Multivariable Fuzzy Control of CFB Boiler Combustion System

Transcription

1 Prodings of th World Congrss on Enginring and Computr Sin 3 Vol II WCECS 3, 3-5 Otobr, 3, San Franiso, USA Multivariabl Fuzzy Control of CFB Boilr Combustion Systm Yu-Fi Zhang, Li-Wi Xu, Pi Chn, Xiao-Chn Guan, Gng-Ji Wang Abstrat Th irulating fluidizd bd (CFB) boilr ombustion systm is a omplx multivariabl dynami systm, holding haratristis, suh as nonlinarity, strong oupling and paramtrs tim-varying. Ths haratristis bring many diffiultis in dsigning ontrollr for suh omplx systm. In this papr, a dirt typ of multivariabl fuzzy ontrollr is dsignd on th basis of th stablishd rlationships btwn output (u) and dviation (), dviation hang rat (), tim onstant (T), lag tim (τ). Som simulations ar ondutd to illustrat th prforman of th dsignd ontrollr. Th simulation rsults suggst that th dsignd multivariabl fuzzy ontrollr an not only liminat th oupling btwn loops fftivly, but also rdu th rgulating tim. Using th dsignd ontrollr an thrfor improv th dynami prforman of th CFB systm. Indx Trms multivariabl ontrol, fuzzy ontrol, irulating fluidizd bd (CFB), boilr ombustion systm C I. INTRODUCTION irulating fluidizd bd (CFB) boilr is a typial omplx multivariabl dynami systm, whih holds many mrits suh as high ful flxibility, and ombustion ffiiny, and low pollution missions. It has bn widly usd in th thrmal powr, mtallurgy and othr industris. Howvr, to mak th CFB boilr work automatially undr a prst ffiint ondition is diffiult but important in prati. Hn, a stratgy usd to dsign robust ontrollr is nssary for optimizd opration. Rntly, som onvntional ontrol mthods [] ar availabl. Nvrthlss, ths onvntional ontrol mthods ar diffiult to ahiv good prforman du to som rasons inluding th ompliatd strutur of th ombustion systm, th omplxity of ombustion mhanisms and th haratristis of th ombustion systm suh as nonlinarity, tim-varying, larg dlay, and strong oupling, Fuzzy ontrol mthods an b fftivly usd to solv a wid rang of ontrol problms of whih th objts hold nonlinarity and tim-varying [5-7]. Thrfor, thr ar som litraturs making som ontributions in dsigning fuzzy ontrollr for CFB boilr ombustion systm. Fu t al. [8] dsignd a fuzzy PID ontrollr for th bd tmpratur of a irulating fluidizd bd boilr. Howvr, th ontrollr strutur was too omplx, and it was dsignd All of th authors ar from Shool of nrgy and nvironmnt, Southast Univrsity, Xuanwu Distrit, Nanjing 96, China(Corrsponding zhangyufly@su.du.n). ISBN: ISSN: (Print); ISSN: (Onlin) without onsidring oupling btwn th loops. Wang t al. [9] proposd a ontrol systm omposd of a PID ontrollr and a fuzzy ontrollr. Howvr, th ontrol systm has poor adaptability. Chng t al. [] mad a dynami fdforward doupling of CFB boilr ombustion systm, and dsignd a slf-adapting fuzzy PID ontrollr. Whil, th fuzzy ontrol ruls wr mpirially obtaind, thy did not put forward th prinipl of fuzzy ontrol ruls. Hn a multivariabl fuzzy ontrollr was dsignd in this prsnt work. Basd on th analysis of th CFB boilr ombustion ontrol systm, th prsnt papr put forward th prinipls of th fuzzy ontrol ruls. With thos ruls, a dirt typ of multivariabl adaptiv fuzzy ontrollr was dsignd. Th ontrollr an liminat th oupling btwn loops, and has good adaptability. II. THE