Design of automatic flight controller for an unmanned helicopter based on SDRE

In accordance with different response rate of state variables in Unmanned Helicopter (UMH), the whole affine nonlinear model was divided into inner, middle and outer loops, and then, a “three-timescale” mathematics model was established. The paper improved state dependent riccati equation (SDRE) control approach, deriving analytical conditions for achieving global asymptotic stability with lyapunov theory. Proof was given. By combining improved SDRE control with nonlinear feed-forward compensation technique, the full envelop attitude control laws was designed. On the basis of achieving decoupling control for attitude, a three-axis speed controller was also developed. Actual flight tests were implemented and test results show the effectiveness of control strategies.