Designing a circuit from a transfer function [linear control]

In summary, the conversation discusses designing a controller with a transfer function of 5(s+0.5)(s+2)/s(s+10). The participant mentions using a constant gain of 5 and an integrator, and asks for guidance on choosing discrete circuit components. Another participant offers a solution for implementing the transfer function digitally using the Bilinear Transform. One participant mentions previous experience with implementing transfer functions as difference equations, but is unable to apply it to this question.
  • #1
Ian_Brooks
129
0

Homework Statement



Linear Control Systems - 2006 past paper

If I wanted to design a controller with a transfer function of the form

[tex]\frac{5(s+0.5)(s+2)}{s(s+10)}[/tex]

How would I go about doing so?


Homework Equations



A constant gain is given as a constant
A differentiator will have an S term in the numerator
An integrator will have an S term in the denominator




The Attempt at a Solution



From the transfer function I can see that a Gain of 5 is used, and an integrator is required

How would i choose discrete circuit components to satisfy the above?

Basicly [tex]\frac{V_{out}}{V_{in}}[/tex] = [tex]\frac{(s+0.5)(s+2)}{(s+10)}[/tex]

So some resistor and capacitor network would be needed to realize the remaining transfer function. And an integrator would be needed with some capacitor fed back.

Still I'm quite confused on how to go about this
 
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  • #2
This is probably not what you are looking for, but I can tell you how to implement it digitally.
(I am a software geek and I don't know how to map a s plane transfer function into analog components -- sorry).

The way I would map it into digital hardware or software is to use the Bilinear Transform to map the transfer function into the z plane and then the time domain expression can be read out directly and easily implemented in hardware or software as shift registers. Matlab provides the function bilinear to do this conversion. Just make sure your sampling time is fast enough (2 times the highest frequency component).
 
  • #3
well i have implemented it with software before in a course called real time instrumentation where we made digital filters and represented our transfer functions as difference equations - however, sadly i can't draw from that to get the 4 marks for this question.

any other help?
 

1. How do I determine the transfer function for my circuit?

The transfer function for a circuit can be determined by using the Laplace transform on the circuit's differential equations. This will result in an algebraic equation that relates the output of the circuit to its input. Alternatively, the transfer function may be provided in the circuit's specifications or can be determined experimentally.

2. What is the significance of the poles and zeros in a transfer function?

The poles and zeros in a transfer function represent the frequencies at which the circuit's response will be affected. Poles indicate frequencies at which the output will exponentially increase, while zeros indicate frequencies at which the output will be attenuated. These values are important in determining the stability and frequency response of the circuit.

3. How can I design a circuit to meet specific performance requirements using a transfer function?

To design a circuit using a transfer function, you can use techniques such as root locus plots, Bode plots, and Nyquist plots to analyze the behavior of the circuit and make adjustments to meet performance requirements. Additionally, you can use the transfer function to calculate specific component values for the circuit.

4. What is the difference between open-loop and closed-loop control systems?

An open-loop control system uses only the input signal to control the output, while a closed-loop control system uses feedback from the output to adjust the input. In a closed-loop system, the transfer function includes the feedback loop, while in an open-loop system, the transfer function only includes the components of the circuit.

5. How can I test and validate the performance of a circuit designed from a transfer function?

To test and validate the performance of a circuit, you can use simulation software or build a physical prototype. The transfer function can be used to compare the simulated or measured output of the circuit to the desired response. Any discrepancies can be addressed by adjusting the circuit's design or components.

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