Active Fault Tolerant Control Scheme For Dissimil

Abstract

The increasing demand of Fault Tolerant Control (FTC) schemes in research is due to reliability and safety needed in industrial systems, especially in life critical systems such as spacecraft, passenger aircrafts, Unmanned Aerial Vehicle (UAV), nuclear and chemical plants. FTC is expected to deal with fault or failure while maintaining the stability and desired performance. It is classified as Passive Fault Tolerant Control (PFTC) and Active Fault Tolerant Control (AFTC). Dissimilar Redundant Actuating Systems (DRAS) are mostly used in modern aircrafts to improve the reliability by evading the Common Mode/Common Cause (CM/CC) failure issue of similar redundant actuating systems. DRAS consists of two actuators i.e. Hydraulic Actuator (HA) and Electro Hydraulic Actuators (EHA). The DRAS are operated in two different modes namely active/active (A/A) mode and Active/Passive (A/P) mode. In A/P mode, the HA actively involve controlling the concerned control surface while the EHA and control surface act as a load to HA while in A/A mode, both actuators are engaged in controlling the control surface at the same time resulting in a force fighting exist between them that can even damage the control surface if the actuators are not synchronized. A lot of research has been carried out on DRAS in different operating modes and a significant contribution has been made to improve its stability. This thesis is about an AFTC scheme for modern aircrafts equipped with DRAS in A/A mode to affirm the reliable actuation and efficient control. The dynamics of both actuators of DRAS are considered that gives the desired control surface deflection. The force fighting issue of actuators being in A/A mode, is also addressed in this research. The effect of fault or failure of HA on system performance is analyzed and an Integral Sliding Mode Controller (ISMC) is designed which together with Control Allocation scheme (CA) improves the system performance at different fault severity level.