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What is root locus technique and root locus analysis ?

Answer»

Root locus Technique:

• Introduced by W. R. Evans in 1948 

• Graphical method, in which movement of poles in the s‐plane is sketched when some parameter is varied 

• The path taken by the roots of the characteristic equation when open loop gain K is varied from 0 to ∞ are called root loci 

• Direct Root Locus = 0 < k < ∞  

• Inverse Root Locus = ‐ ∞ < k < 0

Root Locus Analysis: 

• The roots of the closed‐loop characteristic equation define the system characteristic responses 

• Their location in the complex s‐plane lead to prediction of the characteristics of the time domain responses in terms of:

o damping ratio, ζ

o natural frequency, wn

o damping constant, σ → first‐order modes

o Consider how these roots change as the loop gain is varied   from 0 to ∞ 



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