Panitnart Chawengkrittayanont.. Finite-time higher-order sliding mode controllers and observers for mechanical systems. Doctoral Degree(Applied Mathematics). King Mongkut's University of Technology North Bangkok. Central Library. : King Mongkut's University of Technology North Bangkok, 2020.
Finite-time higher-order sliding mode controllers and observers for mechanical systems
Abstract:
This thesis studies two sliding mode controllers and two sliding mode observers
for a class of multi-input multi-output mechanical systems with uncertainties and
external disturbances. The first controller is a smooth second-order sliding mode
controller and the second controller is a third-order sliding mode controller. Both
controllers provide robustness, high-order accuracy and fast convergence to a desired
state. By using a smooth controller, the high-frequency amplitude oscillations
(chattering) that can be caused by non-smooth controllers are reduced. Lyapunov-
based theorems are used to prove (i) global and finite-time convergence of the
smooth second-order controller and (ii) ultimately uniform convergence for the
third-order controller.
Numerical simulations are presented to illustrate the fast finite-time convergence of the smooth second-order controller by applying it to a two-link robotic
manipulator. Detailed comparisons are also given of the finite-time convergence
and chattering properties of the smooth second-order controller, a super-twisting
controller and a super-twisting like controller for the manipulator. The results
show rapid finite-time convergence of all controllers to neighborhoods of desired
trajectories within approximately three seconds and no chattering for the smooth
second-order controller. We investigate numerically the convergence of the third-
order controller by applying it to an inverted pendulum system. Detailed comparisons are given of the steady-state errors and convergence rates for the third-order
controller, a second-order super-twisting controller and a third-order super-twisting
controller for the inverted pendulum. The results show that the second controller
gives the fastest convergence to a desired trajectory for the inverted pendulum and
the fastest convergence of the sliding variable to a neighborhood of zero.
The two sliding mode observers are based on continuous higher-order sliding
mode and terminal sliding mode concepts. Lyapunov stability theory is used to
prove finite-time global convergence for the first observer and uniformly ultimate
boundedness and global convergence for the second observer. Numerical simulations
are given to show the convergence properties of the two observers by applying them
to estimate states of a simple pendulum system with Coulomb friction and external
perturbations. Detailed comparisons are also given of the convergence properties of
the two observers and a continuous nonlinear differentiator for the pendulum system.
The results show that the two observers give the fastest finite-time convergence
and the smallest error.