Can anyone help me with the algorithm used in fitfrd (used to be fitsys in the previous MATLAB versions)? I know that the command is used to fit the frequency response data with a state space representation model. I want to know the algorithm that is used in these two commands. The MATLAB help document didn't help. By the way, this command (fitfrd) is in Robust Control Toolbox and the (fitsys) was available in mu-synthesis and analysis Toolbox.
Thanks.
(1) Both fitfrd and fitsys can be regarded as mu-synthesis approach proposed for robust control system design.
fitfrd means Fit D-scaling frequency response data with state-space model.
fitfrd delivers a state space representation of a fitted transfer function to the given frequency response of the controller.
The book [OS75] provides the detailed introduction of fitfrd.
[OS75] A.V. Oppenheim and R.W. Schaffer, Digital Signal Processing, Prentice Hall, New Jersey, 1975, p. 513.
fitsys attempts to fit given scalar frequency response data in both magnitude and phase (with a SISO system). This algorithm is based heavily on the algorithm invfreqs. The book [LS88] provides more details.
[LS88] J . N. LITTLE and L. SHUREL, The signal processing toolbox, Mathworks 1988.
(2) The papers [Zames66] and [DGKF89] are two landmark papers in robust control system design.
G. Zames, "On the Input-Output Stability of Time-Varying Nonlinear Feedback Systems--Part I: Conditions Derived Using Concepts of Loop Gain, Conicity, and Positivity; Part II: Conditions Involving Circles in the Frequency Plane and Sector Nonlinearities, " IEEE Transactions on Automatic Control, AC–11, 1966.
The paper [Zames66] was selected by IEEE Control Society as "Control Theory developed in the twentieth century: 25 Seminal Papers (1932-1981)" in 2000.
http://www.wiley.com/WileyCDA/WileyTitle/productCd-0780360214,descCd-tableOfContents.html
http://ieeeexplore.com/xpl/bkabstractplus.jsp?bkn=5265919
[DGKF89] JC Doyle, K Glover, PP Khargonekar, and BA Francis, "State-space solutions to standard H2 and H∞ control problems," IEEE Transactions on Automatic Control, 34(8), 1989, pp. 831-847.
The paper [DGKF89] received IEEE W.R.G. Baker Outstanding Paper Award (The most outstanding paper reporting original work in one of the IEEE publications). It is the first time the award has been given to a paper in the control area.
http://en.wikipedia.org/wiki/IEEE_W.R.G._Baker_Award
(3) The following paper applied the robust control approach proposed by [Zames66] in Internet bandwidth congestion control.
Y. Hong and O.W.W. Yang, "Robust Explicit Congestion Controller Design For High Bandwidth-Delay Product Network: A H∞ Approach," Proceedings of IEEE International Conference on Communications (IEEE ICC), Cape Town, South Africa, May 2010.
Available in the following RG link.
https://www.researchgate.net/publication/221167543_Robust_Explicit_Congestion_Controller_Design_for_High_Bandwidth-Delay_Product_Network_A_H_infinity_Approach
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=5502246
(4) Recent discussions on control system design approaches can be found in the following RG link.
"What are trends in control theory and its applications in physical systems (from a research point of view)?"
https://www.researchgate.net/post/What_are_trends_in_control_theory_and_its_applications_in_physical_systems_from_a_research_point_of_view2
Conference Paper Robust Explicit Congestion Controller Design for High Bandwi...
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