In the theory of control, we deal with two terms: uncertain systems and Variable Structure Systems (VSS). For uncertain systems, the controller synthesis can be accomplished using classical theories such as H-inf, small gain, Mio approach, etc. But when we are faced to VSS, the literature are almost all impressed by Sliding Mode approach.
While it seems to me that both terms refer to the same concept but why in the literature, different techniques has been applied to them? What is/are the difference/s between uncertain systems and VSS?
Thanks Viswanath for your explanation.
So it means that when we talk about VSS, the controller is included in the "system" and the "variability" refer to the "control law" not to "uncertain system". Am I right?
Dear Hossein Parastvand,
I am writing to share my opinion of “robustness in the control law” and “variable system” .
To begin with, as we know, VSC is famous for its robust to the uncertainty that usually is matched. Particularly, VSC's robustness works only when VSC reach the sliding phase. In other words, if the control system is on the reaching phase, it does not have the robustness to the uncertainty.
Also, I think your writing “the controller is included in the system” is right. Actually, the system's structure is changed on the sliding phase. More specifically, due the imaginary control, the order of the original system is reduced. That is one of the reasons why the name of this control method is variable structure control.
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