Discrete-time second-order-sliding-mode observer for state and unknown input estimation: Application to a 3DOF helicopter

This paper demonstrates a discrete-time state observer for a 3DOF helicopter subject to unknown perturbations. The observer is based on a very recent second order sliding mode scheme [12], which is robust in spite of uncertainties and perturbations, ensures finite time convergence to boundary layer, reduces the chattering, increases estimation accuracy and does not require the knowledge of the bound of unknown input, not restricted to matched disturbances. Also, an unknown input estimation scheme is proposed based on the second order sliding mode observer. A practical example of perturbation estimation for a 3DOF helicopter is experimentally demonstrated.