The Design of Control Node of Temperature in Greenhouse based on the Fuzzy Control Technology

Transcription

1 Th Dsign of Control Nod of Tmpratur in Grnhous basd on th Fuzzy Control Tchnology GAO Liang 1,LI Aifng 2 1 Offic of Scintific and Tchnological Managmnt, Agricultural Univrsity of Hbi, Baoding,071001, P.R.China 2 Baoding Bihng Jibao Tchnology Co., Ltd., Baoding,071051, P.R.China zyhbddy@126.com Abstract Tmpratur is an important nvironmntal paramtr in grnhous, how to control th tmpratur accuratly with a unifid mthod is an important task in grnhous automatic control systm. This papr introducs th dsign of th fuzzy control nod of tmpratur in grnhous basd on a MCS196 Micro-computr and th componnt of th grnhous control systm. Th fuzzy control principl and mthod ar prsntd. Th hardwar structur and th fuzzy control ruls and output tabl ar xpatiatd. Th diagram of th nod hardwar function is also prsntd. By practical work in many grnhouss, th rsults prsnt it runs wll, th tmpratur control nod has many advantags, such as convnint installation, asy dbugging, and it has strong robustnss. So, it has a bttr practicality and dsrvs to hav mor widsprad application. Kywords grnhouss, fuzzy control, tmpratur, micro-computr Environmntal control in modrn grnhouss is of grat significanc to improving conomic bnfit of agricultural production. It can crat propr growth condition for plants and mak crops obtain high yild. Tmpratur is an important nvironmntal paramtr in grnhous, how to control th tmpratur accuratly with a unifid mthod is an important task in grnhous automatic control systm, spcially in th variant conditions of grnhous structur and nvironmnt. Thr ar two main factors affct grnhous tmpratur : (1) th impact of grnhous structur and rgions, which includs grnhouss volum, wall thicknss, transparnt ara, th hat capacity of hating, tmpratur and infiltration of outdoor nvironmnt, tc. (2) th ffct of th adjustmnt of othr nvironmntal paramtrs on th tmpratur in grnhous, ths paramtrs includ humidity, light illumination, CO2, tc. So, grnhous nvironmnt systm is a multivariabl, larg inrtia, and nonlinar systm, and also has th phnomnon of tim dlay. Accordingly, it is difficult to st up accurat and unifid mathmatical modls to solv th problm of this kind of systm, also traditional or modrn control mthod is unabl to raliz th control. Whras, fuzzy control nds not th prcis mathmatical modl of th controlld objct, th systm has strong robustnss, and it is suitabl for nonlinar, tim varying and hystrtic systm control. Consquntly, fuzzy control is th propr mthod to analyz th grnhous nvironmnt systm. This papr dvlops th fuzzy control nod of paramtrs in grnhous basd on a MCS196 Microcomputr, and a mor thorough rsarch of th control ruls, dsign and implmntation of th hardwar which ar basd on th Micro- computr fuzzy control systm ar mad. 1 Fuzzy control algorithm Th nod is a fuzzy control dvic of doubl-input and multi output. Th input variabls includ th tmpratur dviation in th grnhous and its chang rat; th output variabls includ th tmpratur controlld variabls and diffrnt combinations of air-vnting, air-ntraining and humidification. Th cor of th control is th fuzzy controllr, aftr th fuzzy procssing of th masurd nvironmnt paramtrs and input variabls, thn is th procssing of fuzzy infrnc and anti-fuzzy, th output of fuzzy control is obtaind. Th principl is shown in Fig Fuzzification of tmpratur and tmpratur dviation Tmpratur dviation is th diffrnc btwn th masurd tmpratur and its st valu. Th 421

