Question

In the Bode plot of a unity feedback control system, the value of phase angle of G (jω) is -90° at the gain cross over frequency of the Bode plot, the phase margin of the system is:
1. -180°
2. +180°
3. -90°
4. +90°

Answer 1

Correct Answer - Option 4 : +90°

Calculation:

Given,

Phase angle at gain cross – over frequency ϕ = -90°

Phase – margin = 180° + ϕ

= 180° - 90°

= 90°