Camille-Alain Rabbath

Design of feedback linearization control and reconfigurable control allocation with application to a quadrotor UAV

Based on the developed nonlinear dynamic equations of a quadrotor (named as Qball-X4) UAV (Unmanned Aerial Vehicle), attitude and trajectory tracking control designs based on an inner/outer loop control structure has been proposed in this paper. Feedback linearization is designed to control the attitude stability in inner loop, traditional PID is designed to follow trajectory in accordance with pre-planned paths based on the Qball-X4 nonlinear model. For taking care of faults occurred in the UAV during the flight, reconfigurable control allocation is implemented together with the above controllers. Performance of constrained optimization algorithm for reconfigurable control allocation design — Fixed-point (Fix) algorithm with applications to Qball-X4 is evaluated under different partial-loss fault cases. Various simulation results have been provided to demonstrate the validity of the fault tolerant control system design and the effectiveness of the reconfigurable control allocation design in trajectory tracking control.

Robust Fault-Tolerant Control using on-line control re-allocation with application to aircraft

This paper investigates the design problem of robust Fault-Tolerant Control (FTC) by using on-line control re-allocation for a class of uncertain systems and its application to flight tracking control. The design procedure consists of two parts: robust fault-tolerant baseline controller design, and realization of a control re-allocation scheme. The baseline controller is obtained by an iterative LMI method, which not only stabilizes the uncertain system but also provides sufficient robustness to allow for an effective operation of the Fault Detection and Diagnosis (FDD) subsystem in the event of actuator failures. The re-allocation scheme redesigns an optimal control law without requiring reconfiguration of the baseline controller, and compensates for actuator saturation via Cascaded Generalized Inverse (CGI) method. Simulation results show the effectiveness of the proposed approach.

Model Reference Adaptive Fault Tolerant Control of a Quadrotor UAV

This paper presents some experimental results on actuator fault-tolerant control (FTC) for a quadrotor Unmanned Aerial Vehicle (UAV) system. The strategy is based on Model Reference Adaptive Control (MRAC) where three di erent MRAC techniques are implemented and compared with a Linear Quadratic Regulator (LQR) baseline controller, namely the MIT rule MRAC, the Conventional MRAC (C-MRAC) and the Modi ed MRAC (MMRAC). The main advantage of the MRAC strategy is that it does not require an explicit information about the fault location and/or amplitude and thus, a fault detection and diagnosis module is not needed to detect, isolate and identify the occurred faults. The performance of this MRAC-based FTC is tested in the presence of three types of actuator faults: loss of e ectiveness in the total thrust, loss of e ectiveness in one of the rotors and partial damage of one propeller.

Towards Decentralized Fault Detection in UAV Formations

A decentralized fault detection (DFD) scheme warranting mission integrity for leader-to-follower formations of almost-lighter-than-air vehicles (ALTAVs) is proposed. Such DFD allows compensating for concurrent communication network and component-level faults that may significantly impact mission integrity despite the presence of on-board fault detection, isolation and recovery for actuator and sensor faults. The formation of unmanned ALTAVs is beforehand stabilized by a distributed formation guidance scheme that uses neighboring vehicle information. Each ALTAV is equipped with an observer based on simplified models of the neighboring ALTAVs. The observer and the guidance law use the same local information. Residues associated with neighboring vehicle states carry the information as to their normal or abnormal flight conditions, thereby determining whether or not there is a fault in the neighboring vehicles. The observer design is formulated as a mixed H2/Hinfin controller synthesis compensating for exogenous disturbance estimates and accounting for noisy measurements. The minimum detectable fault and the associated threshold are shown to be increasing functions of the relative distance between the formation leader and the follower vehicle at hand, which means that the value of the threshold may vary from one follower to another depending on its relative distance from the leader. Simulations based on high-fidelity nonlinear 6DOF ALTAV models show that the proposed team-level DFD scheme combined with a simple guidance adaptation technique enable quick hard fault/failure detection while preserving leader-to-follower formation geometry requirements.

Dead reckoning and Kalman filter design for trajectory tracking of a quadrotor UAV

The dynamic equations of a quadrotor unmanned aerial vehicle (UAV), namely Qball-X4, are analyzed and built, trajectory tracking control design based on an inner/outer loop control structure is proposed in this paper. The method of analytic geometry is used in dead-reckoning, discrete Kalman filter has been applied to trajectory tracking for improving the accuracy of estimated location. Integrated online waypoints pre-planning and trajectory tracking control have been carried out. Simulation results demonstrate the effectiveness of the proposed approach.