CONTROL TARGET ANALYSIS Usually, th ontrol targts for th CFB boilr systm inlud main stam prssur, oxygn lvl in flu gas, bd tmpratur, bd prssur, and pollutant missions. In th prsnt papr, th main stam prssur, bd prssur, and bd tmpratur wr put as th ontrolld objts. A. Main stam prssur ontrol Main stam prssur is an important indx of suprhatd stam quality. CFB boilr oftn partiipats in powr grid load adjustmnt. On th load hangs, th prodution and onsumption rats of th stam ar transintly inonsistnt. It lads to th variation of th main stam prssur, thrfor afft th quality of th stam. At this tim, th input of ful should b adjustd to hang th output of boilr, and to maintain th stability of th main stam prssur []. B. Bd prssur ontrol Bd prssur is an indiator of th thiknss of fluidizd bd matrial. On on hand, if th bd prssur is too high, th quality of bd matrial fluidization will dlin. Many larg partils turn to aumulat at th bottom of th bd. It will ndangr th opration of th boilr. On th othr hand, if th bd prssur is too low, it is diffiult for th bd matrial to form a dns phas zon. So th bd prssur must b maintaind within a rtain rang []. C. Th bd tmpratur ontrol Usually, th bd tmpratur of CFB boilr is kpt btwn 85 and 95, and not allowd to b highr than 97, or lowr than 8. A highr bd tmpratur will aus bd agglomration and furna slagging, and it will also inras NOx formation. A lowr bd tmpratur will aus flamout [3]. Thrfor, th bd tmpratur should WCECS 3

2 Prodings of th World Congrss on Enginring and Computr Sin 3 Vol II WCECS 3, 3-5 Otobr, 3, San Franiso, USA b maintaind in a rtain rang as wll. Howvr, th bd tmpratur will ris whn th CFB boilr load inrass. Hn, if th boilr-load grown up, th bd tmpratur an b allowd to flutuat within a rtain rang whil taking ontrol masur is unnssary [4]. Th main influn fators of th CFB boilr ombustion systm inlud th opning of rturn matrial valv (μν: %), th spd of slag oolr (Q: rpm), and th quantitis of oal (B: t/h) and primary air (F: km3/h). Thy ar shmatially shown in Figur. Fig.. Influn fators of th ombustion systm of a CFB boilr III. MULTIVARIABLE FUZZY CONTROLLER A. Th strutur of multivariabl fuzzy ontrol systm W an dsign th fuzzy ontrollr without onsidring th oupling btwn bd tmpratur loop and main stam prssur and bd prssur loops. Th multivariabl fuzzy ontrollr arhittur of CFB boilr ombustion systm is shown in Figur. ontrollr an automatially hang th univrs of fuzzy variabls siz. Dsign prinipl : Synhronous dsign of fuzzy ontrollr and fdforward ompnsation fuzzy ontrollr Th funtions of th fuzzy ontrollr and th fdforward ompnsation fuzzy ontrollr ar diffrnt. Th fuzzy ontrollr is usd to liminat th main iruit dviation, whil th fdforward ompnsation fuzzy ontrollr is usd to liminat th oupling btwn loops. Tak th R Pb -Pb loop for an xampl, th rol of C Pb-F fuzzy ontrollr is to tak Pb as input signal, to liminat th dviation of th iruit through th ontrol outputs, whil th rol of C Pb-B fdforward ompnsation fuzzy ontrollr is to tak Pb as input signal, to liminat th impat of th output of th fuzzy ontrollr C Pb-F on R P -P loop. Dsign prinipl 3: Subrgional dsign of fuzzy ontrol ruls Th fuzzy ontrol rul tabl is usually dividd into four rgions aording to th signs of dviation and dviation hang rat : rgion