LFT formulation for multivariate polynomial problems

Robust control system analysis and design is based on an uncertainty description, called a linear fractional transformation (LFT), which separates the uncertain (or varying) part of the system from the nominal system. Low-order LFT models are difficult to form for nonlinear parameter-dependent systems. The paper presents a numerical computational method that can be used to construct low-order LFT models for multivariate polynomial and rational problems based on simple matrix computations. This LFT modeling method makes current robust and linear parameter varying (LPV) control analysis and design methods accessible to a broad class of difficult practical problems.