Open-loop reference models for nonlinear control with applications to unmanned helicopter flight

A novel way to design a nonlinear feedforward controller is introduced. Contrary to input-output linearization and pseudo control hedging techniques, the new formulation proposed is based on the states of the reference system instead on the states of the plant. By reshaping the structure commonly used in literature the similarities between the resulting scheme and what is made in model following control are utilized to get a pure nonlinear feedforward system which is completely decoupled from system outputs. This permits the application of the nonlinear control law when knowledge of the system states is not available. Due to the strict separation of plant and reference dynamics in the proposed approach a stability analysis of the reference system can be simplified. This new control scheme has been used for the control of an unmanned helicopter demonstrating its applicability. Results of these flight-test are presented in this paper.