Modeling and Simulation of a Power Conditioning System for the Hybrid Fuel-Cell/Turbine Power Plant

Transcription

1 5th IEEE Conference on Decon and Control and European Control Conference (CDC-ECC) Orlando, FL, USA, December -5, Modeln and Smulaton of a Power Condtonn Sytem for the Hybrd Fuel-Cell/Turbne Power Plant hton Guo and Kwan Y. Lee, Fellow, IEEE Abtract Power condtonn ytem an nterface between dtrbuted eneraton and utlty rd. Th paper preent the model of a power condtonn ytem (PCS) for the hybrd drect fuel-cell/turbne (DFC/T) power plant. It reulate oltae, current and power tranmtted from the hybrd DFC/T power plant to utlty rd. The propoed ytem cont of DC/DC conerter, a rd-connected SPWM DC/AC nerter, and an LCL flter. To reulate and table the DC lnk oltae, DC/DC conerter wth PI controller adopted. Wth the dual-loop PI baed rd-connected SPWM nerter, both acte and reacte power tranmtted to utlty rd from the hybrd DFC/T power plant can be controlled. The LCL flter can reatly reduce the current harmonc dtorton (THD). Theoretcal analy, modeln methodoloe and control cheme are preented. The whole model wa deeloped n Matlab/Smulnk enronment wth all the parameter en. Smulaton reult demontrate that the propoed PCS can follow a dynamc load wth the error le than % and reduce the THD to.65%. Index Term--Power condtonn ytem, DC lnk oltae, power flow control, LCL flter, PI controller, fuel cell plant, rd nterface. I. INTRODUCTION Dtrbuted enery ource, uch a fuel cell, wnd turbne and photooltac, can not only prode clean enery wthout enronmental polluton but alo achee hher enery effcency than tradtonal fol fuel. Furthermore, dtrbuted enery ource can reduce tranmon lo and dtrbuton cot. Amon all dtrbuted eneraton, fuel cell ha become the mot promn power plant due to t hh effcency and, furthermore, not ben lmted to weather condton. Howeer, when fuel cell power plant connected to dtrbuton network, problem n power flow control and power qualty need to be reoled. Power condtonn ytem (PCS) deeloped to ole thee problem and reulate oltae, current and power tranmtted nto the utlty rd []. Preouly, ome reearch ha been done about power Th work wa upported n part by the Natonal Scence Foundaton under rant ECCS 844. hton Guo wth the Department of Electrcal and Computer Enneern, Baylor Unerty, Waco, TX USA. (e-mal: hton_guo@baylor.edu). Kwan Y. Lee wth the Department of Electrcal and Computer Enneern, Baylor Unerty, Waco, TX USA. (phone: ; e-mal: Kwan_Y_Lee@baylor.edu ). condtonn problem. General tructure and bac prncple of PCS for fuel cell power plant hae been netated n []. In conerter den, Bjac, Ban and Volarc created a mathematcal model of the Boot type DC/DC conerter for fuel cell applcaton []. Wan, Lu, Chen and Wan bult a model of DC/DC conerter by un tate pace equaton baed on Matlab/Smulnk [3]. Da, Marwal, Woo and Keyhan concentrated on a power flow control cheme for dtrbuted eneraton by un three phae nerter n [4]. Wan, Nehrr and Gao deeloped an nterface between proton exchane membrane fuel cell (PEMFC) and the power rd, but they dd not concentrated on power qualty ue when PEMFC wa connected to dtrbuton network [5]. Lerre, Blaabjer and Hanen propoed a detaled LCL flter den procedure for threephae rectfer to mproe power qualty n [6]. Guo, Wu and Gu analyed the tablty condton of LCL flter for rd-connected nerter [7]. Lu, Son and Ernen dened an LCL and control cheme for three phae nerter [8]. Th paper preent an nterated power condtonn ytem model for the hybrd drect fuel-cell/turbne (DFC/T) power plant. The propoed PCS compoed of DC/DC conerter, a lare capactor, a three-phae DC/AC nerter and an LCL flter. It connect the hybrd DFC/T power plant wth utlty rd. Va condtonn oltae and current, power flow can be uccefully controlled under dynamc load and power qualty can be mproed throuh the LCL flter. II. INTRODUCTION TO POWER CONDITIONING SYSTEM A. Oerew of Hybrd Fuel-Cell/Turbne Power Plant Fuel-cell power plant conert the