Design and Analysis of Modified Super Twisting Sliding Mode Controller for Single Axis Positioning System

Cher, Wei Sheng (2022) Design and Analysis of Modified Super Twisting Sliding Mode Controller for Single Axis Positioning System. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

This research is aimed to improve the Sliding Mode Controller, specifically the Super Twisting Sliding Mode Controller (ST-SMC). As chattering still exists in ST-SMC, the overall performance can be improved by minimizing the chattering effects. Chattering is an undesired phenomenon that could greatly affect the tracking accuracy of machine tools and it is caused by discontinuous signals. The objectives of this research are to design and evaluate an ST-SMC to be implemented into a single axis direct driven positioning system, the designed controller is required to have greater chattering suppression than the existing controller while making a comparison to it. There are quite a few methods to reduce the chattering effects, alternative smoothening function is chosen. The discontinuous signal causes the chattering effect is produced by the signum function in the control law equation in Sliding Mode Control. The signum function gives a signal that keeps switching from 1, 0, and -1 discontinuously. Therefore, with the replacement of signum function with an alternative smoothening function, the discontinuous signal could be eliminated and the chattering could be reduced. As there are plenty of alternative smoothening functions, this research will design the ST-SMC with various of the smoothening functions implemented. The alternative smoothening functions are Gudermannian function, Hyperbolic tangent function, Inversed tangent function, Logistic function, Error function, Generalized logistic function, and Algebraic function. The design of an ST-SMC requires the determination of switching function, control law, and Lyapunov function. These are the components of the Sliding Mode Controller, the design of the controller will involve modification of the control law, which is where the signum function is used and it shall be replaced with alternative smoothening functions. The designed controllers are tested out in simulation with MATLAB Simulink. There are multiple modified-ST-SMCs fulfils the condition which is able to suppress the chattering effect to minimum meanwhile maintaining the results accurately. Therefore, the modified-ST-SMCs were compared with each other and the trade-off between chattering suppression ability and accuracy of the control output is made, a modified-ST-SMC is selected which is Gudermannian-ST-SMC. The Gudermannian-ST-SMC has achieved all of the objectives in this research.