Dieu Khien Nhiet Do Lo Nhiet Bang PID

IU KHIN NHIT L NHIT BNG PHNG PHP PID

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B GIO DC V O TO I HC S PHM K THUT TP H CH MINH

KHOA: IN- IN T

N MN HC

ti : iu khin nhit l nhit bng phng php PID

GVHD: Ts. Ng Vn Thuyn

Tp.H Ch Minh Thng 01 nm 2010



NHN XT CA GING VIN HNG DN



Mc Lc Trang

A. Gii thiu chung 1.iu khin nhit 4

2. Phng php iu khin PID 4

B. Ni dung I.Vi iu khin PIC 16F877A 4

1.c tnh ni bt ca vi iu khin 2.Kh nng ca b vi iu khin ny 5 3. Cc t tnh ni bt ca thit b ngoi vi trn chip 5 4.S v chc nng cc chn Pic 16F877A 6 5.S khi b vi iu khin Pic 16F877A 8 6. Cc thanh ghi c chc nng c bit 8 7.X l ADC 13

II.Cm bin nhit LM35 15 III.LCD 16x2 16 IV.Phng php iu khin PID 18

V. Giao tip gia my tnh v vi iu khin. 31

VI.S kt ni phn cng 34

VII.Lu gii thut 35

C. Kt lun Ph lc

1.Chng trnh C



A.GII THIU CHUNG

1.iu khin nhit

Vn iu khin v gim st nhit c s dng trong nhiu lnh vc sn xut khc nhau nh: iu khin l p trng g, vt ca b con nng dn hay iu khin v gim st nhit ca l hi.iu quan trng l nhit phi n nh

v s chnh xc tng i.S dng phng php iu khin PID c th m bo cc tiu ch v k thut v kinh t ca nh sn xut yu cu.

2.Phng php PID

Ngy nay, vi s pht trin vt bc ca khoa hc cng ngh, nhng phng php iu khin thng thng khng kh nng p ng nhng yu cu ngy cng kht khe hn ca nhng ng dng. Ngi ta bt u p dng nhiu gii thut iu khin khc nhau nh gii thut PID, Fuzzy logic (iu khin m), mng n ron v thu c nhng kt qu kh quan.Thut ton PID c p dng rng ri trong hu ht cc h thng iu khin t ng t c, nhit, lu cht n in. PID kt hp 3 thut ton t l, tch phn, vi phn; l b iu khin khng c sai lch, khu I b v gim cc dao ng loi b sai s dch chuyn, v gim thi gian tr nh khu D

B.NI DUNG : I.Vi iu khin PIC 16F877A

1.c tnh ni bt ca vi iu khin S dng cng ngh tch hp cao RISC CPU. Ngi s dng c th lp trnh vi 35 cu lnh n gin. Tt c cc cu lnh u c thc hin trong mt chu k ngoi tr mt s

lnh r nhnh c thc hin trong 2 chu k lnh.

Tc hot ng l: -Xung ng h vo DC 20MHz. -Chu k thc hin trong 200ns.

B nh chng trnh flash 8Kx 14words. B nh Ram 368x8bytes. B nh EFPROM 256x8 bytes.



2.Kh nng ca b vi iu khin ny Kh nng ngt: ln ti 15 ngun ngt trong v ngt ngoi. Ngn nh Stack c phn chia lm 8 mc. Truy cp b nh bng a ch trc tip hoc gim tip Ngun khi ng li (POR). B to xung thi gian(PWRT) v b to dao ng (OST). B m xung thi gian(WDT) vi ngun dao ng trn chip ngun dao

ng (RC) hot ng ng tin cy. C mch chng trnh bo v. Phng thc ct gi SLEEP.

C bn la chn dao ng cng ngh CMOS FLASH/EFPROM ngun ma thp , tc cao

Thit k hon ton tnh.

Mch chng trnh ni tip c hai chn.

X l c/ghi ti b nh chng trnh. Di in th hot ng rng 2V n 5.5V. Ngun s dng hin ti 2.5mA. Cng sut tiu th:



Ch bt gi vi 16 bit, vi tc 12,5ns, ch so snh vi 16 bit vi tc x l cc i l 200ns, ch iu ch rng xung vi 10 bit. B chuyn i tin hiu s sang tng t vi 10 bit.

Cng truyn thng ni tip SSP v SPI phng thc ch v I2C ( ch/ph). B truyn nhn thng tin ng b, d b (USART/SCR) c kh nng pht hin 9 bit a ch . Cng ph song song PSP vi 8 bit m rng vi RD , WR , CS iu khin.

