@article{mohanty_2020,
title = {3 DOF Autonomous Control Analysis of an Quadcopter Using Artificial Neural Network},
author = {Mohanty S.; Misra A. },
booktitle = {Modern Approaches in Machine Learning and Cognitive Science: A Walkthrough.},
year = {2020},
institution = {Defense Institute of Advanced TechnologyPuneIndia},
abstract = {The Quadcopter is an Unmanned Aerial Vehicle (UAV) which has turned out to be exceptionally mainstream among specialists in the recent past due to the advantages it offers over conventional helicopters. Quadcopter is extremely unique and interesting, however it is inherently unsteady from streamlined features perspective and aerodynamics point of view. In recent past scientists have proposed many control schemes for the stability of quadcopter, but Artificial Neural Network (ANN) systems provide us with the fusion of human intelligence, logic and reasoning. The research focuses on the use of ANN for the control plant systems whose plant dynamics are expensive to model, inaccurate or change with time and environment. In this paper, we explore the Linear Quadratic Regulator (LQR) and Sliding Mode Control (SMC) control is designed for an quadcopter with 3 Degree Of freedom (DOF) Hover model by Quancer. The main benefits of this approach are the model’s ability of adapt quickly to unmodeled aerodynamics, disturbances, component failure due to battle damage, etc. It eliminates the costs and time associated with the wind tunnel testing and generation of control derivatives for the UAV’s. },
keywords = {Quadcopter, Unmanned aerial vehicle (UAV), Artificial neural network (ANN), Linear quadratic regulator (LQR), Sliding mode control (SMC)},
language = {English},
series = {Studies in Computational Intelligence},
publisher = {Springer, Cham},
isbn = {978-3-030-38444-9},
pages = {39-57}
}

The Quadcopter is an Unmanned Aerial Vehicle (UAV) which has turned out to be exceptionally mainstream among specialists in the recent past due to the advantages it offers over conventional helicopters. Quadcopter is extremely unique and interesting, however it is inherently unsteady from streamlined features perspective and aerodynamics point of view. In recent past scientists have proposed many control schemes for the stability of quadcopter, but Artificial Neural Network (ANN) systems provide us with the fusion of human intelligence, logic and reasoning. The research focuses on the use of ANN for the control plant systems whose plant dynamics are expensive to model, inaccurate or change with time and environment. In this paper, we explore the Linear Quadratic Regulator (LQR) and Sliding Mode Control (SMC) control is designed for an quadcopter with 3 Degree Of freedom (DOF) Hover model by Quancer. The main benefits of this approach are the model’s ability of adapt quickly to unmodeled aerodynamics, disturbances, component failure due to battle damage, etc. It eliminates the costs and time associated with the wind tunnel testing and generation of control derivatives for the UAV’s.

@article{jung_2020,
title = {Event-Triggered H 2 Attitude Controller Design for 3 DOF Hover Systems},
author = {Jung, H.; Han, S.; Lee, S.},
journal = {IEMEK Journal of Embedded Systems and Applications},
year = {2020},
month = {06},
volume = {15},
number = {3},
institution = {Kyungpook National University, Korea},
abstract = {This paper is concerned with the H2 attitude controller design for 3 degree of freedom (DOF) Hover systems with an event-triggered mechanism. The 3 DOF Hover system is an embedded platform for unmanned aerial vehicle (UAV) provided by Quanser. The mathematical model of this system is obtained by a linearization around operating points and it is represented as a linear parameter-varying (LPV) model. To save communication network resources, the event-triggered mechanism (ETM) is considered and the performance of the system is guaranteed by the H2 controller. The stabilization condition is obtained by using Lyapunov-Krasovskii functionals (LKFs) and some useful lemmas. The effectiveness of the proposed method is shown by simulation and experimental results. },
issn = {1975-5066},
keywords = {3 DOF Hover embedded platform, LPV Model, ETM, H2 Attitude controller, LKFs},
language = {Korean},
publisher = {IEMEK},
pages = {139-148}
}

This paper is concerned with the H2 attitude controller design for 3 degree of freedom (DOF) Hover systems with an event-triggered mechanism. The 3 DOF Hover system is an embedded platform for unmanned aerial vehicle (UAV) provided by Quanser. The mathematical model of this system is obtained by a linearization around operating points and it is represented as a linear parameter-varying (LPV) model. To save communication network resources, the event-triggered mechanism (ETM) is considered and the performance of the system is guaranteed by the H2 controller. The stabilization condition is obtained by using Lyapunov-Krasovskii functionals (LKFs) and some useful lemmas. The effectiveness of the proposed method is shown by simulation and experimental results.

@article{silva2_2020,
title = {Fast Nonsingular Terminal Sliding Mode Flight Control for Multirotor Aerial Vehicles},
author = {Silva Jr. A.L.; Santos, D.A.},
year = {2020},
institution = {Instituto Tecnologico de Aeronautica, Brazil},
abstract = {This paper is concerned with the robust flight control of multirotor aerial vehicles (MAVs) subject to bounded force and torque disturbances. The focus is on the entire class of MAVs containing an arbitrary even number (≥ 4) of fixed (not 4 vectoring) rotors. To deal with this problem, firstly, a ubiquitous hierarchical control architecture in which the attitude control loop is nested inside the position control loop is adopted and augmented with a control allocator which makes the design of the control laws themselves independent of the rotor arrangement. Especially, the control allocation problem is formulated as a quadratic program that minimizes the thrust commands and accounts for the thrust range and rate bounds. Secondly, geometric attitude and position control laws are designed separately using a multi-input fast nonsingular terminal sliding mode control (FNTSMC) strategy, which guarantees singularity-free finite-time stability and robustness. The main contributions are: 1) the augmentation of the hierarchical control scheme for extending its applicability to any fixed-rotor MAV; and 2) detailed geometric design and finite-time stability analysis of the position and attitude control loops using the FNTSMC theory. The system is evaluated on computational simulations as well as on a hardware-in-the-loop experiment, showing that it is effective, simple to implement and adjust, and reliable to operate in nonlinear regimes as well as under bounded disturbances. },
keywords = {Multirotor aerial vehicle, quadrotor, flight control, control allocation, terminal sliding mode control, hardware-in-the-loop simulation},
language = {English}
}

This paper is concerned with the robust flight control of multirotor aerial vehicles (MAVs) subject to bounded force and torque disturbances. The focus is on the entire class of MAVs containing an arbitrary even number (≥ 4) of fixed (not 4 vectoring) rotors. To deal with this problem, firstly, a ubiquitous hierarchical control architecture in which the attitude control loop is nested inside the position control loop is adopted and augmented with a control allocator which makes the design of the control laws themselves independent of the rotor arrangement. Especially, the control allocation problem is formulated as a quadratic program that minimizes the thrust commands and accounts for the thrust range and rate bounds. Secondly, geometric attitude and position control laws are designed separately using a multi-input fast nonsingular terminal sliding mode control (FNTSMC) strategy, which guarantees singularity-free finite-time stability and robustness. The main contributions are: 1) the augmentation of the hierarchical control scheme for extending its applicability to any fixed-rotor MAV; and 2) detailed geometric design and finite-time stability analysis of the position and attitude control loops using the FNTSMC theory. The system is evaluated on computational simulations as well as on a hardware-in-the-loop experiment, showing that it is effective, simple to implement and adjust, and reliable to operate in nonlinear regimes as well as under bounded disturbances.

@article{ansari_2019,
title = {Development and experimental investigation of a Quadrotor’s robust generalized dynamic inversion control system},
author = {Ansari, U., Bajodah, A.H.; Kada, B.},
journal = {Nonlinear Dynamics},
year = {2019},
institution = {King Abdulaziz University, Saudi Arabia},
abstract = {The development of a two-loops Quadrotor’s robust generalized dynamic inversion (RGDI)-based control system is presented. The outer (position) loop utilizes PD position control of the Quadrotor’s center of gravity (CG) in the three-dimensional inertial space, and it provides reference pitch and roll tilting angles commands to the inner loop, in addition to the thrust command that is required to track desired altitude trajectories. The inner (attitude) loop applies RGDI control of a prescribed asymptotically stable dynamics of tilting and attitude errors from reference-tilting and desired-attitude trajectories, and it provides the three required control torque values such that desired CG positions in instantaneous horizontal inertial planes and desired-attitude trajectories of the Quadrotor are tracked. The proposed closed loop system is shown to guarantee finite-time semi-global practically stable trajectory tracking. Numerical simulations of the proposed closed loop control system are performed on a six degrees of freedom Quadrotor’s mathematical model for nominal conditions and under parametric uncertainties and exogenous disturbances. Apart from numerical simulations, experimental tests are conducted on a three degrees of freedom Quadrotor test bench to assess performance of the RGDI control loop. Experimental results demonstrate improved tracking performance in comparison with classical Linear-Quadratic optimal control and conventional sliding mode control. },
issn = {0924-090X},
keywords = {Robust generalized dynamic inversion, Sliding mode control, Quadrotor control, Hover experimental test bench, Null control vector, Trajectory tracking, Finite-time stability, Semiglobal practical stability},
language = {English},
publisher = {Springer Nature}
}

The development of a two-loops Quadrotor’s robust generalized dynamic inversion (RGDI)-based control system is presented. The outer (position) loop utilizes PD position control of the Quadrotor’s center of gravity (CG) in the three-dimensional inertial space, and it provides reference pitch and roll tilting angles commands to the inner loop, in addition to the thrust command that is required to track desired altitude trajectories. The inner (attitude) loop applies RGDI control of a prescribed asymptotically stable dynamics of tilting and attitude errors from reference-tilting and desired-attitude trajectories, and it provides the three required control torque values such that desired CG positions in instantaneous horizontal inertial planes and desired-attitude trajectories of the Quadrotor are tracked. The proposed closed loop system is shown to guarantee finite-time semi-global practically stable trajectory tracking. Numerical simulations of the proposed closed loop control system are performed on a six degrees of freedom Quadrotor’s mathematical model for nominal conditions and under parametric uncertainties and exogenous disturbances. Apart from numerical simulations, experimental tests are conducted on a three degrees of freedom Quadrotor test bench to assess performance of the RGDI control loop. Experimental results demonstrate improved tracking performance in comparison with classical Linear-Quadratic optimal control and conventional sliding mode control.