I (<, <), rgion II (<, >), rgion III (>, <), and rgion IV (>, >). It is shown in th tabl I. TABLE Ⅰ FUZZY RULE TABLE OF REGIONAL DIVISION u NL PS NM Ⅰ PS Ⅲ NS ZO ZO PL PM PS ZO NS NM NL PS ZO PM Ⅱ NS Ⅳ PL NS 6 5 b 4 3 a Fig.. Multivariabl fuzzy ontrollr strutur for CFB boilr ombustion systm (C Tb_μν - Bd tmpratur fuzzy ontrollr, C Pb_F - Bd prssur fuzzy ontrollr, C Pb_B - Bd prssur fdforward ompnsation fuzzy ontrollr, C P_F - Main stam prssur fdforward ompnsation fuzzy ontrollr, C P_B - Main stam tmpratur fuzzy ontrollr) B. Th prinipls of multivariabl fuzzy ontrol ruls Th stablishmnt of th fuzzy ontrol ruls is th ky of th fuzzy ontrollr dsign. Aording to th haratristis of th ontrol systm and th faturs of th objts, w formulatd fiv dsign prinipls of fuzzy ontrol ruls dsribd as follows. Dsign prinipl : Fuzzy lassifiation and automati adjustmnt (variabl univrs) Th fuzzy variabls ar dividd into svn grads: NL mans "larg ngativ", NM mans "middl ngativ", NS mans "small ngativ", ZO mans "zro", PS mans "small positiv", PM mans "middl positiv ", and PL mans "larg positiv ". Fuzzy languag [PL,PM,PS,ZO,NS,NM,NL] ar rprsntd by [-3,-,-,,,,3]. In ordr to adapt to th hangs of th objt proprtis, th stratgy of variabl univrs fuzzy variabls ar usd. Th d 5 5 Fig. 3. Fuzzy ruls rgional division rfltd in th output urv In Figur 3, tak rgion I for an xampl, whn <, <, it is illustratd that th valu of th amount hargd is highr than th givn valu, and th dviation is rdud by th ontrol ation. At this tim, if is larg, on should inras th ontrol fft to spd up liminating th dviation. Othrwis, if is small, onsidring th siz, if is larg, on should dras ontrol fft to prvnt th possibl ovrshoot. Othrwis, if is small, on should inras th ontrol fft to spd up liminating th dviation. Similarly, th adjustmnt prinipls of ontrol fft an b obtaind for II, III, IV aras. Dsign prinipl 4: u has a rlationship with th dviation, th dviation hang rat and th dynami haratristis of th objt, u f(,, T, ) ISBN: ISSN: (Print); ISSN: (Onlin) WCECS 3

3 Prodings of th World Congrss on Enginring and Computr Sin 3 Vol II WCECS 3, 3-5 Otobr, 3, San Franiso, USA For most CFB boilr ontrolld objts, thy an b dsribd by on ordr with pur lag forms, i.., K s G( s) () Ts whr: K is th amplifiation fator, T is th tim onstant, and τ is pur lag tim. For ordinary fuzzy ontrollr, ontrol ruls should mt th following rquirmnts: ) If, T, thn u f() ; ) If, T is larg, thn u f (,, T, ) ; and 3) uij, u j, i, i, j3,,,,,,3 Suppos K is positiv, onsidr th rlationship btwn u and,, T,and τ. Du to n rn yn y y T T n n n n and basd on th abov analysis, on an obtaind: whr () u ( f ( T )) f ( / T, ) (3) ij i j i f ( T ) xp( T /) (4) / T. f ( / T, ) (5) Dsign Prinipl 5: Th distribution of th mmbrship funtion mod and th sltion of th sal fator and quantization fator W adopt th non-uniform division of triangl mmbrship funtion, as shown in th Figur 4. This distribution mthod an liminat th systm dviation quikly, and rsult that th stati dviation of th ontrol urv is vry small. (x) Fig. 4. Non-uniform division of triangl mmbrship funtion In th prsnt papr, w dsignd th quantitativ fators and proportional fators. Quantization fators ar usd to adjust th siz of th fuzzy ontrollr input, and th sop of th