4.S v chc nng cc chn Pic 16F877A



5.S khi b vi iu khin Pic 16F877A

6. Cc thanh ghi c chc nng c bit a) Thanh ghi trng thi Status:

- Bit 7_IRP:Lm nhim v nh a ch gin tip cho Ram ni RP=1 bank 2 v bank 3 IRP=0 bank 0 v bank 1 (a ch t 00 -> FFh)

- Bit 6,5_RP1 v PB0: 2 bit ny dng chn bank thanh ghi 00 = Bank 0 ; 01 = Bank 1; 10 = Bank 2; 11= Bank 3 - Bit 4_TO (time_out):bit ny c set ln 1 khi WDT b trn 1 = Cha trn ; 0 = B trn

- Bit 3_PD (power_down bit):bit ny c set mi khi vi iu khin c cp ngun,bt u chy,khi Reset - Bit 2_Z (zero bit):Dng ch kt qu ra 0,c set mi khi kt qu tr v ca 1 php ton s hc hay lun l



c gi tr bng 0 - Bit 1_DC (digit carry):c set khi ta tr s nh hn cho s ln hn,reset nu ngc li. - Bit 0_Carry:bi nh hng bi cc lnh ADDWF, ADDLW, SUBLW, SUBW

b) Thanh ghi iu khin ngt (INTCON): Thanh ghi INTCON c truy xut bng cch chn Bank tng ng.N c

chc nng cho php ngt hoc cm ngt v xc nh cc nguyn nhn ngt

- Bit 7 _ GIE (global interrup enable bit): Bit cho php hay khng cho php ngt

GIE = 1 cho php cc ngt thc hin

GIE = 0 khng cho php ngt

- Bit 6_EEIE (Eeprom write complete interrup enable bit):bit cho php gy ra ti ni kt thc ca vic vit chng trnh con vo Eeprom

- Bit 5_TOIE(TMR0 overfow interrup enable bit):cho php kch hot ngt gy ra bi s trn TMR0 - Bit 4_INT (INT internal interrup enable bit):cho php ngt xy ra ti ngt ngoi ca chn RB0/INT

- Bit 3_RBIE (RB port change interrup enable bit):cho php ngt xy ra khi c s thay i trng thi trn cc chn RB4 n RB7. - Bit

2_T0IF(TMR0 overflow interrup flag bit):c bo trn ca TMR0,bit ny c xa bng phn mm ngt tip theo xy ra. - Bit 1_INTF(INT internal interrup flag bit):C bo xy ra ngt ngoi. - Bit 0_RBIF(RB port change interrup flag bit):bit xc nh s thay i trn chn RB4 n RB7,bit ny c xa trong chng trnh ngt



SS kkhhii ccaa TTIIMMEERR 00

- L mt b timer 8 bit,gi tr n tng t 0 ->255,sau khi m n 255 t reset v cho m li. Thi im m t 255 v 0, bit TOIF trong thanh ghi INTCON c set ln 1. Nu ngt c xy ra th con tr

chng trnh s nhy n chng trnh con phc v ngt. Bn cnh vic

nhn xung ni,gi tr ca Timer c th tng ln nh vic nhn xung t

bn ngoi qua chn RA4/TOCK1,khi Timer hot ng nh mt b m

- Bit TMR0IE l bit iu khin ngt ca TIMER 0 - Mun cho TIMER 0 hot ng ch timer ta Clear bit TOCS - Mun cho TIMER 0 hot ng ch counter ta set bit TOCS S khi v nguyn l hot ng ca TIMER1



- TIMER 1 l b nh thi 16 bits,c ngt l bit TM1RIF(PIR1) - TIMER 1 cng c 2 ch hot ng: timer hoc counter

- Vic la chn ch timer hay counter ph thuc vo bit TMR1CS (T1CON) - TIMER1 c chc nng Reset Input iu khin bi khi CCP

- TIMER1 cn c chc nng m ng b hoc bt ng b iu khin bi bit T1SYNC

S khi v nguyn l

hot ng ca TIMER2

- L b nh thi 8 bit v c h tr bi 2 b chia tn Bit cho php ngt TMR2ON(t2con), c ngt l bit TMR2IF (PIR1) . -T s chia tn s 1:1,1:4 v 1:16 c iu khin bi 2 bit T2CKPS1: T2CKPS0

- Ng ra vi 2 mc chia tn 1:1 v 1:16 iu khin bi 4 bit T2OUTPS3: T2OUTPS0

S khi v nguyn l hot ng ca CCP



-

CCP (capture/compare/PWM) hot ng nh xung m cung cp bi cc b m TIMER1 v TIMER2 - ch PWM,tn hiu sau khi iu ch a ra cc Pin CCP - Thit lp chu k xung a gi tr vo PR2

- Thit lp rng xung a gi tr vo CCPRL

- iu khin Pin CCP output bng cch Clear bit tng ng trong thanh ghi TRISC - Thit lp gi tr b chia tn s - Thit lp gi tr b chia tn s

c) Thanh ghi OPTION_REG

-Bit 7_RBPU (Port B Pull up enable bit):bit kch hot hay tt in tr ni ko ln ca Port B



1 = kch hot

0 = v hiu

-Bit 6_INTEDG (interrup edge sellect bit):Nu c s kin ngt xy ra,bit ny s xem xt tn hiu thay i cnh ln hay cnh xung 1 = cnh ln

