner. Addtonally, energy stored n output capactor C o supples power to load. When t = t 6, swtches M and M 3 are turned off. Operatonal modes of one swtchng cycle are complete. IV. EXPERIMENTAL RESULTS To verfy the analyss and feasblty, a prototype of the proposed HVG was mplemented wth the followng specfcatons. nput voltage: AC 0 V (wth voltage double); swtchng frequency f S : 30 khz ~ 50 khz, output voltage V DC : 0 kv, output current I DC : 0. A, and output power P O : kw. To consder hgh step-up ratos and solaton requrement, the proposed HVG adopts two sets of full-brdge converter and two sets of transformer to generate output voltage of 0 kv, as shown n Fg. 5.That s, each transformer wll boost up a 5 kv dc-lnk voltage. Addtonally, the components of the proposed HVG are determned as follows: swtches M ~ M 4 : IRFP 460, turns rato of transformer T r, T r : 0, magnetzng nductance L m or L m : 3 mh, resonant nductance (nclude leakage nductance) L r or L r : mh, resonant capactor C r or C r : 5 nf, and doded ~ D 4 : UF 00 (7 dodes connected n seres). The measured waveforms of voltage V DS and I DS of swtch M show n Fg. 0 when full-brdge converter wth the conventonal phase-shft control method s adopted. From Fg. 0, t can be seen that hgh spke current occurs due to the hgh equvalent capactance appearng at the prmary sde of the transformers, and there s no ZVS feature. Fgs., show the measured voltage V DS and current I DS of swtches M and M when the proposed HVG s respectvely operated at 0 % and 50 % of full load. From Fgs.,, t can be observed that swtches M and M can be operated wth ZVS at turn-on transton. Measured voltage V D and current I D waveforms of output dode s llustrated n Fg. 3, from whch t can be seen that output dode can reach ZCS feature. Fg. 4 shows effcency measurements of the proposed HVG, from whch t can be seen that the maxmum effcency can reach as hgh as 93 % at 90 % of full load, and around 9 % under full load. The output voltage V DC and current I DC s shown n Fg. 5, llustratng that output voltage rpple s very low wthn %. As mentoned above, the proposed HVG s relatvely feasble n hgh output voltage applcatons, whch has been verfed by the expermental results. (V DS : 00 V/dv, I DS : 5A/dv, 5 μs/dv) Fg. 0. Measured voltage V DS and current I DS waveforms of swtch n full-brdge converter wth phase-shft control method. (V DS : 00 V/dv, I DS : A/dv, 5 μs/dv) (a) (V DS : 00 V/dv, I DS : A/dv, 5 μs/dv) Fg.. Measured voltage V DS and current I DS waveforms of swtches (a) M and M n the proposed HVG under 0% of full load /09/$ IEEE 645

6 V DS I DS (V DS : 00 V/dv, I DS : A/dv, 5 μs/dv) (a) V DS I DS (V DS : 00 V/dv, I DS : A/dv, 5 μs/dv) Fg.. Measured voltage V DS and current I DS waveforms of swtches (a) M and M n the proposed HVG under 50% of full load. (V DS : k V/dv, I DS : 00 ma/dv, 0 μs/dv) Fg. 3. Measured voltage V D and current I D waveforms of output dode. Effcency(% ) % 0% 30% 40% 50% 60% 70% 80% 90% 00% LLC resonant crcut Load (% ) Hand-swtchng crcut Fg. 4. Comparson of converter effcency between full-brdge converter wth hard-swtchng crcut and wth the proposed LLC resonant crcut. (V o : 5 kv/dv, I o : 00 ma/dv, 5μs/dv) Fg. 5. Measured output voltage V DC and output current I DC under full load condton. V. CONCLUSIONS Ths paper has proposed a full-brdge converter wth LLC resonant crcut to form a hgh voltage generator. The proposed HVG can use resonant technology and transformer wth hgh turns rato to reach a hgh