Hi,

sort of an amateur-ish question, but here goes.

i am trying to plot the bode plot of the following transfer function

i am using the margin(tf) call in matlab, but for some reason the phase plot seems to be reversed. i.e. the plot ranges from +180 degrees to -90 degrees.

What I want is the "typical" phase plot which ranges from 0 degrees to -180 degrees. I can't quite seem to figure out what is causing the plot to do this, as my gain factor is not negative and i have 3 left hand poles.

On a somewhat related note, this transfer function also seems strange to me since, even though i have normalised the denominator to a "standard" form, the numerator still has a s^2 term. So, if i was to find the dc gain, would it be zero?

On its own, this would seem ok, but this doesn't quite make sense to me in terms of control loops. When you want to find the uncompensated open loop gain of the loop at s = 0, because of the s^2 term, you would get 0 for the total gain, which seems odd to me. Ideally, as with most examples found in textbooks, i would want the numerator to be equal to 1, but im not sure how i can go about this.

TIA

sort of an amateur-ish question, but here goes.

i am trying to plot the bode plot of the following transfer function

i am using the margin(tf) call in matlab, but for some reason the phase plot seems to be reversed. i.e. the plot ranges from +180 degrees to -90 degrees.

What I want is the "typical" phase plot which ranges from 0 degrees to -180 degrees. I can't quite seem to figure out what is causing the plot to do this, as my gain factor is not negative and i have 3 left hand poles.

On a somewhat related note, this transfer function also seems strange to me since, even though i have normalised the denominator to a "standard" form, the numerator still has a s^2 term. So, if i was to find the dc gain, would it be zero?

On its own, this would seem ok, but this doesn't quite make sense to me in terms of control loops. When you want to find the uncompensated open loop gain of the loop at s = 0, because of the s^2 term, you would get 0 for the total gain, which seems odd to me. Ideally, as with most examples found in textbooks, i would want the numerator to be equal to 1, but im not sure how i can go about this.

TIA

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