chemcal enery tored n fuel nto electrc enery drectly. There are many knd of fuel cell power plant. The Morton Carbonate Fuel Cell (MCFC) ha hh effcency and hh power denty and thu condered to be the mot promn fuel-cell power plant for lare-cale power eneraton [9]. The fuel-cell power plant mathematcal model ued n th paper wa frt deeloped by Luka, Lee and Gheel-Ayah []. Yan, Lee, Junker and Gheel-Ayah optmed the DFC/T model and propoed the ntellent control ytem ncludn fuy fault dano and accommodaton ytem. By nteratn mcro-turbne nto fuel-cell power plant, the oerall plant effcency expected to achee 75% [] //$6. IEEE 3658

2 B. The Propoed Power Condtonn Sytem A F. how, the propoed PCS the nterface between the hybrd DFC/T power plant and utlty rd. It reulate three-phae oltae and three-phae current. It alo control acte and reacte power flow and mproe power qualty. The power enerated by DFC/T power plant reulated and controlled by PCS, whch manly compoed of Buck-Boot DC/DC conerter, a lare capactor and a full brde three-phae nuodal pule-wdth modulaton (SPWM) baed DC/AC nerter and an LCL flter. The DC/DC conerter reulate the untable DC oltae enerated by DFC/T power plant. To further reulate the DC lnk oltae and reduce rpple of the DC lnk oltae, a lare capactor placed between conerter and nerter. Three-phae DC/AC nerter chop DC lnk oltae nto AC. Under the control of dual-loop SPWM baed controller, acte and reacte load follown can be acheed. Before tranmttn the enery to utlty rd, LCL flter can reatly reduce current harmonc dtorton to a ery low leel. Conerter Inerter LCL Flter Tranformer DC Vdc DC V,abc V,abc DC AC abc PWM V,abc Controller Controller,abc V,abc Vref DC DC PWM Controller Vref Lare Capactor Vdc Pref, Qref Power Condtonn Sytem Generator Turbne F.. Oerall tructure of DFC/T, PCS and utlty rd. III. DC/DC CONVERTER AND ITS CONTROLLER.. A. Modeln of DC/DC Conerter In order to tranmt the power to utlty rd, the two output oltae, fuel-cell tack oltae and mcro-turbne oltae hould be conerted to 48V and then connected n parallel wth the three-phae SPWM nerter. A can be een from F., the output oltae of fuel-cell tack and mcroturbne are not table and een ary n a wde rane; from V to 6V. Snce the DC lnk oltae uppoed to be 48V, a Buck-Boot conerter adopted here. A feedback proportonal-nteral (PI) controller adopted to make the conerter table under mall nal dturbance and reulate the duty rato. F. 3 how the topoloy of the buck-boot crcut, where V fc the output oltae of fuel-cell tack or mcro-turbne, DC lnk oltae, L the nductance wth t G Utlty Grd Fuel Cell Stack Volate(V) Volate(V) Tme(Day) Mcro-turbne Voltae 6 4 equalent ere retance (ESR) R L, C the capactance wth t ESR R c, and R eq the equalent load. The wtch, controlled by a PWM nal, control the whole crcut to be buck type or boot type. Accordn to the dfferent poton of the wtch, there are two mode of th crcut. For each mode, mathematcal model can be created accordn to the crcut topoloy. Then by combnn the two et of equaton toether, we et: Rc RL ( S) Rc S + ( ) S L L = L L( R eq + R + c ) L fc c c ( S) C( + Rc ) C( + R c ) R eqrc ( S) L = () dc + Rc + Rc c + V fc R L - F. 3. Topoloy of the Buck-Boot conerter. S L Fuel Cell Stack Voltae Tme(Day) F.. Output oltae of hybrd DFC/T power plant. L When modeln, the wtchn mode S can be ether or, whch due to the wtchn chopper. When S=, the wtch at poton, and the nductor dcharn and the capactor charn. When S=, the wtch at poton, the nductor charn and the capactor dcharn. Thu, th model not an aerae model but a detaled dynamc model. In order to model conerter, we mut fnd the equalent retance R eq. Snce the output oltae reulated to be 48V and acte power of hybrd V c R c C R eq 3659

