Design of fault tolerant control system for quadrotor under sensor faults

In this paper, a fault-tolerant control system is designed for a quadrotor system. First, a control system was designed in the healthy mode then the system is upgraded to a fault-tolerant control system by using an analytical redundancy. This control system consists of two parts: (1) attitude control and, (2) position control. The inner loop is related to the control of the quadrotor attitude, and it is responsible for the stabilization and control of the Euler's Angles (azimuth, pitch and roll) and height. The outer loop is also related to the position control. This loop, according to the command of position, calculates the angles required to execute them and transmit them to the attitude control. The attitude and position control were implemented by using fuzzy and PD controllers respectively. Then, Parity space relations are used to detect and estimate actuator faults. As follow as these, control redesign is performed for fault tolerance and correction inputs by using fault signals. The difference between the healthy and faulty outputs approximately are reached to zero by using the PID controller. Two scenarios are considered for actuator faults. The first one is, the fault occurs in motor 1 and 2, and the second scenario is, fault happens in all motors. Finally, according to the actuator saturation, the critical value (maximum) of fault tolerance is estimated.