Nonlinear symbolic LFT model for UAV

A nonlinear modeling framework is presented for an oceanographic unmanned aerial vehicle (UAV) by using symbolic modeling and linear fractional transformation (LFT) techniques. Consequently, an exact nonlinear symbolic LFT model of the UAV is derived in a standard M-Δ form where M represents the nominal, known, part of the system and Δ contains the time-varying, uncertain and nonlinear components. The advantages of the proposed modeling approach are that: it not only provides an ideal starting point to obtain various final design-oriented models through subsequent assumptions and simplifications, but also it facilitates the control system analysis with models of different levels of fidelity/complexity. Furthermore, a linearized symbolic LFT model of the UAV is proposed based on the LFT differentiation, which is amenable directly to a sophisticated linear robust control strategy such as μ synthesis/analysis. Both of the derived LFT models are validated with the original nonlinear model in time domain. Simulation results show the effectiveness of the proposed algorithm.