3 DFC/T power plant 3kW, the equalent retor calculated a R eq =.964 Ω. B. Conerter Controller Den F. 4 the conerter ytem block daram. A PI type controller mplemented here. The tranfer functon of the PWM enerator jut a an. All ESR han been nelected, the follown equaton e the mall nal tranfer functon of the Buck-Boot conerter []: Vdc Gdc( ) = d V dc V fc ( D) DL V fc = ( D) LCR + L + R ( D) () D = (3) D Here, D the duty rato, whch control the conerter, defned by D=T /T =T /(T +T ), where T the tme perod when S= and T the tme perod when S=, and T =T +T the duty cycle. Thu, the alue of the duty rato a decmal between and. For analy and den purpoe, all parameter n () mut be fxed alue. Thu, the aerae alue are ued here. The aerae method can be ued to analye the tablty of Buck-Boot conerter ytem een f there ext a wtchn dece n the crcut []. The DC lnk oltae 48V and the aerae alue of V fc 3V. Then accordn to (3), the aerae alue of duty rato D.654. Then tranfer functon of each block n F. 4 can be found to den the PI parameter. After that, we can fnd the whole conerter ytem tranfer functon. The bode plot of the open-loop tranfer functon hown n F. 5. The phae marn of the open-loop tranfer functon 97. deree, whch ndcate that the propoed conerter control ytem table. V ref + error - Cotnroller kdp + kd k dcb IV. DC/AC INVERTER DESIGN A. Theoretcal Analy of Power Flow Conder a network, a hown n F. 6, wth two power ource. Theoretcally, acte and reacte power delered from nerter de to rd de are en by [3]: VV V P = co( θ θ ) co( θ ) (4) eq PWM Genreator d k PWM F. 4. Block daram of the DC/DC conerter control ytem. eq DC/DC Conerter G dc() Mantude (db) Phae (de) Sytem: c_ Frequency (rad/ec):.5 Phae (de): -8.8 VV V Q = n( θ θ ) n( θ ) (5) In (4), (5) and F. 6, V the oltae mantude at the rd de wth deree phae anle, V the oltae mantude and θ the oltae phae anle at the nerter de, and the mpedance between nerter and utlty rd, whch nclude the mpedance of LCL flter, tranmon lne and tranformer. From thee equaton, we can ee the mple relatonhp between power and oltae. Acte power manly depend on oltae phae anle and reacte power manly depend on the oltae mantude [3]. Thu, to deler a et of pecfc P and Q to utlty rd, we can mply reulate the oltae mantude and anle at the nerter de. Snce oltae mantude and phae anle at the rd de can be ened and the mpedance between the nerter and rd can be known, thu, accordn to (4) and (5), the correpondn oltae mantude and anle at the nerter de can be calculated a the reference, a en by: V = ( P + Q ) + V co( ) n( ) + P θ + Q θ V (6) P V θ = θ arcco( + co( θ)) (7) V V V θ AC Bode Daram Gm = Inf, Pm = 97. de (at.6 rad/ec) Frequency (rad/ec) F. 5. Bode daram of the DC/DC conerter control loop. P,Q =R+jX F. 6. Power flow between two power ource. AC 366

4 B. Three-Phae DC/AC Inerter and SPWM Controller F. 7 how the den of the nerter ytem, where a three-phae full-brde nerter mplemented. An LCL flter connected between nerter and rd for the purpoe of reducn current harmonc. After on throuh LCL flter, current would be tranferred to utlty rd a tranformer and tranmon lne. The oerall control cheme for three-phae PWM nerter hown n the haded area n F. 7. When pecfc P and Q reference are en, and then accordn to (6) and (7), the reference oltae mantude and phae anle at the nerter de can be calculated. Snce the calculated oltae reference n the three-phae abc-frame, t hould be tranformed nto the oltae reference n the dq-frame. The oltae reference n the dq-frame compared wth the actual oltae n the dq-frame. The error the nput to the PI controller, whoe output ent to the nner loop. The nner current loop work n a mlar way wth the outer oltae loop. But compared wth the outer loop, the nner loop run much fater. After the controlled nal are enerated, they are nere tranformed to the three-phae abc-frame to control the SPWM enerator. C. Control Scheme F. 8 and F. 9 are the block daram of the current loop and oltae loop, repectely. For the nner current loop, the detaled tranfer functon are e n each block dq,ref Controller Current Loop Lne k + p + k dq,ref dq G delay () Rl + Ll k fb F. 9. Block daram of the outer oltae loop. and the tranfer functon of LCL flter e n Secton V. When