simulink transfer function with time constant changing during simulation

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Marian
Marian 2011-12-17
回答： Marian 2020-3-26
I'm trying to create in Simulink a transfer function, say 1/(T1*s+1), with T1 changing during simulation depending on various conditions. Since I cannot change manually the value for T1 the use of Transfer Fcn block is not possible. My question is how can I implement this transfer function?

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Fangjun Jiang
Fangjun Jiang 2011-12-17
Assume your input is x and output is y:
y=x/(T1*s+1)
y*T1*s+y=x
y*T1*s=x-y
y=(x-y)*(1/s)*(1/T1)
1/s is an integrator, use a negative feedback to get (x-y), 1/T1 is the gain, or can be a multiplication block. You can construct your transfer function now.
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Marian
Marian 2018-7-24
Is it a transfer function, such as k/((T1*s+1)(T2*s+1)) or is it another situation?
Molly Brun
Molly Brun 2020-3-25
How would you acheive this with the function looking more like this: K/(T1s^2+T2s+1) ? I am trying to keep it all in the transfer function block and change the denominator coefficient to include these variables.

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Marian
Marian 2020-3-26
The transfer function K/(T1s^2+T2s+1) is associated with the differential equation T1*y'' + T2*y' + y = K*u.
It can be written: y'' = (K*u - T2*y' - y)/T1
So the transfer function can be implemented like in the figure
This is a subsystem like
The transfer function is implemented as a subsystem with its parameters (K, T1, T2) available for change from external blocks.
You can compare the answer of this subsytem with the answer of a transfer function block. In this example, the transfer function is 2/(12s^2+7s+1). You will see that are the same.
I hope this is what you looking for.

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