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Hi,
I'm trying to convert a discrete-time PID-controller to a continuous-time PID using the d2c function.
c_discrete = pid(4.406,0.0114,0.0112,0,0.0050) %Kp, Ki, Kd, Tf, Ts
c_continuous = d2c(c_discrete)
But I keep getting the following Error:
Error using DynamicSystem/d2c (line 108)
The "d2c" conversion failed because the result cannot be expressed as a PID controller.
Does anyone have an Idea, where my mistake is?

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Walter Roberson
Walter Roberson 2024-7-22
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That error is given when Tf < Ts, and apparently exists in order to avoid getting complex-valued outputs.
Your Tf is 0, certainly less than Ts.
Example with Tf > Ts
c_discrete = pid(4.406,0.0114,0.0112,0+0.01,0.0050) %Kp, Ki, Kd, Tf, Ts
c_discrete = Ts 1 Kp + Ki * ------ + Kd * ----------- z-1 Tf+Ts/(z-1) with Kp = 4.41, Ki = 0.0114, Kd = 0.0112, Tf = 0.01, Ts = 0.005 Sample time: 0.005 seconds Discrete-time PIDF controller in parallel form.
c_continuous = d2c(c_discrete)
c_continuous = 1 s Kp + Ki * --- + Kd * -------- s Tf*s+1 with Kp = 4.41, Ki = 0.0114, Kd = 0.00808, Tf = 0.00721 Continuous-time PIDF controller in parallel form.

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Walter Roberson
Walter Roberson 2024-7-22
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c_discrete = pid(4.406,0.0114,0.0112,0,0.0050) %Kp, Ki, Kd, Tf, Ts
c_discrete = Ts z-1 Kp + Ki * ------ + Kd * ------ z-1 Ts with Kp = 4.41, Ki = 0.0114, Kd = 0.0112, Ts = 0.005 Sample time: 0.005 seconds Discrete-time PID controller in parallel form.
c_continuous = d2c(c_discrete, d2cOptions(method='matched'))
Error using DynamicSystem/d2c (line 108)
The "matched" method of the "d2c" command cannot be used for models with negative real zeros with odd multiplicity.
Hi Walter,
thanks a lot for your Help.
Problem solved, System is working.
Greetings
Christoph

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