Ask questions for Matlab PID()

1.What is the meaning of demon = [1 3 1]?

2.What is the meaning of Gp=tr(num,demon)?

3.How to interpret this line:

M=feedback(Gp,H)

This is a website address for this PIC control:

https://www.bilibili.com/video/BV1Aq4y1U7bg?from=search&seid=281292339855222775&spm_id_from=333.337.0.0

Thanks

[Walter Roberson]

you miscopied. The code does not use tr(), it uses tf()

https://www.mathworks.com/help/control/ref/tf.html

Control systems are often expressed as transfer functions, each deals with derivatives. The higher the power of s you see, the higher the derivative. The overall expression is the laplace transform of the time function.

Answer 1

[Sam Chak]

Hi @Chris Yang

It is actually not "demon", but "denom", a shortened form of the word "Denominator". A Demon generally means an evil spirit or devil, whereas the denominator is the part below the fraction line:

.

1. The line denom = [1 3 1] creates a horizonatal vector of numbers with 3 elements in it. These numbers are actually coefficients for that will be used for creating the transfer function model later. Similarly, num = [1] creates the coefficient for in the numerator (the part above the fraction line).
2. The line Gp = tf(num, denom) creates the transfer function model for the Plant (a control theory term that stands for a dynamical system to be controlled).
3. The line M = feedback(Gp, H) creates the closed-loop transfer function that loops around the the feedforward transfer function and the feedback transfer function . The transfer function commonly relates the reference input to the output . Since there is only one feedforward element, (no controller ), then the formula is given by .

Hope the explanations help. Also suggest you to take these TWO (2) short courses:

https://www.mathworks.com/learn/tutorials/matlab-onramp.html

https://www.mathworks.com/learn/tutorials/control-design-onramp-with-simulink.html