Improved SDRE control for an unmanned helicopter based on multi-timescale dynamics model

This paper proposes an improved state-dependent Riccati equation (SDRE) attitude control approach which is applied in an unmanned helicopter (UMH). To deal with inherent unstable dynamics, the flapping, rotational dynamics and translational motion of UMH are organized into a multi-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 avoid the nonlinear feedforward compensator's disadvantage of being directly affected by parametric disturbances, we reform the design method and add a proportion+ integral (PI) controller. SDRE is solved by “θ-D” method. The speed controller uses traditional PID techniques. Simulation results show satisfactory tracking performance of the designed control system.