modeln the outer loop, the nner loop a problem. The nner current loop tranfer functon can be modeled a a an wth a tme delay. The reaon for th that the nner loop run much fater than the outer loop, whch mean the nner loop ha been table when outer loop tll chann. Therefore, the nner loop can be modeled a a an wth a tme delay []. Snce the rd frequency about 6H, the tranformer can be modeled by un the fxed equalent mpedance. A we can ee from F., the phae marn of the nner loop 4.7 deree and the phae marn of outer loop 9.6 deree. Thu, both loop are table under mall nal dturbance. V. LCL FILTER DESIGN,dq A. Topoloy and Tranfer Functon of LCL Flter To tranmt enery to utlty rd, current harmonc mut be reduced nce harmonc are harmful to power ytem.,dq Fuel Cell Power Plant V fc DC/DC Conerter DC/AC Inerter,abc LCL Flter,abc,abc Tranformer Tranmon Lne,abc Utlty Grd SPWM Snal SPWM Generator dq/abc Three-Phae SPWM Controller F. 7. Three-phae SPWM Control Sytem.,abc,abc dq θ PI Controller + - abc/dq dq,ref,dq + - θ PI Controller abc/dq dq,ref Reference,abc Calculaton P ref, Q ref,abc Phae Lock Loop Load PQ Reference Controller SPWM LCL Flter dq,ref error k - dq cp + k c l,dq l,dq Rd + - k PWM + - L + R + C + - L + R f + c,dq l,dq,dq k cfb F. 8. Block daram of the nner current loop. 366

5 Typcally, L flter enouh n reducn low frequency harmonc to a atfactory leel. But nce hh frequency wtchn dece n the three-phae nerter would enerate lot of hh frequency harmonc, an LCL flter wth a dampn retor adopted here n order to reduce both low and hh frequency harmonc. The block daram of the LCL flter hown n F. 8 and we can fnd the tranfer functon of LCL flter a G Mantude (db) Phae (de) LCL ( ) d + R ( ) = = C U ( ) l ( L + R ) ( L + R ) + ( + Rd ) ( L + L + R + R ) C (8) B. LCL Flter Parameter Den The oerall nductance, L +L, uppoed to be a lare a poble n order to hae lower THD. But too lare nductance would lower the ytem repone. Thu, there a tradeoff between low THD and ytem repone. The capactor C f, whch manly reduce the hh frequency harmonc, hould not be too lare n cae t aborb too much reacte power. The ere retor R d, whch ncreae the ytem dampn, eental n order to preent the ytem from reonance ocllaton [7]. Alo, when denn LCL parameter, reonance frequency hould be n a pecfc rane. The detaled parameter den tep can be found n [6]. All retor hae been nelected and (9) e the equaton for reonance frequency: f Frequency (rad/ec) F.. Bode plot of the oltae loop, the nner current loop and LCL flter. re L + L (9) L LC f = π Bode Daram Current Loop: Gm = Inf, Pm = 4.7 de Voltae Loop: Gm = Inf, Pm = 9.6 de Current Loop Voltae Loop LCL Flter F. how the bode plot of the LCL flter. The reonance frequency about 834H, whch meet the requrement of the LCL flter. Snce the wtchn frequency kh, and the hh frequency harmonc enerated by wtchn can be reatly reduced throuh LCL flter. VI. SIMULATION RESULTS A. DC Lnk Voltae In modeln the conerter ytem, F. 4 and Equ. () e the tranfer functon of each block. The parameter ued are: L=3.4mH, R L =.3mΩ, C=86mF, R C =5.mΩ, k dp =., k d =., and k PWM =. The reult of DC/DC conerter model, whch the DC lnk oltae, are hown n F.. Snce t too low and not neceary for u to run for 4 day of mulaton data, we hae only mulated 6 econd here. In th frt 6 econd, the output oltae of hybrd DFC/T power plant ared nfcantly. A we can ee n F., DC/DC conerter and uper capactor hae reulated the oltae nto a table 48V, whch ha already been n teady tate for a lon tme. Therefore, 6 econd of mulaton data uffcent to proe t tablty. The oerhoot alo reduced. Voltae(V) Voltae(V) 6 4 (a) Fuel-Cell Stack Tme() (b) Mcro-turbne Tme() F.. DC lnk oltae of the conerter. B. Power Flow Control The tranfer functon n the nerter control ytem can be found n F. 8, F. 9 and Equ. (8). In the mulaton, the parameter are: k cp =3, k c =7, k PWM =, k p =3, k =5, R l =mω, and L l =.5mH. The LCL parameter can be found n the follown. F. how The PQ reulatn performance. When the power reference are et a P=5kW and Q=6kVAR, the reult how that acte and reacte power can be precely controlled under tatc load. F. 3 decrbe the load follown under a dynamc load. The old lne the acte power output and the dahed lne the acte power reference. The propoed three phae PWM controller can follow dynamc load wth mall error and tme delay. C. Current Harmonc The parameter of LCL flter are: L =.3mH, R =6mΩ, C f =8uF, R d =.6Ω, L =.7mH, and R =5mΩ. In F. 4, the fure on top the current waeform that tranmtted nto utlty rd and the fure on bottom total harmonc 366

