Sunday, March 11, 2018

discrete signals - Transient response of system with single pole $0 le p < 1$


$G(z) = \frac{1-p}{z-p}$




If the value of p satisfies $ 0 \leq p < 1$ there are no oscillations in the transient response.



Question: Why is that $\uparrow$ true? I know roughly what a transient response is but how is the relation between the position of the pole and the nature of the transient response?


Edit: In another paper by the same authors:



Enforcing the stability of the controlled system means ensuring that the pole p is non-negative and less than 1.



Now I'm completely out, stability does not depend upon the position of the pole as long as they are inside the unit circle of the z-plane I have thought?


Paper 2:



http://www.iste.uni-stuttgart.de/fileadmin/user_upload/iste/zss/publications/supplementaryMaterial/2014-ICSE-Control-PaperReviewCopy01.pdf


Look at the sentence short above eq. (10) on page 5


Paper 1 is not available on the internet as fas as I know. It's Antonio Filieri et al. "Software Engineering Meets Control Theory"



Answer



If you have a single real-valued pole, you get a term $k\,p^{(n-n_0)}u[n-n_0],n\ge 0$, with some constant $k$ and some delay $n_0\ge 0$ in the system's impulse response ($u[n]$ is the unit step). Clearly, if $|p|\ge 1$ the transient will never settle. If $-1

$$\left(-\frac12\right)^nu[n]=\left\{1,-\frac12,\frac14,-\frac18,\dots\right\}\tag{1}$$


So for a transient that decays (i.e., for the system to be stable) and that does not oscillate you need $0\le p<1$.


Note that if you only have one real-valued pole $p$, stability implies $$-1

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