0 = cnh xung

-Bit 5_ T0CS(TMR0 clock source sellect bit):xc nh xung kch bn trong hay bn ngoi b dao ng. 1 = xung bn ngoi 0 = xung bn trong -Bit 4_T0SE (TMR0 source edge sellect bit):nu s dng xung bn ngoi thi TMR0 tng ln bng xung cnh ln hay cnh xung 1 = cnh xung

0 = cnh ln

-Bit 3_PSA: xc nh t l gia WDT v TMR0

1 = t l gn cho WDT

0 = t l gn cho TMR0

-Bit 2,1,0_SP2,SP1,SP1:xc nh thi gian mi ln tng ca WDT hay TMR0

7.X l ADC



-PIC16F877 c 8 chn x l ADC vi nhiu cch thc khc nhau. dng ADC bn phi khai bo #DEVICE cho bit dng ADC my bit ( ty chip h tr thng l 8 hay 10 bit).

Cc hm phc v ADC:

a.Setup_ADC (mode): -Dng xc nh cch thc hot ng b bin i ADC. Tham s mode ty thuc file thit b (*.h), c tn tng ng tn chip bn ang dng, nm trong th mc DEVICES ca CCS. Mun bit c bao nhiu tham s dng cho chip bn m file tng ng c, tm ti ch cc dnh ngha cho chc nng ADC dng cho chip tng ng vi hm ny. Sau l cc gi tr mode ca 16F877. b. Setup_ADC_port (value) -Xc nh chn ly tn hiu analog v in th chun s dng. Ty thuc b tr chn trn chip s chn v chn no dng cho ADC v s chc nng ADC mi chip m value c th c nhng gi tr khc nhau.

c. Set_ADC_channel:

-Chn chn c vo gi tr analog bng lnh read_adc(). Gi tr channel ty s chn chc nng ADC mi chip, vi 16F877 channel c gia tr t 0-7:

0-chn A0

1-chn A1

2-chn A2

3-chn A3

4-chn A5 5-chn E0 6-chn E1 7-chn E2



-Hm khng tr v tr nn delay 10us sau hm ny ri mi dng ham read_adc m bo kt qu chnh xc. Hm ch hot ng vi A/D phn cng trn chip.

d.read_adc(mode): -Dng c gi tr ADC t thanh ghi cha kt qu bin i ADC. Nu gi tr ADC l 8bit nh khai bo trong #DEVICE gi tr tr v ca hm l 8 bit, ngc li l 16 bit nu khai bo #DEVICE s dng ADC 10 bit tr ln. Khi dng hm ny n s ly gi tr ADC t chn bn chn trong hm set_adc_channel() trc .

II. Cm bin nhit LM35 y l cm bin nhit c tch hp chnh xc cao ca hng National Semiconductor. in p u ra ca n t l tuyn tnh vi nhit theo thang

Celsius. in p ng ra thay i 10mv (in p bc) cho mi s thay i 10C. Chng khng yu cu cn chnh ngoi.

- Chn 1: V+

- Chn 2: Vout

- Chn 3: V-



IIIIII.. LLCCDD

Chn K hiu I/O M t 1 Vss(GND) - t 2 Vcc - Ngun dng 5V

3 VEE(V0) - Ngun cp iu khin 4 RS I RS=0 chn thanh ghi lnh, RS=1

chn thanh d liu

5 R/W I R/W=1 c d liu, R/W=0 ghi d liu

6 E I/O Cho php

7 D0..D7 I/O Cc bit d liu



1.Chn Vcc, Vss, VEE :

Cp ngun dng 5V,t tng ng v iu khin tng phn ca LCD. 2. Chn chn thanh ghi RS: (register select) RS=0 thanh ghi m lnh c chn cho php ngi dng gi mt lnh chng hn nh xa mng hnh,a con tr v u dng v.v RS=1 th thanh ghi d liu c chn cho php ngi dng gi d liu cn hin th trn LCD. 3. Chn c ghi (R/W): u vo c/ghi cho php ngi dng ghi thng tin ln LCD khi R/W=0 hoc c thng tin t n khi R/W=1.

4. Chn cho php E (Enable): Chn cho php E c s dng bi LCD cht thng tin hin hu trn chn d liu ca n. Khi d liu c cp n chn d liu th mt xung mc cao xung thp c p n chn ny LCD cht d liu trn cc chn d liu. Xung ny phi rng ti thiu l 450ns. 5. Chn D0..D7: y l 8 chn d liu 8bit. c dng gi thng tin ln LCD hoc c ni dung ca cc thanh ghi trong LCD. hin th cc ch ci v cc con s th bt RS=1. Cng c cc lnh m c th gi n LCD xa mng hnh hoc a con tr

v u dng hoc nhap nhy con tr. Chng ta c th s dng RS=0 kim tra bit c bn xem LCD c sng sng nhn thng tin. C bn l D7 v c th c khi R/W=1 v RS=0 nh sau: Nu R/W=1,RS=0 khi D7=1(c bn 1) th LCD bn bi cc cng vic bn trong v s khng nhn bt k thng tin mi no. Lu chng ta nn kim tra c bn trc khi ghi thng tin mi no ln LCD.



