Njira Zowongolera PID mu Automation
Mu dziko la makina odzipangira okha m'mafakitale, kusunga njira yokhazikika komanso yolunjika ndikofunikira kwambiri. Kaya kusunga kutentha kwa uvuni pamtengo winawake, kusunga mulingo wamadzimadzi mu thanki, kuwongolera liwiro la mota yotumizira, kapena kuwongolera kuthamanga kwa mpweya mu dongosolo la pneumatic - zonsezi zimafuna njira yodalirika yowongolera. Njira imodzi yomwe imagwiritsidwa ntchito kwambiri chifukwa cha kusavuta kwake, kugwira ntchito bwino, komanso kosavuta kuyigwiritsa ntchito ndi PID (Proportional–Integral–Derivative). Nkhaniyi ikufotokoza mfundo zoyambira za PID, momwe gawo lililonse limagwirira ntchito, momwe limagwiritsidwira ntchito podzipangira, komanso njira zosinthira kuti dongosolo ligwire bwino ntchito.
Kodi kulamulira kwa PID n'chiyani?
PID ndi njira yowongolera mayankho yomwe imawerengera chizindikiro chowongolera kutengera kusiyana pakati pa mtengo wofotokozera (setpoint) ndi mtengo woyesedwa (process variable/PV). Kusiyana kumeneku kumatchedwa cholakwika. Cholinga cha PID control ndikuchepetsa cholakwika mwachangu momwe zingathere popanda kupangitsa kuti dongosolo lizisinthasintha kwambiri kapena kusakhazikika.
Kawirikawiri, chowongolera chimapanga chotulutsa (monga kutsegula kwa valavu, magetsi a mota, kapena kayendedwe ka ntchito ya PWM) komwe kumakhudza njirayo. Masensa amawerenga chotulutsa ndikuchiyerekeza ndi malo okhazikika. Kuzungulira kumeneku kumapitilira mosalekeza mu chowongolera cha PLC, DCS, kapena chowongolera cholumikizidwa.
Fomula yoyambira ya mawonekedwe osalekeza a PID:
u(t) = Kp e(t) + Ki ∫ e(t) dt + Kd · (de(t)/dt)
Mu makina a digito (monga ma PLC), kuwerengera kumachitika mosiyana kutengera nthawi zina zoyeserera.
Zigawo za PID: P, I, ndi D
1) Kuchuluka (P)
Gawo lofanana limapereka yankho lolingana ndi kukula kwa cholakwika chamakono. Ngati cholakwikacho chili chachikulu, zotsatira zokonza zidzakhalanso zazikulu. Ubwino wake ndi yankho lachangu komanso losavuta.
Komabe, kulamulira kwa P kokha nthawi zambiri kumasiya cholakwika cha steady-state (cholakwika chomwe chimatsala dongosolo litakhazikika). Mwachitsanzo, pakulamulira kutentha, kutentha kumatha kutsika pang'ono pansi pa malo okhazikika chifukwa mphamvu yokonza P imachepa pamene cholakwika chikuchepa.
Chizindikiro chachikulu: Kp (proportional gain)
– Kp yaying'ono kwambiri: kuyankha pang'onopang'ono, nthawi yayitali kuti cholakwika chizimiririke.
– Kp ndi yayikulu kwambiri: chiopsezo cha kuwombera mopitirira muyeso ndi kugwedezeka.
2) Yophatikiza (I)
Gawo lofunikira limawerengera zolakwikazo pakapita nthawi. Ntchito yake ndikuchotsa zolakwika zokhazikika, chifukwa ngakhale zolakwika zazing'ono zidzapitiliza kuyendetsa zotsatira mpaka cholakwikacho chifike pa zero.
Vuto lake ndilakuti ma integral amatha kuchepetsa kuyankha ndipo amatha kupanga overshoot kapena oscillation ngati ali amphamvu kwambiri. Vuto lina lakale ndi integral windup, pomwe ma integral "amamanga" kwambiri pamene actuator ifika pamlingo wake wapamwamba/wocheperako (saturation).
Magawo ofunikira: Ki (integral gain) kapena nthawi zina amafotokozedwa ngati Ti (integral time)
– Ki ndi yaying'ono kwambiri: cholakwika cha steady-state chimatha pang'onopang'ono kwambiri.
– Ki ndi yayikulu kwambiri: imathamanga kwambiri, imagwedezeka, ndipo imatha kugwedezeka mosavuta.
3) Chochokera (D)
Gawo lochokera ku chinthucho limaneneratu za kusintha kwa zolakwika poyang'ana kuchuluka kwa kusintha kwake. D ingathandize kuchepetsa kugwedezeka kwambiri ndikuwonjezera kukhazikika, makamaka m'machitidwe omwe amakonda kugwedezeka.
