On Wednesday, January 27, 2016 at 14:00 in room no. 641 prof. Morten Hovd from NTNU Trondheim will deliver a seminar on "Sum of squares programming for discrete-time non-linear systems - with application to power converters".

Speaker: prof. Morten Hovd, NTNU Trondheim

Title: Sum of squares programming for discrete-time non-linear systems - with application to power converters

Abstract: The presentaton will give a brief introduction to sum of squares (SOS) programming, and will present some key issues and steps in applying this to Lyapunov-based synthesis for discrete-time nonlinear systems. The focus will be on bilinear systems as many power converters can be modelled as bilinear systems, but the concepts can be generalized to polynomial nonlinear systems that are affine in the inputs. The controller synthesis method will then be illustrated on the control of a Modular Multilevel Converter (MMC) for HVDC. The MMC has several advantages compared to conventional converters for HVDC.  However, the internal control of the converter is a challenge due to a high number of internal switches. With an SOS-based controler we are able to obtain good results. Finally, some robustness issues in the SOS design will be addressed, and illustrated on the averaged model of a boost converter (which also is described by a bilinear model).

References:

P. A. Parrilo: Structured semidefinite programs and semaialgebraic geometry methods in robustness and optimization, PhD thesis, Califormia Institute of Technology, 2000.

J. Löfberg, Pre- and post-processing sum-of-squares programs in practice, IEEE TAC, vol 54, no. 5, pp. 1007-1011.

SOSTOOLS users guide http://www.cds.caltech.edu/sostools/

G. Chesi: Domain of Attraction. Analysis and control via SOS programming. Springer LNCIS 415.