IV.Phng php iu khin PID Ngy nay, vi s pht trin vt bc ca khoa hc cng ngh, nhng

phng php iu khin thng thng khng kh nng p ng nhng yu

cu ngy cng kht khe hn ca nhng ng dng. Ngi ta bt u p dng nhiu gii thut iu khin khc nhau nh gii thut PID, Fuzzy logic (iu khin m), mng n ron v thu c nhng kt qu kh quan.

1. L thuyt iu khin t ng L thuyt iu khin t ng c th phn thnh 3 loi theo lch s pht

trin ca n, bao gm: iu khin kinh in, iu khin hin i v iu khin thng minh.

a. iu khin kinh in (classical control) L thuyt iu khin kinh in m t h thng trong min tn s (php

bin i Fouier) v mt phng s (php bin i Laplace). L thuyt ny ch yu p dng cho h tuyn tnh bt bin theo thi gian, mc d cng c mt s m rng p dng cho h phi tuyn. L thuyt iu khin kinh in thch hp thit k h thng mt ng vo mt ng ra, rt kh p dng cho nhng h thng nhiu ng ra v cc h thng bin i theo thi gian.

Cc phng php phn tch v thit k trong l thuyt iu khin kinh in gm c phng php Nyquist, phng php Bode v phng php qu o nghim s. Theo phng php Nyquist v Bode, cn m t h thng di dng p ng tn s (p ng bin v pha). Trong phng php qu o nghim s, h thng cn c m t theo hm truyn. Hm truyn cng c th tnh c t

p ng tn s. Vic m t chnh xc c tnh ng hc bn trong h thng l khng cn thit vi cc phng php thit k kinh in, ch c quan h gia ng

vo v ng ra l quan trng.



Cc khu hiu chnh n gin nh hiu chnh vi tch phn t l (PID), hiu chnh sm tr pha thng c s dng trong cc h thng iu khin kinh in. nh hng ca nhng khu hiu chnh ny n biu Nyquist, biu Bode v qu o nghim s c th thy d dng, nh c th d dng la chn c khu hiu chnh thch hp.

b.iu khin hin i (modern control) K thut thit k h thng hin i da trn min thi gian. M t ton

hc dng phn tch v thit k h thng l phng trnh trng thi. M hnh khng gian trng thi c u im l m t c c tnh ng hc bn trong h thng (cc bin trng thi) v c th d dng p dng cho h thng bin i theo thi gian.

B iu khin c s dng ch yu trong thit k h thng hin i l b iu khin hi tip trng thi. Ty theo cch tnh vector hi tip trng thi m ta

c phng php phn b cc, b iu khin ti u, iu khin bn vng Vi s pht trin ca l thuyt iu khin s v h thng ri rc, l thuyt

iu khin hin i rt thch hp thit k cc b iu khin l cc chng trnh phn mm chy trn vi x l v my tnh s. iu ny cho php thc thi cc b iu khin c c tnh ng hc phc tp hn cng nh hiu qu hn so vi cc

b iu khin n gin nh PID hay sm tr pha trong l thuyt iu khin kinh in.

c.iu khin thng minh (intelligent control) iu khin kinh in v iu khin hin i gi chung l iu khin thng

thng (conventional control), c khuyt im l thit k c h thng iu khin cn phi bit m hnh ton hc ca i tng. Trong khi , thc t c nhng i tng iu khin rt phc tp, rt kh hoc khng th xc nh c

m hnh ton hc. Cc phng php iu khin thng minh nh iu khin m,



mng n ron nhn to, thut ton di truyn m phng / bt chc cc h thng thng minh sinh hc, v nguyn tc khng cn dng m hnh ton hc thit k h thng, do c kh nng ng dng thc t rt ln.

Khuyt im ca b iu khin m l qu trnh thit k mang tnh th sai, da vo kinh nghim ca chuyn gia. Nh kt hp logic m vi mng n ron nhn to hay thut ton di truyn m thng s b iu khin m c th thay i thng qua qu trnh hc hay qu trnh tin ha, nh vy khc phc c nhng

khuyt im th sai. Hin nay, cc b iu khin thng thng kt hp vi cc k thut iu khin thng minh to nn cc b iu khin lai iu khin cc h thng phc tp vi cht lng rt tt.

2. L thuyt iu khin PID Cc b iu khin s ngy nay rt thng dng trong h thng iu khin

cng nghip. Nhng c trng ni bt ca vi x l nh t hiu chnh, iu khin a bin v h chuyn gia cng kh nng giao tip bus v mng cc b a n vic n c s dng ngy cng nhiu trong cc b iu khin s. B iu khin s dng trong h thng iu khin vng kn gm cc ch iu khin t l P, iu khin tch phn t l PI, vi phn t l PD, vi tch phn t l PID.

i vi h thng d tr n nh ln, ta ch cn tng h s khuch i ca lut iu khin t l P.