Optimizing the location of sensors subject to health degradation

One of the main hypotheses supporting the development of cooperative unmanned systems is that the deployment of mobile assets (sensors, weapons) in groups is expected to result in a more effective mission than if conducted with a single asset. Few researches have tackled the design of autonomous decision making for teaming UxVs (unmanned air and ground vehicles) operating under degraded conditions, even though it is common knowledge that real operations are more often than not conducted in less-than-ideal conditions. We consider a team of UxVs that have for mission to persistently monitor an area. We want to ensure they perform as best as possible assuming they are subject to a limited set of degraded conditions. We propose a model to account for variable sensor effectiveness as well as a method to optimize their placement based on a cost balancing heuristic. Numerical simulation suggests accounting for sensor effectiveness improves their placement.

Two Reconfigurable Control Allocation Schemes for Unmanned Aerial Vehicle under Stuck Actuator Failures

Two reconfigurable control allocation (called also as control reallocation) schemes for Unmanned Aerial Vehicle (UAV) under stuck actuator failures have been proposed in this paper. The two control reallocation algorithms include a cascaded generalized inverse algorithm and a fixed-point algorithm. The performance of the two algorithms has been evaluated with a UAV model known as ALTAV (Almost-Lighter-Than-Air-Vehicle). Different stuck faults on the actuators have been implemented in the ALTAV benchmark and used for evaluating the control reallocation schemes. An effective re-distribution of the control surface deflections with the remaining healthy control actuators is used in order to achieve acceptable performance in the presence of control actuator failures. Comparisons were made among the two algorithms with different commanded inputs. Simulation results show the effectiveness of reconfigurable control allocation algorithms for handling stuck failures in such a UAV with less hardware redundancy.

An LMI approach to mixed H 1 /H ∞ robust fault-tolerant control design with uncertainties

This paper studies mixed H1/H∞ robust fault-tolerant control for a class of uncertain systems and its application to flight tracking control. A sufficient condition is derived by introducing some important auxiliary variables, which guarantees that the uncertain closed-loop system is robustly stable and satisfies the mixed H1/H∞ constraint in both normal and fault cases. In the framework of Linear Matrix Inequality (LMI) approach, a multi-objective optimization problem is solved with much less conservative via an iterative algorithm. Simulation results obtained with a nonlinear fighter aircraft model show the effectiveness of the proposed method.

A Variable Communication Approach for Decentralized Receding Horizon Control of Multi-Vehicle Systems

The stability and performance of decentralized receding horizon control (RHC) is often improved by modifying the cost function and constraints of the problem. However, variable communication presents an additional approach for further improvement. In this paper, new methods are developed for variable communication of decentralized RHC. Through modification of stability conditions recently developed for decentralized RHC, an investigation of the effect of faster communication rates, expanded communication radius, and multi-hopping communication on decentralized RHC is performed. The new approach is applied to a group of five mobile robots with different communication topologies.

Reconfigurable Control Allocation Technology Using Weighted Least Squares for Nonlinear System in Unmanned Aerial Vehicle

Reconfigurable control allocation research is important to multidisciplinary science and engineering applications. In particular, the proposed research plays a significant role in enhancing the safety, reliability and fault tolerance capability of Unmanned Aerial Vehicle (UAV), which is one of the most active research and development areas. The main objective of this paper is to introduce and evaluate UAV reconfigurable control system design against control surfaces faults without modifying the baseline controller. The faults introduced are in the form of partial loss and stuck at unknown position on the UAV control surfaces. Weighted Least Squares (WLS) control reallocation algorithm with application to UAV was investigated. The paper is undertaken in a nonlinear UAV model ALTAV (Almost-Light-Than-Air-Vehicles), developed by Quanser incorporation. Different faults have been introduced in control surfaces with different trajectory commanded inputs. Gaussian noise was introduced in the model. Comparisons were made under normal situation, the case without control reallocation, and the case with control reallocation method. Simulation results show the satisfactory reconfigurable flight control system performance using the WLS control reallocation method for ALTAV nonlinear UAV benchmark.