Multi-timescale SDRE control 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 improve the design method and add a proportion+ integral (PI) controller. SDRE is solved by “θ - D” method. The simulation results show satisfactory tracking performance of the designed control system.