Design of Extended Kalman Filter Optimized Fuzzy PID Controller for a Quadcopter in the Event of One Rotor Failure

Abstract

A quadcopter is an Unmanned Aerial Vehicle (UAV) that uses four rotors in a cross or plus configuration for lifting and propulsion. Its basic motion is generated by varying the speeds of all the four rotors. It is an under actuated vehicle with unstable dynamics since it is a 6 degree of Freedom (DOF) device with only four actuators. Moreover, these quadcopters have hardware redundancy limitations thereby calling for design of reliable control systems for efficient performance. It is therefore a challenge to maintain quadcopter stability when one of the rotors is faulty, this is as a result of further under actuation. Previous research in literature assumes the quadcopter is equipped with a fault diagnosis, detection and isolation unit, that continuously assesses the state of the quadcopter or that the fault has already been detected and isolated. Switching is therefore expected between the healthy state controller and a faulty state controller. This procedure is complex and therefore prolong the stabilization time. Most of the available literature also investigated partial rotor failures of up to 20 % only.In this work, an Extended Kalman Filter Fuzzy Proportional, Integration and Derivative (PID) controller is applied for control of a quadcopter in the presence of 100 % fault on a single rotor. The system does not use a fault diagnosis and detection system and only employs a single controller. A fuzzy system is used to tune the PID controller gains while the tuning of the fuzzy Membership Functions (MF) is performed using an Extended Kalman Filter (EKF). The optimized Fuzzy PID controller constrains the system to its set point, returning the system to its stable hovering position. This is accomplished by varying simultaneously the velocity of the three fault free rotors. By computing the adaptive PID gains in real time, the effects of rotor failure are compensated. The controller stabilizes the attitude and altitude of the quadcopter and enables it to make a safe landing without causing further damages to the quadcopter structure.