A HIGH PERFORMANCE 50 KW THREE-PHASE PFC POWER SUPPLY FOR USE WITH A DC ARC PLASMA TORCH

Transcription

1 A HIGH PEFOMANCE 5 KW THEE-PHASE PFC POWE SUPPLY FO USE WITH A DC AC PLASMA TOCH Jean-Paul Dubut, Alexandre Magnu Fernande Guimarãe, André Ortiz Salazar*, André Laurindo Maitelli*, Clodomiro Alve Júnior** Intituto Nacional de Pequia Eaciai - INPE Centro egional de Natal e Fortaleza - CN Av. Salgado Filho, nº 3 Caixa Potal Natal N Brazil Phone: Fax: jean@crn.ine.br, alexandre@crn.ine.br Univeridade Federal do io Grande do Norte - UFN DEE/DCA*/DFTE** Camu Univeritário, /nº Natal N Brazil Phone: Fax: andre@dca.ufrn.br, maitelli@dca.ufrn.br, alvejr@dfte.ufrn.br Abtract - Thi aer decribe the concet, the roject and the ractical contruction of a 5 kw three-hae boot PFC ower uly for ulying a non-tranferred DC arc lama torch ued in a wate treatment lant. Thi PFC ower uly i endowed of three indeendent circuit for ower factor correction to attemt the ower factor and current harmonic level IEC tandard. The PFC reregulator tage ue the average current-mode control imlemented by a PWM control cheme. The ower tage i built on an indutrial IGBT three-hae bridge rectifier module configured in a boot rectifier toology that ulie the 8 DC outut voltage. ZCT oft witching technique were imlemented to minimize the rectifier tructure commutation loe. A dedicated microcontroller unit execute the uerviion, the tak management, the running equence and the main rogramming arameter a well a the rotection function of the aociated ubytem. Uing an external microcomuter, a S-232 erial inut allow the remote rogramming of the PFC ower uly, the lama torch and reactor uerviory, and the overall indutrial roce control. Simulation in PSice were imlemented to aid the definition of the boot rectifier toology and redict the reult. All exerimental tet were realized over a 5 kw rogrammable reitive load. Thi aer highlight the PWM boot rectifier, the PFC reregulator and the comenator loo circuit deign. KEYWODS Power factor correction, three-hae boot rectifier, ZCT oft witching, PWM ower uly, lama torch. I. INTODUCTION In order to have thi work context well ituated and to undertand the rooed develoment imortance of thi roject, it i neceary to remind the recent exigencie imoed by the environmental legilation, national agencie of regulation (CONAM, ANISA, etc.) and other federal, tate and municial inection org demanding the indutrial and medical ector to rovide the adequate treatment and an aroriate detination for the roduced wate. Due to the roceing, torage and dicard high cot roduced by the new environmental exigencie, it i imortant to coniderate the aggregated value to the wate. The non-organic comonent can be recycled or vitrified, and the organic art can be diociated in order to generate ynthei gae, thermal and/or electrical energy in co-generation cheme. The wate treatment lant, exerimentally oerated by the DFTE/UFN deartment, eek to demontrate the otential of lama technology [] and it new alication field, eecially to the hoital and radioactive wate treatment. The decribed three-hae PFC ower uly i detined to have an equied exerimental wate treatment lant uing the thermal lama technique to detroy indutrial wate. A three-hae PFC ower uly, a non-tranferred DC arc lama torch, a roce reactor and it aociated auxiliary ytem eentially contitute the main element lant. Thi roject intend to offer a ignificant contribution to the reearch line on electrical ower converion ytem, held by the automation and control ytem area of the UFN-PPgEE. Alo, it rereent an effort to attemt the univerity-indutry integration rogram [2], by offering effective local olution for the indutrial ark demand. The figure reent the illutrative diagram of the exerimental wate treatment lant, the three-hae PFC ower uly and it everal aociated eriheral ytem. Command and control bu Ga flux control Water flux control 8 DC Ga Preure regulator 5kW Water Feeder lama um Proce S 232 5kW torch Plama Torch PC micro ower reactor Plama refriger. comuter uly Wate N 2 Ar ytem flame 38 AC Slag itreou lag Fig. - Illutrative diagram of the wate treatment lant and the aociated PFC ower uly The PFC ower uly ecification wa done for ulying a 5kW DC arc lama torch leading a.5m 3 internal volume reactor uing a yrolyi roce. The roject attemt to the IEC and IEC tandard for a current harmonic level rejection in the utility line. The emhai given to the article i willfully decritive in order to facilitate the general undertanding of the lama wate treatment ytem and the uroe of it aociated PFC ower uly.

