Wind estimation for lateral path following of UAVs using higher order sliding mode

In design of guidance algorithm's wind is often ignored or only considered implicitly. Persistent winds has a very significant nonlinear effect on the guidance scheme as for small UAVs these disturbances can strongly affect their spatial orientation. This research work extends the idea of sliding mode control for parameter estimation of UAV nonlinear dynamics. The uncertain parameter estimation scheme is designed to estimate wind based on the higher order sliding mode robust differentiator (HOSMD) using rate of change of heading of the vehicle. Further these estimates are then included in the guidance algorithm. The UAVs guidance algorithm's objective is to derive the lateral track error towards zero with graceful and stable manoeuvres and then to keep it as minimum as possible while subject to disturbing winds. In this scheme a second order sliding motion is established along designed sliding manifold and outputs the reference bank commands for improved tracking performance using estimates during curved arcs. The estimation is combined seamlessly with robust guidance algorithm to produce integrated identification and guidance scheme for lateral path following application. The combined framework is capable of robust accurate path following in the presence of wind disturbance. The algorithm is implemented in the flight control simulation of scaled YAK-54 research UAV; simulation test results are presented. These results demonstrate the effectiveness and performance of the proposed lateral guidance scheme.