A nonlinear attitude control method for an unmanned helicopter

This paper proposes an improved state-dependent Riccati equation (SDRE) attitude control approach which is applied to an unmanned helicopter (UMH) through a multi-timescale structure. To deal with inherent unstable internal dynamics, the flapping and rotational dynamics of the helicopter are organized into a two-timescale nonlinear model. To overcome the problem that a number of terms can´t be accounted in the SDRE design, we employ a nonlinear feedforward compensator that is designed to match the vehicle response to the model used in the SDRE design. To overcome the feedforward compensator´s disadvantage of being directly affected by parametric disturbances, we improved the design method and added a proportion+ integral (PI) controller of altitude angle and rotation velocity. The simulation results show satisfactory tracking performance of the designed control system.