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.{{Cite book|title= Variable Structure Control Systems|editor1-last=Emelyanov|editor1-first=S.V.|publisher=Nauka|location=Moscow|year=1967}}
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.{{Cite book|title=Advances in Variable Structure and Sliding Mode Control|editor1-last=Edwards|editor1-first=Christopher|editor2-last=Fossas Colet|editor2-first=Enric|editor3-last=Fridman|editor3-first=Leonid|publisher=Springer-Verlag|location=Berlin|year=2006|series=Lecture Notes in Control and Information Sciences|volume=334|isbn=978-3-540-32800-1}}
See also
- Variable structure system
- Sliding mode control
- Hybrid system
- Nonlinear control
- Robust control
- Optimal control
- H-bridge – A topology that combines four switches forming the four legs of an "H". Can be used to drive a motor (or other electrical device) forward or backward when only a single supply is available. Often used in actuator in sliding-mode controlled systems.
- Switching amplifier – Uses switching-mode control to drive continuous outputs
- Delta-sigma modulation – Another (feedback) method of encoding a continuous range of values in a signal that rapidly switches between two states (i.e., a kind of specialized sliding-mode control)
- Pulse-density modulation – A generalized form of delta-sigma modulation.
- Pulse-width modulation – Another modulation scheme that produces continuous motion through discontinuous switching.
References
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Further reading
{{refbegin}}
- {{cite book
| author = Hasan K. Khalil
| year = 2002
| edition = 3rd
| url = http://www.egr.msu.edu/~khalil/NonlinearSystems/
| isbn = 0-13-067389-7
| title = Nonlinear Systems
| publisher = Prentice Hall
| location = Upper Saddle River, NJ}}
- {{cite book
| author = Utkin, V.I.
| title = Sliding Modes in Control and Optimization
| publisher = Springer-Verlag
| year = 1992
| pages =
| isbn = 978-0-387-53516-6
}}
- {{cite book
| editor-last = Zinober
| editor-first = A.S.I.
| title = Deterministic control of uncertain systems
| publisher = Peter Peregrinus Press
| place = London
| year = 1990
| isbn = 978-0-86341-170-0
| editor-link = Alan S.I. Zinober
}}
- {{cite book
| editor-last = Zinober
| editor-first = Alan S.I.
| title = Variable Structure and Lyapunov Control
| series = Lecture Notes in Control and Information Sciences
| publisher = Springer-Verlag
| place = London
| year = 1994
| volume = 193
| isbn = 978-3-540-19869-7
| doi = 10.1007/BFb0033675
}}
- {{cite book
| editor1-last = Steinberger
| editor1-first = M.
| editor2-last = Horn
| editor2-first = M.
| editor3-last = Fridman
| editor3-first = L.
| title = Variable-Structure Systems and Sliding-Mode Control
| series = Studies in Systems, Decision and Control
| publisher = Springer-Verlag
| place = London
| year = 2020
| volume = 271
| isbn = 978-3-030-36620-9
| doi = 10.1007/BFb0033675
}}
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