Fault-tolerant control based on rough set theory

The human operator is an excellent controller. The sampling data of the control behavior of an operator is used to construct an original information table, the control rules can be extracted from the information table applying the rough set theory, and the operation behavior can be simulated by the rules. The control rules are the core of a rough controller. An actual system consists of a variable frequency controller (VFC), an ac motor, a pump, and a single-tank. The water level of the tank is controlled at a given value through regulating the input voltage of the VFC. The control behavior is sampled under conditions of no-fault and fault. The control rules of both no-fault and fault rough controllers can be obtained using rough set algorithm. The fault is created by opening the bottom valve of the tank, and its detection is fulfilled using rough model. If the output error between the system and its rough model is within the range of a given threshold, the system is in working order, and it is controlled under the no-fault controller. If the error is beyond the threshold, the controller is switched to fault one to ensure the water lever of the tank within the given height, and the fault-tolerant control of the system is achieved.