Q6Control System
Question
2 marks
Q.6. Draw the polar plot for function :
Answer
For G(s) = 1/[s^3(s+1)], the polar plot starts at infinite magnitude with phase -270° at ω→0 and ends at the origin with phase -360° as ω→∞, spiraling through the third and second quadrants.
Substitute s = jω:
Magnitude and phase:
As ω → 0⁺, |G(jω)| → ∞ and ∠G(jω) → -270°. As ω → ∞, |G(jω)| → 0 and ∠G(jω) → -360°. The plot therefore begins at infinity along the -270° radial (i.e., along the positive imaginary axis direction rotated appropriately) and spirals clockwise into the origin, tangential to the -360° (positive real axis) direction, sweeping through angles between -270° and -360° for increasing ω.