Nonlinear state space model representation

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Cosmin Delea
Cosmin Delea on 17 Apr 2016
Commented: Luis Martinez on 27 Mar 2021
Hello everyone,
I would like to compute a continous-time nonlinear model using the state-space related blocks in Simulink (and NOT by using integrator blocks). The difficulties I've encountered were regarding setting up the state matrices: the state matrices (A,B,C) contained functions of the state variables, which I cannot define in the state space Simulink block, but are generated automatically.
I would appreciate very much any suggestions. Thanks.
Best regards, Cosmin
  2 Comments
Cosmin Delea
Cosmin Delea on 25 Apr 2016
Edited: Cosmin Delea on 25 Apr 2016
Hey Stefan,
Thank you for your answer. You are right, state space models have to be linear in Simulink. I also got an official answer from Mathworks saying:
"State Space block in Simulink is designed to implement linear state space systems. It does have A, B, C and D matrices as explicit parameters. Most non-linear systems cannot be expressed in State Space representation (with A,B,C,D matrices) without linearisation. I would suggest to implement the non-linear system with an "integrator" block."
To answer your question, I wanted to implement the non-linear system via SS, instead of integrator blocks, because of the more intelligible and compact aspect. Of course, one can make subsystems to overcome this aspect, but working in Matlab in background, I find working with state matrices more convenientely.
With respect, Cosmin

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Answers (1)

Firas Omran
Firas Omran on 7 Oct 2017
Hello, Can you please tell me how you solved your problem because i am trying to build a nonlinear state space model with some random state space (rss command) and I cannot combine them together in one system.
Thanks Firas
  2 Comments
Luis Martinez
Luis Martinez on 27 Mar 2021
Ok so my system is reasonably complex (w/o linearizing it) , so my plan was to express my matrix A (in state space) as the jacobian matrix without evaluating at the operating point, since my feedback control desing will be in ss so basically i will design in linear and then add the feedback gain to the nonlinear simulink model , thats why i think the jaccobian is the right approach because i need to have a matrix A with the same dimensions as my feedback design. I am think of using "MATLAB function" to implement my A nonlinar jacobian matrix but im not sure on how to do this.

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