Browsing by Author "Yildiz, Y."

Now showing 1 - 7 of 7

Open Access
Computable delay margins for adaptive systems with state variables accessible
(Institute of Electrical and Electronics Engineers Inc., 2017) Hussain, H. S.; Yildiz, Y.; Matsutani, M.; Annaswamy, A. M.; Lavretsky, E.
Robust adaptive control of plants whose state variables are accessible in the presence of an input time delay is established in this paper. It is shown that a standard model reference adaptive controller modified with projection ensures global boundedness of the overall adaptive system for a range of nonzero delays. The upper bound of such delays, that is, the delay margin, is explicitly defined and can be computed a priori. © 1963-2012 IEEE.
Open Access
Control of uncertain sampled-data systems: An Adaptive posicast control approach
(Institute of Electrical and Electronics Engineers Inc., 2017) Abidi K.; Yildiz, Y.; Annaswamy A.
This technical note proposes a discrete-time adaptive controller for the control of sampled-data systems. The design is inspired from the Adaptive Posicast Controller (APC) which was designed for time-delay systems in continuous time. Due to the performance degradation caused by digital approximation of continuous laws, together with the problem of assuming time-delays as integer multiples of sampling intervals, the benefits of APC could not be fully realized. In this technical note, these approximations/assumptions are eliminated. In addition, a disturbance observer is incorporated into the controller design which minimizes the effect of disturbances on the system. Extension to the case of uncertain input time-delay is also presented. The proposed approach is verified in simulation studies. © 1963-2012 IEEE.
Open Access
Explicit time-delay compensation in teleoperation: an adaptive control approach
(John Wiley and Sons Ltd, 2016) Abidi K.; Yildiz, Y.; Korpe, B. E.
This paper proposes a control framework that addresses the destabilizing effect of communication time delays and system uncertainties in telerobotics, in the presence of force feedback. Force feedback is necessary to obtain transparency, which is providing the human operator as close a feel as possible of the environment where the slave robot is operating. Achieving stability and providing transparency are conflicting goals. This is the major reason why, currently, a very few, if at all, fully operational force feedback teleoperation devices exist except for research environments. The proposed framework handles system uncertainty with adaptation and communication time delays with explicit delay compensation. The technology that allows this explicit adaptive time-delay compensation is inspired by Massachusetts Institute of Technology (MIT)'s Adaptive Posicast Controller. We provide simulation results that demonstrate stable explicit adaptive delay compensation in a force-reflecting teleoperation set up. Copyright Â© 2016 John Wiley & Sons, Ltd. Copyright Â© 2016 John Wiley & Sons, Ltd.
Open Access
High-Performance Adaptive Pressure Control in the Presence of Time Delays: Pressure Control for Use in Variable-Thrust Rocket Development
(Institute of Electrical and Electronics Engineers, 2018) Alan A.; Yildiz, Y.; Poyraz U.
Smart defense systems using missiles that can fine-tune their velocity profiles have significant technological superiority over their conventional counterparts. This tuning is possible, in part, due to the deployment of advanced sensing, actuation, and computation capabilities and sophisticated guidance, navigation, and control algorithms. The capability to alter velocity during operation helps sustain optimum performance for different flight conditions. In addition, it makes it possible to slow down while turning and then speed up along a straight path, rendering the maneuvers more efficient. This ability to modify velocity (known as throttleability) is also known to increase a missile's no-escape zone, which is the maximum range that the missile can outrun its target [1]. As presented in »Summary,» this article discusses the advanced control technologies needed to obtain throttleability.
Open Access
Nonlinear hierarchical control of a quad tilt-wing UAV: An adaptive control approach
(John Wiley and Sons Ltd, 2017) Yildiz, Y.; Unel, M.; Demirel, A.E.
In this paper, a nonlinear hierarchical adaptive control framework is proposed for the control of a quad tilt-wing unmanned aerial vehicle (UAV). An outer loop model reference adaptive controller with robustifying terms creates required forces to be able to move the UAV on a reference trajectory, and an inner loop nonlinear adaptive controller realizes the required attitude angles to achieve these forces. A rigorous stability analysis is provided showing the boundedness of all the signals in this cascaded controller structure. The development and the stability analysis of the controller do not use any linearizations and use the full nonlinear UAV dynamics. The controller is implemented on a high-fidelity nonlinear tilt-wing quadrotor model in the presence of uncertainties, wind disturbances, and measurement noise as well as actuator and structural failures. In this work, in addition to earlier modeling studies, the effect of wing-angle variations, actuator failures, and structural failures and their effect on the center of gravity of the UAV are rigorously and systematically investigated and reflected in the model. Simulation results showing the performance of the proposed controller and a comparison with the fixed controller used in earlier studies are presented in the paper. Copyright © 2017 John Wiley & Sons, Ltd.
Open Access
Predicting pilot behavior in medium-scale scenarios using game theory and reinforcement learning
(American Institute of Aeronautics and Astronautics Inc., 2014) Yildiz, Y.; Agogino, A.; Brat, G.
A key element to meet the continuing growth in air traffic is the increased use of automation. Decision support systems, computer-based information acquisition, trajectory planning systems, high-level graphic display systems, and all advisory systems are considered to be automation components related to next generation (NextGen) air space. Given a set of goals represented as reward functions, the actions of the players may be predicted. However, several challenges need to be overcome. First, determining how a player can attempt to maximize their reward function can be a difficult inverse problem. Second, players may not be able to perfectly maximize their reward functions. ADS-B technology can provide pilots the information, position, velocity, etc. of other aircraft. However, a pilot has limited ability to use all this information for his/her decision making. For this scenario, the authors model these pilot limitations by assuming that pilots can observe a limited section of the grid in front of them.
Open Access
Unmanned aircraft systems airspace integration: A game theoretical framework for concept evaluations
(American Institute of Aeronautics and Astronautics Inc., 2017) Musavi, N.; Onural, D.; Gunes, K.; Yildiz, Y.
The focus of this paper is to present a game theoretical modeling framework for the integration of unmanned aircraft systems into the National Airspace System. The problem of predicting the outcome of complex scenarios, where manned and unmanned air vehicles coexist, is the research problem of this work. The fundamental gap in the literature is that the models of interaction between manned and unmanned vehicles are insufficient: 1) They assume that pilot behavior is known a priori, and 2) They disregard pilot reaction and the decision-making process. The contribution of this paper is to propose a realistic modeling framework that will fill this gap. The foundations of the proposed method are formedbygame theory, which investigates strategic decision makingbetween intelligent agents; bounded rationality concept, which is based on the fact that humans cannot always make perfect decisions; and reinforcement learning, which is shown to be effective in human learning in psychology literature. An analysis of integration is conducted using an example scenario in the presence of manned aircraft and fully autonomous unmanned aircraft systems equipped with sense-and-avoid algorithms. © Copyright 2016 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.