Understanding Bode Plots for Second Order Systems with ς‚= 0

[ksurabhi]

hey guys,

i have a question regarding bode plot

g(s)= 1/(s²+4)

i did get the magnitude plot correct but i am unable to understand the phase plot. by calculating on paper i got 0° but in MATLAB it changes from -360° to -180°

i haven't understood how the initial phase is -360 which changed to -180 at the corner frequency(2)

please explain. i would really appreciate if you could explain me how to draw the phase plot for second order system with ς‚= 0

thank you in advance

 

[donpacino]

-360 degrees is equal to 0!

Typically each pole will add a 90 degrees phase shift that begins 1 decade before the pole and ends one decade after. Since there are two poles the phase shift will be 180 degrees