@article{gonzalez_2019,
title = {Event-triggered predictor-based control with gain-Scheduling and extended state observer for networked control systems},
author = {González, A.; Cuenca, A.; Balaguer, V.; García, P.},
journal = {Information Sciences},
year = {2019},
month = {07},
volume = {491},
institution = {Universidad de Zaragoza, Spain; Universitat Politècnica de València, Spain},
abstract = {This paper investigates the stabilization of Networked Control Systems (NCS) with mismatched disturbances through a novel Event-Triggered Control (ETC), composed of a predictor-feedback scheme and a gain-scheduled Extended State Observer (ESO). The key idea of the proposed control strategy is threefold: (i) to reduce resource usage in the NCS (bandwidth, energy) while maintaining a satisfactory control performance; (ii) to counteract the main negative effects of NCS: time-varying delays, packet dropouts, packet disorder, and (iii) to reject the steady-state error in the controlled output due to mismatched disturbances. Moreover, we address the co-design of the controller/observer gains, together with the event-triggered parameters, by means of Linear Matrix Inequalities (LMI) and Cone Complementarity Linearization (CCL) approaches. Finally, we illustrate the effectiveness of the proposed control synthesis by simulation and experimental results in a Unmanned Aerial Vehicle (UAV) based test-bed platform.This paper investigates the stabilization of Networked Control Systems (NCS) with mismatched disturbances through a novel Event-Triggered Control (ETC), composed of a predictor-feedback scheme and a gain-scheduled Extended State Observer (ESO). The key idea of the proposed control strategy is threefold: (i) to reduce resource usage in the NCS (bandwidth, energy) while maintaining a satisfactory control performance; (ii) to counteract the main negative effects of NCS: time-varying delays, packet dropouts, packet disorder, and (iii) to reject the steady-state error in the controlled output due to mismatched disturbances. Moreover, we address the co-design of the controller/observer gains, together with the event-triggered parameters, by means of Linear Matrix Inequalities (LMI) and Cone Complementarity Linearization (CCL) approaches. Finally, we illustrate the effectiveness of the proposed control synthesis by simulation and experimental results in a Unmanned Aerial Vehicle (UAV) based test-bed platform. },
keywords = {Time-varying delay, Networked control system, Packet disorder, Packet loss, Predictor-based control, Gain-scheduling, ESO},
language = {English},
publisher = {Elsevier B.V.},
pages = {90-108}
}

This paper investigates the stabilization of Networked Control Systems (NCS) with mismatched disturbances through a novel Event-Triggered Control (ETC), composed of a predictor-feedback scheme and a gain-scheduled Extended State Observer (ESO). The key idea of the proposed control strategy is threefold: (i) to reduce resource usage in the NCS (bandwidth, energy) while maintaining a satisfactory control performance; (ii) to counteract the main negative effects of NCS: time-varying delays, packet dropouts, packet disorder, and (iii) to reject the steady-state error in the controlled output due to mismatched disturbances. Moreover, we address the co-design of the controller/observer gains, together with the event-triggered parameters, by means of Linear Matrix Inequalities (LMI) and Cone Complementarity Linearization (CCL) approaches. Finally, we illustrate the effectiveness of the proposed control synthesis by simulation and experimental results in a Unmanned Aerial Vehicle (UAV) based test-bed platform.This paper investigates the stabilization of Networked Control Systems (NCS) with mismatched disturbances through a novel Event-Triggered Control (ETC), composed of a predictor-feedback scheme and a gain-scheduled Extended State Observer (ESO). The key idea of the proposed control strategy is threefold: (i) to reduce resource usage in the NCS (bandwidth, energy) while maintaining a satisfactory control performance; (ii) to counteract the main negative effects of NCS: time-varying delays, packet dropouts, packet disorder, and (iii) to reject the steady-state error in the controlled output due to mismatched disturbances. Moreover, we address the co-design of the controller/observer gains, together with the event-triggered parameters, by means of Linear Matrix Inequalities (LMI) and Cone Complementarity Linearization (CCL) approaches. Finally, we illustrate the effectiveness of the proposed control synthesis by simulation and experimental results in a Unmanned Aerial Vehicle (UAV) based test-bed platform.

@article{kandala_2019,
title = {Hybrid method-of-receptances and optimization-based technique for pole placement in time-delayed systems},
author = {Kandala, S.S.; Chakraborty, S.; Uchida, T.K.; Vyasarayani, C. P.},
journal = {International Journal of Dynamics and Control},
year = {2019},
institution = {Indian Institute of Technology Hyderabad, India; University of Ottawa, Canada},
abstract = {In this paper, we propose a pole-placement technique for second-order, time-delayed systems that combines the strengths of the method of receptances and an optimization-based strategy. The method of receptances involves solving an algebraic system of equations to obtain the closed-loop gains that place the poles of the system at desired locations. The method of receptances is simple and efficient, but the placed poles may not be the rightmost poles so the resulting closed-loop system may not be stable. By contrast, an optimization-based approach can explicitly consider the rightmost pole in the objective function and thus can guarantee its location. In this work, we use Galerkin approximations to obtain the characteristic roots of time-delayed systems. When the method of receptances provides an unsatisfactory solution, we use particle swarm optimization to improve the location of the rightmost pole. The proposed approach is demonstrated with numerical studies and is validated experimentally using a 3D hovercraft apparatus. },
keywords = {Time-delayed system, Pole placement, Stability, Method of receptances, Galerkin approximation, Particle swarm optimization},
language = {English},
publisher = {Springer Nature Switzerland}
}

In this paper, we propose a pole-placement technique for second-order, time-delayed systems that combines the strengths of the method of receptances and an optimization-based strategy. The method of receptances involves solving an algebraic system of equations to obtain the closed-loop gains that place the poles of the system at desired locations. The method of receptances is simple and efficient, but the placed poles may not be the rightmost poles so the resulting closed-loop system may not be stable. By contrast, an optimization-based approach can explicitly consider the rightmost pole in the objective function and thus can guarantee its location. In this work, we use Galerkin approximations to obtain the characteristic roots of time-delayed systems. When the method of receptances provides an unsatisfactory solution, we use particle swarm optimization to improve the location of the rightmost pole. The proposed approach is demonstrated with numerical studies and is validated experimentally using a 3D hovercraft apparatus.

@article{kahouadji_2019,
title = {Real-Time Attitude Control of 3 DOF Quadrotor UAV using Modified Super Twisting Algorithm},
author = {Kahouadji, M.; Rida Mokhtari, M.; Choukchou-Braham, A.; Cherki, B.},
journal = {Journal of the Franklin Institute},
year = {2019},
institution = {Université de Tlemcen, Algeria},
abstract = {A new scheme for the attitude control of the quadrotor in presence of uncertainties and disturbances is presented. The proposed algorithm is a modified Super Twisting control -MSTW-. The aim of this technique is to solve the main disadvantage of the classical Super Twisting -STW- which is chattering. Moreover, the proposed scheme allows reduced control effort and accurate tracking. The elimination of the chattering phenomena is due to the continuous outputs generated by the MSTW. The finite time convergence and stability analysis of the closed loop system are derived using Lyapunov function techniques. The experimental validation is done to emphasize the good performances of the new scheme in terms of accuracy, robustness, finite-time convergence and chattering elimination with less control effort. },
keywords = {Modified Super Twisting, robust control, Lyapunov stability, attitude control, Quanser quadrotor},
language = {English},
publisher = {Elsevier Ltd.}
}

A new scheme for the attitude control of the quadrotor in presence of uncertainties and disturbances is presented. The proposed algorithm is a modified Super Twisting control -MSTW-. The aim of this technique is to solve the main disadvantage of the classical Super Twisting -STW- which is chattering. Moreover, the proposed scheme allows reduced control effort and accurate tracking. The elimination of the chattering phenomena is due to the continuous outputs generated by the MSTW. The finite time convergence and stability analysis of the closed loop system are derived using Lyapunov function techniques. The experimental validation is done to emphasize the good performances of the new scheme in terms of accuracy, robustness, finite-time convergence and chattering elimination with less control effort.

@conference{dhaybi_2019,
title = {Real-time Estimation of the Inertia Tensor Elements of a Quadcopter Hover Platform},
author = {Dhaybi, M.; Daher, N.},
booktitle = {2019 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM)},
year = {2019},
institution = {American University of Beirut, Lebanon},
abstract = {The ability of unmanned aerial vehicles (UAVs) to carry variable payloads, and to support various gripping attachments for transportation and delivery services, is under increasing demand. This work aims at designing an online estimator that determines the change in the dynamic system parameters of a three degrees-of-freedom (3 DOF) quadcopter hover platform, as a payload is varied. In particular, the moment of inertia tensor of the 3 DOF quadcopter hover platform is estimated in real-time, while subjected to an additional payload, by analyzing the acquired input-output data and using its rigid body dynamic model. A recursive least squares (RLS) estimation method is employed, and covariance resetting is integrated to improve the estimator’s convergence rate. Simulation and experimental results conducted on the Quanser 3 DOF Hover platform demonstrate the accuracy of the designed estimator, given its ability to accurately and promptly estimate all nine elements of the 3x3 inertia tensor matrix, even in the presence of sudden payload variations. The developed methodology can be extended to design an adaptive scheme that controls the motion of quadcopter UAVs, and utilized in reliable machine health monitoring algorithms. },
issn = {2159-6247 },
keywords = {Identification and Estimation in Mechatronics, Unmanned Aerial Vehicles, Computational Models and Methods},
language = {English},
publisher = {IEEE},
isbn = {978-1-7281-2494-0}
}

The ability of unmanned aerial vehicles (UAVs) to carry variable payloads, and to support various gripping attachments for transportation and delivery services, is under increasing demand. This work aims at designing an online estimator that determines the change in the dynamic system parameters of a three degrees-of-freedom (3 DOF) quadcopter hover platform, as a payload is varied. In particular, the moment of inertia tensor of the 3 DOF quadcopter hover platform is estimated in real-time, while subjected to an additional payload, by analyzing the acquired input-output data and using its rigid body dynamic model. A recursive least squares (RLS) estimation method is employed, and covariance resetting is integrated to improve the estimator’s convergence rate. Simulation and experimental results conducted on the Quanser 3 DOF Hover platform demonstrate the accuracy of the designed estimator, given its ability to accurately and promptly estimate all nine elements of the 3x3 inertia tensor matrix, even in the presence of sudden payload variations. The developed methodology can be extended to design an adaptive scheme that controls the motion of quadcopter UAVs, and utilized in reliable machine health monitoring algorithms.

