Published: CABEQ 22 (1) (2008) 41–47
Paper type: Original Scientific Paper

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Sliding Mode Controller for Unstable Systems

S. Sivaramakrishnan, A. K. Tangirala and M. Chidambaram

The method proposed by Rojas et al.1 for the design of sliding mode controllers (SMC) for unstable first order plus time delay systems, is extended for delay-time constant ratio (ε) up to 1.8. The SMC settings obtained for various ε are fitted by simple equations. Up to ε = 1.2, the method is found to be more robust than that of latest PID Controller proposed by Padmasree et al.2 There is no method available in literature to stabilize unstable systems using PID controller for ε > 1.2. Simulation results are also given for a nonlinear bioreactor control problem.

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Sliding Mode Control, First Order plus Time Delay Systems (FOPDT), Unstable Systems