Disturbance observer based sliding mode control for unmanned helicopter hovering operations in presence of external disturbances

Numerous control techniques are developed for miniature unmanned helicopters to do hover operation with each method having its own advantages and limitations. During the hover operation helicopters suffer from unknown external disturbances such as wind and ground effect. For a stable operation, these disturbances must be compensated accurately. This paper presents a disturbance observer based sliding mode control technique for small-scale unmanned helicopters to do hover operation in presence of external disturbances. To counteract both matched and mismatched uncertainties a new sliding surface is designed based on the disturbances estimations. The controller design is based on the linearized state-space model of the helicopter which effectively describes helicopter dynamics during the hover operations. The model mismatch and external disturbances are estimated as lumped disturbances and are compensated in the controller design. The proposed controller reduces chattering and is capable of handling matched and mismatched uncertainties. The control performance is successfully tested in Simulink.