A transfer function out of a complex function

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Sydney Flowers 2013-6-5

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Hi everyone, got this problem when trying to design a PID controler, so the function is here:

L=(4*exp(-t)+4*t+6)/10

i just can't get it right with all this num and den coefficients since this is a combination of ordinary function and an exponential fucntion. the question is: how do i turn it to a transfer function? got lost really.

Thanks, Sydney.

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Azzi Abdelmalek 2013-6-5

What is L?

Sydney Flowers 2013-6-5

编辑：Sydney Flowers 2013-6-5

L is a function which indicates the change of the location of the rotor in time - Z-axis vibration. The function in question is a simplified law, out of which the sin(omega) was taken away and replaced by 1, for i had no idea how to make it in tf, and c and b coefficients were made numeric constants.

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回答（2 个）

David Sanchez 2013-6-5

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substitute in your L function:

exp(x) = 1 + x + (x^2)/4 % Taylor expansion

Operate until you obtain your num and den, then:

my_sys = tf( num, den )

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Azzi Abdelmalek 2013-6-5

what are num and den?

Sydney Flowers 2013-6-5

numerator and denumenator - coefficient vectors that make up a transfer fucntion.

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Azzi Abdelmalek 2013-6-5

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If L is your impulse response, Maybe L is

%L(t)=0.1(4exp(-t)-4t+6)u(t) % u(t) is a step function

The transfer function of your system is the Laplace transform of your impulse response

%L(p)=0.1*(4*1/(p+1)-4*1/p^2+6/p)
%L(p)=0.4/(p+1)-0.4/p^2+0.6/p=(p^2+0.2p-0.4)/(p^3+p^2)
num=[1 0.2 -0.4]
den=[1 1 0 0]
H=tf(num,den)

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Azzi Abdelmalek 2013-6-5

在 MATLAB Online 中打开

Do you mean

h: your output signal
m,c,k and F are constant

What about your input signal?

Sydney Flowers 2013-6-5

F is a disturbing force, so, if i get you right, the input is initial value of the gap h, and omega, on which the F depends. and output is a new value of the gap.

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