Feedforward Control identifiable disturbance measured,

Transcription

1 Feeforwar Control So far, mot of the focu of thi coure ha been on feeback control. In certain ituation, the erformance of control ytem can be enhance greatly by the alication of feeforwar control. What you nee to look for are two key characteritic: 1. An ientifiable iturbance i affecting ignificantly the meaure variable, in ite of the attemt of a feeback control ytem to regulate thee effect, an 2. Thi iturbance can be meaure, erha with the aition of intrumentation. Alo, we woul be interete in controlling the ource of the iturbance locally, before it affect our main roce, if that were oible. If it i oible, we woul uually imlement cacae control, not feeforwar control.

2 Examle of Feeforwar Control Shower Hear toilet fluh (meaurement) Ajut water to comenate Feeback i when you wait for the water to turn hot before changing the etting Car aroaching hill See how tee the hill i (meaurement) Puh on eal to kee teay ee Feeback i to wait for lowing before ajuting eal Chemical ytem Meaure omething in fee tream like T water,return in heating lant Change heat to reactor

3 Examle Feeback control loo Goal: Cool own hot water with col water tream Controlle & meaure variable: T out Maniulate variable: flow rate of hot tream (q hot )

4 Portion of Block Diagram D G D U G P + + Y How o we maniulate U() to cancel the effect that D() will have on Y()?

5 Derivation 1. Write an algebraic equation for the block iagram Y() = D()G () + U()G () 2. If Y() i to be unaffecte by D(), then we want Y() = 0 3. Solve for U() in term of D() U() = [-G ()/G ()]D() So G ff = -G ()/G ()

6 If G an G are firt orer 1 e G 1 e G Therefore, ff e e e G ynamic tatic

7 When i G ff not feaible? G ff 1 1 e When >, the function will grow without boun

8 Moify block iagram D G D G ff U G P + + Y

9 Fee Forwar with Feeback Trim D G Y E P U Y u + + m G + c G G v P Y ~ - G ff + + Y Y Y m G m

10 Back to equiment iagram Meaure the iturbance (fluctuating col water inlet flow rate) Ajut controller through moel (G ff )

11 Seborg verion Figure 15.11

12 Diturbance Rejection Performance Diturbance Rejection Performance of Single Loo PI Controller reactor exit temerature Diturbance Rejection Performance of PI With Fee Forwar contant et oint contant et oint rai control action from fee forwar iturbance variable te iturbance variable te Feeback (PI) Feeforwar with Feeback (PI)

13 Practice e G e G ff e G

14 Phyically Realizable G ff 1. The exonential term mut be negative < 2. The orer of the numerator mut be le than or equal to that of the enominator Phyically unrealizable Phyically realizable Phyically realizable

15 Comarion of Feeforwar & Cacae Cacae Feeforwar Senor 2 2 Controller 2 1 Valve 1 1 Moel 0 1 Retriction t ettling mall for inner loo <

16 Recommenation Ue cacae firt Ue feeforwar when Diturbance can be iolate There i no inner loo variable that reon to the maniulate variable Cannot ue the ame valve to control the iturbance

17 Fee Forwar v Cacae FeeForwar with Feeback Jackete Reactor Cacae

18 Fee Forwar v Cacae Jackete Reactor FeeForwar with Feeback Cacae

19 Control Station Examle Jackete Reactor Volunteer neee