I am trying to implement a PID controller in a Simscape circuit model but the system doesn't seem to like my format. I am using the PID controller block from Simulink and implementing it within Simscape using the convert from source to Simulink signal block and vice versa for the output. I have already optimized the parameters within a Simulink model but I would like to be able to tune a PID controller within Simscape and not just build three op-amps for the PID parameters.
As i understand from your problem you need to design a controller for your simscape system. So when you design with simscape it's not possible to directly tune the PID parameter.
For this you have to do the tuning manually, first using sensor and PS-S converter block you can store the Input and Output data to the workspace and than do system identification on that data using system identification toolbox and this gives you your system transfer function which helps you to tune PID parameter.
For more information you can read this also
How can I apply different control approach without having a state space model?
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this.