6 Acte Power(kW) Reacte Power(kVAR) 3 (a) Acte Power Acte Power Reference Acte Power Delered Tme() (b) Reacte Power 5-5 Reacte Power Reference Reacte Power Delered Tme() F.. Power flow control under tatc load. Ma (% of Fundamental) Selected nal: cycle. FFT wndow (n red): cycle Tme () Fundamental (6H) =.64, THD=.65% Frequency (H) F. 4. Current and the THD. Acte Power(kW) Tme() F. 3. Power flow control under dynamc load. dtorton,.65%, whch below 5% and meet the IEEE tandard for tranmon [4]. VII. CONCLUSION Acte Power Reference Acte Power Delered Th paper preent the model and mulaton of a power condtonn ytem (PCS) for the hybrd DFC/T power plant. Three man tak of the propoed PCS are DC lnk oltae reulaton, power qualty mproement and power flow control. Correpondnly, PCS compoed of a DC/DC conerter, a DC/AC nerter and an LCL flter. The modeln proce preented for each part. The PI control cheme are adopted and ytem tablty ue are analyed n the conerter and nerter control. Sytem parameter and mulaton reult are en. The PCS modeled and mulated n Matlab/Smulnk. Smulaton reult how that the three man problem are oled ery well. REFERENCES [] T. Cho and K. Y. Lee, Interface of a fuel cell dtrbuted enerator wth dtrbuton ytem network, n Proc. of the IEEE Power Enery Socety General Meetn, Calary, Canada, July 6-3, 9. [] T. Bjac,. Ban and I. Volarc, Control of a fuel cell tack loaded wth DC/DC boot conerter, IEEE Internatonal Sympoum on Indutry Electronc, Cambrde, UK, June3-July, 8, pp [3] R. Wan, J. Lu, Y. Chen and. Wan, A tate-pace model for teady-tate analy of oft-wtchn PWM DC/DC conerter baed on MATLAB/Smulnk, The 4 th Internatonal conference on Power Electronc and Moton Control, X an, Chna, Auut 4-6, 4, pp [4] M. Da, M. N. Marwal, J. Woo and A. Keyhan, Power control of a nle dtrbuted eneraton unt, IEEE Tran. on Power Electronc, Vol. 3, No., pp , January, 8. [5] C. Wan, M. H. Nehrr, and H. Gao, Control of PEM fuel cell dtrbuted eneraton ytem, IEEE Tran. on Enery Coneron, Vol., No., pp , June, 6. [6] M. Lerre, F. Blaabjer and S. Hanen, Den and control of an LCL-flter baed three-phae acte rectfer, IEEE Tran. on Indutry Applcaton, Vol 4, No. 5, pp. 8-9, September, 9. [7] X. Guo, W. Wu and H. Gu, Modeln and mulaton of drect output current control for LCL-nterfaced rd-connected nerter wth parallel pae dampn, Smulaton Modeln Practce and Theory, Vol. 8, No. 7, pp , Auut,. [8] B. Lu, B. Son and B. Ernen, Modeln and analy of an LCL flter for rd-connected nerter, IEEE Power and Enery Socety General Meetn, Detrot, MI,. [9] W. Yan and K. Y. Lee, An optmal reference oernor wth a neural network combned model for hybrd fuel-cell/a turbne, IEEE Power Enery Socety General Meetn, Mnneapol, MN, July 5-9,, pp.-6. [] M. D. Luka, K. Y. Lee and H. Gheel-ayah, An explct dynamc model for drect reformn carbonate fuel cell tack, IEEE Tran. Enery Coneron, ol. 6, pp , September,. [] W. Yan, K. Y. Lee, T. Junker and H. Gheel-ayah, Fuy fault dano and accommodaton ytem for hybrd fuel-a/a-turbne power plant, IEEE Tran. on Enery Coneron, Vol. 5, No. 4, pp.87-94, December,. [] N. Mohan, T. Undeland and W. Robbn, Power Electronc: Conerter, Applcaton, and Den, Wley: New York, USA,. [3] J. D. Gloer, M. S. Sarma and T. J. Oerbye, Power Sytem Analy and Den, Thomon: Toronto, Canada, 8. [4] IEEE Standard 59-99, IEEE recommended practce and requrement for harmonc control n electrcal power ytem,