@article{chakraborty_2019,
title = {Reduced-Ordered Modelling of Time Delay Systems Using Galerkin Approximations and Eigenvalue Decomposition},
author = {Chakraborty, S.; Kandala, S.S.; Vyasarayani, C.P. },
journal = {International Journal of Dynamics and Control},
year = {2019},
number = {7},
institution = {Indian Institute of Technology Hyderabad, India},
abstract = {In this paper, an r-dimensional reduced-order model (ROM) for infinite-dimensional delay differential equations (DDEs) is developed. The eigenvalues of the ROM match the r rightmost characteristic roots of the DDE with a user-specified tolerance of ε. Initially, the DDE is approximated by an N-dimensional set of ordinary differential equations using Galerkin approximations. However, only Nc(},
keywords = {Model order reduction, Galerkin approximation, Time delay, Eigenvalue decomposition,},
language = {English},
publisher = {Springer Nature Switzerland},
pages = {1065-1083}
}

In this paper, an r-dimensional reduced-order model (ROM) for infinite-dimensional delay differential equations (DDEs) is developed. The eigenvalues of the ROM match the r rightmost characteristic roots of the DDE with a user-specified tolerance of ε. Initially, the DDE is approximated by an N-dimensional set of ordinary differential equations using Galerkin approximations. However, only Nc(

@article{yang2_2018,
title = {Aerodynamic parameters identification and adaptive LADRC attitude control of quad-rotor model},
author = {Yang, S.; Xi, L.; Hao, J.; Zhao, Y.; Yang, Y.; Wang, W.},
year = {2018},
institution = {Army Engineering University, China; Beihang University, China; Shijiazhuang Tiedao University, China; China Aerodynamics Research and Development Center, China; University of Warwick, UK},
abstract = {In accordance with problems such as difficulty in obtaining aerodynamic parameters of a quad-rotor model, the change of model parameters with external interference affects the control performances, an aerodynamic parameter estimation method and an adaptive attitude control method based on LADRC are designed. Firstly, the motion model, dynamics model and control distribution model of quad-rotor are established by using the aerodynamic and Newtonian Euler equations. Secondly, the identification tool CIFER is used to identify the aerodynamic parameters with large uncertainties in frequency domain and a more accurate attitude model of the quad-rotor is obtained. Then an adaptive attitude decoupling controller based on LADRC is designed to solve the problem of poor anti-interference ability of the quad-rotor, so that the control parameter b0 can be automatically adjusted to identify the change of the moment of inertia in real time. Finally, a semi-physical simulation platform is used for simulation verification. The results show that the adaptive LADRC attitude controller designed can effectively estimate and compensate the system's internal and external disturbances, and the tracking speed of the controller is faster and the precision is higher which can effectively improve system's anti-interference and robustness. },
keywords = {Quad-rotor; Parameters identification; CIFER; Adaptive LADRC},
language = {English}
}

In accordance with problems such as difficulty in obtaining aerodynamic parameters of a quad-rotor model, the change of model parameters with external interference affects the control performances, an aerodynamic parameter estimation method and an adaptive attitude control method based on LADRC are designed. Firstly, the motion model, dynamics model and control distribution model of quad-rotor are established by using the aerodynamic and Newtonian Euler equations. Secondly, the identification tool CIFER is used to identify the aerodynamic parameters with large uncertainties in frequency domain and a more accurate attitude model of the quad-rotor is obtained. Then an adaptive attitude decoupling controller based on LADRC is designed to solve the problem of poor anti-interference ability of the quad-rotor, so that the control parameter b0 can be automatically adjusted to identify the change of the moment of inertia in real time. Finally, a semi-physical simulation platform is used for simulation verification. The results show that the adaptive LADRC attitude controller designed can effectively estimate and compensate the system's internal and external disturbances, and the tracking speed of the controller is faster and the precision is higher which can effectively improve system's anti-interference and robustness.

@article{prado_2018,
title = {Experimental evaluation of HJB optimal controllers for the attitude dynamics of a multirotor aerial vehicle},
author = {Acampora Prado I.A. , de Freitas Virgílio Pereira M., Ferreira de Castro M., dos Santos D.A., Balthazar J.M.},
journal = {ISA Transactions},
year = {2018},
institution = {Instituto Tecnologico de Aeronautica, Brazil},
abstract = {The present paper is concerned with the design and experimental evaluation of optimal control laws for the nonlinear attitude dynamics of a multirotor aerial vehicle. Three design methods based on Hamilton-Jacobi-Bellman equation are taken into account. The first one is a linear control with guarantee of stability for nonlinear systems. The second and third are a nonlinear suboptimal control techniques. These techniques are based on an optimal control design approach that takes into account the nonlinearities present in the vehicle dynamics. The stability Proof of the closed-loop system is presented. The performance of the control system designed is evaluated via simulations and also via an experimental scheme using the Quanser 3-DOF Hover. The experiments show the effectiveness of the linear control method over the nonlinear strategy. },
keywords = {Multirotor Aerial Vehicles; Hamilton-Jacobi-Bellman equation; Optimal control; Attitude control},
language = {English},
publisher = {Elsevier Ltd.}
}

The present paper is concerned with the design and experimental evaluation of optimal control laws for the nonlinear attitude dynamics of a multirotor aerial vehicle. Three design methods based on Hamilton-Jacobi-Bellman equation are taken into account. The first one is a linear control with guarantee of stability for nonlinear systems. The second and third are a nonlinear suboptimal control techniques. These techniques are based on an optimal control design approach that takes into account the nonlinearities present in the vehicle dynamics. The stability Proof of the closed-loop system is presented. The performance of the control system designed is evaluated via simulations and also via an experimental scheme using the Quanser 3-DOF Hover. The experiments show the effectiveness of the linear control method over the nonlinear strategy.

@article{gonzalez_2018,
title = {Gain-scheduled predictive extended state observer for time-varying delays systems with mismatched disturbances},
author = {Gonzalez, A.; Balaguer, V.; Garcia, P.; Cuenca, A.},
journal = {ISA Transactions},
year = {2018},
institution = {Universidad de Zaragoza, Spain; Universitat Politècnica de València, Spain},
abstract = {In this paper, a novel control scheme for systems with input and output time-varying delays is provided in discrete-time domain. The control strategy combines predictor-like techniques with a delay-dependent gain-scheduled extended state observer. The main goal is twofold: (i) to minimize the negative effect of time-varying delays in the closed-loop performance and, (ii) to actively compensate the effect of mismatched disturbances in the controlled output. Moreover, a sufficient condition based on Linear Matrix Inequalities (LMI) is provided to obtain the maximum delay interval that ensures the stability of the closed-loop system. Finally, the achieved benefits of the proposal are shown by simulation in open-loop unstable plants, and experimentally validated in a test-bed quadrotor platform. },
keywords = {Time-varying delay, Digital control implementation, Mismatched disturbance, Predictor-based control, Gain-scheduling, Extended state observer},
language = {English},
publisher = {Elsevier B.V.}
}

In this paper, a novel control scheme for systems with input and output time-varying delays is provided in discrete-time domain. The control strategy combines predictor-like techniques with a delay-dependent gain-scheduled extended state observer. The main goal is twofold: (i) to minimize the negative effect of time-varying delays in the closed-loop performance and, (ii) to actively compensate the effect of mismatched disturbances in the controlled output. Moreover, a sufficient condition based on Linear Matrix Inequalities (LMI) is provided to obtain the maximum delay interval that ensures the stability of the closed-loop system. Finally, the achieved benefits of the proposal are shown by simulation in open-loop unstable plants, and experimentally validated in a test-bed quadrotor platform.

@article{hoffman_2018,
title = {Quaternion-based Robust Trajectory Tracking Control of a Quadrotor Hover System},
author = {Hoffman, D.; Rehan, M.; MacKunis, W.; Reyhhanoglu, M.},
journal = {International Journal of Control, Automation and Systems},
year = {2018},
institution = {Embry-Riddle Aeronautical University, USA; University of North Carolina, USA},
abstract = {This paper presents a robust nonlinear output feedback control method that achieves three degree of freedom (3-DOF) attitude trajectory tracking of a hover system test bed. The proposed control method formally incorporates dynamic model uncertainty in addition to test bed voltage constraints. To reduce the computational requirement in the closed-loop system, constant feedforward estimates of the input-multiplicative parametric uncertainty are utilized in lieu of adaptive parameter estimates. To eliminate the need for angular rate measurements, the control design employs a bank of dynamic filters, which operates as a velocity estimator in the closed-loop system. A rigorous error system development and Lyapunov-based stability analysis are presented to prove asymptotic 3-DOF attitude trajectory tracking control. Computer simulation and experimental results are also included to illustrate the performance of the attitude control method using the Quanser 3-DOF hover system test bed. },
issn = {1598-6446},
keywords = {Output feedback, quadrotor, quaternion, robust, tracking },
language = {English}
}

This paper presents a robust nonlinear output feedback control method that achieves three degree of freedom (3-DOF) attitude trajectory tracking of a hover system test bed. The proposed control method formally incorporates dynamic model uncertainty in addition to test bed voltage constraints. To reduce the computational requirement in the closed-loop system, constant feedforward estimates of the input-multiplicative parametric uncertainty are utilized in lieu of adaptive parameter estimates. To eliminate the need for angular rate measurements, the control design employs a bank of dynamic filters, which operates as a velocity estimator in the closed-loop system. A rigorous error system development and Lyapunov-based stability analysis are presented to prove asymptotic 3-DOF attitude trajectory tracking control. Computer simulation and experimental results are also included to illustrate the performance of the attitude control method using the Quanser 3-DOF hover system test bed.