2 nod divids th tmpratur control rgion into two parts: fuzzy control rgion and confirmd control rgion. For th tmpratur control, tmpratur dviation of st valu is within ±4 is fuzzy control rgion, th othrs is confirmd control rgion. In fuzzy control rgion, th fuzzy control nod rgulats tmpratur automatically by th ruls of fuzzy control; in confirmd control rgion, th nod maks forcd cooling or hating control, and mits alarm signal whn th tmpratur xcding standard. In fuzzy control rgion, to th convninc for th ralization of singl chip computr, slct th domain of linguistic variabl and :x={-4,-3,-2,-1,0,1,2,3,4},hr, is th dviation btwn th masurd tmpratur and its st valu; is th chang rat of, it can b obtaind by =(kt)-[(k-1)t];to mak th rgulation mor asy, quantization factor k1 and k2 ar introducd, and and ar mad to b dots in th domain. In this domain, th languag tru valu st of and is A and B sparatly, thir domains ar both {NB NS ZE PS PB},in othr words, th tmpratur dviation, rror rat of chang and th output all can b dividd into 5 fuzzy sub-status, sparatly is PB(positiv big), PS (positiv small),ze (zro),ns (ngativ small),nb (ngativ big). Th attribut function of and is shown in Fig K 1 K 2 Fuzzy Fuzzy Fuzzy Controllr K 3 u Objct Y NB NS ZE PS PB u Fig. 1 Diagram of fuzzy control systm Fig. 2 Attribut function of and 1.2 Th ruls and dcisions of fuzzy control Th principl of fuzzy control ruls is to mak th dynamic and static charactristics of output rspons to b th bst. For xampl, whn th tmpratur dviation is much biggr,in ordr to liminat th dviation as quickly as possibl, th controlld variabl should chang rapidly, no mattr how th tmpratur changs. If it is NB, in othr words, th dviation of tmpratur in th grnhous and th st valu is ngativ biggst at th momnt, th tmpratur dcrass to th lowst, now in ordr to liminat th dviation as quickly as possibl, th controlld variabl should incras fastr, so th nod of fuzzy control tak th biggr controlld variabl; if th tmpratur dviation is NS or ZE, th main problm transforms to stability. In ordr to prvnt ovrshoot, and to mak th systm stabl as soon as possibl, th chang of th controlld variabl is confirmd according to th concrt conditions of th changd tmpratur, and chooss th corrsponding control ruls. If is positiv,it indicats that th chang of tmpratur has a dcras trnd, so th fuzzy control systm should tak th smallr controlld variabl;in othr cass, th fuzzy control ruls undr diffrnt situations of th chang of tmpratur can b dducd by analogy. By th analysis of various possibl cass and th corrsponding control dcision in th procss of control, 25 control ruls can b obtaind as Tabl 1. Th control ruls can b dscribd as th following condition sntnc: IF =Ai AND =B j THEN u=c ij ( i =1, 2,,n; j=1,2,, n ) Hr, A i is th languag variabl valu of, B j is th languag variabl valu of, C ij is th languag variabl valu of controlld variabl u which corrsponds to A i and B j. That is A 1 =B 1 =NB,A 2 =B 2 =NS,A 3 =B 3 =ZE,A 4 =B 4 =PS,A 5 =B 5 =PB; C ij can b found in Tabl 1, n is th numbr of languag tru valu st A, B and C,hr, n=5.according to th mthod of f fuzzy rasoning, th fuzzy condition sntnc abov can b dscribd with a fuzzy rlation matrix R l : R l =A i B j C ij (l=1,2,,t) Hr, t=25 is th numbr of fuzzy condition sntncs. Th mmbrship function of ach lmnt in R l is: 422

3 R l µ = Tabl 1 Fuzzy control rulrs NB NS ZE PS PB NB PB PB PB PS NB NS PB PS PS ZE NB ZE PB PS ZE NS NB PS PB ZE NS NS NB PB PB NS NB NB NB µ µ B j µ C ij A i Th fuzzy rlation matrix which corrsponds to th mastr control rul is R. whn and tak fuzzy vctor A and B sparatly, according to th combination rul of fuzzy rasoning, fuzzy subst of output controlld variabl can b obtaind: U=(A B) R Th nod adopts gravity mthod, and by mans of anti- fuzzy to U, th xact output is obtaind. According to th abov analysis, th off-lin calculation of th valus of and ar mad. Thn th output controlld variabl u corrsponding to diffrnt and ar obtaind, th collction of fuzzy control is shown in Tabl 2. Mak this tabl fix in th program mmory of 80C196, and ar multiplid by k1 and k2 sparatly in vry priod, and rounding is mad aftr gtting th rsults, thn th controllr obtains th valu of input domain, thn th domain valu of controlld variabl is gaind by lookup tabl, and thn th actual controlld variabl is obtaind according to th prsnt status of th grnhous actuator, at last, th output controls th controlld objct. As it has crtain coupling btwn tmpratur control and humidity control, in practical control, tmpratur is th prim considration targt, bcaus th fuzzy control has th advantag of insnsitivity of th paramtr prturbation and nois, actually, it implicats th thought of dcoupling whn th fuzzy ruls is institutd, this wakns th influnc of coupling to som xtnt. Tabl 2 Control rsults output Th hardwar dsign of th nod Th Diagram of th nod hardwar function is shown in Fig C196 micro-computr is th control cntr of th nod. Th micro-computr has many charactristics, such as rliabl prformanc, high intgrity, and its word-lngth, opration spd, instruction systm and intrruption function could satisfy th nds of fuzzy control. CPU priphral chip adopts PSD311 programmabl chip, it has 32kEPROM and programmabl gat array insid th chip, and maks th whol systm has th charactristics of compact structur and programming flxibility. 12 bit A/D convrtr with high prcision and pr-multiplxr. 423

