The Unidirectional Auxiliary Surface Sliding Mode Control for Compound High-speed Helicopter

By the introduction of advancing blade concept rotor system, the compound high-speed helicopters become a hot research topic in recent years. Due to the novel coaxial rotor and propeller structure of the compound helicopter, the aerodynamic coupling effect between the coaxial rotor and the fuselage has strong influence to the overall performance of the helicopter at low flying speed. In order to accommodate this problem, this paper presents a novel{unidirectional auxiliary surface sliding mode control method for the attitude control of compound helicopters. In the proposed work, the flight dynamics of the novel structured compound helicopter are firstly introduced. Then, expanding the positive invariant sets with 6 unidirectional auxiliary surfaces and an exponential approaching law and a terminal attractor are incorporated into the framework so as to increase the convergence speed and ensure the state error converges within finite time. The stability of the newly developed algorithm is analyzed through the Lyapunov approach. Comparative simulation results have demonstrated that the proposed method is capable of tracking attitude commands and shown strong robustness to the uncertainties.