Error converting discrete to continous transfer function

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Bernie Ngoh
Bernie Ngoh 2019-4-16
回答： Raj 2019-4-16
Hello, when i run my code:
z =tf('z',0.001)
P = 5
I = 5;
D = 5;
C= P + I*(1/(1-z^(-1))) + D*(1-z^(-1));
Cs=d2c(C)
it gives the error:
Error using DynamicSystem/d2c (line 101)
The "zoh" and "foh" methods cannot be used for discrete models with poles near z=0.
Error in Untitled3 (line 6)
Cs=d2c(C)
May I know how to fix this error and convert my transfer function to continous?

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采纳的回答

Raj
Raj 2019-4-16
Your error message is self explanatory. If you dont specify any method for 'd2c' it takes zero order hold method by default and as the error message says 'zoh' and 'foh' cannot be used when you have a pole at '0'. Infact even 'matched' method will not work in this case.
Just change the method to 'tustin' method with following command:
Cs=d2c(C,'tustin')
For details see here.

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