step-up voltage rato. By adoptng the LLC resonant crcut, energy trapped n the leakage nductor can be recovered, ZVS features can be acheved and current spke can be suppressed effectvely. In the paper, analyss of the generator has been presented n detal, from whch desgn equatons and crcut parameters are derved. Expermental results have verfed that the proposed HVG can acheve hgh effcency over a wde load range. It s relatvely sutable for PEFG applcatons. REFERENCE [] X. Qu, L. Tuhela and H. Zhang, Applcaton of Pulsed Power Technology n Nonthermal Food Processng and System Optmzaton, Proceedngs of Pulsed Power Conf., 997, pp [] J. E. dunn and J. S. Pearlman, Methods and Apparatus of Extendng the Shelf Lfe of Flud Food Products, US patent 4,695,47, 987. [3] U.-R. Pothakamury, et al., Effect of Growth Stage and Processng Temp. on the Inactvaton of E. Col by PEF, Journal. Food Protect. Vol. 59, 996, pp [4] Ja, M., Zhang, Q. H. and Mn, D. B., Pulsed electrc feld processng effects on flavor compounds and mcroorgansms of orange juce, Food Chemstry 65, 999, pp [5] Lado, B. H., et al., Alternatve food-preservaton technologes effcacy and mechansms, Mcrobesand Infecton 4, 00, pp [6] H. S. Karl, et al., Boelectrcs-New Applcatons for Pulsed Power Technology, IEEE Transactons on Plasma scence, Vol.30, No., 00. [7] R. Redl, N. O. Sokal, L Balogh, A Novel Soft swtchng Full Brdge DC/DC Converter: Analyss, Desgn consderatons, and Expermental Result at,5 kw, 00 khz, IEEE PESC `90, 990, pp.6-7. [8] S. J. Beebe, et al., Nanosecond pulsed electrc feld (nspef) applcaton effects on human cells: ntracellular membrane dsrupton and apoptoss nducton, IEEE Transactons on Pulsed Power Plasma Scence, 00, pp.5 [9] T. S. Zheng and R. A. Flavell, Apoptoss: All s Well that Ends Dead, Nature, Vol. 400, 999, pp [0] Danel A. Crowl and Joseph F. Louvar, 990; Chemcal Process Safety : Fundamentals wth Applcatons, ISBN , Prentce-Hall Inc., Englewood Clffs, New Jersey, USA. [] J, Z., Kennedy, S. M., Booske, J. H., Hagness, S. C., Expermental Studes of Persstent Poraton Dynamcs of Cell Membranes Induced by Electrc Pulses, IEEE Trans. On Plasma Scence, vol. 34, Issue 4, Aug. 006, pp [] Zhang, R., Cheng, L., Wang, L., Guan, Z., Inactvaton Effects of PEF on Horseradsh Peroxdase (HRP) and Pectnesterase (PE), IEEE Trans. On Plasma Scence, vol. 34, Issue 6, Aug. 006, pp [3] Mn, S., Evrendlek, G. A., Zhang, H. Q., Pulsed Electrc Felds: Processng System, Mcrobal and Enzyme Inhbton, and Shelf Lfe Extenson of Foods, IEEE Trans. On Plasma Scence, vol. 35, Issue, Feb. 007, pp [4] L. Zhu, A Novel Soft-Commutatng Isolated Boost Full-Brdge ZVS-PWM DC DC Converter for Bdrectonal Hgh Power Applcatons, IEEE Trans on Power Electroncs,vol., Issue, 006, pp [5] Y. Zhongmng, J.C.W. Lam, P.K. Jan and P.C. Sen, A Robust One-Cycle Controlled Full-Brdge Seres-Parallel Resonant Inverter for a Hgh-Frequency AC (HFAC) Dstrbuton System, IEEE Trans. on Power Electroncs, vol., Issue 6, 007, pp [6] C. Cavallaro, et al. A Phase-Shft Full Brdge Converter for the Energy Management of Electrolyzer Systems, IEEE Trans. on Internatonal Symposum,007, pp [7] Y. Zhongmng, P.K. Jan and P.C.Sen, A Full-Brdge Resonant Inverter Wth Modfed Phase-Shft Modulaton for Hgh-Frequency AC Power Dstrbuton Systems, IEEE Trans. on Industral Electroncs, vol. 54, Issue 5, 007, pp [8] W. Chen, X. Ruan, and R. Zhang A Novel Zero-Voltage-Swtchng PWM Full Brdge Converter, IEEE Trans. on Power Electroncs, vol. 3, Issue, 008, pp /09/$ IEEE 646