2 II. POJECT DESCIPTION For the roject ecification of the PFC ower uly and it aociated ubytem [3], the following item were conidered a being of major imortance and for thi reaon they were imlemented in the ytem: a) To rovide the galvanic iolation between the utility line and the DC outut PFC ower uly for eliminating any voltage leakage oibilitie, feedback current and oerator electrocution rik during the lant oeration; b) To aure the automatic and continuou adjutment of the ower factor near the unity and to maintain the harmonic current level and uriou under the limit imoed by the IEC 6 tandard; c) To aure the control and adjutment of the PFC ower uly arameter in the tandalone mode; d) To include an automatic rotection and alarm to rotect the PFC ower uly, the DC arc lama torch, the cooling um, the lama reactor, the flow ga regulator and any aociated equiment, ignaling to the oerator; e) To detect and automatically ure the DC arc dicharge between the lama torch electrode, lama reactor body and metallic wate under treatment; f) To remotely rogram and control the electrical arameter of the PFC ower uly by an auxiliary roce PC microcomuter through the S-232 erial communication ort; g) To reent good functional modularity of the unit in order to allow eay in itu maintenance, a well a to ermit the ytem evolution in the future. The figure 2 reent the imlified PFC ower uly block diagram and it aociated ubytem. 38 AC Boot inductor Phae current amle oltage reference Command & Prot. circuit Keyad & Dilay C boot cell Current & oltage ref. roceing B boot cell Otical fiber Microcontroller A boot cell PWM equencer & Interface DC filter & Temo. Command to IGBT driver 8 DC Meaurem. & oltage comen. S232 (To roce PC treatment) Fig. 2 Simlified block diagram of the three-hae PFC ower uly and aociated ubytem To attemt the electrical ecification and general requet, the ix-ule PWM boot rectifier toology [4] wa choen a being the mot aroriate configuration for thi alication. A 75kW external tranformer rovide the galvanic iolation between the lant utility line and the three-hae PFC ower uly outut connected to the DC arc lama torch. The rimary welding of thi three-hae iolation tranformer i connected in a cheme and the econdary welding in a Υ cheme. The adoted /Υ configuration ermit the free circulation of the third harmonic due to the magnetizing current in the rimary hae and generate a neutral reference for the auxiliary circuit [5]. The rimaryto-econdary winding ratio i made :,58. The utility lineto-line nominal voltage at the tranformer rimary inut i 38 AC and the hae-to-hae nominal voltage at the tranformer econdary i 38 AC. The econdary voltage i alied to the inut PWM boot rectifier. A SEMIKON SFM84-5/4 three-hae low-a filter i inerted between the econdary winding of the iolation tranformer and the PWM boot rectifier inut in order to reduce harmonic current injection and uriou roduced by the 2kHz rectifier IGBT witching. Three LEM LA-5S magneto-reitive enor meaure the PWM boot rectifier three-hae current. Thee current amle are ued for the ower factor correction of the PFC ower uly after they have been rectified, amlified and roceed. Additionally, they are alo ued for the PWM boot rectifier over-current rotection. Two 3A SEMIKON SMT3/ auxiliary mall tranformer, connected between hae and neutral oint, generate the current reference for hae A and B. In order to guarantee the total current equilibrium condition I A I B I C, the hae C current reference i generated by the vectorial um of the hae A and B. Thi i obtained by mean of an electronic adder and rereent the neceary condition for an indeendent hae ower factor correction. Three mh boot inductor are contructed on ironiliceou laminated C core reenting a magnetic area core of 35cm 2. The coil i ditributed on two leg of the core in order to minimize the magnetic dierion and ue aired wiring winding. Each inductor reent a two-3mm air ga. The boot inductor tore a 2J energy and weight about 2kg. The main boot rectifier i built on a SEMIKON SKM45GB23D [6] IGBT three-hae bridge rectifier module including an internal anti-arallel diode. Thee device offer a 5A/2 commutation current caability and they are mounted on an extruded