Questions tagged [nyquist-plot]

For questions about Nyquist plots, often used to assess the stability of an electrical circuit which includes feedback. Consider also using the "frequency-response" tag, and "stability" tag if your question is about the stability of an electrical circuit.

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Sampling frequency of ADC and maximum frequency of input signal

As pair the datasheet of LTC2207, maximum input frequency can be 700MHz. whereas the sampling frequency is 105MSPS. Two times 700MHz is way less than 105MSPS. So how is this not contradicting with ...
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Nyquist stability criterion in discrete time domain

I've been transforming systems from the s-domain to the z-domain, and looking at the Nyquist plots I get in the z-domain. So far I've assumed that the Nyquist stability criterion that applies in the s-...
1 vote
64 views

Allowable process variation for non minimum phase plant

Scenario (plant model subject to process variations) Consider a plant $P(s)$ in series with a controller $D(s)$ with a negative feedback path around it, where the closed loop is given by the ...
1 vote
45 views

Control engineering: how to design a system for desired impulse response

I've designed a system to get a desirable step response. However, I think the impulse response of my system is more important. There are many methods for designing a system for transient response ...
42 views

Why is the second red point also considered a clockwise crossing on the Nyquist plot?

From this page: The image below shows the same Nyquist path, but a different line. In this case there are two clockwise crossings (red) and two counterclockwise crossings, for a total of zero ...
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Assign Bode plots to Nyquist diagrams

How do I assign the following Bode plots to their corresponding Nyquist diagram? Can i tell the number of poles of the transfer function of the nyquist plot, by looking at w→infinity (from which of ...
1 vote
329 views

Deriving a transfer function from Nyquist plot

I am given a half Nyquist plot and exercise as below I know how to plot a Nyquist curve for a given transfer function but I have trouble doing it the other way. I stumbled upon this post Deriving ...
1 vote
81 views

Instability as seen in time domain

It is my understanding that an unstable closed loop in a minimum-phase system occurs when the loop gain (A*B of the characteristic equation) encircles the -1 point on the Nyquist chart. In https://www....
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Nyquist Plot Stability with Angle

I don't understand the solution done here. The Nyquist criteria I know is Z=N+P and I don't see the relation with this solution. Where do the angles come from?
1 vote
446 views

Deriving transfer function from nyquist plot

I am given a half Nyquist plot as below The dashed line stands for the asymptote of the locus and the poles are 0 or negative at real parts, besides there is no double root in the transfer function. ...
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How to check for stability for non-constant controller using Nyquist plots?

Let's say I have a unitary feedback system with one unstable (RHP) pole. Now if my $G_c$ is a constant, say $K$, I know that in order to have stability I should have a single counterclockwise ...
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Recording aliased tones on purpose

For research purposes, I am trying to transmit a tone and record it using sub-Nyquist sampling. Via the PC microphone, for instance, I would expect to see the aliasing effect somewhere in the ...
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1 vote
397 views

Nyquist Criterion: Encirclement around origin

I am studying the Nyquist stability criterion and I am stuck on the following problem. The open-loop transfer function with unity feedback is $\small\mathrm{ G(s)=\large\frac{1}{s-3}}$. Following is ...
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1 vote
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How to determine difference between LHP poles and zeroes by observing Nyquist plot?

I am solving practice problems on Nyquist Plot and I got stuck at a problem having a solution which I do not get at all. Here it is: Which of the following is the transfer function of a system having ...
349 views

Confused regarding gain margin and stability

I plotted the bode plots of the transfer function: G(s)= 2.123×10^6 ((0.105s+1.01))/(s^2 (s+12566.37) ) It is as follows: As can be seen, it shows the gain margin as negative infinity, however loop ...
1 vote
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Nyquist Plot from Bode Plot

How do I know the value at which the Nyquist plot crosses -180 degrees from looking at the Phase plot from the Bode?
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1 vote
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Gain margin and phase margin in Nyquist plots

Finding gain and phase margins from Nyquist plots is basically finding the margin of change in gain and phase beyond which the plot encircles -1, respectively, with the assumption that the Nyquist ...
82 views

What is this functions Phase crossover frequency?

OLTF loop gain My approach What I have done wrong?
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How to find Phase crossover frequency?

I make the imaginary part of $loop \ gain=0$ to find phase crossover frequency. But in one video, the person told that this method can only be applied when Polar plot crosses the real axis and ...
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Questions on Bode Plot and Nyquist Plot

Bode Plot 1) Why the gain plot |G(jw)| drops and then increases for conjugate zeroes ? 2) Why the gain plot |G(jw)| increases and then drops for conjugate poles ? Nyqust Plot 3) For Figure 9-18(B),...
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1 vote
675 views

Stability and Positive/Negative feedback

I often read that positive feedback is used to get oscillators (since the output of the circuit is summed up to its input signal and so leads to instability), while negative feedback to get amplifiers ...
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1 vote
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Why "-1 + 0j" is critical point on Nyquist plot?

I am reading about Nyquist plot from this (http://www.cds.caltech.edu/~murray/books/AM08/pdf/fbs-loopanal_11Nov18.pdf) chapter. On page no. 10-2 its mentioned that "-1 + 0j" is critical point on ...
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Is the book wrong about the Nyquist Sampling Criterion?

Is the following statement from a book wrong? I thought sampling with twice the signal's highest frequency component would be adequate to completely recover the signal. But above it says sampling ...
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How does a time delay affect the Gain and Phase Margin?

How does a time delay affect the gain and phase margin. Answers using nyquist plots would be helpful I know that a time delay of t corresponds to gain multiplying by 1 and phase subtracting omega*T . ...
561 views

According to the Nyquist criterion this system is stable but when I apply an impulse I get an unstable response, why?

I have this open loop transfer function and I have to study the stability of the closed loop transfer function using the Nyquist criterion. What I got is that the characteristic equation 1+GH(s)=0 has ...
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Nyquist Stability Criteria

Find the stability where: Find the stability: $G(s)= \frac{(s+3)(s+5)}{(s-2)(s-4)};$ $H(s)= 1;$ I run this code in matlab: ...
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