Add reference line to a Bode Plot

Greetings!

I used the command

h = bodeplot(Gol,{0.1 0.5});

to plot Bode diagrams (Magnitude x Frequency and Phase Angle x Frequency) to analyze the stability of the closed-loop system. Hence, I need to draw a horizontal reference line at y = 1 on the first graph (Mag. x Freq.) so as to find out if my system stable or not.

How do I do that? Were it a simple plot, I'd use refline but it doesn't work for the bodeplot function, since it generates two plots (like subplot(2,1,1) and subplot(2,1,2)). Thank you.

Answer 1

[Star Strider]

It is not worthwhile to attempt to do anything with the plots that bode and most — if not all — of the other Control System Toolbox plots. They do not allow modifications.

Instead, get the outputs from the bode function:

[mag,phase,wout] = bode(sys);

and plot them using subplot. Remember to use the squeeze command to remove singleton dimensions from the ‘mag’ and ‘phase’ results for simple models.

[Leandro Cavalheiro]

Thanks. I'll try that.

[Star Strider]

It will work.

Remember to use semilogx for the subplots, and 20*log10(mag) for the y-axis of the magnitude plot.

Answer 2

[Rick Giovanini]

check this out. Bodes want LTI - Linear Time invariant objects. You can plot many bode's on one plot if you have many LTI objects. What's the LTI transfer function of a horizontal line? Well it's simply

k*tf([1],[1]), where k is the y value I desire. In other works, k*(1/1), or k. We know it's just k that we want, but matlab wants a transfer function.

so, if I want my bode with some horizontal lines, simply do...

bode(mybode, yourbode, NowIfWe_reTalkingBodes_YouGotAPerfectOneSoPutItOnMe, k*tf([1],[1]), r*tf([1],[1]), s*tf([1],[1]))

which simply produces some bodes and lines at y=k, r, and s.

First ever post. Like if it helps you.

[Mirza Sajjad Hussain]

very thanks

[am]

Lol @Rick Giovanini, thanks it helped!