aluminum heat ink with air forced cooling. The ZCT oft witching auxiliary circuit i built on a SEMIKON SKM75GB23D IGBT three-hae bridge module including an internal anti-arallel diode. Thee device offer a 75A/2 commutation current caability and they are alo mounted on a main extruded aluminum heat ink. Three LC reonant tank are connected between each arm of the main rectifier and auxiliary ZCT leg, working a a nubber. The reonant tank i deigned to make the eak reonant current I k exceed the intantaneou maximal boot inductor current [7] in order to achieve ZCT oeration. A good comromie deign i obtained to fix I k current about.25 time of the maximal witching hae current and the reonant eriod i choen a 4µ to guarantee afe oeration. A 4µH L na inductor and.5µf C na caacitor contitute each reonant tank circuit leg. Six SEMIKON SKH22H4 dual-driver module drive the main and auxiliary IGBT device. Thee module alo rovide the electrical interface between the PWM command unit and the IGBT three-hae bridge. Each dual-driver module incororate the over-voltage and over-current rotection circuit to rotect it IGBT air. The PWM three-hae rectifier ermit the outut voltage adjutment from 7 DC to 9 DC under any load condition. It offer ufficient regulation margin to comly a ±5% utility line voltage variation.

3 The figure 3 reent the imlified electrical diagram of the PWM boot rectifier tructure. a b c N Line harmonic filter 3 x Lf 3 x Cf La Lb Lc S S2 D D2 Sa Laa Caa S2a Da D2a Fig. 3 Simlified electrical diagram of the PWM boot rectifier In order to imlify the IGBT PWM command, the imlemented trategy control doe not ermit the energy revere flux from the load to the ource. Thi condition wa aumed becaue the PFC ower uly doe not oerate with regenerative load. The PWM generator unit i built on three UNITODE UC3854B dedicated PFC reregulator device [8]. Thee integrated circuit, uing an aociated logic, generate the comlementary PWM ignal to command the IGBT main witche, the comlementary ignal to command the IGBT ZCT auxiliary witche and imlement the control trategy. Each hae current i yntheized from a reference generated by the correonding hae. The control loo command the PWM that force the line current in hae with the line voltage, with a dilacement factor near to zero. In thi way, the harmonic generation i minimized and it i oible to uit the ower factor near the unity. Additionally, the UNITODE UC3854B imlement the current and voltage rotection function, duty-cycle limiting or diabling the IGBT PWM ule. A 4N25 otocouler and it aociated circuit are ued to amling and interfacing the outut PWM rectifier to the comenator in order to maintain the outut voltage to the adjuted level. The comenator range i enough to maintain table the outut voltage in deite of the utility line and load variation. The outut DC voltage of the boot rectifier i filtered and tored by a double bank of three 47µF/45 DC electrolytic caacitor connected to a erial cheme. Thi caacitor bank wa dimenioned in order to maintain the rile voltage at the % ecified value under any load condition. At the PFC ower uly tarting the high current charge of the electrolytic caacitor bank i limited by a 2.2Ω/5W erial ower reitor. After ome econd, a temorized contactor hort-circuit thi reitor and the total rectified voltage i alied to the caacitor bank. The microcontroller unit, baed on a FEEDOM 6 commercial board manufactured by INTEC AUTOMATION INC, erform the PFC ower uly command and uerviion. Thi O&M board ue a MOTOOLA 68HC6Z microroceor and offer ome bit A/D inut ort, 2 bit D/A outut ort, two PWM outut ort, ome bi-directional I/O ort, keyad interface and a two line 64 character LCD outut. Alo, it offer both S-232 and S- 485 I/O erial ort. The microcontroller unit i rogrammed in micro C language and rovide a debug comilation ort. Thi unit allow to et the PFC ower uly oerating S3 S4 D3 Lba D4 S3a Cba S4a D3a D4a S5 S6 D5 D6 S5a Lca Cca A cell B cell C cell S6a D5a C D6a T O C H - arameter uch a outut voltage and outut current alied to the DC arc lama torch. In tandalone mode, the arameter rogramming i erformed by it aociated keyad and the aumed value are dilayed on a LCD. In the remote mode, the arameter