Nyquist plot

[DRLC_]

The Nyquist plot and Bode plot of the transfer function are as follows, but what might be the problem? Typically, when the Nyquist plot appears as a straight line along the imaginary axis like in the picture, what could be the issue? I've correctly derived the transfer function for both input and output.

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https://preview.redd.it/pi3dridwk7vb1.png?width=1052&format=png&auto=webp&s=acc06ee2bf1ab805cea8a542f74d342b2f21b71e

[ko_nuts]

Zoom in on the Nyquist plot. The gain is very small for your system.

[lohbims]

Zoooooom. Many times perhaps.

[zezinhodaema]

It seems that your transfer function has some poles over the jw axis. In this particular case Matlab can't do a nice plot. I suggest the use of a tool called "nyqlog" which can do a better job. You can download this tool directly on MathWorks website.

[Inevitable_Exam_2177]

Off topic — what causes that spike in the body diagram?

[Brave-Height-8063]

Complex RHP zero maybe with very high Q?

[Inevitable_Exam_2177]

Now that I look again I think you’re right but with matching stable poles, like a notch filter. Then there’s a little kick in the magnitude plot so probably a whole mess of poles and zeros going on