Bode Plots: Phase Angle is asymptotic to -180. What is the gain margin?

[nyrodydx]

What would be my gain margin if my phase angle doesn't cross -180? Thanks in advance

 

[Julie.]

What would be my gain margin if my phase angle doesn't cross -180? Thanks in advance

I am not sure what you are looking for, the gain margin is usually determined at the phase crossover frequency, where the phase angle crosses -180 degrees.

It would then be either directly observable from the plot, or of course calculated from GM = 0 - G, G being the gain in dB.

However you can calculate the GM at any point, although it is most useful at the crossover frequency.

If a system can not get to -180 degrees, then it can never be unstable, so no matter how much gain you add it will never go unstable.


Is this an example you are working through?

What is the basic form?

If its just a basic question from your training/lectures, work it out - how much gain (number) would be required to make a system unstable if no matter how much gain you add it won't go unstable?

There is a special number for this type of case!