rogramming i realized by mean of a S-232 erial ort under control of the roce PC microcomuter. Additionally, the microcontroller unit activate the alarm and ignalize to the lant oerator, from the rogrammed limit value. The command and rotection unit imlement the running equence, the low tarting and the general rotection of the PFC ower uly. Several electromechanical contactor commanded by a logical circuit board eentially contitute thi unit. A diazed fue et rotect the utility line inut and comlement the rotection of the PFC ower uly. III. POWE FACTO COECTION PEEGULATO TOPOLOGY The boot rectifier oerate in the continuou mode conduction and an indeendent ower factor correction wa imlemented, one for each hae, acting in a current mode control. In a way to imlify the neceary function, UNITODE UC3854B [9] integrated circuit were ued, one for each hae of the rectifier tructure. The figure 4 reent the imlified block diagram of the UC3854B PFC reregulator circuit [] ued in each hae of the PWM boot rectifier. CC.5/ ENA 2.65/2.5 3 SENSE IAC MS 6 8 SS 3 4µA X 2 A Mult. CA PK Out Out Out LMT EF A I A.B B C C 4 UN OSCILAT. ISENSE CT SET 7.5 EF. UN S Q IC POWE Fig. 4 - Simlified block diagram of the UC3854B PFC reregulator circuit Thee device incororate the analog multilier, the voltage reference, the current and voltage comarator, the PWM ocillator and ome amlifier to generate and control the PWM ignal. The PWM ignal to command the IGBT witche i generated at the fixed 2kHz nominal frequency and the three device are ynchronized for minimizing the harmonic beat between the hae. Thee ignal are addreed to the IGBT driver module by mean of an aociated logic that imlement the PWM boot rectifier command trategy. The equential command of the boot rectifier element witching defined by a inuoidal modulation law force the hae current enveloe to be in hae with the inut hae voltage reference, reenting a null dilacement. By a ermanent comarion between the current hae amle and the current reference, it i oible to yntheize the hae current at the boot rectifier inut, reducing the harmonic and, for thi way, reulting in a high ower factor near the unity CC GT 6 Drv Gnd

4 A mentioned in the reviou aragrah, the C hae current i yntheized to the virtual reference generated by the vectorial um of hae A and B reference. Thi artifice i ued to guarantee the equilibrium condition for the inut hae current in the PWM boot rectifier. I. PWM BOOST ECTIFIE, ZCT CICUIT AND COMPENSATOS POJECT The PWM rectifier ower tage to be controlled i comoed by three indeendent boot tructure a hown in figure 3. The ued method for the roject ytem ecifie a mall ignal model and each functional block i rereented by it tranference function. The diagram reented in figure 5 illutrate the mall ignal model and the everal ytem tranference function block. EF oltage comenator k v. i B H () k r. 3L I i - i (-2D). A K.I i 3ωLI i Fig. 5 Diagram of the PFC rectifier mall ignal model 4. Power tage deign: The tranference characteritic [] between the inut voltage, i, alied on each boot circuit and the outut voltage,, i defined by the equation: 2 i ( 2 Dn) () The reviou equation () can be rewritten in term of the effective conduction time, t c, related to eriod witching T. Then: i tc T (2) 2 If conidered the hae A, the voltage alied to inductor i equal to i and defined by: in( ) L I i θ (3) t The maximum inductor voltage L occur for θ 9. Therefore, it i neceary to determine when the maximum t occur, reulting in a maximum current rile [2]. Due to inewave ymmetry it i ufficient to analyze the interval between to 9º. Alying the hae voltage equation and after ome mathematical maniulation: - For the interval between and 3, where B < A < C : θ i L [ in( θ 2 ) in( θ 24 )] n in( ) (4) Where L n can be called the normalized inductance and i defined by: Ln L I (5) T i - For the interval between 3 and 9, where B < C < A : θ i L [ in( θ 2 ) in( θ) ] n in( ) (6) I EF H C() Current comenator (-2D).I i Since the rile voltage in hae A i maximum at 9, then: i.5 i L (7) I f The maximum value of the inut current i determined in function of the outut ower, rectifier efficiency, inut voltage and number of the boot circuit arm that uly ower to the