Komabe, ma derivatives amakhudzidwa kwambiri ndi phokoso la sensor. Mu miyeso yaphokoso, D ingayambitse kugwedezeka kwa zotulutsa. Chifukwa chake, ma implementations a D nthawi zambiri amatsagana ndi fyuluta (monga fyuluta yotsika) kapena amagwiritsidwa ntchito ngati derivative ya PV (m'malo mwa cholakwika) kuti achepetse zotsatira za kusintha kwadzidzidzi kwa setpoint.
Magawo ofunikira: Kd (gain derivative) kapena Td (time derivative)
– Kd ndi yaying'ono kwambiri: mphamvu ya damping siioneka kwenikweni.
– Kd ndi yayikulu kwambiri: kutulutsa kwake kumakhala kogwirizana ndi phokoso, makinawo akhoza kukhala osasangalatsa kapena osakhazikika.
Nchifukwa chiyani PID ndi yotchuka mu automation?
Ma PID ndi otchuka pazifukwa zingapo zothandiza:
1. Zosavuta kugwiritsa ntchito: Pafupifupi ma PLC ndi ma DCS onse ali ndi ma block a ntchito ya PID yomangidwa mkati.
2. Yosinthasintha kwambiri: Ingagwiritsidwe ntchito m'njira zosiyanasiyana (kutentha, mulingo, kuyenda, liwiro, kupanikizika).
3. Sichifuna zitsanzo za masamu zatsatanetsatane: Mosiyana ndi ulamuliro wozikidwa pa chitsanzo, PID ikhoza kusinthidwa pogwiritsa ntchito njira yoyesera.
4. Kugwira ntchito kokwanira pa zosowa zambiri zamafakitale: Pazinthu zambiri, PID ndi "yabwino mokwanira" pamtengo wotsika.
Komabe, PID si yankho la milandu yonse—monga, m'njira zosalunjika kwambiri, zomwe zili ndi nthawi yayitali, kapena njira zomwe zimakhala ndi zinthu zambiri zolumikizana. Muzochitika izi, ulamuliro wapamwamba (monga MPC) nthawi zina umakhala woyenera kwambiri.
Zitsanzo za ntchito za PID m'makampani
1. Kulamulira kutentha (chotenthetsera/uvuni/chotenthetsera)
PV: kutentha kwa thermocouple/RTD
Chotulutsa: mphamvu ya chotenthetsera (SSR/thyristor) kapena kutsegula kwa valavu ya nthunzi
Mavuto: kutentha kwambiri komanso nthawi yopuma.
2. Yang'anirani mulingo wa thanki
PV: mulingo wamadzimadzi (chotumizira cha ultrasonic/pressure)
Kutulutsa: kutsegula kwa valavu yolowera kapena liwiro la pampu
Mavuto: kusokonezeka chifukwa cha kusintha kwa kuchuluka kwa madzi ndi mpweya.
3. Kuwongolera liwiro la injini
PV: RPM ya encoder/tachometer
Chotulutsa: chizindikiro ku VFD/servo drive
Mavuto: kusintha kwa katundu, kukangana, ndi kusakhala ndi mphamvu kwa makina.
4. Kulamulira kuthamanga
PV: chotumizira kuthamanga
Chotulutsa: choyezera valavu kapena kompresa
Mavuto: kupanikizika kwa mpweya ndi kayendedwe ka mapaipi.
Mfundo yokonza PID (kusintha)
Kukonza ndi njira yosankha ma Kp, Ki, ndi Kd kuti makina akwaniritse zofunikira pakugwira ntchito: mwachangu kufika pamalo okhazikika, kupitirira muyeso pang'ono, kukhazikika, komanso kukana kusokonezeka.
Pali njira zingapo zodziwika bwino zosinthira:
1) Kusintha ndi manja (kuyesa ndi zolakwika)
Njira zothandiza zomwe nthawi zambiri zimagwiritsidwa ntchito m'munda:
– Kuyambira pa Ki = 0 ndipo Kd = 0.
- Wonjezerani Kp mpaka yankho litakhala lachangu, koma osagwedezeka kwambiri.
- Onjezani Ki pang'onopang'ono kuti muchotse cholakwika cha steady-state.
- Onjezani Kd ngati pakufunika kuti muchepetse kugwedezeka kwambiri ndi kugwedezeka.
Chofunika kwambiri pakusintha ndi manja ndikusintha pang'ono, kuyang'ana momwe zinthu zikuyendera (kusintha kwa malo kapena kusokoneza), ndikuwonetsetsa kuti makinawo ali otetezeka.
