A second order sliding mode strategy for fault detection and fault-tolerant-control of a MEMS optical switch

摘要

Optical switches are widely used in telecommunication industry due to their many desirable characteristics. In this paper, robust fault detection and fault-tolerant-control (FTC) system for an uncertain nonlinear MEMS optical switch are presented. The design strategy is based on the second order sliding mode approach. A robust second order nonlinear sliding mode observer capable of filtering unwanted high frequencies due to unmodeled dynamics is used to generate quantities called the residuals. The residuals are then used for the purpose of fault detection and alarm generation. Once an alarm is registered, a fault tolerant control strategy is employed. Two different fault-tolerant control strategies for the unhealthy system are considered. The first strategy is based on conventional sliding mode, while the second is based on a second order sliding mode theory. Robustness and convergence of the proposed schemes are proved using the second method of Lyapunov and the super-twisting algorithm. A comparative study is then performed to demonstrate the superior capability of second order sliding mode control strategy in fault accommodation. Finally, the effectiveness of the proposed strategy for detection of faults, and subsequent control of the MEMS optical switch is illustrated through simulation studies.