Study On Chattering Of Variable Structure Control

In the 1950s, Emelyanov, a soviet researcher, fist proposed variable structure control (VSC) based on sliding mode (SM). Then Utkin etc developed the theory. Significant interest on VSC with SM has been in the 1970s. So far, VSC with SM has been deeply studied as an important branch of nonlinear control theory. It has been employed to control discrete—time systems, distributed parameters systems and time—delay systems etc.Variable structure control (VSC) has been known theoretically as a powerful control technique capable of providing very robust control, even in variant under certain condition, with respect to system parameter variations and external disturbances. However, chattering on the sliding mode is an obstacle in an engineering system.In this paper the theory of variable structure control based on sliding mode is applied to the control of linear 2-stage inverted pendulum. Chattering reduction strategies are classified into two kinds: traditional strategy and combined control strategy. The former concentrates on a different structure of VSC, while the latter makes use of other advanced control theories (Fuzzy Control) to reduce chattering.Traditional strategy adopts dummy sliding mode control. The results of simulation explain that the latter is good at the former obviously. Fuzzy control theories combined together with the theory of variable structure control, put forward a approach law based on fuzzy logic. Fuzzy approach law applies fuzzy control to adjust the parameters of approach law of sliding mode timely. This method not only ensures the speediness and robustness of the control system, but also can effectively weaken chattering. The results of simulation show this method is efficacious. Under the premise of parameter change, compared dummy sliding mode with fuzzy approach law, simulation researches reach to a conclusion that the former reduces chattering at the cost of lower robust; the latter is batter than the former, which is more robust. Applied the method to the linear 2-stage inverted pendulum, we get a batter control effect.