4 Monitoring machin Controlling machin Intrfac circuit Driv intrfac of optical-lctrical isolation LED display in small kyboard 80C196 Singl chip mocro compu tr PSD 311 A/D Conditioning circuit Tmpratur snsor Humidity snsor Light intnsity snsor Fig. 3 Diagram of nod Whn th nod works, th snsor convrts th grnhous nvironmntal paramtrs to lctrical signal, thn snds to conditioning circuit, aftr th tratmnt of amplification and linarization, it is inputtd into Micro-computr by A/D convrtr, compars th masurd tmpratur with its st valu, th dviation and chang rat is figurd out, thn call th program of fuzzy control algorithm, th output of controlld variabl is gaind by fuzzy controllr, aftr photolctric isolation, th controlld variabl driv th xtrnal quipmnt by driving circuit and rgulats th tmpratur in grnhous automatically. Manwhil, for th micro-computr, th data of nvironmntal paramtrs and th valu of tim providd by ral-tim clock is stord in NVRAM vry 5min, and th capacity of NVRAM is 32 k byts, it can stor 72h` s history data; Th charactristic of NVRAM is th data will not b lost whn powr off. So, at th innr of NVRAM, bsids storing th history data, it stors th st valu of all paramtrs to guarant th systm still running according to th original st valu whn powr supply coms back. Th kyboard and display constitut input and display board, and ar usd to raliz th ral-tim display of nvironmntal paramtrs and th input of paramtr sttings. Th output circuit adopts th srial transmission mod, th lin can b savd and it is convnint for isolation. By mans of photolctric isolation, it can liminat intrfrnc from xtrnal circuit ffctivly. In ordr to improv th rliability, th circuit adopts optically coupld isolation, morovr, th controllr taks som masurs: (1) adopting softwar watchdog and hardwar watchdog; (2) providing powr supply for micro-computr with prcision DC/DC convrtr; (3) adopting hybrid softwar digital filtr to supprss priodic and pulsd intrfrnc. Humidity snsor, light intnsity snsor and CO 2 snsor ar addd in th nod, and so th nod of diffrnt paramtrs can b constitutd. This is shown in th dashd-lin fram in Fig Composition of grnhous control systm Th structur of grnhous control systm which is composd of control nods is shown in Fig. 4. PC computr, as th cntr of monitoring and control systm, can raliz th managmnt of svral grnhous nvironmntal paramtrs: sub-sctional stting and ral tim monitoring for th nvironmntal paramtrs; storing, display, analyzing and printing th historical data; managing th quipmnt statu in grnhous and providing it to th controllr; th stting of th control paramtr of control algorithms can b mad. Th connction btwn PC and th controllr adopts RS-485 communication protocol, th rang of RS-485 communication protocol is mor than 1km,th numbr of Monitoring cntr computr (PC) RS-485 Nod 1 Nod 2 Nod n Fig. 4 Diagram of control systm 424

5 nods can rach 256, so it can administr multipl grnhous control nods. 4 Conclusion Bcaus of th divrsity of grnhous structur and th complxity of its surrounding nvironmnt, it is difficult to st up accurat mathmatical modls, thrfor, th prcision control can not b ralizd with traditional or modrn control mthod. According to th practical rquirmnt, this papr dvlops th fuzzy controllr basd on micro-computr, th systm nds not th prcis mathmatical modl of th controlld objct, and has strong robustnss. Consquntly, it is th propr mthod to control th tmpratur of th grnhous nvironmnt. Th tmpratur control nod has many advantags, such as convnint installation, asy dbugging, tc. By practical work in many grnhouss, th rsults prsnt it runs wll, so, it has a bttr practicality and dsrvs to hav mor widsprad application. Rfrnc [1] Zhang Zngk, Application of Fuzzy Mathmatics to Automatic Tchnology[M], Bijing: Tsinghua Univrsity Prss,1996 [2]Zhang Wiguo, Yang Xiangzhong, Thory and Application of Fuzzy Mathmatics [M], Xi An:Northwstrn Polytchnical Univrsity Prss, 2004 [3]Rn Zhnhui, Zhang Shuguang, Xi Jingxin, Dvlopmnt of Intllignt Monitoring and Managing Systm of Environmnt Paramtrs for Solar Grnhous [J]. Transactions of th Chins Socity of Agricultural Enginring, 2001, 17(2): [4] Xi Songh, Gan Yong, Dsign and Application Exampls of Fuzzy Controlling Systm on Singl-chip Computr[M], Bijing: Publishing Hous of Elctronics Industry,