@conference{kahouadji_2018,
title = {Super Twisting Control for Attitude Tracking using Quaternion},
author = {Kahouadji, M.; Choukchou-Braham, A.; Rida Mokhtari, M.; Cherki, B.},
booktitle = {Conference Internationale en Automatique & Traitement de Signal (ATS-2018)},
year = {2018},
institution = {Universite de Tlemcen, Algeria},
abstract = {A nonlinear robust control based on super Twisting algorithm for the attitude stabilisation and tracking of quadrotor is developed in this paper. Quaternion based representation is used to obtain the nonlinear model and avoid singularities problems. The stability of the Super Twisting control based on quaternion can be proved through Lyapunov function candidate. The experimental results show the robustness and finite time convergence of the control in presence of parameters uncertainties and external disturbances. },
issn = {2356-5608},
keywords = {Super Twisting algorithm, quaternion representation, sliding variable, robustness, quadrotor platform},
language = {English},
series = {Proceedings of Engineering and Technology},
publisher = {IPCO}
}

A nonlinear robust control based on super Twisting algorithm for the attitude stabilisation and tracking of quadrotor is developed in this paper. Quaternion based representation is used to obtain the nonlinear model and avoid singularities problems. The stability of the Super Twisting control based on quaternion can be proved through Lyapunov function candidate. The experimental results show the robustness and finite time convergence of the control in presence of parameters uncertainties and external disturbances.

@article{sanz_2017,
title = {A generalized smith predictor for unstable time-delay SISO systems},
author = {Sanz, R.; Garcia, P.; Albertos, P.},
journal = {ISA Transactions},
year = {2017},
institution = {Universitat Politecnica de Valencia, Spain},
abstract = {In this work, a generalization of the Smith Predictor (SP) is proposed to control linear time-invariant (LTI) time-delay single-input single-output (SISO) systems. Similarly to the SP, the combination of any stabilizing output-feedback controller for the delay-free system with the proposed predictor leads to a stabilizing controller for the delayed system. Furthermore, the tracking performance and the steady-state disturbance rejection capabilities of the equivalent delay-free loop are preserved. In order to place this contribution in context, some modifications of the SP are revisited and recast under the same structure. The features of the proposed scheme are illustrated through simulations, showing a comparison with respect to the corresponding delay-free loop, which is here considered to be the ideal scenario. In order to emphasize the feasibility of this approach, a successful experimental implementation in a laboratory platform is also reported. },
keywords = {Smith Predictor, Time delay, External disturbances, Single-input single-output system},
language = {English},
publisher = {Elsevier Ltd.}
}

In this work, a generalization of the Smith Predictor (SP) is proposed to control linear time-invariant (LTI) time-delay single-input single-output (SISO) systems. Similarly to the SP, the combination of any stabilizing output-feedback controller for the delay-free system with the proposed predictor leads to a stabilizing controller for the delayed system. Furthermore, the tracking performance and the steady-state disturbance rejection capabilities of the equivalent delay-free loop are preserved. In order to place this contribution in context, some modifications of the SP are revisited and recast under the same structure. The features of the proposed scheme are illustrated through simulations, showing a comparison with respect to the corresponding delay-free loop, which is here considered to be the ideal scenario. In order to emphasize the feasibility of this approach, a successful experimental implementation in a laboratory platform is also reported.

@conference{castillo2_2017,
title = {A novel technique to enlarge the maximum allowable delay bound in sampled-data systems},
author = {Castillo, O.; Benitez Perez, H.},
booktitle = {National Congress on Automatic Control 2017},
year = {2017},
institution = {Instituto de Investigaciones en Matematicas Aplicadas y en Sistemas, UNAM, Mexico},
abstract = { is well known that in physical implementation of control systems delays are induced in the dynamic of the system. Specifically, time is consumed through communication between electronic devices. Therefore, control theory requires algorithms capable of maintaining the stability of the system even if delays in the feedback are significant. So, in this work, we show that by means of a pulse control signal, we can enlarge the classic Maximum Allowable Delay Bound (MADB) on sampled-data systems. Experimental results are presented to prove the effectiveness of our technique. },
keywords = {sampled-data systems, retarded systems, impulsive systems, networked control systems},
language = {English},
pages = {312-316}
}

is well known that in physical implementation of control systems delays are induced in the dynamic of the system. Specifically, time is consumed through communication between electronic devices. Therefore, control theory requires algorithms capable of maintaining the stability of the system even if delays in the feedback are significant. So, in this work, we show that by means of a pulse control signal, we can enlarge the classic Maximum Allowable Delay
Bound (MADB) on sampled-data systems. Experimental results are presented to prove the effectiveness of our technique.

@article{kara-mohamed_2017,
title = {Advanced trajectory tracking for UAVs using combined feedforward/feedback control design},
author = {Kara-Mohamed, K.},
journal = {Robotics and Autonomous Systems},
year = {2017},
volume = {96},
institution = {School of Engineering and The Built Environment, Birmingham City University, UK},
abstract = {Trajectory tracking is a major challenge for UAVs. The more complex the trajectory is, the more accurate tracking is required with minimum divergence from the trajectory. Apart from active trajectory tracking mechanisms, current solutions to accurate trajectory tracking in narrow areas require low speed motions. This paper presents a systematic design methodology using centralised feedforward/feedback control architecture for advanced trajectory tracking without compromising the speed of the vehicle. Using the H-infinity norm as a measure for the design criteria, the proposed method proves fast tracking with no overshooting and less actuators energy compared with single degree-of-freedom feedback control method. The results are verified using simulations for two systems: a tri-rotor VTOL UAV (fully actuated system), and a quadrotor trainer (over-actuated system). },
issn = {0921-8890},
language = {English},
publisher = {Elsevier B.V.},
pages = {143-156}
}

Trajectory tracking is a major challenge for UAVs. The more complex the trajectory is, the more accurate tracking is required with minimum divergence from the trajectory. Apart from active trajectory tracking mechanisms, current solutions to accurate trajectory tracking in narrow areas require low speed motions. This paper presents a systematic design methodology using centralised feedforward/feedback control architecture for advanced trajectory tracking without compromising the speed of the vehicle. Using the H-infinity norm as a measure for the design criteria, the proposed method proves fast tracking with no overshooting and less actuators energy compared with single degree-of-freedom feedback control method. The results are verified using simulations for two systems: a tri-rotor VTOL UAV (fully actuated system), and a quadrotor trainer (over-actuated system).

@article{liang_2017,
title = {An Adaptive Control System for Variable Mass Quad-Rotor UAV Involved in Rescue Missions},
author = {Liang, X.; Chen, G.; Wang, J.; Bi, Z.; Sun, P.},
journal = {International Journal of Simulation Systems, Science & Technology},
year = {2017},
volume = {17},
number = {29},
institution = {School of Automation , Shenyang Aerospace University, China},
abstract = {Because the mass of quad-rotor helicopter Unmanned Aerial Vehicles (UAV) changes after delivering relief supplies, an adaptive control strategy based on model reference adaptation is proposed. First a quad-rotor model is established based on the Quanser 3-DOF hover platform. Then a control strategy is developed consisting of two layers: a baseline controller using a Linear Quadratic Regulator (LQR) and Model Reference Adaptive Controller (MRAC) to eliminate the impact of load change. In simulation, the results illustrate that the strategy can improve the effectiveness of the control system when the mass and the moment of inertia change in applications such as rescue missions. },
keywords = {quad-rotor; rescue mission; variable mass; linear quadratic regulator; model reference adaptive control},
language = {English}
}

Because the mass of quad-rotor helicopter Unmanned Aerial Vehicles (UAV) changes after delivering relief supplies, an adaptive control strategy based on model reference adaptation is proposed. First a quad-rotor model is established based on the Quanser 3-DOF hover platform. Then a control strategy is developed consisting of two layers: a baseline controller using a Linear Quadratic Regulator (LQR) and Model Reference Adaptive Controller (MRAC) to eliminate the impact of load change. In simulation, the results illustrate that the strategy can improve the effectiveness of the control system when the mass and the moment of inertia change in applications such as rescue missions.

@conference{icen_2017,
title = {Optimization of LQR weight matrix to control three degree of freedom quadcopter},
author = {Icen, M.; Ates, A.; Yeroglu, C.},
booktitle = {2017 International Artificial Intelligence and Data Processing Symposium (IDAP)},
year = {2017},
institution = {Inonu University, Turkey},
abstract = {In this study, Q and R weight matrices of a Linear Quadratic Regulator (LQR) were optimized to control three-degree-of-freedom four-rotor Quadrocopter system (3 DOF Hover). The weighted matrices, obtained by Darwinian Particle Swarm Optimization (DPSO) and Fractional Order Darwinian Particle Swarm Optimization (FODPSO) methods, have been tested on the simulation model of Quadrocopter. The weight matrices, which provide good control in simulation, were run in real time on the 3 DOF Hover prototype and the effects on control performance were examined. },
keywords = { LQR, optimization, 3 DOF Hover },
language = {Turkish},
publisher = {IEEE},
isbn = {978-1-5386-1881-3 }
}

In this study, Q and R weight matrices of a Linear Quadratic Regulator (LQR) were optimized to control three-degree-of-freedom four-rotor Quadrocopter system (3 DOF Hover). The weighted matrices, obtained by Darwinian Particle Swarm Optimization (DPSO) and Fractional Order Darwinian Particle Swarm Optimization (FODPSO) methods, have been tested on the simulation model of Quadrocopter. The weight matrices, which provide good control in simulation, were run in real time on the 3 DOF Hover prototype and the effects on control performance were examined.

