Matlab Control Systems Question

[mcfetridges]

I am having a problem with plotting Bode plots in Matlab. We are required to plot a e^(-sT) (simple time shift) as a Bode plot. The "bode" function in Matlab requires either a TF, ZPK, SS, or FRD system as its first input. I cannot seem to find out how to plot the exponential. I can easily plot the normal transfer functions however. If anyone has any idea that would be great.

Stephen McFetridge
University of Alberta

 

[SGT]

I am having a problem with plotting Bode plots in Matlab. We are required to plot a e^(-sT) (simple time shift) as a Bode plot. The "bode" function in Matlab requires either a TF, ZPK, SS, or FRD system as its first input. I cannot seem to find out how to plot the exponential. I can easily plot the normal transfer functions however. If anyone has any idea that would be great.

Stephen McFetridge
University of Alberta

Define a frequency vector, for instance:
omega = 0.1:0.01:10
% omega goes from 0.1 rad/s to 10 rad/s by steps of o.o1 seconds.
Then define your function
H = exp(-i*omega*T)
where T is the known delay
The amplitude in dB is:
Amp = 20*log10(abs(H))
and the phase in radians
Phase = angle(H)
Now you can draw the Bode plots as
semilogx(omega, Amp)
semilogx(omega, Phase)

 

[tacman]

Hi Stephen,

Thank you for reaching out with your question. I understand that you are having trouble plotting a Bode plot for a simple time shift using the "bode" function in Matlab. I would be happy to offer some suggestions to help you solve this problem.

First, let's take a look at the requirements for the first input of the "bode" function. As you mentioned, it requires a transfer function (TF), zero-pole-gain (ZPK), state-space (SS), or frequency response data (FRD) system. This means that you will need to convert your exponential function into one of these forms in order to plot it using the "bode" function.

One approach you could try is to use the "tf" function to create a transfer function from your exponential function. The syntax for this would be: TF = tf(num,den), where "num" is the numerator coefficients and "den" is the denominator coefficients of your exponential function. You can then use this transfer function as the first input for the "bode" function.

Another option is to use the "frd" function to create a frequency response data (FRD) system from your exponential function. The syntax for this would be: SYS = frd(G,w), where "G" is the magnitude and phase of your exponential function and "w" is the frequency vector. Again, you can use this FRD system as the first input for the "bode" function.

I hope these suggestions are helpful in solving your problem. If you continue to have trouble, I recommend reaching out to your professor or a teaching assistant for further assistance. Best of luck with your project!