load. P I MS (8) 3 η MS The maximum current at 6Hz comonent that will flow through the inductor i given by: I k I MS 2 (9) A good comromie between the current rile and the eak current i to allow % rile to average ratio. Then: I L. I k () The value of the outut caacitor effect both hold-u time and outut voltage rile. Chooing the rile criteria, where %, the following equation will give a value for C : r. () C P 2 π 36 (2) The ZCT L na and C na reonant element value for the choen T eriod are defined a: T 2 π L (3) na Cna L na Z (4) Cna I k (5) Z 4.2 Control loo deign In order to imlify the control loo deign it i ued the mall ignal model PFC boot converter. All functional block needed to imlement the PFC boot rectifier function a the PWM modulator, the comarator, the multilier, the current and voltage comenator are rovided by the UNITODE UC3854B integrated circuit Current loo deign: Thi deign ue the average current mode control loo. A LEM LA5S magneto-reitive enor furnihe the meaured inut hae current amle. For deign imlification, it i coniderate the virtual voltage, SH, roduced on the equivalent reitance SH ; the comarator outut voltage, CEA, and the aw ocillator outut voltage,. Then, a tranfer function may be exreed in term of the comarator outut voltage and the ocillator outut voltage. Thu: SH SH GC() (6) CEA L The deign of the average current mode control loo begin with chooing a croover frequency. The witching frequency, f, of the PWM boot rectifier i 2kHz choen and the comenator loo dimenioning hould take into account the amling effect of the tranfer function rereented by the equation:

5 2 HS() 2 f f (7) π The current comenator bandwidth mut be ufficiently large in order to guarantee that the hae current follow the reference ignal. A the current reference i a rectified inuoidal, it i oberved that after the 5 th harmonic being 9Hz, the uerior order comonent do not offer ignificant contribution and they caue a mall degradation in the ower factor. On the other hand, the current comenator criteria deign uggeted by UNITODE are the following: a) To locate the zero comenator at leat one decade of the witching frequency f in order to obtain a fat reone and good tracking of the reference current ignal; b) To locate the ole comenator not more than half of the witching frequency f in order to reduce the rile at the frequency witching; c) To define the current comenator gain in the flat bandwidth at leat db in order to obtain a ecure margin hae; d) To define the oen loo frequency tranfer function croing about ¼ of the witching frequency. In thi ecific deign, the croover frequency, f c, wa fixed to 7.5kHz. The tranfer function for the UNITODE UC3854B current comenator i rereented by: ( Cz z) H c() (8) Cz C i( Cz C) z Cz C In thi way, the tranfer function of the oen loo current TFOL c i rereented by: TFOLc() G() Hc() HS() (9) Subtituting the tranfer function term in the reviou equation (9), then: SH TFOL c() L Cz z (2) Cz C i( Cz C) z Cz C 2 2 f π f After ome mathematical maniulation uing Matlab and regarding to the etablihed criteria, then: a) Comenator loo gain: z H C (2) GC SH i L b) Zero frequency comenator loo: fz f (22) 2 π z Cz c) Pole frequency comenator loo: Cz C f f (23) 2 2 π z Cz C oltage loo deign For deign the voltage loo it i neceary to determine the amount of rile on the outut voltage. In order to meet the 5% THD IEC 6 tandard ecification, the ditortion due to outut rile voltage feeding through the voltage error amlifier mut be limited to %. Thi allow,5% ditortion from the multilier and ome ditortion originated from other ource. To obtain a low ditortion THD and a high ower factor it i neceary that the inut hae current track the reference voltage amle and the outut voltage variation. The voltage loo deign however will be attemt two antagonit criteria. At firt, the bandwidth mut be ufficiently large in order to reent a good reone for the tranient. In econd lace, to reent a low loo voltage reone in order to no modulate the reference ignal through the rile voltage. A low-a filter meet a comromie with a bandwidth fixed at ¼ of the rile frequency. The ower tage gain G () of the converter can be exreed in term of P IN,, C and EA. It i given by: G() P 3 EA C (24) The voltage comenator tranfer function i reented by the equation: EA H () (25) i ( C ) By the derivate and extract term, thu EF i C (26) 2 π 36 f P EF c 2 2 π 3 EA C i C (27) 2 π f C (28) c 4.3 Comonent value Some PWM PFC rectifier comonent value are determinate by the reviou related equation. The Table I yntheize the inut arameter and main comonent value. TABLE I PFC rectifier inut arameter and comonent value Inut arameter IN 22 hae to neutral or 38 hae to hae P 5kW 8 DC % f IN 6Hz 62.5Ω ectifier comonent L b mh r Lb.