domain. Whil, th proportional fators usd to adjust th fuzzy ontrollr output siz. Th position and funtion of th quantitativ fators and proportional fators ar shown in th Figur 5. Fig. 5. Th loation of th quantization fator and th saling fator x(t) K K ( ) (6) a xp( ) K ( ) xp( n ) (7) u C. Multivariabl fuzzy ontrol rul tabl Fuzzy ruls ar dsignd for th fuzzy ontrollr of th CFB boilr ombustion systm. Among thm, th amplifiation fators of rturn valv opning - bd tmpratur, bd prssur - primary air volum and bd prssur - oal amount loops ar ngativ numbrs, thrfor th ruls nd to b rvrsd. Th fuzzy ontrol tabls and th funtions of quantitativ fators and proportional fators ar shown in Tabl Ⅱ-Ⅶ. D. Simulation Aording to th opration data of a 3MW CFB boilr of Mngxi powr plant, China [5], w stablishd th transfr funtion modl of th CFB boilr ombustion systm, xprssd as v Tb Q P b G() s B P F 48s 5s 5s s 33s 68s v 58s 35s 73s 5s Q 63s 85s 9s 35s B 6s 473s 6s 3s F s s 53s s (8) whr: μ v is th fding bak valv opning(%), Q is th slag oolr spd(rpm), B is th quantity of oal(t/h), F is th primary air(km 3 /h), T b is th bd tmpratur( ), P b is th bd prssur(kpa), and P is th main stam prssur(mpa). Th Simulink modl usd for simulating th 3MW CFB boilr ombustion ontrol systm is shown in Figur 6. In th CFB boilr ombustion systm, in ordr to optimiz th ombustion, w nd to adjust th bd tmpratur and bd prssur. Whn th givn valu hangs, th goal of th ontrol systm is following th givn valu quikly and auratly. Figurs 7 and 8 prsnts th simulation rsults for inrasing th givn valu bd prssur by kpa, it an b sn that th main stam prssur flutuations of th PID ontrollr and fuzzy ontrollr ar small. Whil th PID ontrol systm bd prssur urvs tak mor than s to gt stabl, th fuzzy ontrol systm bd tmpratur urv has bn stabl at about 5 s. Figurs 9 and ar th simulation rsults for th givn valu main stam prssur inrasd by MPa, it an b sn that th urvs of fuzzy ontrollr and PID ontrollr ar stabl at about 35 s. Howvr, thr xist ovrshoots in th PID ontrollr urvs. Th bd prssur urv flutuation of th fuzzy ontrollr is lss than that of PID ontrollr. ISBN: ISSN: (Print); ISSN: (Onlin) WCECS 3

4 Prodings of th World Congrss on Enginring and Computr Sin 3 Vol II WCECS 3, 3-5 Otobr, 3, San Franiso, USA TABLE Ⅱ THE FUZZY CONTROL RULES OF BED TEMPERATURE FUZZY CONTROLLER μ v _T b E Tb NL PL PL PM PS PS NS NS NM PL PL PM PS ZO NS NM NS PL PM PM PS NS NM NL E Tb ZO PL PM PS ZO NS NM NL PS PL PM PS NS NM NM NL PM PM PS ZO NS NM NL NL PL PS PS NS NS NM NL NL TABLE Ⅲ THE FUZZY CONTROL RULES OF BED PRESSURE FUZZY CONTROLLER F _P b E Pb NL PL PL PL PS NS NS NM NM PL PL PL PS NS NM NL NS PL PL PM PS NS NM NL E Pb ZO PL PL PM ZO NM NL NL PS PL PM PS NS NM NL NL PM PL PM PS NS NL NL NL PL PM PS PS NS NL NL NL TABLE Ⅳ THE FUZZY CONTROL RULES OF BED PRESSURE FEEDFORWARD COMPENSATION FUZZY CONTROLLER B_P b E Pb NL PL PL PM PS PS NS NS NM PL PL PM PS ZO NS NM NS PL PM PM ZO NS NM NL E Pb ZO PL PM PS ZO NS NM NL PS PL PM PS ZO NM NM NL PM PM PS ZO NS NM NL NL PL PS PS NS NS NM NL NL TABLE Ⅴ THE FUZZY CONTROL RULES OF MAIN STEAM TEMPERATURE FUZZY CONTROLLER B_P E P NL NL NL NM NS NS PS PS NM NL NL NM NS ZO PS PM NS NL NM NM NS PS PM PL E P ZO PS NL NM NS PS PM PM PL PM NM NS ZO PS PM PL PL PL NS NS PS PS