Algebraic loop: PID control DC motor in Simscape

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I am trying to add a PID controller to the elec_motor_dc_pwm.slx DC motor Simscape example:
Original model:
My model:
However, Simscape complains about an algebraic loop in the feedback path.
This answer says models shouldn't contain both "physical signal to simulink" and "simulink to physical signal" converter blocks. (My picture does.) But then how do you design a feedback controller?
This Simscape help page suggests replacing the "PS-to-S" blocks with blocks like "PS Subtract" and "PS Gain". However, there is not a "PS Derivative" block, which would be needed for a PID controller.
Here is a link to these two models.
Thanks for your help.

Accepted Answer

Sebastian Castro
Sebastian Castro on 11 Oct 2017
Check out this blog post -- I think it sums up pretty well how to address algebraic loops with continuous dynamics (like that PID block):
- Sebastian

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