Fractional Study Variable Structure Control Method

Sliding mode variable structure control is a unique nonlinear control methodin which there is a switch in the control. SMC has some significant advantagescompared with other control strategy, including an easier algorithm, theadaptability and complete stability to overcome the uncertain parameter andexternal disturbances, et al. However, there is still room for improvement inmany areas, especially in the state of chattering phenomena of the traditionalSMC and convergence rate. This paper analyzed the current research statusand shortage of the recent SMC method, proposed a variety of improvedfractional-order sliding mode control method with the combination of therecent hot issues, fractional-order theory, and applied to the permanent magnetsynchronous motor speed control system.Firstly, for a class of high-order nonlinear system with uncertain parametersand external disturbances, a new non-singular terminal sliding mode controlmethod was proposed. Slowly decaying with time characteristic offractional-order systems is used to weaken chattering and speed up statusconvergence. On the basis of the proposed method, speed controller ofpermanent magnet synchronous motor was designed, which shows strongrobustness to external disturbance and good control performance.Second, based on global fast sliding mode control method, fractional-ordercalculus operator is used to design sliding plane for a kind of high-ordernonlinear systems, which aims to achieve a faster convergence speed of theglobal state variables, but also suppresses chattering. Fractional global fastsliding mode control strategy is applied to the permanent magnet synchronousmotor speed controller designing, which guarantees robustness, fastperformance and stability.Third, a fractional order adaptive sliding mode control method for PMSMposition-speed loop tracking system was presented, which combines fractionalcalculus theory. The proposed method enables the system to get stronger robustness, shorten the convergence time, weaken chattering phenomenon andget an ideal tracking results.Improved sliding mode control methods proposed in this paper are verifiedthrough simulation and stability analyzed, which shows the proposed methodis feasible and effective.