Sliding mode controller design based on reaching law for hypersonic flight vehicle

For a hypersonic flight vehicle with highly coupling nonlinear, a sliding mode controller based on reaching law is designed for its longitudinal motion model. Two proposals of reaching law are designed. One of which is a variable exponential reaching law, the other one is compound reaching law which consists of a conventional exponential reaching law and a power rate reaching law. The reaching law controller can speed up the system states arriving at the sliding mode condition, at the same time, it can guarantee better robustness. Simulation analysis is conducted for trimmed cruise condition of 110,000 ft and Mach 15, in which the responses of the vehicle to a step change of altitude and velocity respectively are analyzed. Simulation results show that the controller based on variable exponential reaching law enables the system to faster tracking speed than the conventional reaching law. Moreover the compound reaching law controller has shorter tracking time and strong robustness against parameters uncertainties.