@inproceedings{gao_2017,
title = {The controller design of quadrotor UAV based on internal model control},
author = {Gao, Q.; Du, M.; Ji, Y.},
booktitle = {2017 36th Chinese Control Conference (CCC)},
year = {2017},
institution = {Tianjin University of Technology, China},
abstract = {In view of nonlinear, external disturbances and strong coupling features of the quadrotor UAV. A combination of internal model control and tracking differentiator (TD — IMC) is proposed to design a controller for Quadrotor. The function matrix of the quadrotor can be obtained by the LPV method linearizing the nonlinear model. Tracking differentiator (TD) is introduced to arrange the transition process, and utilizing TD's high quality filter and tracking effect, IMC controller is designed to control the quadrotor model, so that the attitude and trajectory tracking can be realized. The simulation results indicate that the control method proposed in this paper has stronger robustness and disturbance rejection performance. },
issn = {1934-1768},
keywords = {Quadrotor UAV, Tracking differentiator, Internal model control, Linear time-varying parameter systems},
language = {English},
publisher = {IEEE},
isbn = {978-1-5386-2918-5 }
}

In view of nonlinear, external disturbances and strong coupling features of the quadrotor UAV. A combination of internal model control and tracking differentiator (TD — IMC) is proposed to design a controller for Quadrotor. The function matrix of the quadrotor can be obtained by the LPV method linearizing the nonlinear model. Tracking differentiator (TD) is introduced to arrange the transition process, and utilizing TD's high quality filter and tracking effect, IMC controller is designed to control the quadrotor model, so that the attitude and trajectory tracking can be realized. The simulation results indicate that the control method proposed in this paper has stronger robustness and disturbance rejection performance.

@conference{prach_2016,
title = {An Experimental Evaluation of the Forward Propagating Riccati Equation to Nonlinear Control of the Quanser 3 DOF Hover Testbed},
author = {Prach, A.; Kayacan, E.; Bernstein, D.S.},
booktitle = {2016 American Control Conference},
year = {2016},
abstract = {This study presents an experimental evaluation of the forward-propagating Riccati equation (FPRE) control. FPRE employs a state-dependent coefficient (SDC) parameterization of the nonlinear dynamics, and the feedback gains are updated in real time. The efficacy of the proposed control algorithm is verified by experimental studies on the Quanser 3 DOF Hover system. The ability of FPRE to follow the desired references is investigated, and its performance is compared with the conventional linear-quadratic regulator. Experimental results show the effectiveness of FPRE for following given references in the considered operating envelope. },
language = {English},
pages = {3710-3715}
}

This study presents an experimental evaluation of the forward-propagating Riccati equation (FPRE) control. FPRE employs a state-dependent coefficient (SDC) parameterization of the nonlinear dynamics, and the feedback gains are updated in real time. The efficacy of the proposed control algorithm is verified by experimental studies on the Quanser 3 DOF Hover system. The ability of FPRE to follow the desired references is investigated, and its performance is compared with the conventional linear-quadratic regulator. Experimental results show the effectiveness of FPRE for following given references in the considered operating envelope.

@conference{prach_2016,
title = {An experimental evaluation of the forward propagating riccati equationton on linear control of the quanser 3 dof hover testbed},
author = {Prach, A., Kayacan, E.; Bernstein, D.S.},
booktitle = {2016 American Control Conference},
year = {2016},
institution = {Nanyang Technological University, Singapore; The University of Michigan, Ann Arbor, USA},
abstract = {This study presents an experimental evaluation of the forward-propagating Riccati equation (FPRE) control. FPRE employs a state-dependent coefficient (SDC) parameterization of the nonlinear dynamics, and the feedback gains are updated in real time. The efficacy of the proposed control algorithm is verified by experimental studies on the Quanser 3 DOF Hover system. The ability of FPRE to follow the desired references is investigated, and its performance is compared with the conventional linear-quadratic regulator. Experimental results show the effectiveness of FPRE for following given references in the considered operating envelope. },
language = {English},
publisher = {AACC}
}

This study presents an experimental evaluation of the forward-propagating Riccati equation (FPRE) control. FPRE employs a state-dependent coefficient (SDC) parameterization of the nonlinear dynamics, and the feedback gains are updated in real time. The efficacy of the proposed control algorithm is verified by experimental studies on the Quanser 3 DOF Hover system. The ability of FPRE to follow the desired references is investigated, and its performance is compared with the conventional linear-quadratic regulator. Experimental results show the effectiveness of FPRE for following given references in the considered operating envelope.

@conference{bermudez-ortega_2016,
title = {Developing web & TwinCAT PLC-based remote Control laboratories for modern web-browsers or mobile devices},
author = {Bermudez-Ortega, J.; Besada-Portas, E.; Lopez-Orozco, Jose A.; Chacon, J.; de la Cruz, J.M.},
booktitle = {2016 IEEE Conference on Control Applications (CCA)},
year = {2016},
institution = {Department of Computer Architecture and Systems Engineering of Universidad Complutense de Madrid, Spain},
abstract = {This paper describes a new approach to develop remote Control laboratories accessible from modern web-browsers and student devices (PCs, laptops, tablets and smartphones) based on TwinCAT Programmable Controllers (PLCs), Easy JavaScript Simulations (EJsS) webpages, and a Node.js laboratory web-server. On the one hand, implementing the laboratory back-end application (responsible of closing the feedback loop over the plant under study) using a TwinCAT PLC provides the laboratory controllers with standard/industrial automation methodologies, real-time support and connectivity to a wide range of input/output signals. On the other hand, defining the controller front-end (graphical/interactive interface used by the students to parametrize the PLC behavior and observe the evolution of the plant and PLC signals) with EJsS facilitates the organization of its visual/interactive elements and allows the generation of a JavaScript and HTML5 webpage that is accessible from modern web-browsers and various types of students devices running different operating systems. Last, but not least, developing the laboratory web-server (in charge of managing the student access to the lab and of hosting its different webpages, including the controller frontend) within the JavaScript development and runtime platform Node.js ensures a lightweight behavior of the remote lab, provides a robust connectivity to the students, and supports efficient (real-time) communication between the controller back & front-ends. This paper also shows how the new strategy is used to update and overcome the current accessibility limitations of some existing (and published) experiences with Proportional/Integral/Differential (PIDs) and Estimator and State Feedback (ESF) Controllers based on TwinCAT PLCs and Easy Java Simulations (EJS) applets front-ends. },
keywords = {Laboratories, Servers, Mobile handsets, Graphical user interfaces, Real-time systems, Robustness, Java},
language = {English},
publisher = {IEEE},
isbn = {978-1-5090-0756-1}
}

This paper describes a new approach to develop remote Control laboratories accessible from modern web-browsers and student devices (PCs, laptops, tablets and smartphones) based on TwinCAT Programmable Controllers (PLCs), Easy JavaScript Simulations (EJsS) webpages, and a Node.js laboratory web-server. On the one hand, implementing the laboratory back-end application (responsible of closing the feedback loop over the plant under study) using a TwinCAT PLC provides the laboratory controllers with standard/industrial automation methodologies, real-time support and connectivity to a wide range of input/output signals. On the other hand, defining the controller front-end (graphical/interactive interface used by the students to parametrize the PLC behavior and observe the evolution of the plant and PLC signals) with EJsS facilitates the organization of its visual/interactive elements and allows the generation of a JavaScript and HTML5 webpage that is accessible from modern web-browsers and various types of students devices running different operating systems. Last, but not least, developing the laboratory web-server (in charge of managing the student access to the lab and of hosting its different webpages, including the controller frontend) within the JavaScript development and runtime platform Node.js ensures a lightweight behavior of the remote lab, provides a robust connectivity to the students, and supports efficient (real-time) communication between the controller back & front-ends. This paper also shows how the new strategy is used to update and overcome the current accessibility limitations of some existing (and published) experiences with Proportional/Integral/Differential (PIDs) and Estimator and State Feedback (ESF) Controllers based on TwinCAT PLCs and Easy Java Simulations (EJS) applets front-ends.

@article{wang_2016,
title = {Hybrid modeling based double-granularity fault detection and diagnosis for quadrotor helicopter},
author = {Wang, Yue; Jiang, Bin; Lu, Ningyun; Pan, Jun},
journal = {Nonlinear Analysis: Hybrid Systems},
year = {2016},
volume = {21},
abstract = {Fault detection and diagnosis (FDD) is an effective technology to assure the safety and reliability of quadrotor helicopters. However, there are still some unsolved problems in the existing FDD methods, such as the trade-offs between the accuracy and complexity of system models used for FDD, and the rarely explored structure faults in quadrotor helicopters. In this paper, a double-granularity FDD method is proposed based on the hybrid modeling of a quadrotor helicopter which has been developed in authorsÍ previous work. The hybrid model consists of a prior model and a set of non-parametric models. The coarse-granularity-level FDD is built on the prior model which can isolate the faulty channel(s); while the fine-granularity-level FDD is built on the nonparametric models which can isolate the faulty components in the faulty channel. In both coarse and fine granularity FDD procedures, principal component analysis (PCA) is adopted for online fault detection. Using such a double-granularity scheme, the proposed FDD method has inherent ability in detecting and diagnosing structure faults or failures in quadrotor helicopters. Experimental results conducted on a 3-DOF hover platform can demonstrate the feasibility and effectiveness of the proposed hybrid modeling technique and the hybrid model based FDD method. },
keywords = {Hybrid modeling; Fault detection and diagnosis; Quadrotor helicopter; Structure fault},
language = {English},
publisher = {Elsevier Ltd.},
pages = {22-36}
}

Fault detection and diagnosis (FDD) is an effective technology to assure the safety and reliability of quadrotor helicopters. However, there are still some unsolved problems in the existing FDD methods, such as the trade-offs between the accuracy and complexity of system models used for FDD, and the rarely explored structure faults in quadrotor helicopters. In this paper, a double-granularity FDD method is proposed based on the hybrid modeling of a quadrotor helicopter which has been developed in authorsÍ previous work. The hybrid model consists of a prior model and a set of non-parametric models. The coarse-granularity-level FDD is built on the prior model which can isolate the faulty channel(s); while the fine-granularity-level FDD is built on the nonparametric models which can isolate the faulty components in the faulty channel. In both coarse and fine granularity FDD procedures, principal component analysis (PCA) is adopted for online fault detection. Using such a double-granularity scheme, the proposed FDD method has inherent ability in detecting and diagnosing structure faults or failures in quadrotor helicopters. Experimental results conducted on a 3-DOF hover platform can demonstrate the feasibility and effectiveness of the proposed hybrid modeling technique and the hybrid model based FDD method.

