Where Am I Going Wrong With This LTIC System Response?

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SUMMARY

The discussion centers on solving the response of an LTIC system defined by the transfer function H(s) = (s + 2) / (s² + 5s + 4) to the input 5*cos(2t + 30 degrees). The user calculated H(jw) = (jw + 2) / (4 - w² + j5w) and derived the magnitude and phase of H(jw). The error occurred when evaluating the phase angle at w = 2, leading to an incorrect interpretation of arctan infinity. The user ultimately recognized that arctan infinity equals π/2, correcting their approach to the problem.

PREREQUISITES
  • Understanding of Laplace transforms and their application in control systems.
  • Familiarity with sinusoidal inputs and their representation in the frequency domain.
  • Knowledge of complex analysis, particularly in evaluating complex functions.
  • Proficiency in using transfer functions to analyze linear time-invariant systems.
NEXT STEPS
  • Study the properties of Laplace transforms, focusing on convolution in the frequency domain.
  • Learn about the significance of phase angles in control systems and how to interpret them correctly.
  • Explore the concept of stability in LTIC systems and how it relates to transfer functions.
  • Investigate the use of MATLAB or Python for simulating LTIC system responses to various inputs.
USEFUL FOR

Control engineers, electrical engineers, and students studying systems dynamics who are working with linear time-invariant systems and need to analyze system responses to sinusoidal inputs.

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Homework Statement


for an LTIC system described by the transfer function
H(s)=\frac{s+2}{s^2+5s+4}

find the response to the following everlasting sinusoidal inputs:
5*cos(2t+30 degrees)


The Attempt at a Solution


H(jw) = \frac{jw+2}{4-w^2+j5w}

|H(jw)|=\sqrt{\frac{w^2+4}{(4-w^2)^2+25w^2}

\angle{H(jw) = TAN^{-1}\frac{w}{2} - TAN^{-1}\frac{5w}{4-w^2}


and that's where things go bad. if the input is 5cos(2t+30) and w=2 then the angle of H(jw) goes to infinity.

Where am I going wrong here?
 
Physics news on Phys.org
What is the LaPlace transform of your input? How do you do a time domain convolution in the frequency domain?
 
I found my error, I just plain forgot that arctan infinity was pi/2.
 

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