山东大学自动化过程控制期末考试题(英文答案).pdf

1 1 The advantages and disadvantages between feedback control and forward control 反馈控制与前馈控制的优缺点 Feedback control advantages Corrective action is taken regardless of the source of the disturbance Reduces sensitivity of the controlled variable to disturbances and changes in the process disadvantage a No corrective action occurs until after the disturbance has upset the process b Very oscillatory responses or even instability Feedforward control advantages Corrective for disturbance before it upsets the process disadvantage a must be able to measure the disturbance b no corrective action for unmeasured disturbance 2 8 Advantages of on off controller and its application situation Advantages simple and cheap Application used in residential heating and domestic refrigerators limited use in process control due to continuous cycling of controlled variables 3 12 Desirable controller features Stable adequate disturbance rejection quick responding good set point tracking steady state errors are eliminated 4 20 when should predictive control be used Processes are difficult to control with standard PID controller such as long time constants Among controls have dynamic interaction Limits on process and manipulated variables are important for normal control 5 12 List Guidance for Common Control Loop such as flow rate liquid level gas pressure temperature and composition 本题可不看 For flow rate PI control is generally used with intermediate values of the controller gain For liquid level integral control action is often used while derivative action is not normally used For gas pressure PI controller are normally used with only a small amount of integral control action For temperature PID controllers are commonly employed to provide quicker than the PI controllers For composition it is generally the same as temperature 6 16 List the advantages and disadvantages of Smith Predictor Advantages a Improve the performance of system containing time delays b Be beneficial for handling disturbance Disadvantages a It is model based that is a dynamic model of process is required 1 2 An isothermal irreversible reaction A k B takes place in the liquid phase in a constant volume reactor The mixing is not perfect Observations of flow patterns indicates that a two tank system with back mixing as shown in the figure below should approximate the imperfect mixing CA0 CA1 CA2 is component of initial F V1 and V2 respect Assume F and FR are constant Write the equation describing the system According to the conservation of mass 物料守恒 物料守恒 221 22 120 11 AARAR A ARARA A FCCFCFF dt CVd CFFCFCF dt CVd After the simplification we can get 21 22 1210 11 AAR A AARAA A CCFF dt CVd CCFCCF dt CVd 2 8 If the input Ym to a PI controller changes stepwise Ym s 2 s and the controller output changes initially as in the figure below what are the values of the controller gain and integral time 1 1 1 0 s K sE sp dtteteKptp I c t I c Thus 2 1 2 62 I c c K K Then the controller gain Kc is 3 and integral time I 5 3 12 A process has the transfer function 1 2 2 0 s e sG s Compare the PI controller settings for the following design approach 1 direct synthesis method c 0 2 2 direct synthesis method c 1 3 ITAE performance index disturbance 4 ITAE performance index set point 1 2 Solve For 1 s Ke sG s Kc K c I Thus 1 0 2 K 2 Then either c 0 2 or c 1 I 1 Kc 2 c when c 0 2 Kc 1 25 and when c 1 Kc 0 417 3 Solve According to 977 0 859 0 BAKKAY c B we can work out that Kc 2 069 According to 680 0 674 0 BAAY I B we can work out that I 0 497 4 Solve According to 916 0 586 0 BAKKAY c B we can work out that Kc According to BA I we can work out that I 4 16 The cascade control system is shown in the figure below 1 Draw the block diagram of the system 2 Explain why the cascade control system can correct the disturbances in fuel gas supply pressure 1 The diagram is below 2 The secondary control loop lies more near the disturbances than the primary loop so it is respond faster than the primary loop Therefore when a disturbance in fuel gas supply pressure the secondary control loop can correct the disturbance as soon as possible rather than the situation that the disturbance upsets the process 5 16 The cascade control system is shown in the figure below where D1 and are variables Develop the transfer function for Y1 D2 Y1 Ysp1 Y2 Ysp2 and Y1 D1 Solve Suppose that D1 Ysp1 0 12121222 21 2 1 111 2211 2 2 222222 211 1 mvppccmpvc dp m mc sp cvpd p GGGGGGGGGG GG D Y YGE YGEGYE EGGGDGY YGY 12121222 12121 1 1 1 mppVccmpVc mppvcc sp GGVGGGGVGG KGGGGG Y Y 222 22 2 1 1 mpVc pvc sp GVGG GGG Y Y 11221222 2221 1 1 1 1 mppvccmpvc mpvcd GGGGGGGGGG GGGGG D Y 6 作业 2 1 建立模型 7 作业 8 2 a show how to obtain this transfer function with a parallel arrangement of two much simpler function in the following figure 1 1 1 2112 2 1 1 s KKsK K s K sE sP b Find expression for K1 K2 and I t