Jaspreet nyquist Stability

Question 1

When will a closed loop system be stable?

Answer 1

When the magnitude of G(s) < 1 and the angle = +- 180
OR
Magnitude = 1 and angle > -180

Question 2

When will a closed loop system be marginally stable?

Answer 2

When Magnitude of G(s) = 1 and angle = 180

Question 3

What do gain and phase margins tell us?

Answer 3

They tell us how stable a system is by defining how much variation we have in G(s) before the system comes unstable. It makes use of the Nyquist Stability criteria

Question 4

What is Gain Margin (Kg)?

Answer 4

It is the change in open loop gain that is needed when the phase plot crosses -180 to make the system unstable.

Question 5

What is Phase Margin(gamma)?

Answer 5

it is the change in open loop phase shift that is needed when the gain crosses 0 to make the system unstable.

Question 6

What is the gain margin frequency?

Answer 6

it is the frequency at which the phase plot will cross the -180 degree line.

Question 7

What is the phase margin frequency?

Answer 7

It is the frequency at which the gain plot will cross the 0db line.

Question 8

If Kg > 0 and gamma > 0 then what does this mean for the stability?

Answer 8

The system will be stable when Kg > 0db and gamma > 0 degrees

Question 9

If Kg < 0 and gamma < 0 then what does this mean for the stability of the system?

Answer 9

The system will be unstable when Kg < 0 and gamma < 0

Question 10

How do we determine if the system is stable when Kg > 0 but gamma < 0 OR Kg < 0 but gamma > 0?

Answer 10

We have to resort to the Nyquist Criterion