Control system design and simulation for a chemical process

Thread Starter

alexjjones567

Joined Dec 12, 2019
3
pid.PNG
Hello, im never one to ask for help but i have been unable to attend lectures on this subject, i have very little time to complete this(tomorrow). im not looking for someone to answer it for me more guidance on how i go about completing this, many thanks

hello, ive missed this semester due to not being able to attend, i've still been doing my own learning but have yet to even begin on this topic, ive searched online and read books but i dont even know where to begin, any help or a starting point would be much appreciated.
A concentration control loop in an industrial chemical process can be represented by a second order dynamics with a long transmission delay. The two time constants of the second order dynamics are T1 = 4 min and T2 = 6 min respectively. The steady state gain is 5 and the dead time is 12 min. The loop is to be controlled to achieve a desired dynamics of first order with time constant Td = 2 min and zero steady-state offset for a step reference. Produce solutions to the following questions.

Identify the plant transfer function and the desired closed-loop system transfer function. Then, design a feedback control system with the controller designed using Direct Synthesis method, where the time-delay is approximated using the first-order Taylor expansion. Implement the controller with a standard industrial PID controller.
 

MrAl

Joined Jun 17, 2014
7,757
So this isnt really homework just self study?

The plant probably looks like this:
5/((s*T1+1)*(s*T2+1))

I think the Taylor approximation looks like this:
1/s-(1-f0)*T

but we should look into that a bit more, and you might want to be aware that the approximation is only supposed to be good for small time delays T, but if that's what they ask for then that's what you have to use i guess.

Direct Synthesis i think just means that before you start you decide on what the output should look like, then using that as a specification you find the required control law that together with the plant will produce that output.

You must have gotten some books for this right or maybe even just one book?
 
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Thread Starter

alexjjones567

Joined Dec 12, 2019
3
thanks for your reply, well this is coursework, thats the first question out of 5, worth 30% of my overall grade for the module.

this is the full set of questions they require,
Identify the plant transfer function and the desired closed-loop system transfer function. Then, design a feedback control system with the controller designed using Direct Synthesis method, where the time-delay is approximated using the first-order Taylor expansion. Implement the controller with a standard industrial PID controller. [15 marks]

Design a feedback control system for the given plant with a PID controller designed using the closed-loop Ziegler-Nichols empirical method. The Simulink model used in the experiment to obtain the sustained oscillatory output curve should be displayed, and the output curve should also be displayed. The controller design with the simulation model and step response curve must be presented. [15 marks]

Design a Smith Predictor control system for the given plant with the controller designed using the Direct Synthesis method. A block diagram must be shown to demonstrate the control system structure. The design details are also required. [15 marks]

Simulate the three control systems designed using the three methods with a unity step input for 100 minutes. The simulation must use one Simulink model with three sub-models, each for a control system. Display the Simulink model and sub-models, and present the simulation parameter settings. Display the three outputs and the set-point in one figure for comparison. Display also the three corresponding control variables in another figure. Compare the three output curves and comment on the performances of the three control systems. [30 marks]


i've been looking on this subject for the past 6 hours, ive got to submit the work by midnight tomorrow so i best get learning.
 

MrAl

Joined Jun 17, 2014
7,757
this is the full set of questions they require,
Identify the plant transfer function and the desired closed-loop system transfer function. Then, design a feedback control system with the controller designed using Direct Synthesis method, where the time-delay is approximated using the first-order Taylor expansion. Implement the controller with a standard industrial PID controller. [15 marks]

Design a feedback control system for the given plant with a PID controller designed using the closed-loop Ziegler-Nichols empirical method. The Simulink model used in the experiment to obtain the sustained oscillatory output curve should be displayed, and the output curve should also be displayed. The controller design with the simulation model and step response curve must be presented. [15 marks]

Design a Smith Predictor control system for the given plant with the controller designed using the Direct Synthesis method. A block diagram must be shown to demonstrate the control system structure. The design details are also required. [15 marks]

Simulate the three control systems designed using the three methods with a unity step input for 100 minutes. The simulation must use one Simulink model with three sub-models, each for a control system. Display the Simulink model and sub-models, and present the simulation parameter settings. Display the three outputs and the set-point in one figure for comparison. Display also the three corresponding control variables in another figure. Compare the three output curves and comment on the performances of the three control systems. [30 marks]


i've been looking on this subject for the past 6 hours, ive got to submit the work by midnight tomorrow so i best get learning.
Yeah if you dont have a book on this it will be hard to do exactly what they are asking i think unless you can find all the methods they ask for online somewhere. I cant see them asking for something you have not been taught yet, is that the case? If you missed lectures then it may be hard to get going unless you can get some notes from a fellow classmate.
Did you look up the three methods they ask for yet?

[LATER]
I found the last two methods on Wikipedia :)
 

Thread Starter

alexjjones567

Joined Dec 12, 2019
3
yes ive missed the lecture due to personal reasons, all the content theyve been taught is available on the learning portal for my university but it doesnt really cover anything like this, ive been watching videos on each of the methods but it doesnt seem to come close to what i need, ill be spending all day tomorrow doing this as well, hopefully try to at least pick up half marks.

ill have to look on how i can complete each step, ive done nothing on this so i was struggling to find where to even begin, thanks for your effort tho.
 

MrAl

Joined Jun 17, 2014
7,757
yes ive missed the lecture due to personal reasons, all the content theyve been taught is available on the learning portal for my university but it doesnt really cover anything like this, ive been watching videos on each of the methods but it doesnt seem to come close to what i need, ill be spending all day tomorrow doing this as well, hopefully try to at least pick up half marks.

ill have to look on how i can complete each step, ive done nothing on this so i was struggling to find where to even begin, thanks for your effort tho.
Well you know it sounds almost like this is your first control system design. If that is true it is going to be a learning curve for sure. I dont know if this is possible in just one or two days, but hey give it a go.

Do you understand what the plant should look like? That's the first step.
 
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