I know that compensators are used for modifying the gain/phase characteristics of a system in the open loop. I would like to know how useful is it in dealing with the dead zone/time lag/ time delay of the system. What are the other advanced measures that can be taken and when ?
Dear Biswajit,
Among the effects of compensation are:
-These compensating networks increase the steady state accuracy of the system. An important point to be noted here is that the increase in the steady state accuracy brings instability to the system.
-Compensating networks also introduces poles and zeros in the system thereby causes changes in the transfer function of the system. Due to this, performance specifications of the system change.
There are many compensation methods, for exemple we have:
Series compensation, Feedback Compensator, a combination of series and feedback compensator is called load compensation, Phase Lead Compensation, Phase Lead Compensation, Phase Lag-Lead Compensation
Here are links and attached files in subject.
-Extras: Designing Lead and Lag Compensators - Control Tutorials for ...
ctms.engin.umich.edu/CTMS/index.php?aux=Extras_Leadlag
-Lead Compensation
https://www.facstaff.bucknell.edu/mastascu/.../Comp/Comp3.htm
-Center for Problem-Oriented Policing | Tool Guides | Implementing ...
www.popcenter.org › Tools › Implementing Responses to Problems
Best regards
Dear Remi, Thanks for your reply !!!
When you say that lead/lag compensators are essentially high pass/low pass filters, what prevents them from being used in the open loop ??? I know that a closed loop configuration yields a better response then an openloop configuration but I think a filter can always affect the response even when used in the openloop. What is your take on that, Remi ??
Your open loop problem is IMHO not exactly a control problem but just a filtering problem. So the lead-lag compensator is not a very useful device here. Besides that, I think it is not a high-pass or low-pass filter; it is more of a gain equalizer (because its gain at 0 or oo is never 0 as in a pure filter.)
The type of filter you should look at is the all-pass filter which, as the name implies, has a constant gain along all the frequency band and only modifies the phase (or delay) of the signal. There are 1st order, 2nd order, etc..., all-pass filters, so choose what you need. All-pass filters are also often called delay equalizers.
You can sse the wikipedia page https://en.wikipedia.org/wiki/All-pass_filter or, better, this nice design note from Analog Devices: http://www.analog.com/media/en/training-seminars/tutorials/MT-202.pdf
About filters in general you can consult chapter 5 of the nice AD book on opamp applications: http://www.analog.com/en/education/education-library/op-amp-applications-handbook.html
Dear Jose, Thanks for the insight !!! But I think inserting a simple time delay would be just as good as inserting an all pass filter as the case may be. What do you say ? Can you point towards some research where it was proven otherwise ???
Remi, that is what a controller would try to do in the first place. The compensator, on the other hand would rather make the ship 'dump' some of its 'cargo' into the sea and help the control action by making the ship 'lighter'. The compensator actually modifies the system while a controller modifies the response without trying to modify the system.
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