@article{sanz_2016,
title = {Predictor-based Control of a Class of Time-Delay Systems and its Application to Quadrotors},
author = {Sanz, R.; Garcia, P.; Zhong, Q.-C.; Albertos, P.},
journal = {IEEE Transactions on Industrial Electronics},
year = {2016},
institution = {Universitat Politecnica de Valencia, Spain},
abstract = {In this paper, a new robust control strategy based on a predictor and the uncertainty and disturbance estimator (UDE) is developed for a class of uncertain nonlinear systems with input/output delays. The closed-loop system is analyzed and sufficient stability conditions are derived based on Lyapunov analysis. The proposed strategy is applied to the particular case of quadrotor systems and validated through extensive simulations to evaluate performance and robustness. The controller is also implemented in a quadrotor prototype and validated in flight tests. },
keywords = {Prediction, nonlinear systems, robust control, time-delay, uncertainty and disturbance estimator (UDE), quadrotor.},
language = {English},
publisher = {IEEE}
}

In this paper, a new robust control strategy based on a predictor and the uncertainty and disturbance estimator (UDE) is developed for a class of uncertain nonlinear systems with input/output delays. The closed-loop system is analyzed and sufficient stability conditions are derived based on Lyapunov analysis. The proposed strategy is applied to the particular case of quadrotor systems and validated through extensive simulations to evaluate performance and robustness. The controller is also implemented in a quadrotor prototype and validated in flight tests.

@article{sanz_2016,
title = {Robust Control of Quadrotors Based on an Uncertainty and Disturbance Estimator},
author = {Sanz, R.; Garcia, P.; Zhong, Q.C.; Albertos, P. },
journal = {Journal of Dynamic Systems, Measurement, and Control},
year = {2016},
volume = {138},
number = {7},
institution = {Universidad Politécnica de Valencia, Spain; Illinois Institute of Technology, Chicago, USA},
abstract = {In this paper, a robust control strategy is proposed to control the attitude and the altitude of quadrotors, based on an uncertainty and disturbance estimator (UDE). It is shown that the proposed controller can be tuned very easily, achieving the desired performance only by selecting an appropriate reference model and tuning a single parameter to tradeoff disturbance rejection with noise amplification in the control signal. The proposed control strategy is extensively validated in real-time applications with an experimental Quanser platform and also with a quadrotor prototype in real flight tests. },
keywords = {quadrotors, attitude control, uncertainty and disturbance estimator},
language = {English},
publisher = {ASME}
}

In this paper, a robust control strategy is proposed to control the attitude and the altitude of quadrotors, based on an uncertainty and disturbance estimator (UDE). It is shown that the proposed controller can be tuned very easily, achieving the desired performance only by selecting an appropriate reference model and tuning a single parameter to tradeoff disturbance rejection with noise amplification in the control signal. The proposed control strategy is extensively validated in real-time applications with an experimental Quanser platform and also with a quadrotor prototype in real flight tests.

@conference{pereira_2015,
title = {Experimental investigation of nonlinear controllers appli ed to a 3DOF Hover: SMC via ALQR approach},
author = {Pereira, R.L.; Kienitz, K.H.},
booktitle = {2015 23rd Mediterranean Conference on Control and Automation (MED)},
year = {2015},
institution = {Instituto Tecnologico de Aeronautica, SP, Brasil},
abstract = {This paper presents an application of sliding mode controllers obtained via amplified linear quadratic regulator (ALQR) strategy to a hover with three degrees of freedom. The purpose of the designed control system is to track reference trajectories and ensure performance and stability in spite of disturbance, noise and unmodeled dynamics. Simulations were performed using MATLAB/Simulink in order to verify/compare the performance of the nonlinear controllers proposed. For validation of the algorithm a didactic plant (3DOF Hover) was chosen produced by Quanser Consulting, that simulates typical behaviors of an VTOL ("vertical taking-off landing") aircraft, also known as X4-flyer. The dynamic of the hover can be described by a 6th order model taking as state variables the angles of yaw, pitch, roll and associated rates. The experiments showed that designed nonlinear controllers using sliding mode control via ALQR are robust to noises and for a range of unmodeled nonlinearities. },
keywords = {Nonlinear Control, Sliding Mode Control via ALQR, Hover 3DOF},
language = {English},
publisher = {IEEE},
pages = {520-524}
}

This paper presents an application of sliding mode controllers obtained via amplified linear quadratic regulator (ALQR) strategy to a hover with three degrees of freedom. The purpose of the designed control system is to track reference trajectories and ensure performance and stability in spite of disturbance, noise and unmodeled dynamics. Simulations were performed using MATLAB/Simulink in order to verify/compare the performance of the nonlinear controllers proposed. For validation of the algorithm a didactic plant (3DOF Hover) was chosen produced by Quanser Consulting, that simulates typical behaviors of an VTOL ("vertical taking-off landing") aircraft, also known as X4-flyer. The dynamic of the hover can be described by a 6th order model taking as state variables the angles of yaw, pitch, roll and associated rates. The experiments showed that designed nonlinear controllers using sliding mode control via ALQR are robust to noises and for a range of unmodeled nonlinearities.

@inproceedings{pan_2015,
title = {Sliding mode fault-tolerant control for uncertain time-delay systems},
author = {Pan, Xu; Yang, Pu; Guo, Ruicheng},
booktitle = {2015 34th Chinese Control Conference (CCC)},
year = {2015},
institution = {Nanjing University of Aeronautics and Astronautics, China},
abstract = {The problem of designing a sliding mode fault-tolerant controller for a class of uncertain time-delay systems in presence of actuator faults is investigated. First, for the effect of time-delay and parameter uncertainty on control performance, a sufficient condition is given with Finsler's lemma and linear matrix inequality(LMI) technique to guarantee the asymptotic stability of the sliding mode of the system; Second, according to the actuator faults, a kind of integral sliding surface is introduced and a global sliding mode equivalent control law is designed to make the system arrive at the sliding surface in finite time, in despite of the position of initial states, so that the safety of system can be guaranteed. Finally, the control algorithm is applied in the quadrotor semi-physical simulation platform, and the effectiveness and feasibility of this algorithm is verified. },
keywords = {Uncertain time-delay systems, Actuator failures, Sliding mode control, Fault-tolerant control, Quadrotor},
language = {English},
publisher = {IEEE},
pages = {6403 - 6407}
}

The problem of designing a sliding mode fault-tolerant controller for a class of uncertain time-delay systems in presence of actuator faults is investigated. First, for the effect of time-delay and parameter uncertainty on control performance, a sufficient condition is given with Finsler's lemma and linear matrix inequality(LMI) technique to guarantee the asymptotic stability of the sliding mode of the system; Second, according to the actuator faults, a kind of integral sliding surface is introduced and a global sliding mode equivalent control law is designed to make the system arrive at the sliding surface in finite time, in despite of the position of initial states, so that the safety of system can be guaranteed. Finally, the control algorithm is applied in the quadrotor semi-physical simulation platform, and the effectiveness and feasibility of this algorithm is verified.

@conference{hu_2014,
title = {Attitude control research for quad-rotor UAV},
author = {Hu Qiong; Lan Tian; Fei Qing; Geng Qingbo},
booktitle = {2014 Fifth International Conference on Intelligent Control and Information Processing (ICICIP)},
year = {2014},
abstract = {Quad-rotor helicopter is a popular platform for unmanned aerial vehicle (UAV) research due to its simplicity of structure and maintenance as well as the capability of hovering and vertical take-off and landing. The attitude controller is of great importance since it ensures the vehicle to keep balance and perform the desired maneuver. In this paper, sliding mode controller for attitude regulation is designed based on variable structure theorem according to the mathematical model of the 3-DOF Quanser hover system. The control objective of the attitude controller is to asymptotically track the different demanded signals, even if there exist unknown disturbances. Considering the chattering existing in the sliding model control system, the high-slope saturation function is utilized instead of the sign function. To validate the effectiveness and efficiency of the proposed method, the comparison among sliding mode, backstepping and PID methods is carried out. The results from both digital simulations and experiments on the hover system show that the sliding mode control law can perform adequately as an attitude controller in terms of better tracking performance and robustness compared with the other two methods. },
keywords = {aircraft control;attitude control;autonomous aerial vehicles;helicopters;three-term control;variable structure systems;3-DOF Quanser hover system;PID method;attitude control;attitude regulation;backstepping;high-slope saturation function;hovering capability;quad-rotor UAV;quad-rotor helicopter;sliding mode controller;unmanned aerial vehicle;variable structure theorem;vertical take-off and landing;Attitude control;Backstepping;Mathematical model;Propellers;Sliding mode control;Trajectory},
publisher = {IEEE},
isbn = {978-1-4799-3649-6},
pages = {41-47}
}

Quad-rotor helicopter is a popular platform for unmanned aerial vehicle (UAV) research due to its simplicity of structure and maintenance as well as the capability of hovering and vertical take-off and landing. The attitude controller is of great importance since it ensures the vehicle to keep balance and perform the desired maneuver. In this paper, sliding mode controller for attitude regulation is designed based on variable structure theorem according to the mathematical model of the 3-DOF Quanser hover system. The control objective of the attitude controller is to asymptotically track the different demanded signals, even if there exist unknown disturbances. Considering the chattering existing in the sliding model control system, the high-slope saturation function is utilized instead of the sign function. To validate the effectiveness and efficiency of the proposed method, the comparison among sliding mode, backstepping and PID methods is carried out. The results from both digital simulations and experiments on the hover system show that the sliding mode control law can perform adequately as an attitude controller in terms of better tracking performance and robustness compared with the other two methods.