Lut iu khin tch phn cn gi l iu khin chm sau v sai s iu

khin c tch ly cho n khi ln th quyt nh iu khin mi c a

ra. H thng s khng c sai lch tnh khi tn hiu vo l hm bc thang n v v hng s thi gian tch phn TI c chn khc 0.

Tng kh nng tc ng nhanh ca h, gim bt thi gian qu iu chnh bng cch thay i hng s thi gian ca lut iu khin vi phn TD cn c gi l iu khin vt trc.



B iu khin PID l mt phn t khng th thiu trong cc qu trnh t

ng khng ch nhit , mc, tc Ngay c khi l thuyt iu khin hin i c s dng, th s kt hp gia cc phng php iu khin hin i v b iu khin PID kinh in vn em li nhng hiu qu bt ng.

i vi nhng h thng thay i theo thi gian, nhng thng s ca b iu khin PID phi c hiu chnh thng xuyn cho ph hp vi nhng thay

i khng bit trc ca h thng cng nh mi trng ngoi. p ng c iu th mi c th m bo c nhng yu cu lm vic ca h thng. Nu nh ta t ng ha c vic thay i nhng thng s ny, b iu khin PID s l b iu khin bn vng vi mi thay i ca h thng cng nh nhng tc ng ca mi trng bn ngoi.

Cc khu trong b iu khin PID B iu khin PID bao gm cc khu t l, vi phn v tch phn to thnh

cc b iu khin t l P, b iu khin vi phn t l PD, b iu khin tch phn t l PI v b iu khin vi tch phn t l PID.

o B iu khin t l P B iu khin loi ny to tn hiu ra iu khin u(t) t l vi sai lch

e(t). Cng gia tng t l th sai s to ra cng nh. iu ny khng c ngha l t l ( li) cng cao th cng tt, bi v khi li cng ln th khuynh hng dao ng ca bin iu khin cng tng. Do , cn c mt s dung ha sao cho li ln m khng to nn s dao ng.

Chng ta nhn thy rng khng th no loi tr hon ton c sai s, m

lun tn ti mt khong sai lch tnh, c gi l sai lch t l (propotional offset). ln ca sai lch tnh ny t l thun vi ln ca s thay i trn ti v t l nghch vi li. Do , b iu khin t l ch c dng khi li ln c th gim sai lch tnh n mc c th chp nhn c.

Tuy nhin, u im ca b iu khin t l l p ng ngay tc khc. Khng h c mt khong thi gian tr no k t khi xy ra s thay i trn ti



cho n khi c tn hiu ra iu khin. V vy, c th dng b iu khin t l cho nhng qu trnh c qun tnh nh.

Phng trnh trong min thi gian

u(t) = KP .e(t) Trong : KP gi l h s khuch i

e(t) l sai lch Hm truyn: GP (s) = KP

o iu khin tch phn I B iu khin tch phn to tn hiu iu khin bng mt lng t l vi

tch phn sai lch ca bin iu khin. V th, nu vn cn sai s th b iu khin vn cn lm vic; v to s thay i ca tn hiu ra t l vi tch phn

lch. Hnh bn di minh ha mi lin h gia sai lch v tn hiu ra ca h thng.

Sai lch v p ng ca b iu khin tch phn

B iu khin tch phn thng dng kt hp vi b iu khin t l nhm trit tiu sai lch tnh. Phng trnh trong min thi gian ca b iu khin tch phn c biu din nh sau:



( ) ( )u t K e t dtI= Hm truyn:

( ) 1( )( )

.

KU s IG sE s s T sI

= = =

Trong : I

I KT 1= gi l hng s thi gian tch phn

o B iu khin vi phn D B iu khin vi phn to tn hiu ra iu khin da trn tc thay i

ca sai lch. S thay i ny c th l do gi tr bin iu khin thay i, thay i im t hoc c hai. iu khin vi phn chng li sai lch bng cch xem n thay i nhanh nh th no, v dng tc thay i to tn hiu iu khin nhm lm gim sai lch. Hnh bn di minh ha p ng ca b iu khin vi phn theo sai lch ca bin iu khin.

Sai lch v p ng ca b iu khin vi phn

Trong mi khong thi gian, u ra ca b iu khin vi phn t l vi dc (tc thay i) ca tn hiu sai lch. Da vo th ta c th nhn nh rng, khng bao gi c b iu khin vi phn l tng trong thc t. Khi hm



nc xut hin, dc ca tn hiu ra l v cng. iu ny c ngha l p ng ca b iu khin vi phn l tng phi thay i vi ln l v cng. Trong thc t, tc thay i ca b iu khin c mt gii hn ca n. y li l mt u im bi v n s lm gim iu khin vi nhng loi nhiu thng gp trong thc t ( cng l l do m nu c b iu khin l tng th cng khng nn dng).