Ω L na 4µH C an.5µf C 3,3µF r C.2Ω f 2kHz Current comenator comonent (f z khz; f 7.5kHz; H() db) z 27kΩ i 4.7kΩ C z.2nf C F oltage comenator comonent (f c 3Hz) kω i kω C 33nF. ESULTS The toology validation of the PFC ower uly wa obtained with aid of the PSice and Matlab imulation. The following figure reent the waveform imulation, a the exerimental reult meaurement in hae A with a high

6 ower dummy load. The reult reented in hae B and C are imilar. The figure 6 reent an amlified view of the voltage and current waveform in hae A around the aage by the zero axi obtained during the PSice imulation circuit. A Current in hae A -A -5 4,8m IA 5 oltage in hae A A 5,8m Fig. 6 Amlified view of the current and voltage waveform in hae A The figure 7 how the dilacement factor waveform between the voltage and current in hae A. 6 25A -25A IA -6 A The figure 8 how the FFT current waveform oberved in hae A with and without the PFC active function. 6Hz 6Hz Fig. 7 - oltage and current waveform in hae A 5 db (a) I A FFT with active PFC (b) I A FFT without PFC I A FFT (log cale) I A FFT (log cale) Fig. 8 - I A current FFT oberved in hae A: (a) with active PFC; (b) without PFC When the PFC i active the current harmonic reduction oberved in hae A i 5dB. Similar reult are oberved in hae B and C, thu the PFC i indeendent in each hae. The global efficiency of the PFC ower uly i nearly 93% at the 5kW nominal ower and the total current harmonic ditortion i inferior to 5%. The ower factor obtained in each hae i,995 and the current harmonic content i quite low. All exerimental tet were realized on a 5kW dummy load contructed for thi alication. I. CONCLUSIONS egarding to obtain reult it i imortant to note that, in deite of it imlicity, the choen PFC boot rectifier tructure uing the average current mode control and the ZCT oft witching imlemented by the auxiliary circuit ha reented good erformance. The utilization of three indeendent ower factor reregulator UNITODE UC3854B integrated circuit imlified the control circuitry, requiring jut an aociated logic to generate the comlementary command for drive the IGBT witche. The PFC ower uly meet the IEC 6 tandard and allow it connection in the utility lant without introducing diturbance. EFEENCES []. Dembovky, Plama metallurgy, Elevier Science Publihing Comany Inc., New York, N Y, USA, 985. [2] C. Alve Júnior, Nitretação em lama ulado: equiamento, rearação e caracterização da camada nitretada, Tee de Doutorado, UFSCar, Florianóoli, SC, Brail, 992. [3] J. P. Dubut, Uma roota de fonte chaveada com correção do fator de otência ara alimentação de um reator de nitretação iônica, Diertação de Metrado, UFN-CT-DEE, Natal, N, Brail, 2. [4]. C. Souza and D. S. Simonetti, Análie de oeração de trê toologia retificadora trifáica com ré-carga de corrente, UFES-DEL-CT, itória, ES, Brail, 997. [5] M. E. Fraer and C. D. Manning, Four-wire ower factor corrected boot rectifier, EPE 95, Sevilla, Sain, 995. [6] SEMIKON, Semikron ower electronic manual, Nürnberg, Deutchland, 998. [7] J. Wu, H. Dai, K. Xing, F. C. Lee and D. Boroyevich, Imlementation of a ZCT oft witching technique in a kw PEBB baed three-hae PFC rectifier, EPEC, Blackburg, USA, 999. [8] Y. Jiang, H. Mao, F. C. Lee and D. Borojevic, Simle high erformance three-hae boot rectifier, EPEC, USA, 994. [9] UNITODE, Power uly deign eminar, Merrimack, USA, 995. [] UNITODE, High ower factor reregulator, Merrimack, USA, 998. [] J. A. Pomílio, Pré-reguladore de fator de otência - PFP, UNICAMP-FEE, Camina, SP, Brail, 997. [2] A.. Borge and A. J. Perin, A high ower factor current ource rectifier with energy regeneration, UFSC-DEE-INEP, Florianóoli, SC, Brazil, 997.