@article{yang_2014,
title = {Direct Self-Repairing Control for Quadrotor Helicopter Attitude Systems},
author = {Huiliao Yang, Bin Jiang, and Ke Zhang},
journal = {Mathematical Problems in Engineering},
year = {2014},
volume = {2014},
institution = {College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, China},
abstract = {A quadrotor helicopter with uncertain actuator faults, such as loss of effectiveness and lock-in-place, is studied in this paper. An adaptive fuzzy sliding mode controller based on direct self-repairing control is designed for such nonlinear system to track the desired output signal, when any actuator of this quadrotor helicopter is loss of effectiveness or stuck at some place. Moreover, using the Lyapunov stability theory, the stability of the whole system and the convergence of the tracking error can be guaranteed. Finally, the availability of the proposed method is verified by simulation on 3-DOF hover to ensure that the system performance under faulty conditions can be quickly recovered to its normal level. And this proposed method is also proved to be better than that of LQR through simulation. },
publisher = {Hindawi}
}

A quadrotor helicopter with uncertain actuator faults, such as loss of effectiveness and lock-in-place, is studied in this paper. An adaptive fuzzy sliding mode controller based on direct self-repairing control is designed for such nonlinear system to track the desired output signal, when any actuator of this quadrotor helicopter is loss of effectiveness or stuck at some place. Moreover, using the Lyapunov stability theory, the stability of the whole system and the convergence of the tracking error can be guaranteed. Finally, the availability of the proposed method is verified by simulation on 3-DOF hover to ensure that the system performance under faulty conditions can be quickly recovered to its normal level. And this proposed method is also proved to be better than that of LQR through simulation.

@conference{zhang_2014,
title = {Fault Tolerant Tracking Control for Quad-Rotor Helicopter via Robust Adaptive Technique},
author = {Zhang, Kang-Kang; Ye, Dan; and Zhao, Xin-Gang},
booktitle = {2014 33rd Chinese Control Conference (CCC)},
year = {2014},
abstract = {This paper presents a robust adaptive H-infinity strategy to solve the attitude of the quad-rotor helicopter control problems with actuator failures and external disturbances. The dynamic motion equations are obtained by the Euler formalism. Based on the linear time-invariant state-space equations of the quad-rotor, a state feedback robust adaptive H-infinity tracking controller is proposed to track the given attitude angles with actuator faults. The controller gain consists of two parts: one part is the fixed gain which is obtained based on LMIs (linear Matrix inequalities), the other one is the time-varying gain which is adjusted on-line by the designed adaptive laws. Simulations based on a 3D Hover System of Quanser, are presented to verify the control strategy in the SIMULINK/MATLAB environment. },
keywords = {quad-rotor, attitude control, actuator failure, adaptive control, H-infinity tracking control},
language = {English},
publisher = {IEEE},
pages = {3233 - 3237}
}

This paper presents a robust adaptive H-infinity strategy to solve the attitude of the quad-rotor helicopter control problems with actuator failures and external disturbances. The dynamic motion equations are obtained by the Euler formalism. Based on the linear time-invariant state-space equations of the quad-rotor, a state feedback robust adaptive H-infinity tracking controller is proposed to track the given attitude angles with actuator faults. The controller gain consists of two parts: one part is the fixed gain which is obtained based on LMIs (linear Matrix inequalities), the other one is the time-varying gain which is adjusted on-line by the designed adaptive laws. Simulations based on a 3D Hover System of Quanser, are presented to verify the control strategy in the SIMULINK/MATLAB environment.

@article{pitarch_2014,
title = {Multicriteria fuzzy-polynomial observer design for a 3DoF nonlinear electromechanical platform},
author = {Pitarch, J.L.; Sala, A.},
journal = {Engineering Applications of Artificial Intelligence},
year = {2014},
volume = {30},
abstract = {This paper proposes local fuzzy-polynomial observer discrete-time designs for state estimation of a nonlinear 3DoF electromechanical platform (fixed quadrotor). A trade-off between H-infinity norm bounds and speed of convergence performance is taken into account in the design process. Actual experimental data are used to compare performance of the fuzzy polynomial design with classical ones based on the Takagi_Sugeno and linearized models, both using the same optimization criteria and design parameters. },
keywords = {Fuzzy polynomial systems; Multicriteria optimisation; Sum of squares; H-infinity attenuation; State estimation; Electromechanical systems},
language = {English},
publisher = {Elsevier Ltd.},
pages = {96-106}
}

This paper proposes local fuzzy-polynomial observer discrete-time designs for state estimation of a nonlinear 3DoF electromechanical platform (fixed quadrotor). A trade-off between H-infinity norm bounds and speed of convergence performance is taken into account in the design process. Actual experimental data are used to compare performance of the fuzzy polynomial design with classical ones based on the Takagi_Sugeno and linearized models, both using the same optimization criteria and design parameters.

@inproceedings{zhang_reliable_2013,
title = {A reliable tracking control for the 3-DOF hovering system of quadrotor with multi-actuator faults},
author = {Zhang, Xinyu and Jiang, Bin and Chen, Fuyang and Zhang, Ke},
booktitle = {2013 25th Chinese Control and Decision Conference, {CCDC},
year = {2013},
abstract = {In this paper, a reliable tracking control method based on the regional poles placement is utilized to solve the attitude tracking problem for the 3 Degree of Freedom (3-DOF) hovering system of Quadrotor with multi-actuator faults. For the uncertain linear system, a more practical and general model of actuator faults is presented. And a sufficient condition on reliable tracking is proposed. The state feedback reliable controller is solved in terms of Linear MatrixInequality (LMI). Finally, the simulation is examined on the Quanser 3-DOF hovering system to verify the feasibility and validity of the method. },
keywords = {Aircraft, Linear matrix inequalities, state feedback, Uncertain systems},
series = {25th Chinese Control and Decision Conference, {CCDC},
publisher = {IEEE Computer Society},
pages = {4961--4966}
}

In this paper, a reliable tracking control method based on the regional poles placement is utilized to solve the attitude tracking problem for the 3 Degree of Freedom (3-DOF) hovering system of Quadrotor with multi-actuator faults. For the uncertain linear system, a more practical and general model of actuator faults is presented. And a sufficient condition on reliable tracking is proposed. The state feedback reliable controller is solved in terms of Linear MatrixInequality (LMI). Finally, the simulation is examined on the Quanser 3-DOF hovering system to verify the feasibility and validity of the method.

@article{chen_adaptive_2013,
title = {Adaptive compensation control of the quadrotor helicopter using quantum information technology and disturbance observer},
author = {Chen, Fuyang and Lu, Feifei and Jiang, Bin and Tao, Gang},
journal = {Journal of the Franklin Institute},
year = {2013},
abstract = {In this paper, an adaptive compensation control scheme is developed via disturbance observer and quantum information technology for the four-rotor helicopter, which can handle the control problems of helicopter'sattitude with the unknown actuator failures and external disturbance effectively. Both the digital simulations and the semi-physical simulationsin a Quanser 3-DOF Hover platform illustrate the effectivenessof the proposed compensation control scheme. },
issn = {160032},
keywords = {Helicopter rotors, Helicopters, Information technology, Quantum optics},
pages = {{in press}
}

In this paper, an adaptive compensation control scheme is developed via disturbance observer and quantum information technology for the four-rotor helicopter, which can handle the control problems of helicopter'sattitude with the unknown actuator failures and external disturbance effectively. Both the digital simulations and the semi-physical simulationsin a Quanser 3-DOF Hover platform illustrate the effectivenessof the proposed compensation control scheme.

@article{pereira_2013,
title = {Projeto de um controlador robusto H-infinity com formatação de malha via dml aplicado em um hover},
author = {Lima Pereira, R.; Kienitz, K.H.},
booktitle = {Proceeding Series of the Brazilian Society of Applied and Computational Mathematics},
year = {2013},
volume = {1},
number = {1},
institution = {Instituto Tecnologico de Aeronautica, Brazil},
abstract = {The purpose of this paper is to present the possible advantages of a H1 loop-shaping robust controller using LMIs (linear matrix inequalities) to solve the problem of tracking references and robust stability in a hover with three degrees of freedom. This hover system is a laboratory system produced by Quanser Consulting and simulates typical behaviors of an VTOL (vertical tanking-off landing) aircraft, also known as X4-flyer. The formulation adopted in this study consist in the H1 synthesis using a four-block framework. This formulation ensures closed-loop robust stability of the system against unstructured uncertainty described via coprime factorization. We present experimental results obtained with the implementation of the designed H1 loop-shaping controller. },
keywords = {Robust Control, Coprime factorization, H1 loop-shaping, LMI},
language = {Portuguese}
}

The purpose of this paper is to present the possible advantages of a H1 loop-shaping robust controller using LMIs (linear matrix inequalities) to solve the problem of tracking references and robust stability in a hover with three degrees of freedom. This hover system is a laboratory system produced by Quanser Consulting and simulates typical behaviors of an VTOL (vertical tanking-off landing) aircraft, also known as X4-flyer. The formulation adopted in this study consist in the H1 synthesis using a four-block framework. This formulation ensures closed-loop robust stability of the system against unstructured uncertainty described via coprime factorization. We present experimental results obtained with the implementation of the designed H1 loop-shaping controller.

@article{lu_2012,
title = {A fault prognosis method using Bayesian network},
author = {Lu, N.; He, K.; Bin, J.},
journal = {Journal of Southeast University},
year = {2012},
month = {09},
volume = {42},
institution = {Nanjing University of Aeronautics and Astronautics, Nanjing, China; Southeast University, Nanjing, China},
abstract = {To find the fault propagation mechanism and predict system-level faults probability according to the abnormalities of key components in a complex engineering system, a fault prognosis method via Bayesian network is proposed.According to the inherent topological structure of an engineering system, a multi-layer Bayesian network is developed firstly, which can handle the time-dependent information by incorporating the qualitative signal trend information into the nodes of the Bayesian network.Therefore, the developed network is suitable for failure propagation analysis and fault prediction.A method for identifying the failure probability of the root nodes in the network is also proposed based on the nodes' integrative health index.Different parameter learning algorithms are adopted to determine the conditional probability table of the Bayesian network for complete and incomplete data sets, respectively.The Pearl's poly tree propagation algorithm is used for joint probability reasoning.The proposed fault prognosis method can predict the probabilities of possible failures based on the current status of root nodes.The application results on a Quanser 3-DOF hover simulation system can verify the effectiveness and feasibility of the proposed method. },
language = {Chinese},
pages = {87-91}
}

To find the fault propagation mechanism and predict system-level faults probability according to the abnormalities of key components in a complex engineering system, a fault prognosis method via Bayesian network is proposed.According to the inherent topological structure of an engineering system, a multi-layer Bayesian network is developed firstly, which can handle the time-dependent information by incorporating the qualitative signal trend information into the nodes of the Bayesian network.Therefore, the developed network is suitable for failure propagation analysis and fault prediction.A method for identifying the failure probability of the root nodes in the network is also proposed based on the nodes' integrative health index.Different parameter learning algorithms are adopted to determine the conditional probability table of the Bayesian network for complete and incomplete data sets, respectively.The Pearl's poly tree propagation algorithm is used for joint probability reasoning.The proposed fault prognosis method can predict the probabilities of possible failures based on the current status of root nodes.The application results on a Quanser 3-DOF hover simulation system can verify the effectiveness and feasibility of the proposed method.

