Attitude Tracking of the Small-Scale Helicopter System using Disturbance Observer based Sliding Mode Control

Control design for a small-scale helicopter is quite challenging due to its nonlinearities, unknown and unmodelled dynamics, strong cross-coupling effects produced by the vehicles actuators, parametric uncertainties and external disturbances. This paper introduces the design of robust and stable disturbance observer (DOB) based sliding mode control (SMC) to meet these issues. It consists of the disturbance observer in the inner control loop which estimates and attenuates plant input generalized disturbance, and the sliding mode controller in the outer control loop which enforces convergence to the reference and stability of the equilibrium. Introduced disturbance observer is a linear low-pass filter capable to compensate unwanted chattering effects of the sliding mode control. The highly nonlinear helicopter model is introduced to illustrate effectiveness of the proposed control method. Designed controllers are implemented in the simulation mode and experimentally tested in a realistic environment. Obtained results showed that developed DOB based SMC controllers improve tracking performances o ver the entire range of the helicopter output variables even in the presence of additional parametric uncertainties, and external disturbances in the form of wind gusts.