Tuy nhin, b iu khin vi phn khng bao gi c s dng n l. Nguyn nhn l u ra ca b iu khin ch thay i khi sai lch thay i. Ngha l, nu sai lch ln m khng thay i th b iu khin vi phn cng khng lm g c, chp nhn sai lch . Do , n thng c dng vi b iu khin t l P hoc b iu khin tch phn t l PI.

Phng trnh trong min thi gian c m t nh bn di:

( )( ) Dde ty t K

dt=

Hm truyn:G(s) = KD .s o B iu khin tch phn t l PI

B iu khin tch phn t l PI l s kt hp gia b iu khin t l v b iu khin tch phn nhm mc ch trit tiu sai lch t l nh ni trn. Trong khi b iu khin t l to tn hiu ra t l vi sai lch th b iu khin vi phn to tn hiu ra t l vi tch phn ca sai lch. Do c tnh ca b iu khin tch phn, sai lch tnh ca h thng s c loi tr. Nghch o ca KI

chnh l khong thi gian cn thit b iu khin tch phn to ra s thay i u ra bng vi s thay i to ra bi b iu khin t l. Hnh bn di minh ha p ng ca b iu khin tch phn t l theo sai s ca bin iu khin.



p ng ca b iu khin tch phn t l PI

B iu khin t l tch phn c u im trit tiu sai lch nh thm b iu khin tch phn vo b iu khin t l. Tuy nhin, vic thm khu tch phn vo cng c nhc im lm gia tng khuynh hng dao ng ca bin iu khin. Do , cn phi gim h s t l i, iu lm h thng p ng chm

hn so vi ban u. Nu qu trnh c tr ln, tn hiu sai lch nhn c s khng phn nh ng sai lch tht s. Nguyn nhn l do tr ny s lm cho p ng ca h thng khng cn ng vi sai lch hin ti, ngha l h lm

vic trn tn hiu c.

Phng trnh trong min thi gian:

( ) . ( ) . ( ).0ty t K e t K e t dtP I= +

Hm truyn:

1 . 1( ) (1 ). .

T sK NIG s K K KP P Ps T s sTN N

+= + = = +

o B iu khin vi phn t l PD B iu khin vi phn thng c kt hp vi b iu khin t l nhm

lm gim khuynh hng dao ng v cho php nng cao li. Trong , b



iu khin t l thay i u ra t l vi ln ca sai lch, cn b iu khin vi phn thay i u ra t l vi tc bin i ca sai lch, tc l b iu khin vi phn tnh trc gi tr tng lai ca sai lch v thay i u ra tng ng vi s

tnh ton . Chnh iu ny gip b iu khin vi phn rt tin dng trong qu trnh iu khin c ti thay i bt ng.

B PD l tng l cu trc ghp song song gia c cu t l v c cu vi phn. Tn hiu ra ca b iu khin PD l tng tn hiu ra ca tng b iu khin ring l. Phng trnh theo min thi gian c m t nh bn di.

( )( )( ) ( ) ( ) de tde tu t u u K e t K K e t TVP D P D P dtdt

= + = + = +

Hm truyn:

( ) (1 . )G s K sTP V= + o B iu khin vi tch phn t l PID

B iu khin vi tch phn t l PID bao gm c ba b iu khin vi phn, tch phn v t l. Nh , b iu khin PID kt hp c tt c nhng u im ca c ba b iu khin: t l gip sai lch b, tch phn loi b sai lch tnh, vi phn gim khuynh hng dao ng.

B PID l tng l cu trc ghp song song ba b iu khin tch phn, vi phn v t l. Phng trnh theo min thi gian ca b PID l tng c trnh by bn di.

( )( ) ( ) ( ) de tu t K e t K e t dt KP I D dt= + +

Hay:

( )( ) ( ) ( )K K de tI Du t K e t e t dtP K K dtP P

= + +



Trong :

KP l h s khuch i ca b PID KI l tc tch phn, hay h s tch phn (s-1) KD l h s vi phn, hay hng s thi gian vi phn

1KIK TP N

= vi TN gi l thi gian hiu chnh

KD TVKP= gi l thi gian tc ng sm

Hm truyn:

21 . . .1( ) 1 .. .

T s T T sN N VG s K T s KP V PT s T sN N

+ + = + + =

hoc:

( )( ) ( )KU s IG s K K sP DE s s

= = + +

u im ca b iu khin PID:

Sai lch e(t) cng ln, tn hiu iu chnh u(t) cng ln nh vai tr khuch i KP

Sai lch e(t) cha bng 0, b iu khin PID vn cn to tn hiu iu chnh nh thnh phn tch phn KI