@article{xinzhe_2011,
title = {Active fault tolerant control for over actuated system based on multiple observers},
author = {Xinzhe, Y.; Bin, J.; Fuyang, C.; Ke, Z.},
journal = {Journal of Nanjing University of Aeronautics and Astronautics},
year = {2011},
institution = {Nanjing University of Aeronautics & Astronautics, Nanjing, China},
abstract = {A novel active fault tolerant control based on multiple observers for over-actuated system is focused on to deal with the difficulty of fault diagnosis caused by the control distribution matrix with no full column rank.The proposed algorithm is combined with the robust control to design an output feedback tracking controller and satisfy the H∞ performance.It can not only effectively detect and estimate the single channel actuator failure,but also compensate the fault adverse effects on the system stability so as to ensure a certain attitude tracking performance in case of the single channel actuator faults.Compared with the state feedback controller, the active fault tolerant control law for Quadrotor which is a class of over actuated system is able to decrease the error brought by state simulation.To some extent, the proposed algorithm improves the accuracy and rapidity.Finally, the method is verified reliable and effective on the Quanser 3-DOF Hover platform. },
language = {Chinese}
}

A novel active fault tolerant control based on multiple observers for over-actuated system is focused on to deal with the difficulty of fault diagnosis caused by the control distribution matrix with no full column rank.The proposed algorithm is combined with the robust control to design an output feedback tracking controller and satisfy the H∞ performance.It can not only effectively detect and estimate the single channel actuator failure,but also compensate the fault adverse effects on the system stability so as to ensure a certain attitude tracking performance in case of the single channel actuator faults.Compared with the state feedback controller, the active fault tolerant control law for Quadrotor which is a class of over actuated system is able to decrease the error brought by state simulation.To some extent, the proposed algorithm improves the accuracy and rapidity.Finally, the method is verified reliable and effective on the Quanser 3-DOF Hover platform.

@conference{korogui_2011,
title = {H-infinity control design for time-delay linear systems: A rational transfer function based approach},
author = {Korogui, R.H.; Fioravanti, A.; Fioravanti, A.; Geromel, J.C.},
booktitle = {2011 50th IEEE Conference on Decision and Control and European Control Conference (CDC-ECC)},
year = {2011},
volume = {-2},
institution = {Sao Paulo State University, Brazil; French National Institute for Computer Science and Applied Mathematics (INRIA), France; University of Campinas, Brazil},
abstract = {The aim of this paper is to cope with the H∞ control synthesis for time-delay linear systems. We extend the use of a finite order LTI system, called comparison system to H∞ analysis and design. Differently from what can be viewed as a common feature of other control design methods available in the literature to date, the one presented here treats time-delay systems control design with classical numeric routines based on Riccati equation and H∞ theory. An illustrative example and a practical application involving a 3-DOF networked control system are presented. },
language = {English},
publisher = {IEEE}
}

The aim of this paper is to cope with the H∞ control synthesis for time-delay linear systems. We extend the use of a finite order LTI system, called comparison system to H∞ analysis and design. Differently from what can be viewed as a common feature of other control design methods available in the literature to date, the one presented here treats time-delay systems control design with classical numeric routines based on Riccati equation and H∞ theory. An illustrative example and a practical application involving a 3-DOF networked control system are presented.

@article{he_2011,
title = {System health evaluation model and application on the 3-DOF Hover platform},
author = {He, K.-L.; Ly, N.-Y.; Jiang, B.},
year = {2011},
institution = {Nanjing University of Aeronautics and Astronautics, Nanjing, China; Southeast University, Nanjing, China},
abstract = {A system health evaluation scheme is proposed by integrating the lifetime prediction method for electronic components and performance evaluation method for large-scale complex systems. The proposed health evaluation model takes into account four major factors: component's importance, reliability, historical break-down frequency and current fault degree. The model takes form of linear or nonlinear weighted model, where fuzzy Analytic Hierarchy Process(AHP) method is adopted to determine the model's parameters. The proposed method is finally verified by the Quanser 3-DOF Hover platform. },
language = {Chinese}
}

A system health evaluation scheme is proposed by integrating the lifetime prediction method for electronic components and performance evaluation method for large-scale complex systems. The proposed health evaluation model takes into account four major factors: component's importance, reliability, historical break-down frequency and current fault degree. The model takes form of linear or nonlinear weighted model, where fuzzy Analytic Hierarchy Process(AHP) method is adopted to determine the model's parameters. The proposed method is finally verified by the Quanser 3-DOF Hover platform.

@conference{Cavalca2009,
title = {Application of TFL/LTR Robust Control Techniques to Failure Accommodation},
author = {Cavalca, M. and K. Kienitz},
booktitle = {20th International Congress of Mechanical Engineering},
year = {2009},
abstract = {Robust control deals with differences between the real system and the mathematic model explicitly during the design stage. Such differences can be caused, for example, by modeling simplifications and faults in the system. In the case of plants with uncertainties, on the assumption of a nominal model plant and a controller, it can be defined the concepts of nominal stability and robust stability. In the nominal stability case, the controller only stabilizes the nominal model, on the other hand, in the robust stability case, it stabilizes all possible process realizations within an uncertainty region. The term "fault" designates any impairment of system components that may result in performance degradation or even a complete stop of system functions. System faults can be classified as sudden (abrupt faults) or incipient faults (when the system suffers a slow degradation). Implementing a fault tolerant system, that keeps its dynamic response inside acceptable limits even under fault occurrence, is not trivial. In such case, the system can have its performance degraded but must continue to be operational. There have been several proposal solutions to the fault tolerant control problem. The proposal of this paper is to apply the TFL/LTR (Target Feedback Loop/Loop Transfer Recovery) robust control design to a 3DOF hover didactic system with uncertainty model and abrupt faults caused, for example, by power loss. TFL/LTR is a two step design procedure. In the first step, desired dynamics are defined for the controlled system (TFL). In this paper a linear quadratic regulator technique that considers a control signal gain will be used to ensure stability margins. These margins shall be defined so as to make the system robust to the abrupt faults. In the second step, a loop transfer recovery method (LTR) is used so that the controlled real system has characteristics close to those of the target feedback loop. Simulation results show that the control system under study has the intended robustness and fault tolerance. },
keywords = {Robust control, Fault tolerant control, Model uncertainty}
}

Robust control deals with differences between the real system and the mathematic model explicitly during the design stage. Such differences can be caused, for example, by modeling simplifications and faults in the system. In the case of plants with uncertainties, on the assumption of a nominal model plant and a controller, it can be defined the concepts of nominal stability and robust stability. In the nominal stability case, the controller only stabilizes the nominal model, on the other hand, in the robust stability case, it stabilizes all possible process realizations within an uncertainty region. The term "fault" designates any impairment of system components that may result in performance degradation or even a complete stop of system functions. System faults can be classified as sudden (abrupt faults) or incipient faults (when the system suffers a slow degradation). Implementing a fault tolerant system, that keeps its dynamic response inside acceptable limits even under fault occurrence, is not trivial. In such case, the system can have its performance degraded but must continue to be operational. There have been several proposal solutions to the fault tolerant control problem. The proposal of this paper is to apply the TFL/LTR (Target Feedback Loop/Loop Transfer Recovery) robust control design to a 3DOF hover didactic system with uncertainty model and abrupt faults caused, for example, by power loss. TFL/LTR is a two step design procedure. In the first step, desired dynamics are defined for the controlled system (TFL). In this paper a linear quadratic regulator technique that considers a control signal gain will be used to ensure stability margins. These margins shall be defined so as to make the system robust to the abrupt faults. In the second step, a loop transfer recovery method (LTR) is used so that the controlled real system has characteristics close to those of the target feedback loop. Simulation results show that the control system under study has the intended robustness and fault tolerance.

@article{Garcia2008,
title = {A new dead-time compensator to control stable and integrating processes with long dead-time},
author = {Garcia, Pedro and Pedro Albertos},
journal = {Automatica},
year = {2008},
volume = {44},
abstract = {This paper presents a new dead-time compensator for stable and integrating processes when a reduced model of the process is considered. The output is estimated from a discrete time representation of the continuous time model and the tuning of the controllers can be made by any classical control design approach for systems without delay. The internal stability and the robust stability of the proposed scheme is proved and a deep analysis of the disturbance rejection performance is included. As a result, a tuning procedure is derived. An illustrative example shows that the robustness and performance of the proposed scheme are similar or better to those of the more recently proposed dead-time compensators for stable and integrating processes, its capability to reject ramp disturbances being also addressed. The proposed scheme has been tested in a real-time application to control the roll angle in a laboratory prototype of a quad-rotor helicopter. },
keywords = {Dead-time compensators; Stable and integrating processes; Robustness; Load disturbance; Real-time implementation},
pages = {1062--1071}
}

This paper presents a new dead-time compensator for stable and integrating processes when a reduced model of the process is considered. The output is estimated from a discrete time representation of the continuous time model and the tuning of the controllers can be made by any classical control design approach for systems without delay. The internal stability and the robust stability of the proposed scheme is proved and a deep analysis of the disturbance rejection performance is included. As a result, a tuning procedure is derived. An illustrative example shows that the robustness and performance of the proposed scheme are similar or better to those of the more recently proposed dead-time compensators for stable and integrating processes, its capability to reject ramp disturbances being also addressed. The proposed scheme has been tested in a real-time application to control the roll angle in a laboratory prototype of a quad-rotor helicopter.