Active adaptive continuous nonsingular terminal sliding mode controller for hypersonic vehicle

An active adaptive continuous nonsingular terminal sliding mode algorithm (ACNTSM) is designed for hypersonic boost glide vehicle to achieve higher control accuracy and faster response speed. Firstly, a continuous nonsingular terminal sliding mode controller is presented to make the tracking error and sliding variable converge to zero under the effect of time-varying disturbance in finite time. Compared with traditional terminal sliding mode control using exponential approach law, the ACNTSM algorithm can generate continuous control signal, which effectively reduces chattering. Secondly, a novel active adaptive law is proposed to reduce convergence error, to avoid excessive gain, and to attenuate chattering by adjusting the gain of ACNTSM. The adaptive scheme includes sliding variable and disturbance estimation. The disturbance estimation is obtained by using the integral term of generalized super twisting sliding mode algorithm. The method takes less computational resources and reduces complexity of algorithm. In addition, the gain can automatically increase to shorten convergent time until the sliding mode is reached and then decrease to reduce chattering until the sliding mode is lost. The novel adaptive law ensures the finite-time convergence to a neighborhood of origin for sliding variable without overestimation of gain. Finally, numerical simulations are carried out to demonstrate the effectiveness and superiority of ACNTSM.