Research On Fractional Order Disturbance Observer

Fractional calculus includes fractional derivatives and fractional integrals. It means to generalize the differentiation and integration into fractional and complex order. It has a history of more than 300 years. Recently, with the rapid development of computer science and the increasing ability of calculation, the realization of fractional calculus becomes feasible and fractional calculus was noticed and researched by more and more engineers. It is a new research direction for fractional calculus to be used in the control field, and it has also become a research hotspot gradually.Almost every one of physical systems due to various reason of the inner part and exterior, which is still influenced by the plant parameter variations and external disturbances. These uncertainties existence will cause serious infections to the system. In order to reduce the influence caused by the uncertainties factors, and assurance the tracking performance and the restraint disturbance performance, the improved robust two- degree-of-freedom control structure (TFOD)—fractional order disturbance observer (FO-DOB) is adopted to reject the disturbances such as the friction, the model uncertainties and the measuring noise for the improvement of the disturbance suppression and robustness performance. The main research work of this dissertation is given as follows:(1) Systematically summarizes the fundamental theories of fractional calculus, introducing several definiens and the conversion between each other.(2) Introducing TFOD and design methods of the traditional integer order DOB.(3) The rational function discrete approximate methods of FO Q-filer are detailed studied, giving the compared result of different methods, adopting the improved Al-Alaoui+CFE method giving the best approximation effect; basing on the Oustaloup arithmetic, we deduced and validated the chose of the filter's approximate order.(4) Chose the torsional experiment system, adopting FO-DOB to validate its actions on the restrain of the vibration and disturbance. The results indicate that FO-DOB can satisfy the requirement of rapidity, robust stability and disturbance suppression better than PI controller.In conclusion, the main innovative points of the dissertation are as follows:(1) Analyze and validate the choice of FO Q-filter's approximation order based on the Oustaloup curve fitting approximation method.(2) Chose the 2-inertia torsional experiment system as an example, using FO calculus to design FO-DOB, solving the problem of robust stability and disturbance suppression better.