Jaspreet nyquist Stability Flashcards
When will a closed loop system be stable?
When the magnitude of G(s) < 1 and the angle = +- 180
OR
Magnitude = 1 and angle > -180
When will a closed loop system be marginally stable?
When Magnitude of G(s) = 1 and angle = 180
What do gain and phase margins tell us?
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
What is Gain Margin (Kg)?
It is the change in open loop gain that is needed when the phase plot crosses -180 to make the system unstable.
What is Phase Margin(gamma)?
it is the change in open loop phase shift that is needed when the gain crosses 0 to make the system unstable.
What is the gain margin frequency?
it is the frequency at which the phase plot will cross the -180 degree line.
What is the phase margin frequency?
It is the frequency at which the gain plot will cross the 0db line.
If Kg > 0 and gamma > 0 then what does this mean for the stability?
The system will be stable when Kg > 0db and gamma > 0 degrees
If Kg < 0 and gamma < 0 then what does this mean for the stability of the system?
The system will be unstable when Kg < 0 and gamma < 0
How do we determine if the system is stable when Kg > 0 but gamma < 0 OR Kg < 0 but gamma > 0?
We have to resort to the Nyquist Criterion