PM PL PL ISBN: ISSN: (Print); ISSN: (Onlin) TABLE Ⅵ THE FUZZY CONTROL RULES OF MAIN STEAM TEMPERATURE FEEDFORWARD COMPENSATION FUZZY CONTROLLER F _P E F NL NL NL NM NS NS PS PS NM NL NL NM NS ZO PS PM NS NL NM NM ZO PS PM PL E F ZO PS NL NM NS ZO PM PM PL PM NM NS ZO PS PM PL PL PL NS NS PS PS PM PL PL TABLE Ⅶ Th funtions of quantitativ fators and proportional fators K ( Tb ) K ( Tb ) K Tb_μv 366. Tb.95 Tb Tb.85 K ( Pb ) K ( Pb ) K Pb_F K Pb_B Pb.35 Pb.9 Pb.9 K ( P ) K ( P ) K P_F K P_B Pb Pb.8.8 Pb In th ontrol systm, th ontrol ation may b afftd by unknown fators. In this as, th ontrol objtiv of th ontrollr is to mak th ontrol ation quikly rturn to pr-disturban siz to minimiz th impat on th ontrolld objt. Whn th bd prssur is stabl, a disturban signal of th primary air volum was issud on 5 s, th simulatd urvs of th ontrol fft and ontrolld variabl ar shown in Figurs and. As an b sn, it taks lss tim for th ontrol fft of th fuzzy ontrollr to rturn to th pr-disturban valus than that of th PID ontrollr. Thrfor, th fuzzy ontrollr has a bttr inhrnt anti-intrfrn ability than th PID ontrollr. Th ontrol systm will not only b afftd by th disturban from th ontrol volum, but also b inflund by othr unknown fators. In ordr to tst th ability of rsisting disturban, a stp disturban of th slag oolr spd was issud on s. Th simulation urvs ar shown in Figurs 3 and 4. As an b sn, th fuzzy ontrollr an quikly liminat th disturban fft, and fftivly limit th amplituds of flutuation of th ontrolld quantitis. Thrfor, th fuzzy ontrollr has a bttr ability of anti-disturban. IV. SUMMARY.3 Pb This papr dsribs th dsign of a dirt typ of multivariabl fuzzy ontrollr. Whn a givn valu of th systm is hangd, th ontrollr an trak th givn valu rapidly. If th ontrol ation is afftd by unknown fators, th ontrollr an mak th ontrol ation rturn to th pr-disturban siz quikly. If th systm is afftd by xtrnal disturbans, th ontrollr an adjust th ontrol funtions quikly so as to liminat th disturban. Hn, th dsignd fuzzy ontrollr an dal with th ontrol problm of th omplx multivariabl dynami systm, holding haratristis inluding nonlinarity, strong oupling and paramtrs tim-varying. WCECS 3

5 Prodings of th World Congrss on Enginring and Computr Sin 3 Vol II WCECS 3, 3-5 Otobr, 3, San Franiso, USA (a) Fuzzy ontrollr simulation diagram (b) Fuzzy ontrollr strutur diagram Fig. 6. Th Simulink modl diagram of CFB boilr ombustion ontrol systm Tb( ) Pb(kpa) P(Mpa) fuzzy ontrol μν fuzzy ontrol B fuzzy ontrol F fuzzy ontrol Pb fuzzy ontrol P fuzzy ontrol Tb Fig. 7. Fuzzy ontrollr output urvs of bd prssur givn valu stp hang Tb( μν(%) F(km3/h) B(t/h ) Pb(kpa) P(Mpa) - - PID ontrol μν PID ontrol B PID ontrol F PID ontrol Pb PID ontrol P - PID ontrol Tb Fig. 8. PID ontrollr output urvs of bd prssur givn valu stp hang Tb/( ) Pb(kpa) P(Mpa) fuzzy ontrol B fuzzy ontrol F fuzzy ontrol μν fuzzy ontrol P fuzzy ontrol Tb fuzzy ontrol Pb Fig. 9. Fuzzy ontrollr output urvs of main stam prssur givn valu stp hang Tb/( ) Pb(kpa) P(Mpa) PID ontrol B PID ontrol F PID ontrol μν PID ontrol P PID ontrol Tb PID ontrol Pb Fig.. PID ontrollr output urvs of main stam prssur givn valu stp hang ISBN: ISSN: (Print); ISSN: (Onlin) WCECS 3

