1,721,098 research outputs found
Robust and Adaptive Control Laws for a mini Quad Rotor UAV
No full textThe scope of this thesis is the implementation of robust and adaptive control theories to guarantee good stability and performance characteristics in formation flight of a multi rotor platform, both for remote piloting and autonomous control. A key point in the evaluation of control laws is the stability dynamic analysis. For this reason a complete mathematical model is implemented, starting from the blade element theory. This model is used for the evaluation of detailed loads in hover conditions. This model can be useful for a modal structural analysis to evaluate the structural frequencies and to customize the data fusion filter with regard to the platform characteristics, to identify the system natural frequencies and to reduce the on board sensor signal noise.
Different control laws have been analyzed, from the classical theory, like Proportional Derivative (PD) and Linear Quadratic Regulator (LQR) controllers, to an innovative theory, that is represented by the L1 adaptive controller. The scope is to verify which of these theories is the most suitable for a rotary wing UAV as quadrotor. The validation of controllers is proposed on the experimental model (derived from flight tests) and in a formation flight application. The L1 controller can be implemented to limit the range of the angular velocities and of the four rotor rotational speed. A quadrotor is a platform with fast dynamics on control axes, thus if a sudden maneuver is implemented can cause glitches on the parameters trend and the aircraft could become uncontrollable. Moreover, the structure vibration could increase the platform unstable behavior and the resulting glitches become a variation of the controller variables, thus they are considered as inputs.
A key aspect of L1 control theory is the definition of control signals as the output of a low pass-filter, in order to remain in the low-frequency range. This feature permits to avoid high frequency oscillations due to the large adaptation gain; in systems that use electronic devices, like the studied platform, these oscillations significantly increase the current draw and it is undesirable. Moreover, this controller is robust in presence of model uncertainties and unmodeled dynamics. The simple structure and the presence of less oscillations during the implementation demonstrate that this controller can be a better candidate for an autopilot (than the classical control theory).
Therefore, a drawback in the L1 controller is the trial and error method to evaluate the low pass filter that is the fundamental component of control law. To provide a systematic method, a mixed deterministic – randomized approach for the control law design (low pass filter) is proposed. The results obtained in the unmatched controller (real platform variables) are thus optimized.
In conclusion, these results are validated on a real platform, designed during this research activity and used as test bed for control law algorithms. Quadrotor realization permits to know in detail the platform dynamics and behavior. This is important to better control the system optimizing control law implementation. The implementation of a L1 controller in the on board autopilot can reduce the measurement noise (due to the low pass filter in the control law). This filter can be useful for improving the data acquisition of the accelerometers and for the flight tests combined with the Kalman filter (to have less noisy results)
Model Predictive Control for Spacecraft Swarm Proximity Operations
No full textIn this paper, the spacecraft swarm guidance and control is addressed by means of Model Predictive Control (MPC) algorithm. A novel distributed nonlinear MPC approach for formation acquisition is presented, with the purpose of minimizing data exchanged by each spacecraft, guaranteeing collision avoidance between each other and with non-collaborative obstacles. The main objective is to design a deterministic method for autonomous swarm formation acquisition around target. Providing only the target position and a distance from it, the swarm moves autonomously to the target, reaching the regular polygon shaped formation around it, and at the given distance. The main feature of the proposed algorithm is the formation adaptability to the number of spacecraft in the swarm, even considering variable-swarm. Finally, preliminary simulations are carried out for proximity operations scenario, both fixed and variable swarm formation. The method effectiveness, the independence of the results from the initial conditions, and closed-loop stability are verified by means of extensive simulations. Results makes this an interesting approach to be investigated, since it allows to not define a single reference for each spacecraft, and requires only the definition of the target position and the distance from it
Tube-based Robust MPC Processor-In-the-Loop Validation for Fixed-Wing UAVs
Full text linkReal systems, as Unmanned Aerial Vehicles (UAVs),
are usually subject to environmental disturbances, which could
compromise the mission accomplishment. For this reason, the
main idea proposed in this research is the design of a robust
controller, as autopilot control system candidate for a fixedwing
UAV. In detail, the inner loop of the autopilot system
is designed with a tube-based robust model predictive control
(TRMPC) scheme, able to handle additive noise. Moreover, the
navigation outer loop is regulated by a proportional-integralderivative
controller. The proposed TRMPC is composed of two
parts: (i) a linear nominal dynamics, evaluated online with an
optimization problem, and (ii) a linear error dynamics, which
includes a feedback gain matrix, evaluated offline. The key
aspects of the proposed methodology are: (i) offline evaluation
of the feedback gain matrix, and (ii) robustness to random,
bounded disturbances. Moreover, a path-following algorithm is
designated for the guidance task, which provides the reference
heading angle as input to the control algorithm. Software-in-theloop
and processor-in-the-loop simulations have been performed
to validate the proposed approach. The obtained performance
have been evaluated in terms of tracking capabilities and
computational load, assessing the real-time implementability
compliance with the XMOS development board, selected as
continuation of previous works
Consensus Control of Multi-Agent Systems via Displacement Feedback
Full text linkA second-order multi-agent consensus is considered, where it is assumed that velocity of each agent is not available and thus a dynamic displacement feedback is employed. It is shown that there always exists such a feedback which achieves the consensus if the graph of the overall system is undirected and connected. A sufficient condition for the consensus is also given in terms of graph Laplacians
Precise Attitude Control Techniques: Performance Analysis from Classical to Variable Structure Control
Full text link
Artificial Potential Field and Sliding Mode Strategies for Rendezvous Maneuver and Obstacle Avoidance
No full text- …