S thay i ca sai lch cng ln, phn ng thch hp ca u(t) s cng nhanh nh thnh phn PD

B iu khin PID c ng dng nhiu trong cc h thng t ng i hi tnh n nh, chnh xc v tc p ng m nhng b iu khin thng thng khng th thc hin c nh: n nh tc ng c v tr, h thng l

nhit, iu khin mc, lu lng, cng ngh robot



2.Thut ton PID s C nhiu kiu iu khin khc nhau c th p dng cho h ri rc. Cch iu

khin thng dng trong cng nghip l hiu chnh ni tip vi b PID s. Thit k b iu khin PID s l xc nh hm truyn vi cc thng s ti u ca b PID s h thng tho mn yu cu v n nh, thi gian qu , sai s xc lp. T

thut ton ta xy dng phng trnh sai phn v vit hm truyn th hin quan h ng vo ng ra ca

Xut pht t m t ton hc ca h lin tc:

( ) ( ) ( ) ( )( ) ( )

dtdeKdtteKteK

tutututu

D

T

IP

DIP

++=

++=

0

Khi chuyn sang m hnh ri rc th u(t) thay bng uK=u(k) Dk

Ik

Pkk uuuu ++=

a. Khu t l ( ) ( )teKtu PP = c thay bng:

B iu khin t l sinh ra hnh ng iu khin

t l vi sai lch.

kPPk eKu =

Khi tng Kp s cho php gim sai lch, gim thi

gian tng trng nhng vt l tng, do tng tn s dao ng v thi gian qu .



b .Khu tch phn ( ) ( )dtteKtuT

o

II = c thay

bng :

TeeKuuIk

Ik

IIk

Ik 2

11

++=

B iu khin tch phn sinh ra hnh ng iu

khin lin tc tng khi tn hiu sai lch vn cn.

Khi tng Ki s cho php gim nhanh thi gian tng

trng, h thng p ng nhanh, tuy nhin vt

l tng d dn n dao ng ca h thng. S tn ti ca thnh phn Ki s cho php loi b hn sai s.

C. Khu vi phn ( ) ( )dt

tdeKtu DD = c thay bng sai phn li

TeeKu kkD

Dk

1=

B iu khin vi phn sinh ra hnh ng iu khin t l vi tc bin i ca tn hiu sai lch .Mc d khu vi phn khng nh hng n sai s nhng khi tng Kd s gim c vt l v thi gian qu

nh hng ca s tng cc thng s Ki,Kp,Kd n p ng ng ra c tng kt bng sau:



p ng ca h

thng

Rise time Over shoot Setting time Steady-state error

Kp Gim Tng t thay i Gim

Ki Gim Tng Tng Trit tiu

Kd t thay i Tng Gim t thay i

Cc khu P,I,D hiu chnh trc tip v ng thi sai s trong h thng iu khin kn.

Ngoi ra cn c th hiu chnh PID trn ng tn hiu phn hi



V.Giao tip gia my tnh v vi iu khin.

1.Chun truyn thng ni tip RS 232

RS-232 l mt trong nhng chun truyn thng c s dng ph bin hin nay bn cnh hai chun truyn thng khc l RS-442 v RS-485. Lc u, RS-232 c xy dng ch yu phc v trong ghp ni im im gia hai thit b u cui (DTE Data Terminal Equipment), chng hn nh gia hai my tnh, gia my tnh v my in, my tnh v modem

ng truyn RS 232

Ngy nay, mi my tnh c nhn u c mt hoc mt vi cng ni tip theo

chun RS-232 (cng COM), c th s dng kt ni vi cc thit b ngoi vi hoc cc my tnh khc. Nhiu thit b cng nghip cng tch hp cng RS-232 phc v cho cng vic lp trnh hoc tham s ha.

2.Cu to cng RS-232 (cng COM) Cng RS-232 c ba loi gic cm khc nhau: dng 9 chn DB 9, dng 25 chn

DB 25, v dng 26 chn ALT A. Trong , hai dng DB 9 v DB 25 c s dng ph bin hn. Trong n ny, loi DB 9 c s dng v n kh ph bin v c h tr cho hu ht cc my tnh ngy nay. S chn v ngha cc chn c trnh by bn di.

TxD (Transmit Data): ng gi d liu RxD (Receive Data): ng nhn d liu

DTE

DTE MODEM (DCE)

MODEM (DCE)

VIN THNG

NG RS-232



RTS (Request To Send): Yu cu gi; b truyn t ng ny ln mc hot ng khi sn sng truyn d liu.

CTS (Clear To Send): Xo gi; b nhn t ng ny ln mc hot ng thng bo cho b truyn l n sn sng nhn d liu.

Cu to cng COM

DSR (Data Set Ready): D liu sn sng; tnh hot ng ging vi CTS nhng c kch hot bi b truyn khi n sn sng nhn d liu.

SG (Signal Ground): t ca tn hiu. DCD (Data Carrier Detect): Pht hin tn hiu mang d liu. DTR (Data Terminal Ready): u cui d liu sn sng; tnh hot ng

ging vi RTS nhng c kch hot bi b nhn khi mun truyn d liu.

