Design of dual-range linear multivariable controllers for nonlinear systems with application to UAV control

In this research, the previous design procedure for single-variable dual-range linear controllers for highly nonlinear systems is extended to the multivariable case. The procedure is based on generating the sinusoidal input describing function models of the plant followed by selection of two of these models for optimization of the dual-range linear controller. A single multivariable controller is designed by optimization to achieve a stable closed-loop system that satisfies a set of user-defined performance measures. Finally, the design is verified by digital simulation of the nonlinear plant and linear controller. Stability is demonstrated by successful generation of the sinusoidal input describing function models of the final closed-loop system. The procedure developed and the associated software are applied to bank-angle control of an unmanned aerial vehicle (UAV) with a discontinuous nonlinear term. It is shown that performance of a dual-range linear controller is superior to that of both a single-range and a multirange linear controller, and it competes with two other nonlinear controllers.