Sliding Mode Tracking Cotrol For Nonlinear Uncertain System

Output tracking control theory is one of the most important researchdirections of control science. The high nonlinearity and uncertainties ofpractical controlled plants have influence on the tracking performance.Study on the robust output tracking of the uncertain nonlinear system isremarkable.Sliding mode control (SMC) which plays an important role in thenonlinear control theory is a type of robust control design. Its mainadvantage is that the controlled system state vector remains insensitive tocertain or matched parameter variations, nonlinearities and disturbancesin the sliding manifold. However, the shortcoming of SMC is thechattering phenomena caused by the discontinuous control action whenthe system operates approach the sliding manifold. To employ the SMCto the nonlinear tracking problem, a lot of studies on this theory areemployed in this paper. The main contributions are described as follows:First of all, an optimal reaching based sliding mode control approachis proposed to deal with the tracking trajectory of the single input single output nonlinear system. The T-S fuzzy logic theory is used to build aglobal uncertain fuzzy state-space linear model. The optimal switchcontrol law which can make sure the robustness of the uncertainfuzzification system is designed to alleviate the chattering phenomenonof controlled system. The self-tuning parameter estimator of switchcontrol gain is applied to compensate the fuzzy modeling errors. Thecontroller ensures asymptotic reference trajectory tracking. Asymptoticstability of the closed loop system is proved.Then an optimal robust regulator is proposed to deal with thenonlinear uncertain system. This control approach hybrids the feedbacklinearization theory with the sliding mode control theory, feedbacklinearization is used to linearize the controlled system, and the slidingmode control theory is applied to design the robust controller. Thesliding surface is integral, which can make sure that the stability error iszero. The definition of the switch control law is designed to compensatethe uncertainties of the system and the unknown external disturbances.In order to ensure the stability of the driving stage without causing toomuch chattering problem, the self-tuning gains of switch control law isemployed.Thirdly, to track the desired output of a complex MIMO nonlinearsystem, a T-S fuzzy based self-tuning sliding mode control approach isproposed. The T-S fuzzy logic theory is used to build a global fuzzy state-space linear model. The sliding surface is defined by using poleassignment method, and the feedback gains can be obtained through thegiven desired poles.in order to avoid the coupling of the complex system,let the input control which has more important impact on the output bethe real control input, other inputs are regarded as the disturbance. Theself-tuning switch control law is used to compensate these uncertaintiesand coupling disturbances.Finally, gain of the sliding mode manifold which is set by the poleplacement has influence on the controlled system output overshootsproblem. A new sliding mode controller is proposed in this paper andapplied to the three tanks water lever control system. The relationshipbetween the sliding mode surface and the controlled output overshoots isinterpreted here. The solution based on this relationship is employed toavoid the output overshoots problem concerning the integral wind upproblem and the system dynamic characteristic. Moreover, the self-tuningswitching control law algorithm is proposed here to decrease thechattering which is the shortcoming of the sliding mode control system.