Pedro Casau

A Set-Valued Approach to FDI and FTC of Wind Turbines

A complete methodology to design robust fault detection and isolation (FDI) filters and fault-tolerant control (FTC) schemes for linear parameter varying systems is proposed, with particular focus on its applicability to wind turbines. This paper takes advantage of the recent advances in model falsification using set-valued observers (SVOs) that led to the development of FDI methods for uncertain linear time-varying systems, with promising results in terms of the time required to diagnose faults. An integration of such SVO-based FDI methods with robust control synthesis is described, to deploy new FTC algorithms that are able to stabilize the plant under faulty environments. The FDI and FTC algorithms are assessed by resorting to a publicly available wind turbine benchmark model, using Monte Carlo simulation runs.

Robust global trajectory tracking for a class of underactuated vehicles

In this paper, we address the problem of trajectory tracking for a class of underactuated vehicles with full torque actuation and only one dimensional force actuation (thrust). For this class of vehicles, the desired thrust is defined by a saturated control law that achieves global asymptotic stabilization of the position tracking error. The proposed control law also assures that the third component of the angular velocity is regulated to zero. To accomplish this task we propose a hybrid controller that is designed using backstepping techniques and recent developments on synergistic Lyapunov functions. Simulations validating the results are also provided.

Fault Detection and Isolation and Fault Tolerant Control of Wind Turbines using Set-Valued Observers

Abstract Research on wind turbine Operations & Maintenance (O&M) procedures is critical to the expansion of Wind Energy Conversion systems (WEC). In order to reduce O&M costs and increase the lifespan of the turbine, we study the application of Set-Valued Observers (SVO) to the problem of Fault Detection and Isolation (FDI) and Fault Tolerant Control (FTC) of wind turbines, by taking advantage of the recent advances in SVO theory for model invalidation. A simple wind turbine model is presented along with possible faulty scenarios. The FDI algorithm is built on top of the described model, taking into account process disturbances, uncertainty and sensor noise. The FTC strategy takes advantage of the proposed FDI algorithm, enabling the controller reconfiguration shortly after fault events. Additionally, a robust controller is designed so as to increase the wind turbines performance during low severity faults. Finally, the FDI algorithm is assessed within a publicly available benchmark model, using Monte-Carlo simulation runs.

A Set-Valued Approach to FDI and FTC: Theory and Implementation Issues

Abstract A complete methodology to design robust Fault Detection and Isolation (FDI) filters and Fault Tolerant Control (FTC) schemes for Linear Time-Varying (LTV) systems is proposed. The paper takes advantage of the recent advances in model invalidation using Set-Valued Observers (SVOs) that led to the development of FDI methods for uncertain linear time-varying systems, with promising results in terms of the time required to diagnose faults. An integration of such SVO-based FDI methods with robust control synthesis is described, in order to deploy new FTC algorithms that are able to stabilize the plant under faulty environments. The FDI algorithm is assessed within a wind turbine benchmark model, using Monte-Carlo simulation runs.

Autonomous Transition Flight for a Vertical Take-Off and Landing aircraft

This paper addresses the problem of autonomous transition between hover and level flight for a model-scale fixed-wing Unmanned Air Vehicle (UAV). The UAV system is described as a Hybrid Automaton where the different operating modes correspond to the hover, transition, and level flight regions of the flight envelope. Reference maneuvers are generated so as to provide robustness to the system with respect to exogenous disturbances and parametric uncertainty when performing single operating mode and transition maneuvers. Controllers rendering the closed-loop system Input-to-State Stable (ISS) with restrictions are designed for all three operating modes allowing for practical tracking of the reference maneuvers in the presence of disturbances. Simulation results demonstrate the performance and robustness of the proposed solution.

Almost global stabilization of a vertical take-off and landing aircraft in hovered flight

This paper proposes a controller which stabilizes a fixed-wing Unmanned Air Vehicle (UAV) in hovered flight. A six degree-of-freedom dynamic model is developed for an underactuated model-scale aircraft and a simpler three degree-of-freedom model is derived for controller design purposes. A novel nonlinear controller which renders the hovering position of the simplified system dynamics almost globally exponentially stable is proposed. Lateral stabilization is achieved by means of classic linear optimal control techniques. The nonlinear controller is designed so as to provide unidirectional thrust. Moreover, the closed-loop system is Input-to-State Stable (ISS) in the presence of unknown disturbances. Realistic simulation results demonstrate the controllers effectiveness and robustness when dealing with the problem at hand.

Wind turbines Fault Detection and identification using Set-Valued Observers

Research on wind turbine Operations & Maintenance (O&M) procedures is critical to the expansion of Wind Energy Conversion systems (WEC). In order to reduce O&M costs and increase the lifespan of the turbine, we study the application of Set-Valued Observers (SVO) to the problem of Fault Detection and Isolation (FDI) of wind turbines, by taking advantage of the recent advances in SVO theory for model invalidation. A simple wind turbine model is presented along with possible faulty scenarios. The SVO algorithm is built upon these dynamics, taking into account process disturbances, model uncertainty, and measurement noise. The FDI algorithm is assessed within a publicly available benchmark model, using Monte-Carlo simulation runs.

Global exponential stabilization on the n-dimensional sphere

In this paper, we show that the existence of centrally synergistic potential functions on the n-dimensional sphere, denoted by Sn, is a sufficient condition for the global asymptotic stabilization of a point in Sn. Additionally, if these functions decrease exponentially fast during flows and are bounded from above and from below by some polynomial function of the tracking error, then the reference point can be globally exponentially stabilized. We construct two kinds of centrally synergistic functions: the first kind consists of a finite family of potential functions on Sn while the second kind consists of an uncountable number of potential functions on Sn. While the former generates a simpler jump logic, the latter is optimal in the sense that it generates flows with minimal length.

A landmark-based controller for global asymptotic stabilization on SE(3)

In this paper, we address the problem of designing a landmark-based control law that robustly globally asymptotically stabilizes a rigid body at a desired equilibrium point on the SE(3) manifold. Synergistic potential functions are combined within a hybrid systems framework to generate such a hybrid control law. The proposed control law is solely a function of vector measurements characterizing the position of some given landmarks. We provide sufficient conditions on the geometry of the landmarks to solve the given problem. Finally, the proposed solution is simulated and compared with an almost global continuous feedback control law.

A hybrid feedback controller for robust global trajectory tracking of quadrotor-like vehicles with minimized attitude error

In this paper, we tackle the problem of trajectory tracking for a particular class of underactuated vehicles with full torque actuation and a single force direction (thrust) that is fixed relative to a body attached frame. Additionally, we consider that thrust reversal is not available. We present the design of a hybrid controller that, under some given assumptions, is able to globally asymptotically stabilize the vehicle to a reference position trajectory while minimizing the angle to the desired attitude trajectory. This objective is achieved robustly and globally, in the sense that small perturbations do not lead to instability and it is achieved regardless of the initial state of the vehicle. The algorithm is tested in a experimental setup, using a small scale quadrotor vehicle and the VICON motion capture system.