Active fault tolerant control of a Remotely Operated Vehicle propulsion system

This paper presents an active fault tolerant control of a Remotely Operated Vehicle (ROV) propulsion system. An open frame ROV usually requires multi-thruster system to generate various motions. A general framework of active fault tolerant control contains the fault detection and diagnosis (FDD) subsystem and controller re-design subsystem. The FDD subsystem consists of fault detection, isolation and estimation while fault accommodation is chosen as the controller re-design method. In harsh operating environment, thrusters are liable to fault. Therefore, each thruster is monitored by a sensor module called thruster monitoring unit (TMU). As part of FDD subsystem, this module generates information regarding the status of thruster in form of armature voltage and current load feedback. In the case of thruster failure, it is possible to exploit the excessive number of available thruster by re-allocating the required control input i.e. forces and moments acting on the vehicle. This re-allocation procedure is done by fault accommodation subsystem. A Takagi-Sugeno (T-S) fuzzy method is used to accommodate the thruster faults by penalizing the affected thruster and allowing others to continue the operation. An experimental result is presented by demonstrating the effect a blocked ducting and power supply malfunction. The fault accommodation using T-S fuzzy method is proved to be reliable, fast and efficient in handling and accommodating the thruster fault.