6 Prodings of th World Congrss on Enginring and Computr Sin 3 Vol II WCECS 3, 3-5 Otobr, 3, San Franiso, USA Tb( ) Pb(kpa) P(Mpa) - - fuzzy ontrol μν fuzzy ontrol B fuzzy ontrol F fuzzy ontrol Pb fuzzy ontrol P - fuzzy ontrol Tb Fig.. Fuzzy ontrollr output urvs of primary air volum stp disturban Tb( ) Pb(kpa) P(Mpa) - PID ontrol B PID ontrol μν PID ontrol F PID ontrol P.5 PID ontrol Pb -.5 PID ontrol Tb Fig. 4. PID ontrollr output urvs of slag oolr stp disturban Tb( ) Pb(kpa) P(Mpa) PID ontrol μν PID ontrol B PID ontrol F PID ontrol Pb PID ontrol P PID ontrol Tb Fig.. PID ontrollr output urvs of primary air volum stp disturban Tb( ) Pb(kpa) P(Mpa) -.5 fuzzy ontrol μν fuzzy ontrol B fuzzy ontrol F fuzzy ontrol Tb fuzzy ontrol Pb fuzzy ontrol P Fig. 3. Fuzzy ontrollr output urvs of slag oolr stp disturban REFERENCES [] H. Zhang, Z. S. Yu, A. D. Xu, Analysis of Combustion Control Systm of 3MW Cirulating Fluidizd Bd Boilr, Powr Systm Enginring, vol. 6, no. 6, pp. 69-7, Nov.. [] Q. Zhang, Q. H. Wang, X. L. Bai, X. H. Wang, Control Dsign and Ralization for Bd Tmpratur in Cirulating Fluidizd Bd Boilr Basd on DMC-PID, Control and Instrumnts in Chmial Industry, vol. 36, no. 6, Jun. 9. [3] H. B. Yu, J. Chu, An Exprt PID Control mthod for lvl Control of CFB Boilr, Mhanial & Eltrial Enginring Magazin, vol. 7, no. 3, Mar.. [4] C. F. Wang, Y. B. Qiu, Th automati ontroi systm of irulatory fluidizd-bd boilr basd on programmabl ontrol thnology, Manufaturing Automation, vol. 3, no., Sp. 9. [5] H. Habbi, M. Zlmat, B. O. Bouamama, A dynami fuzzy modl for a drum-boilr-turbin systm, Automatia, vol. 39, pp. 3-9, Spt. 3. [6] K. Erkki, Advand ontrol of an industrial irulating fluidizd bd boilr using fuzzy logi, Ph.D. dissrtation, Dpt. Pross. Eng., Oulu Univrsity, Oulu, Finland,. [7] L. Yang, M. S. Xu, Fuzzy Control for Bd Tmpratur Control Systm of Cirulation Fluidizd-Bd Boilrs, Journal of Northrn Jiaotong Univrsity, vol. 6, no. 6, Jun.. [8] P. Fu, X. N. Yu, H. Wang, Rsarh on fuzzy ontrol algorithm for bd tmpratur ontrol of irulating fluidizd bd boilr, Mahin Larning and Cybrntis, vol., pp , Aug. 5. [9] J. Wang, C. Y. Liu, X. L. Song, Z. Y. Song, A ralization mthod for fuzzy doupling ontrol of th Cirulating Fluidizd Bd Boilr, Mahin Larning and Cybrntis (ICMLC), vol., pp. 66-7, Jul.. [] Q. M. Chng, R. Q. Guo, X. F. Du, Rsarh on multivariabl doupling ontrol systm for ombustion systm of irulating Fluidizd Bd Boilr, Sustainabl Powr Gnration and Supply, pp. -6, Apr. 9. [] J. F. Yin, L. Liu, Optimization of Main Stam Prssur Control Systm in Cirulating Fluidizd Bd Boilr, Guangdong Eltri Powr, vol. 4, no., pp , Ot.. [] M. Li, X. D. Xu, Cirulating fluidizd bd boilr ontrol systm, Journal of Tsinghua Univrsity (SCIENCE AND TECHNOLOGY), vol. 4, no. 5, pp , May.. [3] J. Q. Yang, W. J. Zhao, R. Guo, W. J. Zhang, Analysis and Dsign of Control Systms of Cirulating Fluidizd Bd Boilrs, Chins Journal of Powr Enginring, vol. 5, no. 4, pp. 57-5, Aug. 5. [4] P. Gong, K. Zhao, J. Xiang, J. L. Yuan, Charatristis and adjustmnt mthods of bd tmpratur for 3MWCFB boilr, Eltri Powr, vol. 44, no. 3, pp. 47-5, Mar.. [5] Y. S. Hao, Rsarh on Modling and Advand Control of a Larg Cirulating Fluidizd Bd Boilr, Ph.D. dissrtation, Dpt. Environmnt. Enrgy, Southast Univrsity, 9. ISBN: ISSN: (Print); ISSN: (Onlin) WCECS 3