I want to know if there is any system that needs to operate on different variants (combinations of the P, I, D constants) of PID controller; like it operates on P-only controller first; then switches to PI and then may be to PD or PID alternatively or simultaneously or may be cascaded? Is there any need to have such a system? If yes where and if not why not?
Tnx for the answer. But my question is Is there any such system/plant that uses variants of PID at the same time? Like using PI at one time and then switches to PID at another instant?
If you want to compare the performance of P-control, PI,PD,PID, you can use different versions of PID simultaneously to any control system.
@Zlatan: Gain Scheduling refers to adjusting the control parameters (Ks) of a PID at different operation conditions while controller does not change. I am looking for something where controller switches among its variants (P to PI to PID or PD).
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Hi, usually IDE applications (e.g. RSLogic - Allen Breadley) have different block (in Leader or FBD) for PI and PID, and for these, from coefficients value is possible to select just PI, PD etc.
Block documentation contains usefully details.
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Ciprian Lupu
Dear Sikandar
In current digital technology, a PID controller is nothing more than a PID algorithm run on some type of microprocessor with the corresponding Input/Output I/O) functionality to be able to communicate with the external world.
Typically, the corresponding variables/parameters for each PID function (Proportional, Integral and Derivative) are readily manipulated independently by the programmer when implementing the control strategy that is desired to obtain. Please bear in mind that P, I & D are functions that are not mandatory to be utilized on each application. Instead the control engineer shall analyze which is the best road to follow given the characteristics/behavior of the process to be controlled. The determining factor is the physical process. Once this is determined, the PID algorithm shall be modified accordingly and determined which modes (P, I D) shall be utilized.
Just to give you a simple example: Typically, flow control applications do not utilize Derivative (D) because flow measurement tends to be noisy and the utilization of D, specially in relatively high frequencies, tends to make the system unstable.
Resuming:
Today's technology shall allow you to manipulate each control mode independently. Which ones shall be utilized on the specific application? Well it is the characteristic of the physical system the determining factor. It is mandatory that these characteristics be very well understood before attempting to configure a control strategy for it.
Hope this helps.
The PID gains determine where are zeros locations of the controller dynamic.
Each control engineer should be able to linearize the system dynamics,
conduct frequency domain analyses and determine where controller zeros should be
located within complex "S" plane in order to achieve specified system performance.
And yes, based on system types you can select: P; Pi; PID or any combination of these
control concepts, as well as many inner loops are needed in order to achieve specified Steady State error and dynamic response.
Each inner loop can have some of above control functions but that better be the
selected by analyses of the system that should be controlled.
Every of these questions are answered in Control Books.
Best Regards
Vladimir Kokotovic
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