Variable structure control
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Variable structure control (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). VSC and associated sliding mode behaviour was first investigated in early 1950s in the Soviet Union by Emelyanov and several coresearchers.[1]
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The main mode of VSC operation is sliding mode control (SMC). The strengths of SMC include:
- Low sensitivity to plant parameter uncertainty
- Greatly reduced-order modeling of plant dynamics
- Finite-time convergence (due to discontinuous control law)
The weaknesses of SMC include:
- Chattering due to implementation imperfections
- Over-focus on matched uncertainties (i.e., uncertainties that enter into the control channel)
However, the evolution of VSC is an active area of research.[2]