Variable structure control, or VSC, is a form of discontinuous nonlinear control. The method alters the dynamics of a nonlinear system by application of a high-frequency switching control. The state-feedback control law is not a continuous function of time; it switches from one smooth condition to another. So the structure of the control law varies based on the position of the state trajectory; the method switches from one smooth control law to another and possibly very fast speeds (e.g., for a countably infinite number of times in a finite time interval). Variable structure control (VSC) and associated sliding mode behaviour was first investigated in early 1950s in the Soviet Union by Emelyanov and several coresearchers.[1]
Presently, the main mode of VSC operation is sliding mode control (SMC). The strengths of SMC include:
The weaknesses of SMC include:
However, the evolution of VSC is presently an active area of research.[2]