3.Ch lm vic

Ch lm vic ca h thng RS-232 l hai chiu ton phn (full duplex), tc l hai thit b tham gia u c th thu pht tn hiu cng mt lc. Nh vy, vic truyn

DSR Data Set Ready RTS Request To Send CTS Clear To Send RI Ring Indicator

DCD

RxD

TxD

DTR

GND

DSR

RTS

CTS

RI

DCD Data Carrier Detect RxD Receive Data TxD Transmit Data DTR Data Terminal Ready

DCD RxD

TxD

DTR

GND DSR RTS CTS

(a) S gic cm (b) S chiu tn hiu



thng cn ti thiu l 3 dy dn; trong , hai dy tn hiu ni cho cc u thu pht ca hai trm v mt dy t, nh minh ha hnh bn di. Vi cu hnh ti thiu ny, vic m bo an ton(chnh xc) truyn dn tn hiu ph thuc trch nhim ca phn mm.

TxD RxD RTS CTS DTR DSR GND




Transmit Data Receive Data

Request To Send Clear To Send

Data Terminal Ready Data Set Ready

Ground

b) Ch bt tay a) Cu hnh ghp ni ti thiu

Cu hnh ghp ni theo chun RS 232

Chng trnh truyn nhn tn hiu c vit da trn phn mm VB. My tnh thu nhn d liu (gi tr lc theo thi gian) do ngi dng nhp vo, ri truyn xung cho vi iu khin PIC qua chn TxD. Sau , d liu c nhn v t chn RxD s c x l v hin th ln mn hnh ha so snh, cho thy p ng ca h thng.



VI.S kt ni phn cng 1.Mch iu khin

Mch iu khin bao gm : B dao ng thch anh c ni vo 2 chn 13,14 ca vi iu

khin. Cm bin LM35 vi u ra c ni vi chn RA0 Mch ng lc c ni vi chn CCP1 LCD

2.Mch ng lc

Mch ng lc c ni vi chn ccp1 ca vi iu khin Hai transitor Q1 va Q2 dng kch dn cho opt ov ti.Ti l 1 n si t sinh nhit.Opto dung cch ly in p gia mch ng lc v mch iu khin mch khng b nhiu.



3.Module UART Vic truyn v nhn d liu vi my tnh c thc hin thng qua cng COM. IC MAX232 cho php chuyn i qua li gia hai chun TTL v RS232 khc nhau v mc in p quy nh mc logic.RS232 [0]: +3V >> +12V [1]: -12V >> -3V TTL [0]: 0V [1]: 5V

VII.Lu gii thut

Lu chng trinh:


Lu tnh ton P,I,D:


C.KT LUN V c bn n a ra c phng php iu khin bng PID.Tuy nhin cn nhiu hn ch .Nhm s c gng hon thin v a vo ng dng trong thc t i sng v sn xut.

PH LC Chng trnh CCS cho vi iu khin PIC

#define #include "16F877A.h" #device *=16 adc=8 #use delay(clock=20000000) #FUSES NOWDT, HS, NOPUT, NOPROTECT, NODEBUG, NOBROWNOUT, NOLVP, NOCPD, NOWRT #use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7) #include int8 read1,read2,m,thuc,dat_pc,dat=40,kp=100,kd=10,ki=2,error,pre_error; int16 P,I,D,sum,duty; #INT_RDA void serial_isr() {dat_pc=getc(); } void send_to_pc(int8 giatri) { printf("%2u\r",giatri); } void main () { set_tris_b(0); set_tris_a(0xFF); set_tris_d(0x00); set_tris_c(0x00); set_tris_b(0x00); // Khoi tao cho ngat ngoai enable_interrupts (INT_RDA); // ext_int_edge(H_TO_L); enable_interrupts (GLOBAL); //Khoi tao ADC setup_adc_ports(AN0_AN1_AN3); setup_adc(ADC_CLOCK_INTERNAL); delay_ms(50); // Khoi tao PWM setup_ccp1(ccp_pwm);


lcd_init(); Printf(LCD_putc,"\LOP 06118"); delay_ms(200); Printf(LCD_putc,"\fDO AN KI THUAT"); delay_ms(200); while(TRUE) { // m=(input_b()&0x01); // if(m=0x01)//Nhan cong tac Run // { set_ADC_channel(1);//Doc adc tu bien tro(nhiet do dat) // delay_ms(10); // read1=read_adc(); // dat=read1*0.1960784314; set_ADC_channel(0);//Doc ADC tu LM35 delay_ms(10); read2=read_adc(); thuc =read2*1.960784314; //Chuong trinh PID so error = dat-thuc; // tinh sai so P = KP*error; // tinh thanh phan ti le I = I+KI*(pre_error+error)/4; // thoi gian lay mau la 0.5s D = KD*(error-pre_error)*2; pre_error= error; // luu lai gia tri sai so truoc do sum = P+I+D; // tin hieu tong khi qua khau PID duty = sum; // cap nhat gia PID vao bo phat PWM if (duty>1023) duty=1023; // gia tri lon nhat cua thanh ghi PWM // if (error==0) // I=255; // duy tri nhiet do khi ngo ra dat yeu cau if (error

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Dieu Khien Nhiet Do Lo Nhiet Bang PID