2) Ziegler–Nichols (njira yozungulira)
Njira yakale: onjezerani Kp mpaka dongosolo litasinthasintha bwino (kuchuluka kwa mtunda), lembani nthawi yosinthasintha, kenako werengani magawo a PID kuchokera patebulo. Njirayi ndi yachangu, koma nthawi zambiri imapanga ma overshoots akuluakulu, kotero si nthawi zonse yoyenera njira zodziwikiratu.
3) Kukonza zokha pa zowongolera zamakono
Ma PLC ambiri/owongolera kutentha amapereka zinthu zodzikonzera okha. Kawirikawiri, chipangizochi chimapereka chizindikiro choyesera, kuzindikira momwe njirayo yayankhidwira, kenako kuwerengera magawo oyamba a PID. Zotsatira zake nthawi zambiri zimakhala zabwino ngati poyambira, koma zingafunike kusintha kutengera zomwe njirayo ikufuna.
Zinthu zofunika kwambiri pakukhazikitsa PID ya digito
1. Nthawi yoperekera zitsanzo (Ts)
Kuyesa pang'onopang'ono kwambiri kungayambitse kuti chowongolera chichitepo kanthu pang'onopang'ono. Kuyesa mwachangu kwambiri kungapangitse kuti phokoso lizikulirakulira komanso kuti CPU ichuluke kwambiri. Sankhani T malinga ndi momwe zinthu zilili: njira zofulumira zimafuna T yaying'ono, pomwe njira zocheperako zingagwiritse ntchito T yayikulu.
2. Kuchuluka kwa zotuluka ndi zotsutsana ndi kutseka
Pamene zotsatira zake zafika pamlingo (monga 0–100%), integral ikhoza kupitiriza kukula ndi kuyambitsa kuchulukira kwa zinthu pamene dongosolo libwerera mwakale. Anti-windup imaletsa kusonkhanitsa zinthu zosafunikira.
3. Kusefa zinthu zochokera ku zinthu zina ndi PV
Masensa nthawi zambiri amakhala ndi phokoso. Fyuluta yotsika mtengo imathandiza, makamaka pamene zigawo za D zikugwiritsidwa ntchito.
4. Setpoint ramp/soft start
Kusintha kwadzidzidzi kwa malo oikika kungayambitse kukwera kwambiri. Kukweza malo oikika kumapangitsa kusintha kukhala kosavuta.
Njira zodziwika bwino zogwirira ntchito zimayesedwa
Mu automation, kusintha kwa PID nthawi zambiri kumafuna kuphatikiza kwa:
- Nthawi yokwera mofulumira (nthawi yokwera mpaka pamalo okhazikika).
- Kuthamanga pang'ono (sikupitirira malire a malo okhazikika).
- Nthawi yochepa yokhazikika (yokhazikika mwachangu).
- Cholakwika chochepa cha steadiness-state.
- Kulimba bwino (kumakhalabe kokhazikika ngakhale pakakhala kusintha kwa katundu/kusokonezeka).
Sizinthu zonse zomwe zingakonzedwe nthawi imodzi. Mwachitsanzo, kuyesetsa kuti zinthu zikwere mwachangu nthawi zambiri kumawonjezera kuchuluka kwa zinthu zomwe zingagwiritsidwe ntchito. Chifukwa chake, kusintha kumadalira zinthu zofunika kwambiri: chitetezo, mtundu wa zinthu, kugwiritsa ntchito bwino mphamvu, kapena chitonthozo pa ntchito.
Kutseka
Njira zowongolera PID ndi maziko a machitidwe ambiri odziyimira pawokha chifukwa cha kuthekera kwawo kuwongolera bwino njira ndi kukhazikitsa kosavuta. Mwa kumvetsetsa ntchito za zigawo za P, I, ndi D, ndikugwiritsa ntchito njira zabwino zosinthira ndi kukhazikitsa—monga anti-windup, filtering, ndi sampling timing—PID ikhoza kupereka magwiridwe antchito okhazikika, oyankha, komanso osalakwitsa m'mafakitale osiyanasiyana. Ngakhale kuti pali njira zamakono zowongolera zamakono, PID ikadali chisankho chomwe chimakondedwa kwambiri panjira zambiri chifukwa cha magwiridwe antchito ake abwino, kuphweka, komanso mtengo wake.
Ngati mukufuna, nditha kusintha nkhaniyi kuti igwirizane ndi nkhani inayake (monga PID pa Siemens/Omron PLC, kuwongolera kutentha ndi ma SSR, kapena chitsanzo cha kuwerengera kosintha kwa makina a mota/thanki).
